# Patent

## Title
Plasma cleaning gas and plasma cleaning method

## Abstract

A plasma cleaning gas for CVD chamber is a gas for cleaning silicon-containing deposits on the surface of a CVD chamber inner wall and the surfaces of members placed inside the CVD chamber after film forming treatment on a substrate by a plasma CVD apparatus. The cleaning gas includes 100% by volume of fluorine gas which gas can generate plasma by electric discharge. When 100% by volume of fluorine gas is plasma-generated by electric discharge and then used as a cleaning gas, an extremely excellent etching rate can be attained and further plasma can be stably generated even in the total gas flow rate of 1000 sccm and at a chamber pressure of 400 Pa. Further, the uniformity of cleaning can be also ensured in the above conditions. Additionally the fluorine gas concentration is 100% so that the apparatus is not complicated and thereby the cleaning gas has excellent practicability.

## Background
FIELD OF THE INVENTION
The present invention relates to plasma cleaning gases for CVD chambers, which gases are used in order to remove deposits on the inner wall surface or other surfaces of CVD chambers during film forming treatment in plasma CVD (Chemical Vapor Deposition) apparatus in which the film forming treatment with silicon oxide, silicon nitride etc. is conducted on the substrate surfaces for semiconductors etc., and further relates to processes for plasma cleaning of the CVD chambers.
More particularly, it relates to plasma cleaning gases for CVD chambers which gases have high uniformity of cleaning deposits on the inner wall, etc. and an excellent etching rate, and relates to processes for plasma cleaning of the CVD chambers. The term “uniformity of cleaning” used herein is an indication of stability of generated plasma and is evaluated in the following manner, as also described in the examples. A wafer previously deposited with SiO2 film by CVD is used as a sample and is placed on the lower electrode, and then the etching rate is measured. The evaluation of the uniformity of the etching rate on the inside of the wafer surface is taken as a typical evaluation of uniformity of cleaning. This property is evaluated likewise hereinafter.
The term “etching rate” used herein is an indication of evaluating the rate of cleaning and is evaluated by measuring the rate of etching a SiO2 thin film on a wafer as described in the examples. The etching rate is taken as a typical evaluation of cleaning. The property is evaluated likewise hereinafter.
BACKGROUND OF THE INVENTION
Conventionally, in plasma CVD apparatus used in processes of producing semiconductors such as LSI, etc., large amounts of perfluoro compounds such as CF4, C2F6, SF6, NF3 etc. are used as a cleaning gas for CVD chambers in order to remove deposits on the surface of the inner wall or other surfaces of the CVD chambers during film forming treatment. These compounds are stable, and have a very long life in the atmosphere and a high infrared absorption. With regard to global warming potential (GWP100) of the above perfluoro compounds, on the basis of carbon dioxide being 1, CF4 has 6500, C2F6 has 9200, SF6 has 23900 and NF3 has 8000 which values are extremely high. Therefore, the compounds have a high greenhouse effect and affect global warming very greatly.
Further, in the case of using the perfluoro compounds such as CF4, C2F6, SF6, NF3 etc. as a plasma CVD chamber cleaning gas, exhaust gases include the perfluoro compounds themselves which compounds are not decomposed even if plasma is generated. Further, in the case of using various compounds containing carbon and fluorine such as perfluoro carbon, hydrofluoro carbon (HFC) etc., exhaust gases contain CF4, etc. which are generated as a by-product. So they induce an environmental problem of exhausting global warming gases.
The gases inviting the greenhouse effect and global warming gas contained in the exhaust gases as described above are hardly absorbed or decomposed by abatement apparatus (water scrubber) which apparatus has conventionally been used mainly, so that a decomposition apparatus by chemical reactions including burning with high temperature and high energy is required.
Further, in the case that these cleaning gases are used for plasma CVD chambers cleaning, a method that the cleaning gases are generated by plasma for cleaning has been attempted for attaining effective cleaning performance.
Usually, in plasma cleaning, a proper amount of an additional gas such as oxygen, argon etc. is mixed with the cleaning gases.
According to the knowledge of the present inventors, in the mixed gas system of the cleaning gases and the additional gases, with increasing the concentrations of the cleaning gases in conditions that the total gas flow rates are constant, the etching rates tend to be increased. However, when the cleaning gas concentrations are over constant concentrations, there are problems such as instability in plasma generation, slowdown or lowering of the etching rate, deterioration in uniformity of cleaning etc. Particularly, using the cleaning gas in a concentration of 100% induces a more marked tendency toward instability in plasma generation, slowdown or lowering of the etching rate and deterioration in the uniformity of cleaning so that it has a problem such that it is lacking in practical use.
On this account, prior to use, the cleaning gases need to be diluted so as to have the peak concentration in the etching rate-cleaning gas concentration curve or a lower concentration than the peak concentration. In order to depress the lowering of the etching rate caused with the dilution, the cleaning condition has been optimized by increasing the chamber pressure or increasing the gas flow rate in cleaning. However, when the chamber pressure is enhanced or the gas flow rate is increased in cleaning, the plasma generation becomes unstable, so that the uniformity of cleaning is deteriorated and efficient cleaning cannot be conducted.
Of the above cleaning gases, for example, in the use of NF3, a remote plasma apparatus in which plasma is generated other than a process chamber of a CVD apparatus is required for securing a high decomposition rate which is one of the objects so that the cleaning efficiency is improved, contamination of undecomposed NF3 into exhaust gases is avoided. However, the CVD apparatus provided with the remote plasma apparatus has a problem in that the apparatus is complicated and thereby the production cost is high.
Further, in conventionally used cleaning gases, when the chamber pressure is enhanced or the gas flow rate is increased, the decomposition rate of the cleaning gases in plasma and the plasma stability (uniformity of cleaning) are remarkably decreased so that the cleaning gases themselves are contained in the exhaust gases resulting in increasing the emission amount of global warming substances. Therefore, it is necessary to take measures for abatement of the gases.
Accordingly, plasma cleaning gases which are used for chamber cleaning after the CVD process in producing semiconductors such as LSI, etc., and have a low greenhouse effect and a low global warming potential, excellent uniformity of cleaning even in diluting conditions or not, and also have an effective etching rate, and a process for plasma cleaning has been desired.
In the light of the foregoing, the present inventors have earnestly studied for solving the above problems, and found that when a mixed gas of fluorine gas and a gas incapable of substantially reacting with fluorine in plasma is used, plasma can be generated stably without a remote plasma apparatus in wider conditions than the use of, for example, NF3 and further the excellent etching rate can be provided without lowering of the etching rate. The present inventors further found that for example, as will be described in Examples 34 and 37, and Comparative Examples 30 and 31 of the present specification, in the case that the total gas flow rate is 1000 sccm, when the chamber pressure condition is changed from 250 Pa to a higher pressure of 400 Pa, in the use of a mixed gas containing 20% by volume of NF3, the uniformity of cleaning is decreased, but in the use of a mixed gas containing the same 20% by volume of fluorine gas, the proper uniformity of cleaning can be secured.
Further, the present inventors found that when 100% by volume of fluorine gas is generated by plasma and then is used as a cleaning gas, the extremely excellent etching rate can be attained without the use of a remote plasma apparatus, and also even in conditions that the total gas flow rate is about 1000 sccm and the chamber pressure is about 400 Pa, plasma can stably be generated and the proper uniformity of cleaning can be secured.
Thus, the present invention has been accomplished.
The present invention is intended to solve the problems associated with the prior arts as described above, it is an object of the present invention to provide a plasma cleaning gas for CVD chambers which gas has excellent uniformity of cleaning and an effective etching rate in cleaning in the conditions that the total gas flow rate is about 1000 sccm and the chamber pressure is about 400 Pa under the dilution condition or under no dilution condition. It is a further object of the invention to provide a process for plasma cleaning CVD chambers.
DISCLOSURE OF THE INVENTION
The first plasma cleaning gas for CVD chambers according to the present invention comprises 100% by volume of fluorine gas capable of generating plasma by electric discharge and is used for cleaning silicon-containing deposits on the surface of a CVD chamber inner wall and the surfaces of members placed inside the CVD chamber after film forming treatment on a substrate by a plasma CVD apparatus.
The first process of plasma cleaning for CVD chambers according to the present invention comprises cleaning silicon-containing deposits on the surface of a CVD chamber inner wall and the surfaces of members placed inside the CVD chamber by plasma generated from 100% by volume of fluorine gas by electric discharge, after film forming treatment on a substrate in a plasma CVD apparatus.
The silicon-containing deposits preferably comprise at least one selected from:

