JP2000349071A - Chemical dry etching - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a dry etching method which can reduce the amount of PFC discharged in the etching and to have less effects on global warming phenomenon, by using an etching gas having a short atmosphere life and GWP. SOLUTION: A mixture gas containing oxygen, octafluorocyclopentane (C5F8) and nitrogen as necessary is activated, and then a semiconductor substrate 9 and a film formed on the substrate are subjected to a dry etching process within an etching chamber 5 with use of the activated gas. A gas of C5F8 is used as an etching gas having short atmospherie life-time and GWP. Thereby the amount of PFC emitted during the etching operation can be reduced to have less effects on global warming phenomenon. The gas of C5F8 having short atmosphere life and GWP used as an alternate gas is expected as gas material for the purpose of reducing the amount of PFC gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chemical dry etching method for a semiconductor device, and more particularly, to a method for etching a semiconductor device.
The present invention relates to an etching method in which the amount of FC (Per Fluoro Carbon) is suppressed.

[0002]

2. Description of the Related Art Conventionally, in the manufacture of a semiconductor device, a semiconductor substrate, a semiconductor film formed on the semiconductor substrate, an insulating film,
It is known to use a chemical dry etching (CDE) method for etching a conductive film or the like. For example, when a connection metal film is buried in a connection hole of an interlayer insulating film reaching a conductive layer such as a diffusion region or a lower wiring layer of a semiconductor substrate, the connection metal film is formed by the following steps. First, an interlayer insulating film is formed over a semiconductor substrate including a conductive layer, and then the interlayer insulating film is etched by a dry etching method or the like using a mask such as a photoresist having a predetermined pattern to reach the conductive layer. Form a connection hole. After that, a composite film of a titanium film and a titanium compound film, called a barrier metal, or a titanium compound film is formed in the connection holes and on the interlayer insulating film by a method such as sputtering. In addition, tungsten film is CV
A film is formed on the interlayer insulating film so as to fill the connection hole by a D (Chemical Vapor Deposition) method or the like. Then, the metal film including the barrier metal layer and the tungsten layer can be embedded in the connection hole by removing the tungsten film and the barrier metal film other than in the connection hole. In this case, the tungsten film other than the inside of the connection hole is removed by a chemical dry etching method (hereinafter, referred to as a CDE method), and then a CMP (Chemical Mechanical Polishing) is performed.
The barrier metal layer on the interlayer insulating film is removed by polishing by the method.

In the CDE method, charged particles are hardly incident because the discharge portion is far away, and damage to the base is small. Further, since etching is performed isotropically, there is no generation of etching residue on the side wall. Etching back of tungsten to form a buried tungsten wiring is performed using this method. When etching a semiconductor such as polysilicon, a silicon compound such as silicon oxide or silicon nitride, a conductor such as tungsten, or an insulator such as a photoresist by the CDE method,
PFC such as CF ₄ is mainly used as an etching gas. However, currently used PFCs have a long atmospheric life and a long GWP (Global Warming Potential) and are highly effective in global warming. Therefore, at present, it is strongly desired to reduce emissions. Table 1 shows a typical PFC used in this chemical dry etching method, the GWP of C ₅ F ₈ used in the present invention, and the atmospheric lifetime (unit: years).

[0004]

[Table 1] Main PFC GWP and atmospheric life (unit: years) At present, when performing chemical dry etching on semiconductor substrates, optimization of process conditions, recovery of PFC, recycling and study of alternative gases, etc. are being implemented as a method of reducing PFC emissions. is there.

[0005]

As described above, when etching semiconductors, silicon compounds, tungsten, photoresists, and the like by the chemical dry etching method, the etching gas mainly has a long atmospheric life and a long GWP, and a global warming. Although PFC with high effect is used,
At present, it is strongly desired to reduce these emissions from the viewpoint of global warming. The present invention has been made in view of such circumstances, and by using an etching gas having a short atmospheric life and GWP, the amount of PFC discharged during etching is reduced, thereby reducing the effect on global warming. An etching method is provided.

