JPWO2008120391A1 - Multi-column electron beam exposure apparatus and multi-column electron beam exposure method - Google Patents

Abstract

To provide a multi-column electron beam exposure apparatus and a multi-column electron beam exposure method capable of improving exposure accuracy and improving exposure throughput by adjusting calibration time. A multi-column electron beam exposure apparatus uses a plurality of column cells, an electron beam characteristic detector, a deflector for deflecting an electron beam based on exposure data, and an electron beam characteristic detector. Prediction of electron beam characteristics using a prediction function that smoothly connects multiple measurement values at multiple calibration times and changes the electron beam characteristics up to the next calibration time continuously with the drawing time A control unit that calculates a value and calculates a correction amount for the exposure data of each column cell. The control unit adjusts the calibration time interval according to the difference between the measured value and the predicted value of the electron beam characteristics. [Selection] Figure 7

Description

  The present invention relates to an electron beam exposure apparatus and an electron beam exposure method, and in particular, a multi-column electron beam exposure apparatus and a multi-column suitable for performing exposure processing by providing a plurality of column cells and performing high-precision beam calibration. The present invention relates to an electron beam exposure method.

  In a conventional electron beam exposure apparatus, a variable rectangular opening or a plurality of stencil mask patterns are prepared in a stencil mask, and these are selected by beam deflection and transferred and exposed on a wafer. In this electron beam exposure apparatus, a plurality of mask patterns are prepared, but only one electron beam is used for exposure, and only one mask pattern is transferred at a time.

  As such an exposure apparatus, for example, Patent Document 1 discloses an electron beam exposure apparatus that performs partial batch exposure. Partial batch exposure refers to irradiating a beam to one pattern area selected by beam deflection from a plurality of, for example, 100 stencil patterns arranged on a mask, for example, an area of 300 × 300 μm, and the beam cross section is the shape of the stencil pattern. Then, the beam that has passed through the mask is deflected back by a later stage deflector, reduced to a constant reduction rate determined by the electron optical system, for example, 1/60, and transferred to the sample surface. The area of the sample surface irradiated at one time is, for example, 5 × 5 μm. If the stencil pattern on the mask is appropriately prepared according to the device pattern to be exposed, the number of exposure shots required is greatly reduced and the throughput is improved as compared with the case of only the variable rectangular aperture.

  Furthermore, there has been proposed a multi-column electron beam exposure apparatus that collects a plurality of such columns each having a smaller size (hereinafter referred to as a column cell) and performs exposure processing in parallel on a wafer. (Refer nonpatent literature 2). Each column cell is equivalent to the column of a single column electron beam exposure apparatus, but the entire multi-column processes in parallel, so that the exposure throughput can be increased by the number of columns.

  In the multi-column electron beam exposure apparatus as described above, throughput can be improved.

  However, a phenomenon occurs in which the connection accuracy of the exposure patterns deteriorates at the boundary between the irradiation regions of the column cells. FIG. 1 shows an example in which a desired pattern cannot be obtained at positions between column cells. FIG. 1A shows a desired pattern 3 at the boundary between the irradiation region 1 of the first column cell and the irradiation region 2 of the second column cell. FIG. 1B shows an example of a pattern obtained as a result of the exposure. In the area 1, the pattern 5 is exposed, and in the area 2 the pattern 4 is exposed, which is different from the desired exposure 3. As described above, the width of the exposure pattern is different in each region, and a desired pattern may not be exposed. In addition, the exposure position is shifted, and in the worst case, the pattern may be cut off.

  There is no particular problem when it is designed not to expose a continuous pattern between column cells as described above, but designing with consideration of the position of multiple column cells significantly reduces the design freedom. Therefore, it is inevitable to expose a continuous pattern between column cells.

  Also, for example, there is no particular problem if the pattern to be drawn is wide, and even if the pattern is displaced even if the pattern is shifted at the connection position between the column cells, there is no problem. When the width is narrow, it is required to increase the connecting accuracy.

  The electron beam in each column cell is considered to be affected by changes in the distance between components inside the column cell due to temperature expansion, rotation of the entire column cell, and expansion / contraction due to atmospheric pressure. For example, when the distance between the column cells is 75 mm, the temperature expansion coefficient of pure iron constituting the column cells is 12 ppm, and thus a positional shift of 900 nm occurs with a temperature change of 1 ° C. Thereby, it is considered that the beam position shifts.

  In order to calibrate the beam position deviation, the beam position is adjusted every predetermined time. As a technique related to this, Patent Document 3 discloses a method of correcting a drift by predicting a beam drift.