    
    
        (1) silicon,
        (2) a compound comprising silicon and at least one of oxygen, nitrogen, fluorine and carbon, and
        (3) a compound of a high melting point-having metal silicide.
    
    


The chamber pressure in the plasma CVD apparatus is preferably from 50 Pa to 1000 Pa, and the flow rate of fluorine gas introducing into a plasma generating part is preferably from 50 sccm to 1000 sccm in the cleaning.
The plasma generation from the above-described fluorine gas is preferably conducted by electric discharge in a process chamber of the plasma CVD apparatus whereinto fluorine gas has been introduced.
The second plasma cleaning gas for CVD chambers according to the present invention comprises fluorine gas capable of generating plasma by electric discharge and a gas substantially incapable of reacting with fluorine in plasma, and is used for cleaning silicon-containing deposits on the surface of a CVD chamber inner wall and the surfaces of members placed inside the CVD chamber after film forming treatment on a substrate by a plasma CVD apparatus.
It is preferred that the concentration of the fluorine gas capable of generating plasma by electric discharge be more than 20% by volume to less than 100% by volume and the concentration of the gas substantially incapable of reacting with fluorine in plasma be more than 0% by volume to not more than 80% by volume provided that the total concentration of the fluorine gas capable of generating plasma by electric discharge and the gas substantially incapable of reacting with fluorine is 100% by volume.
Further, it is more preferred that the concentration of the fluorine gas capable of generating plasma by electric discharge be more than 30% by volume to less than 100% by volume and the concentration of the gas substantially incapable of reacting with fluorine in plasma be more than 0% by volume to not more than 70% by volume provided that the total concentration of the fluorine gas capable of generating plasma by electric discharge and the gas substantially incapable of reacting with fluorine in plasma is 100% by volume.
The gas substantially incapable of reacting with fluorine in plasma is preferably at least one selected from the group of nitrogen, oxygen, carbon dioxide, N2O, dried air, argon, helium and neon.
The second process of plasma cleaning for CVD chambers according to the present invention comprises cleaning silicon-containing deposits on the surface of a CVD chamber inner wall and the surfaces of members placed inside the CVD chamber using a cleaning gas for plasma CVD chambers comprising fluorine gas capable of generating plasma by electric discharge and a gas substantially incapable of reacting with fluorine in plasma after film forming treatment on a substrate by means of a plasma CVD apparatus.
It is preferred that the concentration of the fluorine gas capable of generating plasma by electric discharge be more than 20% by volume to less than 100% by volume and the concentration of the gas substantially incapable of reacting with fluorine in plasma be more than 0% by volume to not more than 80% by volume provided that the total concentration of the fluorine gas capable of generating plasma by electric discharge and the gas substantially incapable of reacting with fluorine is 100% by volume.
The pressure in the chamber is preferably from 50 Pa to 1000 Pa, and the flow rate of fluorine gas is preferably from 50 sccm to 1000 sccm in the cleaning.
The plasma generation from fluorine gas is preferably conducted by electric discharge in a process chamber of the plasma CVD apparatus whereinto fluorine gas has been introduced.



BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a graph showing a relation between a gas concentration and an etching rate concerning the results of Examples 1 to 17 and Comparative Examples 1 to 13.



PREFERRED EMBODIMENTS OF THE INVENTION
The present invention will be described in detail hereinafter.
(Plasma Cleaning Gas for CVD Chambers and Process of Plasma Cleaning According to the First Invention)
The plasma cleaning gas for CVD chambers according to the first invention is used for cleaning silicon-containing deposits on the surface of a CVD chamber inner wall and the surfaces of members placed inside the CVD chamber after film forming treatment on a substrate by a plasma CVD apparatus. The cleaning gas comprises 100% by volume of fluorine gas and generates plasma from fluorine gas by electric discharge to remove the silicon-containing deposits as described above.
The first process of plasma cleaning for CVD chambers according to the invention comprises cleaning, by plasma generated from 100% by volume of fluorine gas by electric discharge, silicon-containing deposits on the surface of a CVD chamber inner wall and the surfaces of members placed inside the CVD chamber after film forming treatment on a substrate by means of a plasma CVD apparatus.
The term “plasma cleaning for CVD chambers” used in the present specification means removing deposits on the surface of a chamber inner wall and the surfaces of members such as jigs, piping or other inside components placed in semiconductor producing apparatus, for example, CVD apparatus or the like after the CVD process in a production process of semiconductors such as LSI, etc.
Further, the term “plasma generation” used in the present specification means that plasma is generated by introducing fluorine gas or the mixed gas of fluorine gas and the gas substantially incapable of reacting with fluorine in plasma and electrically discharging at a plasma generating part (CVD chamber or remote plasma apparatus).
The targeted compound of the CVD chamber cleaning with such 100% by volume of fluorine gas may include the above described silicon-containing deposits on the surfaces of the inner wall of CVD chambers and jigs or the like of CVD apparatus in the CVD method, etc. The silicon-containing deposits comprise, for example, at least one selected from:

    
    
        (1) silicon,
        (2) a compound comprising silicon and at least one of oxygen, nitrogen, fluorine and carbon, and
        (3) a compound of a high melting point-having metal silicide. Specific examples thereof are Si, SiO2, Si3N4, and high melting point-having metal silicides such as WSi.
    
    


