JP7646582B2 - Charged particle beam irradiation method and charged particle beam irradiation device - Google Patents

Description

The present invention relates to a charged particle beam irradiation method and a charged particle beam irradiation device.

Conventionally, in electron beam lithography devices that irradiate a sample on a stage with an electron beam to draw a pattern on the sample, drift, in which the irradiation position of the electron beam deviates from the desired position during drawing, can occur. For example, when an electron beam is irradiated on a sample, reflected electrons are generated. The generated reflected electrons collide with the optical system and detector in the electron beam lithography device, causing charge-up. A new electric field is generated by the charge-up, and the generated electric field changes the trajectory of the electron beam irradiated toward the sample. In this way, the change in the beam trajectory due to the charge-up is one of the causes of electron beam drift. To correct the drift, in electron beam lithography devices, an electron beam is irradiated on a mark provided on a stage, the amount of drift is calculated based on the detection result of the electron beam reflected by the mark, and the irradiation position of the electron beam is corrected based on the calculated amount of drift (see Patent Document 1).

JP 2007-41244 A

However, in conventional electron beam lithography devices, when an error occurs in the mark position due to external factors, it is difficult to correct the irradiation position of the electron beam with high precision. Possible external factors include fluctuations in stage posture (rotation fluctuations) due to distortion and heat caused by the assembly method of each device, the adhesion of the measurement mark, the fixing state of the leaf spring, etc.

The object of the present invention is to provide a charged particle beam irradiation method and a charged particle beam irradiation device that can appropriately correct the irradiation position of a charged particle beam.

A charged particle beam irradiation method according to one aspect of the present invention includes the steps of:
a stage provided in the charged particle beam irradiation device and movable in an XY direction, the stage being configured to place a drawing target on the stage; and measuring a positional variation of a mark provided on the stage in order to correct an irradiation position of the charged particle beam on the drawing target;
Measure the amount of rotational fluctuation of the stage;
determining a correction value based on the amount of positional variation and the amount of rotational variation of the mark;
and correcting the irradiation position of the charged particle beam using the correction value to perform drawing.

In the above-mentioned charged particle beam irradiation method,
When the amount of rotational variation is equal to or greater than a threshold value, a correction value may be obtained based on the amount of positional variation of the mark and the amount of rotational variation.

In the above-mentioned charged particle beam irradiation method, the rotational fluctuation amount may include at least one of the fluctuation amount of the yawing amount, the fluctuation amount of the pitching amount, and the fluctuation amount of the rolling amount of the stage.

In the above-mentioned charged particle beam irradiation method, the sensitivity of the rotational fluctuation amount to the positional fluctuation amount in the charged particle beam irradiation device may be calculated in advance, and the correction value may be calculated based on the sensitivity.

The charged particle beam irradiation apparatus according to one aspect of the present invention comprises:
a stage on which an irradiation target is placed and which is movable in the XY directions;
A mark provided on the stage;
a first measurement unit for measuring a positional variation of the mark;
A second measurement unit that measures a rotation fluctuation amount of the stage;
a correction unit that obtains a correction value based on the positional fluctuation amount and the rotational fluctuation amount and corrects the irradiation position of the charged particle beam;
Equipped with.

According to the present invention, the irradiation position of the charged particle beam can be appropriately corrected.

1 is a diagram showing an electron beam lithography apparatus applicable to the electron beam lithography method according to the present embodiment; FIG. 2 is a perspective view showing a mark for drift correction provided in the electron beam drawing apparatus; 4 is a flowchart showing an electron beam writing method according to the present embodiment. 11A and 11B are explanatory diagrams for explaining an operation of acquiring trend data of the measurement position of the mark and the attitude of the XY stage in a pre-operation step in the electron beam writing method according to the present embodiment; 10 is an explanatory diagram for explaining a selection operation of an electron beam drawing apparatus in a pre-operation step in the electron beam drawing method according to the present embodiment; FIG. 10A to 10C are explanatory diagrams for explaining a calculation operation of sensitivity in a pre-operation step in the electron beam writing method according to the present embodiment.