[0006]

The present invention relates to oxygen (O ₂ ), octafluorocyclopentene (C ₅ F ₈ )
And, if necessary, a gas containing nitrogen (N ₂ ) is mixed, and the mixed gas is activated. Then, a chemical dry etching method for a semiconductor substrate or a film formed on the semiconductor substrate is performed by the activated gas. It is characterized by performing. C as an etching gas with a short atmospheric life and GWP
By using a ₅ F _8, discharge PF during etching
The amount of carbon can be reduced, and the effect on global warming can be reduced. C ₅ F _{8 having} a short atmospheric life and GWP used as a substitute gas in the present invention is expected as a gas material for the purpose of reducing PFC gas. The physical properties of the C ₅ F ₈ gas are as shown in Table 2 below.

[0007]

[0008] In the chemical dry etching method of the present invention, the C ₅ F ₈ concentration is set to 20 vol% or less. In the present invention, when etching a film such as a semiconductor substrate or a photoresist film, a polysilicon film, or a silicon nitride film formed on the semiconductor substrate, the etching is performed even if the concentration of the C ₅ F ₈ gas is more than 20 vol%. Is possible (the etching rate is sufficiently high), but the deposits may accumulate inside the discharge tube of the etching apparatus and become unusable. Therefore, the concentration of C ₅ F ₈ must be limited to 20 vol% or less. Must. As shown in FIG. 3, when the etching according to the present invention is performed on the film, the selectivity to silicon oxide is sufficiently recognized. In addition, uniformity of etching is sufficiently recognized. FIG. 3 shows the etching rate (◆-◆), surface uniformity (■-■) and selectivity to silicon oxide (△-△) in the etching gas when etching a polysilicon film by the method of the present invention. FIG. 4 is a characteristic diagram showing C ₅ F ₈ concentration dependency.

In FIG. 3, the left side of the vertical axis represents the polysilicon etching rate (nm / min), and the right side represents the uniformity (± (%)) of the polysilicon film surface and the selectivity of the polysilicon film to silicon oxide (%). 1 / SiO ₂ ). In FIG. 3, a high etching rate is maintained even when the C ₅ F ₈ concentration exceeds 20 vol%, but a higher concentration is not possible because deposits are deposited as described above. The uniformity is highest when the concentration is 20 vol%, and high uniformity is obtained before and after the concentration. The curve of selectivity to silicon oxide (△-△) shows that this concentration is 2%.
It can be seen that there is a peak at 0 vol%, and that a high selectivity is obtained even at 20 vol% or more.

FIG. 4 shows an etching rate (◆) when a silicon nitride film is etched by the method of the present invention.
FIG. 4 is a characteristic diagram showing the dependence of surface uniformity (■-■) and selectivity to silicon oxide (△-△) on the concentration of C ₅ F ₈ in the etching gas. In FIG. 4, the left side of the vertical axis represents the silicon nitride film etching rate (nm / min), and the right side represents the uniformity (± (%)) of the surface of the silicon nitride film and the selectivity (1) of the silicon nitride film to silicon oxide. / SiO ₂ )
Is represented. In this figure, the C ₅ F ₈ concentration is 20
vol% or less (the range shown is about 8 vol% to 12 vol%)
vol%), a high etching rate is maintained. The uniformity is given a high value (4% or less) when the concentration is 20 vol% or less (the range shown is about 8 vol% to 12 vol%). The curve of the selectivity to silicon oxide (△-△) shows that this concentration is 20 v
ol% or less (the range shown is about 9.4 vol% to 19 vol)
1%), a substantially uniform high value is obtained.

