JPS588577B2 - The best way to do it - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of forming an insulating film, and particularly to a method of forming an insulating film that is deposited on the surface of a semiconductor substrate to protect the surface of the semiconductor substrate and provide insulation between electrodes. This is a proposal.

Conventionally, silicon dioxide (SiO2) and silicon nitride (Si3N) have been used as insulating films to protect the surface of semiconductor substrates.
4), aluminum oxide (Al2O2), phosphosilicate glass (PSG), etc. are often used.

These insulating films are effective for protecting the terminal end of a PN junction formed in a semiconductor substrate and for preventing entry of cations from the outside.

FIG. 1 shows a cross section of a main part of a general Brenna type semiconductor device.

In the figure, for example, P is selectively added to an N-type semiconductor substrate 1.
Type impurities are introduced to form a P-type region 2 and a PN junction 3, an insulating film 4 is formed covering the surface of the semiconductor substrate 1, and a metal electrode 6 is formed through an electrode window 5 provided in the insulating film 4.
shows the state in which is derived.

Here, the insulating film 4 is composed of silicon dioxide, silicon nitride, aluminum oxide, phosphosilicate glass, etc., as described above, formed singly or in a multilayered state.

To form the electrode window 5 on the insulating film 4,
Generally, a photo-etching method is used, and according to this photo-etching method, the opening defining the electrode window 5 is formed so that its peripheral wall is substantially vertical.

Further, the electrode metal 6 extending from within the electrode window 5 onto the insulating film 4 is generally formed by vapor deposition.

Therefore, at the edge of the opening provided in the insulating film 4 that defines the electrode window 5, the electrode metal 6 becomes thinner than other parts, leading to disconnection, poor connection, and the like.

In an attempt to prevent this phenomenon, it has been proposed to make the inner wall of the opening formed in the insulating film 4 have a gentle slope so that the metal film for electrode formation is deposited with a uniform thickness. There is.

As a means for providing a slope during photo-etching to this insulating film, the insulating film is made of silicon dioxide formed by vapor phase growth, and when the silicon dioxide is formed by vapor growth, phosphorus (P) is added therein. Gradually large amounts of are added to form a silicon dioxide film in which the concentration of phosphorus increases as it approaches the surface of the film as a whole, and the silicon dioxide film is etched using a hydrofluoric acid-based etching solution. It has been known.

This is because silicon dioxide containing a higher concentration of phosphorus is
This is because a silicon dioxide film that does not contain phosphorus or contains a smaller amount of phosphorus is more easily etched than a silicon dioxide film.

However, when an insulating film is formed by such a method, the formation of the insulating film requires a chemical vapor phase reaction, for example, a reaction between monosilane (SiH4) and oxygen (O2), and furthermore, phosphine (PH3). Since it is a reaction, the temperature during the reaction must be at least several hundred degrees Celsius or higher, and since it lasts for a long time, the impurity diffusion layer (
For example, the diffusion 2) in FIG. 1 proceeds, making it impossible to obtain a desired PN junction.

Furthermore, due to the high temperature treatment, stricter control is required for the gas phase reactor.

The present invention provides a method for forming an insulating film in which the insulating film can be formed at a lower temperature in place of such conventional methods, and the openings of the insulating film can be etched with a gentle slope. This is what we are trying to provide.

According to the present invention, a ternary insulating film of silicon, nitrogen and oxygen is formed on a substrate by reactive sputtering of silicon (Si) in a mixed gas of nitrogen (N2) and oxygen (O2). In the method of forming an opening (window) in an insulating film, the sputtering is performed in an atmosphere where the partial pressure ratio of nitrogen (or oxygen) is high at the start of film formation, and the partial pressure ratio of oxygen (or nitrogen) gradually increases as the film grows. to form an insulating film, and then a hydrofluoric acid-based etching solution (
It is proposed to form an opening in the insulating film having a gentle slope toward the surface thereof by photo-etching using a phosphoric acid-based etching solution (or phosphoric acid etching solution).

The present invention will be explained in detail with reference to the drawings.

As mentioned above, according to the present invention, the insulating film is composed of three components: nitrogen, oxygen, and silicon, and the lower layer portion and the upper layer (
At the surface), the ratio of nitrogen and oxygen amounts to silicon nitride and (
2) A major feature is that the ratio to silicon oxide is different.

That is, when forming an insulating film, for example, the amount of silicon nitride is set to almost 100 (%) at the beginning of its formation, and as it approaches the surface, the amount of silicon nitride is gradually decreased and the amount of (di)silicon oxide is increased. go.

In the resulting insulating film, by using a hydrofluoric acid-based etchant as the etching solution during photo-etching, an opening (window) whose opening area gradually increases toward the surface is formed as shown in Figure 2. can do.

This means that the amount of etching for hydrofluoric acid-based etching solution is
(2) This is due to the fact that silicon oxide is silicon nitride.

In addition, when forming an insulating film, at the beginning of its formation (
2) The amount of silicon oxide is almost 100 (%), and the amount of (di) silicon oxide is gradually decreased and the amount of silicon nitride is increased toward the surface.

By using a phosphoric acid-based etchant as an etchant during photo-etching, it is possible to form an opening (window) in the resulting insulating film, whose opening area gradually increases toward the surface, as shown in Figure 2. can.

