JPS5828732B2 - How to use hand tools - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for removing a silicon nitride film as a mask in the production of a selectively porous silicon layer.

When a silicon substrate is immersed in an electrolyte solution, such as a solution containing hydrofluoric acid as a main component, and anodized, a porous silicon layer is formed on the main surface of the silicon substrate.

The porous silicon layer has an extremely high thermal oxidation rate compared to single crystal silicon, and can also be thermally oxidized at a low rate. Therefore, a thick silicon oxide film can be obtained by thermal oxidation at low temperature and in a short time. Attempts are being made to apply this to isolation between elements.

When applying a porous silicon layer to insulation separation between IC elements, the porous silicon layer must be selectively grown on the main surface of a silicon substrate.

Conventionally, a method shown in FIG. 1 has been used to selectively produce a porous silicon layer.

In FIG. 1a, an n-type silicon epitaxial layer 3 is formed on the main surface 2 of a p-type silicon substrate 1, and a silicon nitride film 5 is formed with SiH4 as a hydrofluoric acid-resistant film on the surface 4 of the n-type silicon epitaxial layer 3. Deposited by thermal decomposition reaction of NH3,
A window is opened in a desired region 6, the substrate 1 is immersed in an electrolyte solution, for example, a solution containing hydrofluoric acid as a main component, and a porous silicon layer 7 is selectively formed by anodizing.

After forming, for example, an n-type silicon epitaxial layer 3 in FIG. A silicon layer 8 is formed.

In Figure 1C, after forming an impurity layer having a conductivity type opposite to that of the epitaxial layer 3 in step d, a silicon nitride film 5 is added as a hydrofluoric acid-resistant film to the epitaxial layer 3 and the surface 4 of this impurity layer by thermal decomposition of SiH2 and NH3. The porous silicon layer 9 is deposited by reaction, a window is opened in a desired region 6, and a porous silicon layer 9 is selectively formed by anodizing.

In the method shown in FIG. 1, since an anodic reaction film is also formed on the surface of the n-type silicon epitaxial layer 30 when forming the porous silicon layer 8, the method shown in FIG. Alternatively, method C is used.

In this case, the silicon nitride film 5 is mainly used as the electrolyte solution-resistant film.

If the porous silicon layers 7 and 9 are selectively formed by such a method, the silicon nitride film 5 must be removed after the formation.

Conventionally, hot phosphoric acid is generally used to remove silicon nitride films.

However, since the porous silicon layer is chemically very active, it changes in quality in the air and becomes partially soluble in hot phosphoric acid.

Therefore, when a silicon nitride film is immersed in hot phosphoric acid, part or all of the porous silicon layer is dissolved and removed.

For example, when immersed in hot phosphoric acid at 170° C., the entire porous silicon layer is removed in one minute.

Furthermore, even when removing the silicon nitride film with hot phosphoric acid after thermally oxidizing the porous silicon layer to transform it into a silicon oxide film, thermal oxidation at a low temperature for a short time will result in oxidized porous silicon Some or all of the layers had been dissolved and removed.

For example, if a porous silicon layer thermally oxidized at 800° C. for 60 minutes in a steam atmosphere is immersed in hot phosphoric acid at 170° C., it will be completely removed in 5 minutes.

In thermal oxidation at high temperatures and for a long period of time, the oxidized porous silicon layer is hardly dissolved by hot phosphoric acid, and the silicon nitride film can be removed. This is not preferred because the characteristics of the layer are lost.

As mentioned above, in the selective generation of porous silicon using a silicon nitride film as a mask, it is difficult to remove the silicon nitride film after forming porous silicon, and the porous silicon is formed by thermal oxidation at high temperatures and for a long time. Although it is possible to transform a porous silicon layer into a silicon oxide film and then remove the silicon nitride film using hot phosphoric acid, it is possible to form a thick silicon oxide film by thermally oxidizing a porous silicon layer at a low temperature for a short time. will be lost.

The present invention is capable of selectively forming a porous silicon layer by thermally oxidizing a porous silicon layer at a low temperature for a short period of time without impairing the characteristic that a thick silicon oxide film can be formed, and without dissolving part or all of the porous silicon layer. The present invention provides a method for removing a silicon nitride film as a mask during silicon layer growth, and the present invention will be described below.

In order to selectively generate a porous silicon layer, a silicon substrate with a silicon nitride film selectively deposited on its main surface is immersed in an electrolyte solution, such as a solution containing hydrofluoric acid as a main component, and anodized. After short-circuiting both electrodes, the silicon nitride film is removed while remaining immersed in the solution.

According to the above method, the silicon nitride film can be removed while it is immersed in the above solution, so the porous silicon layer will not change in quality in the air, and the porous silicon layer will react with the above solution and dissolve and be removed. It turned out that it was not possible.

After the anodization, the porous silicon layer is subjected to an appropriate treatment in an inert atmosphere, for example, left in an N2 gas atmosphere, and then immersed in an electrolyte solution, such as a solution containing hydrofluoric acid as a main component, to nitride it. It was revealed that even when the silicon film was removed, the porous silicon layer did not change in quality in the N2 gas atmosphere, and the porous silicon layer was not dissolved or removed.

An embodiment of the present invention will be described below with reference to FIG.

As shown in FIG. 2a, a p-type 1Ω silicon substrate 11
An n-type silicon layer 12 is grown on the main surface of the silicon layer 12 by a thermal decomposition reaction between SiH4 and H2, and an SiH layer 12 is grown on the surface of the silicon layer 120.
Due to the thermal decomposition reaction between 4 and NH3, the silicon nitride film 13 is
oooA is deposited and a window is opened in the desired area 14.

Next, as shown in the figure, boron as a p-type impurity is diffused into the n-type silicon layer 12 by thermal diffusivity to form a p-type silicon layer 15.

Next, as shown in Figure C, the substrate 11 is immersed in a 49% hydrofluoric acid aqueous solution and anodized to selectively form a porous silicon layer 16 only on the p-type silicon layer 15.

Thereafter, the silicon nitride film 13 is removed after short-circuiting both electrodes used for anodizing while continuing to immerse in the solution for 50 minutes.

As a result, the silicon nitride film could be removed without changing into a porous silicon layer.

FIG. 3 shows the removal rate of a silicon nitride film with respect to a 49% hydrofluoric acid aqueous solution.

Therefore, as is clear from this figure, the silicon nitride film 2000
For people, the silicon nitride film can be removed by soaking for 50 minutes.

In addition, in the present invention, since the nitride film is removed by short-circuiting the electrodes used for anodizing, even if a positive potential is generated on the silicon substrate side due to the remaining ionized electrolyte and intermediate products, this positive potential is This can prevent the porous silicon layer from dissolving in the electrolyte solution.

As described above, according to the method of the present invention, thermal oxidation of a porous silicon layer at a low temperature for a short period of time does not impair the characteristic that a thick silicon oxide film can be formed (also, a part of the porous silicon layer or It is possible to remove the silicon nitride film as a mask in the selective porous silicon layer production without dissolving the entire material.

[Brief explanation of the drawing]

FIGS. 1a, b, and c are explanatory diagrams of a conventional method for producing a selectively porous silicon layer, and FIGS. 2a to 2c are diagrams of a process for producing a selectively porous silicon layer according to an embodiment of the present invention. FIG. 3 is a diagram showing the removal rate of a silicon nitride film with a 49% hydrofluoric acid aqueous solution. 11...p-type silicon substrate, 12...
n-type silicon layer, 13... silicon nitride film, 14.
... Desired region, 15 ... P-type silicon layer, 16 ... Porous silicon layer.

Claims (1)

[Claims] 1 Selectively deposit a silicon nitride film on the surface of the silicon substrate,
The substrate is immersed in an electrolyte solution to selectively generate a porous silicon layer by anodization, and after the formation of the porous silicon layer, both electrodes used in the anodization are short-circuited and then immersed in the electrolyte solution. A method for manufacturing a semiconductor device, comprising removing the silicon nitride film immersed on the surface of the substrate by immersion.