JP2022112487A - Electron beam lithography device and cathode life prediction method - Google Patents

Abstract

To accurately predict the lifetime of a cathode in advance.SOLUTION: An electron beam lithography device includes a cathode that emits an electron beam, a condition control unit that changes a plurality of conditions for emitting the electron beam from the cathode, and a prediction unit that predicts the lifetime of the cathode on the basis of the time change of the amount of variation in the beam characteristics of the electron beam with respect to the change in the conditions when the conditions are changed.SELECTED DRAWING: Figure 1

Description

An embodiment of the present invention relates to an electron beam lithography apparatus and a cathode life prediction method.

In recent years, with the miniaturization of semiconductor devices, the shot size of electron beams for forming patterns on masks has become smaller. As the shot size decreases, the throughput of mask writing decreases. To improve the throughput, it is necessary to increase the current density of the electron beam on the sample surface, and to increase the current density, it is necessary to increase the emission current flowing through the cathode that emits the electron beam.

Since increasing the emission current shortens the life of the cathode, it is necessary to accurately predict when the cathode will reach the end of its life. In the past, the life of the cathode was predicted by detecting the current distribution of the aperture and the emission current. , it is not possible to accurately predict in advance when the cathode will reach the end of its life.

JP 2016-152251 A

Accordingly, an embodiment of the present invention provides an electron beam lithography apparatus and a cathode life prediction method capable of accurately predicting the life of a cathode in advance.

In order to solve the above problems, according to one aspect of the present invention, a cathode that emits an electron beam;
a condition control unit for changing a plurality of conditions for emitting the electron beam from the cathode;
an electron beam lithography apparatus comprising: a predicting unit that predicts the lifetime of the cathode based on a time change in the amount of variation in beam characteristics of the electron beam with respect to a change in the conditions when the conditions are changed. be.

Based on the time change of the amount of variation in the beam characteristics of the electron beam with respect to the change in the conditions at each of a plurality of times, the time variation in the amount of variation in the beam characteristics of the electron beam with respect to the change in the conditions at an arbitrary time is calculated. A function generation unit that generates a desired function,
The prediction unit may determine that the life of the cathode has reached the end of its life at a time when a change in the beam characteristics of the electron beam with respect to the change in the conditions obtained by the function reaches a predetermined threshold.

a cathode that emits an electron beam;
a condition control unit for changing a plurality of conditions for emitting the electron beam from the cathode;
A predicting unit for predicting the lifetime of the cathode based on a time change in the amount of variation in beam characteristics of the electron beam when the conditions are varied within a certain range.

a function generation unit that generates a function for obtaining a variation amount of the beam characteristics when the conditions are changed at each of a plurality of times;
The prediction unit may determine that the life of the cathode has been reached at the time when the variation obtained by the function reaches a predetermined threshold value.

According to another aspect of the present invention, the conditions for emitting an electron beam from a cathode that emits an electron beam are changed in a plurality of ways,
Provided is a cathode life prediction method for predicting the life of the cathode based on the time change in the ratio of the amount of variation in beam characteristics of the electron beam to the amount of change in the conditions when the conditions are varied in a plurality of ways. be.

changing conditions for emitting the electron beam from the cathode in a plurality of ways;
The lifetime of the cathode may be predicted based on the change over time of the amount of variation in the beam characteristics when the conditions are changed within a certain range.

1 is a block diagram showing a schematic configuration of an electron beam drawing apparatus 2 according to one embodiment; FIG. FIG. 2 is a diagram showing an example of installation locations of an electron lens barrel and a plurality of detectors provided in a writing chamber; FIG. 4 is a diagram plotting the correspondence between cathode conditions and beam characteristics; FIG. 3B is a diagram plotting the correspondence relationship between the time at which the amount of variation in FIG. 3A was obtained and the amount of variation; 4 is a flowchart showing a function generation procedure in the first prediction method; FIG. 4 is a diagram plotting the correspondence between cathode conditions and beam characteristics; FIG. 5B is a diagram plotting the correspondence relationship between the time at which the amount of variation in FIG. 5A was obtained and the amount of variation; 10 is a flowchart showing a function generation procedure in the second prediction method;

Embodiments of an electron beam lithography apparatus and a cathode life prediction method will be described below with reference to the drawings. Although the main components of the electron beam lithography apparatus and cathode life prediction method will be mainly described below, the electron beam lithography apparatus and cathode life prediction method may include components and functions that are not illustrated or described. . The following description does not exclude components or features not shown or described.

