Semiconductor Device and Method of Forming the Same

This invention relates to a semiconductor device and a method of forming the semiconductor device. More particularly, this invention relates to a semiconductor device having a planar surface and a method for forming the same.

Generally, conventional semiconductor devices, are formed as follows.

As shown in FIG. 1A, a field oxide layer 2 is typically formed on a selected region of a silicon semiconductor substrate 1 by a local oxidation silicon(LOCOS) technique thereby defining an active region 100. Next, a gate oxide film 3 at a thickness of approximately 100-200 Angstroms is formed on the silicon substrate 1 by a thermal oxidation technique. Next, a polysilicon layer 4 is deposited on the gate oxide film 3 by a chemical vapor deposition(CVD) method.

Referring to FIG. 1B, polysilicon layer 4 is etched such that the patterned polysilicon layer 4 is arranged at a center portion of the active region 100 to form a gate 4A. Using the gate 4A as the mask, a low concentration impurity ions are implanted into the exposed silicon substrate 1 thereby forming a low concentration impurity layer 5 to either side of the gate 4a. An oxide film 6 is then deposited by a conventional CVD method. Thereafter, as shown FIG. 1C, the oxide film 6 is anisotropically etched such that the oxide film 6 remains at vertical boundaries of gate 4A, to form sidewall spacers 7. Using the sidewall spacers 7 and gate 4A as the mask, a high concentration impurity ions are implanted into the exposed silicon substrate 1 thereby forming a high concentration impurity layer 8. At that point, the impurity layers 5 and 8 are made into junction regions, and the semiconductor device is thus formed.

According to the above-mentioned conventional art, however the semiconductor device has severe topological irregularities in the height of the field oxide layer 2, gate 4A and field transistor which is formed on the field oxide layer 2. Consequently, following the formation of the metal line, shorts may occur between a metal line and a metal line adjacent thereto due to the severe topological irregularities.

In addition, as the area of semiconductor device is reduced, hot carriers are generated due to a high electric field formed at the edge portions of gate 4A. In the case that the generated hot carriers are trapped in the gate oxide film 3, defects are generated in the gate oxide film 3 thereby deteriorating the operation and shortening the life of the semiconductor device.

It is an object of the present invention to provide a semiconductor device and a method of forming the same capable of eliminating the surface topology of the gate and field oxide layer.

Another object of the present invention is to provide a semiconductor device and a method of forming the same capable of preventing shorting between the metal lines due to the severe topological irregularities.

A further object of the present invention is to provide a semiconductor device and method of forming the same capable of preventing the hot carrier effect of the semiconductor device.

In accordance with these and other objects, there is provided a semiconductor device comprising: a plurality of trenches formed in a semiconductor substrate, having a selected depth; a field oxide film formed in any one of the trenches at a selected thickness; a gate insulating film formed on the surface of the semiconductor substrate and inner wall of any one of the other trenches; a plurality of gate electrodes filled in all of trenches, wherein the surface of the gate electrodes is positioned at the same plane with that of the semiconductor substrate; and a plurality of junction regions formed in the semiconductor substrate between the trenches.

In accordance with the present invention, there is provided a method of forming semiconductor device comprises the step of: etching selected regions of semiconductor substrate to form a plurality of trenches; forming a field oxide layer in the inner wall of trench which is corresponding to selected region of field oxide layer among said trenches; filling said trenches with a conductive material to form a gate electrode; and forming junction region in the semiconductor substrate between the trenches.

The preferred embodiment of the present invention will now be described more specifically with reference to the following description, appended claims, and the attached drawing wherein:

FIGS. 1A to 1C are sectional views for explaining step for forming a conventional semiconductor device;

FIGS. 2A to 2H are sectional views for explaining step for forming a semiconductor device according to the present invention; and

FIG. 3 is a sectional view for explaining the formation of a metal-silicide layer on the gate of FIG. 2F.

As shown in FIG. 2A, a first resist pattern 12 is formed on a P-type semiconductor substrate 11 by conventional photolithography technique wherein selected regions are exposed for forming a gate and a field oxide layer. Using the first resist pattern 12, and the exposed semiconductor substrate 11 is then anisotropically etched by reactive ion etching(RIE) technique to form trenches 13A and 13B having depth in the range of 5000-12000 Angstroms.

