US 6,348,376 B2Grant
Method of forming metal nitride film by chemical vapor deposition and method of forming metal contact and capacitor of semiconductor device using the same
Issue Date:2002-02-19
•11 Claims
•16 Drawing Sheets
Abstract
A method of forming a metal nitride film using chemical vapor deposition (CVD), and a method of forming a metal contact and a semiconductor capacitor of a semiconductor device using the same, are provided. The method of forming a metal nitride film using chemical vapor deposition (CVD) in which a metal source and a nitrogen source are used as a precursor, includes the steps of inserting a semiconductor substrate into a deposition chamber, flowing the metal source into the deposition chamber, removing the metal source remaining in the deposition chamber by cutting off the inflow of the metal source and flowing a purge gas into the deposition chamber, cutting off the purge gas and flowing the nitrogen source into the deposition chamber to react with the metal source adsorbed on the semiconductor substrate, and removing the nitrogen source remaining in the deposition chamber by cutting off the inflow of the nitrogen source and flowing the purge gas into the deposition chamber. Accordingly, the metal nitride film having low resistivity and a low content of Cl even with excellent step coverage can be formed at a temperature of 500° C. or lower, and a semiconductor capacitor having excellent leakage current characteristics can be manufactured. Also, a deposition speed, approximately 20 A/cycle, is suitable for mass production.
Metadata
Assignee
- Samsung Electronics Co., Ltd.
Inventors
- Hyun-Seok Lim
- Sang-Bom Kang
- In-Sang Jeon
- Gil-Heyun Choi
Application Information
Application Number:US 09/765,531
Filing Date:2001-01-19
Priority Date:1997-09-29
Art Unit:7
Classifications
IPC:
H01L 218242H01L 2120H01L 2144
Field of Search:
438239438253438296438653438643438648438652438680438681
Patent Drawings (16 sheets)
Description
[0002] This application is a continuation-in-part of U.S. patent application Ser. No. 09/156,724, filed Sep. 18, 1998, entitled METHOD OF FORMING METAL NITRIDE FILM CHEMICAL VAPOR DEPOSITION AND METHOD OF FORMING METAL CONTACT OF SEMICONDUCTOR DEVICE USING THE SAMEMETHOD OF FORMING METAL NITRIDE FILM CHEMICAL VAPOR DEPOSITION AND METHOD OF FORMING METAL CONTACT OF SEMICONDUCTOR DEVICE USING THE SAME, now U.S. Pat. No. 6,197,683.
Background of the Invention
[0003] 1. Field of the Invention
[0004] The present invention relates to a method of fabricating semiconductor devices, and more particularly, to a method of forming a metal nitride film by chemical vapor deposition (CVD) where a metal source and a nitrogen source are used as a precursor, and a method of forming a metal contact and a capacitor of a semiconductor device using the above method.
[0005] 2. Description of the Related Art
[0006] A barrier metal layer, which prevents mutual diffusion or chemical reaction between different materials, is indispensable to stabilize the contact interfaces of semiconductor devices. In general, a metal nitride such as TiN, TaN or WN has been widely used as the barrier metal layer of semiconductor devices. Here, TiN is a representative example among the above metal nitrides.
[0007] However, when the metal nitride film such as TiN is fabricated by sputtering, its application to highly integrated semiconductor devices is not appropriate, due to low step coverage. For an example, FIGS. 9A and 9B show the cross-section of a via contact for connection between metal wiring. FIGS. 9A and 9B show a simple via contact and an anchor via contact, respectively. The formation processes thereof are as follows. A first metal layer 30 composed of aluminum (Al) is formed on a semiconductor substrate 20. A TiN film 40 is formed as a capping film on the resultant structure by sputtering, and then an interlayer insulative film 50 or 51 is deposited. A contact hole is formed by etching the interlayer insulative film 50 or 51 on the first metal layer 30. In FIG. 9B, the step of forming an anchor A by wet etching is added. After Ti as an adhesive layer and TiN 60 or 61 as a barrier metal layer is deposited, a tungsten (W) plug 70 or 71 is formed to fill the contact hole, by CVD. Thereafter, tungsten at the upper portion is removed by chemical mechanical polishing or etch-back, and then a second metal layer is deposited on the resultant structure, thereby completing the connection between metal wiring. However, this last step is not shown.
[0008] Here, in a conventional method, the TiN film 60 or 61, being the barrier metal layer, is deposited by sputtering, with inferior step coverage. Here, the thickness of a TiN film on the bottom, corner and anchor A of the contact hole is reduced, with an increase in the aspect ratio of the via. Accordingly, at a thin portion, Ti or Al combines with fluorine remaining in tungsten source gas WF6during tungsten deposition being a subsequent process, and thus an insulative film X is formed of TiFxor ALFx, leading to a contact failure.
[0009] When the contact failure is avoided by increasing the deposition time to increase the thickness of the TiN film 60 or 61, the thickness of the TiN film increases only at the upper portion of the contact hole, and the upper portion of the contact hole is narrowed or blocked. Thus, voids are likely to be generated upon subsequent tungsten deposition. A process with improved step coverage is required to apply TiN to a contact with a high aspect ratio. Accordingly, a process for fabricating a metal nitride film using CVD (hereinafter called a CVD-metal nitride film) has been developed as a next generation process.
[0010] A general process for forming a CVD-metal nitride film uses a metal source containing chlorine (Cl), e.g., a precursor such as titanium chloride TiCl4. The CVD-metal nitride film using TiCl4as the precursor has a high step coverage of 95% or higher and is quickly deposited, but Cl remains in the metal nitride film as impurities. The Cl remaining as impurities in the metal nitride film causes corrosion of metal wiring such as Al and increases resistivity. Thus, the Cl content in the metal nitride film must be reduced and the resistivity must be lowered, by deposition at high temperature. That is, in the CVD-metal nitride film process using the metal source such as TiCl4, a deposition temperature of at least 675° C. is required to obtain resistivity of 200 μΩ-cm or less. However, a deposition temperature of 600° C. or more exceeds thermal budget and thermal stress limits which an underlayer can withstand. In particular, when the metal nitride film is deposited on an Si contact or a via contact with an Al underlayer, a deposition temperature of 480° C. or lower is required, so that a high temperature CVD-metal nitride film process cannot be used.
