Semiconductor structure

Abstract

The present invention discloses a semiconductor structure comprising a semiconductor substrate having a U-shape trench, a U-shape gate dielectric layer on the U-shape trench, a U-shape gate region on the U-shape gate dielectric layer, a conducting matter in the U-shape gate region, and a cover dielectric layer on the conducting matter. The semiconductor structure may have a minimized size and when recess channels are formed thereby, the integration is accordingly improved without suffering from the short channel effect.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a structure of a semiconductor device, and particularly to a structure of a buried word line.

2. Description of the Prior Art

As electronic products are becoming lighter, thinner, shorter, and smaller, dynamic random access memory (DRAM) geometries are being scaled down to match the trends of high integration and high density. DRAM composed of a lot of memory cells is one of the most popular volatile memory devices. Each memory cell of DRAM comprises a MOS (metal-oxide-semiconductor) transistor and at least a capacitor stacked each other in a series connection. By using word lines and bit lines, DRAM can be read and programmed.

In order to miniaturize DRAM, gate channel length is shortened, but the short channel effect becomes an obstacle to the improvement of the integration of the semiconductor device. Methods of avoiding the short channel effect had been proposed, for example, decreasing the thickness of the gate oxide layer, increasing dopant concentration, and the like. However, theses methods may encounter some problems, such as low element reliability and slow data transfer rates, and are unsuitable to be actually used.

In order to solve these problems, a hole type recess channel MOS transistor has been developed and gradually adopted to increase the integration. In comparison with a conventional horizontal MOS transistor, the hole type recess channel MOS transistor includes the gate and the source/drain formed in an etched trench of a semiconductor substrate, and furthermore, the gate channel region is disposed at the bottom portion of the trench, thereby to reduce the horizontal area of the MOS transistor for improving the device integration.

FIG. 1 illustrates a schematically cross-sectional view of a recess channel MOS transistor device having a gate structure and a word line structure thereabove, which is constructed in a semiconductor substrate 10. The MOS transistor includes a gate oxide layer 12, a polysilicon layer 14, a doped polysilicon layer 16, an inner spacer 18, a polysilicon layer 20, a tungsten metal layer 22, a silicon nitride layer 24, and spacers 26. The tungsten metal layer 22 serving as a word line is disposed above the surface of the semiconductor substrate 10.

To improve the integration of a semiconductor device is constantly a subject to be researched and developed, and, therefore, there is still a need for a novel MOS transistor device structure.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a structure of a buried word line, which has a film stack structure. Each film may be very thin, and accordingly the integration of the semiconductor device can be improved.

The semiconductor structure according to the present invention comprises a semiconductor substrate having a U-shaped trench in the semiconductor substrate; a U-shaped gate dielectric layer formed on a surface of the U-shaped trench; a U-shaped gate region formed on a top surface of the U-shaped gate dielectric layer; a conducting matter formed in the U-shaped trench and enclosed by the U-shaped gate region, wherein the conducting matter is electrically connected to the U-shaped gate region; and a cover dielectric layer formed on top of the U-shaped trench to cover the U-shaped gate region and the conducting matter.

The semiconductor structure according to the present invention is a film stack structure, in which, a buried word line and a recess channel is formed in the semiconductor substrate. Since each film of the film stack structure can be very thin, the integration of the semiconductor device can be improved. Furthermore, due to the design of recess channel, the short channel effect can be avoided.

These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematically cross-sectional view of a conventional recess channel MOS transistor device having a gate structure and a word line structure above the gate structure;

FIGS. 2 and 3 illustrate schematically cross-sectional views of some embodiments of the semiconductor structure according to the present invention; and

FIGS. 4 and 5 illustrate schematically partially cross-sectional views and partially perspective views of some embodiments of the semiconductor structure according to the present invention.

DETAILED DESCRIPTION

FIG. 2 illustrates a schematically cross-sectional view of an embodiment of the present invention, which may be utilized in an EUD type transistor. The semiconductor structure as shown in FIG. 2 comprises a semiconductor substrate 50 and a film stack structure of a U-shape gate dielectric layer 52, a U-shape gate region 54, a conducting layer 56, and a cover dielectric layer 58.