Below, an embodiment of the present invention will be described with reference to the drawings. The embodiment does not limit the present invention. For example, in the following embodiment, a configuration using an electron beam as an example of a charged particle beam will be described, but the charged particle beam is not limited to an electron beam, and may be a beam using charged particles other than an electron beam, such as an ion beam.

Figure 1 is a block diagram showing an electron beam drawing apparatus 1 that can be applied to the electron beam drawing method according to this embodiment. The electron beam drawing method is an example of a charged particle beam irradiation method. The electron beam drawing apparatus 1 is an example of a charged particle beam irradiation apparatus.

As shown in FIG. 1, the electron beam drawing device 1 is broadly composed of a drawing unit 2 and a control unit 3.

The drawing section 2 includes an electron barrel 4 and a drawing chamber 6. Inside the electron barrel 4, in the direction of travel of the electron beam 200, an electron gun 41, which is an electron beam irradiation source, an illumination lens 42, a blanking deflector 43, a blanking aperture 44, a first aperture 45, a first deflector 46, a projection lens 47, a second aperture 48, a second deflector 49, and an objective lens 410 are arranged. The insides of the electron barrel 4 and the drawing chamber 6 are evacuated by a vacuum pump (not shown) to create a vacuum atmosphere with a pressure lower than atmospheric pressure.

In the drawing chamber 6, an XY stage 61 and a detector 62 are arranged. A sample 63 to be drawn is arranged on the XY stage 61. The sample 63 may include an exposure reticle used when manufacturing a semiconductor device, or a semiconductor substrate such as a silicon wafer on which a semiconductor device is manufactured. The sample 63 may also include a mask blank on which resist is applied and on which nothing is yet drawn.

A mark 64 for drift correction is provided on the XY stage 61. The detector 62 detects the electron beam 200 irradiated to and reflected from the mark 64. The detected electron beam 200 is used for drift correction, which will be described later. The mark 64 is fixed to the upper surface of the XY stage 61, for example, via a leaf spring. The mark 64 is made of, for example, a heavy metal film. The mark 64 may be made of a material other than heavy metal as long as it can emit reflected electrons in response to the incidence of the electron beam 200. Although one mark 64 is illustrated in FIG. 2 as an example, multiple marks 64 may be provided. In that case, the multiple marks 64 may be provided at intervals in the X direction, the Y direction, or both.

A mirror 65 for measuring the position of the XY stage 61 is also placed on the XY stage 61. As shown in the conceptual diagram in FIG. 2, the mirror 65 has an X mirror 651 with a reflective surface facing the X direction, and a Y mirror 652 with a reflective surface facing the Y direction. The X mirror 651 and Y mirror 652 are irradiated with lasers L1X, L2X, and L3X in the X direction, and lasers L1Y, L2Y, and L3Y in the Y direction, respectively, to measure the position and attitude of the XY stage 61.

The control unit 3 has a control computer 31, a deflection control circuit 32, digital-to-analog converters (hereinafter referred to as DACs) 33, 34, and 35, a detection amplifier 36, a stage position detector 37, a storage device 38, and a drive circuit 39. The deflection control circuit 32, the detection amplifier 36, the stage position detector 37, the storage device 38, and the drive circuit 39 are connected to the control computer 31 via a bus. The detection amplifier 36 is also connected to the detector 62. The storage device 38 stores drawing data used for drawing a pattern that is input from the outside. The DAC 33 is connected between the blanking deflector 43 and the deflection control circuit 32. The DAC 34 is connected between the first deflector 46 and the deflection control circuit 32. The DAC 35 is connected between the second deflector 49 and the deflection control circuit 32.

The control computer 31 has a first measurement unit 311, a second measurement unit 312, a judgment unit 314, and a correction unit 315 as components for performing drift correction using the reflected electron beam from the mark 64. The components 311 to 315 of the control computer 31 are configured, for example, as hardware such as a computer. At least a portion of the components 311 to 315 of the control computer 31 may be configured as software.

