JPH0677175A - Etching method of silicon nitride on silicon oxide - Google Patents

Abstract

PURPOSE:To etch silicon nitride on silicon oxide without causing any residue and particles while a high selective ratio is made compatible with anisotropy by a method wherein the silicon nitride on the silicon oxide is etched by using a gas system which contains carbon, hydrogen and fluorine and a plasma treatment is then executed by using a fluorine-based gas. CONSTITUTION:An SiO2 film 2 and an Si3N4 film 3 are formed on an Si substrate 1, a photoresist film 4 is formed on them, and the photoresist film 4 is patterned by a G-line stepper by using TSMR-V3. When the Si3N4 film 3 is dry-etched, it is etched by a gas containing C, H and F (CH2F2, CH3F or the like) at a first step. An etching residue which is easily produced at this time is removed by using a gas containing F (SF6, NF3, ClF3 or the like) at a second step. Thereby, the Si3N4 film on the SiO2 film can be etched without any problem of a residue and particles while high selectivity is made compatible with good isotropy.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for etching silicon nitride on silicon oxide. The present invention can be applied to, for example, Si in a manufacturing process of electronic materials such as semiconductor devices.
It can be used when the Si ₃ N ₄ film formed on the O ₂ film is etched to selectively perform anisotropic processing.

[0002]

_2. Description of the Related Art Conventionally, Si ₃ N ₄ on a SiO ₂ thin film has been used.
The selective anisotropic processing of a film is widely used, for example, in a mask formation process for selective oxidation in the LOCOS method which is widely used as an element isolation method for LSI. In such a technique, the CD-LOS is used as the device is miniaturized.
The demand for S, that is, the demand for eliminating the conversion difference, is becoming increasingly severe, and the demand for selectivity, that is, the demand for even higher selection is becoming more and more demanding.

[0003] In the this type of conventional technology, using gas mixture of O ₂ in CF _4, or CF ₄ to O ₂ and mixed gas, etc. Ar as etching gas, and a tunnel type plasma etcher parallel An etching process using a flat plate type anode coupling type etcher, a discharge chamber separation type CDE (chemical dry etcher) and the like has been put into practical use. In this process, Si ₃ N ₄
Selective ratio of the film to the underlying SiO ₂ film (about 5)
It is possible to etch with.

However, in this conventional process, since the basic reaction mechanism is mainly based on fluorine radicals, the etching shape naturally results in undercutting. Furthermore, regarding the selection ratio with respect to the underlying SiO ₂ ,
When a further improvement is required, it is inevitable to increase the apparent selection ratio by increasing the etching rate of Si ₃ N ₄ rather than suppressing the etching rate of SiO _{2 in} a process mainly using fluorine radicals. As a result, the undercut of Si ₃ N ₄ is further increased.

Therefore, silicon nitride on silicon oxide (typically Si ₃ N ₄₎ that achieves both a high selectivity and anisotropy is obtained.
/ SiO ₂ ) selective etching process has been earnestly desired, and various companies have proposed the following countermeasures.

Freon 32 (CH ₃ F ₂ ) and Freon 41
Process using (CH ₃ F) as an etching gas (International Electric D
device Meeting, 1983, "VLAl
Device Fabrication Using
a Unique Highly-Selective
Si ₃ N ₄ Dry Etching ”)

A process utilizing FCl radicals generated from NF ₃ + Cl ₂ by using CDE (S. Suto et al., “Highly Selective Etching”).
of Si ₃ N ₄ to SiO ₂ Employi
ng Fluorine and Chlorine
Atoms Generated by Micro
ave Discharge ”, 1987, Proc
of symposium on Dry Proce
(See ss)

Process in which CO ₂ is added to Freon 32 (see Japanese Patent Laid-Open No. 61-142744)

Of these, it is true that Si ₃ N ₄ / S
High selective ratio anisotropic processing between iO ₂ is possible, but C / F
Since a gas with a high ratio is used, there are problems with surface residues and particles that use the polymer as a mask, and it is difficult to say that this is a practical process. Is sufficiently satisfactory in terms of selection ratio, but anisotropic processing cannot be performed due to the use of CDE. Is a method proposed by the present inventor in order to remedy the drawback of (1), which is an excellent technique because etching can be performed without causing the problems of (1) such as particles and residues. However, the maximum selection ratio that can be obtained is 7
Therefore, an even higher selection ratio is desired. In addition, excess CO
_The addition ratio of ₂ may lower the selectivity ratio to resist, leaving a risk that the shape may be tapered.

Therefore, the Si ₃ N ₄ film on the SiO ₂ film is
There is a strong demand for a practical process that achieves both high selectivity and anisotropy while etching without producing residues or particles.

[0011]

It is an object of the present invention to solve the above-mentioned problems by etching silicon nitride on silicon dioxide while achieving both a high selectivity and good anisotropy without causing the problem of residues and particles. The present invention is intended to provide a dry etching method that can be performed.

[0012]

According to the invention of claim 1 of the present application, in a dry etching method for etching silicon nitride on silicon oxide, a gas containing carbon, hydrogen and fluorine as constituent elements in the first step. A method for etching silicon nitride on silicon oxide, characterized in that etching is performed using a gas system containing at least: and etching residues are removed by plasma treatment using a fluorine-based gas in the second step. This achieves the above-mentioned object.

According to a second aspect of the present invention, in a dry etching method for etching silicon nitride on silicon oxide, a gas containing at least a gas containing carbon, hydrogen and fluorine as constituent elements in the first step. A method for etching silicon nitride on silicon oxide, characterized in that etching is carried out using a system, and etching residues are removed by over-etching using FCl radicals in the second step, whereby the above object is achieved. It is a thing.

According to the first aspect of the present invention, in the course of intensive investigations by the present inventor to achieve the above-mentioned object, etching is performed in two steps, and a gas containing carbon, hydrogen and fluorine as constituent elements, for example, CH. Based on this finding, it was found that a process of removing the residue generated at the time of etching using ₂ F ₂ or CH ₃ F by etching with a fluorine radical in the second step is preferable.
It is proposed. That is, according to the present invention, in the etching process of the silicon nitride such as Si ₃ N ₄ based film on the silicon oxide such as SiO ₂ , the etching is made into two steps, for example, as the first step, for example, CH ₂ F ₂ and / or CH ₃ F That can be embodied in such a manner that a fluorine-based gas such as SF ₆ , NF ₃ , ClF ₃ or the like is used as a second step in overetching, and thereby fluorine radicals are supplied to perform etching. Is.

According to the second aspect of the present invention, similarly, in the course of earnestly studying to achieve the above-mentioned object, etching is performed in two steps and a gas having carbon, hydrogen and fluorine as constituent elements, for example, CH ₂ F. ₂ or a process of removing the residue generated during etching using CH ₃ F by performing etching in a radical mode in the second step, which is also a process capable of highly selective processing with respect to silicon oxide (SiO ₂ etc.) Is found to be suitable, and is proposed based on this finding. That is, this invention
Silicon oxide, eg silicon nitride on SiO ₂ , eg S
In the etching process of the i ₃ N ₄ film, the etching is
In steps, as the first step, for example, CH ₂ F ₂
And / or CH ₃ F is used for etching, and the second step during over-etching can be embodied by using, for example, a long-life FCl radical obtained by discharging fluorine-based gas and chlorine-based gas. is there.

[0016]

According to the dry etching method of the first aspect of the present invention, the C, H, and F containing gas (CH ₂ F) in the first step is used.
₂ or CH ₃ F, etc.) can perform highly selective anisotropic processing of silicon nitride (Si ₃ N ₄ / SiO ₂ structure, etc.) on silicon oxide by a known action, and The etching residue due to the polymer mask or the like that may be generated here can be removed by the fluorine radicals generated from the fluorine-based gas by using the fluorine-based gas in the second step, so that good etching can be realized without any problems. it can.

Usually, in a process utilizing fluorine radicals, the side wall of silicon nitride such as Si ₃ N ₄ which is an etching pattern is attacked by fluorine radicals to cause an undercut, but in the present invention, the etching in the first step is performed. There is no concern of undercutting in the residue removal process since the side walls are covered with the sometimes strong polymer. The concept of protecting the side wall with this strong polymer is known as an etching method of a W-polycide structure using a specific chlorofluorocarbon (F113) (Nojiri et al., 1989 Spring Conference on Applied Physics, 1p. -L-5).

In the present invention, a strong polymer is formed on the side wall by the C, H, and F gases themselves such as CH ₂ F ₂ and CH ₃ F used for selective etching to form a strong polymer on the side wall of the fluorine radical during overetching. Since the residue is removed while preventing the attack, the high selectivity anisotropic processing is satisfactorily realized without any problem due to the residue.

In addition, this over-etching can also serve as a cleaning action for the polymer deposited in the chamber by the contribution of the fluorine radicals at this time, so that it is also effective in suppressing particles.

According to the dry etching method of the second aspect of the present invention, first, as in the first aspect of the invention, the C, H, and F gases (CH ₂ F ₂ or CH ₃ F, etc.) in the first step are contained.
By performing etching by means of etching, silicon nitride (Si ₃ N ₄ / SiO ₂
(For example, structure) can be performed, and then etching residues due to a polymer mask or the like that may occur here can be removed by FCl radicals in the present invention in the second step, so that a favorable result can be obtained. Etching can be realized without problems.

Usually, in a process utilizing fluorine radicals, an undercut is produced by attacking a silicon nitride side wall such as Si ₃ N ₄ which is an etching pattern. In the present invention, the same steps as in the first aspect of the invention are performed. 1
Since the side wall is covered with the strong polymer generated at the time of etching, there is no fear of undercut in the residue removal process.

Further, the FCl radical used in the second step is known as a gas capable of performing ultrahigh selective etching of a silicon nitride / silicon oxide structure while isotropically etching (S. Suto, N. Hayasasaka e.
tal “Highly Selective Etch
ing of Si ₃ N ₄ to SiO ₂ Empl
oyig Fluorine and Chlorin
e Atoms Generated by Micr
owave DISCHARGE ”1987, Proc
of Symposium on Dry Proc
ess), by using this during over-etching, there is no need to worry about attack on silicon oxide when removing residues.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the invention of the present application will be described below with reference to the drawings. However, as a matter of course, the invention of the present application is not limited to the following examples.

Example 1 In this example, a sample having a silicon oxide 2 and a silicon nitride 3 formed on a substrate 1 as shown in FIG. 1A was dry-etched for anisotropic processing. It was More particularly, this sample, the SiO ₂ 100 Å, LP (the low pressure) -Si ₃ N ₄ to 2000Å is formed as a silicon nitride 3 as silicon oxide 2 on the Si substrate 1, a photoresist film 4 on the Then, this photoresist film 4 is obtained by patterning with a G-line stepper using TSMR-V3.

In this example, the structure of FIG. 1A was etched in the first step as follows. A bias application type ECR etcher was used as the apparatus, and the first step etching of the two step etching was performed under the following conditions. Gas system used: CH ₂ F ₂ = 50 SCCM Pressure: 10 mTorr RF power: 200 W (2 MHz) μ wave power: 850 Watt The state at this time is shown in FIG. 1 (b). Polymer deposits 5 on the sidewalls of the anisotropically processed pattern
And a residue 3a that is considered to have acted as a mask by a polymer or the like is present on the bottom surface to be etched.

In this state, subsequently, as the second step, etching was performed under the following conditions. Gas system used: NF ₃ 50 SCCM Pressure: 15 mTorr RF power: 0 W Microwave power: 850 Watt In this second step, the residue was quickly removed by the action of the F radical, and the side wall was etched with the polymer deposit 5. However, it did not affect the pattern.

Also, the effect on the underlying SiO ₂ is that the etching is performed by supplying a large amount of F radicals, the etching rate of Si ₃ N ₄ is large, and the residue can be removed in a short time. Etching was sufficient and did not affect the underlying Si. Further, this plasma treatment also had the effect of cleaning the carbon-based polymer atmosphere in the chamber, and did not cause an increase in particles. FIG. 1C shows the state after completion of the etching in the second step. Good anisotropic processing with high selectivity was achieved without any problems.

Example 2 Using the sample having the structure of FIG. 1A similar to that of Example 1, etching was performed by magnetron type RIE. The following etching conditions were adopted as the first step of the two-step etching. Gas system used: CH ₃ F 50SCCM Pressure: 5Pa RF power: 1KWatt

As a result, a structure similar to that of Example 1 in the state of FIG. 1 (b) was obtained. That is, the deposit 5 is attached to the side wall of the pattern that has been anisotropically processed, and the residue 3a that is considered to be a mask of polymer or the like is present on the surface to be etched.

