JPH06132252A - Dry etching method - Google Patents

Abstract

PURPOSE:To provide a dry etching method which can selectively etch the silicon oxide film on a silicon nitride film. CONSTITUTION:This is equipped with a process of forming a BPSG2 film 6 on an Si3N4 film, a process of forming a photoresist pattern 7 on the BPSG2 film 6, and a process of putting the etching gas, which includes CHF gas and CO gas, into plasma condition, and selectively etching the BPSG film 6, with the photoresist pattern 7 as a mask, by the plasma of mixed gas, under the conditions that the temperature is 90 deg.C or over, that the pressure is from 40 to 100mTorr, and that the ratio of the flow of CO gas to the flow of mixed gas between the CHF3 gas and CO gas is from 40 to 80%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry etching method, and more particularly to a dry etching method for selectively etching a silicon oxide film on a silicon nitride film.

[0002]

2. Description of the Related Art In recent years, a large-scale integrated circuit formed by integrating a large number of transistors, resistors, etc., on one chip in an important part of a computer or communication equipment so as to achieve an electric circuit ( LSI) is frequently used. Therefore, the performance of the entire device is largely linked to the performance of the LSI alone.

The performance improvement of the LSI itself can be realized by increasing the degree of integration, that is, by miniaturizing the elements. For this reason, the miniaturization of elements continues to progress, and there is an increasing demand for higher precision pattern dimensions. Generally, a semiconductor integrated circuit is formed by laminating an insulating film such as a silicon oxide film having a predetermined pattern and a conductive film such as aluminum on a semiconductor substrate such as a silicon substrate.

As a technique for processing these insulating films and conductive films into a desired pattern, conventionally, a photosensitive photoresist is applied on a film to be processed such as an insulating film or a conductive film,
Lithography technology that exposes the photoresist with light or ultraviolet rays according to the desired pattern, then selectively removes the exposed or unexposed portion of the photoresist by development, and forms the photoresist pattern. Then, the photoresist pattern is used as a mask for processing. A dry etching technique for etching a film and a peeling technique for removing a photoresist pattern are used.

By the way, at present, a film to be processed is processed into a desired pattern by using a fine photoresist pattern.
As one method, a reactive ion etching (RIE) technique using plasma is widely used. This etching is performed, for example, by placing the substrate on which the film to be processed is deposited in a vacuum container equipped with a pair of parallel plate electrodes, evacuating the interior of the vacuum container, and then vacuuming the reactive gas containing a halogen element or the like. The film is introduced into a container, the reactive gas is turned into plasma by discharge by applying high-frequency power, and the film to be processed is etched using the generated plasma.

According to RIE, among various particles in plasma, ions are accelerated by a DC electric field (self-bias) generated in the ion sheath on the electrode surface, so that the film to be processed is bombarded with great energy. , An ion-promoted chemical reaction is triggered. For this reason, the etching proceeds in the ion incident direction, and it is possible to perform processing with excellent directivity without undercut.

Next, a silicon oxide film (SiO
The etching of ₂ films will be described.

In RIE of a SiO ₂ film, a gas containing C and F such as CF ₄ , CHF ₃ , C ₂ F _{6 is} usually used as a reactive gas.

Therefore, for example, CHF ₃ is used to produce Si.
When a contact hole is formed in the SiO ₂ film formed on the substrate, CF ₃ radicals generated by the discharge are Si
It will be adsorbed on the surface of the O ₂ film. And this CF
By colliding with accelerated CF ₃ ions by ₃ radicals and the self-bias, CF ₃ radicals and CF ₃ ions are dissociated into F and C.

[0010] As a result, the F reacts with Si in the SiO ₂ film vaporizes leaving become SiF _4, C vaporizes leaving become CO reacts with O in the SiO ₂ film, SiO ₂
The film is etched. On the other hand, CF ₃ is adsorbed on the surface of the Si substrate exposed by the etching of the SiO ₂ film, but F of some CF ₃ is extracted by H, so CF _x (0 ≦ X A polymerized film of ≦ 3) will be formed.