However, if calibration is frequently performed in order to make the beam position highly accurate, there arises a problem that the exposure throughput is lowered. For example, if four column cells are used, it takes 5 seconds for the calibration time, and assuming that calibration is performed every 60 seconds, 1/12 of the total exposure time is a useless time that does not contribute to exposure. turn into.
In Patent Document 3, when predicting the beam drift, the result obtained by drawing the same pattern on the same wafer as the wafer to be actually drawn to obtain the beam drift is used. For this reason, the influence due to the temperature change of the column cell is not considered, and it is difficult to predict the beam drift with high accuracy.
JP 2004-88071 A T. Haraguchi et.al. J. Vac. Sci. Technol, B22 (2004) 985 Japanese Patent Laid-Open No. 11-8171

  The present invention has been made in view of the problems of the prior art, and an object thereof is to provide a multi-column electron beam exposure apparatus and a multi-column electron beam exposure apparatus capable of improving exposure accuracy by adjusting calibration time and improving exposure throughput. A column electron beam exposure method is provided.

  The above-described problems are related to a plurality of column cells, a wafer stage on which a sample holder having an electron beam characteristic detection unit for measuring electron beam characteristics is mounted, and each column cell that deflects an electron beam based on exposure data. Using the provided deflector and the electron beam characteristic detector, a continuous function that smoothly connects a plurality of measured values at a plurality of past calibration times and draws the electron beam characteristics up to the next calibration time A multi-column electron, comprising: a control unit that calculates a predicted value of electron beam characteristics using a prediction function that continuously changes with time, and calculates a correction amount for exposure data of each column cell. This is solved by a beam exposure apparatus.

  In the multi-column electron beam exposure apparatus according to this aspect, the electron beam characteristic may be a beam position or a beam intensity of an irradiated electron beam, and the electron beam characteristic detection unit includes a calibration chip having a reference mark. Or it may be a Faraday cup. The reference mark may be formed on the sample holder, and a positioning mark formed on the wafer or any other mark may be applied.

The predetermined prediction function may be a function represented by the following equation.

  Here, Δ (T) is a predicted value at time T, pi is a measured value of electron beam characteristics at time Ti, and n is a natural number.

  Further, in the multi-column electron beam exposure apparatus according to this aspect, an allowable error of the connection accuracy between the column cells is set as an optimal allowable error and a limit allowable error having a wider error range than the optimal allowable error, and the control unit When the difference between the measured value and the measured value is larger than the limit tolerance, the calibration time interval is shortened, and the exposure is performed between the time when the measured value is measured and the time measured immediately before the measured time. The processed area is set as an area that needs to be inspected, and when the difference between the predicted value and the measured value is smaller than the optimum allowable error, the calibration time interval is increased and the predicted value and the measured value are When the difference is between the optimum tolerance and the marginal tolerance, the calibration time interval is adjusted by setting the calibration time interval as a standard time interval. It may be.

  In the present invention, the measurement values of several electron beam characteristics are applied to a prediction function for predicting the beam drift to predict the drift of the beam position or the beam intensity. The prediction function is a function that represents a curve passing through several points measured in the past. The voltage value applied to the deflector is calculated based on this drift prediction value until the actual measurement of the electron beam characteristics in the next calibration. This makes it possible to improve the accuracy of the beam irradiation position and beam intensity. As a result, the connection accuracy between a plurality of column cells is improved, and the exposure throughput is improved.

  Further, the calibration interval for actually measuring the beam characteristics is adjusted according to the difference between the predicted value and the measured value of the electron beam characteristics. For example, the tolerance of the accuracy of connection between column cells is the optimum tolerance and the marginal tolerance with a wider error range than the optimum tolerance, and the difference between the predicted value and the measured value at the time of the forecast value is smaller than the optimum tolerance. When the calibration time interval is long. Thereby, the time taken for calibration can be shortened, and the exposure throughput can be improved.

  According to another aspect of the present invention, there is provided a multi-column electron beam exposure method implemented in the multi-column electron beam exposure apparatus according to the above aspect. A multi-column electron beam exposure method according to an embodiment includes an electron beam characteristic detected by an electron beam characteristic detection unit at a predetermined time interval in each column cell of a multi-column electron beam exposure apparatus including a plurality of column cells. An exposure method for performing calibration, measuring an electron beam characteristic at a calibration time to obtain a measured value of the electron beam characteristic, and applying the measured value to a predetermined prediction function to calculate the calibration time. A step of calculating a predicted value of the electron beam characteristics up to the calibration time immediately after, a step of correcting exposure data based on the predicted value of the electron beam characteristics, and a step of performing an exposure process according to the corrected exposure data It is characterized by having.

