JP2020027866A - Charged particle beam lithography apparatus and charged particle beam drawing method - Google Patents

Abstract

To reduce deviation of a drawing position of a beam.SOLUTION: A charged particle beam lithography apparatus comprises: a stage on which a substrate of a drawing object is mounted and which can be moved; a drawing part that draws a pattern on a surface of a substrate mounted onto the stage moving by using a charged particle beam; a measurement part that measures a height distribution of the substrate mounted on the stage in rest; a correction part that adds a height fluctuation of the substrate on the basis of a moving speed of the stage to a substrate surface height of a drawing position calculated by the height distribution of the substrate to correct the substrate surface height at the drawing position; and a control part that adjusts a focal position of the charged particle beam on the basis of the substrate surface height at the drawing position.SELECTED DRAWING: Figure 1

Description

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

  With high integration of LSIs, circuit line width required for semiconductor devices has been miniaturized year by year. In order to form a desired circuit pattern on a semiconductor device, a high-precision original pattern formed on quartz using a reduction projection type exposure apparatus (a mask or, particularly, a pattern used in a stepper or a scanner is also called a reticle). ) Is reduced and transferred onto a wafer. A high-accuracy original pattern is drawn by an electron beam drawing apparatus, and a so-called electron beam lithography technique is used.

  In an electron beam drawing apparatus, a pattern is drawn on a substrate mounted on a moving stage while measuring a stage position. When drawing a pattern on a substrate using an electron beam lithography system, measure the exact height of the substrate surface to avoid misalignment of the drawing position and defocus of the electron beam. The lens was adjusted to focus the electron beam on the substrate surface. For example, using a height measuring unit of an electron beam drawing apparatus, before drawing, the substrate surface is irradiated with light to detect reflected light, and the height distribution of the substrate surface is measured.

  However, even if the focal position of the electron beam is adjusted using the height distribution measured before writing, the displacement of the electron beam cannot be sufficiently suppressed.

JP 2008-277373 A JP 2010-123694 A JP 2011-151111 A JP 2009-147254 A JP 2010-117507 A

  An object of the present invention is to provide a charged particle beam writing apparatus and a charged particle beam writing method that reduce a deviation of a writing position of a beam.

  As a result of intensive studies by the present inventors to solve the above problems, the surface height of the substrate mounted on the stage changes according to the stage speed. It has been found that the above problem can be solved by calculating the height and adjusting the focal position. That is, the gist of the present invention is as follows.

  A charged particle beam writing apparatus according to one embodiment of the present invention includes a movable stage on which a substrate to be written is mounted, and a surface of the substrate mounted on the moving stage using a charged particle beam. A drawing unit for drawing a pattern, a measuring unit for measuring a height distribution of a substrate placed on the stationary stage, and a substrate surface height at a drawing position determined from the height distribution of the substrate, A correction unit that adds a height variation of the substrate based on the moving speed of the stage to correct the substrate surface height at the writing position, and the charged particle beam based on the corrected substrate surface height at the writing position. And a control unit that adjusts the focal position.

  In the charged particle beam writing apparatus according to an aspect of the present invention, the correction unit may change a substrate height variation based on a moving speed and an acceleration of the stage to a substrate surface height at a writing position determined from a height distribution of the substrate. The addition is performed to correct the substrate surface height at the drawing position.

  In the charged particle beam writing apparatus according to one aspect of the present invention, the moving speed of the stage changes according to the density of a pattern written on the substrate.

  A charged particle beam writing method according to one embodiment of the present invention is a charged particle beam writing method for writing a pattern on a surface of a substrate placed on a moving stage using a charged particle beam, Measuring the height distribution of the substrate placed on the stage in a state where the stage is stopped, and to the substrate surface height at the drawing position determined from the height distribution of the substrate, to the moving speed of the stage Correcting the substrate surface height at the writing position by adding the substrate height variation based on the correction, and adjusting the focal position of the charged particle beam based on the corrected substrate surface height at the writing position. And

  In the charged particle beam writing method according to one aspect of the present invention, the height of the substrate based on the moving speed and the acceleration of the stage is added to the substrate surface height at the writing position determined from the height distribution of the substrate to perform writing. Correct the substrate surface height at the position.

  ADVANTAGE OF THE INVENTION According to this invention, the shift of the drawing position of a beam can be reduced.

1 is a schematic diagram of a charged particle beam drawing apparatus according to an embodiment of the present invention. It is a figure showing an example of stage movement. FIG. 4 is a diagram illustrating an example of a change in the shape of a main deflection area. 4 is a flowchart illustrating a drawing method according to the embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present embodiment, a configuration using an electron beam will be described as an example of a charged particle beam. However, the charged particle beam is not limited to an electron beam, but may be a beam using charged particles such as an ion beam.

  The drawing apparatus shown in FIG. 1 includes a drawing unit 100 that irradiates an object such as a mask or a wafer with an electron beam to draw a desired pattern, and a control unit 200 that controls a drawing operation performed by the drawing unit 100. The drawing unit 100 has an electron beam column 102 and a drawing chamber 104.

  In the electron beam column 102, an electron gun 101, an illumination lens 112, a projection lens 114, an objective lens 116, a blanking aperture 120, a first aperture 122, a second aperture 124, a blanking deflector 130, and a shaping deflector 132 , A main deflector 134 and a sub deflector 136.

  In the drawing room 104, an XY stage 140 movably arranged is arranged. On the XY stage 140, a substrate 150 to be drawn is placed. The substrate includes, for example, a wafer and an exposure mask for transferring a pattern to the wafer. The mask includes, for example, a mask blank on which no pattern is formed yet.

  In the drawing chamber 104, a Z sensor 160 (high) having an irradiation unit that irradiates laser light obliquely from above the substrate 150 toward the surface of the substrate 150 and a light receiving unit that receives laser light reflected by the surface of the substrate 150 Measurement unit).

  The control unit 200 includes storage devices 202, 204, 206, a control computer 210, a deflection control unit 220, and a stage control unit 230. The storage devices 202, 204, and 206 are, for example, magnetic disk devices. The storage device 202 stores drawing data. The shape and position of the graphic pattern are defined in the drawing data.

  The control computer 210 includes a Z map creation unit 212, a shot data creation unit 214, a drawing control unit 216, a function creation unit 217, and a correction unit 218. Each function of the Z map creation unit 212, the shot data creation unit 214, the drawing control unit 216, the function creation unit 217, and the correction unit 218 may be configured by software or hardware.

  The electron beam 103 emitted from the electron gun 101 illuminates the entire first aperture 122 having a rectangular hole by the illumination lens 112. Here, the electron beam 103 is shaped into a rectangle. Then, the electron beam 103 of the first aperture image that has passed through the first aperture 122 is projected onto the second aperture 124 by the projection lens 114. The position of the first aperture image on the second aperture 124 is deflection controlled by the shaping deflector 132 to change the beam shape and size. The electron beam 103 of the second aperture image that has passed through the second aperture 124 is focused by the objective lens 116, is deflected by the main deflector 134 and the sub deflector 136, and is deflected by the substrate 150 on the continuously moving XY stage 140. A desired position is irradiated.

  The electron beam 103 emitted from the electron gun 101 is controlled by a blanking deflector 130 so as to pass through a blanking aperture 120 when the beam is on, and the entire beam is shielded by the blanking aperture 120 when the beam is off. To be deflected. The electron beam that has passed through the blanking aperture 120 from the beam-off state to the beam-on state until the beam-off state becomes one shot of the electron beam. The irradiation amount of the electron beam applied to the substrate 150 per shot is adjusted according to the irradiation time of each shot.

  FIG. 2 is a diagram illustrating an example of stage movement during pattern drawing. In the case of drawing on the substrate 150, the drawing area 10 is virtually divided into a plurality of strip-shaped stripes (frames) 20 having a width capable of deflecting the electron beam 103 while continuously moving the XY stage 140 in the x direction, for example. The electron beam 103 is irradiated on one stripe 20 of the substrate 150. The continuous movement can reduce the drawing time. When the writing of one stripe 20 is completed, the XY stage 140 is stepped in the y direction, and the writing operation of the next stripe 20 is performed in the x direction (reverse direction).

  The moving speed of the XY stage 140 is variable and changes depending on, for example, the pattern density of the drawing pattern. For example, the stage speed is reduced when writing a dense pattern, and the stage speed is increased when writing a sparse pattern.

  The width of the stripe 20 is a width that can be deflected by the main deflector 134. Each stripe 20 is also divided in the y direction by the same width as the width of the stripe in the x direction. The divided area is a main deflection area that can be deflected by the main deflector 134. An area obtained by further subdividing the main deflection area becomes a sub deflection area.

  The sub deflector 136 is used to control the position of the electron beam 103 for each shot at high speed and with high accuracy. Therefore, the deflection range is limited to the sub-deflection area, and deflection beyond that area is performed by moving the position of the sub-deflection area by the main deflector 134. On the other hand, the main deflector 134 is used to control the position of the sub deflection area, and moves within a range (main deflection area) including a plurality of sub deflection areas. Also, since the XY stage 140 is continuously moving in the x direction during drawing, the drawing origin of the sub-deflection area is moved (tracked) as needed by the main deflector 134 to follow the movement of the XY stage 140. Can be.

  In the electron beam writing apparatus, the lens system is adjusted so that the focal height position (Z = 0) matches the surface of the substrate 150. When the height of the substrate 150 deviates from the focal height position, as shown in FIG. 3, the shape of the main deflection area on the substrate surface rotates or expands and contracts. In the example shown in FIG. 3, as the surface height of the substrate shifts in a negative direction (a direction away from the lens system), the main deflection area gradually rotates counterclockwise, and the area size increases. To go. Conversely, as the surface height of the substrate shifts in the positive direction (the direction approaching the lens system), the main deflection area gradually rotates clockwise, and the area size decreases.

  In the present embodiment, the distribution of the surface height of the substrate 150 is measured in advance, and correction of the optical system (focusing, expansion / contraction / rotation correction of the shape of the main deflection area) according to the height of the drawing position is performed. . Furthermore, in the present embodiment, focusing on the fact that the height of the substrate 150 changes according to the moving speed of the XY stage 140, the surface height of the substrate 150 is corrected based on the stage moving speed (and acceleration), and the corrected Optical system is corrected based on the height of the optical system.

  The drawing method according to the present embodiment will be described with reference to the flowchart shown in FIG. In the flowchart of FIG. 4, steps S101 to S105 and S111 to S115 are pre-processes before starting drawing.

  First, the evaluation substrate is placed on the XY stage 140, and the height position (Z value) of the evaluation substrate surface is measured using the Z sensor 160 (step S101). The measurement is performed with the XY stage 140 stopped. The output of the Z sensor 160 is output to the control computer 210. The accuracy of the position where the Z value is measured is more improved when it is subdivided. For example, the Z value is measured at approximately 8 × 8 positions.

  The Z map creation unit 212 creates a height distribution (Z map) by fitting the obtained Z values (step S102).

  An evaluation pattern is drawn on the evaluation board (step S103). The shot data generation unit 212 reads out the drawing data of the evaluation pattern from the storage device 202 and performs a plurality of stages of data conversion processing to generate shot data unique to the device. The shot data includes, for each shot, a figure code indicating the figure type of each shot figure, figure size, shot position, irradiation time, and the like. The shot data is temporarily stored in a memory (not shown). The drawing control unit 216 outputs the shot data to the deflection control unit 220.

  The deflection control unit 220 generates a deflection signal for controlling the deflectors 130, 132, 134, 136 based on the shot data. The deflection signal is D / A converted by a DAC amplifier (not shown), amplified, and applied to the electrodes of the deflectors 130, 132, 134, 136. Thereby, a desired position of the evaluation substrate can be irradiated with an electron beam having a desired shape for a desired irradiation time (irradiation amount). The evaluation pattern is drawn with the evaluation board stopped. The evaluation pattern may be a line pattern or a hole pattern.

  The position of the drawn evaluation pattern is measured, and the rotation amount and the expansion / contraction amount of the main deflection area are measured (step S104). For example, the amount of rotation and the amount of expansion and contraction of the main deflection area at each position can be calculated by fitting the measurement position of the drawn evaluation pattern with a linear function of two variables x and y.

  Based on the Z map created in step S102 and the amount of rotation and expansion / contraction of the main deflection area at each position calculated in step S104, how much the shape of the main deflection area rotates and expands by changing the substrate surface height Then, the Z-dependent position shift coefficients b1 and b2 are calculated (step S105). The calculated coefficients b1 and b2 are used in a correction formula described later, and are stored in the storage device 206.

  Further, correction coefficients a0, a1, a2, and the like for correcting distortion of the main deflection area according to the drawing position are calculated and stored in the storage device 206. For example, the XY stage 140 is moved to move a mark (not shown) on the stage to each position of a desired main deflection area. Then, the electron beam is deflected to each position in the main deflection area, the mark position is measured, and the residual is obtained. Then, the coefficients a0, a1, a2, and the like are calculated by fitting the obtained residual with a functional expression using x and y as variables. The coefficients a0, a1, a2, etc. are also used in the correction formula described later.

  The coefficients a1 and a2 when the height of the mark is z and the coefficients a1 'and a2' when the height of the mark is z 'are obtained, and the Z-dependent displacement coefficient b1 is calculated as b1 = (a1-a1'). / (A2-a2 ') may be calculated.

  The evaluation substrate is placed on the XY stage 140, and the height position (Z value) of the evaluation substrate surface is measured using the Z sensor 160 while the XY stage 140 is moved (Step S111). In the measurement, the Z value at a plurality of speeds and accelerations is measured while changing the speed v and the acceleration a of the XY stage 140 (steps S113 and S114). The function generation unit 217 calculates a function f representing the amount of change in the height of the substrate surface due to the stage speed v and the acceleration a from the measurement results (step S115). The function f is stored in the storage device 206.

  After obtaining the coefficients a0, a1, a2, b1, b2 and the function f, the actual drawing is performed on the substrate 150 to be drawn. Drawing data of a pattern to be drawn on the substrate 150 is externally input to the storage device 202 and stored.

  The height distribution of the substrate 150 is measured using the Z sensor 160 (step S121). The Z map creating unit 212 creates a height direction distribution (Z map) using the height position (Z value) measured at each position (step S122). The Z map is stored in the storage device 204.

  The drawing process is started (step S123). For example, the shot data generation unit 214 reads out the drawing data from the storage device 202 and performs a plurality of stages of data conversion processing to generate device-specific shot data. In order to draw a figure pattern by the drawing apparatus, it is necessary to divide each figure pattern defined in the drawing data into a size that can be irradiated with one beam shot. Thus, the shot data generation unit 214 generates a shot figure by dividing the figure pattern indicated by the drawing data into a size that can be irradiated by one beam shot. Then, shot data is generated for each shot figure. In the shot data, for example, a figure type, a figure size, an irradiation position, and an irradiation amount are defined. The generated shot data is temporarily and sequentially stored in a memory (not shown).

  The drawing control unit 216 outputs the shot data to the deflection control unit 220. The deflection control unit 220 generates a deflection signal for controlling each deflector based on the shot data.

  The drawing control unit 218 outputs a speed command signal to the stage control unit 230 so that the stage speed corresponds to the drawing pattern density. The stage control section 230 controls the speed (acceleration) of the XY stage 140 based on the speed command signal.

  The correction unit 218 acquires information on the speed v and the acceleration a of the XY stage 140 from the speed command signal (Step S124). The velocity v and the acceleration a may be obtained in real time by differentiating displacement data obtained from a laser length meter that measures the position of the XY stage 140.

  The correction unit 218 acquires the drawing positions (beam irradiation positions) x and y from the shot data output to the deflection control unit 220 (Step S125).