Since this polymerized film functions as an etching protection film for the Si substrate, the etching of Si is suppressed, and as a result, the etching selectivity ratio of the SiO ₂ film to the Si substrate is increased, and the selective etching of the SiO ₂ film is possible. Becomes

However, the silicon nitride film (Si ₃ N
_There are the following problems with respect to RIE of the SiO ₂ film formed on the ₄ film).

That is, as in the case of the SiO ₂ film on the Si substrate described above, when RIE of the SiO ₂ film is performed using CHF ₃ , F reacts with Si to become SiF ₄ and vaporized and desorbed, Since C reacts with N to become CN and is vaporized and released, the Si ₃ N ₄ film is etched in the same manner as the SiO ₂ film, and the etching selection ratio of the silicon oxide film to the Si ₃ N ₄ film cannot be increased, resulting in RIE. Of SiO ₂ film by Si
_The selective etching for the ₃ N ₄ film was impossible.

[0014]

As described above, the conventional R
In the IE, the insulating film (silicon oxide film) formed on the conductive film (Si substrate) could be selectively etched, but the insulating film (silicon oxide film) formed on the insulating film (silicon nitride film) was possible. However, there is a problem that the selective etching is impossible.

The present invention has been made in consideration of the above circumstances, and an object thereof is to provide a dry etching method capable of selectively etching a silicon oxide film formed on a silicon nitride film. is there.

[0016]

In order to achieve the above object, the dry etching method of the present invention comprises the following steps.

That is, the dry etching method of the present invention (claim 1) comprises a step of forming an oxide film on the silicon nitride film, the dry etching of the oxide film, and the exposure of the silicon nitride film during the dry etching. And a step of forming a substance containing a Si—C bond on the surface of the film.

In another dry etching method of the present invention (claim 2), a step of forming an oxide film on a silicon nitride film, an etching gas containing fluorine and carbon is made into a plasma state, and the etching gas While etching the oxide film by plasma, replacing the nitrogen on the surface of the silicon nitride film exposed during the etching and the carbon adsorbed on the surface of the silicon nitride film, on the surface of the silicon nitride film. And a step of forming a substance containing a Si—C bond.

It is characterized in that

Further, in order to achieve the above object, the dry etching method of the present invention comprises steps having the following etching conditions.

That is, according to the dry etching method of the present invention (claim 3), a step of forming a silicon oxide film on a silicon nitride film, an etching gas containing fluorine and carbon is brought into a plasma state, and the plasma of the etching gas is used. When etching the silicon oxide film, the ratio of the number of fluorine to the number of carbon and fluorine adsorbed on the surface of the silicon nitride film exposed during the etching is less than 3/2, or Selectively the silicon oxide film with respect to the silicon nitride film under the condition that the number of carbons adsorbed on the surface of the silicon nitride film exposed during the etching is equal to or more than the number of nitrogens on the surface of the silicon nitride film. And a step of etching.

In another dry etching method of the present invention (claim 4), the step of forming a silicon oxide film on the silicon nitride film and the etching gas containing CHF ₃ gas and CO gas are brought into a plasma state. Along with the temperature of 90 ℃
Above, and pressure is 40mTorr to 100mTorr
r, and the ratio of the flow rate of the CO gas to the flow rate of the mixed gas of the CHF ₃ gas and the CO gas is 40% to 8
And a step of selectively etching the silicon oxide film by plasma of the mixed gas under the condition of 0%, preferably 50% to 80%.

The silicon nitride film is not only made of pure silicon and nitrogen, but is also a silicon nitride film as an insulating film in a broad sense made of silicon and nitrogen containing other substances such as oxygen. is there.

In the present invention, a mask pattern (including a carbon film) made of an organic substance or the like may be provided on the oxide film and the oxide film may be etched using this as a mask. Alternatively, the entire surface may be etched without the mask. (For example, the side wall left by anisotropic etching is also included).

[0025]

The dry etching method of the present invention (claim 1,
According to 2), during the dry etching of the oxide film, a substance containing Si—C bonds is formed on the exposed surface of the silicon nitride film. This substance functions as an etching protection film for the silicon nitride film, and when an etching gas containing fluorine and carbon is used, the substance contains Si of the above substance.
Since CF _x (0 ≦ x ≦ 3) is bonded to C of the —C bond to form a polymerized film of CF _x having a stronger etching protection film function, the oxide film may be removed from the silicon nitride film. It can be selectively dry-etched.

