JPH03274730A - Manufacturing method of semiconductor device - Google Patents

Abstract

PURPOSE:To prevent in-crystal dislocation from generating in a substrate by etching an entire oxidized region to expose a silicon surface at the time of selective oxidation, and further forming an oxidized film at the periphery of the oxidized region via a coat for forming insulated film for baking formation (SOG) containing silicon oxides to reduce a bird's beak over a thin silicon oxide film 2 formed by thermal oxidation on a silicon substrate 1. CONSTITUTION:A silicon nitride film 3 is formed into a pattern by chemical vapor-phase epitaxy over a thin silicon oxide film 2 formed by thermal oxidation on a silicon substrate 1. Subsequently, a silicon nitride film 3 is made into a mask and the surfaces of the thin silicon oxide film 2 and the silicon substrate 1 are subjected to etching. Furthermore, the SOG is coated by the spinner, baked to form a silicon oxide film 20 which is subjected to thermal oxidation for selective oxidation, and a thick silicon oxide film 22 necessary for separation of elements is formed on the oxidized region. Formation of the thick oxidized film via the SOG in the periphery of the oxidized region in this manner can reduce penetration of the thick oxidized film 22 for separation of elements into the non-oxidized region.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in a selective oxidation method for silicon substrates. Concerning preventing intrusion into territory.

[Summary of the invention]

The present invention relates to selective oxidation of silicon substrates, which is generally widely used as one of element isolation methods.

In selective oxidation using the conventional method, the silicon oxide film formed by one selective oxidation fits under the silicon nitride film as an oxidation prevention film, and the cross-sectional shape of the silicon oxide film is such that the silicon oxide film and the silicon oxide film formed by selective oxidation are separated. A smoothly connected bird's beak shape, or a bird's beak, is formed. Therefore, in the present invention, during selective oxidation, the entire oxidized region is etched to expose the silicon surface, and the peripheral edge of the oxidized region is etched with so-called 5OG (SpinOn).
The bird's beak is reduced by forming an oxide film using an insulating film forming coating liquid for baking formation that contains silicon oxide called Glass.

[Conventional technology]

Selective oxidation of a silicon substrate is generally widely used as one of element isolation methods for MOS or bipolar transistors.

Conventionally, this selective oxidation is performed by the method shown in FIGS. 2(,) to (C). That is, as shown in FIG. 2(a), a silicon substrate 1 is thermally oxidized in a dry 02 atmosphere to form a thin silicon oxide film 2 with a thickness of about 50 nm. Next, a silicon nitride film 3 is formed as an oxidation prevention film by chemical vapor deposition. In FIG. 2(b), the silicon nitride film 3 is patterned on a non-oxidized region by photoetching. Further, thermal oxidation is performed in a wet 02 atmosphere to form a silicon oxide film 22 in the oxidized region which is thicker than the silicon oxide film 2 in the non-oxidized region. Since this silicon oxide film 221 is intended for device isolation, its thickness is usually about 800 nm.

After this, the silicon nitride film 3 in FIG. 2(c) is removed and the process proceeds to the next step.

In the conventional selective oxidation shown here, so-called bird's beaks are formed. This is a silicon oxide film 2 formed by selective oxidation as shown in FIG. 2(c).
2 is inserted under the silicon nitride film 3 as an oxidation prevention film, and the cross-sectional shape of the silicon oxide film is a bird's beak shape in which the silicon oxide film 2 and the silicon oxide film 22 formed by selective oxidation are smoothly connected. It is the shape.

Here, a thin silicon oxide film 2 is formed under the silicon nitride film 3.
The purpose of forming 9 is that during selective oxidation, the silicon oxide film 2 on the oxidized region shown in FIG. This is to reduce the stress that is applied to the silicon oxide film 22 from the end of the silicon nitride film 3 when it goes under the end of the silicon nitride film 3.

[Problem to be solved by the invention]

Now, it can be seen that the selective oxidation by the conventional method shown here has the following drawbacks. first.

As mentioned earlier, the silicon oxide film 2 shown in FIG. 2(c)
2, a bird's beak is generated and the bird's beak penetrates under the edge of the silicon nitride film 3, so that the non-oxidized region for forming the element becomes the length b into which the bird's beak penetrates.
It becomes narrower by that amount.

Further, since a bird's beak is generated under the edge of the silicon nitride film 3, the silicon oxide film 22 that has been selectively oxidized receives stress from the silicon nitride film 3.

Although this stress is weakened by the thin silicon oxide film 2 previously formed under the silicon nitride film 3, it actually causes intracrystal dislocations to occur on the silicon substrate at the ends of the non-oxidized regions. It is the cause. This dislocation causes leakage current in the device.

The purpose of the present invention is to prevent the oxidized region from spreading into the non-oxidized region in two-selective oxidation, and to prevent the stress applied to the edge of the oxidized region from the silicon nitride film as an oxidation prevention film patterned on the non-oxidized region during selective oxidation. The objective is to further reduce the occurrence of intracrystalline dislocations in the silicon substrate at the ends of this non-oxidized region.