The electron beam drawing apparatus 1 having the above configuration emits an electron beam 200 from the electron gun 41. The emitted electron beam 200 illuminates the entire first aperture 45 having a rectangular hole by the illumination lens 42. The first aperture 45 shapes the electron beam 200 into a rectangle by passing a part of the electron beam 200. Here, in order to prevent the electron beam 200 from being irradiated on the sample 63 more than necessary, the blanking deflector 43 applies a deflection voltage to the electron beam 200 to deflect the electron beam 200. The deflected electron beam 200 is cut by the blanking aperture 44 and does not reach the sample 63. The deflection voltage of the blanking deflector 43 is controlled by the deflection control circuit 32 and the DAC 33. In the case of beam ON (blanking OFF), the electron beam 200 emitted from the electron gun 41 proceeds along the trajectory shown by the solid line in FIG. 1. On the other hand, when the beam is OFF (blanking is ON), the electron beam 200 emitted from the electron gun 41 travels along the trajectory shown by the dotted line in Figure 1.

The electron beam 200 that has passed through the first aperture 45 is projected onto the second aperture 48 by the projection lens 47. At this time, the first deflector 46 applies a deflection voltage to the electron beam 200 to deflect the electron beam 200. The projection position of the electron beam 200 onto the second aperture 48 is controlled by the deflection of the electron beam 200 by the first deflector 46. The deflection voltage of the first deflector 46 is controlled by the deflection control circuit 32 and the DAC 34. A portion of the electron beam 200 according to the projection position onto the second aperture 48 passes through the second aperture 48, changing the shape and dimensions of the electron beam 200. As a result, the electron beam 200 is shaped.

The electron beam 200 that passes through the second aperture 48 is focused on the sample 63 by the objective lens 410 and deflected by the second deflector 49. As a result, the electron beam 200 is irradiated onto the desired position of the sample 63 on the continuously moving XY stage 61, and a pattern is drawn. The XY stage 61 is driven by the drive circuit 39.

Next, an electron beam drawing method using the electron beam drawing device 1 will be described. FIG. 3 is a flowchart showing the electron beam drawing method according to this embodiment. First, as shown in FIG. 3, a preparatory process for drift correction is carried out (step S1).

In the preliminary work process, first, as shown in FIG. 4, trend data is acquired for the measurement position of the mark 64 and the attitude (rotation amount) of the XY stage 61 specific to each electron beam drawing device 1 that affects the position accuracy of the mark 64 during drawing. Trend data is acquired for each electron beam drawing device 1. In the example shown in FIG. 4, the trend data has trend data on the X direction side and trend data on the Y direction side. The trend data on the X direction side has the measurement time (i.e., time) on the horizontal axis, and the X coordinate MkX [nm] of the measurement position of the mark 64 and the yawing amount YawX [μrad] and pitching amount PitchX [μrad] on the X direction side, which are an example of the attitude of the XY stage 61, on the vertical axis. The trend data on the Y direction side has the measurement time on the horizontal axis, the Y coordinate MkY [nm] of the measurement position of the mark 64, and the yawing amount YawY [μrad] and pitching amount PitchY [μrad] on the Y direction side of the XY stage 61 on the vertical axis. The yawing amount YawX on the X direction side is the amount of rotation of the XY stage 61 around the Z axis. The yawing amount YawY on the Y direction side is the amount of rotation of the XY stage 61 around the Z axis. The pitching amount PitchX on the X direction side is the amount of rotation of the XY stage 61 around the Y axis. The pitching amount PitchY on the Y direction side is the amount of rotation of the XY stage 61 around the X axis. Note that the attitude of the XY stage may include the yawing amount, pitching amount, and the rolling amount, and it is sufficient to include at least one of these.

