JPH1116886A - Etching - Google Patents

Abstract

PROBLEM TO BE SOLVED: To apply to mass production a self-alignment forming process of a contact hole that uses a silicon nitride film of a base layer as an etching stopper without using a highly toxic process gas like a CO2 gas when the silicon nitride film is etched. SOLUTION: A test sample comprising a semiconductor substrate 100, a gate 101 laminated on the substrate 100, a silicon nitride film 102 in which the gate 101 is buried, a BPSG film 103 and a resist mask 104 formed on the BPSG film 103 is inserted into an etching device. The BPSG film 103 exposed in the opening of the resist mask 104 is etched off by a plasma etching technique of C4 F8 and CH3 OH gases to form a contact hole 105 extending to the surface of the silicon nitride film 102.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for etching a silicon oxide film on a semiconductor substrate, and more particularly to an etching method requiring a high selectivity to a silicon oxide film immediately below the silicon oxide film.

[0002]

2. Description of the Related Art In an etching process of a silicon oxide-based material used for an LSI, it is possible to form a contact hole having a fine and high aspect ratio, and to form a base material (nitride) immediately below the silicon oxide-based material. Silicon,
Si and the like are required to have a high selectivity. A fluorocarbon-based gas is mainly used for etching a silicon oxide-based material. The selectivity between the silicon oxide-based material and the base material is determined by competition between an etching reaction and a deposition reaction by a plasma dissociation component. Roughly, it has been confirmed that the higher the C / F ratio in the plasma, the higher the selectivity with the underlying material. However, a sufficient selectivity cannot be obtained with fluorocarbon-based gas alone. As means for improving the selectivity, for example, Japanese Patent Application Laid-Open No. 5-94974
As described in Japanese Patent Application Laid-Open Publication No. H11-107, a technique of adding CO in addition to a fluorocarbon-based gas which is a main etching gas is being studied. It is considered that the added CO supplies the C component by dissociation, reduces F in the form of COFx, and increases the C / F ratio in the etching atmosphere.

[0003]

In the conventional example described above, C
Although O is used as an additive gas, CO gas is extremely toxic to the human body, and its use in a semiconductor mass-production factory is not preferable in terms of safety.

An object of the present invention is to provide an etching method which has a high selectivity with respect to an underlying silicon nitride film without using a highly toxic process gas when etching a silicon oxide film.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to etch a silicon oxide film using a gas containing a fluorocarbon-based gas and a saturated alcohol and stop the etching near the surface of the silicon nitride film immediately below the silicon oxide film. Achieved by including steps.

In the present invention, a saturated alcohol such as CH
CH3 is added in the etching atmosphere because 3OH is added.
There is a large amount of CO dissociated from OH. Therefore, there is an effect of effectively increasing the C / F ratio similar to that of the above-described conventional CO gas addition.

Further, since H and H2 are dissociated from CH3OH, the effect of removing F by hydrogen is added, and a higher C / OH ratio is obtained.
F ratio can be obtained. As a result, the selectivity with respect to the silicon nitride film can be greatly increased. Saturated alcohols used in the present invention have extremely low toxicity compared to CO gas.
It is often used in semiconductor cleaning processes.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION

[Embodiment 1] An embodiment of the present invention will be described with reference to the process chart of FIG.

In FIG. 1, a sample (FIG. 1A) in which a resist mask 104 is formed on a silicon nitride film 102 and a BPSG film 103 in which a gate 101 on a semiconductor substrate 100 is stacked and buried is put into an etching apparatus. The etching apparatus used was a load-lock type magnetic field microwave etching apparatus.

Next, the BPSG film 103 exposed from the opening of the resist mask 104 is removed by etching using a C 4 F 8 and CH 3 OH gas plasma etching technique, and the contact hole 10 reaching the surface of the silicon nitride film 102 is removed.
5 was formed (FIG. 1B).

The main etching conditions are gas flow rate C4F
8:30 sccm, CH3OH: 70 sccm, total gas pressure 3P
a, The substrate temperature is −10 ° C.

In this embodiment, by using C4F8 and CH3OH, the etching rate of the silicon nitride film 102 is reduced to 1/10 to 1 as compared with the etching of the BPSG film 103.
/ 50 can be reduced. As a result, the silicon nitride film 102
A good etching stopper layer can be obtained even if the film thickness is small.