FIGS. 1A and 1B are diagrams for explaining problems in a multi-column electron beam exposure apparatus. FIG. 2 is a block diagram of a multi-column electron beam exposure apparatus according to the present invention. FIG. 3 is a block diagram of one column cell in the exposure apparatus according to FIG. FIG. 4 is a schematic diagram of a column cell control unit of the exposure apparatus according to FIG. FIG. 5 is a diagram showing an exposure range when there are four column cells. FIG. 6 is a diagram showing a prediction curve of beam position deviation. FIG. 7 is a diagram for explaining the prediction of the beam position deviation and the difference from the measured value. FIG. 8 is a flowchart for explaining the calibration time adjustment processing. FIG. 9 is a diagram showing a prediction curve of beam position deviation considering holder replacement. FIG. 10 is a diagram for explaining the change over time between the column cells.

  Embodiments of the present invention will be described below with reference to the drawings.

(Configuration of multi-column electron beam exposure system)
FIG. 2 is a schematic block diagram of the multi-column electron beam exposure apparatus according to the present embodiment.
The multi-column electron beam exposure apparatus is roughly divided into an electron beam column 10 and a controller 20 that controls the electron beam column 10. Among these, the electron beam column 10 is composed of a plurality of equivalent column cells 11, for example, 16 to form an entire column. All the column cells 11 are composed of the same unit described later. Under the column cell 11, for example, a wafer stage 13 on which a 300 mm wafer 12 is mounted is disposed.

  On the other hand, the control unit 20 includes an electron gun high-voltage power supply 21, a lens power supply 22, a digital control unit 23, a stage drive controller 24, and a stage position sensor 25. Among these, the electron gun high-voltage power supply 21 supplies power for driving the electron gun of each column cell 11 in the electron beam column 10. The lens power supply 22 supplies power for driving the electromagnetic lens of each column cell 11 in the electron beam column 10. The digital control unit 23 is an electric circuit that controls each part of the column cell 11 and outputs a high-speed deflection output or the like. The number of digital control units 23 corresponding to the number of column cells 11 is prepared.

  The stage drive controller 24 moves the wafer stage 13 based on the position information from the stage position sensor 25 so that the electron beam is irradiated to a desired position on the wafer 12. Each of the above-described units 21 to 25 is controlled in an integrated manner by an integrated control system 26 such as a workstation.

  In the above-described multi-column electron beam exposure apparatus, all the column cells 11 are composed of the same column unit.

  FIG. 3 is a schematic configuration diagram of each column cell 11 used in the multi-column electron beam exposure apparatus.

  Each column cell 11 is roughly divided into an exposure unit 100 and a column cell control unit 31 that controls the exposure unit 100. Among these, the exposure unit 100 includes an electron beam generation unit 130, a mask deflection unit 140, and a substrate deflection unit 150.

  In the electron beam generator 130, the electron beam EB generated from the electron gun 101 is converged by the first electromagnetic lens 102, then passes through the rectangular aperture 103 a of the beam shaping mask 103, and the cross section of the electron beam EB is rectangular. To be shaped.

  Thereafter, the electron beam EB is imaged on the exposure mask 110 by the second electromagnetic lens 105 of the mask deflection unit 140. The electron beam EB is deflected to a specific pattern P formed on the exposure mask 110 by the first and second electrostatic deflectors 104 and 106, and the cross-sectional shape thereof is shaped into the pattern P.

  Although the exposure mask 110 is fixed to the mask stage 123, the mask stage 123 is movable in a horizontal plane, and the deflection range (beam deflection region) of the first and second electrostatic deflectors 104 and 106 is set. In the case of using the pattern P in the part exceeding, the pattern P is moved into the beam deflection region by moving the mask stage 123.

  The third and fourth electromagnetic lenses 108 and 111 arranged above and below the exposure mask 110 play a role of forming an image of the electron beam EB on the substrate by adjusting their current amounts.

  The size of the electron beam EB that has passed through the exposure mask 110 is reduced by the fifth electromagnetic lens 114 after being returned to the optical axis C by the deflection action of the third and fourth electrostatic deflectors 112 and 113.

  The mask deflection unit 140 is provided with first and second correction coils 107 and 109, which correct beam deflection aberrations generated by the first to fourth electrostatic deflectors 104, 106, 112, and 113. Is done.

  Thereafter, the electron beam EB passes through the aperture 115a of the shielding plate 115 constituting the substrate deflecting unit 150, and is projected onto the substrate by the first and second projection electromagnetic lenses 116 and 121. As a result, the pattern image of the exposure mask 110 is transferred to the substrate at a predetermined reduction ratio, for example, a reduction ratio of 1/10.

  The substrate deflecting unit 150 is provided with a fifth electrostatic deflector 119 and an electromagnetic deflector 120, and the electron beam EB is deflected by these deflectors 119 and 120, and the exposure mask is placed at a predetermined position on the substrate. An image of the pattern is projected.

  Further, the substrate deflection unit 150 is provided with third and fourth correction coils 117 and 118 for correcting the deflection aberration of the electron beam EB on the substrate.

