Abstract:
An electron beam generating device, wherein a high-resistance film is formed on the outer surface of an insulator provided with a cathode for emitting thermal electrons and a grid for collecting thermal electrons and forming an electron beam to allow a feeble current to flow to the high-resistance film, thereby preventing the accumulation of thermal electrons on the insulator and discharging. The upper portion of the high-resistance film connected to a chamber supplies an approximate reference potential to the upper portion of the film, and the lower portion of the high-resistance film connected to the grid supplies almost the same potential as that of the grid to the lower portion of the film to allow a feeble current to flow to the film. The prevention of accumulation of thermal electrons on the insulator can prevent discharging, accurately control the current capacity of an electron beam, and give the electron beam generating device a longer service life.

Description:
The present application is a continuation application of PCT/JP01/10020 filed on Nov. 16, 2001, claiming priority from a Japanese patent application No. 2000-360076 filed on Nov. 27, 2000, the contents of which are incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an electron beam exposure apparatus and an electron beam generating device for exposing a wafer by an electron beam. More particularly, it relates to an electron beam exposure apparatus and an electron beam generating device which prevents electric discharge between an insulator, on which an electron gun is mounted, and ground potential. 
   2. Description of Related Art 
   With miniaturization of semiconductor devices in recent years, improvement in irradiation uniformity of an electron beam in an electron beam exposure apparatus is required. The irradiation uniformity of the electron beam is deteriorated by change of potential difference between a cathode and a grid in the electron beam exposure apparatus, exhaustion of the cathode, etc. Conventionally, the potential difference between the cathode and the grid is adjusted by an element called self-bias resistance. 
   On the other hand, since there is no effective remedy for preventing the exhaustion of the cathode, it has been desired to extend the service life of the cathode. The cause of the cathode exhaustion greatly originates in decreasing of the degree of vacuum in the vacuum area of the electron beam exposure apparatus due to, for example, the electric discharge in the vicinity of the electron beam generating device. Discharge gas is generated in an electric discharge path by the energy release during the electric discharge, the discharge gas is ionized by the electron beam, and the cathode is spattered with the ionized discharge gas, by which the cathode is exhausted. 
   In the conventional electron beam exposure apparatus, thermal electrons emitted from cathode are accumulated in an insulating part of an insulator, the electric discharge occurs by the accumulated thermal electrons, and the degree of vacuum of the vacuum area is decreased. The electric discharge on the surface of the insulator generates the great amount of the discharge gas, and degrades the degree of vacuum more than an order of magnitude. Moreover, due to the electric discharge on the surface of the insulator, the acceleration voltage for accelerating the thermal electrons emitted from the cathode in the direction of the wafer is fluctuated, the current of the electron beam is also fluctuated, and accuracy of the wafer exposure was degraded. 
   SUMMARY OF THE INVENTION 
   Therefore, it is an object of the present invention to provide a testing device which can solve the foregoing problem. The above and other objects can be achieved by combinations described in the independent claims. The dependent claims define further advantageous and exemplary combinations of the present invention. 
   According to the first aspect of the present invention, there is provided an electron beam generating device for generating an electron beam. The electron beam generating device includes: a cathode for generating thermal electrons; a cathode voltage source for applying negative voltage to the cathode so that the thermal electrons are emitted from the cathode; a grid for collecting the thermal electrons emitted from the cathode and forming the electron beam; a grid voltage source for applying negative voltage to the grid, the potential of the grid being lower than that of the cathode; and an insulator for insulating the cathode voltage source and the grid voltage source from the thermal electrons generated by the cathode. At least a part of outer surface of the insulator is covered with high-resistance film. 
   In the first aspect of the present invention, it is preferable that the outer surface of the insulator is covered with the high-resistance film or conductor. Moreover, it is preferable that an upper portion of the high-resistance film electrically connects with a reference potential unit having reference potential. Moreover, it is preferable that a lower portion of the high-resistance film electrically connects with the grid. Moreover, the insulator may include a first electrode on the outer surface, the first electrode being electrically connected to the reference potential unit, and the upper portion of the high-resistance film may be electrically connected to the first electrode. Moreover, the insulator may include a second electrode on the outer surface, the second electrode being electrically connected to the grid, and the lower portion of the high-resistance film may be electrically connected to the second electrode. Moreover, the high-resistance film of the insulator may include metal oxide. The metal oxide may be indium oxide. 
   According to the second aspect of the present invention, there is provided an electron beam exposure apparatus for exposing a wafer by an electron beam. The electron beam exposure apparatus includes: an electron beam generating device for generating the electron beam; a deflector for deflecting the electron beam to a predetermined position on the wafer; and a stage for supporting the wafer. The electron beam generating device includes: a cathode for generating thermal electrons; a cathode voltage source for applying negative voltage to the cathode so that the thermal electrons are emitted from the cathode; a grid for collecting the thermal electrons emitted from the cathode and forming the electron beam; a grid voltage source for applying negative voltage to the grid, the potential of the grid being lower than that of the cathode; and an insulator for insulating the cathode voltage source and the grid voltage source from the thermal electrons generated by the cathode. At least a part of outer surface of the insulator is covered with high-resistance film. 
   In the second aspect of the present invention, The electron beam exposure apparatus may further include: a chamber for storing the electron beam generating device, the deflector, and the stage; and a pressure reduction means for reducing pressure inside the chamber. A vacuum area, which is an area evacuated by the pressure reduction means, in the chamber may be surrounded with the high-resistance film or a conductor. An upper portion of the high-resistance film may electrically connect with the chamber. 
   The summary of the invention does not necessarily describe all necessary features of the present invention. The present invention may also be a sub-combination of the features described above. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a configuration of the electron beam exposure apparatus according to an embodiment of the present invention. 
       FIG. 2  is a drawing exemplary showing a configuration of an electron beam generating device. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The invention will now be described based on the preferred embodiments, which do not intend to limit the scope of the present invention, but exemplify the invention. All of the features and the combinations thereof described in the embodiment are not necessarily essential to the invention. 
     FIG. 1  shows a configuration of the electron beam exposure apparatus  300  according to an embodiment of the present invention. The electron beam exposure apparatus  300  includes an exposure section  350  for performing a predetermined exposure processing on the wafer  392  by an electron beam, and a control system  340  for controlling operation of each component of the exposure section  350 . 
   The exposing unit  350  includes an electron optics system which includes an electron beam forming means  360  for generating a plurality of electron beams and forming cross-sectional shape of the electron beams into desired forms inside a chamber  352 , an irradiation switching means  370  for independently switching whether or not the plurality of electron beams are to be irradiated on the wafer  392 , and a wafer projection system  380  for adjusting direction and size of an image of a pattern which is transcribed on the wafer  392 . The exposing unit  350  also includes a stage section including a wafer stage  396  for supporting the wafer  392  on which the pattern is exposed, and a wafer stage drive unit for driving the wafer stage  396 . 
   The electron beam forming means  360  includes a plurality of electron beam generating apparatuses  100  for generating a plurality of electron beams, a first forming member  362  and a second forming member  372  having a plurality of apertures which form the cross-sectional shapes of the irradiated electron beams by allowing the electron beams to pass through the apertures, a first multi-axis electron lens  364  for adjusting focal points of the plurality of electron beams by independently collecting each of the plurality of electron beams, and a first forming deflector  366  and a second forming deflector  368  for independently deflecting the plurality of electron beams which have passed through the first forming member  362 . 
   Each of the electron beam generating apparatuses  100  includes: a cathode  10  for generating thermal electrons; a cathode voltage source for applying negative voltage to the cathodes  10  so that the thermal electrons are emitted from the cathodes  10 ; a grid  30  for collecting the thermal electrons emitted from the cathode  10 , and for forming the electron beam; a grid voltage source for applying negative voltage, which is lower than the voltage of the cathode  10 , to the grid  30 ; and an insulator  40  for insulating the cathode voltage source and the grid voltage source from the thermal electrons generated by the cathode  10 . At least a part of outer surface of the insulator  40  is covered with high electric resistance film. According to the present embodiment, an upper portion of the high electric resistance film connects with the chamber  352 , and the chamber  352  is grounded. A lower portion of the high electric resistance film electrically connects with the grids  30  via a field limiting flange. Negative voltage is applied to the grid  30  from the grid voltage source, and substantially the same electric potential as the grid  30  is applied to the lower portion of the high electric resistance film. Feeble current flows on the high electric resistance film by electric potential difference between the upper portion of the high electric resistance film and the lower portion of the high electric resistance film, so that accumulation of the thermal electrons emitted from the cathode  10  on a surface of the insulator  40  is avoided. 
   The exposure switching unit  370  includes a second multi-axis electron lens  374  for adjusting focal points of a plurality of electron beams by independently collecting each of a plurality of electron beams, a blanking electrode array  376  for independently switching whether or not each of the electron beams is to be irradiated on the wafer  392  by deflecting each of the plurality of electron beams independently, and an electron beam blocking unit  382 , which includes a plurality of apertures through which the electron beams pass, for blocking the electron beam deflected by the blanking electrode array  376 . In another embodiment, the blanking electrode array  376  is a blanking aperture array device. 
   The wafer projection system  380  includes a third multi-axis electron lens  378  for independently collecting each of a plurality of electron beams and decreasing irradiated cross-sectional area of the electron beams, a fourth multi-axis electron lens  384  for independently collecting each of a plurality of electron beams and adjusting a focal point of each of the electron beams, a deflecting unit  386  for independently deflecting each of the plurality of electron beams into a desired location on the wafer  392 , and a fifth multi-axis electron lens  388 , which acts as an object lens for the wafer  392 , for independently collecting each of the plurality of electron beams. 
   The control system  340  includes a general control unit  330  and an individual control unit  320 . The individual control unit  320  includes an electron beam control section  332 , a multi-axis electron lens control section  334 , a forming deflection control section  336 , a blanking electrode array control section  338 , a deflection control section  340 , and a wafer stage control section  342 . For example, the general control unit  330  is a workstation which generally controls each of the controllers included in the individual control unit  320 . 
   The electron beam control section  332  controls the electron beam generating apparatus  100 . The multi-axis electron lens control section  334  controls electric current provided to the first multi-axis electron lens  364 , the second multi-axis electron lens  374 , the third multi-axis electron lens  378 , the fourth multi-axis electron lens  384 , and the fifth multi-axis electron lens  388 . The forming deflection control section  336  controls the first forming deflector  366  and the second forming deflector  368 . The blanking electrode array control section  338  controls voltage applied to deflection electrodes of the blanking electrode array  376 . The deflection control section  344  controls voltage applied to the deflection electrodes of a plurality of deflectors of the deflecting unit  386 . The wafer stage control section  342  controls the wafer stage driver  398  so that the wafer stage  396  is caused to move to a predetermined location. 
     FIG. 2  is a drawing exemplary showing a configuration of the electron beam generating device  100 . The electron beam generating apparatus  100  includes: a cathode  10  for generating thermal electrons; a cathode voltage source  22  for applying negative voltage to the cathode  10  so that the thermal electrons are emitted from the cathodes  10 ; a grid  30  for collecting the thermal electrons emitted from the cathode  10 , and for forming the electron beam; a grid voltage source  24  for applying negative voltage, which is lower than the voltage of the cathode  10 , to the grids  30 ; an insulator  40  for insulating the cathode voltage source  22  and the grid voltage source  24  from the thermal electrons generated by the cathode  10 ; and a field limiting flange  12  for adjusting the electric field. At least a part of outer surface of the insulator  40  is covered with high-resistance film  20 . Alternatively, the insulator  40  includes the first electrode  16  on its outside, which is conductor electrically connects with a reference potential section, and the upper portion of the high-resistance film  20  electrically connected to the first electrode  16 . It is preferable that the first electrode  16  electrically connects with the reference potential through the chamber  352 . 
   Moreover, it is preferable that the lower portion of the high-resistance film  20  electrically connects with the grid  30 . For example, the insulator  40  includes a second electrode  14  on its outside, which is conductor electrically connected to the grid  30 , and the lower portion of the high-resistance film  20  electrically connects with the second electrode  14 . By applying substantially the same electric potential as that of the grid  30  to the lower portion of the high-resistance film  20  and applying the approximate reference potential to the upper portion of the high-resistance film  20 , feeble current flows between the upper portion and the lower portion of the high-resistance film  20 , and accumulation of the thermal electrons on the high-resistance film  20  is prevented. 
   The insulator  40  is fixed to the upper portion of the chamber  352 , and the thermal electrons emitted from the cathode  10  are collected by the grid  30  and irradiated on the wafer  392  as an electron beam. Since at least a part of the outer surface of the insulator  40  is covered with the high-resistance film  20  to generate the potential difference between the upper portion and the lower portion of the high-resistance film  20 , even if the thermal electrons emitted from the cathode  10  reaches the outer surface of the insulator  40 , the thermal electrons are not accumulated on the insulator  40 . 
   It is preferable that the electron beam generating apparatus  300  further includes a pressure reduction means  70  for reducing a pressure inside the chamber  352 . It is also preferable that a vacuum area  60 , where the pressure is reduced by the pressure reduction means  70 , in the chamber  352  is surrounded by the high-resistance film  20  or the conductor. That is, it is preferable that insulating material is not exposed inside the vacuum area  60  of the chamber  352 . In the present embodiment, the outer surface of the insulator  40  is covered with the high-resistance film  20  or the conductor. Moreover, it is preferable that the pressure reduction means  70  is capable of reducing the pressure of the vacuum area  60  of the chamber  352  to about 7.5×10 −11  Pascal (1×10 −8  torr). By covering the outer surface of the insulator  40  with the high-resistance film  20  or the conductor, the insulating material  18  of the insulator  40  is isolated from the vacuum area  60 , and accumulation of electric charge by the thermal electrons is prevented. 
   Moreover, it is preferable that the upper portion of the high-resistance film  20  connects with the chamber  352 . By connecting the upper portion of the high-resistance film  20  and the chamber  352 , the electric charge of the thermal electrons which reached the high-resistance film  20  flows to the reference potential through the chamber  352  before starting discharging the accumulated charges. In the present embodiment, although the upper portion of the high-resistance film  20  electrically connects with the reference potential through the chamber  352  and the first electrode, in another embodiment, the upper portion of the high-resistance film  20  electrically connects with the reference potential. 
   It is preferable that a value of resistance of the high-resistance film  20  is selected so as to prevent overload of the grid voltage source  24 . For example, when a voltage of −50 kilovolts is applied to the grid  30 , it is preferable that the resistance between the upper portion of the high-resistance film  20  and the lower portion of the high-resistance film  20  is in the neighborhood of 0.5 to 500 gigaohms. In this case, the current of about 0.1-100 microamperes flows between the upper portion and the lower portion of the high-resistance film  20 , so that the accumulation of the electric charge due to the thermal electrons on the high-resistance film  20  is prevented, and the overload of the grid voltage source  24  is also prevented. 
   It is preferable that the high-resistance film  20  includes metal oxide, such as indium oxide. In this case, the high-resistance film  20  may be hyaline material in which the indium oxide is mixed substantially evenly. By the high-resistance film  20  including the indium oxide, it is easy to manufacture the high-resistance film  20  of which the value of resistance between the upper portion of the high-resistance film  20  and the lower portion of the high-resistance film  20  is in the neighborhood of 0.5 to 500 gigaohms. 
   Moreover, in the present embodiment, while the lower portion of the high-resistance film  20  electrically connects with the grid  30  and the electric potential of the high-resistance film  20  is substantially the same as that of the grid  30 , the cathode voltage source  22  or a grid voltage source  24  applies the electric potential to the lower portion of the high-resistance film  20  which is different from the reference potential in another embodiment. In this case, it is preferable that the electric potential applied to the lower portion of the high-resistance film  20  is substantially same as that of the cathode  10  or a grid  30 . In yet another embodiment, the electron beam generating device  100  further includes a voltage source for applying electric potential, which is different from the reference potential, to the lower portion of the high-resistance film  20 . 
   Height of the field limiting flange  12  is substantially the same as that of the grid  30  in the electron beam irradiation direction. Moreover, it is preferable that the field limiting flange  12  is formed so that it projects into a direction of the first electrode more than the surface on which the cathode  10  and the grid  30  of the insulator  40  are provided. The field limiting flange  12  moderates change of the electric field in the vicinity of the insulator  40 , prevents concentration of equipotential lines in the vicinity of the insulator  40 , and prevents the electric discharge. The field limiting flange  12  is constructed from conductor, and electrically connects with the grid  30 , and has substantially the same electric potential as that of the grid  30 . The field limiting ring  12  electrically connects with the lower portion of the high-resistance film  20  or the second electrode  14 , and applies substantially the same electric potential as that of the grid  30  to the lower portion of the high-resistance film  20  or the second electrode  14 . 
   Alternatively, the insulator  40  includes a terminal for connecting the cathode  10  and the cathode voltage source  22 , and a terminal for connecting the grid  30  and the grid voltage source  24 . The terminals are filled up with high melting point wax material in order to maintain the sealing between the vacuum area  60  of the chamber  352  and a high-pressure area  50 . Alternatively, the terminals and the exposed surface of the high melting point wax material are covered with oxidation-resistant film, such as golden paste. In this case, the oxidation-resistant film is formed on the insulator  40 , and then the high-resistance film  20  is burned on the outer surface of the insulator  40 . By burning the high-resistance film  20 , the high-resistance film  20  is formed in oxidization atmosphere. Moreover, it is preferable that the melting point of the high melting point wax material is higher than the burning temperature of the high-resistance film  20 . 
   Operation of the electron beam exposure apparatus  300 , which has been explained in relation to  FIGS. 1 and 2 , will be explained hereinafter. First, the plurality of electron beam generating devices  100  generate the plurality of electron beams. The first forming member  362  forms the plurality of electron beams, which are generated by the plurality of electron beam generating devices  100  and irradiated on the first forming member  362 , by allowing them to pass through a plurality of apertures of the first forming member  362 . In alternate embodiment, a plurality of electron beams are generated by further including means for dividing an electron beam generated by the electron beam generating device  100  into a plurality of electron beams. 
   The first multi-axis electron lens  364  independently collects each of the plurality of electron beams, which is formed into rectangular shape, and independently adjusts focal point of each of the electron beams to the second forming member  372 . The first forming deflector  366  independently deflects the plurality of electron beams, which are formed into rectangular forms by the first forming member, so that the plurality of electron beams are irradiated on desired positions on the second forming member  372 . 
   The second forming deflector  368  deflects the plurality of electron beams deflected by the first forming deflector  366  in substantially perpendicular direction to the second forming member  372 , and irradiates them on the second forming member  372 . Then the second forming member  372 , which includes a plurality of apertures having rectangular forms, further forms the electron beams, which have rectangular cross-sectional forms and are irradiated on the second forming member  372 , into the electron beams having desired cross-sectional forms for irradiating them on the wafer  392 . 
   The second multi-axis electron lens  374  independently collects the plurality of electron beams, and independently adjusts the focal point of each of the electron beams to the blanking-electrode array  376 . Then, the plurality of electron beams, of which the focal points are adjusted by the second multi-axis electron lens  374 , respectively pass through a plurality of apertures of the blanking-electrode array  376 . 
   The blanking electrode array control section  338  controls whether or not the voltage is applied to the deflecting electrodes provided in the vicinity of each of the apertures of the blanking-electrode array  376 . The blanking-electrode array  376  selects whether or not each of the electron beams are irradiated on the wafer  392  based on the voltage applied to each of the deflecting electrodes. 
   The electron beam which is not deflected by the blanking-electrode array  376  passes through the third multi-axis electron lens  378 . Then the third multi-axis electron lens  378  reduces the diameter of the electron beam which passes through the third multi-axis electron lens  378 . The reduced electron beam passes through an aperture of the electron beam blocking member  382 . Moreover, the electron beam blocking member  382  blocks the electron beam deflected by the blanking-electrode array  376 . The electron beam which has passed through the electron beam blocking member  382  enters the fourth multi-axis electron lens  384 . Then, the fourth multi-axis electron lens  384  independently collects each of the entered electron beams, and respectively adjusts the focal point of each of the electron beams to the deflecting section  386 . The electron beam, of which the focal point is adjusted by the fourth multi-axis electron lens  384 , enters the deflecting section  386 . 
   The deflection control section  340  controls a plurality of deflectors of the deflecting section  386 , and independently deflects each of the electron beams, which enters the deflecting section  386 , into the position where it is to be irradiated on the wafer  392 . The fifth multi-axis electron lens  388  adjusts the focal point of each of the electron beams to the wafer  392  which passes through the fifth multi-axis electron lens  388 . Then, each of the electron beams, having the cross-sectional shape which is to be irradiated on the wafer  392 , is irradiated on a desired position of the wafer  392 , where it is to be irradiated. 
   During the exposure processing, it is preferable that the wafer stage drive section  398  continuously moves the wafer stage to a predetermined direction based on a direction from the wafer stage control section  342 . Then, according to the movement of the wafer  392 , a desired circuit pattern is exposed on the wafer  392  by forming the cross-sectional shape of each of the electron beams to the forms which are to be irradiated on the wafer  392 , by selecting the apertures, which allow the passage of the electron beams which are to be irradiated on the wafer  392 , and by deflecting each of the electron beams so that it is irradiated on the desired position of the wafer  392 . 
   In the electron beam exposure apparatus  300  explained in relation to  FIGS. 1 and 2 , while each of the plurality of electron beam generating devices  100  includes the insulator  40  respectively, in another embodiment, the plurality of electron beam generating devices  100  share one insulator  40 . That is, the electron beam exposure apparatus  300  includes an electron beam generating device  100  having: a plurality of cathodes  10  for generating thermal electrons; a cathode voltage source unit  22  for applying negative voltage to the plurality of cathodes  10  so that the thermal electrons are emitted from the cathodes  10 ; a plurality of grids  30 , which correspond to the plurality of cathodes  10  respectively, for collecting the thermal electrons emitted from the plurality of cathodes  10  respectively and for forming the plurality of electron beams; the grid voltage source unit  24  for applying negative voltage to the plurality of grids  30 , where the potential of each the plurality of grids  30  is lower than the potential of the corresponding cathode  10 ; and an insulator  40  for insulating the cathode voltage source unit  22  and the grid voltage source unit  24  from the thermal electrons generated by the plurality of cathodes  10 . Moreover, in the present embodiment, while the electron beam exposure apparatus  300  includes the plurality of electron beam generating devices  100 , the electron beam exposure apparatus  300  includes one electron beam generating device  100  in another embodiment. 
   As described above, according to the present invention, electric discharge is prevented and the current of the electron beam is controlled accurately by the electron beam generating device  100 . Moreover, by preventing electric discharge, exhaustion of the cathode is decreased and the service life of the electron beam generating device  100  is extended. 
   Although the present invention has been described by way of an exemplary embodiment, it should be understood that those skilled in the art might make many changes and substitutions without departing from the spirit and the scope of the present invention. It is obvious from the definition of the appended claims that embodiments with such modifications also belong to the scope of the present invention.