[0011] A low temperature deposition CVD-metal nitride film process is possible, by adding MH (methylhydrazine, (CH3)HNNH2) to the metal source such as TiCl4, but this method has a defect in that step coverage is decreased to 70% or lower.
[0012] Another method capable of low temperature deposition is to form a MOCVD-metal nitride film using a metalorganic precursor such as TDEAT (tetrakis diethylamino Ti, Ti(N(CH2CH3)2)4), or TDMAT (tetrakis dimethylamino Ti, Ti(N(CH3)2)4). The MOCVD-metal nitride film has no problems due to Cl and can be deposited at low temperature. However, the MOCVD-metal nitride film contains a lot of carbon (C) as impurities, giving high resistivity, and has inferior step coverage of 70% or less.
[0013] A method of forming a metal nitride film using atomic layer epitaxy (ALE) has been tried as an alternative to deposition, in order to overcome the problems due to Cl. However, the ALE grows the metal nitride film in units of an atomic layer using only chemical absorption, and the deposition speed (0.25 A/cycle or less) is too slow to apply the ALE to mass production.
[0014] A TiN film is also used as the electrode of a semiconductor capacitor. In particular, the TiN film is usually used in a capacitor which uses tantalum oxide (Ta2O5) as a dielectric film. Semiconductor capacitors, which use the TiN film as an electrode, also have the above-described problems.
[0015] That is, in order for a semiconductor capacitor to have a high capacitance per unit area of a semiconductor substrate, its electrode is designed three-dimensionally, as in cylindrical capacitors. Hence, the shape of the semiconductor capacitor is so complicated that it is critical to guarantee step coverage of deposited materials as its electrode. Accordingly, a TiN electrode formed by CVD using a Cl-containing metal source having an excellent step coverage as a precursor has been used as the electrode of a capacitor. However, as described above, the CVDed TiN film provokes corrosion of metal wiring and gives high resistivity, due to a high concentration of Cl, resulting in a degradation in the leakage current characteristics of a capacitor.
Summary of the Invention
[0016] To solve the above problems, an objective of the present invention is to provide a method of forming a metal nitride film, which gives excellent step coverage even at a high deposition speed and a low temperature, low impurity concentration, and low resistivity.
[0017] Another objective of the present invention is to provide a method of forming a metal contact having a barrier metal layer which has excellent step coverage even at a high deposition speed and a low temperature, low impurity concentration, and low resistivity, by applying the metal nitride film formation method to a metal contact of a semiconductor device.
[0018] Still another objective of the present invention is to provide a method of forming a capacitor which gives excellent step coverage, low impurity concentration and low resistivity, using the metal nitride film formation method.
[0019] Accordingly, to achieve the first objective, there is provided a method of forming a metal nitride film using chemical vapor deposition (CVD) in which a metal source and a nitrogen source are used as a precursor. In this method, first, a semiconductor substrate is introduced into a deposition chamber, and the metal source flows into the deposition chamber. After a predetermine time, the flow of the metal is stopped, and a purge gas is introduced into the deposition chamber. After a predetermined time, the purge gas is cut off and the nitrogen source gas flows into the deposition chamber to react with the metal source adsorbed on the semiconductor substrate. Again, after a predetermined time, the nitrogen source gas remaining in the deposition chamber is removed by cutting off the inflow of the nitrogen source gas and flowing the purge gas into the deposition chamber. Thus, the metal nitride film is formed on the semiconductor substrate.
[0020] In the metal nitride film formation method of the present invention, a gas inflow cycle of a sequence of the metal source, the purge gas, the nitrogen source, and the purge gas, can be repeated until a metal nitride film having a desired thickness is obtained.
[0021] Here, a titanium nitride film TiN can be formed by using TiCl4(titanium chloride), TiCl3(titanium chloride), TiI4(titanium iodide), TiBr2(titanium bromide), TiF4(titaniumfluoride), (C5H5)2TiCl2(bis(cyclopentadienyl)titanium dichloride), ((CH3)5C5)2TiCl2(bis(pentamethylcyclopentadienyl) titanium dichloride), C5H5TiCl3(cyclopentadienyltitanium trichloride), C9H10BCl3N6Ti (hydrotris (1-pyrazolylborato) trichloro titanium), C9H7TiCl3(indenyltitanium trichloride), (C5(CH3)5)TiCl3(pentamethylcyclopentadienyltitanium trichloride), TiCl4(NH3)2(tetrachlorodiaminotitanium), (CH3)5C5Ti(CH3)3(trimethylpentamethylcyclopentadienyltitanium), TDEAT or TDMAT as the metal source, and using NH3as the nitrogen source. Alternatively, the tantalum nitride film TaN can be formed using a material selected from the group consisting of TaBr5(tantalum bromide), TaCl5(tantalum chloride), TaF5(tantalum fluoride), TaI5(Tantalum iodide), and(C5(CH3)5)TaCl4(pentamethylcyclopentadienyltantalum tetrachloride), as the metal source, and using NH3as the nitrogen source.
[0022] Also, it is preferable that the purge gas is an inert gas such as Ar or N2.
[0023] Preferably, 1-5 sccm of the metal source flows into the deposition chamber for 1 to 10 seconds, 5-200 sccm of the nitrogen source flows thereinto for 1 to 10 seconds, and 10-200 sccm of the purge gas flows thereinto for 1 to 10 seconds.
[0024] Also, an atmospheric gas such as Ar, He and N2can be continuously flowed into the deposition chamber, to maintain a constant pressure in the deposition chamber.
[0025] Meanwhile, when the TiN film is formed using TDEAT or TDMAT as the metal source, it is preferable to maintain the pressure in the deposition chamber to be 0.1-10 torr and the deposition temperature to be between 250° C. and 400° C. When materials other than TDEAT and TDMAT are used as the metal source, the pressure in the deposition chamber is maintained to be 1 to 20 torr and the deposition temperature is maintained to be between 400° C. and 500° C.
