Abstract:
A method of forming an organic film disposes a substrate on which the organic film is formed in a chamber capable of reducing a pressure therein, introduces a gas including a deuterium compound or a trideuterium compound in the chamber, to generate a plasma by ionizing the gas; and etches and patterning the organic film by the plasma.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2005-32169, filed on Feb. 8, 2005, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method of processing an organic film and a method of manufacturing a semiconductor device, in which a plasma etching is used. 
     2. Related Art 
     Dry etching which uses radicals generated by plasma discharge is widely used as a method of processing a semiconductor substrate or a method of processing various thin films formed on a semiconductor substrate. 
     In a case where a trench is formed in an organic film by using a protective film pattern disposed on the organic film as a mask, if plasma etching is performed using a gas which contains hydrogen as a main component, there arises the problem that a plasma causes not negligible damage to an underlayer film exposed to the bottom part of the trench of the organic film. 
     Particularly, with miniaturization and high integration of the semiconductor device, when a dielectric film having a smaller dielectric constant than that of a silicon oxide film is used as an underlayer film, the above-described damage may easily occur. 
     Plasma etching techniques which form trenches in a silicon substrate by using a gas which contains deuterium (D 2 ) as a main component have hitherto been known. For example, see the Japanese Patent Laid-Open No. 6-84841 (page 2, FIG. 1). 
     In the plasma etching technique disclosed in the above patent document, trenches are formed in a silicon substrate by performing plasma etching using a silicon oxide film as a mask and using a gas which contains deuterium as a main component. In this technique, etching rates which are an order of magnitude higher than when hydrogen (H 2 ) gas is used are obtained. 
     However, the above patent document discloses only an example in which a silicon substrate is etched by a gas which contains deuterium as a main component. Furthermore, it neither discloses nor suggests gases other than deuterium. 
     SUMMARY OF THE INVENTION 
     A method of processing an organic film according to one embodiment of the present invention, comprising: 
     disposing a substrate on which the organic film is formed in a chamber capable of reducing a pressure therein; 
     introducing a gas including a deuterium compound or a trideuterium (that is, tritium) compound in the chamber, to generate a plasma by ionizing the gas; and 
     etching and patterning the organic film by the plasma. 
     Furthermore, a method of processing an organic film according to another embodiment of the present invention, comprising: 
     disposing a substrate on which the organic film covered by a patterned protective film is formed in a chamber capable of reducing a pressure therein; 
     introducing a gas including a deuterium compound or a trideuterium compound in the chamber, to generate a plasma by ionizing the gas; and 
     etching the organic film by the plasma by using the protective film as a mask. 
     Furthermore, a method of manufacturing a semiconductor device according to one embodiment of the present invention, comprising: 
     disposing a substrate which has a laminated film obtained by laminating an insulating film, an organic film and a patterned protective film in order in a chamber capable of reducing a pressure therein; 
     introducing a gas including a deuterium compound or a trideuterium compound in the chamber, to generate a plasma by ionizing the gas; and 
     etching the organic film by the plasma by using the protective film as a mask. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic configuration diagram of a plasma etching apparatus used in a method of processing an organic film according to the first embodiment of the present invention. 
         FIG. 2  is a sectional view which shows an example of a section structure of the unprocessed workpiece substrate  12 . 
         FIG. 3  is a sectional view which shows an example of a section structure of the processed workpiece substrate  12 . 
         FIG. 4A  is a sectional view which schematically shows a damaged region of this embodiment, and  FIG. 4B  is a sectional view which schematically shows a damaged region when plasma etching is performed using a gas which contains an ordinary hydrogen compound NH 3  in place of a deuterium compound or a trideuterium compound. 
         FIG. 5  is a sectional view which shows an example in which side wall parts of the organic film  32  are etched mainly by a D radical and an undercut region  36  is formed. 
         FIG. 6  is a sectional view which shows an undercut region  36  of the organic film  32  when plasma etching has been performed by using a gas which contains a hydrogen compound NH 3 . 
         FIG. 7  is a sectional view which shows an example in which a workpiece substrate  12  has an organic film  53  which covers a patterned dielectric film  52 . 
         FIG. 8  is a sectional view showing an example in which the organic film is etched by the generated plasma. 
         FIG. 9  is a manufacturing process diagram which shows a method of manufacturing a semiconductor device related to the second embodiment of the present invention. 
         FIG. 10  is a manufacturing process diagram subsequent to  FIG. 9 . 
         FIG. 11  is a manufacturing process diagram subsequent to  FIG. 10 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, embodiments of the present invention will be described with reference to the drawings. 
     First Embodiment 
       FIG. 1  is a schematic configuration diagram of a plasma etching apparatus used in a method of processing an organic film according to the first embodiment of the present invention. The plasma etching apparatus  10  shown in  FIG. 1  is provided with a chamber  11  capable of reducing pressure therein, a lower electrode  13  provided within the chamber  11 , a temperature adjusting mechanism  15  built in the lower electrode  13 , a workpiece substrate  12  placed on the lower electrode  13 , a focus ring  14  disposed in a manner of enclosing an outer circumferential part of the substrate  12 , a nozzle unit  16  composed of multiple nozzles which introduce an etching gas into the chamber  11 , a high-frequency power source  17  which supplies a high-frequency voltage to the lower electrode  13  in order to generate a plasma within the chamber  11 , a gas supply unit  18  which supplies an etching gas, an evacuation unit  19  which reduces the pressure within the chamber  11 , and inside observation windows  20 ,  21  which are provided on side walls of the chamber  11  and disposed opposite to each other. 
     The lower electrode  13  is a cathode electrode within the chamber  11  and the nozzle unit  16  is an anode electrode within the chamber  11 . 
     The focus ring  14  is formed of silicon, for example, as a material and controls a plasma in the outer peripheral part of the workpiece substrate  12 . 
     An etching gas is introduced into the chamber  11  from the gas supply unit  18  via the nozzle unit  16 . In this state, the inside of the chamber  11  is kept in a pressure-reduced condition by the evacuation unit  19 , and high-frequency power is supplied from the high-frequency power source  17 . This leads to generation of a plasma within the chamber  11 . 
     An etching gas is a gas which contains a deuterium compound or a trideuterium compound. An etching gas which contains a deuterium compound is made of a material which contains D 2 O, NH 2 D, NHD 2 , ND 3 , CH 3 D, CH 2 D 2 , CHD 3  or CD 4  (D denotes deuterium). An etching gas which contains a trideuterium compound is made of a material which contains T 2 O, NH 2 T, NHT 2 , NT 3 , CH 3 T, CH 2 T 2 , CHT 3  and CT 4  (T denotes trideuterium). 
     When a gas which contains a deuterium compound or a trideuterium compound is introduced into the chamber  11  and a high-frequency voltage of 100 to 5000 W is applied, with the pressure within the chamber  11  kept at 5 to 250 mTorr, for example, the gas which contains a deuterium compound or a trideuterium compound is excited and a plasma is generated under the formation of ions and radicals. 
     For example, when the deuterium compound is ND 3 , an ND 2  radical, a D radical, an ND 2  ion and a D ion are formed. 
       FIG. 2  is a sectional view which shows an example of a section structure of the unprocessed workpiece substrate  12 . The substrate of  FIG. 2  has a structure in which an underlayer film  31  formed on a silicon substrate  30 , an organic film  32  formed on the underlayer film  31 , and a patterned protective film  33  formed on the organic film  32  are laminated in order. 
     The underlayer film  31  is, for example, a silicon oxide film. The organic film  32  is, for example, a hydrocarbon film. The protective film  33  is, for example, a silicon oxide film. Upon the protective film  33  is formed a pattern having a trench-like opening  34  by the photolithography process, for example. This protective film  33  serves as a mask when plasma etching is performed for the organic film  32 . 
     The workpiece substrate  12  shown in  FIG. 2  is disposed in the chamber  11  of  FIG. 1 , and then ND 3  gas is introduced as a deuterium compound gas into the chamber  11 . When the ND 3  gas is excited by the high-frequency power source  17 , a plasma is generated in the chamber  11 , thereby generating an ND 2  ion, a D ion, an ND 2  radical and a D radical. 
       FIG. 3  is a sectional view which shows an example of a section structure of the processed workpiece substrate  12 . As shown in the figure, the organic film  32  is etched by the generated plasma via the opening  34  of the protective film  33  and a trench  35  is formed in the organic film  32 . 
     When this trench  35  reaches the underlayer film  31 , the underlayer film  31  is then irradiated with an ND 2  ion and a D ion. Therefore, during a period until the excitation by the high-frequency power source  17  is stopped, the ND 2  ion and the D ion enter the underlayer film  31  and damage occurs in the ion entry region  36  of the underlayer film  31 . 
     The entry depth of the ND 2  ion and the D ion in a region where such damage has occurred (hereinafter, referred to as a damaged region) can be measured by a SIMS (Secondary Ion Mass Spectroscopy) analysis or Auger Electron Spectroscopy. 
     For example, when ion energy is 200 to 1000 eV and the underlayer film  31  is a silicon oxide film, the entry depth of the D ion is 4 to 15 nm or so and the entry depth of the ND 2  ion is 1.5 to 4 nm or so. 
       FIG. 4A  is a sectional view which schematically shows a damaged region of this embodiment, and  FIG. 4B  is a sectional view which schematically shows a damaged region when plasma etching is performed using a gas which contains an ordinary hydrogen compound NH 3  in place of a deuterium compound or a trideuterium compound. 
     As shown in  FIG. 4A , when an ND 2  ion and a D ion are applied to the underlayer film  31 , an entry region  40  of ND 2  ion and an entry region  41  of D ion are formed. 
     Because of a mass difference between the ND 2  ion and the D ion, the velocity of the D ion with a smaller mass is higher with the same ion energy. As a result, the ND 2  ion enters up to a distance X 1 , whereas the D ion enters deeper up to a distance X 2 , causing damage to the underlayer film  31 . 
     On the other hand, as shown in  FIG. 4B , when an NH 2  ion and an H ion are applied to the underlayer film  42 , an entry region  43  of NH 2  ion and an entry region  44  of H ion are formed. 
     Because of a mass difference between the NH 2  ion and the H ion, the velocity of the H ion with a smaller mass is higher than that of the NH 2  ion when compared with the same ion energy. 
     As a result, the NH 2  ion enters up to a distance X 3 , whereas the H ion enters deeper than a distance X 4 , causing damage to the underlayer film  42 . 
     However, because the mass of the NH 2  ion is smaller than the mass of the ND 2  ion, the entry distance X 3  of the NH 2  ion becomes longer than the entry distance X 1  of the ND 2  ion. 
     Also, because the mass of the H ion is smaller than the mass of the D ion, the entry distance X 4  of the H ion is longer than the entry distance X 2  of the D ion. 
     As a result, the damaged region of the underlayer film  31  extends up to the distance X 2 , whereas the damaged region of the underlayer film  42  extends up to the distance X 4 , and the damage of the underlayer film  42  becomes larger than that of the underlayer film  31 . 
     According to experiments by the present inventor, it was ascertained that the entry distance X 2  of the D ion into the underlayer film  31  decreases to about 1/1.5 of the entry distance X 4  of the H ion into the underlayer film  42 . 
     Therefore, according to plasma etching using ND 3  gas, the depth of the damaged region of the underlayer film  31  can be reduced to about 1/1.5, compared with plasma etching using NH 3  gas. 
     Furthermore, the ND 3  gas has an etching rate of the organic film  32  which is about twice higher than the single D 2  gas. Because of this, according to this embodiment, it is possible to reduce the damage to the underlayer film  31  and to increase the etching rate. 
     While an ND 2  ion and a D ion are being applied to the underlayer film  31 , side walls of the organic film  32  removed by etching are exposed to an ND 2  radical and a D radical. Because the D radical is more active than the ND 2  radical, mainly the D radical reacts with the carbon in the organic film  32 , and carbon deuterium (CD) generated as a reaction product. Therefore, the organic film  32  is etched in a horizontal direction of the substrate, in order to form an undercut region. 
       FIG. 5  is a sectional view which shows an example in which side wall parts of the organic film  32  are etched mainly by a D radical and an undercut region  36  is formed. On the other hand,  FIG. 6  is a sectional view which shows an undercut region  36  of the organic film  32  when plasma etching has been performed by using a gas which contains a hydrogen compound NH 3 . 
     The D radical enters into the undercut region  36  with the depth X 5 . Because of a mass difference between the D radical and the H radical, the temperature of the H radical is higher than that of the D radical. Therefore, the H radical reacts easily with the organic film  32 . As a result, a large undercut with the depth X 6  is formed to generate a deeper undercut region  36  along the side wall of the trench. In other words, in order to etch the organic film  32 , the bond between atoms which constitute the organic film  32  must be cut and energy is required for this purpose. The energy depends on the temperature of a radical, and the higher the temperature is, the larger the energy becomes. Because the H radical has a higher temperature than the D radical, the H radical cuts more bonds than the D radical and a larger undercut region  36  is formed in the organic film  32 . 
     The large size of the undercut region  36  of the organic film  32  means that the widthwise dimensional accuracy of the trench is low. Therefore, the widthwise dimensional accuracy during etching is higher when plasma etching is performed by using a gas which contains a deuterium compound than when plasma etching is performed by using a gas which contains a hydrogen compound. 
     As stated above, because in the first embodiment, the organic film  32  is processed by plasma etching using a gas which contains a deuterium compound, a D ion having a lower rate than an H ion is applied to the underlayer film  31  and damage occurring in the underlayer film  31  can be reduced. Therefore, a semiconductor device which has stable device characteristics, high reliability and a high accumulation level can be realized. 
     Also, when plasma etching is performed by using a gas which contains a deuterium compound as in this embodiment, the widthwise undercut region  36  of the patterned organic film  32  can be further reduced and the widthwise dimensional accuracy during etching can be further improved. 
     In the above-described embodiment, the description has been given of an example in which ND 3  is used as a gas which contains a deuterium compound. However, the gas may contain as a deuterium compound, in place of ND 3  or along with ND 3 , at least one of D 2 O, NH 2 D, NHD 2 , CH 3 D, CH 2 D 2 , CHD 3  and CD 4 . That is, even when the gas is a deuterium compound gas in which deuterium is substituted for part of the hydrogen in a hydrogen compound gas, the gas can reduce the depth of the damaged region of the underlayer film  31  according to the substitution ratio of deuterium for hydrogen. 
     Also, the above-described embodiment has been described in the case where the underlayer film  31  and the protective film  33  are both a silicon oxide film. However, the underlayer film  31  may be a Low-k film silicon body or a silicon nitride film, and the protective film  33  may be a silicon nitride film, a silicon carbide film or a metal film. 
     Incidentally, in the above-described embodiment, the description has been given in terms of an example in which a trench is formed by removing part of the organic film  32  on the underlayer film  31  by plasma etching. However, the gas which contains the deuterium compound or the trideuterium compound can be further applied to the organic film in a case where the patterned organic film is used as a mask to perform patterning of the underlayer film  31 , and the organic film used as the mask is removed by plasma etching. 
       FIG. 7  is a sectional view which shows an example in which a workpiece substrate  12  has an organic film  53  which covers a patterned dielectric film  52 . The workpiece substrate  12  in  FIG. 7  has a structure in which an underlying film  51  formed on a silicon substrate  50 , a dielectric film  52  which functions as a underlayer film patterned on the underlying film  51 , and an organic film  53  which covers the dielectric film  52  as the mask are laminated. The organic film  53  has an opening  54 . 
     The underlying film  51  is, for example, a silicon oxide film. The dielectric film  52  is, for example, what is called a Low-k film (a low dielectric constant film) which contains, as main components, carbon (C), silicon (Si) and oxygen (O). The organic film  53  is, for example, a photoresist and is patterned beforehand. A trench  55  is formed in the dielectric film  52  by using the patterned organic film  53  as the mask. 
     When the workpiece substrate which is shown in  FIG. 7  is subjected to plasma etching by using a gas which contains a deuterium compound or a trideuterium compound as in the first embodiment (for example, ND 3  gas), as shown in  FIG. 8 , an organic film  53  is etched by a generated plasma. 
     At this time, an ND 2  radical and a D radical generated by the plasma collide against side walls  56  of the trench  55  in the dielectric film  52 , mainly the D radical reacts with the carbon in the dielectric film  52 , and damage occurs due to pullout of carbon. 
     The extent of this damage is smaller than when plasma etching is performed by using an ordinary hydrogen compound. The reason for this is that the temperature of the D radical becomes lower than the temperature of the H radical and that the energy used to cut bonds between atoms of the dielectric film is lower in the D radical. 
     Therefore, also in a case where as shown in  FIG. 7 , the organic film  53  on the dielectric film  52  is removed by plasma etching, the widthwise dimensional accuracy of the dielectric film  52  can be improved. 
     Second Embodiment 
     In a second embodiment, an opening in which interconnections of dual-damascene structure is formed is formed by plasma etching. 
       FIG. 9  is a manufacturing process diagram which shows a method of manufacturing a semiconductor device related to the second embodiment of the present invention. First, a laminated substrate in which a via hole  61  is formed is prepared. This laminated substrate has a substrate  63  in which a Cu interconnection layer  62  is formed and a laminated film  64  formed on this substrate  63 . This laminated film  64  is obtained by laminating a porous film  65 , an organic film  66  formed on the porous film  65  and a protective film  67  formed on the organic film  66 . 
     The porous film  65  is, for example, an insulating film formed from SiCOH as a material. The protective film  67  is formed of a silicon oxide film or a Low-k film as a material. The protective film  67  is used as a protective mask during plasma etching, and patterned to overlap with a via hole  61  beforehand in conformity to the shape of the organic film  66  which is removed by plasma etching. 
     In this embodiment, the laminated substrate of  FIG. 9  is disposed within the chamber  11  of  FIG. 1  and a gas which contains a deuterium compound or a trideuterium compound is introduced into the chamber  11 , whereby plasma etching is started. The pressure in the chamber  11  and the applied high-frequency voltage are similar to the first embodiment. As a result, the gas which contains a deuterium compound or a trideuterium compound is excited and a plasma is generated under the formation of ions and radicals. 
     For example, when a gas which contains a deuterium compound consisting of ND 3  is introduced into the chamber  11 , an ND 2  ion, a D ion, an ND 2  radical and a D radical are formed. 
     As shown in  FIG. 10 , the organic film  66  is etched and removed by the generated ions along the pattern shape of the protective film  67  and a trench  68  is formed. At the same time, the ions enter the top surfaces of the protective film  67 , the porous film  65  and the substrate  63 , and damage occurs in the entry region of the ions. The radicals formed by the plasmas collide against side walls of the organic film  66  and remove the side walls of the organic film  66 . 
     As described above, by performing plasma etching, damage occurs to the top surfaces of the protective film  67 , porous film  65  and substrate  63  and an undercut region  69  is formed on the side walls of the organic film  66 . 
     Because in this embodiment a gas which contains a deuterium compound or a trideuterium compound is introduced into the chamber  11 , the damage given to the protective film  67 , the porous film  65  and the substrate  63  can be reduced compared with a case where a gas which contains a ordinary hydrogen compound is introduced. As a result of this, device characteristics become stable and a semiconductor device having high reliability can be obtained. Although the undercut region  69  is formed by the generated radicals on the side walls of the organic film  66 , the size of the undercut region  69  can be reduced compared with a case where a gas which contains a usual hydrogen compound is used, and the widthwise dimensional accuracy of the trench  68  can be improved. 
     Next, as shown in  FIG. 11 , Cu  70  is filled in the inside of the via hole  61  and the trench  68  formed by plasma etching. After that, if necessary, the surface is polished by a required amount by CMP (Chemical Mechanical Polishing), to form the interconnection of the dual-damascene structure. 
     Although  FIG. 9  shows an example in which the via hole  61  is formed beforehand in the laminated film  64 , the via hole  61  is not always necessary and part of the organic film  66  on a porous film  65  with no via hole  61  may be removed by etching. 
     As described above, in the second embodiment, the organic film  66  is subjected to plasma etching by introducing a gas which contains a deuterium compound or a trideuterium compound into the chamber  11  for the purpose of forming an interconnection embedding region in the laminated film  64  constituted by the porous film  65 , the organic film  66  and the protective film  67 . Therefore, it is possible to form the opening excellent in dimensional accuracy while reducing the damage caused to the porous film  65 , the organic film  66  and the protective film  67 .