KR20040103218A - Method for forming field oxide of semiconductor device - Google Patents

Abstract

PURPOSE: A method for forming a field oxide layer of a semiconductor device having an uniform surface is provided to perform easily a gap-fill process and form uniformly a surface of the field oxide layer by forming a spacer in an inner wall of a trench. CONSTITUTION: The first oxide layer is selectively formed on a peripheral region of a semiconductor substrate(200). A pad nitride layer is formed on the peripheral region and a cell region. A trench is formed by etching selectively the peripheral region and the cell region. The trench is buried by forming a primary oxide layer on the entire structure. The primary oxide layer is etched back. The second oxide layer is formed on the entire surface of the structure including the trench. A spacer is formed on a lateral part of the trench by etching the second oxide layer. The trench is buried by forming a secondary oxide layer on the structure including the spacer.

Description

Field oxide film formation method of a semiconductor device {METHOD FOR FORMING FIELD OXIDE OF SEMICONDUCTOR DEVICE}

The present invention relates to a semiconductor device and a method of manufacturing the same.

In a rapidly developing information society, a high-integration device having a high data transfer rate is required to process a large amount of information faster. In order to form components intensively in a semiconductor device of a certain size, methods for reducing the size of the device isolation region for defining an active region have been proposed.

As a device isolation region formation method, a LOCal Oxidation of Silicon (LOCOS) process has been proposed, which is simple and has excellent reproducibility, but as the device is gradually integrated, Bird's Beak occurs at the edge of the isolation oxide layer. Therefore, it is known that the area of the active area is reduced and is not suitable for use in 64 MB or more DRAM (Dynamic Random Access Memory: DRAM) devices.

The Advanced LOCOS process has been proposed as a method to solve the problem of Buzzvik, but the isolation region using the advanced LOCOS process also has an area occupied by the isolation region in a GIGA class or higher DRAM. This is still great.

Accordingly, a method of forming an isolation region using trenches that can easily control the thickness of the isolation region and increase the isolation effect as a method of forming an isolation region of a giga DRAM or more class has been proposed.

In general, trenches formed by Shallow Trench Isolation (STI, hereinafter referred to as "STI") processes have the advantage of no buzzing and the ability to achieve complete isolation of devices by vertical device isolation. It is known as the device isolation technology that is currently attracting most attention because of.

The general STI process sequentially forms a pad nitride film and a photoresist pattern on the front surface of the silicon substrate. The pad nitride layer and the silicon substrate are etched using the photoresist pattern as an etching mask to form a trench having a predetermined depth, and then the photoresist pattern is removed.

After depositing an oxide on the entire surface of the semiconductor substrate including the trench, a planarization process such as a chemical mechanical polishing (CMP, hereinafter referred to as "CMP") process is performed on the entire surface using the pad nitride layer as an end point. Conduct. After the planarization, the pad nitride film is removed.

At present, the integration rate of semiconductor devices is further reduced. Therefore, since it is impossible to fill the trench at one time by the general gap fill method, gap filling is performed over a multi-step process.

In order to proceed with the multi-level gap filling process, a trench is first formed, and the trench is first filled with oxide. After the first trench is buried, wet etching is performed to reduce the step difference caused by the trench. Subsequently, secondary filling is performed to completely fill the trench to form a field oxide film. In this case, an oxide film for adjusting a voltage provided in the ferry region of the semiconductor device is further provided. In addition, due to the difference in the width of the region of the cell and the ferry region to be etched in the semiconductor device, the etching of the inside of the trench of the ferry region is excessively increased compared to the trench of the cell region, thereby removing all of the first buried oxide. However, at this time, the oxide film exposed to the inner wall of the trench is partially eroded to generate undercut.

1 is a cross-sectional view of some steps in a field oxide film formation process by a general field oxide film formation method.

Referring to FIG. 1, the oxide film 100 formed in the ferry region is damaged by the wet etching. If the oxide film is damaged and partially eroded in this manner, a subsequent defect such as voids 120 may be caused when the trench is subsequently buried. Therefore, if the pad nitride film is subsequently removed, the voids are exposed to the surface to form a field oxide film having an uneven surface. That is, if a conductive pattern such as polysilicon is subsequently applied to form a conductive pattern, a shortness may be caused due to the conductive material applied to the voids.

Accordingly, an object of the present invention is to provide a trench formation method for easily forming gaps by smoothly forming sidewall profiles of trenches.

1 is a cross-sectional view of some steps in a field oxide film formation process by a general field oxide film formation method.