[0026] To achieve the second objective, there is provided a method of forming a metal contact of a semiconductor device, wherein a first metal layer, an interlayer insulative film, a contact hole, a barrier metal layer, a metal plug, and a second metal layer are sequentially formed on a semiconductor substrate. A process for forming the barrier metal layer is as follows. A metal source flows into the semiconductor substrate having the interlayer insulative film in which the contact hole exposing the first metal layer is formed. The metal source is adsorbed to the resultant structure. After a while, the metal source remaining in the deposition chamber is removed by cutting off the inflow of the metal source and flowing a purge gas into the deposition chamber. After a predetermined time, the purge gas is cut off, and a nitrogen source flows into the deposition chamber. The nitrogen source reacts with the metal source adsorbed on the semiconductor substrate, to thus form a metal nitride film, being the barrier metal layer, on the exposed first metal layer and the contact hole. Again, after a while, the nitrogen source remaining in the deposition chamber is removed by cutting off the inflow of the nitrogen source and flowing the purge gas into the deposition chamber.
[0027] The barrier metal layer formation process can be repeated until a barrier metal layer having a desired thickness is obtained.
[0028] Here, a titanium nitride film TiN as the barrier metal layer is formed by using a material selected from the group consisting of TiCl4, TiCl3, TiI4, TiBr2, TiF4, (C5H5)2TiCl2, ((CH3)5C5)2TiCl2, C5H5TiCl3, C9H10BCl3N6Ti, C9H7TiCl3, (C5(CH3)5)TiCl3, TiCl4(NH3)2, (CH3)5C5Ti(CH3)3, TDEAT and TDMAT as the metal source, and using NH3as the nitrogen source. Alternatively, the tantalum nitride film TaN as the barrier metal layer is formed using a material selected from the group consisting of TaBr5, TaCl5, TaF5, TaI5, and (C5(CH3)5)TaCl4as the metal source, and NH3as the nitrogen source.
[0029] Also, it is preferable that the purge gas is an inert gas such as Ar or N2.
[0030] The flow amounts and flow times of the metal source, nitrogen source, and purge gas flowing into a deposition chamber are within the same ranges as in the above-mentioned method of forming the metal nitride film.
[0031] Also, in order to maintain a constant pressure within the deposition chamber while forming a barrier metal layer, the pressure within the deposition chamber is kept at about 0.1 to 10 torr when TDEAT or TDMAT is used as the metal source, and about 1 to 20 torr when materials other than TDEAT and TDMAT are used as the metal source. The constant pressure is maintained using an atmospheric gas such as Ar, He, or N2.
[0032] It is preferable that a deposition temperature upon the formation of the barrier metal layer is about between 250° C. and 400° C. when TDEAT or TDMAT is used as the metal source, and between 400° C. and 500° C. when materials other than TDEAT and TDMAT are used as the metal source.
[0033] To achieve the third objective, there is provided a method of forming a semiconductor capacitor, wherein a lower conductive layer, a dielectric film and an upper conductive layer are sequentially formed on the underlayer of a semiconductor substrate. In a process for forming the lower and/or upper conductive layer, a semiconductor substrate on which an underlayer or a dielectric film is formed is introduced into a deposition chamber, and a metal source flows into the deposition chamber. The metal source is chemically and physically adsorbed onto the substrate. After a predetermined period of time, the metal source is purged from the deposition chamber. After a predetermined period of time, a nitrogen source flows into the deposition chamber, and is chemically and physically adsorbed onto the substrate. The adsorbed metal source and nitrogen source are reacted to form a metal nitride film on the substrate. After another predetermined period of time, the nitrogen source is purged from the deposition chamber.
[0034] The step of forming a metal nitride film can be repeated until a lower and/or upper conductive layer having a desired thickness is obtained.
[0035] Here, when Ti is used, the metal source used to form the lower and/or upper conductive layer is selected from the group consisting of TiCl4, TiCl3, TiI4, TiBr2, TiF4, (C5H5)2TiCl2, ((CH3)5C5)2TiCl2, C5H5TiCl3, C9H10BCl3N6Ti, C9H7TiCl3, (C5(CH3)5)TiCl3, TiCl4(NH3)2, (CH3)5C5Ti(CH3)3, TDEAT and TDMAT. When Ta is used, the metal source is selected from the group consisting of TaBr5, TaCl5, TaF5, TaI5, and (C5(CH3)5)TaCl4. The nitrogen source is NH3.
[0036] Also, it is preferable that the purge gas is an inert gas such as Ar or N2.
[0037] The flow amounts and inflow times of a metal source, a nitrogen source and a purge gas flowing into the deposition chamber are within the same ranges as those in the metal nitride film formation method according to the present invention.
[0038] Also, in order to maintain a constant pressure within the deposition chamber while forming a lower and/or upper conductive layer, the pressure within the deposition chamber is maintained to be about 0.1-10 torr when TDEAT or TDMAT is used as a metal source, and the pressure within the deposition chamber is maintained to be about 1-20 torr when materials other than TDEAT and TDMAT are used as the metal source. The constant pressure is maintained by the use of an atmospheric gas such as Ar, He or N2.
[0039] Preferably, when TDEAT or TDMAT is used as the metal source, the deposition temperature in each of the steps for forming a lower conductive layer and/or an upper conductive layer is between 250° C. and 500° C. Also, preferably, when other materials are used as the metal source, the deposition temperature in each of the steps for forming a lower conductive layer and/or an upper conductive layer is between 400° C. and 500° C.
[0040] According to the present invention, a metal nitride film having low resistivity of 200μΩ-cm or less and a low content of Cl can be obtained even with excellent step coverage. Also, a CVD-metal nitride film can be formed at a temperature of 500° C. or less even at a deposition speed of about 20 A/cycle, so that the deposition speed of the present invention is higher than that of a metal nitride film formation method using ALE having a growth speed of 0.25 A/cycle. A capacitor, in which a metal nitride film formed by the method according to the present invention is used as a lower and/or upper conductive layer, has excellent step coverage and excellent leakage current characteristics.
