Abstract:
It is an object of the present invention to cure an insulating film of a semiconductor device in a short time while keeping a low dielectric constant. In the present invention, a coating film made of porous MSQ is formed on a substrate, the substrate on which the porous MSQ is formed is placed in a vacuum vessel, and high-density plasma processing at a low electron temperature based on microwave excitation is applied to the coating film by using a plasma substrate processing apparatus, thereby causing an intermolecular dehydration-condensation reaction of hydroxyls in a molecule and another molecule included in the porous MSQ to bond the molecules together, so that a cured insulating film is generated while a low dielectric constant is maintained.

Description:
[0001]     This is a continuation in part of PCT Application No. PCT/JP2004/009330, filed on Jul. 1, 2004, which claims the benefit of Japanese Patent Application No. 2003-190501, filed on Jul. 2, 2003, all of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to a forming method of a low dielectric constant insulating film of a semiconductor device, a semiconductor device, and a low dielectric constant insulating film forming apparatus, and more particularly, to a method and an apparatus which generate plasma by using a microwave, thereby curing a low dielectric constant coating film used as an interlayer insulation film of a semiconductor device while maintaining a low dielectric constant.  
       DESCRIPTION OF THE RELATED ART  
       [0003]     In accordance with an increase in integration degree of a semiconductor integrated circuit, an increase in wiring delay time ascribable to an increase in inter-wiring capacitance, which is a parasitic capacitance between metal wirings, comes to be a hindrance to achieving a higher performance of the semiconductor integrated circuit. The wiring delay time is proportional to a product of a resistance of the metal wiring and the wiring capacitance. In order to lower the resistance of the metal wiring for achieving a shorter wiring delay time, highly conductive copper (Cu) is used instead of conventionally used aluminum (Al).  
         [0004]     Further, a possible way of reducing the wiring capacitance is to lower a dielectric constant (k) of an interlayer insulating film formed between the metal wirings. As a low dielectric constant interlayer insulating film, used is an insulating film which is lower in dielectric constant than conventional oxide silicon (SiO 2 ). Such a low dielectric constant insulating film is formed on a wafer by, for example, a SOD (Spin-on-Dielectric) system. Specifically, the SOD system coats the wafer with a high-molecular forming material in liquid form and applies curing such as heating thereto, thereby forming an insulating film. The dielectric constant of the coating film, at the stage where it is formed by the SOD system, keeps a low value.  
         [0005]     However, the insulating film, if left as it is after being formed, is low in mechanical strength and low in adhesiveness to a base substrate. Therefore, the insulating film is thermally cured while keeping its low dielectric constant. The insulating film increases in strength by a chemical bonding force when molecules thereof are bonded into a polymer by this thermal curing, so that the peeling of the films at the time of chemical mechanical polishing (CMP) is prevented.  
         [0006]     Conventionally, for curing the insulating film, for example, 30 to 60 minute heating is applied by using a furnace. However, this method not only requires a long time for the processing but also cannot attain predetermined mechanical hardness, and the long heating may possibly increase the dielectric constant.  
         [0007]     Another curing method is to use an electron beam, but this method, though only taking 2 to 6 minutes for curing, can only achieve insufficient hardness. Therefore, a method of curing the insulating film in a short time while further lowering the dielectric constant is being demanded.  
         [0008]     Further, Japanese Patent Application Laid-open No. Hei 8-236520 describes a method of curing an insulating film by generating plasma in a parallel-plate plasma reactor.  
         [0009]     A first object of the method of curing the insulating film by generating the plasma in the parallel-plate plasma reactor described in the above Japanese Patent Application Laid-open No. Hei 8-236520 is to cure a SOG film without producing any residues or the like. A second object of this method is to prevent property deterioration of current/voltage due to moisture generation when a photosensitive film is removed after a subsequent masking process.  
         [0010]     The above-described method reduces a defect in the SOG film such as —OH and —CH 3  causing leakage current by curing the insulating film at a temperature of 200° C. to 450° C. for 60 minutes. However, in order to maintain the low dielectric constant, CH 3  is indispensable, and exposing the SOG film to the plasma atmosphere for no less than 60 minutes has a problem that CH 3  disappears to make the dielectric constant higher.  
       SUMMARY OF THE INVENTION  
       [0011]     It is a major object of the present invention to provide a forming method of an insulating film of a semiconductor device capable of curing the insulating film of the semiconductor device in a short time while maintaining a low dielectric constant, and to provide a semiconductor device having an insulating film formed by, for example, this method, and a low dielectric constant insulating film forming apparatus.  
         [0012]     A forming method of a low dielectric constant insulating film of a semiconductor device of the present invention includes the step of placing in a vacuum vessel a substrate on which a coating film is formed and applying, to the coating film, high-density plasma processing at a low electron temperature, thereby curing the coating film while keeping a low dielectric constant.  
         [0013]     Accordingly, it is possible to cure the coating film in a short time while keeping the low dielectric constant.  
         [0014]     Preferably, the curing step includes curing the coating film in a processing time of five minutes or less. This can increase the number of the substrates processable per hour, resulting in an improved throughput in semiconductor processing steps.  
         [0015]     Preferably, the curing step includes generating plasma with a low electron temperature of 0.5 eV to 1.5 eV and an electron density of 10 11  to 10 13  electrons/cm 3 . Thus curing the coating film at the low electron temperature makes it possible to reduce energy of an electron absorbed in the coating film, so that a damage given to the coating film when the electron collides with the coating film can be alleviated.  
         [0016]     Preferably, the curing step includes causing an intermolecular dehydration-condensation reaction by hydroxyls in a molecule and another molecule included in the coating film.  
         [0017]     According to another aspect, a semiconductor device of another invention of the present invention includes: a substrate; and a low dielectric constant insulating film applied on the substrate and cured by high-density plasma processing at a low electron temperature.  
         [0018]     An example of a molecular structure of the insulating film cured by the high-density plasma processing is one including a Si—O—Si bond.  
         [0019]     According to still another aspect, a low dielectric constant insulating film forming apparatus of the present invention includes: a curing means for curing a coating film while keeping a low dielectric constant, by placing in a vacuum vessel a substrate on which a coating film is formed and applying, to the coating film, high-density plasma processing at a low electron temperature based on microwave excitation.  
         [0020]     An example of the curing means is one generating plasma with a low electron temperature of 0.5 eV to 1.5 eV and an electron density of 10 11  to 13 13  electrons/cm 3 .  
         [0021]     According to this invention, the substrate on which the low dielectric constant coating film is formed is placed in the vacuum vessel and the high-density plasma processing is applied to the coating film at the low electron temperature based on the microwave excitation, whereby it is possible to cure the coating film in a short time while keeping the low dielectric constant and in addition, to bring the coating film in close contact with the base substrate.  
         [0022]     Further, setting a processing time of the curing to five minutes or less makes it possible to increase the number of the substrates processable per hour, so that the throughput in the semiconductor processing processes can be improved.  
         [0023]     In addition, generating the plasma with the low electron temperature of 0.5 eV to 1.5 eV and the electron density of 10 11  to 13 13  electrons/cm 3  makes it possible to reduce electron energy absorbed by the coating film, so that the damage given thereto when the electron collides with the coating film can be alleviated. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]      FIG. 1  is a cross-sectional view showing a plasma substrate processing apparatus used for forming a low dielectric constant insulating film of the present invention;  
         [0025]      FIG. 2  is a perspective view partly in section of a slot plate shown in  FIG. 1 ;  
         [0026]      FIG. 3A  to  FIG. 3C  are cross-sectional views of an insulating film, showing processes for forming the low dielectric constant insulation film according to one embodiment of the present invention,  FIG. 3A  showing a substrate before being processed,  FIG. 3B  showing a state in which a coating film is formed on the substrate, and  FIG. 3C  showing a state in which the insulating film is formed by curing the coating film;  
         [0027]      FIG. 4A  is a view showing a molecular structure of the insulating film before being cured and  FIG. 4B  is a view showing a molecular structure of the insulating film cured by the plasma substrate processing apparatus;  
         [0028]      FIG. 5  is a chart showing the correlation between curing time and dielectric constant in curing in the embodiment of the present invention and in conventional curing using an electron beam;  
         [0029]      FIG. 6  is a chart showing the correlation between curing time and modulus of elasticity in the curing in the embodiment of the present invention and in the conventional curing using the electron beam;  
         [0030]      FIG. 7A  is a table showing, for comparison, concrete experiment results of curing in another embodiment of the present invention and in conventional curing using a furnace,  FIG. 7B  is a table showing, for comparison, concrete experiment results of the curing in the other embodiment of the present invention and the curing using the electron beam, and  FIG. 7C  is a table showing, for comparison, concrete experiment results of the curing in the other embodiment of the present invention and the curing using the electron beam;  
         [0031]      FIG. 8  is a chart showing changes in dielectric constant and modulus of elasticity when a mixture ratio of hydrogen gas is varied in the embodiment of the present invention;  
         [0032]      FIG. 9  is a chart showing a change in methyl residual ratio when the mixture ratio of the hydrogen gas is varied in the embodiment of the present invention;  
         [0033]      FIG. 10  is a chart showing changes in dielectric constant and modulus of elasticity when process pressure is varied in the embodiment of the present invention; and  
         [0034]      FIG. 11  is a chart showing a change in methyl residual ratio when the process pressure is varied in the embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0035]     Hereinafter, embodiments of the present invention will be described with reference to the drawings.  FIG. 1  is a cross-sectional view of a plasma substrate processing apparatus used for forming an insulating film of the present invention.  FIG. 2  is a perspective view partly in section of a slot plate shown in  FIG. 1 .  
         [0036]     As shown in  FIG. 1 , the plasma substrate processing apparatus  100  has a plasma processing chamber  101  in a cylindrical shape as a whole, with a sidewall  101   a  and a bottom portion  101   b  thereof, for example, being made of conductors such as aluminum, and an inner part of the plasma processing chamber  101  is formed as an airtight processing space S. The plasma processing chamber  101  may be formed in a box shape.  
         [0037]     This plasma processing chamber  101  houses a mounting table  102  for placing a processing target (for example, a semiconductor wafer W) on an upper surface thereof. The mounting table  102  is made of, for example, anodized aluminum or the like and formed in a substantially columnar shape. The mounting table  102  has therein a heater H for heating the wafer W when necessary. The mounting table  102  further provides lift pins  103  for lifting the wafer W.  
         [0038]     On the upper surface of the mounting table  102 , an electrostatic chuck or a clamping mechanism (not shown) for keeping the wafer W supported on the upper surface is provided. Further, the mounting table  102  is connected to a matching box (not shown) and a high-frequency power source for bias (for example, for 13.56 MHz; not shown) via a feeder (not shown). Note that in a case of CVD processing or the like, that is, when the bias is not applied, this high-frequency power source for bias need not be provided.  
         [0039]     A ceiling portion of the plasma processing chamber  101  has an opening, in which an insulating plate  104  (for example, about 20 mm in thickness) made of a ceramic dielectric such as, for example, quartz or Al 2 O 3  and transmissive for a microwave is airtightly provided via a sealing member (not shown) such as an O-ring.  
         [0040]     On an upper surface of the insulating plate  104 , a slot plate  105  functioning as an antenna is provided. The slot plate  105  has a circular conductor plate  105   a  made of, for example, a disk-shaped thin copper plate, and a large number of slots  105   b  are formed in the circular conductor plate  105   a , as shown in  FIG. 2 . Owing to these slots  105   b , uniform electric field distribution is formed for a space in the processing space S.  
         [0041]     The circular conductor plate  105   a  is constituted of a thin disk made of a conductive material, for example, silver- or gold-plated copper or aluminum. The circular conductor plate  105   a  may be in a square shape or a polygonal shape, not limited to the disk shape. In this embodiment, as the slot plate  105 , used is a RLSA (Radial Line Slot Antenna) having a plurality of pairs of slots, the slots in each pair making a T shape or perpendicularly facing each other, and these pairs being arranged for example, concentrically, circularly, or spirally.  
         [0042]     On an upper surface of the slot plate  105 , a retardation plate  106  made of a highly dielectric material, for example, quartz, Al 2 O 3 , AlN, or the like is provided to cover the slot plate  105 . The retardation plate  106 , which is sometimes called a wavelength shortening plate, lowers the propagation speed of a microwave to shorten the wavelength thereof, thereby improving propagation efficiency of the microwave emitted from the slot plate  105 .  
         [0043]     The microwave is propagated from the waveguide  107  to the slot plate  105 . The frequency of the microwave is not limited to 2.45 GHz but other frequency, for example, 8.35 GHz may be used. The microwave is generated by, for example, a microwave generator  108 . The waveguide  107  has a rectangular waveguide  114  and a coaxial waveguide  115 , and the coaxial waveguide  115  is composed of an outer conductor  115   a  and an inner conductor  115   b . The microwave generated by the microwave generator  108  is uniformly propagated to the slot plate  105  via the rectangular waveguide  114  and the coaxial waveguide  115  and is further supplied uniformly from the slot plate  105  via the insulating plate  104 .  
         [0044]     A conductive shield cover is disposed on the retardation plate  106  to cover the slot plate  105 , the retardation plate  106 , and so on. A cooling plate  112  for cooling the slot plate  105 , the retardation plate  106 , the insulating plate  104 , and so on is disposed on the shield cover, and refrigerant paths  113  for cooling these members are provided inside the cooling plate  112  and the sidewall  101   a . The cooling plate  112  has an effect of preventing thermal deformation and breakage of the slot plate  105 , the retardation plate  106 , and the insulating plate  104  for stable plasma generation.  
         [0045]     In the sidewall  101   a  of the aforesaid plasma processing chamber  101 , gas supply nozzles  120  as gas supply ports for introducing rare gas such as Ar and Kr, and oxidizing gas such as O 2 , nitriding gas such as N 2 , or vapor-containing gas into the processing space S are provided at equal intervals. In the plasma substrate processing apparatus  100 , for the purpose of uniform exhaust of the atmosphere in the processing space S, a gas baffle plate  121  is disposed to be substantially perpendicular to the sidewall  101   a . The gas baffle plate  121  is supported by a supporting member  122 . Further, on inner sides (sides facing the processing space S) of the sidewall  101   a  and the gas baffle plate  121 , liners  123  made of, for example, quartz glass are disposed for preventing the occurrence of particles such as metal contamination generated from the walls due to the sputtering by ions.  
         [0046]     Gas in the atmosphere in the plasma processing chamber  101  is uniformly exhausted by an exhaust device  125  via exhaust ports  124 A,  124 B.  
         [0047]     As gas supply sources to the aforesaid gas supply nozzles  120  being the gas supply ports, an inert gas supply source  131 , a process gas supply source  132 , and a process gas supply source  133  are prepared, and these gas supply sources are connected to the gas supply nozzles  120  via inner opening/closing valves  131   a ,  132   a ,  133   a , massflow controllers  131   b ,  132   b ,  133   b , and outer opening/closing valves  131   c ,  132   c ,  133   c , respectively. Flow rates of the gases supplied from the gas supply nozzles  120  are controlled by the massflow controllers  131   b ,  132   b ,  133   b.    
         [0048]     A controller  140  controls ON-OFF and output control of the aforesaid microwave generator  108 , the flow rate adjustment by the massflow controllers  131   b ,  132   b ,  133   b , adjustment of an exhaust amount of the exhaust device  125 , the heater H of the mounting table  102 , and so on so as to allow the plasma substrate processing apparatus  100  to perform the optimum processing.  
         [0049]     This invention uses the plasma substrate processing apparatus  100  shown in  FIG. 1  to apply plasma processing to be described below, thereby curing an insulating film in a short time while keeping a low dielectric constant.  
         [0050]      FIG. 3A  to  FIG. 3C  are cross-sectional views of an insulating film, showing processes for forming the insulating film according to one embodiment of the present invention.  FIG. 4A  and  FIG. 4B  are views showing a molecular structure of the insulating film before being cured and a molecular structure of the insulating film plasma-processed by the plasma substrate processing apparatus  100 .  
         [0051]     First, a substrate  1  shown in  FIG. 3A  is prepared, the substrate  1  is coated with a low dielectric constant insulating film material by, for example, a generally-known SOD system, so that a coating film  2  is formed, as shown in  FIG. 3B . Here, the applied insulative material is a low dielectric constant insulating film such as, for example, porous MSQ (Methyl Silsesqueoxane) whose dielectric constant is, for example, 2.4 or lower. As shown in  FIG. 4A , the porous film MSQ has a structure such that one molecule is terminated with a hydroxyl bonded to Si of O—Si—O and the other molecule is terminated with a hydroxyl bonded to Si of O—Si—O, and it also includes a structure such that one molecule and the other molecule are dissociated.  