In this embodiment, the flow rate of CH3OH is [CH3OH gas flow rate / CH3OH gas flow rate + C4F
8 gas flow rate] = 70%, but it has been confirmed that the same effect is obtained even when the gas ratio is in the range of about 20 to 90%.

The other etching conditions (total gas pressure, substrate temperature) are not limited to the above-mentioned values, and can be adjusted and optimized according to the etching apparatus and the sample. .

In the above embodiment, C4F8 and C4F8
Although the entire thickness of the BPSG film 103 is etched by H3OH, a high selectivity with respect to the silicon nitride film 102 is required only when the BPSG film 103 near the silicon nitride film 102 is etched and at the time of subsequent over-etching. It is time.

Therefore, the first etching of the BPSG film 103 is performed with a C4F8-based gas to which no CH3OH is added, and the BPSG film 103 near the silicon nitride film 102 is etched.
The above-described effects can be obtained by adding CH3OH only in the step of etching and in the over-etching step.

In this embodiment, C4F8 and CH
Although etching is performed using 3OH gas, He, N
The same effect can be obtained by adding a rare gas such as e, Ar, Kr, and Xe gas together.

In this embodiment, C4F8 and CH
Etching is performed using 3OH gas, but CF4, C2F6, C3F8, C4
Including at least one of F8 and C as saturated alcohol-based gas
The same effect can be obtained by using a gas system containing at least one of H3OH and C2H5OH.

In this embodiment, the BPSG film 103 is etched, but the other silicon oxide films are made of PSG and SiO.
The same effect is obtained with two films or the laminated film. In addition to the silicon nitride film 102, in addition to the Si3N4 film,
The same effect can be obtained even with a SiN film containing a small amount of H or O.

In this embodiment, a magnetic field microwave etching apparatus is used. However, another plasma etching apparatus, for example, an ICP (Inductively Coupled Plasma) etching apparatus or a high frequency etching apparatus using parallel plate electrodes is used. Has the same effect.

Embodiment 2 Another embodiment of the present invention is shown in FIG.
The process will be described with reference to FIGS.

In FIG. 2, the BP formed on the entire surface of the semiconductor substrate 200 by selectively covering the upper surface and side surfaces of the gate 201 on the semiconductor substrate 200 with a silicon nitride film 202.
A sample (FIG. 2A) in which a resist mask 204 was formed on the SG film 203 was put into an etching apparatus. The etching apparatus used was a load-lock type magnetic field microwave etching apparatus.

Next, the BPSG film 203 exposed from the opening of the resist mask 204 is removed by etching using a plasma etching technique based on C 4 F 8 and CH 3 OH gas to form contact holes 205 reaching the surface of the silicon nitride film 202 and the semiconductor substrate 200. Was formed (FIG. 2B).
Main etching conditions are gas flow rate C4F8: 30sccm,
CH3OH: 70 sccm, total gas pressure 3 Pa, substrate temperature -1
0 ° C.

In this embodiment, by using C4F8 and CH3OH, the etching rate of the silicon nitride film 202 is 1/10 to 1 compared with the etching of the BPSG film 203.
/ 50 can be reduced. As a result, the silicon nitride film 202
A good etching stopper layer can be obtained even if the film thickness is small.

In this embodiment, the flow rate of CH3OH is [CH3OH gas flow rate / CH3OH gas flow rate + C4F
8 gas flow rate] = 70%, but it has been confirmed that the same effect is obtained even when the gas ratio is in the range of about 20 to 90%. Here, other etching conditions (total gas pressure, substrate temperature) are not limited to the above-mentioned numerical values, but can be adjusted and optimized according to the etching apparatus and the sample.

In the embodiment described above, the entire thickness of the BPSG film 203 is etched by C4F8 and CH3OH, but the silicon nitride film 202 and the semiconductor substrate 20 are etched.
A high selectivity to 0 is required because at least the BPSG near the silicon nitride film 202 and the semiconductor substrate 200 is required.
When etching the film 103 and subsequent over-
This is the time of etching.

Therefore, the first etching of the BPSG film 203 is performed by using a C4F8-based gas without addition of CH3OH, and the BPSG film 203 near the silicon nitride film 202 is etched.
The above-described effects can be obtained by adding CH3OH only in the step of etching and in the over-etching step.