In the process of plasma cleaning for CVD chambers according to the invention, the plasma generation from fluorine gas by electric discharge may be conducted in a remote chamber or in a process chamber of a plasma CVD apparatus whereinto fluorine gas is introduced without using the remote chamber.
Of these, it is desired to generate plasma from fluorine gas in the process chamber of the plasma CVD apparatus.
When plasma is generated from fluorine gas in the process chamber, the cleaning treatment of deposits in the CVD chamber can be conducted efficiently for a short time, and also plasma can be stably generated. Further, the apparatus can be compacted so that it is practical as compared with the plasma generation in the remote chamber.
The first cleaning gas of the invention comprises 100% by volume of fluorine gas and is used for plasma cleaning for CVD chambers. Usually, in the case that C2F6 or NF3 is used as a cleaning gas, 100% by volume of the gas is not used, and it is necessary to mix the gas with a diluting gas such as oxygen, argon, nitrogen etc. for use. Depending to the conditions, in the case of C2F6 or NF3, when the C2F6 or NF3 concentration in the cleaning gas is more than about 20 to 40% by volume, the rise of the etching rate based on the concentration in the cleaning gas, in a constant total gas flow rate, is slowed down and the etching rate is lowered finally. In the case that the total gas flow rate is 1000 sccm and the chamber pressure is about 400 Pa as described above, these gases cannot generate plasma stably. When the gas concentration or the chamber pressure is increased, the uniformity of cleaning becomes worse.
However, in the plasma cleaning gas and the process of plasma cleaning for CVD chambers according to the first or second invention, fluorine gas is used and the cleaning gas has a specific characteristic such that the etching rate is increased almost linearly with the increase of the concentration of fluorine gas in the condition that the total gas flow rate is constant. Even if the cleaning gas comprises 100% by volume of fluorine gas, the extremely excellent etching rate can be attained and also the uniformity of cleaning is extremely excellent.
When 100% by volume of fluorine gas is used, plasma can be stably generated, not only in the case that the chamber pressure is 150 Pa (flow rate 150 sccm) but also in the case that the chamber pressure is 250 Pa (flow rate 300 sccm). The cleaning gas having the specific characteristic as above has not been found out previously so long as the present inventors have investigated.
When the cleaning is conducted with the plasma cleaning gas according to the first invention, the chamber pressure is preferably from 50 Pa to 1000 Pa, more preferably from 150 Pa to 1000 Pa. The fluorine gas flow rate is preferably from 50 sccm to 1000 sccm, more preferably 150 to 1000 sccm.
When the chamber pressure and the fluorine gas flow rate are in the above ranges, the excellent etching rate can be attained, and the stabilization of plasma generation and the uniformity of cleaning can be kept excellent.
The chamber pressure is an inner pressure of a process chamber in a CVD apparatus and, in general, is automatically regulated by setting.
(Plasma Cleaning Gas for CVD Chambers and Process of Plasma Cleaning According to the Second Invention)
The plasma cleaning gas for CVD chambers according to the second invention is used for cleaning silicon-containing deposits on the surface of a CVD chamber inner wall and the surfaces of members placed inside the CVD chamber after film forming treatment on a substrate by a plasma CVD apparatus. The plasma cleaning gas comprises fluorine gas capable of generating plasma by electric discharge and a gas substantially incapable of reacting with fluorine in plasma.
The second process of plasma cleaning for CVD chambers according to the invention comprises cleaning silicon-containing deposits on the surface of a CVD chamber inner wall and the surfaces of members placed inside the CVD chamber by plasma generated from fluorine gas by electric discharge using the plasma cleaning gas for CVD chambers composed of fluorine gas capable of generating plasma by electric discharge and the gas substantially incapable of reacting with fluorine in plasma, after film forming treatment on a substrate by means of a plasma CVD apparatus.
In the present specification, “fluorine” contained in the gas substantially incapable of reacting with fluorine includes fluorine molecules, fluorine atoms, fluorine radicals, fluorine ions etc.
The concentration of the fluorine gas capable of generating plasma by electric discharge is preferably more than 20% by volume to less than 100% by volume, and the concentration of the gas substantially incapable of reacting with fluorine in plasma is preferably more than 0% by volume to not less than 80% by volume. The sum of the concentration of the fluorine gas capable of generating plasma by electric discharge and the concentration of the gas substantially incapable of reacting with fluorine in plasma is 100% by volume.
The concentration of the fluorine gas capable of generating plasma by electric discharge is, further, preferably more than 30% by volume to less than 100% by volume, more preferably not less than 40% by volume to less than 100% by volume, and especially not less than 70% by volume to less than 100% by volume, and the concentration of the gas substantially incapable of reacting with fluorine in plasma is, further, preferably more than 0% by volume to not more than 70% by volume, more preferably more than 0% by volume to less than 60% by volume, and especially more than 0% by volume to less than 30% by volume.
When the fluorine gas concentration is in the above range, the excellent etching rate can be attained and the uniformity of cleaning is good even in the conditions that the total gas flow rate is about 1000 sccm and the chamber pressure is about 400 Pa. Further, plasma can be generated stably in the presence of fluorine gas.
As described above, the etching rate has a specific characteristic such that the etching rate and the concentration of fluorine gas are increased almost linearly so that the etching rate is easily predictable from the fluorine gas concentration and it is effective in practical use.
In the case when fluorine gas concentration is limited to be not more than 50% by volume in transportation, etc., the concentration of fluorine gas for submitting to plasma treatment is preferably more than 20% by volume, more preferably more than 30% by volume. Particularly, it is preferably not more than 50% by volume, so that the cleaning gas has a practicability maintainable etching rate and also, as a cleaning gas, excellent transportation property and storage stability, and simple handling. Furthermore, as described above, although this concentration range is a relatively low concentration range, the uniformity of cleaning is not deteriorated even if the chamber pressure is increased in order to increase the etching rate in this concentration range.
Further, even if the concentration of fluorine gas for submitting to plasma treatment is in a low range of 5 to 20% by volume, the uniformity of cleaning is not deteriorated by increasing the chamber pressure in order to increase the etching rate.
The gas substantially incapable of reacting with fluorine in plasma is preferably at least one selected from the group of nitrogen, oxygen, carbon dioxide, N2O, dried air, argon, helium and neon. Among them, it is more preferably at least one selected from the group of oxygen, carbon dioxide and dried air.
The fluorine gas introduced in plasma generates fluorine radicals. Using the gas substantially incapable of reacting with the fluorine radicals, fluorine molecules, fluorine ions etc., the by-product generation can be depressed and the cleaning can be conducted efficiently.
Further, using oxygen, carbon dioxide and dried air, fluorine radicals can be generated stably at low cost.
When the cleaning is conducted using the plasma cleaning gas according to the second invention, the chamber pressure is preferably from 50 Pa to 1000 Pa, more preferably 150 Pa to 1000 Pa. The fluorine gas flow rate is preferably from 50 sccm to 1000 sccm, more preferably 150 sccm to 1000 sccm.
When the chamber pressure and the fluorine gas flow rate are in the above ranges, the excellent etching rate can be attained and also the stabilization of plasma generation and the uniformity of cleaning can be kept excellent.
In the case of using the plasma cleaning gas for CVD chambers according to the second invention, the plasma generation from fluorine gas by electric discharge may be conducted in a remote chamber or by introducing fluorine gas into a plasma CVD apparatus and generating plasma from fluorine gas in a process chamber of the CVD apparatus, without using the remote chamber.
Of these, it is desirable to generate plasma from fluorine gas in the process chamber of the plasma CVD apparatus.
When plasma is generated from fluorine gas in the process chamber, the cleaning treatment of deposits in the CVD chamber can be conducted efficiently for a short time, and also plasma can be stably generated similar to the first invention. Further, the apparatus can be compacted so that it is practical as compared with the plasma generation in the remote chamber.
EXAMPLES
The present invention will be described in more detail with reference to the following non-limiting examples hereinafter.
In the present examples, as one of the properties of the cleaning gas, the cleaning rate for deposits, which should be removed was unequivocally evaluated by the etching rate of a SiO2 thin film on a wafer.
The method of measuring the etching rates of fluorine gas and diluted fluorine gas is shown below. A Si wafer previously deposited SiO2 film thereon having a thickness of about 11000 Å by the plasma CVD method was used as a sample and a parallel plate plasma enhanced CVD apparatus was used. In the conditions as described in Examples, the wafer as a sample was placed on a lower electrode of the parallel plate electrodes and etched. The etching rate was determined by accurately measuring the film thickness on nine fixed points of the sample before and after the etching with a spectroscopic reflectmeter film thickness measuring instrument and measuring the decrease in the film thickness.
The uniformity of cleaning was determined from the maximum value and the minimum value of the etching rates on the nine fixed points with the following formula.