Brief Description of the Drawings
[0041] The above objectives and advantages of the present invention will become more apparent by describing in detail a preferred embodiment thereof with reference to the attached drawings in which:
[0042] FIG. 1 shows a deposition chamber of a chemical vapor deposition (CVD) apparatus for depositing a metal nitride film on a semiconductor substrate, according to the present invention;
[0043] FIG. 2 shows gas inflow timings for depositing a metal nitride film on a semiconductor substrate, according to the present invention;
[0044] FIG. 3 is a graph of the results of Rutherford back scattering (RBS) of a metal nitride film deposited according to the present invention;
[0045] FIG. 4 is a graph illustrating the resistivity and deposition speed of a metal nitride film with respect to flow amount of NH3,when the metal nitride film is deposited according to the present invention;
[0046] FIG. 5 is a graph illustrating the resistivity and deposition speed of a metal nitride film with respect to pressure in a deposition chamber, when the metal nitride film is deposited according to the present invention;
[0047] FIG. 6 is a graph illustrating the deposited thickness of a metal nitride film versus the number of cycles when the metal nitride film is deposited according to the present invention;
[0048] FIG. 7 is a graph illustrating the deposition speed of a metal nitride film versus the number of cycles when the metal nitride film is deposited according to the present invention;
[0049] FIG. 8 is a graph illustrating the resistivity of a metal nitride film versus deposition temperature when the metal nitride film is deposited according to the present invention;
[0050] FIGS. 9A and 9B are cross-sections of a via contact formed by a conventional method;
[0051] FIGS. 10A through 10F are cross-sectional views illustrating an example of a process for forming a via contact using the metal nitride film formation method of the present invention;
[0052] FIGS. 11A through 11F are cross-sectional views illustrating another example of a process for forming a via contact using the metal nitride film formation method of the present invention;
[0053] FIG. 12 is a graph illustrating the relationship between via resistivity and via width when a barrier metal layer is formed according to the present invention and the prior art;
[0054] FIG. 13 is a graph illustrating via resistivity distributions when barrier metal layers are formed according to the present invention and the prior art;
[0055] FIGS. 14A through 14D are cross-sectional views illustrating a process for forming a semiconductor capacitor using a metal nitride film formation method according to the present invention;
[0056] FIGS. 15A and 15B are graphs showing the X-ray phonon spectroscopy (XPS) results of metal nitride films formed by a conventional method and a method according to the present invention, respectively; and
[0057] FIG. 16 is a graph showing the leakage current characteristics of capacitors formed by a conventional method and a method according to the present invention.
Description of the Preferred Embodiments
[0058] Referring to FIG. 1, a plurality of gas lines 114aand 114bfor introducing reaction gases into a deposition chamber 100 are installed into the deposition chamber 100. Here, the number of gas lines depends on the number of metal sources and nitrogen sources, i.e., the number of reaction gases, flowed into the deposition chamber 100. In an embodiment of the present invention, two gas lines 114aand 114bare installed.
[0059] The two gas lines 114aand 114bhave one end connected to a supply source (not shown) for a metal source and to a supply source (not shown) for a nitrogen source, respectively. When a TiN film is deposited on a semiconductor substrate 104, TiCl4is used as the metal source and NH3is used as the nitrogen source. Meanwhile, the other ends of the gas lines 114aand 114bare connected to a shower head 110 isolated by a predetermined distance (D of FIG. 1) from the semiconductor substrate 104 seated in the deposition chamber 100. Accordingly, the reaction gases from the gas supply sources (not shown) enter the deposition chamber 100 via the gas lines 114aand 114band the shower head 110 connected to the ends of the gas lines 114aand 114b. The reaction gases react with each other in the deposition chamber, and the resultant forms a film on the semiconductor substrate 104.
[0060] It is preferable that the shower head 110 is a multi-port shower head which allows the reaction gases to enter the deposition chamber 100 in an unmixed state. In this embodiment, a two-port shower head is used. Also, it is preferable that the gas lines 114aand 114bare provided with purge gas supply lines 114cand 114dto supply to the deposition chamber 100 a purge gas for exhausting residual gases after reaction.
[0061] Valves 112 are installed on the respective gas supply lines. According to the on/off state of the valves 112, the purge gases or reaction gases may enter into the deposition chamber 100 or be cut off. It is preferable that the valves 112, such as pneumatic valves, are controlled by a programmed control unit to be periodically turned on or off. Reference numeral 102 is a heater for heating the semiconductor substrate 104.
[0062] A method of depositing a metal nitride such as TiN on a semiconductor substrate seated in the deposition chamber of a CVD apparatus having such a configuration, according to the present invention, will now be described in detail referring to FIGS. 1 and 2.
[0063] First, the semiconductor substrate 104 is introduced into the deposition chamber 100. The semiconductor substrate 104 may have devices such as transistors formed on its surface (see FIG. 1).
[0064] A metal source such as TiCl4flows into the deposition chamber 100 for the time of tsvia the metal source supply line 114a. Alternatively, the metal source can be mixed with a carrier gas such as Ar or N2to provide a smooth gas flow into the deposition chamber 100. At this time, valves other than the valve of the gas supply line 114afor supplying a metal source are in off state. Accordingly, only the metal source such as TiCl4flows into the deposition chamber 100. At this time, a part of the entering metal source is chemically and physically adsorbed on the surface of the substrate 104, and the residual remains in the deposition chamber 100. As described above, only one type of gas enters the deposition chamber 100 for a predetermined time, instead of simultaneously flowing reaction gases into the deposition chamber 100. This is called gas pulsing (see FIG. 2).
[0065] When inflow of the metal source into the deposition chamber 100 is completed, the valve of the gas supply line 114afor introducing the metal source is closed, and then the valve of the purge gas supply line 114cis opened to introduce the purge gas such as Ar or N2into the deposition chamber 100 for the time of tp, thereby exhausting TiCl4gases from the shower head 110 and the deposition chamber 100 (in the purge gas pulsing step of FIG. 2). At this time, the flow of the purge gas and the pressure of the deposition chamber are appropriately controlled to prevent the metal source chemically and physically adsorbed into the semiconductor substrate from being separated and exhausted, thereby exhausting only the source gas remaining within the deposition chamber.
[0066] Then, the valve of the purge gas supply line 114cis closed, and the valve of the nitrogen gas source supply line 114bis opened to introduce a nitrogen gas such as NH3into the deposition chamber 100 for a time tr. The nitrogen gas reacts with the metal source such as TiCl4chemically and physically adsorbed into the substrate 104, thus forming the metal nitride such as TiN on the semiconductor substrate 104. That is, because of the purge gas pulsing step before the nitrogen source such as NH3enters into the deposition chamber 100, the metal source such as TiCl4remaining in the deposition chamber 100 is exhausted via the pump (see FIG. 1). Accordingly, the nitrogen source such as NH3does not react with the metal source such as TiCl4within the deposition chamber 100, except for on the semiconductor substrate 104. Thus, the metal nitride is formed on only the semiconductor substrate 104 into which TiCl4and NH3are adsorbed (in the NH3pulsing step of FIG. 2).
[0067] At this time, the carrier gas such as Ar or N2can be mixed with the nitrogen gas such as NH3for a smooth gas flow into the deposition chamber 100.
[0068] In a conventional method of forming a metal nitride film using ALE, only the chemically-adsorbed source remains, after purging the source physically adsorbed on the substrate. On the other hand, in the metal nitride film formation method of the present invention, the sources both physically and chemically adsorbed on the substrate remain and react. This is the fundamental difference between the prior art and the present invention.
[0069] Next, the residual nitrogen source remaining within the deposition chamber 100 after the reaction with the metal source is exhausted by another purge gas pulsing step (in the purge gas pulsing step of FIG. 2).
[0070] Meanwhile, while the pressure in the deposition chamber 100 is controlled during the above-described steps, it is preferable that an atmospheric gas such as Ar or N2is continuously supplied into the deposition chamber 100.
[0071] As described above, in the method of forming a metal nitride film using gas pulsing, according to the present invention, the metal nitride film such as TiN having a predetermined thickness is deposited through a cycle having a sequence of the TiCl4pulsing step, the purge gas pulsing step, the NH3pulsing step, and the purge gas pulsing step. Here, a deposition speed is about 20 A/cycle, and when this cycle is repeated, the thickness of a thin film is proportionally increased, so that a thin film having a desired thickness can be deposited on the semiconductor substrate 100. Here, the thickness of the metal nitride film deposited for one cycle is determined by the flow amounts of the metal source and nitrogen source entering the deposition chamber 100, the gas pulsing times, the flow amount of the purge gas, and the purge time.
[0072] Hereinafter, experimental examples of forming a TiN film according to the present invention will be described.
[0073] <First Experimental Example>
[0074] A TiN film is deposited by the cycles comprising the gas pulsing steps, under the following reaction conditions, on the semiconductor substrate 104 which is maintained at a temperature of 500° C. or lower by the heater 102 of FIG. 1.
[0075] Deposition Conditions
[0076] object material: TiN
[0077] atmospheric gas: Ar
[0078] pressure in deposition chamber: 1-20Torr
[0079] metal source, nitrogen source: TiCl4, NH3
[0080] flow amount of TiCl4, pulsing time (ts) of TiCl4:1-5 sccm, 5 sec
[0081] flow amount of NH3, pulsing time (tr) of NH3: 5-30 sccm, 5 sec
[0082] purge gas, flow amount of purge gas, purge time (tp): Ar, 10-100 sccm, 10 sec
[0083] carrier gas, flow amount of carrier gas: Ar, 10-100 sccm
[0084] time (tt) for one cycle: 30 sec
[0085] FIG. 3 shows the results of checking the state of the TiN thin film deposited on the semiconductor substrate 104 under the aforementioned conditions using an RBS method. In FIG. 3, a horizontal axis indicates channels in a multi-channel analyzer (MCA), and a vertical axis indicates the standardized yields of elements detected by the MCA. Here, the relationship between each channel and energy is given by equation, E[eV]=4.05′ channel+59.4.
[0086] The TiN film deposited on the semiconductor substrate 104 under the aforementioned conditions has a unique gold color, and has a perfect composition of Ti:N=1:1 as shown in FIG. 3. Cl is 0.3% or less of the total elements contained in the TiN thin film, which is the detection limit by RBS, as shown in FIG. 3. Also, the resistivity of the TiN film deposited on the semiconductor substrate 104 under the above conditions was measured as a low value of about 130 μΩ-cm. Meanwhile, according to several experiments, it was verified that the thickness of the TiN thin film deposited for each cycle must be 20 A or less to provide such an excellent thin film property.
[0087] FIGS. 4 and 5 show the resistivity and deposition speed of the TiN film deposited according to the present invention, at various flow amounts of the nitrogen source NH3and pressures in the deposition chamber, respectively. As shown in FIGS. 4 and 5, the deposition speed increases with an increase in the flow amount of NH3and the pressure in the deposition chamber, and thus the resistivity also increases. Accordingly, it is preferable that the conditions for deposition are set in consideration of the thickness and the deposition speed and resistivity of the metal nitride film required according to places to apply the metal nitride film.
[0088] <Second Experimental Example>
[0089] A deposition speed for each cycle, the thickness and deposition speed of a TiN film deposited according to an increase in the number of cycles, and resistivity according to a change in deposition temperature, are measured under four deposition conditions as shown in the following Table 1. Here, the metal source is TiCl4, the nitrogen source is NH3, and the purge gas is Ar.
