KR100204022B1 - Method for forming an element isolation region in a semiconductor device - Google Patents

Abstract

The present invention relates to a method of forming a device isolation film for electrical isolation between active regions in a semiconductor device manufacturing process, the method comprising: forming a pad oxide film and a nitride film on a semiconductor substrate; Etching the nitride film and the pad oxide film in the device isolation layer forming region, and leaving the pad oxide film to a predetermined level; A third step of depositing a polysilicon film over the entire structure of the first and second steps, and then doping impurities onto the surface of the polysilicon film; Forming a device isolation film; And a fifth step of removing the nitride film, thereby minimizing the reduction of the active area due to the buzz beak, thereby relieving stress at the edge of the device isolation layer, thereby improving the reliability of the gate oxide film, and between the cells and the cells. This has the effect of improving the electrical characteristics of the device, such as reducing leakage current and reducing junction leakage current.

Description

Device isolation film formation method of semiconductor device

1A to 1D are cross-sectional views of a device isolation film forming process according to an embodiment of the present invention.

2A and 2D are cross-sectional views of a device isolation film forming process according to another embodiment of the present invention.

* Explanation of symbols for main parts of the drawings

11, 21: silicon substrate 12, 22: pad oxide film

13, 23: nitride film 14, 24: photoresist pattern

15, 25: polysilicon film 17, 27: field oxide film

The present invention relates to a method of forming an isolation layer for electrical isolation between active regions during a semiconductor device fabrication process.

In general, one important step in the fabrication of semiconductor devices is the electrical isolation process between active regions, and the electrical isolation methods include a junction separation method, an oxide separation method, and a trench isolation method, among which the convenience of the process and the excellent isolation (isolation) Characteristics and oxidative separation methods that can use nitride films as an oxide mask of silicon substrates, especially LOCal Oxidation of Silicon (LOCOS) process, which provide a thick line of oxide layers between devices, have been widely used. .

However, in the LOCOS method, the edge of the device isolation layer becomes smooth due to the stress of the nitride film, so that a bird's beak is generated in the narrow region to reduce the active area, thereby limiting the high integration of the device.

In addition, there is a problem that not only causes a large amount of leakage current, but also greatly reduces the reliability of the gate oxide film.

The present invention devised to solve the problems of the prior art as described above can minimize the reduction of the active area due to the buzz bee by allowing the oxidation rate of the upper portion of the region where the device isolation film is to be formed to be 5 to 10 times higher than the oxidation rate of the side wall. An object of the present invention is to provide a method for forming a device isolation film of a semiconductor device.

Another object of the present invention is to provide a method for forming a device isolation layer of a semiconductor device capable of reducing stress at the edge of the device isolation layer to reduce leakage current between the cell and the cell.

The present invention for achieving the above object is a first step of forming a pad oxide film and a nitride film on a semiconductor substrate; Etching the nitride film and the pad oxide film in the device isolation layer forming region, and leaving a partial thickness of the pad oxide film on the pad oxide film in the device isolation film forming region; A third step of removing the pad oxide film remaining in the second step and a part of the pad oxide film under the nitride film by wet etching; Forming a polysilicon film on the entire structure where the third step is completed and simultaneously filling the polysilicon film under the nitride film from which the pad oxide film is removed in the third step; A fifth step of doping an impurity to a surface of the polysilicon film except for the polysilicon film under the nitride film; A sixth step of forming an isolation layer by performing an oxidation process; And a seventh step of removing the nitride film.

Hereinafter, a method of forming an isolation layer of a semiconductor device according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

First, referring to FIGS. 1A to 1D, which are cross-sectional views of a device isolation film forming process of a semiconductor device, according to an embodiment of the present disclosure.

As shown in FIG. 1A, the pad oxide film 12 and the nitride film 13 are sequentially formed on the silicon substrate 11, and the photoresist pattern 14 is formed on the nitride film 13 outside the predetermined field region. The nitride film 13 and the pad oxide film 12 are etched using the photosensitive film pattern 14 as a mask. At this time, the pad oxide film 12 is left to a predetermined thickness on the field region of the silicon substrate 11 by underetching.

