Method of forming a gate electrode in a semiconductor device

[0002] Priority is claimed from Republic of Korean Patent Application No. 99-60557 filed Dec. 22, 1999, which is incorporated in its entirety by reference.

[0003] 1. Field of the Invention

[0004] The invention relates generally to a method of forming a gate electrode in a semiconductor device. More particularly, the present invention relates to a method of forming a gate electrode in a semiconductor device by which (TiO₂)_x(Al₂O₃)_1-x, wherein x has a value ranging from approximately 0.05 to approximately 0.85, in which a titanium oxide film (TiO₂) having a high dielectric constant and leakage characteristic and an aluminum oxide film having a good interfacial property are mixed, is used as a gate insulating film.

[0005] 2. Description of the Prior Art

[0006] In a semiconductor device such as DRAM, logic, etc. that has been mass-produced presently, a silicon oxide film (SiO₂) grown by thermal process or a rapid thermal process is mainly used as a gate insulating layer. As the design rule is scaled downed, however, the thickness of the silicon oxide film is scaled down below approximately 25 to approximately 30 A being a limit to the tunneling. Thus, it is expected that the gate insulating film of 0.1 μm technology will result in approximately 15 to approximately 20 A in thickness. Due to the off current increased by direct tunneling, however, there is a possibility that it may adversely affect the operation of a device. Particularly, in case of a memory device, every effort to reduce the leakage current has been made. Recently, as a result of these efforts, many researches into attempt to adopt an insulating material having a high dielectric constant as a gate insulting film have been carried out. Among them, a research by which an tantalum oxide film (Ta₂O₅) used as a dielectric film of a capacitor is used as a gate insulating film had been mostly actively carried out. However, if the tantalum oxide film is used as the gate insulating film and a polysilicon film is used as the gate electrode, due to reaction between the tantalum oxide film and the polysilicon film in an interface between the tantalum oxide film and the polysilicon oxide film, a silicon oxide film is formed, resulting in increase in the thickness of the entire oxide film. At this time, in order to prevent this reaction, a metal structure of a barrier metal layer such as TiN and tungsten may be used. In this case, however, as variations such as the threshold voltage shift, etc. are caused, various types of optimization such as counter doping within a channel, etc. are required. Therefore, it is found that there is a limit to applying the conventional technology.

[0007] On the other hand, it was found that a dielectric film or a gate insulating film of a capacitor using an aluminum oxide film (Al₂O₃), that has been recently researched actively, has a good leakage current characteristic of <10-9A/cm²and a god interfacial property (D_it<1×10¹¹eV⁻¹cm⁻¹). Also, it shows a preferred effect and a stable characteristic during process at high temperature. Meanwhile, in case of a titanium oxide film (TiO₂) having a dielectric constant of about 25 about 3 5, it has a high dielectric constant, but has a drawback that it has a high leakage current since bulk traps or interface defects within a thin film are great.

[0008] In order to accomplish the above object, a method of forming a gate electrode in a semiconductor device according to the present invention is characterized in that it comprises the steps of forming a (TiO₂)_x(Al₂O₃)_1-xfilm on a semiconductor substrate, forming a conductive film on the entire structure and patterning the conductive film and the (TiO₂)_x(Al²O₃)_1-xfilm to form a gate electrode.

[0009] The aforementioned aspects and other features of the present invention will be explained in the following description, taken in conjunction with the accompanying drawings, wherein:

[0010] FIGS. 1A to 1C are cross-sectional views of a device for explaining a method of forming a gate electrode in a semiconductor device.

[0011] The present invention will be described in detail by way of a preferred embodiment with reference to accompanying drawings.

[0012] The present invention employs, as a gate insulating film, (TiO₂)_x(Al₂O₃)_1-x, wherein x has a value ranging from approximately 0.05 to approximately 0.85, in which a titamium oxide film (TiO₂) having a dielectric constant of 7 times higher than a silicon oxide film (k=3.85) and an aluminum oxide film having a good leakage current and an interfacial property are mixed. At this time, the titanium has an energy band gap of about 3.25 eV and has a high dielectric constant of 50 but has a poor leakage characteristic. Also, the aluminum oxide film has an energy band gap of about 9 eV and has a high dielectric constant of about 7 about 10. Particularly, the aluminum oxide film has a good interfacial property and is thermally very stable during reactive sputtering using doped aluminum. Therefore, it is possible to form a gate insulating film having good leakage interfacial property and also having a good high dielectric constant, by mixing an aluminum oxide and a titanium oxide film in a certain composition.