[Means for solving problems]

In order to achieve the above object, the present invention etches the entire oxidized region during two-selective oxidation to expose the silicon surface.
Furthermore, so-called SOG (S
An oxide film is formed using a coating liquid for forming a sintered film for baking formation, which contains silicon oxide and is called pin-on-G1ass.

[Effect]

Next, nine aspects of the present invention will be described in detail. When a silicon oxide film is formed by thermal oxidation, it is known that the following relationship exists between the thermal oxidation time and the film thickness. This means that when the oxidation time is short, it increases in proportion to the oxidation time, and as the oxidation time increases, it increases in proportion to the square of the oxidation time. Here, it is known that the oxide film thickness is proportional to time in a region where the film thickness is 20 nm or less. The present invention applies this relationship.

That is, on a silicon substrate on which a thin silicon oxide film has been formed during two-selective oxidation, a silicon nitride film is patterned by photoetching as an oxidation prevention film by chemical vapor deposition, and then a thin silicon oxide film is formed using this silicon nitride film as a mask. Then, the surface of the silicon substrate is further etched to a certain depth. Further, a silicon oxide film is formed by SOG on the silicon surface exposed by this etching, that is, on the difference between the peripheral edge of the oxidized region and the cross-sectional area consisting of the silicon nitride film, thin silicon oxide film, and silicon. Then, thermal oxidation as 9 selective oxidation is performed.

Then, since the peripheral edge of the oxidized region where the silicon oxide film is formed by SOG is a thick oxide film from the beginning during thermal oxidation, the thickness of the silicon oxide film is The growth rate is much slower than in oxidized regions other than the peripheral edge.

Here, the purpose of etching the oxidized region to below the surface of the silicon is to create a sufficient SOG film thickness at the boundary between the non-oxidized region and the oxidized region so that the growth of the silicon oxide film at the peripheral edge of the oxidized region is slowed down during two-selective oxidation. This is to form a difference to obtain . Normally, a silicon nitride film as an oxidation prevention film has a thickness of about 00 nm, so even if this silicon nitride film is etched and SOG is formed at the gap, the maximum thickness is about 1100 nm, which is sufficient. Thickness cannot be obtained.

Therefore, it is necessary to perform etching below the surface of the silicon.

It can be seen that the present invention further has the following advantages. By etching the silicon surface to a depth equal to the thickness of the silicon oxide film at the end of selective oxidation, the non-oxidized region and the oxidized region can finally be planarized as a whole.

〔Example〕

An embodiment according to the present invention will be described below with reference to FIG. FIGS. 1(a) and 1(b) are FIG. 2(a) of a conventional example.

The same process as in (b) was performed, in which a silicon nitride film 3 was patterned by chemical vapor deposition on a thin silicon oxide film 2 formed by thermally oxidizing a silicon substrate 1.

Subsequently, the thin silicon oxide film 2 and the surfaces of the silicon substrate 1 are etched using the silicon nitride film 3 as a mask. This situation is shown in FIG. 2(C).

The depth to which this silicon substrate 1 is etched must be equal to or less than the thickness of the silicon oxide film 22 after selective oxidation. Furthermore, apply SOG using a spinner.

The silicon oxide film 20 is formed by firing as shown in FIG. 2(d).
).

Then, thermal oxidation for selective oxidation is performed to form a thick silicon oxide film 22 necessary for element isolation in the oxidized region.

As mentioned before, by etching the silicon substrate surface in the oxidized region during selective oxidation and forming a thick silicon oxide film by SOG on the peripheral edge of the oxidized region, as shown in FIG. 2(e), In addition, it is possible to reduce the intrusion of the thick oxide film 22 for element isolation into the non-oxidized region.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to prevent the bird's beak of the silicon oxide film formed at the boundary between the oxidized region and the non-oxidized region from penetrating into the non-oxidized region during selective oxidation of the silicon substrate. can.

As a result, it is possible to prevent the oxidized region from spreading into the non-oxidized region during selective oxidation, and further to reduce the force applied to the edge of the oxidized region from the silicon nitride film as an oxidation prevention film patterned in the non-oxidized region.

[Brief explanation of drawings]

FIGS. 1(a) to 1(e) are cross-sectional views of the selective oxidation process of a silicon substrate according to the present invention. FIGS. 2(a) to 2(c) are cross-sectional views of a selective oxidation process of a silicon substrate according to a conventional method. Engineering: silicon substrate, 2, 22: silicon oxide film. 3: silicon nitride film, 20: silicon oxide film by SOG, b, b': length of baize beak that goes under the silicon nitride film.

Claims (1)

[Claims] 1. Forming a thermal oxidation prevention film on a semiconductor substrate, selectively etching the thermal oxidation prevention film using an etching mask material such as photoresist to remove the mask material, and then thermally oxidizing the semiconductor substrate, A method of manufacturing a semiconductor device, comprising etching the surface of the semiconductor substrate using the thermal oxidation prevention film as a mask, and then applying a coating liquid for forming an insulating film for baking formation.