2A to 2H are cross-sectional views of a method of forming a field oxide film of a semiconductor device according to a preferred embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

100: oxide film 120: void

200 silicon substrate 205 high voltage oxide film

205a: undercut 210: pad nitride film

220a: first photoresist pattern 220b: second photoresist pattern

230a: first trench 230b: second trench

240: inner wall oxide film 245: intermediate temperature oxide film

250: primary oxide film 255: first buried film

257 spacer oxide film 258a first spacer

258b: second spacer 260: secondary oxide film

270a: first field oxide film 270b: second field oxide film

In order to achieve the above object, the present invention provides a method for forming a semiconductor device, the method comprising: selectively forming a first oxide film in a ferry region of a semiconductor substrate in which a cell and a ferry region are defined; forming a pad nitride film over the cell and the ferry region; Selectively etching the ferry region to form a trench; first filling the trench by applying a first oxide on the resultant product including the trench to form a primary oxide layer; and forming a trench in the cell region. Etching back the primary oxide layer so that all of the primary oxide layer in the trench of the ferry region is removed while partially leaving the secondary oxide layer, forming a second oxide layer uniformly on the resultant product including the trench, and the second oxide layer Anisotropic etching to form a spacer on the side of the trench and on the resultant formed spacer Applying a second oxide to provide the trench with the second field oxide film formation method of a semiconductor device including the step of embedding, by forming the second oxide film.

In this way, by forming a spacer on the inner wall of the trench, gap filling can be easily performed to form a field oxide film having a uniform surface.

Hereinafter, the present invention will be described in detail.

A first oxide film is selectively formed in the ferry region of the semiconductor substrate in which the cell and the ferry region are defined, and a pad nitride film is formed over the cell and the ferry region.

The cell and ferry regions are selectively etched to form trenches. The trench in the ferry region has a wider width than the trench in the cell region. The inner wall oxide film and the MTO film are uniformly formed on the resultant product including the trench.

The trench is first buried by forming a primary oxide film made of USG on the resultant product including the trench, and the primary oxide film in the trench of the ferry region is partially filled, leaving a portion of the primary oxide film in the trench of the cell region. The primary oxide film is etched back to be removed.

A second oxide film is uniformly formed on the resultant including the trench, and the second oxide film is anisotropically etched to form a spacer on the trench side surface.

The trench is secondly buried by forming a second oxide film of an HDP method on the resultant spacer. After planarizing the secondary oxide film with the pad nitride film as an end point, the pad nitride film is removed to complete the field oxide film.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Example

2A to 2H are cross-sectional views of a method of forming a field oxide film of a semiconductor device according to a preferred embodiment of the present invention.

Referring to FIG. 2A, a high voltage oxide (hereinafter referred to as an "HV oxide film") is formed on the ferry region B of the silicon substrate 200 divided into the cell region A and the ferry region B. 205 is formed. The HV oxide layer 205 is formed in the cell and ferry regions to differentiate driving voltages of the devices.

The pad nitride layer 210 is formed on the entire silicon substrate including the cell and the ferry region. After applying the photoresist on the pad nitride film 210, a portion of the photoresist is irradiated with light and developed. Therefore, the first photoresist pattern 220a and the second photoresist pattern 220b are formed to expose portions of the substrate 200 positioned in the cell region A and the ferry region B, respectively. In this case, an area exposed by the second photoresist pattern 220b is wider than an area exposed by the first photoresist pattern 220a.

Referring to FIG. 2B, the pad nitride layer 210 exposed on the surface is etched using the first and second photoresist patterns 220a and 220b as an etching mask, and the silicon substrate 200 and the ferry exposed to the cell region are exposed. The HV oxide film 205 exposed to the region and the silicon substrate are sequentially anisotropically etched to form first and second trenches 230a and 230b. In this case, the second trench is formed to have a wider width than the first trench.

Referring to FIG. 2C, the substrate 200 may be cleaned to remove foreign substances present in the substrate 200 on which the trench 230 is formed. Subsequently, an exposed portion of the silicon substrate 200 may be heat-treated in an oxidizing atmosphere to form an oxide film on the inner wall of the trench by an oxidation reaction between the exposed silicon and the oxidant. The inner wall oxide film 240 formed by the oxidation reaction may be formed to cover damages caused by etching for forming the first and second trenches 230a and 230b. It is formed on the bottom surface and sidewalls.

A middle temperature oxide film (MTO) process may be performed on the trench in which the inner wall oxide film is formed to uniformly form the middle temperature oxide film 245 to reduce damage caused by a subsequent process. USG is applied to the entire surface of the substrate to fill the first and second trenches 230a and 230b to form a first oxide film 250 to fill the first and second trenches.