According to another dry etching method of the present invention (claim 3), carbon on the exposed surface of the silicon nitride film becomes excessive as compared with nitrogen, so C is removed by the reaction of C + N → CN. The remaining C on the surface of the silicon nitride film is combined with Si on the exposed surface of the silicon nitride film to form a substance containing Si—C bond on the exposed surface of the silicon nitride film. This substance and CF formed on this substance
_Since the polymerized film of _x (0 ≦ x ≦ 3) functions as an etching protection film for the silicon nitride film, the silicon oxide film can be selectively dry-etched.

According to the research conducted by the present inventors, the temperature in the magnetron dry etching is 90 ° C. or higher,
The pressure is set to 40 mTorr to 100 mTorr, and the ratio of the flow rate of the CO gas to the flow rate of the mixed gas of the CHF ₃ gas and the CO gas is set to 40% to 80%, more preferably 50% to 80%. It was found that when the silicon oxide film on the silicon nitride film was etched, the etching selection ratio of the silicon oxide film to the silicon nitride film was close to 20. Therefore, according to the dry etching method of the present invention employing the above etching conditions (claim 4), the silicon oxide film can be selectively dry etched.

[0028]

Embodiments will be described below with reference to the drawings.

1A to 1D are process sectional views showing a method of forming a contact hole in a gate electrode portion according to an embodiment of the present invention.

First, as shown in FIG. 1A, a thin SiO ₂ film 2 is formed on a Si substrate 1, and then this SiO ₂ film is formed.
A polysilicon film 3 and a Si ₃ N ₄ film 4 (silicon nitride film) are sequentially formed on the ₂ film 2. Next, this Si ₃ N ₄ film 4
After forming a resist pattern (not shown) on the polysilicon film, the polysilicon film 3, S is formed by using this resist pattern as a mask.
The i ₃ N ₄ film 4 is etched into a gate electrode shape.

Next, after depositing a thin Si ₃ N ₄ film 5 (silicon nitride film) on the entire surface, a BPSG film 6 (oxide film) is formed on the entire surface.
Is deposited to planarize the device surface. Then this BPSG
A photoresist pattern 7 for forming a contact hole is formed on the film 6.

Next, the Si substrate 1 is loaded into a dry etching apparatus as shown in FIG.

In the figure, reference numeral 20 denotes a conductive container forming the etching chamber 21, which is grounded to a reference potential and is also used as an anode. A cathode 26 is installed at the bottom of the etching chamber 21, and the cathode 26 has a frequency of 13.56 M via a matching circuit 27.
It is connected to a high frequency power supply 28 of Hz. In addition, the cathode 26
A cooling pipe 29 is provided in the cooling pipe 29, and the cooling medium is supplied to the cathode 26 through the cooling pipe 29 to cool the cathode 26. The cooling tube 29 also serves as a lead for applying high frequency power.

Further, a copper plate 31 held by a polyimide film 30 is attached on the cathode 26, and a voltage of about 2 kV to 4 kV is applied to the copper plate 31 by a power source 32, so that the substrate 36 to be processed (main In the case of the embodiment, the Si substrate 1) is electrostatically adsorbed on the cathode 26.

A gas inlet 22 for introducing a reactive gas is provided on the upper wall of the etching chamber 21, and the reactive gas and the like in the etching chamber 21 are exhausted through the gas exhaust port 2.
It is designed to be exhausted to the outside via 3. Also,
A magnetic field generator including a plurality of permanent magnets 24 and a driving mechanism 25 thereof is installed outside the upper part of the etching chamber 21, and a magnetic field is applied to a space facing the cathode 20 and the anode.

In the figure, 33 is a gas introduction tube for introducing gas into the back side of the substrate to be processed 36 to increase heat conduction, and 34 is an insulation for insulating the cathode 26 and the container 20. The member 35 is the lead of the copper plate 31 and the cathode 2.
The insulating member for insulating 6 and 6 is shown.