The correction unit 218 calculates the variation amount f (v, a) of the substrate surface height due to the speed v and the acceleration a of the XY stage 140, and calculates the substrate surface height Zmap (x , Y) are corrected (step S126). The corrected substrate surface height z (x, y, v, a) at the drawing position is represented by the following equation.
z (x, y, v, a) = Zmap (x, y) + f (v, a)

  From the shot data, the deflection positions mx and my of the electron beam by the main deflector 134 (main deflection position; drawing origin of the sub deflection area) are obtained (step S127).

Using the following correction formula, a DAC value (a value output to a DAC (not shown) that determines a voltage value set in the main deflector 134) is obtained, and the shape of the main deflection area is corrected (step S128). .
DAC value X = (a0 + b0 * z) + (a1 + b1 * z) mx + (a2 + b2 * z) my
The DAC value Y can be calculated similarly. The correction formula does not have to be linear, and may be, for example, a cubic formula.

  The drawing control unit 216 controls the objective lens 116 based on the calculated shape correction amount of the main deflection region, adjusts the focal position, corrects rotation / contraction of the main deflection region, and performs a drawing process.

  As described above, according to the present embodiment, the substrate surface height measured in advance can be corrected in consideration of the fluctuation of the substrate surface height due to the stage speed (acceleration), and the substrate surface height can be calculated with high accuracy. . Therefore, adjustment of the focal position and the like can be performed with high accuracy, and deviation of the beam drawing position can be reduced.

  In the above embodiment, the description has been given of the fluctuation of the substrate surface height due to the change of the stage speed and the acceleration. However, the function f for converting the speed / acceleration into the fluctuation amount of the substrate surface height further includes the position as a variable. It may be.

  In the above embodiment, the example in which the change in the board surface height due to the change in the speed and the acceleration of the stage is considered is described. However, the acceleration is omitted, and only the change in the board surface height due to the change in the stage speed is considered. You may.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying constituent elements in an implementation stage without departing from the scope of the invention. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the above embodiments. For example, some components may be deleted from all the components shown in the embodiment. Further, components of different embodiments may be appropriately combined.

Reference Signs List 100 drawing unit 101 electron gun 102 electron beam column 103 electron beam 104 drawing room 112 illumination lens 114 projection lens 116 objective lens 120 blanking aperture 122 first aperture 124 second aperture 130, 132, 134, 136 deflector 140 XY stage 160 Z sensor 200 Control units 202, 204, 206 Storage device 210 Control computer 214 Shot data generation unit 216 Drawing control unit 220 Deflection control unit 230 Stage control unit

Claims (5)

A movable stage on which a substrate to be drawn is placed;
Using a charged particle beam, a drawing unit that draws a pattern on the surface of a substrate placed on the moving stage,
A measuring unit for measuring the height distribution of the substrate placed on the stationary stage,
A correction unit that adds the substrate height variation based on the moving speed of the stage to the substrate surface height at the drawing position determined from the substrate height distribution, and corrects the substrate surface height at the drawing position.
A control unit that adjusts a focal position of the charged particle beam based on the corrected substrate surface height at the drawing position,
Charged particle beam writing apparatus comprising:   The correction unit corrects the substrate surface height at the drawing position by adding the substrate height variation based on the moving speed and acceleration of the stage to the substrate surface height at the drawing position obtained from the substrate height distribution. The charged particle beam drawing apparatus according to claim 1, wherein   3. The charged particle beam drawing apparatus according to claim 1, wherein a moving speed of the stage changes according to a density of a pattern drawn on the substrate. 4. Using a charged particle beam, a charged particle beam drawing method for drawing a pattern on the surface of a substrate placed on a moving stage,
While the stage is stopped, a step of measuring the height distribution of the substrate placed on the stage,
Adding a substrate height variation based on the moving speed of the stage to the substrate surface height at the drawing position determined from the substrate height distribution, and correcting the substrate surface height at the drawing position;
Based on the corrected substrate surface height at the drawing position, adjusting the focal position of the charged particle beam,
Charged particle beam drawing method comprising: It is characterized by adding a substrate height variation based on the moving speed and acceleration of the stage to a substrate surface height at a drawing position obtained from the substrate height distribution, and correcting the substrate surface height at the drawing position. The charged particle beam writing method according to claim 4.

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