| TABLE 1 | ||||||
|---|---|---|---|---|---|---|
| amount | amount | amount and | amount | amount of | ||
| deposition | and time | and time | time of | and time | atmospheric | |
| conditions | of metal source | of purge gas | nitrogen source | of purge gas | pressure | gas |
| TiN 00 | 5 sccm, | 40 sccm, | 150 sccm, | 40 sccm, | 3 torr | 50 sccm |
| 5 sec | 5 sec | 5 sec | 5 sec | |||
| TiN 01 | 3 sccm, | 150 sccm, | 30 sccm, | 150 sccm, | 2 torr | 30 sccm |
| 3 sec | 3 sec | 3 sec | 3 sec | |||
| TiN 02 | 3 sccm, | 150 sccm, | 50 sccm, | 150 sccm, | 3 torr | 30 sccm |
| 2 sec | 2 sec | 2 sec | 2 sec | |||
| TiN 03 | 3 sccm, | 150 sccm, | 100 sccm, | 150 sccm, | 3 torr | 30 sccm |
| 2 sec | 2 sec | 2 sec | 2 sec | |||
[0090] Deposition speeds per cycle under the above deposition conditions are as follows:
[0091] TiN 00:20 A/cycle (60 A/min, since one cycle is 20 seconds)
[0092] TiN 01:2 A/cycle (10 A/min, since one cycle is 12 seconds)
[0093] TiN 02:3.5 A/cycle (26.3 A/min, since one cycle is 8 seconds)
[0094] TiN 03:6 A/cycle (45 A/min, since one cycle is 8 seconds).
[0095] FIGS. 6 and 7 show the deposition thickness and deposition speed, respectively, according to an increase in the number of cycles. Here, a deposition temperature is 500° C. As can be seen from FIGS. 6 and 7, the deposition speed increases slowly with an increase in the number of cycles, and the deposition thickness increases in proportion to the number of cycles. Thus, the thickness of the TiN film to be deposited can be controlled by adjusting the number of cycles under consistent deposition conditions.
[0096] FIG. 8 is a graph showing resistivity of the TiN film with respect to deposition temperature according to the four deposition conditions described above. It can be seen from FIG. 8 that the resistivity decreases with an increase in the deposition temperature. Particularly, it can be seen that the resistivity sharply decreases under the deposition condition (TiN 00) in which the deposition speed is high. Also, we can recognize that resistivity of 200μΩ-cm or less is obtained at about 500° C. under all the four deposition conditions.
[0097] An example of applying the metal nitride film formation method of the present invention to a via contact will now be described in detail, referring to FIGS. 10A through 11F.
[0098] First, a first metal layer 210 such as Al is formed on a semiconductor substrate 200, and a TiN film 220 is deposited as a capping film on the resultant structure, as shown in FIG. 10A. The TiN film 220 can be deposited by sputtering. Then, an interlayer insulative film 230 is deposited, and a portion on which a via is to be formed is etched, thereby forming the structure of FIG. 10B. A thin Ti film (not shown) is formed on the resultant structure to improve attachment strength of the TiN film, before the TiN film, being a barrier metal layer, is deposited. This Ti film can also be formed by sputtering.
[0099] Next, the TiN film 240, being a barrier metal layer, is deposited by the metal nitride film formation method of the present invention, thus forming the structure of FIG. 10C. That is, as described above, a metal source, a purge gas, and a nitrogen source flow into the deposition apparatus of FIG. 1 in the sequence of the metal source, the purge gas, the nitrogen source, and the purge gas. This is repeated until a desired thickness is obtained. Here, the metal source is TiCl4and the nitrogen source is NH3. The amounts of the metal source, the nitrogen source and the purge gas are 1 to 5 sccm, 5 to 200 sccm, and 10 to 200 sccm, respectively, and the inflow times thereof are about 1 to 10 seconds. A deposition temperature is 480° C. or lower, and the pressure in the deposition chamber is between 1 torr and 20 torr. If necessary, an atmospheric gas such as Ar, He, or N2, and a carrier gas of Ar, N2, etc., can be used. These deposition conditions are appropriately controlled considering the deposition apparatus, the deposition speed, the thickness of the TiN film deposited, and the resistivity of the TiN film.
[0100] A metal plug 250 such as W is formed by a typical method, in FIG. 10D, and a metal deposited on the upper surface of an interlayer insulative film 230 is removed by chemical mechanical polishing or etch back, in FIG. 10E. Then, when a second metal layer 260 is formed on the resultant structure as shown in FIG. 10F, interconnection between metal layers is accomplished.
[0101] FIGS. 11A through 11F are cross-sectional views illustrating a process for forming an anchor via contact, which is fundamentally the same as the process of FIGS. 10A through 10F except that an anchor A is formed on the lower portion of a contact hole to lower resistance by increasing a contact area as shown in FIG. 11B. The anchor A is formed by wet etching the interlayer insulative film 335 after forming the contact hole as shown in FIG. 11A. The other steps are the same as those of FIGS. 10A through 10F, so they will not be described again.
[0102] As described above, when the metal nitride film formation method of the present invention is applied to the via contact, a barrier metal layer having an excellent step coverage can be obtained at low temperature. Thus, a contact failure X such as TiFx or AlFx shown in FIGS. 9A and 9B can be prevented.
[0103] <Third Experimental Example>
[0104] A Ti film is deposited to a thickness of 100A on contact holes of various different widths, by sputtering. Then, as a barrier metal layer, a TiN film according to the present invention, and a collimated TiN film formed by sputtering by a conventional method, are deposited to different thicknesses, and a plug is formed of CVD-W. The third experiment measures via resistance in this case. Here, the deposition conditions of the TiN film according to the present invention are equal to the deposition conditions of TiN 00 of the aforementioned second experiment, with a deposition temperature of 450° C.
[0105] Via widths: 0.24 μm, 0.32 μm, 0.39 μm (via depth: 0.9 μm)
[0106] Thickness of TiN film: 100 A, 200 A, 400 A, 600 A (these are deposited by the method of the present invention), 700 A (collimated TiN film)
[0107] As the results of measurement, resistivity generally decreases with an increase in via width as shown in FIG. 12, and resistivity decreases with decreasing the thickness of the TiN film of the present invention. The 100 A-thick TiN film according to the present invention has a similar resistance to the collimated TiN film. In particular, when the via width is 0.39 μm, the above five TiN films have similar via resistances. Meanwhile, in the second experiment and as shown in FIG. 8, the TiN films of the present invention were formed at a high deposition speed per cycle (20 A/cycle) and with large resistivity (300μΩ-cm at 450° C.). Accordingly, if the TiN films of the present invention are formed at a lower deposition speed and with smaller resistivity, their via resistances can be significantly improved.