In the trend data acquisition operation, the position of the mark 64 is measured by driving the XY stage 61 to a position where the mark 64 is irradiated with the electron beam 200, and then detecting the electron beam 200 irradiated to and reflected from the mark 64 with the detector 62. More specifically, the control computer 31 acquires the detection result of the electron beam 200 detected by the detector 62, amplified by the detection amplifier 36, and converted into digital data, while causing the stage position detector 37 to measure the position (X coordinate, Y coordinate) and attitude (Yaw, Pitch) of the XY stage 61 based on the detection result of the laser irradiated to and reflected from the mirror 65.
The control computer 31 calculates the measured position (MkX, MkY) of the mark 64, the yawing amount (YawX, YawY) and the pitching amount (PitchX, PitchY) of the XY stage from the detection result of the electron beam 200. The control computer 31 obtains trend data of the electron beam drawing apparatus 1 by repeating the position measurement of the mark 64 with one drawing operation (for one mask) as one data in the same electron beam drawing apparatus 1. Note that the stage position detector 37 can calculate the X coordinate of the XY stage 61 based on the average value of the detection time required for three lasers L1X, L2X, and L3X irradiated on and reflected by the X mirror 651, for example, as shown in FIG. 2. The laser L1X and the laser L2X are spaced apart in the Y direction. The laser L1X and the laser L3X are spaced apart in the Z direction. Furthermore, the stage position detector 37 can calculate the Y coordinate of the XY stage 61 based on the average value of the detection times of the three lasers L1Y, L2Y, and L3Y irradiated on and reflected by the Y mirror 652. There is a gap between the lasers L1Y and L2Y in the X direction. There is a gap between the lasers L1Y and L3Y in the Z direction.

In the trend data acquisition operation, YawX can be calculated based on, for example, the difference in the detection time required by the stage position detector 37 for the two lasers L1X and L2X irradiated on and reflected by the X mirror 651. YawY can be calculated based on, for example, the difference in the detection time required by the stage position detector 37 for the two lasers L1Y and L2Y irradiated on and reflected by the Y mirror 652. PitchX can be calculated based on, for example, the difference in the detection time required by the stage position detector 37 for the two lasers L1X and L3X irradiated on and reflected by the X mirror 651. PitchY can be calculated based on, for example, the difference in the detection time required by the stage position detector 37 for the two lasers L1Y and L3Y irradiated on and reflected by the Y mirror 652.

Based on the trend data thus obtained, a correlation coefficient (hereinafter also simply referred to as correlation coefficient) between the positional fluctuation amount of the mark 64 and the rotational fluctuation amount of the XY stage 61 that depends on the electron beam drawing device 1 is calculated for each electron beam drawing device 1. The correlation coefficient is a number that serves as an index for measuring the strength of the linear relationship between the positional fluctuation amount of the mark 64 and the rotational fluctuation amount of the XY stage 61. Specifically, the correlation coefficient is the covariance between the positional fluctuation amount of the mark 64 and the rotational fluctuation amount of the XY stage 61 divided by the product of the standard deviation of the positional fluctuation amount of the mark 64 and the standard deviation of the rotational fluctuation amount of the XY stage 61.

The amount of positional variation of the mark 64 includes the amount of variation ΔMkX of the X-coordinate and the amount of variation ΔMkY of the Y-coordinate of the mark 64 measured at a certain measurement time and the measurement time immediately before that.

The rotational fluctuation amount of the XY stage 61 includes the YawX fluctuation amount ΔYawX, the YawY fluctuation amount ΔYawY, the PitchX fluctuation amount ΔPitchX, and the PitchY fluctuation amount ΔPitchY measured at a certain measurement time and the measurement time immediately before that.

The correlation coefficients include a correlation coefficient between ΔMkX and the amount of fluctuation in YawX ΔYawX, a correlation coefficient between ΔMkY and the amount of fluctuation in YawY ΔYawY, a correlation coefficient between ΔMkX and the amount of fluctuation in PitchX ΔPitchX, and a correlation coefficient between ΔMkY and the amount of fluctuation in PitchY ΔPitchY.

The correlation coefficient is calculated for each electron beam drawing device 1. The calculated correlation coefficients for each electron beam drawing device 1 may be displayed on a display device in a comparable state. FIG. 5 is a diagram for explaining an electron beam drawing device 1 to which the electron beam drawing method according to this embodiment is applied. The correlation function shown in FIG. 5 is the correlation coefficient between ΔMkX and the Yaw fluctuation amount ΔYaw. A graph similar to FIG. 5 can also be defined for other correlation functions. When the absolute value of the correlation coefficient is equal to or greater than a threshold value, that is, in FIG. 5, the drift correction of this embodiment can be applied to device A and device B whose absolute value of the correlation coefficient is equal to or greater than a threshold value TH.