Next, in order to perform etching of the BPSG film 6 using the dry etching apparatus configured as described above, first, CHF _{3 with} a flow rate of 25 SCCM and CO with a flow rate of 75 SCCM are introduced into the etching chamber 21 from the gas inlet 22.
Is introduced, the temperature of the substrate to be processed (hereinafter, also simply referred to as temperature) is 100 ° C., and the pressure in the etching chamber 21 is 60.
Set to mTorr to generate plasma,
As shown in FIG. 5, the BPSG film 6 is etched using the photoresist pattern 6 as a mask to open a contact hole 8.

Under such etching conditions, BPS
Although G film 6 is completely etched, the etching of the Si ₃ N ₄ film is stopped in the middle of the thin the Si ₃ N ₄ film 5, is selectively BPSG film 6 is etched. Therefore, the opening width L ₁ of the contact hole 8 can be made smaller than the opening width L ₂ of the photoresist pattern 7.

In general, since the stepper used for forming the photoresist pattern is less accurate than the stepper used for forming the gate electrode, in the prior art, the opening width of the contact hole is larger than the width between the gate electrodes.
It was difficult to form a fine contact hole.

On the other hand, according to the dry etching method of this embodiment, as described above, the BPSG film 6 can be selectively etched, so that a contact hole having an opening width about the width between the gate electrodes can be formed. Further, the above effect could be similarly confirmed when the SiO ₂ film was used instead of the BPSG film.

Next, under the above-mentioned etching conditions, BPSG
The reason why the film and the SiO ₂ film can be selectively etched will be described.

FIG. 3 is a characteristic diagram showing the temperature dependence of the etching rate of the SiO ₂ film and the Si ₃ N ₄ film. The dry etching apparatus shown in FIG. 2 is used for this, the flow rate of CHF ₃ is 100 SCCM, the pressure is 40 mTorr, and the RF power is 8
It was obtained by setting it to 00W. The horizontal magnetic field strength on the substrate to be treated at this time was 100 Gauss.

From FIG. 3, the etching rate of the SiO ₂ film is
It can be seen that there is almost no change with temperature. On the other hand, Si
It can be seen that the etching rate of the ₃ N ₄ film significantly decreases with increasing temperature, and becomes lower than the etching rate of the SiO ₂ film at 90 ° C. or higher.

In order to clarify the cause of the drastic change in the etching rate of the Si ₃ N ₄ film with respect to the temperature change, the present inventors have set the temperature of the substrate to be treated at 70 ° C. (electrode temperature 20 ° C.),
When the temperature of the substrate to be treated was 150 ° C. (electrode temperature was 100 ° C.), the surface of the Si ₃ N ₄ film in the middle of etching was examined by using X-ray photoelectron spectroscopy (XPS).

FIG. 4 is an XPS spectrum of the surface of the Si ₃ N ₄ film showing the result. From this XPS spectrum, S at the temperature of 150 ° C. is higher than that at the temperature of 70 ° C.
It can be seen that the peak values of C and F on the surface of the i ₃ N ₄ film are high.

That is, when the temperature is 150 ° C., Si ₃ N
_The fluorocarbon polymerized film {(CF _x ) n (0
≦ x ≦ 3)} was formed. Moreover, if the temperature of the fluorocarbon polymer film is 90 ° C. or higher,
It was confirmed that it was formed on the surface of the Si ₃ N ₄ film.

From the above facts, it is considered that the etching rate of the Si ₃ N ₄ film changes drastically with respect to the temperature change depending on the presence or absence of the fluorocarbon polymer film on the film surface.

That is, when the temperature rises above 90 ° C., Si ₃
Fluorocarbon polymer film of sufficient thickness to function as an etching protective mask of N ₄ film is formed on the surface of the Si ₃ N ₄ film, is considered to SiO ₂ film is selectively etched.

The reason why the fluorocarbon polymer film is formed on the surface of the Si ₃ N ₄ film is considered as follows. Here, a case where CHF ₃ is used as an etching gas will be described as an example.

CHF ₃ is decomposed and dissociated by plasma discharge, and C radicals, CF radicals, CF ₂ radicals, CF
₃ Radicals are generated. Adhesion probability of these radicals to the surface of the substrate to be treated {P (CF _x ) | CF _x = C, CF, CF ₂ ,
The magnitude relation of CF ₃ } is P (C)> P (CF)> P (CF ₂ )> P (CF ₃ ).

