Abstract:
An electron beam control method has the following steps, selecting one of a plurality of pattern openings by a character beam electrode having a plurality of electrode units to allow an electron beam to pass through any pattern opening on an aperture mask on which the plurality of pattern openings are formed, determining whether or not a synchronization error of deflected operation of the electron beam performed by the plurality of electrode units is equal to or less than a tolerance, determining whether or not the electron beam is irradiated with a sample by selecting the pattern openings in sequence by the character beam electrode in a state of controlling a path of the electron beam by a blanking electrode not to irradiate the sample with the electron beam, when determined that the synchronization error is equal to or less than the tolerance, and decreasing the tolerance when determined that the electron beam is irradiated with the sample.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of priority under 35 USC§119 to Japanese Patent Application No. 2004-314076, filed on Oct. 28, 2004, the entire contents of which are incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electron beam control method of controlling a path of an electron beam, an electron beam drawing apparatus and a method of fabricating a semiconductor device. 
     2. Related Art 
     To improve a throughput of an electron beam drawing apparatus, an electron beam drawing apparatus of a character projection scheme has been proposed. In this scheme, a plurality of pattern openings having a plurality of shapes are formed in an aperture mask and selectively irradiates the pattern openings with an electron beam. Therefore, a beam pattern generated by the electron beam passing through the pattern openings is projected with a reduced size on a sample such as a semiconductor wafer (see Japanese Patent Laid-Open No. 11-54396). 
     In the character projection scheme, the pattern openings corresponding to a repeated pattern included in a drawing pattern are formed in advance in the aperture mask. The surface of the sample is scanned while a CP selective deflector deflects the electron beam to pass through an arbitrary pattern opening. 
     However, the character projection scheme uses the CP selective deflector to deflect the electron beam by a larger amount than conventional variable shaping schemes. Consequently, the electron beam is likely to deviate from an ideal optical axis, and beam leakage may occur. 
     When such beam leakage occurs, the pattern cannot be accurately drawn on the sample, thereby deteriorating yield. 
     SUMMARY OF THE INVENTION 
     An electron beam control method according to one embodiment of the present invention, comprising: 
     selecting one of a plurality of pattern openings by a character beam electrode having a plurality of electrode units to allow an electron beam to pass through any pattern opening on an aperture mask on which the plurality of pattern openings are formed; 
     determining whether or not a synchronization error of deflected operation of the electron beam performed by the plurality of electrode units is equal to or less than a tolerance; 
     determining whether or not the electron beam is irradiated with a sample by selecting the pattern openings in sequence by the character beam electrode in a state of controlling a path of the electron beam by a blanking electrode not to irradiate the sample with the electron beam, when determined that the synchronization error is equal to or less than the tolerance; and 
     decreasing the tolerance when determined that the electron beam is irradiated with the sample. 
     An electron beam drawing apparatus according to one embodiment of the present invention, comprising: 
     a blanking electrode which controls a path of an electron beam not to irradiate a sample with the electron beam; 
     a character beam electrode having a plurality of electrode units, which selects one of a plurality of pattern openings formed on an aperture mask to allow the electron beam to pass through the selected pattern opening; and 
     a deflected control unit which controls voltages or currents applied to the blanking electrode and the character beam electrode, 
     wherein the deflected control unit includes: 
     a synchronization error determination unit which determines whether or not a synchronization error of the deflected operation of the electron beam performed by the plurality of electrode units is equal to or less than a predetermined tolerance; 
     a beam irradiation determination unit which selects in sequence the plurality of pattern openings by the character beam electrode in a state of driving the blanking electrode when determined that the synchronization error is equal to or less than the tolerance, to determine whether or not the electron beam is irradiated with the sample; and 
     a tolerance control unit which decreases the tolerance when determined that the electron beam is irradiated with the sample by the beam irradiation determination unit. 
     A method of fabricating a semiconductor device according to one embodiment of the present invention, comprising: 
     selecting one of a plurality of pattern openings by a character beam electrode having a plurality of electrode units to allow an electron beam to pass through any pattern opening on an aperture mask on which the plurality of pattern openings are formed; 
     determining whether or not a synchronization error of deflected operation of the electron beam performed by the plurality of electrode units is equal to or less than a tolerance; 
     determining whether or not the electron beam is irradiated with a sample by selecting the pattern openings in sequence by the character beam electrode in a state of controlling a path of the electron beam by a blanking electrode not to irradiate the sample with the electron beam, when determined that the synchronization error is equal to or less than the tolerance; 
     decreasing the tolerance when determined that the electron beam is irradiated with the sample; and 
     performing a fabrication of the semiconductor device after adjusting the synchronization error of the deflected operation of the electron beam to be equal to or less than the tolerance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing the entire configuration of an electron beam drawing apparatus in accordance with an embodiment of the present invention; 
         FIG. 2  is a diagram showing an example of locus of an electron beam; and 
         FIG. 3  is a flowchart showing an example of a processing operation of the electron beam drawing apparatus in accordance with the present embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An embodiment of the present invention will be described below with reference to the drawings. 
       FIG. 1  is a block diagram showing entire configurations of an electron beam drawing apparatus according to an embodiment of the present invention. The electron beam drawing apparatus in  FIG. 1  includes a sample chamber  1 , a conveying member  2  that controllably conveys samples (wafers or the like) into and out of the sample chamber  1 , a sample chamber control device  3  that controls each section of the sample chamber  1 , an electric lens system  4  provided above the sample chamber  1 , a lens control device  5  that controls a lens in the electric lens system  4 , a deflection control device  6  that controls various electrodes in the electric lens system  4 , a drawing circuit  7 , and a control computer  8  that controls the whole apparatus. 
     The sample chamber  1  has a stage  12  on which a sample  11  such as a semiconductor wafer is placed, a Z detector  13  that detects a height of a sample surface, and a vacuum device  14 . 
     The sample chamber control device  3  has a signal processing section  21  that performs signal processing on reflected electrons, scattered electrons, or secondary electrons detected by an electron detector (not shown) placed above the stage  12 , a Z detection control device  22  that controls the Z detector  13 , which detects the height of the sample surface, a laser length measuring member  23  that detects the position of the stage  12 , a position circuit  24  that controls the position of the stage  12 , a motor driving circuit  25  that moves the stage  12 , a stage control device  26  that controls movement of the stage  12 , a temperature monitor section  27  that monitors the temperature of the sample chamber  1 , a vacuum control device  28  that controls the degree of vacuum in the sample chamber  1 , and a conveyer control device  29  that controls conveyance of the sample  11 . 
     The electric lens system  4  has a blanking deflector  31  that controls a path of an electron beam so that the electron beam is not irradiated with the sample  11 , a CP selective deflector  32  which has a plurality of electrode units to guide the electron beam to any pattern opening in an aperture mask substrate, a main deflector  33  that roughly adjusts a direction in which the electron beam is deflected, a sub-deflector  34  that finely adjusts the deflecting direction of the electron beam, a lens  35  that refracts the electron beam, a monitor section  36  that monitors the operation of each deflector, an aperture  40 , and an electron detector (not shown) that detects reflected electrons, scattered electrons, or secondary electrons when the sample  11  is irradiated with the electron beam. 
     The lens control device  5  has a lens power source  37 , an electron lens control system  38 , and a monitor section  39 . 
     The control computer  8  (EWS) operates in accordance with control software  41  and stores the results of calculations in a magnetic disk device. External drawing data is supplied to the control computer  8 . 
     The electron beam drawing apparatus according to the embodiment adopts a character projection scheme. Drawing data to be drawn on the sample  11  is stored in a magnetic disk  42  connected to the control computer  8 . In accordance with the software  41 , the control computer  8  sends the drawing data read from the magnetic disk  42  to a drawing circuit  7 . A pattern generator  43  in the drawing circuit  7  generates a drawing pattern corresponding to the drawing data. In accordance with the drawing pattern, a deflection control circuit  44  in the drawing circuit  7  controls voltages applied to the main deflector  33 , the sub-deflector  34 , the CP selective deflector  32  (character beam electrode), and the blanking deflector  31  (blanking electrode). The CP selective deflector  32  has a plurality of electrode units and voltages applied to the electrode units are individually controlled. 
     Although not shown in  FIG. 1 , the aperture mask substrate (referred to as a mask substrate below) is placed between the CP selective deflector  32  and the main deflector  33 . Character openings of various shapes are formed in the mask substrate. The deflection control circuit  44  controls each deflector so that an electron beam passes through any of the character openings in the mask substrate. 
       FIG. 2  is a diagram showing an example of the locus of an electron beam. As shown in the figure, the CP selective deflector  32  has a plurality of electrode units  32   a  and  32   b . An electron beam is deflected by the CP selective deflector  32  and then passes through any of the character openings  30   a  in the mask substrate  30  to produce image on the sample  11 . To switch the character opening  30   a  through which the electron beam passes, the electron beam must be deflected out of the sample  11 . Thus, as shown by a dotted line in  FIG. 2 , the blanking deflector  31  is used to significantly change the direction of the electron beam. In this manner, the blanking deflector  31  is utilized to switch the character opening  30   a  on the mask substrate  30 . 
       FIG. 3  is a flowchart showing an example of a processing operation of the electron beam drawing apparatus according to the present embodiment. The flowchart is implemented by, for example, the deflection control device  6 . First, a tolerance for a synchronization error in the CP selective deflector  32  is initialized (step S 1 ). The synchronization error means differences of switching timings of voltages applied to a plurality of electrode units in the CP selective deflector  32 . 
     Then, the CP selective deflector  32  is controlled to sequentially select at least two character openings  30   a  and  30   b  on the mask substrate  30 . An electron beam is then guided to the selected character openings  30   a  and  30   b  (step S 2 ). 
     Then, the deflection control device determines whether or not the synchronization error in the selective operation of step S 2  is equal to or smaller than the tolerance (step S 3 ). The amount of deflection is converted using deflection sensitivities of the plurality of electrode units in the CP selective deflector  32 . The deflection control device then determines whether or not timing errors in accordance with the amount of deflection is equal to or smaller than the tolerance. If yes, the blanking deflector  31  is used to perform a beam blank operation of deflecting the electron beam in an outside direction of the sample  11  (step S 4 ). 
     During the beam blank operation, as in the case of step S 2 , at least two character openings  30   a  and  30   b  on the mask substrate  30  are consecutively selected. An electron beam is then guided to the selected character openings  30   a  and  30   b  (step S 5 ). Then, the deflection control device determines whether or not the electron beam has reached the sample  11  or the stage  12  (step S 6 ). If the electron beam has not reached the sample  11 , the deflection control device determines that the beam blank operation has been correctly performed, and the processing is finished. If the electron beam has reached the sample  11 , the tolerance for the synchronization error is narrowed down (step S 7 ). 
     If the value for the synchronization error is determined to be larger than the tolerance in step S 3  or the processing in step S 7  is finished, the apparatus shown in  FIG. 1  is adjusted (step S 8 ). The process subsequently returns to step S 2 . In the step S 8 , a circuit not shown for applying voltages to a plurality of electrode units in the CP selective deflector  32  is adjusted. More specifically, a timing adjustment for applying voltages to a plurality of electrode units and adjustment of voltage levels are conducted. 
     The processing in  FIG. 3  may be conducted in a state of placing a dummy sample  11  or the like on the stage  12 . In this case, the sample surface of the dummy sample  11  is coated with a resist that is sensitive to electron beams. Then, the processing in step S 5  is conducted and then the dummy sample  11  is subjected to development processing. The sample surface is observed using an optical microscope, an electron microscope, or a position measuring apparatus to determine whether or not the sample surface has been irradiated with an electron beam. 
     Alternatively, a Faraday cup placed on the stage  12  may be used to detect a current to determine whether or not the electron beam has deflected out of the sample  11 . Here, the Faraday cup is a cup-shaped detector that measures the current value corresponding to the electron beam. 
     Alternatively, an electron detector placed above the stage  12  may be used to detect reflected electrons, scattered electrons, or secondary electrons from the sample  11  to determine whether or not the electron beam has reached the sample  11 . 
     By conducting the processing operations in  FIG. 3 , the electron beam drawing apparatus is adjusted so that the synchronous error of the deflected operation of the electron beam becomes equal to or less than the tolerance in the end. And then, fabrication of the semiconductor device is conducted by using the exposure apparatus. The processing operation in  FIG. 3  is conducted regularly and irregularly. 
     Thus, in the present embodiment, during the beam blank period, the values for the synchronization errors of the plurality of electron sections in the CP selective deflector  32  are adjusted to be equal to or less than the tolerance. This enables the electron beam to be reliably deflected out of the sample surface during the beam blank period. As a result, defective patterning can be reliably prevented which results from beam leakage. This makes it possible to improve the yield of semiconductor devices produced using the electron beam drawing apparatus. 
     According to the present embodiment, if a large number of character openings  30   a  are formed in the mask substrate  30 , drawing can be achieved using only the character openings  30   a  free from beam leakage. Further, by using the dummy sample  11  to adjust a synchronization error in the CP selective deflector  32 , it is possible to set an appropriate reference for each device generation. Moreover, by using an electron detector to detect beam leakage, it is possible to adjust synchronization errors under the same conditions as those for the actual production of devices. Consequently, the adjustment can be accurately made. Further, by using a Faraday cup to detect beam leakage, it is possible to easily detect whether or not beam leakage occurs.