[maximum value−minimum value)/(maximum value+minimum value)]×100(%)

Examples 1 to 17 and Comparative Examples 1 to 16
The dependency of the etching rate on the gas kind and the gas concentration was examined using F2, C2F6 and NF3 as a cleaning gas and the gases shown in the tables as a dilution gas in the following conditions. The results are shown in Tables 1 to 7. Further, the results are shown in FIG. 1.

















Total gas flow rate:
300
sccm



Chamber pressure:
250
Pa



Electrode temperature:
300°
C.



RF electric power:
750
W



Distance between electrodes:
50
mm



Electric discharge time:
30
sec























TABLE 1







Ex. 1
Ex. 2
Ex. 3
Ex. 4
Ex. 5





















Cleaning gas







composition


F2 amount (mol %)
10
25
50
75
100


O2 amount (mol %)
90
75
50
25
0


Ar amount (mol %)
—
—
—
—
—


N2 amount
—
—
—
—
—


(mol %)







Total gas amount
100
100
100
100
100


(mol %)


Etching rate (Å/min)
3460
8190
15960
21800
29420


Uniformity of cleaning
3
3.2
4
3.9
4.1


(%)























TABLE 2







Ex. 6
Ex. 7
Ex. 8
Ex. 9
Ex. 10
Ex. 11






















Cleaning gas








composition


F2 amount
5
10
20
25
50
75


(mol %)


O2 amount
—
—
—
—
—
—


(mol %)


Ar amount
95
90
80
75
50
25


(mol %)


N2 amount
—
—
—
—
—
—


(mol %)








Total gas
100
100
100
100
100
100


amount


(mol %)


Etching rate
2190
4230
7090
8800
16440
22240


(Å/min)


Uniformity of
4.2
3.6
3.3
3.9
3.4
4.5


cleaning (%)




















TABLE 3







Ex. 12
Ex. 13
Ex. 14





















Cleaning gas composition






F2 amount (mol %)
25
50
75



O2 amount (mol %)
—
—
—



Ar amount (mol %)
—
—
—



N2 amount mol %
75
50
25



Total gas amount (mol %)
100
100
100



Etching rate (Å/min)
8570
16230
22450



Uniformity of cleaning (%)
3.2
6.2
4.2



















TABLE 4









Dried air











Ex. 15
Ex. 16
Ex. 17
















Cleaning gas composition






F2 amount (mol %)
25
50
75



O2 amount (mol %)
15
10
5



Ar amount (mol %)
—
—
—



N2 amount (mol %)
60
40
20



Total gas amount (mol %)
100
100
100



Etching rate (Å/min)
8490
16180
22320



Uniformity of cleaning (%)
3.2
4.3
4



















TABLE 5









Comparative Example















1
2
3
4
5
6
7











Cleaning gas composition














C2F6 amount (mol %)
20
40
45
50
55
60
70


O2 amount (mol %)
80
60
55
50
45
40
30


NF3 amount (mol %)
—
—
—
—
—
—
—


Ar amount (mol %)
—
—
—
—
—
—
—


Total gas amount (mol %)
100
100
100
100
100
100
100


Etching rate (Å/min)
7810
11810
12270
12410
12140
11140
7590


Uniformity of cleaning (%)
4.7
4.3
4
3.5
4
3.1
1.9


















TABLE 6









Comparative Example














8
9
10
11
12
13

















Cleaning gas








composition


C2F6 amount
—
—
—
—
—
—


(mol %)