The sticking probability depends on the temperature of the substrate to be treated, and generally becomes smaller as the temperature rises, and the amount of change becomes larger as the sticking probability becomes smaller. For this reason, when the temperature of the substrate to be processed reaches a certain high temperature, CF ₂ radicals, CF _2
3 The sticking probability of radicals becomes sufficiently small, and the radicals adsorbed on the surface of the substrate to be treated are essentially only C radicals and CF radicals. The C radical and the CF radical have four and three unpaired electrons, respectively, and are in a state of being easily bonded to other particles.

When the temperature of the substrate to be treated is high, Si ₃ N
_{4 Since a} large amount of C radicals and CF radicals are adsorbed on the surface of the film, Si and C are more likely to be bonded than Si and F.
The probability that and will bond (Si-C bond) is higher.
Therefore, N and C on the surface of the Si ₃ N ₄ film are combined to form C.
After N is formed, S on the surface of the Si ₃ N ₄ film from which N has been removed
Since i preferentially bonds with C, a substance containing Si—C bond is formed on the surface of the Si ₃ N ₄ film.

Further, F adsorbed on the surface of the Si ₃ N ₄ film,
Since C is released from the surface of the Si ₃ N ₄ film by the reaction of Si ₃ N ₄ + 6F + 4C → 3SiF ₂ + 4CN, when the ratio of C to F (C / F) is 2/3 or more, C is excessive. Is all of the C adsorbed on the Si ₃ N ₄ film is CN
It can not be detached from the surface of the Si ₃ N ₄ film in the form of, Si ₃
C remains on the surface of the N ₄ film, and the remaining C bonds with Si on the surface of the Si ₃ N ₄ film to form a Si—C bond.
A substance containing a Si—C bond is formed on the surface of the ₃ N ₄ film.

The layer containing the Si--C bond itself also functions as an etching protection film, but S is formed on the surface of the Si ₃ N ₄ film.
When a layer containing an i-C bond is formed, _CFx (0≤x≤
The polymerized film of 3) is formed, and the SiO ₂ film can be selectively etched with respect to the Si ₃ N ₄ film.

Next, referring to FIG. 5, a SiO ₂ film and a Si ₃ N film are formed.
The pressure dependence of the etching rate of the _four films will be described. This uses the dry etching device of FIG.
₃ gas flow rate is 25SCCM, CO gas flow rate is 75SCC
M, RF power was set to 800 W, and the temperature of the substrate to be treated was set to 70 ° C.

As shown in FIG. 5, the etching rate of the Si ₃ N ₄ film changes greatly with respect to the change of the pressure as compared with the SiO ₂ film. For example, when the pressure is 80 mTorr, the pressure is 20 mT.
It can be seen that the value is significantly lower than 1/10 of that of orr. It can also be seen that the etching rate of the Si ₃ N ₄ film is lower than the etching rate of the SiO ₂ film when the pressure is 40 mTorr or more.

In order to clarify the reason why the etching rate of the Si ₃ N ₄ film becomes lower than the etching rate of the SiO ₂ film when the pressure increases to some extent, the present inventors
When the pressure was 100 mTorr, the surface of the Si ₃ N ₄ film during etching was examined by X-ray photoelectron spectroscopy, and it was found that a fluorocarbon polymer film was formed on the surface of the Si ₃ N ₄ film. .

This is because when the pressure becomes high to some extent, Si ₃
Fluorocarbon polymer film of sufficient thickness to function as an etching protective mask of N ₄ film, which means that it is formed on the surface of the Si ₃ N ₄ film.

The reason why the fluorocarbon polymer film is formed on the surface of the Si ₃ N ₄ film is considered as follows.

As the pressure increases, the number of particles in plasma increases, and the number of CF _x radicals (0 ≦ x ≦ 3) adsorbed on the surface of the Si ₃ N ₄ film increases. Further, since the Si ₃ N ₄ film C and the Si ₃ N ₄ film CN high vapor pressure and N react on the surface of which is adsorbed on the surface of the is formed, adsorbed on the surface of the Si ₃ N ₄ film C Are removed.