FIG. 5 shows a photoresist according to the method of the present invention.
Rate when ashing a film
Ashing gas for (及 び-◆) and surface uniformity (■-■)
C inside _FiveF₈FIG. 4 is a characteristic diagram showing concentration dependency. FIG.
The left side of the vertical axis shows the photoresist film ashing rate (nm /
min), and the right side shows the uniformity of the photoresist film surface
(± (%)). In this figure, C_Five
F₈High ashing in the concentration range of 20 vol%
Maintaining the rate. Especially about 3vol% -3.6v
high ashing rate in the low concentration range of ol%
ing. In addition, the uniformity is such that the concentration is 20 vol%.
High values are given in the following ranges. Especially about
10% or less in the range of 3 vol% to 4 vol%
You. FIG. 6 shows a silicon nitride film etched by the method of the present invention.
Etching rate (◆-◆) and
In the etching gas for surface and surface uniformity (■-■)_Twoconcentration
FIG. 4 is a characteristic diagram showing dependency. In Fig. 6, the left side of the vertical axis is silicon
Represents the etching rate (nm / min) of the nitride film.
The right side shows the uniformity (± (%)) of the silicon nitride film surface.
are doing. In this figure, N_TwoThe concentration is 20vol%
Even if it exceeds, the high etching rate is maintained. Also,
The uniformity and etching rate are about 10 vol%
High uniformity and etching rate in the range of 20 vol%
Has been obtained.

That is, the chemical dry etching method of the present invention comprises a step of activating a mixed gas containing oxygen and octafluorocyclopentene; and a step of introducing the activated gas to form a semiconductor substrate or a semiconductor substrate formed on the semiconductor substrate. And etching the coated film. The mixed gas may further include nitrogen. The film may be any one of a photoresist film, a polysilicon film, and a silicon nitride film. The mixed and activated gas containing nitrogen may etch a silicon nitride film. The nitrogen concentration in the mixed gas is 20 vol.
%. The octafluorocyclopentene concentration in the mixed gas is 20 vol.
%.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic sectional view of a downflow type discharge separation type chemical dry etching apparatus (hereinafter, referred to as a CDE apparatus) used for carrying out the present invention. CDE equipment is a reaction vessel (etching room)
And a substrate 9 to be processed such as a silicon wafer.
Is mounted on a sample table 6 housed in a reaction vessel 5. The temperature of the sample stage 6 can be controlled, and the substrate 9 to be processed can be adjusted to a predetermined temperature. A mixed gas containing oxygen gas, C ₅ F ₈ gas, and nitrogen gas contained as needed is introduced from a gas inlet 1 upstream of the discharge tube. The microwave waveguide 2 is provided at the center of the discharge tube 3. The mixed gas introduced from the gas inlet 1 is excited by the microwave (2.45 GHz) irradiated by the microwave waveguide 2. The excited gas passes through the gas transport pipe 4 and is introduced into the reaction vessel 5 from the excited gas supply port 7 downstream of the gas transport pipe 4. The excited mixed gas becomes radical and neutral gas and is introduced into the reaction vessel 5. Further, the microwave power and the pressure in the reaction vessel 5 are automatically controlled to predetermined set values.

After the substrate 9 to be processed is dry-etched by the excited mixed gas, the mixed gas is exhausted from the exhaust pipe 8 to the outside as exhaust gas. Exhaust gas discharged from the exhaust pipe 8 is sent to the exhaust gas abatement apparatus 11 by the pump 10 and discharged to the outside from the exhaust gas discharge port 13. The analysis of PFC in the exhaust gas is performed by using the pump 10 and the exhaust gas
The measurement is performed by a gas chromatograph measuring device 12 provided between the two. Next, the CD constructed as described above
A chemical dry etching method for a polysilicon film performed using the E apparatus will be described. The temperature of the sample stage placed in the reaction vessel is set at 25 ° C., and the temperature of the polysilicon film formed on the silicon wafer placed on the sample stage is adjusted. The pressure in the reaction vessel is kept constant at 40 Pa,
The flow rates of C ₅ F ₈ and O ₂ are 100 sccm and 40, respectively.
0 sccm of the mixed gas was flowed from the upstream of the discharge tube,
The mixed gas is excited by irradiating the discharge tube with a microwave of 0 W from the waveguide, and the mixed gas radical is introduced into the reaction vessel from the transport tube.