FIG. 1 is a block diagram showing a schematic configuration of an electron beam drawing apparatus 2 according to one embodiment. The electron beam drawing apparatus 2 in FIG. 1 includes a drawing section 3 and a control section 4 . The drawing unit 3 draws a desired pattern on the sample. A control unit 4 controls the drawing unit 3 .

The drawing unit 3 has an electron lens barrel 5 and a drawing chamber 6 . Inside the electron barrel 5 are an electron gun 7, an illumination lens 8, a blanking deflector 9, a blanking aperture 10, a first shaping aperture 11, a shaping lens 12, a shaping deflector 13, A second shaping aperture 14, a reduction lens 15, an objective lens 16, a sub-deflector 17 and a main deflector 18 are provided. Inside the drawing chamber 6, an XY stage 19 is provided so as to be movable. The XY stage 19 is provided with a beam absorption electrode (Faraday cup) 20 for measuring the current of the irradiated electron beam. A sample to be drawn is placed on the XY stage 19 . The sample is, for example, an exposure mask substrate for transferring a pattern onto a semiconductor wafer. Using a semiconductor wafer as a sample, a pattern may be drawn directly on the semiconductor wafer. The electron gun 7 has a cathode 21 and an anode 22 . The cathode 21 has an emitter 23 , a Wehnelt electrode 24 and a pair of filaments 25 . A high voltage is applied between the pair of filaments 25 . The emitter 23 is connected to one end of each of the pair of filaments 25 . The Wehnelt electrode 24 is arranged to face the emitter 23 . Anode 22 is grounded.

The control unit 4 has an electron gun power supply unit 31 and a drawing control unit 32 . The electron gun power supply section 31 has a constant current source 33 , a variable voltage source 34 , an ammeter 35 , a voltmeter 36 and a drive control section 37 . A constant current source 33 supplies a predetermined heating current to both electrodes of the emitter 23 . The variable voltage source 34 applies a predetermined bias voltage (Wehnelt voltage) between the intermediate voltage node of both polarities of the emitter 23 and the Wehnelt electrode 24 . An ammeter 35 is connected to one end of the variable voltage source 34 via a DC voltage source 38 . Ammeter 35 measures the emission current flowing through cathode 21 . A voltmeter 36 is connected in parallel to the variable voltage source 34 . A voltmeter 36 measures the above-described bias voltage (Wehnelt voltage). The drive control unit 37 monitors the measurement results of the ammeter 35 and the voltmeter 36 and controls the variable voltage source 34 based on the output signal of the drawing control unit 32 .

The drawing control unit 32 has a current density measurement unit 41 and a PID control unit 42 . A current density measurement unit 41 measures the current density on the sample surface. The PID control unit 42 calculates a target value of the emission current based on the current density of the sample surface measured by the current density measurement unit 41 . The calculated target value is sent to the drive control section 37 . The drive controller 37 controls the variable voltage source 34 based on the target value received from the PID controller 42 . More specifically, the drive control section 37 feedback-controls the bias voltage based on the target value.

The PID control section 42 has a condition control section 43 and a prediction section 44 . The condition control unit 43 changes the conditions for emitting electron beams from the cathode 21 (hereinafter also referred to as cathode conditions) in a plurality of ways. The cathode conditions include, for example, at least one of the emission current flowing through the emitter 23, the bias voltage applied to the filament 25, the filament power supplied to the filament 25, and the temperature of the filament 25.