However, a large amount of C is present on the surface of the Si ₃ N ₄ film.
Since the F _x radicals are adsorbed, C of all CF _x radicals cannot be removed as CN, and this C is N
Bonds to the Si bond that has been disconnected from. Furthermore, Si
CF _x radicals remain on the surface of the ₃ N ₄ film. Also, Si
₃ on the surface of the N ₄ film, the surface of the Si ₃ N ₄ film Si and Si
_The CF _x radicals F adsorbed on the surface of the ₃ N ₄ film react with each other to form SiF ₄ having a high vapor pressure, and Si on the surface of the Si ₃ N ₄ film is removed.

[0062] As a result, Si ₃ N ₄ film layer containing Si-C bonds which functions as an etching protective film is formed on the surface of the, and functions as an etching protective mask strength by the upper layer containing the Si-C bond CF _x (0 ≦ x ≦
The polymerized film of 3) is formed, and the SiO ₂ film can be selectively etched.

Next, referring to FIG. 6, a SiO ₂ film and a Si ₃ N film are formed.
_The dependence of the etching rate of the _four films on the CO / (CHF ₃ + CO) flow rate ratio will be described. This is performed by using the dry etching apparatus of FIG. 2 with a total gas flow rate of 100 SCCM and a pressure of 4
It was obtained by setting 0 mTorr, RF power at 800 W, and the temperature of the substrate to be treated at 70 ° C.

From FIG. 6, the etching rate of the Si ₃ N ₄ film is higher than that of the SiO ₂ film by CO / (CH
F ₃ + CO) flow rate ratio largely changes, and for example, when the CO / (CHF ₃ + CO) flow rate ratio is 75%, the etching rate of the Si ₃ N ₄ film is CO / (CHF ₃ +
It can be seen that the CO) flow rate ratio is greatly reduced to 1/3 or less of that when it is 0%. Further, the etching rate of the Si ₃ N ₄ film is 40 / COF (CHF ₃ + CO) flow rate ratio.
It can also be seen that when the content is more than 100%, it becomes lower than the etching rate of the SiO ₂ film.

CO / (CHF ₃ + CO) flow rate ratio is 75%
For the case of, when the surface of the etching halfway the Si ₃ N ₄ film was examined by X-ray photoelectron spectroscopy, Si ₃
It was confirmed that a fluorocarbon polymer film was formed on the surface of the N ₄ film.

[0066] That is, CO / if (CHF ₃ + CO) flow rate ratio increases to some extent, Si ₃ N ₄ film sufficient thickness of the fluorocarbon polymer film to function as an etching protective mask is, Si ₃ N ₄ film surface Was found to be formed.

Next, the effect of the photoresist pattern on the etching of the Si ₃ N ₄ film will be described with reference to FIG.

FIG. 7 is a characteristic diagram showing the relationship between the etching time and the etching depth with and without the photoresist pattern on the Si ₃ N ₄ film. This was obtained by using the dry etching apparatus of FIG. 2 and setting the flow rate of CHF ₃ to 25 SCCM, the flow rate of CO to 70 SCCM, the pressure to 40 mTorr, the RF power to 800 W, and the temperature of the substrate to be processed to 70 ° C. .

It can be seen from FIG. 7 that the etching depth of the Si ₃ N ₄ film changes linearly with the etching time when there is no photoresist pattern.

On the other hand, when there is a photoresist pattern, the etching rate immediately after the start of etching (about 10 seconds) is the same as when there is no photoresist pattern, but after that, the etching rate drops sharply.
Then, it becomes constant at the low etching rate.

The reason why the etching rate decreases when there is a photoresist pattern is considered as follows.

[0072] In the etching of the SiO ₂ film photoresist pattern on the SiO ₂ film is formed, since the surface in fluorocarbon polymerization film of a photoresist pattern is formed by ion bombardment during the etching of the surface of the photoresist pattern fluorocarbon The polymer film is sputtered. Therefore, the polymerized film of C is released into the plasma, and the released polymerized film of C is also adsorbed on the Si ₃ N ₄ film in the same manner as that formed in the plasma, and CF _x (0 ≦ x ≦
Since it contributes to the formation of the polymerized film of 3), S having a higher selection ratio
This allows selective etching of the iO ₂ film.