O2 amount
—
—
—
—
—
—


(mol %)


NF3 amount
10
20
30
40
50
60


(mol %)


Ar amount
90
80
70
60
50
40


(mol %)








Total gas
100
100
100
100
100
100


amount


(mol %)


Etching rate
5070
9080
12510
15310
17180
16080


(Å/min)


Uniformity of
3.3
3.4
3.4
4.1
24
36


cleaning (%)


















TABLE 7









Comparative Example











14
15
16
















Cleaning gas composition






C2F6 amount (mol %)
—
—
—



O2 amount (mol %)
—
—
—



NF3 amount (mol %)
10
30
40



N2 amount (mol %)
90
70
60



Total gas amount (mol %)
100
100
100



Etching rate (Å/min)
4872
12298
14316



Uniformity of cleaning (%)
3.2
5.4
31.5










As is clear from the results, fluorine gas in any concentration until 100% had almost no influence on the uniformity of etching independent on the kind of the added gas.
On the contrary, with respect to C2F6, in a high C2F6 concentration, the uniformity of cleaning was not deteriorated, however, the etching rate was largely lowered.
With regard to NF3, in the case that the added gas was argon, when the NF3 concentration was not less than 50%, the uniformity of cleaning was largely deteriorated and when the NF3 concentration was 60%, the lowering of the etching rate was observed. In the case that the added gas was nitrogen, when the NF3 concentration was 40%, the uniformity of cleaning was largely deteriorated. It is presumed that the deterioration shows an indication such that plasma generated is biased and thereby plasma is not generated stably.
Examples 18 to 37
The dependency of the etching rate on the gas flow rate and the chamber pressure was examined by using F2 as a cleaning gas and Ar as a dilution gas in a low F2 concentration of 5 to 20% by volume in the conditions as shown in Tables 8 to 11. The results are shown in Tables 8 to 11.

















Electrode temperature:
300°
C.



RF electric power:
750
W



Distance between electrodes:
50
mm



Electric discharge time:
30
sec






















TABLE 8







Ex 18
Ex 19
Ex 20
Ex. 21




















Total gas flow rate (sccm)
300
300
300
300


Chamber pressure (Pa)
250
250
250
150


Cleaning gas composition


F2 amount (mol %)
5
10
20
5


Ar amount (mol %)
95
90
80
95


Total gas amount (mol %)
100
100
100
100


Etching rate (Å/min)
2192
4234
7089
2731


Uniformity of cleaning (%)
4.2
3.6
3.3
2.9






















TABLE 9







Ex 22
Ex 23
Ex 24
Ex 25
Ex 26





















Total gas flow rate
500
500
500
500
500


(sccm)


Chamber pressure (Pa)
250
250
250
150
400


Cleaning gas


composition


F2 amount (mol %)
5
10
20
5
5


Ar amount (mol %)
95
90
80
95
95


Total gas amount (mol
100
100
100
100
100


%)


Etching rate (Å/min)
2543
4801
8473
3324
6297


Uniformity of cleaning
3.8
3.4
3.5
2.6
2.6


(%)






















TABLE 10







Ex 27
Ex 28
Ex 29
Ex 30
Ex 31





















Total gas flow rate
700
700
700
700
700


(sccm)


Chamber pressure (Pa)
250
250
250
150
400


Cleaning gas


composition


F2 amount (mol %)
5
10
20
5
5


Ar amount (mol %)
95
90
80
95
95


Total gas amount (mol
100
100
100
100
100


%)


Etching rate (Å/min)
2777
5241
9114
3308
6923


Uniformity of cleaning
3.7
3.2
3.4
2.3
5.3


(%)


















TABLE 11









Example














32
33
34
35
36
37

















Total gas flow
1000
1000
1000
1000
1000
1000


rate (sccm)


Chamber
250
250
250
150
400
400


pressure (Pa)


Cleaning gas


composition


F2 amount
5
10
20
5
5
20


(mol %)


Ar amount
95
90
80
95
95
80


(mol %)








Total gas
100
100
100
100
100
100


amount


(mol %)


Etching rate
2978
5519
9893
3531
7800
13552


(Å/min)


Uniformity of
3.6
3.3
3.4
2.3
5.3
4.8


cleaning (%)









As is clear from the results, in the case that the cleaning gas having a F2 concentration of 5 to 20% was used, even if the flow rate was increased in the experimental range or the pressure is increased, the uniformity of cleaning proved to be excellent.
Examples 38 to 55
The dependency of the etching rate on the gas flow rate and the chamber pressure was examined by using a cleaning gas having a F2 concentration of 100% by volume in the conditions as shown in Tables 12 to 16. The results are shown in Tables 12 to 16.

















Electrode temperature:
300°
C.



RF electric power:
750
W



Distance between electrodes:
50
mm



Electric discharge time:
30
sec




















TABLE 12









Example











38
39















Total gas flow rate (sccm)
100
100



Chamber pressure (Pa)
50
80



Cleaning gas composition
100
100



F2 amount (mol %)



Total gas amount (mol %)
100
100



Etching rate (Å/min)
5119
8239



Uniformity of cleaning (%)
1.6
1.5



















TABLE 13









Example











40
41
42
















Total gas flow rate (sccm)
150
150
150



Chamber pressure (Pa)
50
80
100



Cleaning gas composition
100
100
100



F2 amount (mol %)



Total gas amount (mol %)
100
100
100



Etching rate (Å/min)
4664
8981
10939



Uniformity of cleaning (%)
1.6
0.6
2.4



















TABLE 14









Example












43
44
45
46















Total as flow rate (sccm)
200
200
200
200


Chamber pressure (Pa)
50
80
100
150


Cleaning gas composition
100
100
100
100


F2 amount (mol %)


Total gas amount (mol %)
100
100
100
100


Etching rate (Å/min)
5144
8270
11173
17812


Uniformity of cleaning (%)
1.4
1.7
2.5
2.7


















TABLE 15









Example












47
48
49
50















Total gas flow rate (sccm)
250
250
250
250


Chamber pressure (Pa)
50
80
100
200


Cleaning gas composition
100
100
100
100


F2 amount (mol %)


Total gas amount (mol %)
100
100
100
100


Etching rate (Å/min)
4468
8733
12406
23590


Uniformity of cleaning (%)
2
1.2
1.9
3


















TABLE 16









Example













51
52
53
54
55
















Total gas flow rate
300
300
300
300
300


(sccm)


Chamber pressure (Pa)
50
80
100
150
250


Cleaning gas
100
100
100
100
100


composition


F2 amount


(mol %)







Total gas amount
100
100
100
100
100


(mol %)


Etching rate (Å/min)
5012
9235
10927
18484
29416


Uniformity of cleaning
1.5
1.3
2.1
2.6
4.1


(%)









As is clear from the results, in an F2 concentration of 100%, even if the flow rate was increased in the experimental range, or the pressure is increased, the uniformity of cleaning proved to be excellent.
Comparative Examples 17 to 29 and Comparative Examples 8 to 13 (Shown Again)
With regard to the etching rate and the uniformity of cleaning, the dependency of NF3 on the concentration and the chamber pressure was examined using NF3 as a cleaning gas and Ar as a dilution gas in the conditions as shown in Tables 17 to 20. The results are shown in Tables 17 to 20.

















Total gas flow rate:
300
sccm



Electrode temperature:
300°
C.



RF electric power:
750
W



Distance between electrodes:
50
mm



Electric discharge time:
30
sec



















TABLE 17









Comparative Example













17
18
19
20
21
















Chamber pressure (Pa)
100
100
100
100
100


Cleaning gas


composition


NF3 amount (mol %)
40
50
80
90
100


Ar amount (mol %)
60
50
20
10
0


Total gas amount
100
100
100
100
100


(mol %)


Etching rate (Å/min)
8430
10198
12170
13082
13390


Uniformity of cleaning
0.8
1.6
4.1
14.2
24.8


(%)


















TABLE 18









Comparative Example












22
23
24
25















Chamber pressure (Pa)
150
150
150
150


Cleaning gas composition


NF3 amount (mol %)
60
70
80
90


Ar amount (mol %)
40
30
20
10


Total gas amount (mol %)
100
100
100
100


Etching rate (Å/min)
12594
13779
13574
14389


Uniformity of cleaning (%)
5.7
21.1
34.6
40.9


















TABLE 19









Comparative Example












26
27
28
29















Chamber pressure (Pa)
200
200
200
200


Cleaning gas composition


NF3 amount (mol %)
40
50
60
70


Ar amount (mol %)
60
50
40
30


Total gas amount (mol %)
100
100
100
100


Etching rate (Å/min)
12308
14366
15214
14987


Uniformity of cleaning (%)
3.4
8.2
28.4
38.2


















TABLE 20









Comparative Example














8
9
10
11
12
13

















Chamber
250
250
250
250
250
250


pressure (Pa)


Cleaning gas


composition


NF3 amount
10
20
30
40
50
60


(mol %)


Ar amount
90
80
70
60
50
40


(mol %)








Total gas
100
100
100
100
100
100


amount


(mol %)


Etching rate
5070
9080
12510
15310
17180
16080


(Å/min)


Uniformity of
3.3
3.4
3.4
4.1
24
36


cleaning (%)









As is clear from the results, in the case that NF3 was used as a cleaning gas, the uniformity of cleaning was largely deteriorated with the increase of the NF3 concentration. Further, the uniformity of cleaning was largely deteriorated with the increase of the chamber pressure.
Examples 34 and 37 (Shown Again) and Comparative Examples 30 and 31
The dependency of the etching rate and that of the uniformity of cleaning on the chamber pressure were examined by using F2 or NF3 as a cleaning gas and Ar as a dilution gas in a concentration of F2 or NF3 of 20% by volume in the conditions as shown in Tables 21 and 22. The results are shown in Tables 21 and 20.

















Total gas flow rate:
1000
sccm



Electrode temperature:
300°
C.