The prediction unit 44 predicts the lifetime of the cathode 21 based on the time change of the amount of change in the beam characteristics of the electron beam with respect to the amount of change in the cathode condition when the cathode condition is changed in a plurality of ways. Specifically, the amount of change in beam characteristics over time is the amount of transmitted electrons through the aperture, the amount of current of reflected electrons, the amount of current of secondary electrons, and the amount of change in the bias voltage applied to the filament 25 of the cathode 21. contains at least one of

The prediction unit 44 predicts the lifetime of the cathode 21, for example, based on the change over time in the amount of change in beam characteristics with respect to the amount of change in cathode conditions. In this case, the PID controller 42 may have a function generator 45 . The function generation unit 45 calculates the amount of variation in the beam characteristics of the electron beam with respect to the change in the cathode condition at an arbitrary time based on the time change in the amount of variation in the beam characteristics of the electron beam with respect to the change in the cathode condition at a plurality of times. Generate a function that finds the time change of . The prediction unit 44 determines that the cathode 21 has reached the end of its service life at the time when the amount of change in the beam characteristics of the electron beam with respect to the change in the cathode condition obtained by the function reaches a predetermined threshold value.
Here, when the time change in the amount of variation in the beam characteristics is represented by an absolute value, the prediction unit 44 determines that the lifetime of the cathode 21 has reached the time when the time change in the amount of variation becomes equal to or greater than a predetermined threshold. to decide. If the direction in which the amount of variation increases over time is taken as a positive value, it is determined that the cathode 21 has reached the end of its service life at the time when the amount of variation increases over time. On the other hand, when the direction in which the amount of variation increases over time is taken as a negative value, it is determined that the cathode 21 has reached the end of its life at the time when the amount of variation falls below a predetermined threshold value.

Alternatively, the prediction unit 44 may predict the lifetime of the cathode 21 based on the change over time in the amount of variation in beam characteristics when the cathode conditions are changed. In this case, the function generation unit 45 in the PID control unit 42 generates a function that obtains the absolute value of the amount of variation in beam characteristics when conditions are changed at each of a plurality of times. The prediction unit 44 determines that the cathode 21 has reached the end of its service life at the time when the amount of variation in the beam characteristics obtained from the function reaches the threshold.

A plurality of detectors 46 are provided at a plurality of locations in the electron lens barrel 5 and the writing chamber 6 . FIG. 2 is a diagram showing an example of installation locations of a plurality of detectors 46 provided in the electron lens barrel 5 and the writing chamber 6. As shown in FIG. In the example of FIG. 2, the detectors 46 are provided above the blanking aperture 10, the first shaping aperture 11, the second shaping aperture 14, and the lower surface of the objective lens 16 in the electron lens barrel 5, and the sample surface is detected. A detector 46 is also provided above. A detector 46 in the electron lens barrel 5 detects the amount of transmitted electrons, the amount of reflected electrons, or the amount of secondary electrons of each aperture. A detector 46 on the sample surface detects the current amount of reflected electrons or secondary electrons on the sample surface. Based on the detected currents of these detectors 46, the prediction unit 44 detects the time change of the ratio of the variation amounts of the beam characteristics.

The prediction unit 44 described above predicts the life of the cathode 21 in advance by, for example, the first prediction method or the second prediction method. The first prediction method and the second prediction method will be described in order below.

(First prediction method)
3A and 3B are diagrams for explaining the first prediction method, and FIG. 4 is a flowchart showing the processing procedure of the first prediction method. The first prediction technique plots the correspondence between cathode conditions and beam characteristics, as shown in FIG. 3A. In the example of FIG. 3A, when an electron beam is emitted from the electron gun 7 of the electron beam writing apparatus 2, the horizontal axis represents the emission current, which is the cathode condition, and the transmitted electron amount or the reflected electron amount, or the secondary electron amount, which is the beam characteristic. The values of the transmitted electron amount, the reflected electron amount, or the secondary electron amount when the emission current is changed are plotted with the electron amount as the vertical axis. As shown in FIG. 3A, each plot is generally arranged on a common straight line. That is, the amount of change in the amount of transmitted electrons, the amount of reflected electrons, or the amount of secondary electrons with respect to the amount of change in the emission current is substantially constant while the cathode 21 has not reached the end of its life. The process of obtaining the above-described amount of variation is repeated multiple times over a predetermined period (for example, several months).

In FIG. 3B, the time when the horizontal axis is time and the vertical axis is the above-described variation amount, and the corresponding relationship between the time when the variation amount in FIG. 3A is obtained and the variation amount is plotted. A plurality of plots are illustrated in FIG. 3B, and each plot indicates the value of the amount of variation in each period during which the processing of FIG. 3A is performed.