Since it takes some time for the fluorocarbon polymer film formed on the surface of the photoresist pattern to be sputtered by ion bombardment, the etching rate of the Si ₃ N ₄ film immediately after the start of etching is Si.
This is the same as when the photoresist pattern is not formed on the O ₂ film.

FIG. 8 is a diagram showing the temperature and pressure dependence of the etching depth of the Si ₃ N ₄ film when a resist pattern is provided. This is performed by using the dry etching apparatus of FIG. 2 with a flow rate of CHF ₃ of 25 CCM and a flow rate of CO of 75.
It was obtained by setting SCCM and RF power to 800W.

From this figure, regardless of the temperature, the higher the pressure, the smaller the etching depth, and the higher the temperature, the greater the etching depth decreased with respect to the change in pressure. It can be seen that the higher the temperature, the smaller the etching depth.

When the temperature is 20 ° C., the pressure is 100
When the etching is performed at 80 nm with mTorr and the temperature is 90 ° C. or higher and the pressure is 60 mTorr or higher, the etching depth is less than 20 nm, and in this case, the etching selection ratio of the Si ₃ N ₄ film to the SiO ₂ film is 10 or more. .

As described above, the temperature of the substrate to be treated,
If the pressure and the etching gas flow rate ratio are set to appropriate values, a fluorocarbon polymer film is formed on the surface of the Si ₃ N ₄ film, and RIE using carbon fluoride such as CHF ₃ which has been considered impossible in the past has been performed. This enables selective etching of the SiO ₂ film.

In this example, the temperature was 100 ° C., the pressure was 60 mTorr, and the CO / (CHF ₃ + CO) flow rate ratio was 75.
%, The BPSG film 6 was etched under the conditions of a temperature of 90 ° C. or higher and a pressure of 40 mTorr.
r to 100 mTorr, and CO / (CHF ₃ + C
It has been found that an etching selection ratio close to 20 can be obtained under the etching conditions of O) flow rate ratio of 40 mTorr to 80%, more preferably 50% to 80%.

FIG. 9 shows SiO according to another embodiment of the present invention.
FIG. 4 is a process cross-sectional view showing a selective etching method for _two films.

First, as shown in FIG. 9A, the Si ₃ N ₄ film 12 is deposited on the Si substrate 11 by the CVD method. Then, as shown in FIG. 9B, Si ₃ N ₄ is deposited. C13 is ion-implanted into the surface of the film 12.

Next, as shown in FIG. 9C, Si ₃ N _{4 is used.}
A BPSG film 14 (oxide film) is deposited on the film 12 using the CVD method.

Next, as shown in FIG. 9D, a resist pattern 15 is formed on the BPSG film 14 by using a light exposure method.

Finally, as shown in FIG. 9E, the BPSG film 14 is etched using the resist pattern 15 as a mask. This etching is performed using the dry etching apparatus of FIG. 2 with the flow rate of CHF _{3 set} to 100 SCCM, the pressure set to 40 mTorr, the temperature set to 70 ° C., and the RF power set to 800 W.

Under the above etching conditions, the etching selectivity of the Si ₃ N ₄ film 12 to the BPSG film 14 should be as small as 2 from the above-mentioned results, but the actual etching selectivity is as large as 15. It was

Since C is ion-implanted into the surface of the Si ₃ N ₄ film 12, this is effectively the same as the state in which a large amount of C is adsorbed on the surface of the Si ₃ N ₄ film. As a result, Si-
A fluorocarbon polymer film 12 having a C bond and having a sufficient thickness as an etching protection film on the surface of the Si ₃ N ₄ film 12.
Is formed.

Such an effect is obtained by using the BPSG film instead of
It was confirmed that the same effect was obtained when the SiO ₂ film was used.