The semiconductor substrate 50 has a U-shaped trench therein. The U-shape gate dielectric layer 52 is disposed on the surface of the U-shape trench of the semiconductor substrate 50 and may be for example a silicon oxide compound layer formed by the oxidation of the silicon at the surface of the semiconductor substrate. It has to be mentioned here that the surface of the U-shape trench of the semiconductor substrate 50 means for the inner surface of the U-shape trench or the outer surface of the U-shape trench.

The U-shape gate region 54 is disposed in the U-shape trench formed in the U-shape gate dielectric layer 52. The gate region 54 may be deposited into the trench by deposition and then etched back to form a recess for subsequent formation of the conducting layer therein. The gate region 54 may comprise, for example, polysilicon.

The conducting layer 56 is disposed in the recess of the U-shape gate region 54 to serve as a word line and may comprise, for example, one selected from the group consisting of tungsten, nickel, copper, cobalt, a combination thereof, and a silicide thereof or a material of low resistance.

A cover dielectric layer 58 covers the top of the conducting layer 56 and the top of the U-shape gate region 54. The cover dielectric layer 58 and the gate dielectric layer 52 together separate the conducting layer 56 and the U-shape gate region 54 from the semiconductor substrate 50. The cover dielectric layer may include dielectric material such as silicon nitride, silicon oxide, and the like. The height of the bottom of the cover dielectric layer 58 is substantially lower than the height of the top 60 of the semiconductor substrate 50. In such structure, the semiconductor structure according to the present invention is entirely buried in the semiconductor substrate, such that the part of the semiconductor substrate 50 surrounding the U-shape gate dielectric layer 52 forms a gate channel.

Furthermore, an adhesive layer 62 may be optionally disposed between the U-shape gate region 54 and the conducting layer 56, as shown in FIG. 3. The adhesive layer 62 is also in a U-shape because it is between the U-shape gate region and the conducting layer. The adhesive layer 62 may comprise one selected from the group consisting of titanium, tantalum, an alloy thereof, and a nitride thereof, for example, Ti, Ta, TiN, TaN, TiTa alloy, and the like, or a material of low resistance. The adhesive layer improves the adhesion of the conducting layer to the gate region and also plays a role as a barrier layer to inhibit the diffusion of the ingredients of the conducting layer into the gate region to affect the electric properties.

Furthermore, the semiconductor structure according to the present invention may have other modified aspects. For example, referring to FIG. 4 showing a schematically partially cross-sectional view and partially perspective view of a semiconductor structure according to the present invention, the bottom portions of the U-shape trench of the semiconductor substrate, the U-shape gate dielectric layer 52, the U-shape gate region 54, and the conducting layer 56 together may have an indent, such that the semiconductor substrate has a corresponding fin structure. Alternatively, the semiconductor structure may further have an adhesive layer, as shown in FIG. 5. The bottom portions of the U-shape trench of the semiconductor substrate, the U-shape gate dielectric layer 52, the U-shape gate region 54, the adhesive layer 62, and the conducting layer 56 may together have an indent, such that the semiconductor substrate has a corresponding fin structure. Such structure may be utilized in a fin transistor.

Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention.

Claims

1. A semiconductor structure comprising:

a semiconductor substrate having a U-shaped trench in the semiconductor substrate;

a U-shaped gate dielectric layer formed on a surface of the U-shaped trench;

a U-shaped gate region formed on a top surface of the U-shaped gate dielectric layer;

a conducting matter formed in the U-shaped trench and enclosed by the U-shaped gate region, wherein the conducting matter is electrically connected to the U-shaped gate region; and

a cover dielectric layer formed on top of the U-shaped trench to cover the U-shaped gate region and the conducting matter.

2. The semiconductor structure of claim 1, wherein the conducting matter is served as a word line.

3. The semiconductor structure of claim 1, wherein the conducting matter comprises a material selected from the group consisting of tungsten, nickel, copper, cobalt, a combination thereof, and a silicide thereof.

4. The semiconductor structure of claim 1 further comprising a U-shaped adhesive layer formed between the U-shaped gate region and the conducting matter.

5. The semiconductor structure of claim 4, wherein the adhesive layer comprises a material selected from the group consisting of titanium, tantalum, an alloy thereof, and a nitride thereof.

6. The semiconductor structure of claim 4, wherein the cover dielectric layer covers the adhesive layer on top of the U-shaped trench.