Semiconductor device manufacturing: process – Coating of substrate containing semiconductor region or of... – Insulative material deposited upon semiconductive substrate
Reexamination Certificate
2002-08-21
2004-12-07
Zarneke, David A. (Department: 2829)
Semiconductor device manufacturing: process
Coating of substrate containing semiconductor region or of...
Insulative material deposited upon semiconductive substrate
Reexamination Certificate
active
06828257
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to a method for forming an interlayer dielectric film in a multi-level inter-connection structure for a semiconductor integrated circuit device. More particularly, the present invention relates to a method for forming an interlayer dielectric film with a low dielectric constant by polymerizing an organic/inorganic hybrid material (e.g., a siloxane material with organosilicon bonds) within plasma.
Examples of the interlayer dielectric film made of a siloxane material with organosilicon bonds include: an organic SOG film formed by a coating technique; and a siloxane film with organosilicon bonds, which is formed by polymerizing an organosilicon compound within plasma.
An organic SOG film is usually formed in the following manner. First, the surface of a substrate is coated with a solution of a siloxane polymer with organosilicon bonds at room temperature to obtain a coating film. Next, the coating film is heated with a hot plate to vaporize the solvent of the solution. Then, the film is hardened at an elevated temperature of 400° C. within an inert gas environment. During this hardening process, silanol (Si—OH) bonds, of which the siloxane polymer is made up, cause dehydration and condensation reactions to form a siloxane polymer. As a result, the organic SOG film is densified.
A siloxane film with organosilicon bonds may be formed by the plasma polymerization process in the following manner. First, an organosilicon compound and an oxidizing agent such as nitrogen monoxide are polymerized with each other by a plasma CVD process, thereby generating organic silanol. Then, the organic silanol bonds themselves are polymerized with each other to obtain a siloxane film with organosilicon bonds.
According to the known method for forming an organic SOG film, however, the solvent is vaporized from the coating by heating the coating. Thus, the solvent in the organic SOG film may not be removed completely, but left in the coating. In such a situation, an outgassing phenomenon, or gradual vaporization of the residual solvent from the organic SOG film, is observed during the heat treatment conducted after the film has been formed. Then, a contact hole cannot be filled in with a metal film satisfactorily due to the outgassing phenomenon. As a result, the resistance of a contact formed in this manner becomes higher than expected.
A similar phenomenon is also observable in forming a siloxane film with organosilicon bonds by a plasma polymerization process. Specifically, when a silanol polymer is formed as a result of the dehydration and condensation reactions of silanol bonds, unreacted silanol is left in the siloxane film. Thus, depending on the conditions of a thermal process during an integration process performed after the film has been formed, the dehydration and condensation reactions of the residual silanol proceed gradually. As a result, an outgassing phenomenon, i.e., vaporization of water produced by the dehydration and condensation reactions of the residual silanol, is also observed and the resistance of a contact formed in this manner rises, too.
In addition, if a siloxane film with organosilicon bonds is formed at 300° C. or more by the plasma polymerization process, then the organosilicon bonds cannot be incorporated into the resultant film effectively. As a result, the dielectric constant of that film is not so low as expected.
To solve these problems, an alternative method of forming a siloxane film was proposed. According to this method, a siloxane film is formed at a temperature as low as room temperature, and then subjected to a special heat treatment at about 200° C., thereby stabilizing the siloxane film obtained. This method is, however, impractical, because the temperature and environment should be controlled too precisely to execute the special heat treatment successfully.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to form an insulating film having a low dielectric constant with the outgassing phenomenon suppressed and without conducting any special heat treatment.
A first inventive method for forming an interlayer dielectric film includes the step of forming the interlayer dielectric film out of an organic/inorganic hybrid film by plasma-polymerizing a source material at a relatively high pressure within an environment containing nitrogen gas as a dilute gas. The source material includes an organosilicon compound.
According to the first method, the plasma polymerization is produced at a relatively high pressure within an environment containing nitrogen gas. Thus, the electron temperature of the plasma is controllable to a low temperature and the energy of the plasma can be consumed in exciting the nitrogen gas. That is to say, it is possible to suppress the organosilicon bonds from being decomposed by the plasma. As a result, the organosilicon bonds can be effectively incorporated into the organic/inorganic hybrid film and the dielectric constant of the resultant interlayer dielectric film can be reduced.
In addition, since the organosilicon bonds can be incorporated into the organic/inorganic hybrid film effectively, the creation of silanol, which usually causes the outgassing phenomenon, can be suppressed. Furthermore, the organosilicon bonds are more stable thermally than silanol, and are less likely to react irrespective of the conditions of a thermal process during the integration process after the film has been formed. Thus, it is possible to prevent the outgassing phenomenon from being produced in the interlayer dielectric film.
In the first method, the pressure is preferably 650 Pa or more.
Generally speaking, the pressure of a vacuum created differs depending on various process conditions including the temperature inside the reaction chamber of a CVD system, the temperature of a process gas and the volume of the reaction chamber. Thus, the process is preferably controlled by the residence time of the process gas, because the time is constant irrespective of the conditions such as these. Specifically, a one-to-one correspondence is definable between the residence time T of the process gas and the vacuum by the following conversion equation:
T
=(volume of reaction chamber)/
V
2
=(volume of reaction chamber)×(
P
1
/
P
2
)×(
T
2
/
T
1
)×
V
1
where V
1
is the flow rate of the process gas, V
2
is the flow rate of the gas inside the reaction chamber, P
1
is the pressure of the process gas, P
2
is the partial pressure of the process gas inside the reaction chamber, T
1
is the temperature of the process gas and T
2
is the temperature inside the reaction chamber.
In the present invention, the volume of the reaction chamber was 127000 ml. The flow rate V
1
, pressure P
1
and temperature T
1
of the process gas were kept constant at 2000 ml/min., 101325 Pa and room temperature (=25° C.), respectively. And the temperature T
2
inside the reaction chamber was also kept constant at 200° C. Since nitrogen gas was introduced as a dilute gas at 5000 ml/min., the partial pressure P
2
of the process gas inside the reaction chamber can be calculated as two-sevenths of the vacuum. The following Table 1 shows the relationship between the vacuum and the residence time of the gas we obtained under these conditions:
TABLE 1
Atmos-
pheric
pressure
Vacuum
T2
T1
V1
V2
T
(Pa)
(Pa)
(° C.)
(° C.)
(ml/min.)
(ml/min.)
(min.)
101325
100
200
25
2000
4632000
0.027
101325
200
200
25
2000
2316000
0.055
101325
300
200
25
2000
1544000
0.082
101325
400
200
25
2000
1158000
0.110
101325
500
200
25
2000
926400
0.137
101325
600
200
25
2000
712600
0.178
101325
700
200
25
2000
661700
0.192
101325
800
200
25
2000
579000
0.219
101325
900
200
25
2000
514700
0.247
101325
1000
200
25
2000
463200
0.274
101325
1100
200
25
2000
421100
0.302
101325
1200
200
25
2000
386000
0.329
101325
1300
200
25
2000
356300
0.356
101325
1400
200
25
2000
330900
0.384
As shown in Table 1, if the vacuum is 650 Pa or more, then the residence time of the process gas should be 0.178 minute or
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