Under such conditions, the polysilicon film is etched.
The etching rate was 307 nm / mi
n, uniformity of the surface to be treated ± 2.6%, oxidation to silicon
The selectivity of the product becomes 39, and the CF_Fourgas
Process (700W, 40Pa constant, O_Two/ CF_Four= 6
At 0/150 seem, the etch rate is 356
nm / min, uniformity of the surface to be treated is ± 2.2%,
Etching characteristics similar to that of 37)
I was able to get the sex. Table 3 shows C_FiveF₈Process and CF
_FourSummarizes the etching characteristics of the polysilicon film of the process
You. Also, C_FiveF ₈The flow rate is 20 vol of the total gas flow rate.
% To the discharge tube and the transport tube._FiveF₈
The generation of intermediate products between oxygen and oxygen could be suppressed. Moth
C by chromatograph_FiveF₈Process and CF_FourProfessional
Table 4 shows the measurement results of greenhouse gas emissions in exhaust gas during
Summarized in C_FiveF₈During the process, C_TwoF₆And C_Three
F₈CF such as_FourOf other greenhouse gases
Was. C_FiveF₈By using gas, CF_FourGasp
Measurement of warming effect per wafer compared to process
Fixed results (PFC emissions x GWP = global warming effect value)
Was reduced by 93% or more.

[0016]

[Table 3]

Similarly, the effect of the C ₅ F ₈ gas when the silicon nitride film and the photoresist film are chemically dry-etched using the CDE apparatus will be described. First,
The temperature of the sample stage set in the reaction vessel is set at 25 ° C., and the temperature of the silicon nitride film formed on the silicon wafer is adjusted. The pressure in the reaction vessel was kept constant at 90 Pa, and C ₅
The flow rates of F ₈ , O ₂ and N ₂ are 130 sccm and 9 respectively.
A mixed gas of 45 sccm and 145 sccm is passed through the discharge tube, and a microwave of 700 W is irradiated from the waveguide to the discharge tube to excite the mixed gas. Then, radicals of the excited mixed gas are introduced into the reaction vessel.

[0018]

[Table 4]

Similarly, the effect of the C ₅ F ₈ gas when the silicon nitride film and the photoresist film are chemically dry-etched using the CDE apparatus will be described. First,
The temperature of the sample stage set in the reaction vessel is set at 25 ° C., and the temperature of the silicon nitride film formed on the silicon wafer is adjusted. The pressure in the reaction vessel was kept constant at 90 Pa, and C ₅
The flow rates of F ₈ , O ₂ and N ₂ are 130 sccm and 9 respectively.
A mixed gas of 45 sccm and 145 sccm is passed through the discharge tube, and a microwave of 700 W is irradiated from the waveguide to the discharge tube to excite the mixed gas. Then, radicals of the excited mixed gas are introduced into the reaction vessel. When the silicon nitride film is subjected to chemical dry etching under these conditions, the etching rate is 135 nm / min, the uniformity of the surface of the film to be processed is ± 1.5%, and the selectivity of silicon oxide to 11 is 11. CF ₄ process (700 W, 90 Pa, O ₂ / CF ₄ / N ₂ = 320)
At / 400/80 sccm, the etching rate is 9
6 nm / min, uniformity of the surface of the film to be processed is ± 2.9%,
Etching characteristics similar to those of the selection ratio of silicon oxide to 10) were obtained. Table 5 shows the etching characteristics of the C ₅ F ₈ process and the CF ₄ process. Table 6 shows the measurement results of the amount of greenhouse gas generated in the exhaust gas during the C ₅ F ₈ process and the CF ₄ process by the gas chromatograph. During C ₅ F ₈ process, the generation of CF ₄ other greenhouse gases, such as C ₃ F ₆ and C ₃ F ₈ was observed.
Then, the C ₅ F ₈ gas flow rate is reduced to about 11 v of the total gas flow rate.
ol%, the warming effect per wafer (PFC emission x GW) compared to the CF ₄ gas process
P = global warming effect value) was able to be reduced by 97.9% or more.