The function generator 45 described above generates a function (polynomial) by, for example, fitting based on the plot in FIG. 3B. The fitting function is obtained from past actual measurements as in the first prediction method, but may be obtained by simulation. Here, fitting processing and extrapolation processing are performed based on all plots to obtain fitting parameters. The fitting function may be obtained by simulation and depends on at least one of the operating state of the cathode and the optical system. In this embodiment, for example, a quadratic function can be preferably used. In the function of FIG. 3B, the value of the amount of variation on the vertical axis decreases with the lapse of time. This indicates that the amount of change in the amount of transmitted electrons, the amount of reflected electrons, or the amount of secondary electrons with respect to the amount of change in emission current gradually decreases over time. The reason for such characteristics is that when the life of the cathode 21 approaches, even if the emission current is increased, the amount of transmitted electrons, the amount of reflected electrons, or the amount of secondary electrons that pass through each aperture does not increase.

The prediction unit 44 determines that the life of the cathode 21 is the time when the function generated by the function generation unit 45 crosses the threshold indicated by the dashed line in FIG. 3B, and prompts replacement of the cathode 21 before reaching this time. be able to.

The threshold is, for example, the result of performing a process of determining the amount of change in the amount of transmitted electrons, the amount of reflected electrons, or the amount of secondary electrons with respect to the amount of change in the emission current from the start of use of the cathode 21 to the end of its life. set based on Alternatively, a function may be generated by simulation and the threshold may be determined from the curve shape of the function.

In FIG. 3A, the values of the amount of transmitted electrons, the amount of reflected electrons, or the amount of secondary electrons when the emission current is changed are plotted, but the horizontal axis may be other cathode conditions such as bias voltage instead of the emission current. Also, the vertical axis may be other beam characteristics such as the beam size on the sample surface instead of the amount of transmitted electrons, the amount of reflected electrons, or the amount of secondary electrons.

FIG. 4 is a flow chart showing the function generation procedure in the first prediction method. First, by changing the emission current at a certain time, the amount of change in the amount of transmitted electrons, the amount of reflected electrons, or the amount of secondary electrons with respect to the amount of change in the emission current is obtained (step S1). As described above, it may take several months or the like to obtain the amount of variation in step S1. Next, the correspondence relationship between the time when the process of step S1 was performed and the value of the amount of variation is temporarily stored in a storage device (not shown) (step S2).

Next, it is determined whether or not the processes of steps S1 and S2 have been repeated M times (M is an integer equal to or greater than 2) (step S3). The processing of steps S1 to S3 is repeated until the number of repetitions reaches M times. That is, for example, the process of obtaining the amount of variation over several months is repeated M times. When the number of times reaches M, the correspondence relationship between the time and the value of the variation for the M times stored in the storage device in step S2 is shown in FIG. Plot in a two-dimensional coordinate space.

Next, a function as shown in FIG. 3B is generated by fitting processing and extrapolation processing based on multiple plots in the two-dimensional coordinate space (step S4). The processing of step S4 is performed by the function generator 45. FIG. The function generated in step S4 uses the time as a parameter to obtain the value of the variation amount, and can be expressed by a predetermined formula or table. Therefore, in step S4, a predetermined formula or table representing the function is Store in a memory device.

Next, the service life of the cathode 21 is determined by extrapolation from the function generated in step S4 (step S5). The prediction unit 44 performs the process of step S5. The dashed line in FIG. 3B indicates the threshold, and the time at which the function crosses the threshold indicates the lifetime of the cathode 21 . The threshold may be determined in advance, or may be set according to the curve shape of the function. In practice, the life of the cathode 21 is predicted from newly measured plot positions on the function before the life of the cathode 21 is reached, and the cathode 21 is replaced before the life of the cathode 21 is reached.

Thus, in the first prediction method, at each of a plurality of times, the amount of variation in beam characteristics with respect to the amount of change in cathode conditions is obtained, a function is generated from the obtained values, and the function intersects with the threshold. The life of the cathode 21 is predicted from the time when the This makes it possible to accurately predict when to replace the cathode 21 before the cathode 21 actually reaches the end of its service life, taking cathode conditions and beam characteristics into consideration.

(Second prediction method)
5A and 5B are diagrams for explaining the second prediction method, and FIG. 6 is a flow chart showing the processing procedure of the second prediction method. A second technique plots the correspondence between cathode conditions and beam characteristics, as shown in FIG. 5A. In the example of FIG. 5A, when an electron beam is emitted from the electron gun 7 of the electron beam drawing apparatus 2, the horizontal axis represents the filament temperature, which is the cathode condition, and the vertical axis represents the current detected by the detector 46, which is the beam characteristic. , the value of the detected current when the filament temperature is changed is plotted, and the fluctuation amount of the detected current when the filament temperature is changed is detected.
Similar to the first prediction method, the cathode condition includes at least one of, for example, the emission current flowing through the emitter 23, the bias voltage applied to the filament 25, the filament power supplied to the filament 25, and the temperature of the filament 25. I'm in. In addition, the time change of the amount of fluctuation of the beam characteristics is at least one of the amount of electrons transmitted through the aperture, the amount of current of reflected electrons, the amount of current of secondary electrons, and the amount of change in the bias voltage applied to the filament 25 of the cathode 21. contains.

FIG. 5B plots the time at which the amount of variation in FIG. 5A was obtained and the corresponding relationship between the amount of variation, with the horizontal axis representing time and the vertical axis representing the amount of variation in the detected current. A plurality of plots are shown in FIG. 5B, and each plot shows the amount of change in the detected current at the time when the processing of FIG. 5A is performed.

The function generator 45 described above generates a function (polynomial) based on all the plots in FIG. 5B. The fitting function is obtained from past actual measurements as in the first prediction method, but may be obtained by simulation. Here, fitting processing and extrapolation processing are performed based on all plots to obtain fitting parameters. In the function of FIG. 5B, the amount of variation on the vertical axis decreases with the lapse of time. This indicates that as the life of the cathode 21 approaches, even if the filament temperature is changed, the detected current does not change much and the sensitivity decreases. Therefore, by determining the time at which the function generated by the function generator 45 intersects the threshold indicated by the broken line in FIG. can. As described above, in the second prediction method, the condition control unit 43 changes the conditions for emitting the electron beam from the cathode 21 in a plurality of ways. The prediction unit 44 predicts the lifetime of the cathode 21 based on the time change of the amount of variation in the beam characteristics when the conditions are changed within a certain range. More specifically, the function generation unit 45 generates a function for determining the time change of the beam characteristic fluctuation amount when the cathode condition is changed at each of a plurality of times. The prediction unit 44 determines that the cathode 21 has reached the end of its service life at the time when the change over time of the variation obtained by the function generated by the function generation unit 45 reaches a predetermined threshold value.

The threshold in FIG. 5B is set based on the fluctuation amount of the detected current of the cathode 21 that has actually reached the end of its life, similarly to the threshold in FIG. 3B. Alternatively, a function may be generated by simulation and the threshold may be determined from the curve shape of the function.

FIG. 6 is a flow chart showing the function generation procedure in the second prediction method. First, by changing the filament temperature at a certain time, the amount of change in the current detected by the detector 46 is obtained (step S21). Next, the correspondence relationship between the time when the process of step S21 was performed and the current detected by the detector 46 is temporarily stored in a storage device (not shown) (step S22).

Next, it is determined whether or not the processes of steps S21 and S22 have been repeated N times (N is an integer equal to or greater than 2) (step S23). The processing of steps S21 to S23 is repeated until the number of repetitions reaches N times. When the N number of times has been reached, the correspondence relationship between the time and the variation amount values for the N times stored in the storage device in step S22 is represented by a two-dimensional graph in which the horizontal axis is the time and the vertical axis is the variation amount value, as shown in FIG. 5B. Plot in a dimensional coordinate space.

Next, a function as shown in FIG. 5B is generated by fitting processing and extrapolation processing of a plurality of plots in the two-dimensional coordinate space (step S24). The function generated in step S24 is for determining the amount of variation in the detected current using time as a parameter, and can be expressed by a predetermined formula or table. Store the table in storage.

Next, the life of the cathode 21 is determined based on the function generated in step S24 (step S25). The dashed line in FIG. 5B indicates the threshold, and the time at which the function crosses the threshold indicates the lifetime of the cathode 21 . The threshold may be determined in advance, or may be set according to the curve shape of the function. In practice, the life of the cathode 21 is predicted from newly measured plot positions on the function before the life of the cathode 21 is reached, and the cathode 21 is replaced before the life of the cathode 21 is reached.

Thus, in the second prediction method, the amount of variation in the current detected by the detector 46 is obtained at each of a plurality of times, the function is generated from the obtained amount of variation, and the cathode Predict the replacement time of 21. This makes it possible to accurately predict when to replace the cathode 21, taking into account the cathode conditions and beam characteristics.

In both the first prediction method and the second prediction method described above, since the life of the cathode 21 is predicted based on changes in the beam characteristics when the cathode conditions are changed in a plurality of ways, the cathode 21 reaches the end of its life. In advance, the life time of the cathode 21 can be accurately predicted.

Aspects of the present disclosure are not limited to the individual embodiments described above, but include various modifications that can be conceived by those skilled in the art, and the effects of the present disclosure are not limited to the above-described contents. That is, various additions, changes, and partial deletions are possible without departing from the conceptual idea and spirit of the present disclosure derived from the content defined in the claims and equivalents thereof.

2 electron beam drawing apparatus, 3 drawing section, 4 control section, 5 electron lens barrel, 6 drawing chamber, 7 electron gun, 8 illumination lens, 9 blanking deflector, 10 blanking aperture, 11 first shaping aperture, 12 shaping lens, 13 shaping deflector, 14 second shaping aperture, 15 reduction lens, 16 objective lens, 17 sub-deflector, 18 main deflector, 19 XY stage, 20 beam absorption electrode, 21 cathode, 22 anode, 23 emitter, 24 Wehnelt electrode, 25 filament, 31 electron gun power supply, 32 drawing control unit, 33 constant current source, 34 variable voltage source, 35 ammeter, 36 voltmeter, 37 drive control unit, 41 current density measurement unit, 42 PID control unit , 43 condition control unit, 44 prediction unit, 45 function generation unit, 46 detector

Claims (6)

a cathode that emits an electron beam;
a condition control unit for changing a plurality of conditions for emitting the electron beam from the cathode;
an electron beam lithography apparatus, comprising: a predicting unit that predicts the lifetime of the cathode based on a time change in the amount of variation in beam characteristics of the electron beam with respect to a change in the conditions when the conditions are changed. Based on the time change of the amount of variation in the beam characteristics of the electron beam with respect to the change in the conditions at each of a plurality of times, the time variation in the amount of variation in the beam characteristics of the electron beam with respect to the change in the conditions at an arbitrary time is calculated. A function generation unit that generates a desired function,
2. The prediction unit determines that the cathode has reached the end of its service life at a time at which a time change in the amount of variation in the beam characteristics of the electron beam with respect to the change in the conditions determined by the function reaches a predetermined threshold. The electron beam lithography apparatus according to . a cathode that emits an electron beam;
a condition control unit for changing a plurality of conditions for emitting the electron beam from the cathode;
an electron beam lithography apparatus, comprising: a prediction unit that predicts the lifetime of the cathode based on the time change of the amount of variation in the beam characteristics of the electron beam when the conditions are changed within a certain range. a function generation unit that generates a function for obtaining a variation amount of the beam characteristics when the conditions are changed at each of a plurality of times;
4. The electron beam lithography apparatus according to claim 3, wherein said predicting unit determines that said cathode has reached the end of its service life at the time when said variation obtained by said function reaches a predetermined threshold value. The conditions for emitting electron beams from the cathode that emits electron beams are changed in a plurality of ways,
A method for predicting the life of a cathode, wherein the life of the cathode is predicted based on the time change of the ratio of the amount of variation in beam characteristics of the electron beam to the amount of change in the conditions when the conditions are varied in a plurality of ways. changing conditions for emitting the electron beam from the cathode in a plurality of ways;
6. The cathode life prediction method according to claim 5, wherein the life of said cathode is predicted based on the time change of said beam characteristic when said condition is changed within a certain range.

Images