Method of manufacturing a capacitor in a memory device

[0002] 1. Field of the Invention

[0003] The present invention relates to a semiconductor memory device. In particular, the present invention relates to a method of manufacturing a capacitor of a high-integrated memory device using a tantalum oxide film (Ta₂O₅) as a dielectric.

[0004] 2. Description of the Prior Art

[0005] Currently, the semiconductor memory device can be mainly classified into a read/write memory and a read only memory (ROM). In particularly, the read/write memory may be classified into a dynamic RAM (hereinafter called DRAM) and a static RAM. The DRAM is currently the highest integrated device, which is consisted of one unit cell composed of one transistor and one capacitor.

[0006] Meanwhile, as the integration degree of the memory device is advanced, the capacity of the memory has increased four times in three years. Currently, many studies have been focused on 256 Mb(mega bit) DRAM and 1 Gb (giga bit). However, as the integration degree of the DRAM becomes higher, the cell area functioning to read and write the electrical signal must be reduced to 0.5 μm²in case of 256 Mb. Also, the area of the capacitor that is one of the basic elements of the cell, must be reduced to 0.3 μm². Due to this reason, in case of a higher integrated device more than 256 Mb class, the technology used in the conventional semiconductor process has its limitation. In other words, if the capacitor is manufactured by using SiO₂/Si₃N₄etc. of the conventional dielectric materials in manufacturing a 64 Mb DRAM even though the thickness of the thin film becomes thinner, the area in which the capacitor occupies must exceed 6 times the cell area in order to secure the necessary capacitance. Due to this reason as the capacitor can not be used as a flat shape, the sectional area has to be extended in other ways. Thus, various technologies to increase the sectional area, that is, to increase the surface area of the storage node of the capacitor such as a stack capacitor structure or a trench type capacitor structure or a semi-spherical type poly-silicon film, have been proposed so far.

[0007] However in case of the device more than 256 Mb class using SiO₂/Si₃N₄group dielectric materials, the thickness of the device could not be further reduced in order to increase the capacitance. Also, if the structure of the device becomes complicated in order to increase the sectional area of the capacitor, it makes the manufacturing process complicated, thus increasing the manufacturing cost and lowering the throughput. Thus, it is extremely difficult that the conventional method is applied the DRAM more than 256 Mb class, by which a three dimensional cubic structure is formed to increase its sectional area for satisfying the storage static capacitance.

[0008] In order to solve these problems, a study has been made on Ta₂O₅dielectric thin film so as to replace the SiO₂/Si₃N₄group dielectric. However, the capacitance of the Ta₂O₅dielectric thin film is at most 2-3 times compared to that of the SiO₂/Si₃N₄group dielectric. Thus, in order that the Ta₂O₅dielectric thin film can be applied to the DRAM more than 256 Mb class, its dielectric thin film has to be reduced at its minimum. In this case, there is a problem that the leak current is increased. That is, in case of the Ta₂O₅thin film, it is said that the leak current characteristic of the Ta₂O₅capacitor is good at its amorphous state, but the Ta₂O₅thin film can not be used itself since its effective oxide film (Tox) is thick in thickness. Therefore, though a method of crystallizing the Ta₂O₅thin film at high temperature may be used so as to reduce the effective oxide film (Tox), there is a problem that the value of the leak current of the Ta₂O₅capacitor is increased.

[0009] Meanwhile, the technology for manufacturing the capacitor using Ta₂O₅is advantageous in securing a given static capacitance due to its high dielectric constant. However, it must use only TiN as an upper electrode material or a TiN/poly-silicon double structure, in order to prohibit the interface reactance of Ta₂O₅with an upper electrode and a lower electrode and to prevent deterioration of its capacitance characteristic. Further, the lower electrode must use poly-silicon to the surface of which RTN (rapid thermal nitration) is processed.

[0010] However the conventional Ta₂O₅capacitor constructed above may cause deterioration in the electrical characteristic such as an increase of the effective oxide film (Tox), an increase of the leak current etc. upon a high thermal process. Also, it may cause a problem of the step coverage due to a higher integration of the device. Thus, a lot of studies have been made on solving these problems.

[0011] It is an object of the present invention to solve the problems involved in the prior art, and to provide a method of manufacturing a capacitor of a semiconductor memory device, which can improve the step coverage of the electrode while preventing deterioration of the electrical characteristic due to a subsequent thermal process.

[0012] In order to accomplish the above object, the method of manufacturing a method of manufacturing a capacitor of a memory device according to the present invention comprises a method of manufacturing a capacitor of a memory device comprises forming a lower electrode; forming a tantalum oxide film of a dielectric thin film on lower electrode; forming a CVD TiN layer on the tantalum oxide film; forming a MOCVD TiN layer on the CVD TiN layer: and forming a poly-silicon layer on the MOCVD TiN layer whereby an upper electrode in which said CVD TiN layer, said MOCVD TiN layer and said poly-silicon layer arc stacked is formed.

[0013] In the present method, the step of forming the lower electrode includes forming a poly-silicon layer on a substrate, forming a MOCVD TiN layer on the poly-silicon layer and the a CVD TiN layer on the MOCVD TiN.

[0014] The above object, and other features and advantages of the present invention will become more apparent by describing the preferred embodiment thereof with reference to the accompanying drawings, in which:

[0015] FIGS. 1 and 2 are the graphs for showing the changes in thickness of the effective oxide film (Tox) of the Ta₂O₅according to a subsequent annealing process when MOCVD TiN and CVD TiN are each applied to upper electrodes.

[0016] FIG. 3 is the sectional view for illustrating the structure of the upper electrode according to one embodiment of the present invention.

[0017] FIG. 4 is the sectional view for illustrating the structure of the lower electrode according to another embodiment of the present invention.

[0018] TiN can be deposited by chemical vapor deposition (CVD), which can be further divided into TiN by a MOCVD (metal organic CVD) method (hereinafter called “MOCVD TiN”) and CVD TIN depending on its raw material used. FIGS. 1 and 2 are the graphs for showing the changes in thickness of the effective oxide film (Tox) of the Ta₂O₅according to a subsequent annealing process when MOCVD TiN and CVD TiN are each applied to upper electrodes.

[0019] Referring now to FIG. 1. MOCVD TiN which uses TDMAT[Ti(N(CH₃)₂)₄] as a raw material does not allow oxygen within Ta₂O₅thin film to diffuse into the interface of TiN and poly-silicon upon a subsequent thermal process. On the contrary, as it is absorbed into the TiN film, the thickness of the effective oxide film is reduced due to increase of the dielectric constant of the Ta₂O₅film depending on a subsequent thermal process.

[0020] Referring to FIG. 2, though CVD TiN using TiCl₄as a raw material has a good step coverage compared to MOCVD TiN, it does not prevent oxygen from diffusing into the Ta₂O₅film. Thus, due to the oxide film generated at the Ta₂O₅/TiN interface, the thickness of the effective oxide film of Ta₂O₅becomes thicker. If CVD TiN is used instead, the thickness of the effective oxide film (Tox) depending on the temperature of the thermal process shows that it does not change in the range of temperature up to about 750° C., but if the temperature becomes higher it does increase.

[0021] The present invention is to manufacture a capacitor so that it can maintain the thickness of the effective oxide film of Ta₂O₅and it will have an improved step coverage, even after a subsequent flattening process, by using the characteristic of each of MOCVD TiN and CVD TiN.

[0022] FIG. 3 is a sectional view of the capacitor structure according to one embodiment of the present invention. Referring to FIG. 3, the capacitor according to one embodiment of the present invention has a stacked structure in which a poly-silicon film 301 is formed as a lower electrode having a surface processed by RTN, a Ta₂O₅film 302 as a dielectric thin film, a CVD TiN film 303 and a MOCVD TiN film 304 are sequentially stacked from bottom to top. On the MOCVD TiN film 304 may be further formed poly-silicon that is doped as an upper electrode material.

[0023] First, a poly-silicon film 301 is deposited as the lower electrode of Ta₂O₅capacitor and the surface of the poly-silicon film 301 is then processed by RTN. The RTN is performed using NH₃gas at the temperature of 750° C. through 900° C. Then, the Ta₂O₅film 302 as a dielectric thin film is deposited by LPCVD method. At this time, in the method, a tantalum etoxide, Ta(C₂H₅O₅), is used as a raw material, N₂and O₂are used as a carrier gas of reactive material and oxidizer, respectively, the flow of the N₂and O₂gas are maintained at 350 sccm through 450 sccm and 20 sccm through 50 sccm, respectively, the pressure within the reactive furnace is maintained 0.1 Torr through 0.6 Torr, and the substrate is maintained at the temperature of 350° C. through 450° C.

[0024] Next, a N₂O plasma anneal process is performed at 300° C. through 500° C. to remove impurities within the Ta₂O₅film 302 and then to fill depletion of oxygen. Then, a N₂O furnace anneal process is performed at 750° C. through 900° C. to crystallize the Ta₂O₅film 302.

[0025] Thereafter, the CVD TiN film 303 is deposited at 200 Å through 500 Å, wherein TiCl₄is used as a raw material and NH₃is used as a reactive gas. Also, the flow of the raw material and the reactive gas is about 10 sccm through 1000 sccm, the pressure within the reactive furnace is maintained at 0.1 Torr through 2 Torr and the temperature of the substrate is maintained at 300° C. through 500° C.

[0026] Then, the MOCVD TiN film 304 is deposited at 400 Å through 800 Å, wherein TDMAT[Ti(N(CH₃)₂)₄] is used as a raw material, NH₃is used as a reactive gas, and He and Ar is used as a carrier gas. Also, the flow of the raw material is 200 sccm through 500 sccm, the flow of He and Ar of the carrier gases is 100 sccm through 300 sccm, respectively, the pressure within the reactive furnace is maintained at 2 Torr through 10 Torr, and the temperature of the substance is maintained at 300° C. through 500° C.

[0027] Next, a plasma process is performed at the power of 500 Watt through 1000 Watt during 20 seconds through 50 seconds. Then, a MOCVD TiN deposition process and a plasma process may be performed 2 times through 3 times repeatedly.

[0028] Thereafter, the poly-silicon film doped on the MOCVD TiN is deposited at 800 Å through 1200 Å and then a thermal process is performed at the temperature of 650° C. through 850° C.

[0029] FIG. 4 is a sectional view for showing a capacitor structure according to another embodiment of the present invention. Referring to FIG. 4, the capacitor according to another embodiment of the present invention includes a poly-silicon film 401, a MOCVD TiN film 402 and a CVD TiN film 403 as a lower electrode. At this time, the surface of the poly-silicon film 401 may not be processed by RTN. On the CVD TiN film 403 is formed a Ta₂O₅film 404 as a dielectric thin film. Meanwhile, though not shown in FIG. 4, the upper electrode, as in one embodiment of the present invention, may have a structure in which the CVD TiN film (303 in FIG. 3) and the MOCVD TiN film (304 in FIG. 3) are sequentially stacked. Also, on the MOCVD TiN film (304 in FIG. 3) of the upper electrode can be further formed a poly-silicon that is doped as an upper electrode materials.

[0030] The method of manufacturing the capacitor having the structure of FIG. 4 will be explained below.

[0031] First, a poly-silicon film 401 is deposited as the lower electrode of the capacitor and the MOCVD) TiN film 402 is deposited at 400 Å through 800 Å. [DMAT(Ti(N(CH₃)₂)₄)] is used as a raw material, and He and Ar are used as carrier gases. Also, the flow of the raw material is 200 sccm through 500 sccm, and the flow of carrier gases, He and Ar is 100 sccm through 300 sccm. Then, a plasma process is performed with the power of 500 Watt through 1000 Watt during about 20 seconds through 50 seconds. Next, a MOCVD TiN deposition process and a plasma process may be performed 2 times through 3 times repeatedly.

[0032] Then, the CVD TiN film 403 is deposited on the MOCVD TiN film 402 at 200 Å through 500 Å, wherein TiCl₄is used as a raw material and NH₃is used as a reactive gas. Also, the flow of the raw material and the reactive gas is about 10 sccm though 1000 sccm, the pressure within the reactive furnace is maintained at 0.1 Torr though 2 Torr and the temperature of the substrate is maintained at 300° C. through 500° C.

[0033] Next, the Ta₂O ₅film 404 is deposited by LPCVD method. At this time, a tantalum etoxide, [TA(C₂H₅O₅)] is used as a raw material, N₂and O₂are used as a carrier gas of reactive materials and oxidizer, respectively, the flow of the N₂and O₂gases are maintained at 350 sccm through 450 sccm and 20 sccm through 50 sccm, respectively, the pressure within the reactive furnace is maintained 0.1 Torr though 0.6 Torr, and the substrate temperature is maintained at 350° C. through 450° C.

[0034] Next, a N₂O plasma anneal process is performed at the temperature of 300° C. through 500° C. to remove impurities within the Ta₂O₅film 404, and then a N₂O furnace anneal process is performed at 750° C. through 900° C. to crystallize Ta₂O₅.

[0035] As described above, the present invention is characterized in that it forms a capacitor by stacking a CVD TiN film and a MOCVD TiN film, and a poly-silicon film sequentially, in forming an electrode on the Ta₂O₅dielectric thin film. Thus, by applying this method, the present invention can manufacture the shape of the capacitor into a cylinder type, pin type and also can apply the capacitor structure using a semi-spherical poly-silicon.

[0036] While the present invention has been described and illustrated herein with reference to the preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

[0037] The present invention relates to a method of forming an electrode by stacking a CVD TiN film and a MOCVD TiN film, and a poly-silicon film sequentially. It can prevent changes in thickness of the effective oxide film of the Ta₂O₅capacitor against the characteristics of each of the CVD TiN film and the MOCVD TiN film, even after a rapid thermal process. It can also improve the step coverage, thus greatly improving the stability and reliability of the capacitor.