In this state, as the second step,
Etching was performed under the following conditions. Gas system used: SF ₆ 100 SCCM Pressure: 10 Pa RF power: 400 Watt

As a result, the residue was promptly removed by the action of the F radical, and the sidewall was only etched with the deposit 5, and the pattern was not affected. Furthermore,
The influence on the underlying SiO ₂ film and the particle level were the same as in Example 1.

Embodiment 3 This embodiment embodies the invention of claim 2.
A sample of FIG. 2 (a) similar to that used in Example 1
The first step etching was performed under the same conditions as in Example 1. As a result, the structure shown in FIG. 2B was obtained.

In the present example, the structure of FIG. 2B was subsequently transferred to a downstream type chemical dry isotropic etcher, and the second step etching was performed under the following conditions. Gas system used: NF ₃ / Cl ₂ = 40/60 SCCM Pressure: 0.2 Torr μ-wave power: 1 kWatt

In the etching apparatus used, charged particles are removed, and etching using only radicals proceeds. By this discharge, FCl radicals, which are Si ₃ N ₄ etchants, are generated, the residue is promptly removed by the action of the FCl radicals, and the sidewall is only etched with the polymer deposit 5 and the pattern is not formed. It had no effect. In addition, the effect on the underlying SiO ₂ is FC
Due to the action of the l radical, the selectivity between Si ₃ N ₄ / SiO ₂ was almost infinite, and it was not etched at all. FIG. 2C shows the state after the etching is completed.

According to this embodiment, the residue which is a defect of the high selective etching by the conventional 32 freon and 41 freon, and the anisotropic processing which is a fault of the high selective etching using FCl radical cannot be performed. Supplemented,
Good Si ₃ N ₄ / SiO ₂ highly selective anisotropic processing can be realized.

Example 4 Using the sample of FIG. 2A having the same structure as in Example 3, etching was performed by magnetron type RIE. The following etching conditions were adopted as the first step of the two-step etching. Gas system used: CH ₃ F = 50 SCCM Pressure: 5 Pa RF power: 1 kWatt

As a result, FIG. 2B, which is the same as that of the third embodiment, is shown.
The structure of was obtained. That is, the deposit 5 is attached to the side wall of the pattern that has been anisotropically processed, and the residue 3a that is considered to be a mask of polymer or the like is present on the surface to be etched. In this state, the sample was subsequently transferred to a downstream type isotropic etcher, and etching was performed under the following conditions as the second step. Used gas system: NF ₃ / Cl ₂ = 40/60 SCCM Pressure: 0.2 Torr μ Wave power: 1 kWatt By this, the residue is promptly removed by the action of the FCl radical, and the deposit 5 is only etched on the side wall. So it didn't affect the pattern. The influence on the underlying SiO ₂ film was the same as in Example 2, and there was no problem.

The invention of the present application is not of course limited to the above-mentioned embodiment, and the apparatus, conditions, etc.
It is needless to say that the selection can be appropriately made without departing from the spirit of the invention.

[0039]

As described above, according to the dry etching method of the invention of the present application, the problem of residues and particles is generated while achieving both high selectivity and good isotropy of silicon nitride on silicon dioxide. If it is possible to etch without doing so, it is possible.

[Brief description of drawings]

FIG. 1 shows the steps of Example 1 in order in a schematic sectional view of a sample used.

FIG. 2 shows the steps of Example 3 in order with schematic cross-sectional views of a sample used.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Silicon oxide (SiO ₂ ) 3 ... Silicon nitride (Si ₃ N ₄ ) 4 ... Photoresist 5 ... Deposit (polymer) 3a ... Etching residue

Claims (2)

[Claims] 1. A dry etching method for etching silicon nitride on silicon oxide, wherein in the first step, etching is performed using a gas system containing at least a gas containing carbon, hydrogen and fluorine as constituent elements, A method for etching silicon nitride on silicon oxide, characterized in that the etching residue is removed by plasma treatment using a fluorine-based gas in the second step. 2. A dry etching method for etching silicon nitride on silicon oxide, wherein in the first step, etching is performed using a gas system containing at least a gas containing carbon, hydrogen and fluorine as constituent elements, A method of etching silicon nitride on silicon oxide, characterized in that the etching residue is removed by over-etching using FCl radicals in the second step.