Referring to FIG. 2B, the first resist pattern 12 is removed by conventional method. A pad oxide film 14 having a thickness of 200-400 Angstroms is then formed on semiconductor substrate 11 by thermal oxidation. Subsequently, a silicon nitride film 15 having a thickness of 1000-1200 Angstroms is deposited by a low pressure chemical vapor deposition(LPCVD) technique. A second resist pattern 16 is then formed on silicon nitride film 15 such that the silicon nitride film 15 formed in trench 13B for forming the field oxide layer is exposed. Using the second resist pattern 16, exposed silicon nitride film 15 is etched by phosphine(PH4) solution having a temperature of 160.degree.-175.degree. C. The etching procedure employed is typically an isotropic wet etching procedure, whereby a portion of the silicon nitride film 15 lying underneath the second resist pattern 16 is also etched as shown in FIG. 2C.

With reference to FIG. 2D, the second resist pattern 16 is removed by conventional method, and inner-wall of the trench 13B is exposed. The inner-wall of the trench is then thermally oxidized to form a field oxide film 17 having a thickness of 4000-7000 Angstroms.

As shown in FIG. 2E, the silicon nitride film 15 is removed by a PH.sub.4 solution, and the pad oxide film 14 is removed by a HF solution. Thereafter, as shown in FIG. 2F, a gate oxide film 18 is formed on surface of the semiconductor substrate 11 including the trenches 13A and 13B where the above-mentioned steps are completed. Subsequently, a doped polysilicon layer 19 having a sufficient thickness of 2000-5000 Angstroms is deposited on the resultant structure formed the gate oxide film 18.

Referring now to FIG. 2G, the doped polysilicon layer 19 is etched by an etchback technique to expose the gate oxide film 18 and surface of the field oxide layer 17. Accordingly, the remaining doped polysilicon layer 19 is filled in trench 13A and 13B, thereby forming a gate 19A. A mixture gas of Cl.sub.2 gas, HBr gas and He gas is used in the above etching of the doped polysilicon.

Referring to FIG. 2H, N-type high concentration impurity ions such as arsenic, having a concentration of 1E13-1E17 ions/cm.sup.3 and an implantation energy of 30-50 KeV, are implanted into the semiconductor substrate 11 to form a high concentration impurity region 21. Thereafter, N-type low concentration impurity ions such as phosphorous, having a concentration of 1E11-1E15 ions/cm.sup.3 and an implantation energy of 40-60 KeV, are implanted in the semiconductor substrate 11 to form a low concentration impurity region 22, wherein the implantation energy for the low concentration impurity region 22 is higher than that for the high concentration impurity region 21. Accordingly, as shown in FIG. 2H, the high concentration impurity region 21 is formed on the low concentration impurity region 22, thereby forming double doped drain(DDD) structure capable of preventing the hot carrier effect. In the above-mentioned embodiment, the high concentration impurity ions were implanted prior to the implantation of the low concentration impurity ions. The low concentration impurity ions, however, may be first implanted to produce the same results.

FIG. 3 is a sectional view for explaining the formation of a metal-silicide layer on the gate in accordance with another embodiment of the present invention.

In a process of FIG. 3, process steps to the formation step of the gate electrode 19A are identically performed. Afterwards to increase conductivity of the gate electrode 19A, a metal silicide layer 20 such as tungsten silicide is formed on the gate electrode 19A by tungsten deposition method or by tungsten silicide deposition method. The tungsten deposition method requires a thermal annealing step for formation of tungsten silicide, and a removal step of unreacted remaining tungsten metal whereas the tungsten silicide deposition method deposits tungsten silicide in one step. WF.sub.6 is used as a source gas for formation of the tungsten silicide layer.

When a metal silicide thickness for fabrication of a memory device is selected to be in the range of 2,000-4,000 Angstroms, a projection height of the formed tungsten-silicide layer from the surface of the semiconductor substrate 11 in the tungsten deposition method is 1,000-2,000 Angstroms. On the other hand, when the tungsten silicide deposition method is used, the projection height is 2,000-4,000 Angstroms, being higher than that of the tungsten deposition method from the surface of the semiconductor substrate 11. The difference due to the fact that tungsten deposited on the semiconductor substrate 11, reacting with the underlying semiconductor substrate 11 when forming the tungsten silicide.

As described previously, the present invention decreases surface topology of a semiconductor device by forming the field oxide and gate electrode inside the silicon substrate and prevents the hot carrier effect by forming a semiconductor device to have DDD structure.

Although the preferred embodiment of the present invention has been disclosed for illustrative purpose, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the present invention as disclosed in the accompanying claims.