  On the other hand, the column cell control unit 31 includes an electron gun control unit 202, an electron optical system control unit 203, a mask deflection control unit 204, a mask stage control unit 205, a blanking control unit 206, and a substrate deflection control unit 207. Among these, the electron gun control unit 202 controls the electron gun 101 to control the acceleration voltage of the electron beam EB, beam emission conditions, and the like. Further, the electron optical system control unit 203 controls the amount of current to the electromagnetic lenses 102, 105, 108, 111, 114, 116 and 121, and the magnification and focus of the electron optical system in which these electromagnetic lenses are configured. Adjust the position. The blanking control unit 206 controls the voltage applied to the blanking electrode 127 to deflect the electron beam EB generated before the start of exposure onto the shielding plate 115, and before the exposure, the electron beam EB is applied onto the substrate. Is prevented from being irradiated.

  The substrate deflection control unit 207 controls the applied voltage to the fifth electrostatic deflector 119 and the amount of current to the electromagnetic deflector 120 so that the electron beam EB is deflected to a predetermined position on the substrate. To do. The above-described units 202 to 207 are controlled in an integrated manner by an integrated control system 26 such as a workstation.

  FIG. 4 is a schematic diagram of the column cell control unit 31 in the multi-column electron beam exposure apparatus. Each column cell 11 has a column cell control unit 31. Each column cell control unit 31 is connected by a bus 34 to an integrated control system 26 that controls the entire multi-column electron beam exposure apparatus. Further, the integrated storage unit 33 is composed of, for example, a hard disk, and stores data necessary for all column cells such as exposure data. The integrated storage unit 33 is also connected to the integrated control system 26 via the bus 34.

  In the multi-column electron beam exposure apparatus configured as described above, exposure data of a pattern to be exposed on the wafer 12 placed on the wafer stage 13 is transferred from the integrated storage unit 33 to the column cell storage unit 35 of each column cell control unit 31. Forward to. The transferred exposure data is corrected by the correction unit 36 of each column cell control unit 31 if correction is necessary, and the same pattern is exposed in the exposure region on the wafer 12 assigned to each column cell 11.

  Next, processing for appropriately correcting the beam drift of the electron beam used in each column cell will be described. In the present embodiment, beam position characteristics and beam intensity characteristics are targeted as beam characteristics. The beam position characteristic is a characteristic indicating whether or not a desired beam is accurately irradiated to a desired position. The beam intensity characteristic is a characteristic indicating, for example, whether or not the beam current has a desired shape when the beam is shaped into a variable rectangular beam. In addition, as a device for detecting beam characteristics, a case where a calibration chip is used and a case where a Faraday cup is used are targeted.

  FIG. 5 is a diagram showing a region irradiated with the electron beams of four column cells in the sample 43. Reference numerals 43a to 43d denote irradiation areas of the column cells. For example, in the irradiation region 43d, exposure processing is performed for each field from the left side of FIG. Similarly, in the irradiation region 43a, the exposure processing is performed in the order indicated by the arrow 52.

  In such an exposure process, when a pattern extending between the irradiation regions 53 of the column cells is exposed, a phenomenon that the pattern joining accuracy is deteriorated occurs.

  If the beam characteristics between the column cells are completely equidistant, the above problem does not occur. As a factor that impairs the equidistant property of the beam characteristics, thermal expansion and change in atmospheric pressure of the electromagnetic lens used in each column cell can be considered. Since these factors change from moment to moment, it is necessary to follow them.

  Usually, calibration of an electron beam is performed at a predetermined time interval. In this case, for example, the irradiation position of the electron beam is calibrated at a certain time, and correction is performed using the same correction value until the next calibration. That is, during this time, although the positional deviation amount of the electron beam irradiation position has changed, the correction value for the position actually measured at the time of calibration is used. Cause.

  In this embodiment, after actually measuring the amount of positional deviation, the exposure data is corrected by predicting how the positional deviation will change.

  FIG. 6 is a diagram illustrating a beam position prediction curve in which a deviation of the irradiation position with respect to time when the electron beam is irradiated is predicted. The horizontal axis in FIG. 6 represents time, and the vertical axis represents the irradiation position. In addition, although it is necessary to consider the x direction and the y direction for the positional deviation, FIG. 6 deals with the positional deviation in one direction of x or y.

  P1, P2, and P3 in FIG. 6 are measured values measured at calibration times T1, T2, and T3, respectively. The detection of the beam position characteristic is performed by a known method using a reference mark formed on the calibration chip. That is, the wafer stage is moved so that the center of the reference mark is located immediately below the optical axis of each column cell, and the electron beam is scanned using a deflector so that the electron beam is irradiated on the reference mark. A backscattered electron signal is detected by the backscattered electron detector, and the backscattered electron signal is signal-processed to calculate a beam irradiation position. By comparing with the position where the actual reference mark is arranged, the irradiation position of the electron beam is calculated, and the beam position characteristic is measured.

Curves D1 (T) to D4 (T) in FIG. 6 are beam position prediction curves calculated using a prediction function in each of the four column cells. In this embodiment, the prediction function shown in Formula (1) is adopted.

  Here, Δ (T) is a predicted value at time T, pi is a measured value of electron beam characteristics at time Ti, and n is a natural number.

For example, in the equation (1), n = 3, data of the past three time points T1, T2, and T3 (T1 <T2 <T3) are used, and the measured value at T1 is changed to the measured value at P1 and T2. Assuming that the measured values at P2 and T3 are P3, the predicted value Δ (T) of the beam position at time T can be obtained by the following quadratic expression.

  FIG. 7 is a diagram showing a beam position prediction curve D1 (T) for one column cell in FIG. In FIG. 7, between the time T3 and the next calibration, the beam position is calculated by the equation (2) calculated at the time T3. The beam position prediction curve D1 (T) is a curve fitting prediction curve that passes through the measurement values P1, P2, and P3. When n = 2 is applied in Δ (T), for example, the prediction curve that passes through the measurement values P2 and P3 is a straight line.

  The time interval from time T3 to the next calibration may be set arbitrarily. For example, the time interval is determined so as to match the exposure time of one field.

  After calculating the beam position, a beam deflection amount that cancels the deviation amount is calculated. For example, assume that P3 'is predicted at T3' in FIG. In this case, a value for correcting the amount of voltage applied to the fifth electrostatic deflector 119 of each column cell is calculated so as to be −P3 ′.

The voltage applied to the electrostatic deflector having two electrodes in the X direction and the Y direction of the deflector that changes the irradiation position of the electron beam on the sample is expressed by the equation (3), the input in the Y direction. Is represented by equation (4).
X ′ = AX + BY + HxXY + Ox (t) (3)
Y ′ = CX + DY + HyXY + Oy (t) (4)
A voltage proportional to this value is applied to the electrode of the electrostatic deflector to deflect the electron beam. In this equation, A, B, C, D, Hx, Hy, Ox, and Oy are adjustment coefficients.

  Of the voltages applied to the deflector, for example, Ox and Oy are adjusted to eliminate the above-described positional deviation.

  These values are stored in each column cell storage unit 35, and the electron beam is deflected with a voltage amount corrected when the electron beam is irradiated on each column cell.

  Next, optimization of the interval for performing calibration will be described.

As shown in FIG. 7, after actually measuring the beam characteristics at the calibration time T3, correction is performed based on the prediction function until the _next calibration time _Tnext . The predicted value Pp (T _next ) at time T _next is also calculated based on the prediction function.

An exposure process is performed according to the corrected exposure data, and the beam characteristic is measured again at time T _next . At this time, a difference Pa (T _next ) −Pp (T _next ) between the predicted value Pp (T _next ) and the measured value Pa (T _next ) is set as a beam characteristic error δ.

  The calibration interval is adjusted according to the value of the beam characteristic error δ. In the present embodiment, it is assumed that the optimum allowable error δas of the connection accuracy between the column cells is 0.6 nm and the limit allowable error δal is 1 nm. The optimum allowable error δas is the most desirable error. If the allowable error δas does not fall within this allowable error, it is assumed that it is a state of caution. The limit tolerance δal is considered to be ineligible if it does not fall within this tolerance.

  If the error of the beam characteristics of each column cell is smaller than the optimum allowable error δas of the connection accuracy, the connection accuracy is 1.2 nm or less. On the contrary, if the error of the beam characteristics of each column cell is larger than the allowable error δal of the limit of the connection accuracy, it is determined that the normal range is exceeded. In this case, it is determined that the portion drawn based on the prediction function is abnormal, and after the exposure processing, the drawn portion is applied to the inspection machine.

  Depending on the value of the beam characteristic error δ, the calibration interval is adjusted in the following three cases.

(I) In the case of | δ | <0.6 nm In this case, since it is within the range of the optimum allowable error δas of the connection accuracy between the column cells, the exposure process is accurately performed by the beam position correction based on the predicted value. It can be carried out. Therefore, the calibration interval can be extended. Thereby, the throughput can be improved.

(Ii) In the case of 0.6 nm ≦ | δ | ≦ 1 nm In this case, it is not within the range of the optimum allowable error δas, but is within the range of the allowable error δal at the limit of the connection accuracy between the column cells. Therefore, the calibration interval at this time is set as the standard time interval, and the calibration interval is not changed.

(Iii) In the case of 1 nm <| δ | In this case, if the calibration is performed at this calibration interval without entering the range of the allowable error δal of the limit of the connection accuracy between the column cells, the accuracy deteriorates. Therefore, the calibration interval is shortened so that the error from the measured value becomes small. Thereby, a predetermined joining accuracy can be maintained.