[0013] FIGS. 1A to 1C are cross-sectional views of a device for explaining a method of forming a gate electrode in a semiconductor device.

[0014] Referring now to FIG. 1A, there is shown a sectional view of a device in which after a device separation film (not shown) is formed on a given region of a semiconductor substrate 11, a (TiO₂)_x(Al₂O₃)_1-xfilm 12 is formed on the entire structure in thickness of about 10 about 250A, by reactive sputtering method under O₂/Ar atmosphere using TiAl_xas a target.

[0015] The (TiO₂)_x(Al₂O₃)_1-xfilm may be formed by reactive sputtering using DC magnetron or RF plasma having the power density of about 0.14 about 7 W/cm²(in case of 8 inch wafer, 100 W about 5 kW). If the RF plasma is employed, Al or Ti is used as a RF coil and the electric power for controlling the bias between the coil and the substrate is about −300 about 300 W. Also, the reactive sputtering process may be performed under Ar atmosphere having O₂of 10 about 100 sccm and Ar of 10 about 45 sccm and its deposition temperature is about −25° C. to about 750° C.

[0016] Also, doped TiAl_xmay be used as the target for forming the (TiO₂)_x(Al₂O_3x-1film other than TiAlx and Si, Zr, HF, Y and W having the concentration of 0.1˜7 mole % may be used as the dopant at this time.

[0017] Meanwhile, the (TiO₂)_x(Al₂O₃)_1-xfilm may be formed by other process than the reactive sputtering process. That is, a target in which TiO₂and Al₂O₃are mixed, may be deposited using DC magnetron or RF power under Ar atmosphere. Also, it may be deposited by CVD method using inorganic source, in which AlCl₃(or DEMA) and TiCl₃precursor is used along with H₂and H₂O vapor and a plasma CVD or LPCVD of about 200 about 850° C. is used. Further, it may be deposited by CVD method using metal organic source, in which a Ti precursor of TDMAT, TDEAT and Ti(CH₃)₃(trimethyl Ti) an Al precursor of Al (CH₃)₃(trimethyl Al) are used along with H₂and H₂O vapor, and a plasma CVD or LPCVD of about 150 about 750° C. isused.

[0018] After the (TiO₂)_x(Al₂O₃)_1-xfilm is formed, an annealing process may be implemented in order to improve the quality of the thin, in which a furnace annealing process may be implemented under oxygen or nitrogen atmosphere at the temperature of about 450 about 850° C. for 30 minutes and a rapid thermal process may be implemented under O₂or N₂O atmosphere on the lamp-up condition of 20-80° C./sec at the temperature of about 450 about 850° C. for about 10 about 120 seconds.

[0019] FIG. 1 (c) is a cross-sectional view of the device in which after the conductive film 13 and the (TiO₂)_x(Al₂O₃)_1-xfilm 12 are patterned to form a gate electrode.

[0020] As another embodiment of the present invention, before the (TiO₂)_x(Al₂O₃)_1-xfilm is deposited, a very thin silicon oxide film of 2-10 A may be formed in order to improve the interfacial property between the semiconductor substrate and the (TiO₂)_x(Al₂O₃)_1-xfilm.

[0021] Further, the present invention is not limited to a method of forming a gate insulating film but may be applied to a dielectric film in a capacitor of a DRAM device.

[0022] As mentioned above, the present invention cannot only improve the leakage current characteristic of a semiconductor device by forming a (TiO₂)_x(Al₂O₃)_1-xfilm as a gate insulating film. Also, it is expected that the present invention can assist in early developing a high-speed device having a high density in the future.

[0023] The present invention has been described with reference to a particular embodiment in connection with a particular application. Those having ordinary skill in the art and access to the teachings of the present invention will recognize additional modifications and applications within the scope thereof.

[0024] It is therefore intended by the appended claims to cover any and all such applications, modifications, and embodiments within the scope of the present invention.