[0020]

[Table 5]

[0021]

[Table 6]

Next, the temperature of the sample stage set in the reaction vessel
The temperature is set to 70 ° C, and the
The temperature of the photoresist film is adjusted. The pressure inside the reaction vessel is 50
Pa constant, C_FiveF₈And O_TwoFlow rate of each 20s
A mixed gas of ccm and 530 sccm flows into the discharge tube.
Further, a microwave of 700 W is supplied from the waveguide to the discharge tube.
To excite the mixed gas. And the excited mixture
The radical of the combined gas is introduced into the reaction vessel. like this
Chemical dry etching of the photoresist film under the conditions
As a result, the etching rate was 2129 nm / min,
The uniformity of the treated film surface becomes ± 2.9%.
CF_FourGas process (700W, 30Pa, O_Two/
CF _Four= 300/50 sccm, etching rate
Degree is 1700 nm / min, and the uniformity of the film surface to be treated is ±
(1.8%). Table 7
To C_FiveF₈Process and CF_FourProcess photoresist
Describe the etching characteristics of the film. And gas chromatography
C by measuring instrument_FiveF₈Gas process and CF_FourGas process
Table 8 shows the measurement results of greenhouse gas emissions in exhaust gas during
Describe. C_FiveF₈During the gas process, C_TwoF₆And C
_ThreeF₈CF such as_FourNo generation of greenhouse gases other than
won. C_FiveF₈The gas flow rate is about 4 vo of the total gas flow rate.
1%_FourC compared to gas processes
Warming effect per wafer (PFC emissions x GWP =
Global warming effect value) can be reduced by 98.1% or more.
it can.

[0023]

[Table 7]

[0024]

[Table 8]

Next, a method of chemically dry-etching a metal film such as a tungsten film formed on a semiconductor substrate will be described. FIG. 2 is a cross-sectional view showing a configuration of a metal film formed on a semiconductor substrate to be etched by the method of the present invention and formed on the semiconductor substrate. A silicon oxide film (Si) as an interlayer insulating film is formed on the silicon semiconductor substrate 100 on which the lower wiring 101 is formed via the insulating film 102.
O ₂ ) 20 are formed. The silicon oxide film 20 is covered with a photoresist (not shown), and is patterned, and the silicon oxide film 20 is dry-etched using the patterned photoresist as a mask to form a connection hole 24 in contact with the lower wiring 101. I do. The lower wiring 101 is exposed inside the connection hole 24. Next, a titanium (Ti) film 2 is formed on the silicon oxide film 20 and in the connection hole 24 thereof.
1 and a titanium nitride (TiN) film 22 are sequentially formed by a sputtering method or a CVD method. After that, a tungsten (W) film 23 is formed using a CVD method so as to fill the connection holes 24. At this time, the tungsten film 23 is also formed on the barrier metal films 21 and 22 other than the connection holes 24.

Next, using the CDE apparatus shown in FIG.
Of a metal film formed on the body substrate 100
Film 23 and barrier between titanium film 21 and titanium nitride film 21
Chemical dry etching of the metal film. And the side
Connected inside connection hole 24 with barrier metal film formed on wall
A tungsten film 23 serving as a wiring is buried, and a connection hole 2 is formed.
The tungsten film other than 4 is removed by etching. Use
C as reactive gas used_FiveF₈Gas, O_TwoGas, C1
_TwoUsing gas, C _FiveF₈Gas and O_TwoThe total amount of gas
210 sccm, C1_TwoWhen the gas flow rate is 40 sccm,
Conditions where the microwave power was 700 W and the pressure was 30 Pa
Perform etching. Connection wiring with a flat surface
can get. As described above, in the method of the present invention,
C for the purpose of reducing the emission PFC in the etching method
_FiveF₈Before chemical dry etching using gas
It is not limited to the substrate to be processed and the etching gas.
Replacement material for etching using PFC
be able to.