  As described above, in the present embodiment, position shifts at several past points are extracted from the position shift history, and a prediction curve is obtained using the prediction function. When the reliability of the prediction curve is high, it is possible to calculate the positional deviation in advance and adjust the beam irradiation position in each column cell to an accurate position. As a result, the connecting accuracy in the case of multi-column is improved, and the exposure throughput is improved.

  In the present embodiment, the calibration time interval is adjusted based on the difference between the predicted value and the measured value. When the error between the predicted value and the measured value is smaller than the predetermined value, the calibration frequency can be reduced while maintaining the exposure accuracy, and the exposure throughput can be improved by reducing the time not contributing to exposure. it can.

  Further, when the error between the predicted value and the measured value is larger than a predetermined value, it is possible to increase the calibration frequency and improve the exposure accuracy. If the exposure accuracy improves as a result of increasing the frequency of calibration, the frequency of calibration can be reduced again, and the exposure throughput can be improved while maintaining the exposure accuracy from the start to the end of exposure. Become.

  Note that the beam intensity also varies with the passage of time, like the beam position. Therefore, the beam intensity drift is applied to a prediction function based on the measurement value to calculate a prediction value between calibrations.

For example, in the case of a variable rectangle, an electron beam whose cross section is shaped into a rectangle is overlapped with a rectangular opening of the mask and shaped into a rectangle of horizontal Sx and vertical Sy. At this time, the voltage applied to the electrostatic deflector having the two electrodes in the x direction and the y direction is expressed by the equation (5) for the input in the x direction and the equation (6) for the input in the y direction.
Sx ′ = ASx + BSy + HxSxSy + Ox (t) (5)
Sy ′ = CSx + DSy + HySxSy + Oy (t) (6)
In the above formulas (5) and (6), the coefficients Ox, Oy, or the coefficients A to D are adjusted to return the drifted amount to the normal value. Further, the beam shot time may be adjusted to adjust the beam current to a normal value. These values are stored in each column cell storage unit 35, and exposure processing is performed according to this data when actually exposing.

(Explanation of multi-column electron beam exposure method)
Next, an exposure method in the above-described multi-column electron beam exposure apparatus will be described.

  FIG. 8 is a flowchart for explaining exposure processing including beam drift prediction and calibration time interval adjustment processing by the multi-column electron beam exposure apparatus according to the present embodiment. Note that the beam drift prediction and calibration time interval adjustment processing is targeted for processing in one column cell.

  First, in step S11, initialization is performed. In the initial setting, the calibration time interval is determined. For example, 5 minutes. Also, a counter n indicating the calibration time is set to 1.

  Next, in step S12, it is determined whether it is time for calibration. If it is the calibration time, the process proceeds to step S13, and if it is not the calibration time, the process proceeds to step S18.

  Next, in step S13, the beam position at the calibration time T (n) is measured, and a measurement value of the beam position deviation is acquired and recorded in the storage unit. The beam position is scanned by the deflector of the column cell so that the electron beam passes over the reference mark, the reflected electrons of the reference mark are acquired, and the signal processing is performed to acquire the beam position.

  In the next steps S14 and S15, the calibration interval is adjusted.

  In step S <b> 14, the predicted value of the beam position deviation at the time T (n) predicted in the immediately previous calibration time T (n−1) is acquired from the storage unit 35.

  Next, in step S15, a difference (beam characteristic error) between the measured value of the beam position deviation actually measured in step S13 and the predicted value of the beam position deviation predicted by the prediction function acquired in step S14 is calculated.

  The calibration time interval is adjusted according to the calculated beam characteristic error. For example, the optimum allowable error δas and the limit allowable error δal of the connection accuracy between the column cells are assumed. If the beam characteristic error of each column cell is smaller than the optimum allowable error δas, the calibration interval is not changed or the calibration interval is extended. When the beam characteristic error is between the optimum allowable error δas and the limit allowable error δal, the calibration interval is not changed from the standard value. When the beam characteristic error exceeds the limit allowable error δal, the calibration interval is shortened.

  Next, in step S <b> 16, the beam position deviation from the time T (n) at which calibration is performed to the next calibration T (n + 1) is predicted and stored in the storage unit 35.

  The beam position deviation is calculated by applying the measurement values of the n beam positions before the calibration is performed to the prediction function. This prediction function is a function shown in Formula (1) demonstrated in this embodiment. For example, a quadratic prediction function is obtained based on the measurement values at three points in the equation (1).

  Next, in step S17, based on the beam position deviation calculated in step S16, the correction amount of the voltage applied to the deflector so as to eliminate the beam position deviation after the calibration is performed until the next calibration is performed. Is calculated. For example, the correction amount is calculated every time (for example, 2 seconds) when one field of the wafer (sample) is exposed.

  Next, in step S18, an exposure process is performed by applying a voltage corresponding to the correction amount calculated in step S17 and stored in the storage unit 35 to the deflector.

  Next, in step S19, it is determined whether or not the exposure is completed. If the exposure is completed, the process is terminated. If the exposure is not completed, n is incremented by 1 in step S20, and the process returns to step S12 to continue the process.

(Modification 1)
In this modified example, prediction of beam characteristics in consideration of beam drift due to exchange of the sample holder will be described.

  When exposure of one sample is completed in the exposure apparatus, the next sample is mounted on the sample holder and placed on the wafer stage. A plurality of sample holders are prepared, and reference marks for measuring beam characteristics are formed on these sample holders.

  The beam position prediction curve is affected by the newly introduced sample holder in addition to the effect of the column cell change by exchanging the sample holder.

  The column cell is affected by changes in pressure and temperature, but the sample holder is not affected by pressure and is affected by changes in temperature and material. Therefore, the beam drift due to the change of the column cell and the beam drift due to the change of the sample holder can be defined independently.

  Moreover, it is practically impossible to form all the reference marks at the same position in a plurality of sample holders. Accordingly, the reference of the irradiation position of the electron beam varies due to the exchange of the sample holder.

  FIG. 9 is a diagram showing a change in beam characteristics with time. Immediately after exchanging the sample holder, as shown in FIG. 9A, discontinuous displacement occurs in the beam position prediction curve.

  Thereafter, the beam position characteristic is represented by a beam drift curve G1 (T) of an orbit different from the curve passing through the measurement values shown in the above embodiment. Furthermore, when time elapses, the beam position prediction curve before exchanging the sample holder is expressed by a parallel translation curve (D1 (T) + G1 (T) + A).

  That is, the beam position prediction function includes a holder drift prediction function Gk (T) that depends on the sample holder, an independent column cell drift prediction function D (T) that does not depend on the sample holder, and is unique to the sample holder. The sum with the constant A is defined as in Expression (7).

  Here, Gk (T) is a holder drift function after the start of mounting of the kth sample holder, and Ak is a constant specific to the sample holder.

  The beam drift due to the change of the column cell uses the function defined in the above embodiment. Further, the beam drift due to the change of the sample holder is represented by a function Gk (T), and this function may be a function similar to the function defined in the above embodiment.

  The sample holders have different characteristics due to manufacturing variations. Therefore, the behavior from immediately after the sample holder is mounted until the beam characteristics are not changed is used as a fixed function by averaging the movements used in the past. For example, for Gk (T), a new prediction function may be calculated from an average value of measured values obtained by past calibration when the sample holder is used. The time that the sample holder affects is 1 to 10 hours.

(Modification 2)
In the above embodiment, in order to correct the beam characteristics with high accuracy, the beam drift is detected by actually measuring the beam position and the like of the electron beam used in the column cell, and the beam drift is predicted using the prediction function. . In this modification, the prediction of the beam drift of the electron beam used in some column cells among a plurality of column cells is performed using the predicted value of the beam drift of the electron beam used in other column cells. Different.

  FIG. 10 is a diagram for explaining the change over time between the column cells. C1 to C16 in FIG. 10A indicate positions where 16 column cells are arranged. FIG. 10B shows a state in which the column cell has changed after a certain time has passed since the exposure process was started. As a result of measuring the beam characteristics of the electron beams used in the four outermost column cells C1, C4, C13, and C16 in the state shown in FIG. 10B, the positions shifted to the positions of M1, M4, M13, and M16, respectively. Shall be found. That is, in this case, it is presumed that the behavior of the column cell rotating as shown in FIG. At this time, it is presumed that the column cells sandwiched between these column cells and the inner column cells behave in the same manner.

  This is because the column cells are arranged in one chamber, so that the influence of the atmospheric pressure applied to a plurality of column cells is considered to be common to all the column cells with some errors. Therefore, it is not necessary to perform actual measurement for calibration on the electron beams of all column cells.

  In this case, after calculating the correction amount for the electron beams used in the column cells C1, C4, C13, and C16 at the four corners, the calculated correction amounts are proportionally distributed to the electron beams of the other column cells. .

  For the same reason as described above, if the electron beam of the outermost column cell does not need to be corrected, it can be considered that the electron beam of the inner column cell does not need to be corrected.

In this way, the actual measurement of the beam position and the like for calibration may be performed on the electron beams of some column cells. For this reason, it is possible to reduce the time not contributing to exposure and improve the exposure throughput.