Next, in the pre-operation process, a process is carried out to calculate the sensitivity, which is the slope of a linear function of the amount of rotational fluctuation of the XY stage 61 relative to the amount of positional fluctuation of the mark 64, for the electron beam drawing device 1 that irradiates the electron beam. The sensitivity includes the sensitivity of ΔYawX to ΔMkX, the sensitivity of ΔYawY to ΔMkY, the sensitivity of ΔMkX and ΔPitchX, and the sensitivity of ΔPitch to ΔMkY.

The sensitivity is calculated, for example, by the calculation unit 313 in the control computer 31 or by a computer outside the device. FIG. 6 is an explanatory diagram for explaining the calculation of sensitivity in the pre-operation process in the electron beam drawing method according to this embodiment. FIG. 6 shows a graph with ΔMkX on the vertical axis y and the fluctuation amount ΔYawX of YawX on the horizontal axis x. In FIG. 6, a linear function y=ax+b is established between the horizontal axis x and the vertical axis y. In this case, the calculated sensitivity is a [nm/μrad], which is the slope of the linear function. Note that the sensitivity shown in FIG. 6 is the sensitivity of ΔYawX to ΔMkX, but other sensitivities can be defined in the same way.

After the preparatory work process, drawing is started as shown in FIG. 3. After drawing starts, drawing is paused at a predetermined timing when drift correction should be performed (step S2).

Then, the first measurement unit 311 of the control computer 31 starts measuring the position of the mark 64 (step S3). Specifically, the first measurement unit 311 drives the XY stage 61 by the drive circuit 39 so that the mark 64 is irradiated with the electron beam, and causes the detector 62 to detect the electron beam 200 irradiated and reflected by the mark 64. The first measurement unit 311 then obtains the detection result of the electron beam 200 from the detector 62 via the detection amplifier 36. The first measurement unit 311 also continuously obtains the position of the XY stage 61 from the stage position detector 37. The first measurement unit 311 then calculates the position of the mark 64 (i.e., the X coordinate and the Y coordinate) from the position of the XY stage 61 detected when the detection result of the electron beam 200 is obtained.

When measurement of the position of the mark 64 is started, the second measurement unit 312 of the control computer 31 starts measuring the amount of rotation of the XY stage 61. In the example shown in FIG. 3, the second measurement unit 312 starts measuring Yaw (YawX and YawY) and Pitch (PitchX and PitchY) (step S4).

Next, the second measurement unit 312 calculates the measured rotational fluctuation amount of the XY stage 61. In the example shown in FIG. 3, the second measurement unit 312 calculates the Yaw fluctuation amount (ΔYawX and ΔYawY) and the Pitch fluctuation amount (ΔPitchX and ΔPitchY) (step S5). In addition, the first measurement unit 311 calculates the position fluctuation amount (ΔMkX and ΔMkY) of the mark 64 based on the calculated position of the mark 64.

Next, the determination unit 314 of the control computer 31 determines whether the calculated rotational fluctuation amount of the XY stage 61 is equal to or greater than a threshold value. In the example shown in FIG. 3, the determination unit 314 determines whether the Yaw fluctuation amount (ΔYawX, ΔYawY) and the Pitch fluctuation amount (ΔPitchX, ΔPitchY) are equal to or greater than a threshold value (step S6).

If the calculated rotational fluctuation amount of the XY stage 61 is equal to or greater than the threshold value (step S6: Yes), the correction unit 315 of the control computer 31 performs drift correction by correcting the irradiation position of the electron beam using a correction value based on the positional fluctuation amount of the mark 64 and the calculated rotational fluctuation amount of the XY stage 61 (step S7). In the example shown in Fig. 3, the correction unit 315 performs drift correction according to the following formulas (1) and (2).
Correction value X'=ΔMkX-(YawX sensitivity×ΔYawX+PitchX sensitivity×ΔPitchX) (1)
Correction value Y′=ΔMkY−(YawY sensitivity×ΔYawY+PitchY sensitivity×ΔPitchY) (2)

The correction value X' is the correction value for the irradiation position of the electron beam in the X direction. The correction value Y' is the correction value for the irradiation position of the electron beam in the Y direction. Note that each sensitivity is calculated in advance from the correlation between the amount of positional fluctuation and the amount of rotational fluctuation, as described above.