[0108] FIG. 13 is a graph showing the distribution of the via resistance of each TiN film when the via width is 0.39 μm. From the graph of FIG. 13, we can recognize that the collimated TiN film and the TiN films according to the present invention are evenly distributed, without a big difference, around 1.0Ω.
[0109] Up to now, the present invention has been described by taking as an example the method wherein the TiN film is formed as a metal nitride film by using TiCl4and NH3as a precursor. However, the present invention can be applied to a TiN film using TiCl3, TiI4, TiBr2, TiF4, (C5H5)2TiCl2, ((CH3)5C5)2TiCl2, C5H5TiCl3, C9H10BCl3N6Ti, C9H7TiCl3, (C5(CH3)5)TiCl3, TiCl4(NH3)2, (CH3)5C5Ti(CH3)3, TDEAT or TDMAT instead of TiCl4as the precursor, and also to other metal nitride films such as TaN firm using TaBr5, TaCl5, TaF5, TaI5,or (C5(CH3)5)TaCl4as precursors, and further to almost any material layers deposited using CVD.
[0110] However, when the TiN film is formed using TDEAT or TDMAT as the precursor, it is preferable that a deposition temperature is between 250° C. and 400° C. and a pressure is about 0.1 to 10 torr, in contrast with the cases using the other materials as the precursor. Since the above precursors for forming the TaN film are all solid, a solid bubbler must be used to form a source gas.
[0111] An example of forming a semiconductor capacitor by applying the metal nitride formation method according to the present invention to a capacitor electrode will now be described in detail with reference to FIGS. 14 through 16.
[0112] A semiconductor capacitor is formed by sequentially stacking a lower conductive layer, a dielectric film and an upper conductive layer. The process for forming a lower and/or upper conductive layer to form a semiconductor capacitor according to the present invention adopts the metal nitride film formation method according to the present invention described above. That is, as described above, a metal source, a purge gas, and a nitrogen source flow into the deposition apparatus of FIG. 1 in the sequence of the metal source, the purge gas, the nitrogen source, and the purge gas. This is repeated until a desired thickness is obtained. Here, the metal source is TiCl4and the nitrogen source is NH3. The amounts of the metal source, the nitrogen source and the purge gas are 1 to 5 sccm, 5 to 200 sccm, and 10 to 200 sccm, respectively, and the inflow times thereof are about 1 to 10 seconds. A deposition temperature is 480° C. or lower, and the pressure in the deposition chamber is between 1 torr and 20 torr. If necessary, an atmospheric gas such as Ar, He, or N2, and a carrier gas of Ar, N2, etc., can be used. These deposition conditions are appropriately controlled considering the deposition apparatus, the deposition speed, the thickness of the TiN film deposited, and the resistivity of the TiN film.
[0113] Up to now, the present invention has been described by taking as an example the method wherein the TiN film is formed as a metal nitride film by using TiCl4and NH3as a precursor. However, TiCl3, TiI4, TiBr2, TiF4, (C5H5)2TiCl2, ((CH3)5C5)2TiCl2, C5H5TiCl3, C9H10BCl3N6Ti, C9H7TiCl3, (C5(CH3)5)TiCl3, TiCl4(NH3)2, (CH3)5C5Ti(CH3)3, TDEAT or TDMAT can be used as the precursor. In case that a TaN film is formed as a metal nitride film, TaBr5, TaCl5, TaF5, TaI5, or (C5(CH3)5)TaCl4can be used as precursors.
[0114] When the TiN film is formed using TDEAT or TDMAT as the precursor, it is preferable that a deposition temperature is between 250° C. and 400° C. and a pressure is about 0.1 to 10 torr. Since the above precursors for forming the TaN film are all solid, a solid bubbler must be used to form a source gas.
[0115] <Fourth Experimental Example>
[0116] FIGS. 14A through 14D are cross-sectional views illustrating a process for forming a semiconductor capacitor having a cylindrical electrode structure for measuring step coverage and leakage current characteristics. Referring to FIG. 14A, an SiO2sacrificial oxide film 440 is formed on a semiconductor substrate 400 on which a predetermined contact 420 and an etch stop film 430 are formed. The contact 420 electrically connects the active region of the semiconductor substrate to the electrode of a capacitor via the interlayer dielectric film 410.
[0117] Referring to FIG. 14B, cylindrical holes 447 are formed by dry etching the sacrificial oxide film 440, and then a lower conductive layer 450 is formed by chemical vapor depositing polysilicon. Continuously, as shown in FIG. 14C, a lower electrode 455 is formed by node separating the lower conductive layer 450, and then the sacrificial oxide film 440 of FIG. 14B remaining between the lower electrodes 455 is removed. Next, as shown in FIG. 14D, a dielectric film 460 is formed by chemical vapor depositing Ta2O5on the semiconductor substrate on which the lower electrode has been formed, and an upper conductive layer is formed on the dielectric film at about 480° C. using TiCl4nitrogen precursor and an NH3nitrogen source by the metal nitride film formation method according to the present invention. Thereafter, a polysilicon film is formed on the upper conductive layer, thereby forming the structure of a capacitor according to the present invention. A conventional capacitor is formed by the same method as the above-described method by which the capacitor according to the present invention is formed, except that an upper conductive layer is formed by chemical vapor depositing a TiN film at about 620° C. using TiCl4and NH3as a source gas. Here, 10 sccm of TiCl4and 50 sccm of NH3are used when TiN is chemical vapor deposited.
[0118] As to the capacitor formed by a method according to the present invention (expressed as SLD-TiN) and the capacitor having a chemically vapor deposited (CVDed) TiN upper conductive layer (expressed as CVD-TiN), the step coverage of an upper conductive layer and the leakage current characteristics are measured and shown in Table 2 and FIG. 16, respectively.
| TABLE 2 | |||
|---|---|---|---|
| Classification | Lower thickness | Upper thickness | Step coverage |
| CVD-TiN | 35A | 156A | 22.6% |
| SLD-TiN | 188A | 208A | 90.1% |
[0119] In Table 2, the upper and lower thicknesses denote the thicknesses of an upper conductive layer at portions pointed by reference characters t1and t2shown in FIG. 14D, respectively. As can be seen from Table 2, the step coverage of the capacitor according to the present invention is significantly higher than that of the capacitor having a CVD'ed TiN upper conductive layer. The CVD technique can also improve step coverage by increasing the flow ratio of TiCl4/NH3, but has a drawback in that the leakage current characteristics is degraded due to an increase in the concentration of Cl remaining within a film.
[0120] In FIG. 16, the leakage current value of the capacitor according to the present invention (SLD-TiN) is lower than that of the capacitor having a CVDed upper conductive layer (CVD-TiN) in most of an applied voltage section. In particular, around ±1.2 V, which is the basis of the leakage current characteristics of a capacitor, the leakage current value of the capacitor according to the present invention is only about ⅓ or {fraction (1/15)} times that of the capacitor having a CVDed upper conductive layer.
[0121] FIGS. 15A and 15B show the content of Cl contained in a conductive layer formed by a method according to the present invention and the content of Cl contained in a CVDed conductive layer, respectively. The measurement of the Cl content is achieved by performing XPS with respect to a TiN film formed by the metal nitride film formation method according to the present invention and a CVDed TiN film which are separately formed on SiO2substrates. In the graphs of FIGS. 15A and 15B, the left portion corresponds to a TiN film region, and the right portion, where etching is further progressed, corresponds to an SiO2substrate region. As shown in FIGS. 15A and 15B, the Cl content of the TiN film formed by a method according to the present invention is a maximum of 0.4 atomic % in the TiN film region, but the Cl content of the TiN film formed by CVD is a maximum of 3.9 atomic % in the TiN film region. Preferably, the Cl content in a general capacitor is maintained below 1%. Thus, it can be seen that the TiN film formed by a method according to the present invention has a Cl content that is suitable for the conductive layer of a semiconductor capacitor.
[0122] According to the metal nitride film fonnation method of the present invention as described above, a metal nitride film has low resistivity of 200μΩ-cm or less even with excellent step coverage and contains only a small amount of Cl. Also, the metal nitride film can be formed at a temperature of 500° C. or lower, and also a deposition speed, approximately 20 A/cycle, is considerably higher than that in the metal nitride film formation method using ALE with a growth speed of 0.25 A/cycle.
[0123] Accordingly, as opposed to when a metal nitride film is deposited at a temperature of 650° C. or higher in a conventional method, corrosion of metal wiring and high resistivity due to impurities (Cl) remaining in the metal nitride film can be solved, so that the present invention is applicable to a via contact which has a high aspect ratio and requires a low temperature. Also, since the present invention has a higher deposition speed than the metal nitride film formation method using ALE, it is suitable for mass production.
[0124] Also, the metal nitride film formation method according to the present invention can be used to form the electrode of a semiconductor capacitor having a three-dimensional electrode structure, leading to the formation of a semiconductor capacitor having a very low content of Cl and excellent leakage current characteristics.
Claims
What is claimed is:
1. A method of forming a semiconductor capacitor by sequentially forming a lower conductive layer, a dielectric film and an upper conductive layer on the underlayer of a semiconductor substrate, wherein the process for forming a lower conductive layer and/or an upper conductive layer comprises the steps of:
(a) inserting a semiconductor substrate on which the underlayer on the dielectric film is formed, into a deposition chamber;
(b) admitting a metal source into the deposition chamber
(c) chemisorbing a first portion of the metal source onto the substrate, and physisorbing a second portion of the metal source onto the substrate;
(d) purging the metal source from the deposition chamber;
(e) admitting a nitrogen source into the deposition chamber;
(f) chemisorbing a first portion of the nitrogen source onto the substrate, and physisorbing a second portion of the nitrogen source onto the substrate;
(g) reacting the chemisorbed and physisorbed metal source with the chemisorbed and physisorbed nitrogen source to form a metal nitride film on the substrate; and
(h) purging the nitrogen source from the deposition chamber.
2. The method as claimed in claim 1, wherein the metal source is selected from the group consisting of TiCl4, TiCl3, TiI4, TiBr2, TiF4, (C5H5)2TiCl2, ((CH3)5C5)2TiCl2, C5H5TiCl3, C9H10BCl3N6Ti, C9H7TiCl3, (C5(CH3)5)TiCl3, TiCl4(NH3)2, and (CH3)5C5Ti(CH3)3, and the nitrogen source is NH3.
3. The method as claimed in claim 2, wherein the deposition temperature in the steps (b) through (h) is between 400° C. and 500° C., and the pressure in the deposition chamber is 1 to 20 torr.
4. The method as claimed in claim 1, wherein TDEAT or TDMAT is used as the metal source, and NH3is used as the nitrogen source.
5. The method as claimed in claim 4, wherein the deposition temperature in the steps (b) through (h) is between 250° C. and 400° C. and the pressure in the deposition chamber is 0.1 to 10 torr.
6. The method as claimed in claim 1, wherein a material selected from the group consisting of TaBr5, TaCl5, TaF5, TaI5, and(C5(CH3)5)TaCl4is used as the metal source, and NH3is used as the nitrogen source.
7. The method as claimed in claim 6, wherein the deposition temperature in the steps (b) through (h) is between 400° C. and 500° C., and the pressure in the deposition chamber is 1 to 20torr.
8. The method as claimed in claim 1, wherein the purge gas is Ar or N2.
9. The method as claimed in claim 1, wherein 1-5 sccm of the metal source flows into the deposition chamber for 1 to 10 seconds, 5-200 sccm of the nitrogen source flows thereinto for 1 to 10 seconds, and 10-200 sccm of the purge gas flows thereinto for 1 to 10 seconds.
10. The method as claimed in claim 1, wherein an atmospheric gas, which is at least one selected from the group consisting of Ar, He and N2, is continuously flowed into the deposition chamber during the steps (b) through (h), to maintain a constant pressure in the deposition chamber.
11. The method as claimed in claim 1, wherein the thickness of the lower and/or upper conductive layer is controlled by repeating the steps (b) through (h).