Claims (13)

A plurality of column cells;
A wafer stage on which a sample holder equipped with an electron beam characteristic detector for measuring electron beam characteristics is mounted;
A deflector provided in each column cell for deflecting an electron beam based on exposure data;
Using the electron beam characteristic detection unit, a continuous function that smoothly connects a plurality of measurement values at a plurality of past calibration times and continuously changes the electron beam characteristics up to the next calibration time with the drawing time. A multi-column electron beam exposure apparatus comprising: a control unit that calculates a predicted value of electron beam characteristics using a prediction function and calculates a correction amount for exposure data of each column cell.   The multi-column electron beam exposure apparatus according to claim 1, wherein the electron beam characteristic is a beam position or a beam intensity of an irradiated electron beam.   The multi-column electron beam exposure apparatus according to claim 1, wherein the electron beam characteristic detection unit is a calibration chip or a Faraday cup having a reference mark. The multi-column electron beam exposure apparatus according to claim 1, wherein the predetermined prediction function is represented by the following equation.

Here, Δ (T) is a predicted value at time T, pi is a measured value of electron beam characteristics at time Ti, and n is a natural number. The tolerance of the connection accuracy between the column cells is the optimum tolerance and the limit tolerance with a wider error range than the optimum tolerance,
When the difference between the predicted value and the measured value is greater than the limit allowable error, the control unit shortens the interval of the calibration time and measures the time when the measured value is measured and immediately before the time. The area that was exposed during the specified time is set as the area that needs to be inspected,
When the difference between the predicted value and the measured value is smaller than the optimum tolerance, the calibration time interval is increased,
When the difference between the predicted value and the measured value is between an optimum tolerance and a marginal tolerance, the calibration time interval is adjusted by setting the calibration time interval as a standard time interval. The multi-column electron beam exposure apparatus according to any one of claims 1 to 4.   The control unit calculates a predicted value of a beam characteristic of another column cell based on a predicted value of an electron beam characteristic in a column cell arranged at the outermost of the plurality of column cells. To 5. The multi-column electron beam exposure apparatus according to any one of claims 1 to 5. In each column cell of a multi-column electron beam exposure apparatus comprising a plurality of column cells, an exposure method for calibrating electron beam characteristics detected by an electron beam characteristic detection unit at a predetermined time interval,
Measuring an electron beam characteristic at a calibration time to obtain a measurement value of the electron beam characteristic;
Applying the measured value to a predetermined prediction function to calculate a predicted value of electron beam characteristics up to a calibration time immediately after the calibration time;
Correcting exposure data based on the predicted value of the electron beam characteristics;
And a step of performing an exposure process according to the corrected exposure data.   The multi-column electron beam exposure method according to claim 7, wherein the electron beam characteristic is a beam position or a beam intensity of an irradiated electron beam.   9. The multi-column electron beam exposure method according to claim 7, wherein the electron beam characteristic detection unit is a calibration chip or a Faraday cup having a reference mark. The multi-column electron beam exposure method according to claim 7, wherein the predetermined prediction function is expressed by the following equation.

Here, Δ (T) is a predicted value at time T, pi is a measured value of electron beam characteristics at time Ti, and n is a natural number. Between the step of obtaining the measured value of the electron beam and the step of calculating the predicted value,
Obtaining a predicted value of the electron beam characteristic at the calibration time predicted at the calibration time immediately before the calibration time;
The tolerance of the connection accuracy between the column cells is the optimum tolerance and the limit tolerance with a wider error range than the optimum tolerance,
When the difference between the predicted value and the measured value is larger than the limit tolerance, the calibration time interval is shortened, and the time between the time when the measured value is measured and the time measured immediately before the time is measured. Set the area that was exposed to the area that requires inspection,
When the difference between the predicted value and the measured value is smaller than the optimum tolerance, the calibration time interval is increased,
Adjusting the calibration time interval by setting the calibration time interval as a standard time interval when the difference between the predicted value and the measured value is between an optimum allowable error and a limit allowable error. The multi-column electron beam exposure method according to claim 7, wherein: In the step of calculating the predicted value of the beam characteristic,
12. The predicted value of the beam characteristic of another column cell is calculated based on the predicted value of the electron beam characteristic in the column cell arranged at the outermost of the plurality of column cells. The multi-column electron beam exposure method according to one item. A plurality of column cells;
A deflector provided in each column cell for deflecting an electron beam based on exposure data;
A sample holder that holds an electron beam characteristic detector that holds a wafer as a sample and measures electron beam characteristics;
A wafer stage that horizontally moves by placing the sample holder;
The electron beam property detection unit includes a reference mark formed on the sample holder for measuring the electron beam property,
Based on the reference mark, the irradiation position of the electron beam of each column cell is measured,
Based on the irradiation position information measured at a plurality of past times, a prediction curve to be curve-fitted is calculated, a correction amount that will change in the future is calculated from the calculated prediction curve, and the deflection amount of the deflector is calculated based on the calculated correction amount A control unit that continuously corrects
A multi-column electron beam exposure apparatus.

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