This means that the amount of etching for phosphoric acid etching solution is
This is due to the fact that silicon nitride>(di)silicon oxide.

According to the present invention, in forming such an insulating film,
A reactive sputtering method is used.

By using silicon (Si) as the target material, using nitrogen and oxygen as the reaction gas atmosphere, and changing the gas partial pressure ratio of nitrogen and oxygen, it is possible to form an insulating film having the above-described structure on the substrate.

FIG. 3 schematically shows a sputtering apparatus used in the present invention.

In the figure, 11 is a semiconductor substrate, 12 is a support for the semiconductor substrate (anode), 13 is silicon, 14 is a cathode, and 15
16 is a shutter, 16 is a bell jar, and 17 and 17' are nitrogen (N2) and oxygen (O2) introduction pipes, respectively.

In such an apparatus, a DC voltage of several thousand volts is applied between the support base 12 and the cathode 14 to cause discharge, sputtering the silicon 13, and at this time the silicon 13 is sputtered.
C) react with nitrogen and oxygen to form an insulating film made of silicon nitride and silicon oxide on the surface of the semiconductor substrate 11.

At this time, by gradually changing the partial pressure ratio of nitrogen and oxygen,
An insulating film is formed in which the ratio of silicon nitride to silicon (di)oxide as described above is gradually changed.

The oxygen partial pressure ratio when forming the insulating film formed in this way and the hydrofluoric acid-based etching solution (
Looking at the relationship between the etching rate and the 49% hydrofluoric acid (13: ammonium fluoride: 112: water: 78 volume ratio), the fourth
It was like the picture.

As is clear from this figure, the etching rate changes significantly depending on the change in oxygen partial pressure, and by gradually changing the oxygen partial pressure, it is possible to form an insulating film with a different amount of etching toward the surface. It should be obvious.

Next, the present invention will be explained in detail using examples.

Example 1 In the sputtering apparatus shown in FIG. 3, each condition was set as follows.

Semiconductor substrate material: Diffused silicon (Si) substrate heating temperature: 200 [°C] Cathode material: Silicon atmosphere gas: Nitrogen (N2) + oxygen (O2) gas pressure: 6× 10-3 [Torr] Generated power...600
[w] Under such generation conditions, an insulating film with a thickness of 1 [μm] is formed on the semiconductor substrate while gradually increasing the partial pressure ratio of oxygen in the atmospheric gas from 0 [%] to 60 [%]. Formed.

(Therefore, the nitrogen partial pressure ratio changes from 100 [%] to 40 [%]) The resulting insulating film is coated with a hydrofluoric acid-based etching solution (49% hydrofluoric acid 13: ammonium fluoride 112: water 78-
As shown in FIG. 5, the width of the semiconductor substrate surface at the center of the opening is 2 [μm], and the width of the insulating film 4 in contact with the photoresist 7 is 2 [μm] wide. It was possible to form an opening having a width of 6 [μm].

That is, it was shown that an opening (window) having a gentle slope from the center of the opening toward the surface of the insulating film could be formed in the opening.

According to the present invention as described above, since the sputtering method is used as the method for forming the insulating film, the temperature at which the semiconductor substrate is heated can be as low as 200 [°C], and therefore The progress of diffusion of introduced impurities can be suppressed.

Furthermore, neither the sputtering reaction system nor strict measures against high temperatures are required.

Furthermore, as mentioned above, by gradually changing the gas partial pressures of nitrogen and oxygen that constitute the atmospheric gas, it is possible to form an insulating film having a desired amount of etching, and to form an opening (window) with a necessary slope. Obtainable.

As a result, a semiconductor device without problems such as disconnection or poor connection during electrode formation can be obtained.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view showing the structure of a general semiconductor element, Figure 2 is
Figure 3 is a cross-sectional view of a semiconductor element having an improved structure according to the present invention, Figure 3 is a schematic diagram of a sputtering apparatus according to the present invention, and Figure 4 shows the relationship between oxygen partial pressure and etching rate. The curve diagram and FIG. 5 are cross-sectional views of a semiconductor device in which the effects of the present invention are clearly demonstrated. 1 to 5, 1 and 11 are semiconductor substrates, 2
1 is a diffusion region, 3 is a PN junction, 4 is an insulating film, 5 is an electrode window, 6 is a metal electrode, 7 is a photoresist, 12 is a support base, 13 is silicon, 14 is a cathode, 15 is a shutter, 1
6 is a bell jar, and 17, 17 is a gas introduction pipe.

Claims (1)

[Claims] 1 Silicon is deposited on a substrate by reactive sub-ringing of silicon in a mixed gas of nitrogen and oxygen. In a method of forming a ternary insulating film of nitrogen and oxygen and forming an opening (window) in the insulating film, nitrogen (
The insulating film is formed by performing the sputtering in an atmosphere in which the partial pressure ratio of oxygen (or oxygen) is large and the partial pressure ratio of oxygen (or nitrogen) gradually increases as the film grows, and then subjected to hydrofluoric acid etching (or phosphoric acid etching solution). 1. A method for forming an insulating film, which comprises performing a photo-etching process using an insulating film (1) to form an opening having a gentle slope toward the surface of the insulating film.