JPH02208929A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To assure the impurity diffused amount on a silicon semiconductor substrate while thinning a protective film by a method wherein the impurity is diffused in the state of a doped oxide layer covered with a covering layer. CONSTITUTION:An opening part 3 is formed in an oxide film 12 formed on the surface of a silicon semiconductor substrate 11 and then a doped oxide layer 14 containing phosphorus as an impurity is formed in the thickness required for attaining the specified diffusion amount. Next, a covering layer 20 containing no impurity is formed and then heat-treated to form a diffused region 15 in the substrate 11. At this time, the doped oxide layer 14 being covered with the covering layer 20, sufficient amount of phosphorus is diffused in the substrate 11. Furthermore, during the process removing the later covering layer 20 as well as the doped oxide layer 14 and the oxide film 12 in the opening part 13 by etching process, the effect of side etching in the etching process after diffusion can be lessened due to the relatively thin protective film 19 comprising the oxide film 12 and the doped oxide layer 14.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to impurity diffusion technology in the manufacturing process of semiconductor devices.

[Prior art] During the manufacture of semiconductor devices, there is a diffusion process in which impurities such as phosphorus are diffused into predetermined portions of a silicon semiconductor substrate.The diffusion technique involves forming a doped oxide layer on the substrate and diffusing it. A method of using it as a source is known.

That is, as shown in FIG. 3, a doped oxide layer 4 containing phosphorus is formed on a Si substrate 1 in which an opening 3 is formed by partially removing the Si 02 film 2, and then a doped oxide layer 4 containing phosphorus is formed by heat treatment. By diffusing phosphorus in the doped oxide layer 4, S
A diffusion region 5 was formed on the i-substrate 1, and then the oxide layer 4 in the opening 3 was removed by etching.

[Problems to be Solved by the Invention] In the above-described diffusion technology, a large amount of phosphorus diffuses into the atmosphere from the doped oxide layer 4 when heat treatment is performed, so that phosphorus is not absorbed into the substrate 1. In order to maintain the amount of diffusion at a predetermined level, it was necessary to increase the thickness of the doped oxide layer 4 to ensure that the doped oxide layer 40 diffuses into the substrate 1 from the vicinity of the substrate interface.

Therefore, there was a problem in that the protective film 9 (Si02 film 2 and oxide layer 4) of the silicon substrate 1 became thicker than necessary.

Furthermore, as a result of the thicker protective film 9, the influence of side etching increases in the etching process after diffusion, resulting in poor step coverage around the periphery of the opening 3 in the protective layer 9, as shown in FIG. However, there is a problem in that it may cause breakage of the laminated layers in the subsequent manufacturing process. This phenomenon is particularly remarkable when the impurity is phosphorus. That is, the phosphorus content concentration of the oxide film 2 and the oxide layer 4 after phosphorus diffusion becomes higher at the interface between the oxide layer 4 and the oxide film 2 (the mesh line part 6 in FIG. 4), and The portion on the substrate interface side (portion 7 in FIG. 4) is low due to diffusion into the substrate 1, and the surface side portion of the oxide layer 4 (portion 8 in FIG. 4) is low due to diffusion into the atmosphere. It is lowered due to diffusion. For this reason, as is well known, the etching rate of a glass layer containing phosphorus increases depending on its content, so that the deterioration of step coverage becomes even more remarkable.

The present invention has been made in view of the above-mentioned conventional circumstances, and an object of the present invention is to provide a method for manufacturing a semiconductor device that rationally solves the conventional problems.

[Means for Solving the Problems] A method for manufacturing a semiconductor device according to the present invention includes a step of forming an opening in an oxide film of a silicon semiconductor substrate, and forming a doped oxide layer containing an impurity on the oxide film. a step of forming an impurity-free covering layer on the doped oxide layer; a step of performing heat treatment to diffuse the impurities in the doped oxide layer into the silicon semiconductor substrate from the opening; and a step of forming the covering layer. The method is characterized by comprising a step of performing an etching process after removing the doped oxide layer and the oxide film in the opening portion.

[Operation] In the step of diffusing impurities in the doped oxide layer into the silicon semiconductor substrate by applying heat treatment, this doped oxide layer is covered with a coating layer to suppress diffusion toward the interface between the two, thereby This greatly promotes sideward diffusion compared to conventional methods.

As a result, the protective film for multiple substrates consisting of oxide films and oxide layers is thinned to reduce the effects of side etching, and the impurity concentration in the protective film increases as it moves away from the substrate interface, increasing the etching rate. It increases in size as it moves away from the substrate interface to provide good step coverage around the periphery of the opening.

[Example 2] A method for manufacturing a semiconductor device according to the present invention will be specifically explained based on an example shown in FIGS. 1 and 2.

First, a resist is provided on a desired portion of the oxide film (Si02 film) 12 formed on the surface of the silicon semiconductor substrate 110 and etched to form an opening 13 in the 5i02 film 12.

Next, the SiO2 film 12 is formed by a known method such as the CVD method.
Doped Oxai containing phosphorus as an impurity from above)! 1
4 is formed to a thickness necessary to obtain a predetermined amount of diffusion, and this doped oxide layer 14 forms openings 13 and 5i0.
Cover 2PA12.

Next, an impurity-free coating layer (for example, Si
An O2 layer) 20 is formed.

Next, heat treatment is performed to diffuse phosphorus in the doped oxide layer 14 into the silicon semiconductor substrate 11 from the opening 13, thereby forming a diffusion region 16 in the substrate 11. At this time, since the doped oxide layer 14 is covered with the coating layer 20, diffusion toward the substrate 11 is promoted, and a sufficient amount of phosphorus is diffused into the substrate 11. Phosphorus remains in the doped oxide layer 14 and also diffuses into the 5i02 film 12, but the diffusion is suppressed on the interface side of the coating layer 20 and is allowed to diffuse freely on the interface side of the substrate 11. ,
The concentration of phosphorus contained in the protective film 19 composed of the 5i02 film 12 and the oxide Fi 14 increases as the distance from the interface of the substrate 11 increases.

Next, the covering layer 2 is etched using a hydrofluoric acid solution or the like.
Remove 0.

Next, a resist is provided in the area other than the opening 13 and an etching process is performed to remove the doped oxide layer 14 and the 5i02 film 12 in the opening 13. At this time, 5
A protective film 19 consisting of an i02 film 12 and an oxide layer 14
Since the protective film 19 is relatively thin, the influence of side etching is small, and due to the concentration distribution of phosphorus contained in the protective film 19, it is etched at a higher rate as it moves away from the interface of the substrate 11, and the step coverage of the fixing of the opening 13 is reduced. As shown in FIG. 2, the result is a good one with an open surface.

After this, the steps necessary for manufacturing the semiconductor device are performed.
Stack predetermined layers.

[Effects] According to the present invention, since impurity diffusion is performed while covered with a coating layer, a sufficient amount of impurity diffusion into the silicon semiconductor substrate can be ensured even if the doped oxide layer is made relatively thin. The protective film of the semiconductor substrate can be made thinner. For this reason, the influence of side etching can be reduced in the etching process after diffusion, and furthermore, when phosphorus is used as an impurity, the etching rate can be increased as the distance from the substrate interface increases, causing step breaks. Not able to get good step coverage.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an embodiment of the present invention, FIG. 2 is a sectional view of a main part thereof, FIG. 3 is a sectional view of a conventional example, and FIG. 4 is a sectional view of a main part thereof. 11 is a silicon semiconductor substrate, 12 is a 5i02 film, 13 is an opening, 14 is a doped oxide layer, 15 is a diffusion region, and 20 is a covering layer.

Claims (1)

[Claims] A step of forming an opening in an oxide film of a silicon semiconductor substrate, a step of forming a doped oxide layer containing an impurity over the oxide film, and a step of forming a covering layer not containing an impurity over the doped oxide layer. Then, heat treatment is performed to diffuse impurities in the doped oxide layer from the opening into the silicon semiconductor substrate, and after the covering layer is removed, etching is performed to remove the doped oxide layer and oxide film in the opening. A method for manufacturing a semiconductor device, comprising the steps of: