Abstract:
A sample chamber and a column are connected to each other and comprise a magnetic substance. An exhaust section controls a pressure in the sample chamber and the column. A stage controller controls a stage, above which a sample is placed, in the sample chamber. An electron beam source power supply supplies power to an electron beam source, which emits an electron beam to the sample. A power supply supplies voltage to electron optic system, which controls the electron beam. The sample chamber, exhaust section, stage controller, electron beam source power supply and power supply are grounded by a first, second, third, fourth and fifth grounding point, respectively. The electron beam source and the electron optic system are electrically insulated from the sample chamber, column, exhaust section and stage. One of the first, second and third grounding point is different from the fourth or fifth grounding point.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2004-301714, filed Oct. 15, 2004, the entire contents of which are incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an electronic beam apparatus and a method for manufacturing a semiconductor device using the electron beam apparatus, and more specifically, to the configuration of a vacuum container and column for an electronic beam apparatus. 
   2. Description of the Related Art 
   An apparatus using an electron beam can achieve a higher resolution than an apparatus using light, owing to the small wavelength of an electron beam. Thus, the electron beam is used for a transmission electron microscope, a scanning electron microscope, an electron beam drawing apparatus, and the like. The electron beam is composed of charged particles and is thus controlled by electromagnetic fields. However, a grounding environment may disturb the electromagnetic fields to affect the electron beam. This may make it difficult to control the electron beam. That is, the precision of control of the electron beam may be degraded. To avoid this, a vacuum chamber and a column are made of a magnetic substance having a lower magnetic resistance than the atmosphere, for example, iron; the vacuum chamber stores a sample and the column stores an objective and a condensing lens (Japanese Patent No. 2,993,504). This configuration attracts the magnetic disturbance into the chamber and column. Then, magnetic flux from a magnetic disturbance pass through the chamber and column and are thus prevented from affecting the electron beam. 
   Magnetic Problem 
   As described above, the chamber and column are made of the magnetic substance. Thus, when the magnetic disturbance reaches the chamber, a magnetic flux resulting from the magnetic disturbance flows through the magnetic substance constituting the chamber and then toward the column. The column is electromagnetically joined to the objective and condensing lens. Thus, the magnetic flux from the column passes through magnetic poles of the objective and condensing lens. The magnetic flux then seeps from gaps in the lenses. The magnetic flux may degrade the control of the electron beam EB. 
   Electric Noise Problem 
   The chamber connects to a pump for vacuum pumping, an measuring instrument for the degree of vacuum, a stage controller, pipe and solenoid valve which sets the pressure in the chamber equal to atmospheric pressure. Further, a solenoid valve for valve control is attached to vacuum pipe. These electric apparatuses make electric noise. The electric noise may vary the reference potentials of power supplies that control the chamber, column, and beam. This degrades the ability to control the electron beam. 
   BRIEF SUMMARY OF THE INVENTION 
   According to a first aspect of the present invention, there is provided an electron beam apparatus comprising: a sample chamber grounded by a first grounding point and comprising a magnetic substance; a column connected to the sample chamber and comprising a magnetic substance; an exhaust section controlling a pressure in the sample chamber and a pressure in the column and grounded by a second grounding point; a stage provided in the sample chamber, a sample being placed above the stage; a stage controller driving the stage and grounded by a third grounding point; an electron beam source provided in the column and emitting an electron beam to the sample; an electron beam source power supply supplying power to the electron beam source and grounded by a fourth grounding point; and electron optic system provided in the column and controlling the electron beam; a power supply supplying voltage to the electron optic system and grounded by a fifth grounding point; wherein the electron beam source and the electron optic system are electrically insulated from the sample chamber, the column, the exhaust section and the stage, and a grounding point selected from a group including the first grounding point, the second grounding point and the third grounding point is different from either the fourth grounding point or the fifth grounding point. 
   According to a second aspect of the present invention, there is provided an electron beam apparatus comprising: a sample chamber; a column connected to the sample chamber; an exhaust section which controls a pressure in the sample chamber and the column; a stage stored in the sample chamber, a sample being placed above the stage; a stage controller driving the stage; a cylinder provided in the column and electrically insulated from the column; an electron beam source provided in the cylinder and emitting an electron beam to the sample; an electron beam source power supply supplying power to the electron beam source; electron optic system provided in the cylinder and controlling the electron beam; and a power supply supplying a voltage to the electron optic system. 
   According to a third aspect of the present invention, there is provided a method for manufacturing a semiconductor device, the method comprising drawing a pattern on film located above a semiconductor substrate using an electron beam apparatus comprising: a sample chamber grounded by a first grounding point and comprising a magnetic substance; a column connected to the sample chamber and comprising a magnetic substance; an exhaust section controlling a pressure in the sample chamber and a pressure in the column and grounded by a second grounding point; a stage provided in the sample chamber, a sample being placed above the stage; a stage controller driving the stage and grounded by a third grounding point; an electron beam source provided in the column and emitting an electron beam to the sample; an electron beam source power supply supplying power to the electron beam source and grounded by a fourth grounding point; and electron optic system provided in the column and controlling the electron beam; a power supply supplying voltage to the electron optic system and grounded by a fifth grounding point; wherein the electron beam source and the electron optic system are electrically insulated from the sample chamber, the column, the exhaust section and the stage, and a grounding point selected from a group including the first grounding point, the second grounding point and the third grounding point is different from either the fourth grounding point or the fifth grounding point. 
   According to a fourth aspect of the present invention, there is provided a method for manufacturing a semiconductor device, the method comprising drawing a pattern on film located above a semiconductor substrate using an electron beam apparatus comprising: a sample chamber; a column connected to the sample chamber; an exhaust section which controls a pressure in the sample chamber and the column; a stage stored in the sample chamber, a sample being placed above the stage; a stage controller driving the stage; a cylinder provided in the column and electrically insulated from the column; an electron beam source provided in the cylinder and emitting an electron beam to the sample; an electron beam source power supply supplying power to the electron beam source; electron optic system provided in the cylinder and controlling the electron beam; and a power supply supplying a voltage to the electron optic system. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       FIG. 1  is a diagram schematically showing the configuration of an electronic beam drawing apparatus in accordance with a first embodiment; 
       FIG. 2  is a diagram showing the flow of magnetic fluxes produced when magnetic disturbance reaches the electron beam drawing apparatus shown in  FIG. 1 ; 
       FIG. 3  is a diagram showing the flow of magnetic fluxes produced when a nonmagnetic opening is formed in a magnetic path in the electron beam drawing apparatus shown in  FIG. 1 ; 
       FIG. 4  is a diagram showing the flow of magnetic fluxes produced if a chimney-like magnetic substance is provided at the nonmagnetic opening in accordance with the first embodiment; 
       FIG. 5  is a diagram schematically showing the configuration of an electronic beam drawing apparatus in accordance with a second embodiment; 
       FIG. 6  is a diagram showing the flow of magnetic fluxes produced when magnetic disturbance is applied to the electron beam drawing apparatus shown in  FIG. 5 ; 
       FIG. 7  is a diagram schematically showing the configuration of an electronic beam drawing apparatus in accordance with a third embodiment; and 
       FIG. 8  is a flowchart of a process for manufacturing a semiconductor device using the electron beam drawing apparatuses in accordance with any of the first to third embodiments. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Embodiments of the present invention will be described below with reference to the drawings. 
   First Embodiment 
     FIG. 1  is a diagram schematically showing the configuration of an electronic beam drawing apparatus in accordance with a first embodiment. 
   A column  20  is connected to a vacuum chamber (sample chamber)  10 . Internal spaces in the vacuum chamber  10  and column  20  are connected together. The vacuum chamber  10  and the column  20  are made of a magnetic substance (for example, iron). The vacuum chamber  10  and the column  20  are electrically connected together. The vacuum chamber  10  is grounded by a D type earth E D  via a grounding line. 
   A stage  11  is placed in the vacuum chamber  10 . A stage controller  15  moves the stage controller  11  to a desired position by. 
   A sample holder  13  is installed on the stage  11  via a holder support  12  consisting of an insulating material such as ceramic. A sample  14  is installed on the sample holder  13 . Thus, the sample  14  is insulated from the stage  11 . The sample  14  is also insulated from the vacuum chamber  10  and column  20 . The sample holder  13  is connected to an A type earth EA via a grounding line. The ground terminal of the stage controller  15  is grounded by the D type earth E D . 
   The following are arranged in the column  20 : an electron gun (electron beam source)  21 , a condensing lens (electron optics system)  22 , an electrostatic deflector (electron optics system)  23 , and an objective (electron optics system)  24 . The condensing lens  22  is fixed to the column  20  by a condensing lens support  25  consisting of an insulating material such as ceramic. The condensing lens support  25  magnetically and electrically insulates the condensing lens  22  from the column  20 . The electrostatic deflector  23  is fixed to the column  20  by a deflector support  26  consisting of an insulating material such as ceramic. The deflector support  26  magnetically and electrically insulates the electrostatic deflector  23  from the column  20 . The objective  24  is fixed to the column  20  by an objective support  27  consisting of an insulating material such as ceramic. The objective support  27  magnetically and electrically insulates the objective  24  from the column  20 . Accordingly, the condensing lens  22 , the electrostatic deflector  23 , and the objective  24  are also insulated from the vacuum chamber  10  and from the stage  11 . 
   The condensing lens  22 , the electrostatic deflector  23 , and the objective  24  are grounded by the A type earth E A  via a grounding line. The A type earth E A  offers a ground resistance of at most 10Ω. The D type earth E D  offers a ground resistance of at most 100Ω. 
   The electron gun  21  is provided in the column  20  and emits an electron beam EB. The electron gun  21  is insulated from the column  20 , vacuum chamber  10 , and stage  11 . The condensing lens  22  adjusts electron beam irradiation conditions. The electrostatic deflector  23  deflects the electron beam EB to control the position irradiated with the electron beam EB. Moreover, the objective  24  focuses the electron beam EB on the surface of the sample  14 . 
   An electron gun power source  31  sets an acceleration voltage and a filament current to allow the electron gun  21  to emit an electron beam. The reference potential of the electron gun power supply  31  is grounded by the A type earth E A . 
   The condensing lens  22  is composed of a magnetic pole  22   a  and a coil  22   b . Similarly, the objective  24  is composed of a magnetic pole  24   a  and a coil  24   b . The intensities of the condensing lens  22  and objective  24  are controlled in accordance with a current supplied to the coils  22   b  and  24   b  by a lens power supply (control power supply)  32 . The reference potential of the lens power supply  33  is grounded by the A type earth E A . 
   The electrostatic deflector  23  is composed of metal. The position to which the electron beam EB is deflected is controlled by a voltage applied to the electrostatic deflector  23  by the deflecting power supply (control power supply)  33 . The reference potential of the deflecting power supply  32  is grounded by the A type earth E A . 
   The vacuum chamber  10  and the column  20  are composed of a magnetic substance and constitute a boundary between the vacuum and atmosphere. A turbo molecular pump (exhaust section)  41  is connected to the vacuum chamber  10 . A roots pump (MBP, exhaust section)  42  is connected to an exhaust side of the turbo molecular pump  41 . The turbo molecular pump  41  and the roots pump (MBP, exhaust section)  42  subject the vacuum chamber  10  to vacuum pumping. 
   A vacuum gauge (exhaust section)  43  is connected to the vacuum chamber  10  and measures the pressure (degree of vacuum) in the vacuum chamber  10 . The vacuum chamber  10  connects to a solenoid valve (exhaust section)  44  and pipe  45  which are required to set the pressure in the vacuum chamber  10  equal to atmospheric pressure. 
   A measurement signal from the vacuum gauge  43  is input to a vacuum controller  46 . The vacuum controller (exhaust section)  46  controls the turbo molecular pump  41 , the roots pump  42 , and the solenoid valve  44 . The reference potential of the vacuum controller  46  is grounded by the D type earth E D  via a grounding line. 
   The turbo molecular pump  41 , roots pump  42 , vacuum gauge  43 , solenoid valve  44 , and vacuum controller  46  are electrically insulated from the electron gun  21 , the condensing lens  22 , electrostatic deflector  23 , objective  24 , and sample  14 . As described above, the sections are insulated from one another, so that the group consisting of the electron gun  21 , the condensing lens  22 , electrostatic deflector  23 , objective  24 , and sample  14  is electrically insulated from the group consisting of the vacuum chamber  10 , column  20 , turbo molecular pump  41 , roots pump  42 , vacuum gauge  43 , solenoid valve  44 , vacuum controller  46 , and stage  11 . 
   Application of magnetic disturbance M EX  will be described with reference to  FIG. 2 . As described above, the chamber  10  and the column  20  are made of a magnetic substance. Thus, when the magnetic disturbance M EX  are applied to the chamber  10 , a magnetic flux M 1  flows through the chamber  10  and column  20 , which offer a lower magnetic resistance than the surrounding space. The column  20  is magnetically insulated from the objective  23  and condensing lens  22 . Consequently, the magnetic flux M 1  flows only through the column  20  rather than flowing from the column  20  to the magnetic poles  22   a  and  24   b . Thus, the magnetic flux M 1  flowing through the magnetic poles  22   a  and  24   b  does not degrade the ability to control the electron beam EB. 
   The vacuum chamber  10  connects to the turbo molecular pump  41 , roots pump  42 , vacuum gauge  43 , the stage controller  15 , and solenoid valve  44 . Electric noise is made by the turbo molecular pump  41 , roots pump  42 , vacuum gauge  43 , solenoid valve  44 , and stage controller  15  (collectively referred to as first group apparatuses): The electric noise is transmitted through the chamber  10  and into the D type earth E D . 
   The reference potential of the electron gun power supply  31 , deflecting power supply  32 , and lens power supply  33  (collectively referred to as second group apparatuses), which control electron beam EB, is grounded by the A type earth EA, which is different from the earth to which the first group apparatuses, making noise, are connected. Consequently, the reference potential of the second group apparatus is not affected by noise from the first group apparatuses. 
   The potential of the D type earth ED is varied by noise generated by, for example, the roots pump  42 . However, this potential does not directly affect the electron beam EB. 
   Further, the reference potential of the second group apparatuses, which control the electron beam EB, is grounded by the A type earth E A . The first group apparatuses such as the roots pump  42  are grounded by the D type earth E D . Thus, even if the potential of the D type earth E D  is varied by noise generated by any of the first group apparatuses, for example, the roots pump  42 , the variation does not affect the second group apparatuses. 
   The present configuration provides a vacuum chamber that makes it possible to block electromagnetic disturbance and to prevent the entry of noise from the apparatuses (first group apparatuses) connected to the vacuum chamber. As a result, the ability to control the electron beam EB can be improved. 
   Further, as shown in  FIG. 3 , a magnetic opening may be formed in the middle of a magnetic path constituting the column  20 ; the magnetic opening is a nonmagnetic substance, for example, a feed-through  51  used to apply a voltage to an electric pole. In this case, the magnetic flux M 1  generated near the feed-through  51  by magnetic disturbance M d  leaks across the optical axis of the electron beam EB to degrade the positional accuracy of the electron beam. 
   To suppress the degradation of positional accuracy of the electron beam EB, a chimney-like shield portion (projecting portion)  52  may be provided opposite the optical axis as shown in  FIG. 4 . The shield portion  52  consists of a magnetic substance. Such a configuration allows a magnetic flux M 2  located near the feed-through  51  after having flowed through the column  20  to pass through the shield portion  52 . The magnetic flux M 2  then leaks in a direction opposite to the optical axis. Accordingly, the optical axis is not affected. If the opening is rectangular, the height of the shield portion  52  may be at least twice as large as the length of a short side of the opening. If the opening is elliptical, the height of the shield portion  52  may be at least twice as large as the minor axis of the opening. 
   Second Embodiment 
     FIG. 5  is a diagram schematically showing the configuration of an electronic beam drawing apparatus in accordance with a second embodiment. In  FIG. 5 , the same components as those in  FIG. 1  have the same reference numerals and will not be described below. 
   The chamber  10  and the column  20  are joined together via a ferrite (junction)  61 . In the first embodiment, the column  20 , which consists a magnetic substance, is electrically coupled to the chamber  10 . Accordingly, a noise current from the chamber  10  is likely to flow into the column  20 . High-frequency noise propagates through a vacuum and reaches the condensing lens  22 , electrostatic deflector  23 , objective  24 , and the like More specifically, the high-frequency noise is superimposed on voltage application lines from the deflecting power supply  32  and lens power supply  43 . As a result, the control of the electron beam EB is affected. To prevent this, the ferrite  61  is placed at the junction between the chamber  10  and the column  20 . 
   The column  20  is grounded by the A type earth E A . The chamber  10  is grounded by the D type earth E D  as in the case of the first embodiment. 
   The ferrite  61  has a high magnetic permeability and a high volume resistivity. Electric noise flowing through the chamber  10  does not pass through the ferrite  61 , having the high volume resistivity. Consequently, almost no electric noise flows through the column  20 . A high-resistance magnetic substance different from the ferrite may be sandwiched between the chamber  10  and the column  20 . 
   Further, since the ferrite  61  has the high magnetic permeability, the magnetic flux M 1  flows through the ferrite  61  and into the column  20 , composed of a magnetic substance, as shown in  FIG. 6 . Then, as in the case of the first embodiment, the magnetic flux M 1  does not flow from the column  20  to the magnetic pole  22   a  or  24   b . Thus, even the application of magnetic disturbance is prevented from degrading the ability to control the electron beam EB as in the case of the first embodiment. 
   This configuration not only produces the effects of the first embodiment but also enables a reduction in electric noise flowing through the column  20 . It is thus possible to reduce electric noise flowing from the column  20  to the condensing lens  22 , electrostatic deflector  23 , objective  24 , and the like. This makes it possible to improve the ability to control the electron beam. 
   If there is an opening in the magnetic path through which the magnetic flux travels, a chimney-like shield portion may be provided which consists of a magnetic substance. 
   Third Embodiment 
     FIG. 7  is a diagram schematically showing the configuration of an electronic beam drawing apparatus in accordance with a third embodiment. 
   An internal cylinder  71  composed of a conductor is provided in the column  20 . The internal cylinder  71  is fixed to the column  20  using an insulating support  72 . Accordingly, the internal cylinder  71  is electrically insulated from the column  20  and chamber  10 . The condensing lens  22  and the objective  24  are fixed to the internal cylinder  71 . The electrostatic deflector  23  is fixed to the internal cylinder  71  using the deflector support  26 . The electron gun  21  is fixed to the internal cylinder  71 . 
   The internal cylinder  71  is grounded by the independent A type earth E A . The chamber  10  is grounded by the D type earth E D . The chamber  10  also controls the electron beam EB. The electron gun power source  31 , deflecting power supply  32 , and lens power supply  33  are grounded by the A type earth E A  in order to obtain the reference potential. 
   The stage controller  15  and the vacuum controller  46  are grounded by the D type earth E D  in order to obtain the reference potential. The chamber  10  configured as described above will be described below. 
   In the electron beam apparatus shown in  FIG. 1 , the assembly accuracy of the condensing lens  22 , electrostatic deflector  23 , and objective  24  depends greatly on the machining accuracy of the column  20 . However, the assembly accuracy of the condensing lens  22 , electrostatic deflector  23 , and objective  24  configured in accordance with the present embodiment does not depend on the machining accuracy of the column  20  but on the machining accuracy of the internal cylinder  71 . The internal cylinder  71  is smaller than the column  20  and can thus be machined more easily than the column  20 . Accordingly, the machining accuracy of the internal cylinder  71  can be improved. In particular, the condensing lens  22  and objective  24  configured to be of an electrostatic type are lighter and smaller. This also makes it possible to reduce the size of the internal cylinder  71 . Thus, more accurate assembly can be accomplished. 
   The present configuration not only produces the effects of the first embodiment but also prevents electric noise from the apparatuses (first group apparatuses) connected to the vacuum chamber  10  from reaching the condensing lens  22 , electrostatic deflector  23 , objective  24 , and the like via the column  20 . It is also possible to improve the assembly accuracy of the condensing lens  22 , electrostatic deflector  23 , and objective  24  and thus the ability to control the electron beam EB. 
   If an opening is formed in the magnetic path through which a magnetic flux travels, arrangements similar to those in the first embodiments may be used. Further, as in the second embodiment, a high-resistance magnetic substance may be provided between the chamber  10  and the column  20 . 
   Other Embodiments 
   A semiconductor device is manufactured by irradiating a process-target substrate as the sample  14  with an electron beam using the electron beam drawing apparatus in accordance with any of the first to third embodiments. That is, as shown in  FIG. 8 , a semiconductor manufacturing process involves executing various known semiconductor manufacturing steps at predetermined stages a predetermined number of times, the steps including layer formation (step S 1 ), film process (step S 2 ), impurity introduction (step S 3 ), and thermal treatment (step S 4 ). As a result, a semiconductor device is formed (step S 10 ). 
   In the film process, the electron beam drawing apparatus in accordance with any of the embodiments is used. That is, first, in the film formation, an insulating film or conductive film (target film) to be processed is formed on a semiconductor substrate. A resist film is then formed on the target film. Then, the electron beam drawing apparatus is used to irradiate the resist film with an electron beam so as to draw a pattern corresponding to a desired shape of the target film (step S 21 ). Then, the resist film is developed (step S 22 ) to form a pattern with desired openings on the resist film. Then, the target film is etched by anisotropic etching such as reactive ion etching (RIE) using the resist film as a mask (step  23 ). As a result, the target film is processed into a desired pattern. 
   The present invention is not limited to the above embodiments. The above configurations are also applicable to, for example, a transmission electron microscope, or a scanning electron microscope. 
   Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.