RF electric power:
750
W



Distance between electrodes:
50
mm



Electric discharge time:
30
sec




















TABLE 21







Ex 34
Ex 37




















Total gas flow rate (sccm)
1000
1000



Chamber pressure (Pa)
250
400



Cleaning gas composition



F2 amount (mol %)
20
20



Ar amount (mol %)
80
80



Total gas amount (mol %)
100
100



Etching rate (Å/min)
9893
13552



Uniformity of cleaning (%)
3.4
4.8




















TABLE 22









Comparative











Ex 30
Ex 31















Total gas flow rate (sccm)
1000
1000



Chamber pressure (Pa)
250
400



Cleaning gas composition



NF3 amount (mol %)
20
20



Ar amount (mol %)
80
80



Total gas amount (mol %)
100
100



Etching rate (Å/min)
12260
15380



Uniformity of cleaning (%)
3.7
19.2










As is clear from the results, in the case that the total gas flow rate is 1000 sccm, when the chamber pressure was changed from 250 Pa to a higher pressure of 400 Pa, the uniformity of cleaning was deteriorated in the use of 20% by volume of NF3, but the good uniformity of cleaning is ensured in the use of 20% by volume of fluorine gas.
INDUSTRIAL APPLICABILITY
In the present invention, because fluorine gas is used as a cleaning gas, silicon-containing deposits after CVD process can be cleaned at a high rate without using CF4, C2F6, SF6, NF3 etc. which have a high global warming potential, and exhaust gas can be treated with conventional water scrubber. Therefore, the cleaning can be accomplished with exhausting a slight amount of exhaust gases having the greenhouse effect and the global warming effect.
Further, using the mixed gas of fluorine gas and the gas incapable of substantially reacting with fluorine in plasma in specific amounts, plasma can stably be generated even in the conditions that the total gas flow rate is about 1000 sccm and the chamber pressure is about 400 Pa. Additionally, the etching rate is not lowered and the excellent etching rate can be provided. Further, for example, even if the mixed gas has a low concentration of fluorine gas of 5 to 20% by volume, the uniformity of cleaning can be ensured even in the conditions that the total gas flow rate and the chamber pressure are as described above. Further, the mixed gas having a low concentration of fluorine gas is simple in handleability.
Furthermore, when plasma is generated from 100% by volume of fluorine gas by electric discharge and submitted to use as a cleaning gas, the extremely excellent etching rate can be attained, and plasma can stably be generated even in high-pressure conditions and also the uniformity of cleaning can be ensured even in high-pressure conditions. Additionally, the cleaning gas has a fluorine gas concentration of 100% so that the device is not complicated and the cleaning gas is excellent in practicability.

## Claims

1. A process of plasma cleaning for CVD chambers, comprising cleaning silicon-containing deposits on a surface of an inner wall of a CVD chamber and surfaces of members placed inside the CVD chamber by plasma generated from 100% by volume of a fluorine gas by electric discharge, after film forming treatment on a substrate by a plasma CVD apparatus, wherein a chamber pressure in the plasma CVD apparatus is from 150 Pa to 1000 Pa, and a flow rate of the fluorine gas introduced into a plasma generating part is from 150 sccm to less than 1000 sccm during the plasma cleaning.

2. The process of plasma cleaning for CVD chambers according to claim 1, wherein the silicon-containing deposits comprise at least one selected from the group consisting of:
(1) silicon,
(2) a compound comprising silicon and at least one of oxygen, nitrogen, fluorine and carbon, and
(3) a compound of a high melting point-having metal silicide.

3. The process of plasma cleaning for CVD chambers according to claim 1, wherein a plasma generation from the fluorine gas is conducted by electric discharge in a process chamber of the plasma CVD apparatus, and the fluorine gas is introduced into the process chamber of the plasma CVD apparatus.

4. A process of plasma cleaning for CVD chambers, comprising cleaning silicon-containing deposits on a surface of an inner wall of a CVD chamber and surfaces of members placed inside the CVD chamber by plasma generated from a fluorine gas by electric discharge using a plasma cleaning gas for CVD chambers comprising the fluorine gas capable of generating plasma by electric discharge and a gas substantially incapable of reacting with fluorine in plasma, wherein a concentration of the fluorine gas is more than 20% by volume to less than 100% by volume, a concentration of the gas substantially incapable of reacting with fluorine in plasma is more than 0% by volume to not more than 80% by volume, a total concentration of the fluorine gas and the gas substantially incapable of reacting with fluorine is 100% by volume, after film forming treatment on a substrate by a plasma CVD apparatus, a pressure in the CVD chamber is from 150 Pa to 1000 Pa, and a flow rate of the fluorine gas is from 150 sccm to less than 1000 sccm during the plasma cleaning.

5. The process of plasma cleaning for CVD chambers according to claim 4, wherein a plasma generation from the fluorine gas is conducted by electric discharge in a process chamber of the plasma CVD apparatus, and the fluorine gas is introduced into the process chamber of the CVD apparatus.

6. The process of plasma cleaning for CVD chambers according to claim 2, wherein a plasma generation from the fluorine gas is conducted by electric discharge in a process chamber of the plasma CVD apparatus, and the fluorine gas is introduced into the process chamber of the CVD apparatus.