Method for forming aluminum oxide as a gate dielectric

[0002] The present invention relates to a semiconductor device; and, more particularly, to a method for manufacturing a gate structure incorporated therein aluminum oxide as a gate dielectric.

[0003] As is well known, a semiconductor device has been down-sized by a scale down of a design rule. Therefore, a gate oxide tends to rapidly approach 30 Å in thickness and below to increase the capacitance between a gate electrode and a channel region. However, the use of silicon dioxide as a gate dielectric is limited at this thickness and below. Once silicon dioxide SiO₂is formed to a thickness of less than 30 Å, direct tunneling may occur through the gate dielectric to the channel region, thereby increasing a leakage current associated with the gate electrode and the channel region, causing an increase in power consumption.

[0004] Since reducing the thickness of the gate dielectric inherently increases the gate-to-channel leakage current, alternative methods have been developed to reduce this leakage current while maintaining thin SiO₂equivalent thickness. One of these methods is to use a high K dielectric material such as Ta₂O₅as the gate dielectric material to increase the capacitance between the gate and the channel.

[0005] However, if a poly-silicon is utilized as a gate electrode, the use of Ta₂O₅for gate dielectric materials has a disadvantage in integrating the semiconductor device. That is, an undesired SiO₂and TaSi₂are formed at an interface between Ta₂O₅and the poly-silicon, which, in turn, increases an equivalent oxide thickness. In order to overcome this problem, a barrier metal such as TiN is employed. However, the TiN makes a threshold voltage shift changed.

[0006] In addition, the use of high K dielectrics for gate dielectric materials is disadvantageous in integrated circuits because high dielectric materials contain great number of bulk traps and interface traps than gate dielectrics made from thermally grown SiO₂. These traps adversely effect sub-threshold slope and threshold voltage operation of electric devices.

[0007] If the above-described problems are overcome, a high K dielectric is utilized as a gate oxide with excellent leakage current as well as a low interface state with both a gate electrode and a silicon substrate.

[0008] It is, therefore, an object of the present invention to provide a method for manufacturing a gate structure incorporated therein aluminum oxide as a gate oxide for use in a semiconductor device.

[0009] In accordance with one aspect of the present invention, there is provided a method for manufacturing a gate structure for use in a semiconductor device, the method comprising the steps of: a) preparing a semiconductor substrate provided with an isolation region formed therein; b) forming an aluminum oxide (Al₂O₃) layer on top of the semiconductor substrate with doping a dopant in situ; c) forming a conductive layer on top of the Al₂O₃layer; and d) patterning the conductive layer, thereby obtaining the gate structure.

[0010] In accordance with another aspect of the present invention, there is provided a method for method for manufacturing a gate structure for use in a semiconductor device, the method comprising the steps of: a) preparing a semiconductor substrate provided with an isolation region formed therein; b) forming an Al₂O₃layer on top of the semiconductor substrate; c) forming a conductive layer on top of the Al₂O₃layer; d) implanting dopants into the Al₂O₃layer; e) patterning the conductive layer and the Al₂O₃layer into the gate structure; and f) selectively reoxidizing the dopants.

[0011] The above and other objects and features of the present invention will become apparent from the following description of the preferred embodiments given in conjunction with the accompanying drawings, in which:

[0012] FIGS. 1A to 1E are schematic cross sectional views setting forth a method for the manufacture of a gate structure incorporated therein aluminum oxide as a gate oxide in accordance with a first preferred embodiment of the present invention; and

[0013] FIGS. 2A to 2E are schematic cross sectional views setting forth a method for the manufacture of a gate structure incorporated therein aluminum oxide as a gate oxide in accordance with a second preferred embodiment of the present invention.

[0014] There are provided in FIGS. 1A to 1E and FIGS. 2A to 2E cross sectional views setting forth methods for manufacturing gate structures 100, 200 for use in a semiconductor device in accordance with preferred embodiments of the present invention.

[0015] Referring to FIG. 1A, the process for manufacturing the gate structure 100 begins with the preparation of a semiconductor substrate 110 including an isolation region 120 for defining an active region. The isolation region 120 may be formed in a structure of local oxidation of silicon (LOCOS) or in a structure of shallow trench isolation (STI).

[0016] Optionally, an ultra thin silicon dioxide (SiO₂) layer (not shown) may be thermally grown on the semiconductor substrate 110 by using a wet H₂/O₂or a dry O₂at a temperature ranging from approximately 650° C. to approximately 950° C. It is preferable that the ultra thin silicon SiO₂layer has a thickness ranging from approximately 3 Å to approximately 20 Å. Alternatively, it is possible that the ultra thin silicon SiO₂layer can be formed by using a rapid thermal process (RTP) at a temperature ranging from approximately 700° C. to approximately 900° C. in the presence of oxygen gas or N₂O gas. It is preferable that the RTP is carried out in a pressure ranging from approximately 0.1 torr to approximately 1.0 torr.

[0017] Referring to FIG. 1B, an aluminum oxide (Al₂O₃) layer 130 is formed on top of the semiconductor substrate 110 by using a low pressure chemical vapor deposition (LPCVD) at a temperature ranging from approximately 150° C. to approximately 700° C. In this case, Al source gas can be selected from a group consisting of tri methyl aluminum (TMA), Al(CH₃)₂Cl, AlCl₃or the like. It is possible that the Al₂O₃layer 130 is formed by using a plasma enhanced chemical vapor deposition process (PECVD) at a temperature ranging from approximately 150° to approximately 700° C. Dopants 132 are doped into the (Al₂O₃) layer 130 in situ by using an atomic layer deposition (ALD) at one to two monolayer thickness of dopant. The dopants 132 can be selected from the group consisting of silicon (Si), zirconium (Zr), hafnium (Hf), niobium (Nb) or the like. If the dopants 132 are Si, a source gas can be selected from a group consisting of SiH₄, SiCl₄, Si₂H₄or the like. In this case, the concentration of Si is controlled within a range from approximately 0.1 to approximately 5% on the basis of weight by diluting the source gas with Ar gas. Alternatively, if dopants are Zr, a source gas can be selected from a group consisting of ZrCl₄, HfCl₄, tetrakis (tetramethylamido) zirconium [(C₁₀H₁₉O₂)₄Zr] or the like. In this case, it is preferable that a concentration of Zr is controlled within a range from approximately 0.1% to approximately 5% on the basis of weight by diluting the source gas with Ar gas.

