Patent Publication Number: US-2002009881-A1

Title: Conductor member formation and pattern formation methods

Description:
[0001] This patent application claims priority based on a Japanese patent application, 2000-210285 filed on Jul. 11, 2000, the contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002] 1. Field of the Invention  
       [0003] The present invention relates to a conductor member formation method and a pattern formation method. In particular, the present invention relates to a conductor member formation method using a plurality of mask layers to form a fine conductor member.  
       [0004] 2. Description of the Related Art  
       [0005]FIG. 1 shows an intermediate process of a conventional conductor member formation method. According to this method, in order to form a conductor member  14 , a resist  12  is first coated on a base material  10 . A prescribed pattern is then formed by exposing and developing the resist  12 . Next, using the resist  12  as a mask, a conductor member  14  is deposited via sputtering or the like. The conductor member  14  deposited on the resist  12  is partially removed by gradually removing the resist  12  using a liquid developer so that the conductor member  14  will remain only on the prescribed region of the base material  10 . As shown in FIG. 1( a ), an opening  16  which extends in the direction of the exposure direction can be formed by controlling an exposure parameter when the resist  12  is exposed.  
       [0006] As miniaturization of semiconductor devices has progressed in recent years, an exposure system that uses an electron beam has started to be used in order to form conductor members such as electrodes and wires to be installed on semiconductor devices. In this exposure system, an electron beam resist is used. However, when an electron beam is irradiated onto an electron beam resist, the energy of the electron beam causes the top layer of the electron beam resist to melt down. As a result, as shown in FIG. 1( b ), an opening part, which narrows down in the direction of the electron beam irradiation or is substantially vertically shaped, is formed. Therefore, forming an opening part which extends in width in the direction of the electron beam irradiation as shown in FIG. 1( a ) is very difficult.  
       [0007] When a conductor member  14  is formed via sputtering or the like using a resist  12  for a mask which has an opening part that is substantially vertically shaped or narrows down in the direction of the electron beam irradiation, the portion of the conductor member  14  deposited on the base material  10  comes in contact with the portion of the conductor member  14  deposited on the resist  12  as shown in FIG. 1( b ). In this case, it is very difficult to form a conductor member  14  having a prescribed shape on the base material  10  by removing the resist  12 . Moreover, the thickness of the conductor member  14  to be formed on the base material  10  is restricted by the thickness of the resist  12 . Since the thickness of the electron beam resist  12  needs to be made sufficiently small, it has been very difficult to form a thick conductor member  14 .  
       SUMMARY OF THE INVENTION  
       [0008] Therefore, it is an object of the present invention to provide conductor formation methods and pattern formation methods which overcome the above issues in the related art. This object is achieved by combinations described in the independent claims. The dependent claims define further advantageous and exemplary combinations of the present invention.  
       [0009] According to the first aspect of the present invention, a conductor member formation method having a process for forming a first film on a base material, a process for forming on the first film a second film which is etched more slowly than the first film by a prescribed etchant, a process for forming a first opening part on the second film so that the second film will have a prescribed pattern, a process for forming a hole part on the first film by removing a first portion of the first film beneath the bottom of the first opening part and a second portion of the first film which forms adjacent to the first portion of the first film using a prescribed etchant, a process for forming a hole part which penetrates through the first film, a process for forming a conductor member inside the hole part on a portion of the base material, and a process for removing the first film and the second film. In this case, a process for removing the first and second films after the conductor member has been formed in the hole part may be added.  
       [0010] Moreover, it is preferable that the process for forming the second film will include a process for coating an electron resist, which reacts to an irradiated electron beam, onto the first film, and the process for forming the first opening part include a process for exposing the electron beam resist and a process for developing the electron beam resist. It is further preferable that the process for forming the first film include a process of forming a film that reacts to an electron beam less than the electron beam resist.  
       [0011] Further, a process for removing a portion of the surface layer of the base material may be added. Moreover, the process of removing a portion of the surface layer of the base material may contain a process for removing a first portion of the surface layer of the base material which is beneath the bottom of the hole part, and a second portion of the surface layer of the base material which is adjacent to the first portion of the surface layer of the base material.  
       [0012] Moreover, the process for forming a hole part may contain a process for forming a second opening part on the first film by removing at least the first portion of the first film that lies beneath the bottom of the first opening part, a process for removing a portion of the surface layer of the base material, and a process for creating a hole part by removing a portion of the first film which is in the neighborhood of the second opening part. Moreover, the process for removing a portion of the surface layer of the base material may contain a process for removing a first portion of the surface layer of the base material which is beneath the bottom of the second opening part and a second portion of the surface layer of the base material which forms an adjacent region of the first portion of the surface layer.  
       [0013] Moreover, the process for forming a second opening part may contain a process for removing at least a portion of the first film beneath the bottom of the first opening part via an anisotropic etching.  
       [0014] According to the second aspect of the present invention, a pattern formation method having a process for forming a film on a base material, a process for forming an electron beam resist, which reacts to an irradiated electron beam, on the film, a process for forming an opening part on the electron beam resist by exposing and developing the electron beam resist so that the electron beam resist will have a prescribed pattern, and a process for forming a hole part on the film by removing a first portion of the film beneath the bottom of the opening part and a second portion of the film which is adjacent to the first portion of the film.  
       [0015] It should be noted here that the summary of the invention described above does not list all the characteristics of the present invention. Sub combinations of these characteristics are also included in the technical range of application of the present invention. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0016]FIG. 1 shows an intermediate process of the conventional conductor member formation method.  
     [0017]FIG. 2 shows a conductor member formation method according to an embodiment of the present invention.  
     [0018]FIG. 3 shows another embodiment of the conductor member formation method according to the present invention.  
     [0019]FIG. 4 shows yet another embodiment of the conductor member formation method according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0020] In what follows, the present invention will be explained with embodiments of the present invention. However, the following embodiments do not restrict the scope of the invention described in the claims. Moreover, not all the combinations of the characteristics of the present invention described in the embodiments are essential to the problem solving means by the present invention.  
     [0021]FIG. 2 shows a conductor member formation method according to an embodiment of the present invention. First, as shown in FIG. 2( a ), a base material  100  is prepared.  
     [0022]FIG. 2( b ) shows a process for forming a first film  106  and a process for forming a second film  108 . It is desirable that the first film  106  be formed using a material that is hard to remove when a portion of the second film  108  is removed in the process of forming a first opening that is to be discussed later. To be specific, it is desirable that a material for forming the first film  106  be selected appropriately so that the first film  106  will be etched significantly more slowly than the second film  108  by the etchant to be used for removing the second film  108 , such as a liquid developer, an etching solution, or an etching gas. Moreover, in the process of forming a hole part to be discussed later, it is desirable that an appropriate material for forming the first film  106  be selected  80  that the first film  106  will be etched significantly faster than the second film  106  by an etchant to be used for removing a portion of the first film  106 , such as a liquid developer, an etching solution, or an etching gas. The first film  106  may be formed using a material having a degree of adhesion to the base material  100  higher than the degree of adhesion of the second film  108  to the first film  106 . In the present embodiment, the first film  106  is formed using an organic material containing cyclopentanon (C 5 H 8 O). It is desirable that at least 90% of the organic material be constituted of cyclopentanon (C 5 H 8 O).  
     [0023] In the case the second film  108  is formed using a material such as a resist, which is photo-sensitive to a light source having a prescribed wavelength, it is desirable that a material for forming the first film  106  be suitably selected so that it has a lower photo-sensitivity to the light source than the material used for forming the second film  108 . It is further desirable that a material for forming the first film  106  be suitably selected so that, when the second film  108  is developed using a liquid developer, the first film  106  will be removed by the liquid developer at a rate significantly slower than the rate at which the region on which the first opening part is to be formed is removed, where the region refers to either the portion of the second film  108  exposed to the light source or the remaining portion of the second film  108  not exposed to the light source.  
     [0024] In the present embodiment, the first film  106  is formed in the following process using a material that is significantly less prone to react to an electron beam, i.e., to a lower degree, than the material used to form the second film  108  and is also soluble to a prescribed liquid developer. First, a precursor, which is a material for forming the first film  106 , is coated on the base material  100  via spin-coat method. The precursor is deposited on the base material  100 , for example, by coating the precursor onto the base material  100  while rotating the base material  100  at a rate between 1000 and 3000 rotations per minute for a length of time between 60 seconds and 180 seconds. In this case, it is preferable that the first film  106  (precursor) be deposited to a thickness between 50 nm and 300 nm (nanometer). It is further preferable that the first film  106  (precursor) be deposited to a thickness between 100 nm and 200 nm. Next, by heat-processing (baking) the precursor for 5 minutes at the temperature of 160° C. using a hot plate, the first film  106  is formed on the base material  100 .  
     [0025] The second film  108  is formed on the first film  106 . In the present embodiment, the second film  108  is formed in the following process using an electron beam resist which reacts to an irradiated electron beam. First, an electron beam resist is coated on the first film  106  via spin-coat method. Next, the electron beam resist is baked for 3 minutes at the temperature of 120° C. using a hot plate to form a second film  108  on the first film  106 . The second film  108  is formed to a thickness, for example, between 200 nm and 1000 nm. In the case the first film  106  is also formed using a resist, the first film  106  may be formed by coating the resist onto the base material  100  several times.  
     [0026] The first film  106  and/or the second film  108  may be formed, for example, using an inorganic material such as silicon oxide, silicon nitride, or the like. Moreover, the first film  106  and/or the second film  108  may be formed using a semiconductor, a metallic material, or the like. In this case also, it is desirable that the first film  106  be formed using a material that is etched faster than the second film  108  by a prescribed etchant when forming a hole part in the first film  106 .  
     [0027]FIG. 2( c ) shows a process for forming the first opening part  110 . The first opening part  110  is formed by removing a portion of the second film  108 . For example, in the case the second film  108  has photo-sensitivity, the first opening part  110  maybe formed by exposing and developing the second film  108 . In this case, it is desirable that the diameter and/or width of the first opening part  110  be between 50 nm and 250 nm. In the present embodiment, the first opening part  110  is formed by the following process. First, using an electron beam exposure apparatus, an electron beam is irradiated onto a prescribed region of the second film  108  which is an electron beam resist. In this case, in the process to be discussed later, when the region on which a conductor member is to be formed on the base material  100  is narrower than the region on which the conductor member is not to be formed, it is desirable that the electron beam resist forming the second film  108  be a positive type. By forming the second film  108  using a positive type electron beam resist, the length of time for exposing the electron beam can be shortened by a significant degree.  
     [0028] Next, the first opening part  110  is formed on the second film  108  so that the second film  108  will have a prescribed pattern by removing the region of the electron beam resist on which an electron beam has been irradiated. In this case, the first opening part  110  maybe formed substantially vertical to the plane on which the first film  106  contacts the base material  100 . Alternatively, the first opening part  110  may be formed so as to extend in the direction from the second film  108  to the base material  100 .  
     [0029]FIG. 2( d ) shows a process for forming the hole part  112 . It is desirable that the hole part  112  be formed by removing a first portion of the first film  106  which lies at the bottom of the first opening part  110  and a second portion of the first film  106  which constitutes an adjacent neighborhood of the first portion of the first film  106 . To be specific, it is desirable that the hole part  112  be formed by removing a portion of the first film  106  in such a manner that the second film  108  forms a hood.  
     [0030] It is desirable that the hole part  112  be formed by a removing method which selectively removes the first film  106 . To be specific, the hole part  112  may he formed using an etchant which etches the second film  108  more slowly than the first film  106 . In the present embodiment, the hole part  112  is formed using a liquid developer by removing a first portion of the first film  106  that lies at the bottom of the first opening part  110  and a second portion of the first film  106  which constitutes an adjacent neighborhood of the first portion of the first film  106 . It is preferable that the liquid developer be able to develop (remove) the first film  106  selectively. For example, a weak alkaline liquid developer may be used.  
     [0031] In the process of forming the hole part  112 , the size of the hole part  112  can be controlled by controlling the length of time for etching the first film  106 . Alternatively, the size of the hole part  112  may be controlled by controlling the concentration of the etchant.  
     [0032]FIG. 2( e ) shows a process for forming a conductor member  114 . The conductor member  114  is formed by depositing a conductive material. In the present embodiment, the conductor member  114  is formed by vapor-depositing a conductive material. More specifically, a conductor member  114   a  is formed when the conductive material passes through the opening part  110  and the hole part  112  and reaches the base material  100 , and the conductive material deposited on the second film  108  forms a conductor member  114   b . In this case, it is desirable that the conductor member  114   a  be formed to a thickness between 100 nm and 500 nm.  
     [0033] In the process of forming the conductor member  114 , the second film  108  and the first film  106  serve as hoods. Therefore, the conductor member  114  is unlikely to adhere to the interior wall of the hole part  112  which constitutes the side wall of the first film  106 . As a consequence, the conductor member  114   a  can be formed in such a manner that the conductor member  114   a  will not come in contact with the conductor member  114   b . Moreover, even in the case the film thickness of the conductor member  114  is large, by increasing the thickness of the first film  116 , the conductor member  114   a  can be formed in such a manner that the conductor member  114   a  will not come in contact with the conductor member  114   b.    
     [0034]FIG. 2( f ) shows a process for removing the first film  106  and the second film  108 . By removing the first film  106  and the second film  108 , the conductor member  114   b  is removed (lifted off). As a result, only the conductor member  114   a  remains on the base material  100 . It is desirable that the first film  106  and the second film  108  be removed using an etchant capable of dissolving both the first film  106  and the second film  108 . In the present embodiment, the first film  106  and the second film  108  are removed using a liquid developer capable of dissolving both the first film  106  and the second film  108 . In another embodiment, the conductor member  114   b  may be removed by removing only the second film  108 . In this case, an insulating film or a metal film may be further deposited on the first film  106 . Alternatively, the conductor member  114   b  may be used as another wire without removing the first film  106  and the second film  108 .  
     [0035]FIG. 3 shows another embodiment of the present invention. FIG. 3( a ) shows a state in which a hole part  112  has been formed via the process that has been explained with reference to FIGS.  2 ( a ) through ( d ). In the present embodiment, the base material  100  has a first layer  102  and a second layer  104 .  
     [0036]FIG. 3( b ) shows a process for removing a portion of the surface layer of the base material  100 . It is desirable that a portion of the surface layer of the base material  100  be removed using the first film  106  as a mask. In the case the base material  100  has several layers, the layer adjacent to the first film  106  may be removed. In the present embodiment, a portion of the second layer  104 , which is part of the surface layer of the base material  100 , is removed via wet etching. To be specific, a first portion of the second layer  104 , which is at the bottom of the hole part  112  and is part of the surface layer of the base material  100 , and a second portion of the second layer  104  which constitutes an adjacent neighborhood of the first portion of the second layer  104  are removed via wet etching.  
     [0037] In the process of forming a hole part  112 , a first portion of the first film  106 , which lies directly beneath the bottom of the opening part  110  (note FIG. 2( c )), and a second portion of the first film  106 , which constitutes an adjacent neighborhood of the first portion of the first film  106 , are removed. As shown in FIG. 2( c ) and FIGS.  3 ( a ) and ( b ), in the process of removing a portion of the second layer  104  which forms the surface layer of the base material  100 , the range of removal of the second layer  104  can be controlled by controlling the amount of removal of the second portion of the first film  106  in the process of forming a hole part  112 . Moreover, in the process of removing a portion of the second layer  104  (the surface layer) of the base material  100 , by controlling the length of time the portion of the second layer  104  is etched, the range of removal of the second layer  104  can be controlled.  
     [0038]FIG. 3( c ) shows a process for forming a conductor member  114 . A conductor member  114  is formed by depositing a conductive material. In the present embodiment, a conductor member  114  is formed by vapor-depositing a conductive material. More specifically, a conductor member  114   a  is formed when the conductive material passes through the opening part  110  and the hole part  112  and reaches the first layer  102  of the base material  100 , and the conductive material deposited on the second film  108  forms a conductor member  114   b.    
     [0039]FIG. 3( d ) shows a process for removing the first film  106  and the second film  108 . By removing the first film  106  and the second film  108 , the conductor member  114   b  is removed (lifted off). As a result, only the conductor member  114   a  remains on the first layer  102  of the base material  100 . It is desirable that the first film  106  and the second film  108  be removed using an etchant capable of dissolving both the first film  106  and the second film  108 . In the present embodiment, the first film  106  and the second film  108  are removed using a liquid developer capable of dissolving both the first film  106  and the second film  108 .  
     [0040] A high electron mobility transistor (HEMT) having a first layer  102 , which serves as a carrier supply layer, and a second layer  104 , which serves as a cap layer of the carrier supply first layer  102 , may be used for the base material  100 . A gate electrode formed on the HEMT may constitute the conductor member  114   a . In this case, it is desirable that a source electrode and/or drain electrode be formed on the top layer of the first layer  102  or second layer  104 .  
     [0041]FIG. 4 shows another embodiment of the conductor member formation method of the present invention. FIG. 4( a ) shows a state in which a first opening part  110  has been formed through the processes that have been explained with reference to FIGS.  2 ( a ) through ( c ). In the present embodiment, the base material  100  has a first layer  102  and a second layer  104 .  
     [0042]FIG. 4( b ) shows a process for forming a second opening part  116 . It is desirable that the second opening part  116  be formed by removing at least the portion of the first layer  106  that lies at the bottom of the first opening part  110 . Moreover, it is desirable that the second opening part  116  be formed via an anisotropic etching. In the present embodiment, the second opening part  116  is formed via an anisotropic etching by removing at least the portion of the first layer  106  that lies at the bottom of the first opening part  110 . It is desirable that the width of the second opening part  116  be less than or substantially equal to the width of the first opening part  110 . Alternatively, the second opening part  116  may be formed via an anisotropic etching in such a manner that its width will decrease in the direction of the etching process.  
     [0043]FIG. 4( c ) shows a process for removing a portion of the surface layer of the base material  100 . It is desirable to remove a portion of the surface layer of the base material  100  using the first film  106  as a mask. In the case the base material  100  has several layers, the layer adjacent to the first film  106  may be removed. In the present embodiment, a portion of the second layer  104 , which constitutes the surface layer of the base material  100 , is removed via wet etching. To be specific, the first portion of the second layer  104  beneath the bottom of the second opening part  116 , which is part of the surface layer of the base material  100 , and a second portion of the first film  106 , which is an adjacent neighborhood of the above-mentioned first portion of the first film  106 , are removed via wet etching. In this case, it is preferable to use an etchant which etches the second layer  104  sufficiently faster than the first layer  102 .  
     [0044] In the process of forming the second opening part  116 , the second opening part  116  is created by removing a portion of the first film  106  via an anisotropic etching. As a result, in the process of removing a portion of the surface layer of the base material  100 , the portion of the second layer  104 , which is to be removed, can be made narrow. Moreover, in FIG. 4( c ), the region of the second layer  104  damaged by the anisotropic etching can be removed.  
     [0045]FIG. 4( d ) shows a process for forming a hole part  112 . It is desirable that the hole part  112  be formed by removing a side wall portion of the first film  106  which surrounds the second opening part  116 . More specifically, it is desirable to form the hole part  112  by removing a side wall portion of the first film  106  in such a manner that the second film  108  serves as a hood over the hole part  112 .  
     [0046] It is desirable that the hole part  112  be formed via an etching method by which the first film  106  can be selectively removed. To be specific, the hole part  112  may be formed using an etchant which etches the first film  106  sufficiently faster than the second film  108 . In the present embodiment, the hole part  112  is formed using a liquid developer by first removing a first portion of the first film  106  which lies beneath the bottom of the first opening part  110  (note FIG. 2( b )) and then further removing a second portion of first film  106  adjacent to the above-mentioned first portion of the first film  106  (note FIG. 2( d )). In this case, it is preferable to use a liquid developer that is able to selectively develop (remove) the first film  106 . For example, a weakly alkaline liquid developer may be used.  
     [0047]FIG. 4( e ) shows a process for forming a conductor member  114 . The conductor member  114  is formed by depositing a conductive material. In the present embodiment, the conductor member  114  is deposited by vapor-depositing a conductive material. More specifically, a conductor member  114   a  is formed when the conductive material passes through the opening part  110  and the hole part  112  and reaches the first layer  102  of the base material  100 , and the conductive material deposited on the second film  108  forms a conductor member  114   b.    
     [0048]FIG. 4( f ) shows a process for removing the first film  106  and the second film  108 . By removing the first film  106  and the second film  108 , the conductor member  114   b  is removed (lifted off). As a result, only the conductor member  114   a  remains on the first layer  102  of the base material  100 . It is preferable that the first film  106  and the second film  108  be removed using an etchant capable of dissolving both the first film  106  and the second film  108 . In the present embodiment, the first film  106  and the second film  108  are removed using a liquid developer capable of dissolving both the first film  106  and the second film  108 .  
     [0049] In the present embodiment, for example, a HEMT having a first layer  102 , which serves as a carrier supply layer, and a second layer  104 , which serves as a cap layer of the carrier supply first layer  102  may be used for the base material  100 . A gate electrode formed on the HEMT may constitute the conductor member  114   a . In this case, it is desirable that a source electrode and/or drain electrode be formed on the upper layer of the first layer  102  or second layer  104 . Moreover, the base material  100  maybe a portion of a photo conductor. In this case, it is preferable that the conductor member  114   a  be formed in the shape of a comb on the base material  100 .  
     [0050] In the process of forming a second opening part  116 , the second opening part  116  is formed by removing a portion of the first film  106  via an anisotrpic etching. As a result, in the process of removing a portion of the base material  100 , the area of the region of the second layer  104  to be removed, which is the region of the surface layer of the base material  100  to be removed, can be controlled. By controlling the area of the region of the second layer  104  to be removed, the distance between the drain and the source can be controlled. As a consequence, characteristics of the HEMT such as the gate voltage and the drain current can be controlled. Moreover, in the case a device having a conductor member such as a HEMT is installed on a wafer, the degree of formation accuracy of the conductor member within the wafer can be significantly improved.  
     [0051] As explained above, according to the present invention, a fine pattern can be formed.  
     [0052] Although the present invention has been described by way of exemplary embodiments, it should be understood that many changes and substitutions may be made by those skilled in the art without departing from the spirit and the scope of the present invention which is defined only by the appended claims.