Referring to FIG. 2D, the first oxide layer 250 is etched back by wet etching using a solution made of LAL or HF. Accordingly, the primary oxide film on the silicon substrate of the cell region A is recessed to form the first buried film 255 only in the first trench. However, since the second trench of the ferry region B has a wider width than the first trench, the primary oxide layer inside the second trench is etched relatively quickly. Therefore, when the etch back process is performed based on the cell region A, not only the primary oxide layer of the ferry region B but also all of the intermediate temperature oxide layer and the inner wall oxide layer are removed. As a result, an undercut 205a in which the HV oxide film 205 exposed to the inner wall of the second trench is partially eroded occurs.

Referring to FIG. 2E, an oxide is uniformly coated on the entire product including the cell region and the ferry region to form a spacer oxide layer 257. Accordingly, the spacer oxide layer 257 on the ferry region is formed uniformly along the inner wall and the bottom including the undercut 205a of the second trench.

Referring to FIG. 2F, the spacer oxide layer 257 is anisotropically etched to form first and second spacers 258a and 258b on sidewalls of the first trench and the second trench. The anisotropic etching may be performed until the top surface of the first buried film and the bottom surface of the second trench are exposed. In this case, the first buried film may be partially exposed by being exposed before the bottom of the second trench, but does not cause an increase in an aspect ratio to inhibit subsequent gap filling.

Therefore, since the second spacer 258b is formed while filling the region where the undercut 205a is formed, the profile of the side surface of the second trench 230b exposed to the outside is not curved.

Referring to FIG. 2G, an oxide filling a first trench and a second trench is secondarily provided by using HDP to fill the first trench and the second trench including the first buried oxide layer 255. An oxide film 260 is formed.

Since the first buried oxide film 255 is already formed in the first trench, the first trench is easily buried because the aspect ratio is reduced. In addition, the second trench is completely buried without forming voids because the undercut formed in the sidewall is filled by the spacer and has a gentle profile.

That is, when considering a trench having a wider upper width than a lower width, the first trench formed with the first buried oxide film 255 in the lower portion of the first trench has a relatively low aspect ratio of the trench, so that the secondary oxide film 260 is easily formed. It can be seen that it can be formed.

In addition, the second trench having a width wider than that of the first trench is easy to fill gaps, but void side defects are generated by subsequent secondary filling because the side undercut of the trench generated during the formation of the first buried oxide film is covered by the spacer. I never do that.

Referring to FIG. 2H, the pad nitride layer 210 is planarized by using a conventional chemical mechanical polishing (CMP) method by using the upper portion of the secondary oxide layer 260 as the end of the pad nitride layer 210. The first field oxide film 270a and the second field oxide film 270b are completed by removing by an additional etching process.

As described above, according to the present invention, after forming the HV oxide film and the pad nitride film on the semiconductor substrate in which the cell and the ferry region are defined, the trench is formed. Since the trench of the cell region has a large aspect ratio, the gap filling should be performed twice, but undercut occurs in the HV oxide film exposed to the inner wall of the trench by etching during the gap filling process. Therefore, after the spacer is formed on the inner wall of the trench, gap filling is performed.

In this way, by forming a spacer on the inner wall of the trench, gap filling can be easily performed to form a field oxide film having a uniform surface. Therefore, it is possible to improve the reliability of the semiconductor device by preventing defects from occurring when the conductive pattern is subsequently formed using a conductive material such as polysilicon.

As described above, although described with reference to a preferred embodiment of the present invention, those skilled in the art will be variously modified without departing from the spirit and scope of the invention described in the claims below. And can be changed.

Claims (5)

Selectively forming a first oxide film in the ferry region of the semiconductor substrate in which the cell and the ferry region are defined; Forming a pad nitride film over the cell and ferry regions; Selectively etching the cell and ferry regions to form trenches; First embedding the trench by applying a first oxide on the resultant including the trench to form a primary oxide film; Etching back the primary oxide to remove all of the primary oxide in the trench of the ferry region while leaving a portion of the primary oxide in the trench of the cell region; Forming a second oxide film uniformly on the resultant product including the trench; Anisotropically etching the second oxide layer to form a spacer on a side of the trench; And And filling the trench with a second oxide by coating a second oxide on the resultant material on which the spacer is formed. The method of forming a field oxide film of a semiconductor device according to claim 1, wherein the primary oxide film is made of USG and the secondary oxide film is made of HDP. The method of forming a field oxide film of a semiconductor device according to claim 1, further comprising an inner wall oxide film and an MTO film uniformly on the resultant product including the trench. The method of claim 1, wherein the trench of the ferry region has a width wider than that of the cell region. 2. The semiconductor of claim 1, further comprising performing a second filling of the trench, planarizing the second oxide film as an end point of the pad nitride film, and removing the pad nitride film. Method for forming a field oxide film of a device.