         [0052]     Next, the substrate  1  on which the coating film  2  is formed is carried into the processing space of the plasma substrate processing apparatus  100  shown in  FIG. 1  by a not-shown carrier. Then, non-mixed gas of argon (Ar), hydrogen (H 2 ), or helium (He) or mixed gas made of the combination of these is introduced into the processing space of the plasma substrate processing apparatus  100 , and at the same time, the 2.45 GHz microwave is supplied to the coaxial waveguide  115 , whereby plasma with a low electron temperature of 0.5 eV to 1.5 eV and an electron density of 10 11  to 10 13  electrons/cm 3  is generated in the processing space at a temperature of about 250° C. to about 400° C. By this high-density plasma, plasma processing is applied for curing the coating film  2 , with a processing time of, for example, five minutes or less, more preferably, one minute to two minutes, so that the coating film  2  turns to a cured insulating film  3 , as shown in  FIG. 3C .  
         [0053]     Note that the aforesaid low electron temperature was measured by a Langmuir probe in a space between the gas nozzles  120  of raw material gas and the silicon wafer W under the same condition in advance. Further, the electron temperature was also confirmed by Langmuir probe measurement.  
         [0054]     By this plasma processing, one and the other molecules adjacent to each other are bonded together as shown in  FIG. 4A  and  FIG. 4B . That is, hydrogen of the hydroxyl of one molecule shown in  FIG. 4A  is dissociated and the bond of the hydroxyl and Si of the other molecule is dissociated. Then, the dissociated hydrogen and hydroxyl are bonded into water, and this water is removed, so that intermolecular dehydration-condensation reaction takes place. By such intermolecular dehydration-condensation reaction, the Si—O—Si bond takes place as shown in  FIG. 4B . By such Si—O—Si bond, the insulating film  3  cures.  
         [0055]      FIG. 5  is a view showing the correlation between curing time and dielectric constant in curing in the embodiment of the present invention and in conventional curing using an electron beam, and  FIG. 6  is a view showing the correlation between curing time and modulus of elasticity in the curing in the embodiment of the present invention and in the conventional curing using the electron beam. In these drawings, circular marks represent the results of the conventional curing using the electron beam, and triangular marks represent the results of the plasma processing in the embodiment using the plasma substrate processing apparatus  100 .  
         [0056]     As shown in  FIG. 5 , in the curing by the electron beam, the dielectric constant is about 2.25 when the processing time is 120 seconds, and the dielectric constant becomes higher to about 2.3 when the processing time is set longer to 360 seconds. On the other hand, in this embodiment using the plasma substrate processing apparatus  100 , the dielectric constant is about 2.2 when the plasma processing time is 60 seconds, and when the plasma processing time is set longer to 300 seconds, the dielectric constant only slightly exceeds the value of 2.2 and thus no significant change is seen in the dielectric constant. When the plasma processing time is between 60 seconds and 300 seconds, the dielectric constant also keeps the value of about 2.2. The processing time is preferably 1000 seconds or less, more preferably, 600 seconds or less.  
         [0057]     That is, it is seen from  FIG. 5  that the plasma processing using the plasma substrate processing apparatus  100  can achieve a lower dielectric constant than the curing by the electron beam. Further, it is seen that the use of the plasma substrate processing apparatus  100  can keep the dielectric constant substantially the same even when the plasma processing time becomes longer, while the use of the electron beam tends to increase the dielectric constant as the curing time becomes longer.  
         [0058]     As is apparent from the correlation between modulus of elasticity and processing time shown in  FIG. 6 , in the case of using the electron beam, when the curing time is 120 seconds, modulus of elasticity is about 6 GPa, and when the curing time is 300 seconds, modulus of elasticity increases to about 8 GPa. On the other hand, in the case of using the plasma substrate processing apparatus  100 , when the plasma processing time is 60 seconds, modulus of elasticity is about 6.5 GPa, and when the plasma processing time is 360 seconds, modulus of elasticity increases to about 8.2 GPa. When the plasma processing time falls within the range from 60 seconds to 300 seconds, the value of modulus of elasticity falls within the range from 6.5 GPa to 8.2 GPa. Thus, modulus of elasticity presents an increasing tendency as the processing time becomes longer both in the case of using the electron beam and in the case of using the plasma substrate processing apparatus  100 . The processing time is preferably 60 seconds to 1000 seconds, more preferably, 60 seconds to 600 seconds.  
         [0059]     Therefore, it is confirmed from the results shown in  FIG. 5  and  FIG. 6  that the curing using the electron beam can increase modulus of elasticity but also increases the dielectric constant when the processing time is set longer. On the other hand, the plasma processing using the plasma substrate processing apparatus  100  can not only increase modulus of elasticity and but also keep the dielectric constant at the same value when the processing time is set longer. In this case, the processing time is preferably 60 seconds to 1000 seconds, more preferably, 60 seconds to 600 seconds.  
         [0060]      FIG. 7A  to  FIG. 7C  are tables showing, for comparison, concrete experiment results of curing in another embodiment using the plasma substrate processing apparatus  100  and concrete experiment results of conventional curing using a furnace and conventional curing using the electron beam. Note that a MSQ1 film is used in  FIG. 7A , while a MSQ2 film is used in  FIG. 7B  and  FIG. 7C .  
         [0061]     As shown in  FIG. 7A , as a result of the curing by the furnace under the conditions that the temperature was 420° C. and the processing time was 60 minutes, the following film quality was obtained: dielectric constant 2.16, modulus of elasticity 5.4 GPa, hardness 0.5 GPa, and methyl residual ratio (Si—Me/SiO) 0.025. On the other hand, as a result of the plasma processing using the plasma substrate processing apparatus  100  under the condition that the temperature was 350° C. and the processing time was one minute, the following film quality was obtained: dielectric constant 2.39, modulus of elasticity 6.9 GPa, hardness 0.6 Gpa, and methyl residual ratio 0.011.  
         [0062]     It is apparent from these results that the plasma processing in the embodiment using the plasma substrate processing apparatus  100  can extremely shorten the time taken for the curing, and as for the film quality, can increase modulus of elasticity and hardness, though slightly increasing a dielectric constant, compared with the conventional curing by the furnace.  
         [0063]     Further, as shown in  FIG. 7B , as a result of the curing by the electron beam under the condition that the temperature was 350° C. and the processing time was two minutes, the following film quality was obtained: dielectric constant 2.24, modulus of elasticity 5.9 GPa, and hardness 0.52 GPa. At this time, the residual ratio of a methyl group could not be confirmed. On the other hand, as a result of the plasma processing by the plasma substrate processing apparatus  100  under the condition that the temperature was 350° C. and the processing time was one minute, the following film quality was obtained: dielectric constant 2.21, modulus of elasticity 7.6 GPa, hardness 0.7 GPa, and methyl residual ratio 0.026. It is seen from these results that the dielectric constant can be made lower while the methyl group is allowed to exist.  
         [0064]     Moreover, as shown in  FIG. 7C , as a result of the curing by the electron beam under the condition that the temperature was 350° C. and the processing time was six minutes, the following film quality was obtained; dielectric constant 2.31, modulus of elasticity 8.2 GPa, and hardness 0.75 GPa. At this time, the residual ratio of the methyl group could not be confirmed. On the other hand, as a result of the plasma processing by the plasma substrate processing apparatus  100  under the condition that the temperature was 350° C. and the processing time was five minutes, the following film quality was obtained: dielectric constant 2.21, modulus of elasticity 8.6 GPa, hardness 0.8 GPa, and methyl residual ratio 0.021.  
         [0065]     It is seen from these results that the value of the dielectric constant in the conventional curing by the electron beam is substantially the same as the value of the dielectric constant in the plasma processing by the plasma substrate processing apparatus  100 , but the processing by the plasma substrate processing apparatus  100  can more increase modulus of elasticity and hardness while allowing the methyl group to remain.  
         [0066]     Next,  FIG. 8  shows changes in modulus of elasticity (GPa) and dielectric constant to. a hydrogen gas ratio when the MSQ2 film is cured by the plasma processing by the plasma substrate processing apparatus  100  while a flow rate ratio of argon gas/hydrogen gas in the process gas is varied. At this time, the temperature for processing the substrate  1  is 350°, the process pressure is 0.5 Torr, and the processing time is 60 seconds. It is seen from the results that modulus of elasticity increases from 6.0 to 7.1 GPa, while the dielectric constant keeps a low value of 2.2 even when the hydrogen gas ratio is increased up to 50 percent. Further, as for the methyl residual ratio when the processing is applied under the same conditions, the methyl residual ratio gets lower as the hydrogen gas ratio increases, and when the hydrogen gas ratio is 50%, the methyl residual ratio is 0.019, as shown in  FIG. 9 .  
         [0067]     As is seen from the above, when the curing is applied by the plasma processing by the plasma substrate processing apparatus  100 , increasing the hydrogen gas mixture ratio makes it possible to increase modulus of elasticity as film quality while keeping the low dielectric constant. More preferably, the hydrogen gas mixture ratio is 50% or lower. This is because the increase in the H 2  ratio lowers a ratio of high-energy Ar+, so that the decomposition of Si—Me is inhibited, resulting in increased hardness.  
         [0068]     For reference,  FIG. 8  and  FIG. 9  also show results obtained when non-mixed gas of helium is used as the process gas used in the plasma processing. It has been found out from these results that it is possible to obtain a still higher value for modulus of elasticity while the dielectric constant keeps the same low value as in the case of using argon gas/hydrogen gas.  
         [0069]     Next, pressure dependency was studied. Specifically, as a process gas condition, a flow rate ratio of hydrogen gas in argon gas/hydrogen gas was fixed to 10% (argon gas/hydrogen gas=1000/100 SCCM), the temperature of the substrate was set to 350°, and the processing time was set to 60 seconds. Changes in modulus of elasticity (Gpa) and dielectric constant under these conditions with the process pressure being varied from 0.1 Torr to 2.0 Torr are shown in  FIG. 10 , and a change in methyl residual ratio in the same case is shown in  FIG. 11 .  
         [0070]     From these results, it has been found out that even the processing under the increased process pressure causes no change in dielectric constant, but causes an increase in modulus of elasticity from 6.5 to 7.1 GPa. Further, as for the methyl residual ratio, it has been found out that the increase in the process pressure causes a decrease in the methyl residual ratio, but even under the process pressure of 2.0 Torr, the methyl residual ratio keeps 0.018. Therefore, the processing under the increased process pressure makes it possible to increase modulus of elasticity as film quality while keeping the low dielectric constant. The process pressure is preferably 2.0 Torr or lower. Such processing under the high pressure contributes to hardness increase of the film since the plasma mainly composed of radicals inhibits the decomposition of Si—Me in the film.  
         [0071]     Incidentally,  FIG. 10  and  FIG. 11  also show results when non-mixed gas of helium is used as the process gas in the plasma processing. It has been found out from these results that the dielectric constant is the same as in the case of hydrogen gas, but a still higher value is obtained for modulus of elasticity.  
         [0072]     Further, in this embodiment, since the use of the plasma substrate processing apparatus  100  using the microwave can produce the atmosphere at a low electron temperature, damage to the insulating film can be alleviated. Specifically, high electron temperature increases sheath bias voltage, which increases energy when electrons in the plasma are directed to the insulating film, so that the insulating film is damaged when the electrons collide with the insulating film. On the other hand, when the electron temperature is low, the energy when the electrons are directed to the insulating film gets small, which can alleviate the damage to the insulating film when the electrons collides with the insulating film and can lower the dielectric constant without lowering the methyl group residual ratio.  
         [0073]     Further, setting the curing time to five minutes or less, more preferably, one minute to two minutes makes it possible to process  20  to  30  wafers per hour, even if the transfer time of the wafers is taken into consideration, which enables improved throughput in semiconductor processing processes.  
         [0074]     In the above-described example, the plasma is generated by the microwave, but a plasma generating means (plasma source) in the present invention is not limited to any specific one. That is, besides the microwave, plasma sources such as, for example, ICP (inductively coupled plasma), ECR, a surface reflected wave, magnetron, and the like are also usable.  
         [0075]     Hitherto, the embodiment of the present invention has been described with reference to the drawings. However, the present invention is not limited to the shown embodiment. Various kinds of changes can be made to the shown embodiment within the same range as or an equivalent range to that of the present invention.  
         [0076]     The present invention is useful for forming a low dielectric constant insulating film in manufacturing processes of various kinds of semiconductor devices.