In this embodiment, C4F8 and CH
Although etching is performed using 3OH gas, He, N
The same effect can be obtained by adding a rare gas such as e, Ar, Kr, and Xe gas together.

In this embodiment, C4F8 and CH
Etching is performed using a 3OH gas, but CF4, C2F6, C3F8,
The same effect can be obtained by using a gas containing at least one of C4F8 and at least one of CH3OH and C2H5OH as a saturated alcohol-based gas.

In this embodiment, the BPSG film 203 is etched.
The same effect is obtained with two films or the laminated film. In addition to the silicon nitride film 202, in addition to the Si3N4 film,
The same effect can be obtained even with a SiN film containing a small amount of H or O.

In this embodiment, a magnetic field microwave etching apparatus is used. However, another plasma etching apparatus, for example, an ICP (Inductively Coupled Plasma) etching apparatus or a high frequency etching apparatus using a parallel plate electrode is used. Has the same effect.

[0032]

According to the present invention, when a silicon oxide film such as a BPSG film is etched, a highly selective process can be performed with respect to the underlying silicon nitride film without using a highly toxic process gas such as CO gas. Ratio can be secured. Therefore,
Etching of silicon nitride film during BPSG film etching
It can be utilized as a stopper layer, and can be applied to a process of forming a self-aligned contact hole. As a result, high integration and high performance of semiconductor elements can be promoted in a mass production factory.

[Brief description of the drawings]

FIG. 1 is a process chart of one embodiment of the present invention.

FIG. 2 is a process chart of another embodiment of the present invention.

[Explanation of symbols]

Reference Signs List 100 semiconductor substrate, 101 gate, 102 silicon nitride film, 103 BPSG film, 104 resist mask, 105 contact hole, 200 semiconductor substrate, 20
DESCRIPTION OF SYMBOLS 1 ... Gate, 202 ... Silicon nitride film, 203 ... BPSG
Film, 204: resist mask, 205: contact hole.

Claims (10)

[Claims] An etching method characterized by etching a silicon oxide film exposed from a resist mask opening formed on a semiconductor substrate using a gas containing a fluorocarbon-based gas and an alcohol. 2. A silicon oxide film exposed from a resist mask opening formed on a semiconductor substrate using a gas containing a fluorocarbon-based gas and an alcohol, and etched by an etching stop layer immediately below the silicon oxide film. Stopping the etching. 3. The process of etching a silicon oxide film exposed from a resist mask opening formed on a semiconductor substrate and stopping the etching near the surface of the silicon nitride film immediately below the silicon oxide film, comprising: And a step of performing plasma etching using a gas containing alcohol. 4. The step of etching a silicon oxide film exposed from a resist mask opening formed on a semiconductor substrate includes a step of performing plasma etching using a gas containing a fluorocarbon-based gas, an alcohol, and a rare gas. An etching method characterized by the above-mentioned. 5. The step of etching a silicon oxide film exposed from a resist mask opening formed on a semiconductor substrate and stopping the etching by an etching stop layer immediately below the silicon oxide film, the method comprising the steps of: And a step of performing plasma etching using a gas containing a rare gas. 6. A step of etching a silicon oxide film exposed from a resist mask opening formed on a semiconductor substrate and stopping the etching with a silicon nitride film immediately below the silicon oxide film, comprising the steps of: And a step of performing plasma etching using a gas containing a rare gas. 7. The gas flow ratio of the fluorocarbon-based gas and the alcohol [alcohol gas flow] / [alcohol gas flow + fluorocarbon-based gas flow] is 20 to 90%.
The etching method according to claim 1, wherein the etching method falls within the range. 8. The method according to claim 8, wherein said fluorocarbon-based gas is CF4, C
5. The etching method according to claim 1, wherein the etching method comprises at least one of 2F6, C3F8 and C4F8, and wherein the alcohol comprises at least one of CH3OH and C2H5OH. 9. The etching method according to claim 4, wherein said rare gas comprises at least one of He, Ne, Ar, Kr, and Xe gases. 10. The method according to claim 1, wherein the silicon oxide film is BPSG, PSG,
7. The etching method according to claim 3, wherein the etching method includes any one of a SiO2 film and the silicon nitride film is a Si3N4 film.