Note that if some of the four fluctuation amounts ΔYawX, ΔYawY, ΔPitchX, and ΔPitchY are less than the threshold value, the fluctuation amounts less than the threshold value may be set to zero in formulas (1) and (2).

On the other hand, if all of the calculated rotational fluctuation amounts of the XY stage 61 are less than the threshold fluctuation amount (step S6: Yes), the correction unit 315 corrects the irradiation position of the electron beam 200 according to conventional drift correction (step S8). In this case, the correction unit 315 can use ΔMkX as the correction value X' and ΔMkY as the correction value Y'.

After correcting the irradiation position of the electron beam 200, drawing is resumed (step S9).

According to this embodiment, the position of the mark 64 is measured, the amount of rotational fluctuation of the XY stage 61 specific to the electron beam drawing device 1 that affects the positional accuracy of the mark 64 is measured, and it is determined whether the amount of rotational fluctuation is equal to or greater than a threshold amount of fluctuation. If the amount of rotational fluctuation is equal to or greater than the threshold amount of fluctuation, the irradiation position of the electron beam is corrected using a correction value based on the amount of positional fluctuation of the mark 64 and the calculated amount of rotational fluctuation.

This makes it possible to appropriately correct the irradiation position of the electron beam even if an error occurs in the position of the mark 64 due to external factors specific to the device, such as fluctuations in stage posture (rotation fluctuations) caused by distortion or heat due to the assembly method of each device, adhesion of the measurement mark, or the fixed state of the leaf spring.

The above-described embodiments are presented as examples and are not intended to limit the scope of the invention. The embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are within the scope of the invention and its equivalents as set forth in the claims, as well as the scope and spirit of the invention.

1 Electron beam drawing device, 64 Mark, 200 Electron beam, 311 First measurement unit, 312 Second measurement unit, 313 Calculation unit, 314 Judgment unit, 315 Correction unit

Claims (4)

a stage provided in a charged particle beam irradiation device and movable in an XY direction, a target to be drawn is placed on the stage, and a positional fluctuation amount of a mark provided on the stage is measured at a predetermined timing and a rotational fluctuation amount of the stage is measured in order to perform drift correction of an irradiation position of the charged particle beam on the target to be drawn ;
determining a position correction value based on the rotational fluctuation amount and a correlation between the rotational fluctuation amount and the positional fluctuation amount that is determined in advance for each of the charged particle beam irradiation devices;
and correcting the irradiation position of the charged particle beam based on the measured amount of positional variation of the mark and the position correction value, and performing drawing. The charged particle beam irradiation method according to claim 1 , further comprising the step of: determining the position correction value when the amount of rotational fluctuation is equal to or greater than a threshold value. The charged particle beam irradiation method according to claim 1 or 2, wherein the rotational fluctuation amount includes at least one of the fluctuation amount of the yawing amount, the fluctuation amount of the pitching amount, and the fluctuation amount of the rolling amount of the stage. a stage on which an irradiation target is placed and which is movable in the XY directions;
A mark provided on the stage;
a first measurement unit that measures a positional variation amount of the mark at a predetermined timing in order to perform drift correction of an irradiation position of the charged particle beam on the irradiation target ;
a second measurement unit that measures a rotation fluctuation amount of the stage at the predetermined timing ;
a correction unit that calculates a position correction value based on the rotational fluctuation amount and a correlation coefficient between the rotational fluctuation amount and the position fluctuation amount that is calculated in advance for each of the charged particle beam irradiation devices, and corrects the irradiation position of the charged particle beam based on the measured position fluctuation amount of the mark and the position correction value ;
A charged particle beam irradiation device comprising: