JPH0377376A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To avoid short circuit between conductor film patterns which are so formed as to cross reverse-tapered steps by a method wherein the side walls of the tapered steps are covered with insulating films and a conductor film is built up on them and selectively etched to form the conductor film patterns which cross the thin film pattern and are separated from each other. CONSTITUTION:Side walls 7 composed of polycrystalline silicon films are formed on the ends of a gate electrode 4 to eliminate a reverse-tapered shape, and a thermal treatment is performed in an oxidizing gas atmosphere to oxidize the side walls 7. Apertures are formed in an oxide film 3 on a source diffused layer 6a and a drain diffused layer 6b. A conductor film 8 composed of an Al film or a polycrystalline silicon film is built up over the whole surface and patterned by anisotropic etching with an RIE method to form a source electrode 8a and a drain electrode 8b. As the reverse-tapered region K at the end of the gate electrode 4 is filled with the side walls 7 composed of the polycrystalline silicon films and, further, the polycrystalline silicon films are insulated from the conductor film 8 leakage current between the source electrode 8a and the drain electrode 8b can be eliminated.

Description

[Detailed Description of the Invention] [Summary] Regarding a method for forming a conductive film pattern, the purpose of this method is to form a thin film with an inverted tapered shape, with the aim of preventing short circuits in a conductive film pattern formed across steps in an inverted tapered shape. A step of depositing a polycrystalline silicon film on a substrate having a pattern and performing anisotropic etching to form a sidewall made of the polycrystalline silicon film at the edge of the thin film pattern, and oxidizing all or at least the surface of the sidewall. Alternatively, a step of covering the side wall with an insulating film, and a step of depositing a conductive film on this and selectively etching it to form conductive film patterns that intersect with the thin film pattern and are separated from each other. Configure to include.

[Industrial Field of Application] The present invention relates to a method for manufacturing a semiconductor device, and particularly to a method for forming a conductive film pattern.

[Prior Art] The leakage current between the saws 171 and 147 of a MOS transistor, which is a component of a semiconductor IC, is normally required to be an extremely small value of about 10-''A.

However, conventionally, it has been difficult to stably suppress the leakage current to a very small value and reduce its variation, which has caused deterioration in the characteristics of semiconductor ICs. One reason for the increase in leakage current is that the end shape of the gate electrode pattern is reversely tapered, as described below.

3(a) to 3(C) are process cross-sectional views of a conventional MOS transistor, and FIG. 4 is a plan view of a MO3I-transistor. Compatible. As shown in FIG. 3(a), first, a p-type semiconductor substrate 1
An active region separated by a field oxide film 12 is formed on the active region 1, and a thermal oxide film 13 is formed on the surface thereof.

A gate electrode 14 is then formed by depositing a polycrystalline silicon film and selectively etching it. When the end shape of the gate electrode 14 is shaped into a reverse tapered shape as shown in the figure by this etching, a reverse taper region K is generated at the end of the gate electrode 14. After forming the gate electrode 14 as described above, heat treatment is performed to cover the surface of the gate electrode 14 with an oxide film 15. Next, using the gate electrode 14 as a mask, n-type impurity ions are implanted through the thermal oxide film 15 to form a source diffusion layer 16a and a drain diffusion Ji 16b. Next, as shown in FIG. 6B, the thermal oxide film 13 on the source diffusion layer 16a and the drain diffusion layer 1i 16b is opened, and a conductive film 1 made of an AI film or a polycrystalline silicon film doped with impurities is formed on the entire surface.
8 is deposited, but in this case, as a matter of course, the inside of the reverse tapered region is also filled with the conductive film 18. Next, as shown in FIG. 2C, the conductive film 18 is patterned to form a source electrode 18a and a drain electrode 18
Separate and form b. In order to improve pattern accuracy, the patterning is usually performed by anisotropic etching using reactive ion etching (RIE). Therefore, the conductor film embedded in the reverse taper region remains without being removed, with the eaves above the reverse taper region acting as a mask. In this way, the conductor film left inside the reverse taper region becomes the fourth conductor film.
As seen in the figure, the source electrode 18a and the drain electrode 18b are brought into conduction, resulting in an increase in leakage current between the source and drain.

[Problem to be solved by the invention]

In the above process, if the patterning of the gate electrode 14 is performed by anisotropic etching using the RIE method, the end portions of the pattern will normally have a vertical shape, and a reverse tapered shape will rarely occur. However, it is difficult to completely prevent the reverse taper shape that slightly occurs due to variations in etching conditions during etching, and in particular, the leakage current between the saw 171147 of the MOS transistor is about 10-''A as described above. Since this is a very small value, even if a slight reverse taper shape occurs, the leakage current increases.

Further, the above-mentioned problems occur not only when manufacturing MOS transistors, but also generally occur when forming a conductor film pattern that intersects a thin film pattern on a semiconductor substrate, leading to deterioration of device characteristics.

Therefore, an object of the present invention is to prevent short-circuiting of a conductor film pattern formed to intersect with a reversely tapered step.

[Means for Solving the Problems] To solve the above problems, a polycrystalline silicon film is deposited on a substrate having a thin film pattern having an inverted tapered shape, and anisotropic etching is performed to form the polycrystalline silicon film at the edge of the thin film pattern. A step of forming a side wall made of a film, a step of oxidizing all or at least the surface of the side wall, or a step of covering the side wall with an insulating film, and depositing a conductive film on the side wall and selectively etching it. This is achieved by a method for manufacturing a semiconductor device characterized by including the step of forming conductor film patterns that intersect with the thin film pattern and are separated from each other.

[Function] In the present invention, first, a polycrystalline silicon film having excellent step coverage is deposited on a substrate having a thin film pattern, so that the inverted tapered regions at the ends of the three film patterns are completely covered with the polycrystalline silicon film. Embed in.

Then, by anisotropically etching the polycrystalline silicon film, the polycrystalline silicon embedded in the reverse taper region is left as a sidewall at the end of the thin film pattern.

Through the above steps, the inverse tapered shape of the end portion of the thin film pattern can be completely eliminated. Next, by oxidizing all or at least the surface of the sidewall formed as described above, or covering the sidewall with an insulating film, the conductor film and the polycrystalline silicon deposited thereon in the next step are formed. Separate and insulate.

When a four-layer film is then deposited and buttered by anisotropic etching, the conductor film at the ends of the thin film pattern is completely etched away because the reverse tapered shape at the ends of the thin film pattern has been eliminated.

Therefore, the conductor film pattern will not leak (no leakage will occur).Also, since the polycrystalline silicon forming the sidewalls was insulated from the conductor film pattern in the previous process, the conductor film pattern will pass through the polycrystalline silicon. No leaks.

(Example) An example in which the method according to the present invention is applied to the manufacturing process of an MO3I-transistor will be described with reference to the process cross-sectional view of FIG.

First, as shown in FIG. 2(a), an active region separated by a field oxide film 2 is formed on a p-type semiconductor substrate l, and a thermal oxide film 3 is formed on the surface of the active region. A polycrystalline silicon film is deposited and anisotropically etched using the RIE method to form a gate electrode 4. When the end shape of the gate electrode 4 is shaped into a reverse tapered shape due to a change in the etching conditions during the etching, a reverse taper region K is generated as shown in the figure. Thereafter, the surface of the gate electrode 4 is oxidized by heat treatment to form an oxide film 5. Next, using the gate electrode 4 as a mask, ions of an n-type impurity, such as phosphorus (P), are implanted through the thermal oxide film 3 to form a source diffusion layer 6a and a drain diffusion layer 6h.

After depositing a polycrystalline silicon film 8 on the entire surface, RIE
As shown in FIG. 3B, side walls 7 made of polycrystalline silicon film are formed at the ends of the gate electrode 4 to eliminate the reverse tapered shape. Subsequently, the side wall 7 is oxidized by heat treatment in an oxidizing gas atmosphere. At this time, it is not necessary to oxidize the entire polycrystalline silicon film constituting the sidewall 7, and oxidizing only its surface will not affect the subsequent results. Alternatively, an oxide film may be formed on the surface of the side wall 7 by using the CVD method without oxidizing the side wall 7. Then, as shown in FIG. 2C, windows are opened in the oxide film 3 on the source diffusion layer Fi6a and the drain diffusion layer 6b, and a conductive film 8 made of an Al film or a polycrystalline silicon film is deposited on the entire surface. Then, as shown in FIG. 2D, the conductor film 8 is patterned by anisotropic etching using the RIE method to form a source electrode 8a and a drain electrode 8b. FIG. 2 shows a plan view of the MOS transistor formed by the above steps, and the cross-sectional view taken along the line AA' is the first one.
This corresponds to figure (d). As seen in FIG. 2, the reverse tapered region at the end of the gate electrode 4 is composed of a side wall 7 made of a polycrystalline silicon film, and this polycrystalline silicon film was insulated from the conductive film 8 in the previous step. Therefore, no leakage occurs between the source electrode 8a and the drain electrode 8b.

[Effects of the Invention] As described above, according to the present invention, even when a conductive film pattern is formed that intersects a thin film pattern having an inversely tapered step, leakage does not occur between the conductive film patterns. This is useful in improving the reliability of semiconductor devices.

[Brief explanation of drawings]

Figures 1 (a) to (d) are process sectional views showing an embodiment of the present invention, Figure 2 is a plan view showing an embodiment of the present invention, and Figures 3 (a) to
(C) is a process sectional view showing the problems of the conventional example, and FIG. 4 is a plan view showing the problems of the conventional example. In the figure, 1.11 is a semiconductor substrate, 2.12 is a field oxide film, 3.13 is a thermal oxide film, 4.14 is a gate electrode, 5.15 is an oxide film, 6a and 16a are source diffusion layers, 6b, 16b is a drain diffusion layer, 7 is a side wall, 8.18 is a conductive film, 8a and 18a are source electrodes, and 8b and 18b are drain electrodes. 4th floor plan showing the problems of the conventional example

Claims (2)

[Claims] (1) A polycrystalline silicon film is deposited on a substrate (1) having an inversely tapered thin film pattern (4), and anisotropic etching is performed to remove the polycrystalline silicon film from the edge of the thin film pattern (5). a step of forming a side wall (7);
), and depositing a conductive film (8) thereon and selectively etching it to form conductive film patterns that intersect with the thin film pattern (5) and are separated from each other. A method for manufacturing a semiconductor device, comprising the steps of forming (8a) and (8b). 2. The method of manufacturing a semiconductor device according to claim 1, further comprising the step of: (2) covering the sidewall made of the polycrystalline silicon film with an insulating film.