Subsequently, after the photoresist pattern 14 is removed, the pad oxide layer 12 under the nitride layer 13 is locally laterally etched by wet etching, and then the sacrificial polysilicon layer 15 is removed as shown in FIG. Deposit. Subsequently, the exposed sacrificial polysilicon film 15 is doped with a phosphorus ¹⁶ having a dose of about 10 ¹⁴ / cm 2 to about 10 ¹⁶ / cm 2. In this case, phosphorus is not injected into the sacrificial polysilicon layer 15 embedded in the region where the pad oxide layer 12 is laterally etched. As such, when a high concentration of impurities are injected into the surface of the sacrificial polysilicon film, the oxidation rate of the upper portion of the sacrificial polysilicon film is made higher than the oxidation rate of the sidewall, so that 10% of the sidewalls of the sacrificial polysilicon film 15 are oxidized in a subsequent oxidation process. Since the oxidation of the sacrificial polysilicon film 15 occurs more quickly, the silicon substrate may be exposed to oxidation, thereby reducing the Burj beak. In addition, by using a relatively thick pad oxide film, the active region is uniformly oxidized after the sidewall polysilicon film is completely oxidized, thereby not only smoothing the profile of the edge of the device isolation layer but also relieving stress at the edge.

Next, through the thermal oxidation process, as shown in FIG. 1C, a field oxide film 17 as an isolation layer is formed. At this time, in the process of FIG. 1b, the strongly doped (10 ¹⁵ / cm ² ) sacrificial silicon film 15 exhibits an oxidation rate of about 10 times higher than that of the lightly doped 10 ¹³ / cm ^2. The process is easy.

Finally, the oxide layer on the nitride layer 13 is removed by a wet etchant such as BOE or HF, the nitride layer 13 is removed by a nitride layer etchant, and then a sacrificial oxide layer is formed and removed, as shown in FIG. 1D. The field oxide film 17 having the same cross-sectional structure is completed.

A method of forming a device isolation film of a semiconductor device according to another exemplary embodiment of the present invention will be described with reference to FIGS. 2A through 2D.

First, as shown in FIG. 2A, a pad oxide film 22 and a nitride film 23 are sequentially formed on the silicon substrate 21, and a photoresist pattern (not shown) is formed on the nitride film 23 outside the predetermined field region. Next, the nitride layer 23 and the pad oxide layer 22 are etched using the photoresist pattern as a mask. At this time, the pad oxide layer 22 remains on the field region of the silicon substrate 21 by a predetermined etching.

Subsequently, after removing the photoresist layer pattern, the sacrificial polysilicon layer 25 is deposited on the entire structure, and a force of about 10 ¹⁴ / cm 2 to 10 ¹⁶ / cm 2 is applied to the surface of the sacrificial polysilicon layer 25. Doping the porous 26. The impurity doping at this time is to promote oxidation in the subsequent oxidation process.

FIG. 2B is a cross-sectional view of a field oxide film 27 formed as a device isolation film through a thermal oxidation process.

Next, in FIG. 2C, a part of the field oxide layer 27 is wet-etched with a wet etchant such as BOE or HF to sufficiently expose the nitride layer 23.

Finally, the nitride film 23 is completely removed with a hot phosphoric phosphate etchant, and the field oxide film 27 is wet etched back to be planarized to form a cross-sectional structure as shown in FIG. 2D. An element isolation film is formed.

According to the present invention, the oxidation rate of the upper portion of the silicon in the region where the device isolation layer is to be formed is 5 to 10 times higher than the oxidation rate of the sidewall, thereby minimizing the reduction of the active region due to the buzz bee.

In addition, the present invention has the effect of reducing the stress at the edge of the device isolation layer to improve the electrical characteristics of the device, such as improving the reliability of the gate oxide film, reducing the leakage current between the cell, the junction leakage current.

The present invention described above is not limited to the above-described embodiments and the accompanying drawings, and various substitutions, modifications, and changes can be made in the art without departing from the technical spirit of the present invention. It will be apparent to those of ordinary knowledge.

Claims (2)

A method of forming a device isolation film of a semiconductor device, comprising: a first step of forming a pad oxide film and a nitride film on a semiconductor substrate; Etching the nitride film and the pad oxide film in the device isolation layer forming region, and leaving a partial thickness of the pad oxide film on the pad oxide film in the device isolation film forming region; A third step of removing the pad oxide film remaining in the second step and a part of the pad oxide film under the nitride film by wet etching; Forming a polysilicon film on the entire structure where the third step is completed and simultaneously filling the polysilicon film under the nitride film from which the pad oxide film is removed in the third step; A fifth step of doping an impurity to a surface of the polysilicon film except for the polysilicon film under the nitride film; A sixth step of forming an isolation layer by performing an oxidation process; And a seventh step of removing the nitride film. The method of claim 1, wherein in the fifth step, an impurity of 10 ¹⁴ / cm 2 to 10 ¹⁶ / cm 2 dose is implanted.