The present invention is not limited to the above embodiment. For example, in the above embodiment, the case where the Si ₃ N ₄ film is used as the silicon nitride film has been described, but the present invention can be applied to the silicon nitride film having another composition.
Further, it can be applied to a silicon nitride film containing other element such as oxygen. Although the case where the SiO ₂ film or the BPSG film is used as the oxide film has been described, the present invention is also effective for other oxide films such as tantalum and aluminum oxide films. Further, a device other than the magnetron type dry etching device described above may be used.

Further, even if the entire surface is etched without providing a mask, the silicon nitride film of the oxide film can be selectively etched. For example, it is possible to provide a wiring of aluminum or the like on the underlying silicon nitride film, form a silicon oxide film on the wiring, and then anisotropically etch the entire surface to leave the silicon oxide film on the sidewall of the wiring.

In addition, various modifications can be made without departing from the scope of the present invention.

[0090]

As described above in detail, according to the present invention, the etching protection film can be formed on the silicon nitride film, and thus the silicon oxide film can be selectively etched.

[Brief description of drawings]

FIG. 1 is a process sectional view showing a method of forming a contact hole in a gate electrode portion according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a schematic configuration of a dry etching apparatus according to an embodiment of the present invention.

FIG. 3 is a characteristic diagram showing temperature dependence of etching rates of a SiO ₂ film and a Si ₃ N ₄ film.

FIG. 4 is a diagram showing an XPS spectrum of a surface of a Si ₃ N ₄ film.

FIG. 5 is a characteristic diagram showing pressure dependency of etching rates of SiO ₂ film and Si ₃ N ₄ film.

FIG. 6 is a characteristic diagram showing the CO / (CHF ₃ + CO) flow ratio dependency of the etching rate of the SiO ₂ film and the Si ₃ N ₄ film.

FIG. 7 shows S depending on the presence or absence of a photoresist pattern.
i ₃ N ₄ film shows a difference in etching characteristics of.

FIG. 8 is a diagram showing the relationship between etching depth, temperature, and pressure.

FIG. 9 is a process sectional view showing a dry etching method according to another embodiment of the present invention.

[Explanation of symbols]

1 ... Si substrate 2 ... SiO ₂ film 3 ... polysilicon film 4,5 ... Si ₃ N ₄ film (silicon nitride film) 6 ... BPSG film (oxide film) 7 ... photoresist pattern 8 ... contact hole 11 ... Si substrate 12 ... Si ₃ N ₄ film (silicon nitride film) 13 ... C ions 14 ... BPSG film (oxide film) 15 ... photoresist pattern

Claims (4)

[Claims] 1. A step of forming an oxide film on a silicon nitride film, dry etching the oxide film, and applying S to the surface of the silicon nitride film exposed during the dry etching.
and a step of forming a substance containing an i-C bond. 2. A step of forming an oxide film on a silicon nitride film, an etching gas containing fluorine and carbon is brought into a plasma state, and the oxide film is etched by the plasma of the etching gas, and during the etching. Replacing the nitrogen on the surface of the silicon nitride film exposed to the surface with the carbon adsorbed on the surface of the silicon nitride film to form a substance containing Si—C bonds on the surface of the silicon nitride film. And a dry etching method. 3. A step of forming a silicon oxide film on a silicon nitride film, and an etching gas containing fluorine and carbon is brought into a plasma state, and when the silicon oxide film is etched by the plasma of the etching gas, this etching is performed. The ratio of the number of fluorine to the number of carbon is less than 3/2 with respect to carbon and fluorine adsorbed on the surface of the silicon nitride film exposed inside, or on the surface of the silicon nitride film exposed during the etching. Dry etching characterized by including the step of selectively etching the silicon oxide film with respect to the silicon nitride film under the condition that the number of adsorbed carbons is equal to or more than the number of nitrogen atoms on the surface of the silicon nitride film. Method. 4. A step of forming a silicon oxide film on a silicon nitride film, an etching gas containing CHF ₃ gas and CO gas in a plasma state, a temperature of 90 ° C. or higher, and a pressure of 40 mTorr to 100 mTorr, And the CHF
_Under the condition that the ratio of the flow rate of the CO gas to the flow rate of the mixed gas of the ₃ gas and the CO gas is 40% to 80%, the silicon oxide film is selectively selected by the plasma of the mixed gas with respect to the silicon nitride film. A dry etching method, which comprises: