JP2010192508A - Charged particle beam-drawing device and charged particle beam-drawing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charged particle beam-drawing device capable of maximally removing a nonlinear error component included in a measurement signal of a laser interferometer without removing a mechanical vibration component generated by servo control; and to provide a charged particle beam-drawing method. <P>SOLUTION: A laser interferometer is used for measuring the position of a stage for mounting a sample thereon. A cutoff frequency of a filter part for removing a nonlinear error component included in a measurement signal of the laser interferometer is set to an inverse number (1/Ts) of a cycle Ts in which servo control for bringing the stage position after control by a stage movement control part close to a target position is executed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a charged particle beam writing apparatus and a charged particle beam writing method.

  Along with the high integration of semiconductor devices, the circuit pattern of the semiconductor device is miniaturized. In order to form a fine circuit pattern in a semiconductor device, a highly accurate original pattern (that is, a reticle or mask) is required. In order to produce a highly accurate original pattern, an electron beam drawing apparatus having excellent resolution is used.

  In this type of electron beam drawing apparatus, a pattern is drawn on a sample by irradiating an electron beam while moving a stage on which the sample is placed. In order to increase the accuracy of the drawing position, it is necessary to accurately measure the position of the stage. A laser interferometer is generally used for measuring the position of the stage. In order to remove a non-linear error component included in the measurement signal of the laser interferometer, a drawing apparatus including a digital filter in which a predetermined cut-off frequency is set is known (for example, see Patent Document 1). Note that this Patent Document 1 does not disclose a specific method for setting the cutoff frequency.

  In order to increase the accuracy of the drawing position, so-called servo control is performed in which the stage is moved so that the position of the stage after the movement control approaches the target position.

  Here, the frequency of the nonlinear error component is proportional to the stage speed. If the stage speed at the time of servo control is slowed to cope with the recent miniaturization and high density of the drawing pattern, the frequency of the nonlinear error component included in the measurement signal of the laser interferometer becomes low. In order to remove such a low-frequency nonlinear error component, the cutoff frequency of the digital filter may be set low.

  However, if the cut-off frequency is set low, not only the nonlinear error component but also the mechanical vibration component of the drawing device generated by the servo control of the stage is removed, resulting in a decrease in the measurement accuracy of the stage position. Accuracy is reduced. Therefore, in order to improve the measurement accuracy of the stage position, the filter unit is designed to remove the nonlinear error component contained in the measurement signal of the laser interferometer to the maximum without removing the mechanical vibration component generated by the servo control. It is necessary to set the cutoff frequency.

JP 2007-33281 A

  In view of the above problems, an object of the present invention is to provide a charged particle beam drawing apparatus capable of removing nonlinear error components included in a measurement signal of a laser interferometer to the maximum without removing mechanical vibration components generated by servo control. And a charged particle beam writing method.

  In order to solve the above-described problems, a first aspect of the present invention controls a stage that is movable in a horizontal direction and the stage acceleration to a predetermined target position by digitally controlling the stage acceleration at a predetermined cycle. A stage movement control unit, a servo control unit that performs servo control for moving the stage so that the position of the stage after the control by the stage movement control unit approaches the target position, and laser interference that measures the position of the stage A filter unit that removes the nonlinear error component contained in the measurement signal of the laser interferometer by setting the cutoff frequency to the reciprocal of the servo control cycle, and a measurement signal from which the nonlinear error component has been removed by the filter unit. And a stage position detector for detecting the position of the stage.

  In the first aspect, it is preferable that the servo control cycle is set shorter than the digital control cycle by the stage movement control unit.

  In the first aspect, the servo control unit and the stage movement control unit may be configured integrally.

  According to a second aspect of the present invention, in a charged particle beam writing method for drawing a pattern by irradiating a sample placed on a stage movable in a horizontal direction with a charged particle beam, the acceleration of the stage is digitalized at a predetermined cycle. To control the movement of the stage to a predetermined target position and to perform servo control to move the stage so that the stage position after the stage movement control is brought closer to the target position at a predetermined cycle Measuring a stage position using a laser interferometer, removing a non-linear error component included in a laser interferometer measurement signal using a filter unit having a predetermined cutoff frequency, and The stage position is detected based on the measurement signal from which the nonlinear error component has been removed, and the cutoff frequency is set to the servo control frequency. Characterized in that it comprises a step of setting the reciprocal.

  In the second aspect, it is preferable to set the servo control cycle to be shorter than the digital control cycle.

  According to the present invention, since the cutoff frequency of the filter unit is set to the reciprocal of the servo control period, the nonlinear error included in the measurement signal of the laser interferometer can be obtained without removing the mechanical vibration component generated by the servo control. Maximum removal of components.

In Embodiment 1 of this invention, it is a conceptual diagram which shows the structure of an electron beam drawing apparatus. It is a figure explaining the mode of drawing by an electron beam. It is a figure which shows the cut-off frequency set to a digital filter. In the embodiment of the present invention, (a) is a diagram for explaining a servo control cycle Ts, and (b) is a diagram showing a mechanical vibration waveform generated by servo control.

  Hereinafter, embodiments of the present invention will be described in detail.

  FIG. 1 is a conceptual diagram showing a configuration of an electron beam drawing apparatus in Embodiment 1 of the present invention. An electron beam drawing apparatus 1 shown in FIG. 1 includes a drawing chamber 101 and an electron column 130 disposed on the drawing chamber 101.

  In the drawing chamber 101, a mask which is a sample 102 is placed, and an XY stage (hereinafter referred to as “stage”) 103 which is movable in the horizontal direction is accommodated. The stage 103 moves in the X direction (direction parallel to the paper surface) and the Y direction (direction perpendicular to the paper surface). The motor that is the drive unit 104 that drives the stage 103 is controlled by the stage movement control unit 122. Thereby, the movement of the stage 103 to a predetermined target position is controlled.

  A mirror 111 is attached to the end of the stage 103. The position of the stage 103 is measured by a laser interferometer 110. The laser interferometer 110 includes a laser head 113 that is a light projecting unit that projects a laser, an optical system 112, and a light receiving unit 114. When laser light is applied from the laser head 113 to the mirror 111 via the optical system 112, the laser light reflected by the mirror 111 is received by the light receiving unit 114 via the optical system 112. The measurement signal of the laser interferometer 110 is input to the stage position detector 120. The stage position detection unit 120 includes a filter unit 121 to be described later, and detects the position of the stage 103 based on the measurement signal of the laser interferometer 110.

  In the electron column 130, an electron gun 131, an illumination lens 133, a first aperture 134 having a rectangular opening, a projection lens 135, a beam shaping deflector 136, a second aperture 137, an objective lens 138, and a beam A deflector 139 for scanning is provided.

  The electron beam 132 emitted from the electron gun 131 illuminates the entire first aperture 134 with the illumination lens 133. The electron beam 132 of the first aperture image that has passed through the first aperture 134 is projected onto the second aperture 137 by the projection lens 135. Since the position of the first aperture image on the second aperture 137 is controlled by the deflector 136, the beam shape and size can be changed. The electron beam 132 of the second aperture image that has passed through the second aperture 137 is focused by the objective lens 138, deflected by the deflector 139, and placed on the stage 103 in the drawing chamber 101. The desired position 102 is irradiated.

  An electron beam drawing apparatus 1 shown in FIG. 1 includes a control computer 200 that performs overall control of the electron beam drawing apparatus 1. The control computer 200 includes a cutoff frequency setting unit 201. The cut-off frequency setting unit 201 sets the cut-off frequency of the filter unit 121.

  A storage device 210 such as a magnetic disk device, a shot data generation unit 220, a deflection control unit 230, a stage position detection unit 120, a stage movement control unit 122, and a servo control unit 123 are connected to the control computer 200. The storage device 210 stores LSI drawing data. In this drawing data, the shape and position of a graphic pattern are defined.

  The control computer 200 reads out drawing data necessary for drawing a desired stripe area from the storage device 201 and transfers it to the shot data generation unit 220. The shot data generation unit 220 generates shot data obtained by dividing a graphic pattern defined in drawing data into shot units. The deflection control unit 230 generates a deflection signal for controlling the beam shaping deflector 136 based on the shot data generated by the shot data generation unit 220. The deflection signal is D / A converted by a well-known DAC amplifier unit (not shown) and then amplified and applied to the electrode of the deflector 136. Further, the deflector control unit 230 generates a deflection signal for controlling the deflector 139 for beam scanning based on the shot data. This deflection signal is amplified after being D / A converted by a known DAC amplifier (not shown) and applied to the electrode of the deflector 139.

  FIG. 2 is a diagram for explaining a state of drawing with an electron beam. When drawing on the sample 102, the stripe region divided into strips according to the deflection width of the deflector 139 while continuously moving the stage 103 in the X direction by the driving unit 104 controlled by the stage movement control unit 122. 102a is irradiated with an electron beam 132.

  Here, the movement of the stage 103 in the X direction is a continuous movement, and at the same time, the shot position of the electron beam 132 also follows the movement of the stage. Drawing time can be shortened by continuously moving. Further, stage variable speed drawing may be performed in which the stage speed is variable in accordance with the pattern density (that is, the number of shots in the predetermined area). With this stage variable speed drawing, the drawing time can be further shortened.

  When the drawing of one stripe region 102a is completed, the stage 103 is stepped in the Y direction by the driving unit 104, and the next stripe region 102a is drawn in the opposite X direction. By repeating this, each stripe region 102a is sequentially drawn.

  Next, the detection of the stage position in the drawing process will be described.

  In order to increase the accuracy of the drawing position, it is necessary to detect the position of the stage 103 with high accuracy. A laser interferometer 110 is generally used for measuring the stage position. The measurement signal of the laser interferometer 110 is input to the stage position detection unit 120.

  Here, in order for the stage position detection unit 120 to accurately detect the stage position based on the measurement signal of the laser interferometer 110, a complete linear relationship must be established between the measurement signal and the stage position. Is desirable. However, in reality, a perfect linear relationship is not established between the two. This is because a measurement signal is obtained when a vertical wave and a horizontal wave mixed in the laser light used in the laser interferometer 110 interfere with each other, and these vertical wave and horizontal wave are obtained from the optical system 112 of the laser interferometer 110. This is because the measurement signal of the laser interferometer 110 includes a nonlinear error component as a result.

  Therefore, before the stage position detection unit 120 detects the stage position based on the measurement signal, the filter unit 121 in which a predetermined cutoff frequency is set by the cutoff frequency setting unit 201 uses the nonlinearity included in the measurement signal. Remove error components. FIG. 3 shows the gain characteristic of the filter unit 121 in which the cutoff frequency fc is set. According to the filter unit 121, it is possible to remove a nonlinear error component having a frequency equal to or higher than the cutoff frequency fc.

  In addition, servo control is performed by the servo control unit 123 in order to increase the accuracy of the drawing position. That is, control is performed to move the stage 103 so that the position of the stage after the control by the stage movement control unit 122 approaches the target position.

By the way, as expressed by the following equation (1), when the stage speed Vs changes, the frequency f _{nl of the} nonlinear error component appearing in the measurement signal of the laser interferometer 110 changes. According to the following equation (1), when the stage speed Vs is decreased, the frequency f _nl of the nonlinear error component is decreased.

(Λ / 4) / Vs = 1 / f _nl (1)
In the above equation (1), “λ / 4” represents the spatial frequency of the nonlinear error component. For example, the spatial frequency (λ / 4) when the HeNe laser beam is used in the laser interferometer 110 is 632.8 nm.

When a high-density pattern is drawn, the stage speed Vs may be decreased by the stage movement control unit 122 and the stage speed Vs may be decreased by the servo control unit 123. When the stage speed Vs is thus reduced, the frequency f _{nl of the} nonlinear error component included in the measurement result of the laser interferometer 110 is lowered.

In order to remove the nonlinear error component having the low frequency f _nl in this way, the cut-off frequency fc of the filter unit 121 may be set as low as possible. However, if the cut-off frequency fc is set low, mechanical vibrations caused by stage movement control and servo control are also removed, resulting in a decrease in stage position detection accuracy.

  Therefore, in this embodiment, the cutoff frequency fc is set to the reciprocal (1 / Ts) of the servo control cycle Ts, that is, the servo frequency fs. Hereinafter, this point will be specifically described.

  As shown by the solid line in FIG. 4A, the servo control unit 123 digitally controls the torque applied from the drive unit 104 to the stage 103 in a pulse shape with a unit control cycle Ts. That is, the acceleration of the stage 103 during servo control is digitally controlled in a pulse shape with a unit control cycle Ts. FIG. 4B shows a mechanical vibration waveform generated by such servo control.

  In FIG. 4A, the absolute value of the acceleration on the + (plus) side and the absolute value of the acceleration on the-(minus) side are the same, and the time during which the acceleration is made constant is always the unit cycle Ts. Although a regular control waveform is illustrated, the absolute value of the acceleration may be different, and the time during which the acceleration is made constant may be a natural number multiple of the unit period Ts.

  Here, the mechanical vibration A indicated by a thin line in FIG. 4B, that is, the mechanical vibration A having a cycle shorter than the servo control cycle Ts does not occur. Therefore, mechanical vibrations B, C, and D having a period equal to or greater than the period Ts can be generated by the servo control. Therefore, by setting the cut-off frequency fc of the filter unit 121 to the reciprocal number (1 / Ts) of the period Ts, the measurement of the laser interferometer 110 is performed without removing the mechanical vibrations B, C, and D caused by the servo control. The nonlinear error component contained in the signal can be removed to the maximum extent.

  Here, the stage movement control unit 122 digitally controls the acceleration of the stage 103 in a pulse shape with a unit control cycle Ta as shown by a broken line in FIG. When the stage movement control cycle Ta is set shorter than the servo control cycle Ts, if the cutoff frequency fc of the filter unit 121 is set to the reciprocal (1 / Ts) of the servo cycle Ts, the stage movement control The generated mechanical vibration may be removed by the filter unit 121. For example, the mechanical vibration B having the same cycle as the cycle Ta may be removed. When such mechanical vibration is removed, the detection accuracy of the stage position is lowered.

  Therefore, in the present embodiment, as shown in FIG. 4A, the servo control period Ts by the servo control unit 123 is set shorter than the digital control period Ta by the stage movement control unit 122. As a result, the mechanical vibration generated by the stage movement control of the stage movement control 122 is not removed, so that the detection accuracy of the stage position is not lowered.

  As described above, in this embodiment, the cut-off frequency fc of the filter unit 121 is set to the reciprocal 1 / Ts (= servo frequency fs) of the servo control cycle Ts. The nonlinear error component included in the measurement signal of the laser interferometer 110 can be removed as much as possible without removing the component. Then, the stage position can be detected with high accuracy by the stage position detector 120 based on the measurement signal from which the nonlinear error component has been removed to the maximum. Thereby, the drawing position accuracy can be improved.

  In the present embodiment, the servo control period Ts of the servo control unit 123 is set to be shorter than the digital control period Ta of the stage movement control unit 122, so that the cutoff frequency fc of the filter unit 121 is set to the servo as described above. Even if the reciprocal of the control cycle Ts is set, the mechanical vibration component generated by the stage movement control is not removed and the detection accuracy of the stage position is not lowered.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, although the electron beam is used in the above embodiment, the present invention is not limited to this, and the present invention can also be applied to cases where other charged particle beams such as an ion beam are used.

  Moreover, in the said embodiment, although the filter part 121 was provided in the inside of the stage position detection part 120, you may comprise so that the filter part 121 may be provided in the exterior of the stage position detection part 120.

  Moreover, in the said embodiment, although the stage movement control part 122 and the servo control part 123 are comprised separately, you may integrate. Thereby, the apparatus configuration can be simplified.

1 Electron beam lithography system (charged particle beam lithography system)
102 Sample 103 Stage 110 Laser Interferometer 120 Stage Position Detection Unit 121 Filter Unit 122 Stage Movement Control Unit 123 Servo Control Unit 201 Cutoff Frequency Setting Unit

Claims (5)

A stage that can move horizontally,
A stage movement control unit that digitally controls the acceleration of the stage at a predetermined period and controls the movement of the stage to a predetermined target position;
A servo control unit that performs servo control for moving the stage so that the position of the stage after the control by the stage movement control unit approaches the target position at a predetermined period;
A laser interferometer for measuring the position of the stage;
A filter unit for removing a nonlinear error component contained in the measurement signal of the laser interferometer by setting a cutoff frequency to the reciprocal of the servo control period;
A charged particle beam drawing apparatus comprising: a stage position detection unit configured to detect a position of the stage based on a measurement signal from which the nonlinear error component has been removed by the filter unit.   The charged particle beam drawing apparatus according to claim 1, wherein the servo control cycle is set shorter than a digital control cycle by the stage movement control unit.   The charged particle beam drawing apparatus according to claim 1, wherein the servo control unit and the stage movement control unit are integrally configured. In a charged particle beam drawing method of drawing a pattern by irradiating a sample placed on a stage movable in a horizontal direction with a charged particle beam,
Digitally controlling the acceleration of the stage at a predetermined period, and controlling the movement of the stage to a predetermined target position;
Performing servo control for moving the stage so as to bring the position of the stage after performing the movement control of the stage closer to the target position at a predetermined period;
Measuring the position of the stage using a laser interferometer;
Removing a non-linear error component included in the measurement signal of the laser interferometer, using a filter unit in which a predetermined cutoff frequency is set;
Detecting a stage position based on the measurement signal from which the nonlinear error component has been removed;
And a step of setting the cut-off frequency to a reciprocal of the servo control period.   5. The charged particle beam writing method according to claim 4, wherein the servo control cycle is set shorter than the digital control cycle.

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