[0027]

According to the present invention, PFC emissions together by mixing oxygen and C ₅ F ₈ to a gas used in the chemical dry etching, the same degree of etching characteristics and when using CF ₄ gas to obtain The amount can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a CDE apparatus for performing chemical dry etching of the present invention.

FIG. 2 is a cross-sectional view of a semiconductor substrate illustrating chemical dry etching of the present invention.

FIG. 3 shows C ₅ F ₈ in an etching gas for etching rate, surface uniformity and selectivity to silicon oxide when a polysilicon film is etched by the method of the present invention.
FIG. 4 is a characteristic diagram showing concentration dependency.

FIG. 4 shows C ₅ F ₈ in an etching gas having an etching rate, a surface uniformity, and a selectivity ratio to silicon oxide when a silicon nitride film is etched by the method of the present invention.
FIG. 4 is a characteristic diagram showing concentration dependency.

FIG. 5 is a characteristic diagram illustrating the dependence of the ashing rate and the surface uniformity on the C ₅ F ₈ concentration in the ashing gas when ashing a photoresist film according to the method of the present invention.

FIG. 6 is a characteristic diagram illustrating the dependence of the etching rate and the surface uniformity on the C ₅ F ₈ concentration in the etching gas when a silicon nitride film is etched by the method of the present invention.

[Explanation of symbols]

1 ... gas inlet, 2 ... microwave waveguide,
3 ... discharge tube, 4 ... gas transport tube, 5 ...
Reaction vessel (etching chamber), 6 ... Sample table, 7.
..Excited gas supply port, 8 ... exhaust pipe, 9 ... substrate to be processed (wafer), 10 ... pump, 11 ...
・ Exhaust gas abatement system, 12 ・ ・ ・ Gas chromatograph, 13 ・ ・ ・ Exhaust gas outlet, 20 ・ ・ ・ Silicon oxide film, 21 ・ ・ ・ Titanium film (barrier metal film), 22
... titanium nitride film (barrier metal film), 23 ... tungsten film, 24 ... connection hole, 100 ... semiconductor substrate, 101 ... lower wiring, 102 ... insulating film.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Sadayuki Jimbo 8-8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture Inside the Toshiba Yokohama Office (72) Inventor Yukimasa Yoshida 8-8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa (72) Inventor Makoto Muto 1000-1, Kasamacho, Sakae-ku, Yokohama-shi, Kanagawa Prefecture Shibaura Mechatronics Co., Ltd. (72) Inventor Yasushi Tazawa 1000-1, Kasama-cho, Sakae-ku, Yokohama, Kanagawa Shibaura Mechatronics 5F004 AA01 AA16 BA03 BB14 CA04 DA00 DA04 DA25 DA26 DB02 DB07 DB08 DB10 DB26 EB01 EB03 5F033 JJ18 JJ19 JJ33 PP06 PP15 QQ08 QQ09 QQ11 QQ15 QQ37 RR04 WW04 XX00

Claims (6)

[Claims] 1. A method comprising: activating a mixed gas containing oxygen and octafluorocyclopentene; and introducing the activated gas to etch a semiconductor substrate or a film formed on the semiconductor substrate. A chemical dry etching method, characterized in that: 2. The chemical dry etching method according to claim 1, wherein the mixed gas further contains nitrogen. 3. The chemical dry etching method according to claim 1, wherein the film is one of a photoresist film, a polysilicon film, and a silicon nitride film. 4. The chemical dry etching method according to claim 2, wherein the activated mixed gas containing nitrogen etches a silicon nitride film. 5. The nitrogen concentration in the mixed gas is 20 vol.
5 or less than 1%.
3. The chemical dry etching method according to item 1. 6. The chemical dry etching method according to claim 1, wherein an octafluorocyclopentene concentration in the mixed gas is 20 vol% or less.