[0018] Referring to FIG. 1C, the dopants 132 are diffused into the Al₂O₃layer 130 by heat-treating the Al₂O₃layer 130, thereby obtaining a doped Al₂O₃layer 134. Optionally, the doped Al₂O₃layer 134 is annealed by using a UV ozone (O₃) at a temperature ranging from approximately 300° C. to approximately 550° C. for 3-30 minutes to remove an unwanted organic materials in the Al₂O₃layer 130.

[0019] Referring to 1D, a conductive layer 140 is formed on top of the Al₂O₃layer 130. The conductive layer 140 can be made of a material selected from a group consisting of, a poly-Si, a doped poly-Si, amorphous-Si, W-polycide, Ti-polycide, Co-polycide, Mo-polycide, W, Ta, WN, TiN or the like.

[0020] Referring to FIG. 1E, the conductive layer 140 and the doped Al₂O₃layer 134 are patterned into a predetermined configuration, thereby obtaining a gate electrode 142 and a gate dielectric 136.

[0021] Referring to FIGS. 2A to 2E, there are schematic cross sectional views setting forth a method for the manufacture of a gate structure incorporated therein aluminum oxide as a gate oxide in accordance with a second preferred embodiment of the present invention.

[0022] Referring to FIG. 2A, the process for manufacturing the gate structure 200 begins with the preparation of a semiconductor substrate 210 including an isolation region 220 for defining an active region. The isolation region 220 may be formed in a structure of LOCOS or in a structure of STI.

[0023] Optionally, a thin SiO₂layer (not shown) may be thermally grown on the semiconductor substrate 210 by using a wet H₂/O₂or a dry O₂at a temperature ranging from approximately 650° C. to approximately 950° C. It is preferable that the ultra thin silicon SiO₂layer has a thickness ranging from approximately 3 Å to approximately 20 Å. Alternatively, it is possible that the ultra thin silicon SiO₂layer can be formed by using RTP at a temperature ranging from approximately 700° C. to approximately 900° C. in the presence of an oxygen gas or a N₂O gas. It is preferable that the RTP is carried out in a pressure ranging from approximately 0.1 torr to approximately 1.0 torr.

[0024] Referring to FIG. 2B, an Al₂O₃layer 230 is formed on top of the semiconductor substrate 210 by using CVD at a temperature ranging from approximately 150° C. to approximately 700° C. In this case, Al source gas can be selected from a group consisting of TMA, Al(CH₃)₂Cl, AlCl₃or the like. It is possible that the Al₂O₃layer 230 is formed by using an ALD in the presence of oxygen.

[0025] Thereafter, a conductive layer 240 is formed on top of the Al₂O₃layer 230. The conductive layer 240 can be made of a material selcted from a group consisting of, a poly-Si, a doped poly-Si, amorphous-Si, W-polycide, Ti-polycide, Co-polycide, Mo-polycide, W, Ta, WN, TaN, TiN or the like. It is preferable that the conductive layer 240 has a thickness ranging from approximately 500 Å to approximately 2,000 Å.

[0026] Referring to FIG. 2C, dopants are doped into the Al₂O₃layer 230 by using an ion implantation method. The dopants can be selected from a group consisting of Si, Zr, Hf, Nb or the like. The ion implantation is carried out at a low energy with high dosage. It is preferable that a dosage of dopants is ranged from approximately 5*10¹⁴to approximately 1*10¹⁶ions/cm².

[0027] Referring to FIG. 2D, the dopants are diffused into the Al₂O₃layer 230 by using an annealing method, thereby obtaining a doped Al₂O₃layer 232. The annealing process can be carried out by using UV ozone at a temperature ranging from approximately 300° C. to approximately 500° C. Alternatively, the annealing process can be carried out by using a furnace at a temperature ranging from approximately 300° C. to approximately 500° C. in the presence of N₂O. It should be noted that implementing the ion implantation and the annealing processes reduces metal vacancy of the Al₂O₃layer 230. Further, since the ion implantation process is carried out after the formation of the conductive layer 240, the semiconductor substrate 210 is protected from the ion implantation process.

[0028] Referring to FIG. 2E, the conductive layer 240 and the doped Al₂O₃layer 232 are patterned into a predetermined configuration, thereby obtaining a gate electrode 242 and a gate dielectric 234. A material such as SiO₂, SiON, Al₂O₃, or Si₃N₄can be used as a hard mask during the patterning process. Finally, a lightly doped drain (LDD) selective oxidation process is carried out on the gate dielectric 234 and the gate electrode 242 at a temperature ranging from approximately 700° C. to approximately 850° C. in the presence of oxygen or nitrous oxide, which selectively reoxidizes the dopants.

[0029] The present invention thus provides gate dielectrics having a higher dielectric constant than SiO₂, excellent leakage current, low interface state density, and good thermal stability with Si by utilizing Al₂O₃as a gate dielectric. This is achieved by doping a dopant such as Si, Zr, Hf, Nb or the like into the Al₂O₃gate dielectric.

[0030] While the present invention has been described with respect to the particular embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.