JPH0437152A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To reduce protruded and recessed areas at the etching surface and alleviate concentration of stress at the trench corner area by forming a groove to the area in which an element isolating region of a semiconductor substrate is to be formed, then implanting oxygen ion to such groove and thereafter forming an oxide film by the heat treatment. CONSTITUTION:A groove 14 is formed to the area wherein an element isolating region of a semiconductor substrate B is to be formed, next oxygen ions one implanted to such groove 14 and thereafter an oxide film 16 is formed to an oxygen ion implanting region 15 by the heat treatment. For instance, the trench etching is carried out, by the RIE method, to the semiconductor substrate B consisting of a single crystalline Si layer 11, a doped Si layer 12 and an epitaxial Si layer 13 to form a U-shaped groove 14. When the oxygen ions one implanted to the substrate B with an inclination angle of 10 to 60 degrees from the perpendicular direction while the substrate B is rotating, the side wall of groove 14 is flattened and an amorphous layer 15 including large amount of oxygen is formed, where the corner is rounded and the bottom part is thick. Thereafter, annealing is conducted at 800 to 900 deg.C and an oxide film 16 showing strong bonding strength can be formed at the external surface of groove.

Description

[Detailed Description of the Invention] [Summary of the Invention] Regarding a method for manufacturing a semiconductor device, the present invention relates to a method for manufacturing a semiconductor device, in which a groove is formed in a semiconductor substrate and is then subjected to an oxidation treatment. After that, oxygen ions are implanted into the trench before annealing.

[Industrial application field]

The present invention relates to a method for manufacturing a semiconductor device, and more specifically, the present invention relates to a method for manufacturing a semiconductor device, and more particularly, to flattening a trench (such as a U trench) used for element isolation in a semiconductor device (trench isolation), and flattening the trench during oxidation and subsequent thermal processing. The present invention relates to a method for manufacturing a semiconductor device that prevents stress from occurring at a portion of a corner.

[Prior Art and Problems to be Solved by the Invention] In large-scale integrated circuits (LSI), it is necessary to electrically isolate each element formed on a silicon substrate surface. Conventionally, selective oxidation has been employed for such element isolation.

On the other hand, as LSIs have become highly integrated in recent years, it is necessary to make element isolation as thin as possible to increase the degree of integration, thereby reducing the area required for isolation. Therefore, instead of selective oxidation, trench isolation, which requires a small area for element isolation, is attracting attention and being used.

This trench isolation method is shown in Figure 2 (1) to (
3) For example, a semiconductor substrate A in which an impurity-doped Si layer 2 is formed on a single crystal silicon layer 1 and an epitaxial S1 layer 3 is further formed as shown in FIG. 2(2) is etched in a predetermined manner. A U-shaped groove is dug vertically by reactive ion etching (Rr8) using gas, and then, as shown in FIG. 2 (3), an oxide film 5 is formed on the surface by thermal oxidation, and then the groove is This method performs element isolation by burying an insulator such as polysilicon. However, in this method, as shown in FIG. 2 (2), the epitaxial S1
Stress concentration occurred in the layer 3 and a portion of the doped S1 layer 2, and as a result, crystal defects 6 were generated in the groove wall portion and a portion of the corner due to oxidation.

As described above, stress concentration during the oxidation process and subsequent thermal process induces dislocations and crystal defects in the substrate.These problems also cause leakage between emitter and collector in bipolar devices, for example.

[Means for Solving the Problems] In view of the above points, the present invention has been made for the purpose of reducing the unevenness of the etching surface and alleviating the stress concentration at a part of the trench corner. The method is characterized in that a trench is formed at a position where an element isolation region is to be formed, and then oxygen ions are implanted into the trench, followed by heat treatment to form an oxide film.

That is, in the method of the present invention, after trench etching,
Highly concentrated oxygen ions are injected into the trench, and low-temperature annealing is performed in a vacuum or in an oxygen atmosphere to form an oxide film and perform element isolation. In such a method of the present invention, oxygen ions are implanted in a direction perpendicular to the substrate at approximately 10 to 6
Inject into the groove at a 0 degree angle.

The reason for performing ion implantation at a certain angle is that a large amount of oxygen ions are implanted near some corners of the groove where crystal defects are likely to occur, forming a rounded implantation region and reducing stress concentration. This is to alleviate the situation. In other words, if the implantation angle exceeds about 60 degrees, the angle becomes shallow, making it difficult for oxygen ions to penetrate into the lower part and implanting them only into the sidewalls, which is undesirable.

On the other hand, if the temperature is less than about 10° C., a rounded implanted region will not be formed near the bottom, resulting in poor conditions.

Furthermore, in the method of the present invention, the annealing step after trench etching is preferably carried out at a relatively low temperature (800 to 900 DEG C.) in vacuum or in an oxygen atmosphere. In this case, 800
Annealing temperatures below 900°C will result in extremely slow oxidation rates, while high annealing temperatures above 900°C will oxidize the dopants if they have already formed a diffusion layer in a previous step.
(P, B, etc.) tend to diffuse, which is not very preferable.

Therefore, the above annealing temperature is preferably employed.

[For production]

In the method according to the present invention, by implanting oxygen ions into the groove, an amorphous layer is formed around the groove as shown in figure 15 in FIG. 1(3).
The amorphous region is rounded at a portion of the trench corner, and the unevenness of the trench sidewall surface is reduced due to the sputtering effect. Then, the subsequent oxidation starts preferentially from regions made amorphous by ion implantation or from defective regions.

Therefore, stress at a portion of the trench corner due to deposition expansion during oxidation is reduced, and the trench sidewalls are flattened, so crystal defects induced by thermal processes are reduced.

The present invention will be further explained below with reference to Examples.

Pretext flow side: As shown in FIG. 1, single crystal silicon layer 11, doped S
A semiconductor substrate B consisting of an i-layer 12 and an epitaxial Si layer 13 is trench-etched in a conventional manner by RIE to form a U-groove 14. Next, while rotating the substrate B, the oxygen ions are irradiated with I
Ions of O":l/cj~2XIO":) are implanted (FIG. 2 (2)). As a result, as shown in FIG. 1(3), the side walls of the trench 14 were flattened, and an amorphous layer 15 containing a large amount of oxygen was formed, which was rounded at some corners and thick at the bottom.

Next, an annealing step was performed in vacuum or in an oxygen atmosphere at an annealing temperature of 800 to 900° C. to form an oxide film 16 with strong bonding strength on the outer surface of the groove.

In the subsequent steps, an insulator was filled in the grooves to isolate the elements according to a conventional method.

〔Effect of the invention〕

As explained above, in the method of the present invention, high concentration oxygen ions are implanted at a certain angle to the substrate immediately after trench etching, and then annealing is performed at a relatively low temperature. This has the effect of reducing stress concentration at a portion of the groove corner, and also reducing unevenness on the groove sidewalls.

As a result, the occurrence of crystal defects within the substrate can be completely prevented, and the leakage characteristics between the emitter and collector can also be improved.

[Brief explanation of drawings]

FIG. 1 is a process diagram showing one implementation of the method of the present invention, and FIG. 2 is a process diagram showing an example of isolation by a conventional method. DESCRIPTION OF SYMBOLS 11... Single crystal silicon layer, 12... Doped Si layer, 13... Epitaxial Si layer, 14... Groove, 15... Amorphous layer, 16... Oxide film, B... Semiconductor substrate. / B... Semiconductor substrate 1 National policy 1 figure showing an embodiment of the method of the present invention Process national policy 1 figure showing an embodiment of the method of the present invention (Continued)

Claims (1)

[Claims] 1. A groove is formed in a semiconductor substrate at a position where an element isolation region is to be formed, and then oxygen ions are implanted into the groove, and then heat treatment is performed to form an oxide film in the oxygen ion implanted region. 1. A method of manufacturing a semiconductor device, comprising: forming a semiconductor device. 2. The oxygen ions are implanted into the trench at an angle of about 10 to 60 degrees from a direction perpendicular to the substrate.
A method of manufacturing the semiconductor device described above.