JPH04209453A - Optical axis adjusting method for electron beam apparatus - Google Patents

Abstract

PURPOSE:To adjust an optical axis quickly and well by searching a path of an electron beam passing an electro-optical system while scanning a preset x-y region and obtaining rough parameters for indicating the path. CONSTITUTION:A matching coil control circuit 26 generates a signal (ATX, ATY) for TILT and a signal (ASX, ASY) for SILT. A preset region is designated according to lengths of the X-axis and the y-axis by ASX, ASY. The region is scanned, a quantity of secondary electrons from a sample 18 is monitored, and the peak value of a corresponding electric signal S2 is detected by a peak- hold circuit 31. When a reference value is exceeded, a signal S4 is generated. Values of deflection signals ASX, ASY at this time are taken as x-y parameters to be used as initial values of matching and are transferred smoothly from coarse to fine adjustment. In the coarse processing part, a crossed image is shifted to the CRT center by ATX, ATY, symmetry of the image is unified by ASX, ASY to finish the matching scan. Accordingly, even an optical axis deviated to much extent can be matched quickly and well.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to an optical axis adjustment method for an electron beam device, and an object of the present invention is to quickly obtain good optical axis adjustment results even when the optical axis is significantly misaligned, such as during start-up. In an electron beam device that has an electron optical system interposed between an electron beam generation source and a predetermined sample and deflects and scans the electron beam with the electron optical system, when adjusting the optical axis of the electron beam, Specify a predetermined x-y area, and while scanning the area, detect an electron beam passing through the electron optical system, and set the X-y parameters of the area at the time of detecting the passing electron beam to the optical axis. Preferably, when the amount of electron beam irradiation on the sample is converted into an amount of electricity, and the peak value of the amount of electricity exceeds a predetermined value,
It is characterized by detecting the passing electron beam.

[Industrial application field]

The present invention relates to an optical axis adjustment method for an electron beam device.

SEM (scanning electron microscope), STEM (transmission electron microscope), EB tester or EB drawing device, etc.
Electron beam devices (hereinafter sometimes simply referred to as devices) that use a convergent electron beam have the following problems: the distance from the electron beam source to the irradiation target is long, and a complicated electron optical system is interposed in between. Extremely precise optical axis adjustment is required because the beam path formed by each optical system is extremely narrow.

In addition, in a so-called standby state where the equipment is temporarily stopped, the electron gun is left running to avoid instability of the electron beam when restarted, but in such a case, the electron beam may be deflected significantly. In order to prevent the sample from being irradiated with the electron beam, the inside of the lens barrel is exposed to the electron beam and becomes electrically charged, and this electrical charge bends the optical axis.
It is often necessary to adjust the optical axis while using the device.

[Prior Art] Conventional electron beam devices are equipped with an optical axis adjustment function called gun alignment.

This is to align the optical axis with the center of the electron optical system (e.g. pre-lens, condenser lens) interposed between the electron gun and the sample. ) is the main structure.

The optical axis is adjusted (alignment adjustment) by adjusting the deflection current in the x-y direction applied to this coil.

Alignment adjustment consists of the following two modes.

The first mode is called the 5HTFT (shift) mode, and as shown in Figure 9(a), the crossover (
The optical axis of the electron beam can be moved in parallel in the x-y direction without changing the position of the electron source (electron source). The amount of movement is
Corresponds to the amount of deflection current given to the coil.

The second mode is called the TILT mode, in which the position of the crossover virtual image changes as shown in FIG. 9(b). That is, the beam can be deflected using a certain point (e.g. pre-aperture) as a fulcrum,
The density of the electron beam (ie, beam current) passing through the pre-aperture is kept constant.

Actual gun alignment begins with alignment 1-T.
Using the ILT's two-dimensional scanning function (alignment scan), we roughly find the deflection conditions for the electron beam to reach the sample surface, and then adjust the deflection conditions precisely so that the beam current reaching the sample surface is maximized. Make appropriate adjustments.

[Problem to be solved by the invention]

However, such conventional optical axis adjustment relies heavily on manual operation by the operator, which requires considerable effort and effort, places a heavy burden on the operator, and has the disadvantage that the accuracy of adjustment is easily influenced by individual differences.

In particular, when starting up the equipment, the deviation of the optical axis is extremely large, so a high level of skill is required to align the optical axis in such a case, and an unscrupulous operator may not be able to start up the equipment, or Even if it is possible to start up, there is a problem in that it takes a considerable amount of time.

The present invention was made in view of these problems, and
In particular, the purpose is to quickly obtain good optical axis adjustment results even when the optical axis misalignment is extremely large, such as during startup.

[Means to solve the problem]

In order to achieve the above object, the present invention provides an electron beam apparatus in which an electron optical system is interposed between an electron beam generation source and a predetermined sample, and the electron beam is deflected and scanned by the electron optical system. When adjusting the optical axis of the system, a predetermined x-y region is specified, and while scanning the region, an electron beam passing through the electron optical system is detected, and the region at the time when the passing electron beam is detected is detected. Preferably, when the electron beam irradiation amount on the sample is converted into an electrical quantity, and the peak value of the electrical quantity exceeds a predetermined value, The method is characterized in that the passing electron beam is detected.

[Effect]

In the present invention, while scanning a predetermined x-y 9M area,
The path of the electron beam passing through the electron optical system is searched, and rough parameters representing the path are determined.

〔Example〕

Hereinafter, the present invention will be explained based on the drawings.

1 to 8 are diagrams showing an embodiment of the method for adjusting the optical axis of an electron beam device according to the present invention.

In FIG. 2, IO is an electron beam device, and the electron beam device 10 is divided into a lens barrel section 10a and a control section 10b.

The lens barrel section 10a includes an electron gun 11 that emits or stops the electron beam E according to an on/off signal S1, and an electron gun 1.
Optical axis adjustment coil (or alignment coil) 1 located in the immediate vicinity of (directly below in the figure) 1, which generates a magnetic field according to the magnitude of the optical axis adjustment current ia to adjust the optical axis of the electron beam E.
2, Briar Percha 13, and blanking plate 1
4, an objective aperture 15, a movable Faraday cup 16 that generates a signal S3 corresponding to the magnitude of the beam current of the electron beam E, and a movable Faraday cup 16 that generates a magnetic field corresponding to the magnitude of the deflection current ib to generate the electron beam E. A deflection coil 17 that deflects and scans the optical axis of the
It includes a stage 19 movable in the direction, an analyzer 20, and a detector 21 that generates a signal S2 corresponding to the amount of reflected electrons (for example, secondary electrons) from the sample 18.

On the other hand, the control unit 10b is a control computer (hereinafter referred to as a computer)
22, display device (or CRT) 23, electron gun control circuit 24, alignment coil drive circuit 25, alignment coil control circuit 26, blanking plate control circuit 2
7. Faraday cup control circuit 28, deflector control circuit 2
9, a signal processing circuit 30, a peak hold circuit 31, a memory device 32, an analyzer driving device 33, etc., and a computer 2
According to the instructions from 2, for example, a predetermined analysis process is executed on the sample 18, or an "optical axis adjustment process" is executed as necessary.

Here, the alignment coil control circuit 26 sends an x-y deflection signal (ATX,
ATV) and X-y deflection signal for S I FT mode (
ASX, ASY), but in the initial stage of adjustment,
Each deflection signal is generated according to the following procedure, and the values of ASX and ASY to be used as initial values for subsequent optical axis adjustment are roughly determined.

In other words, with the alignment scan operating,
Roughly determine the conditions under which a crossover image appears on a CRT screen. At this time, ATX and ATV are scanned two-dimensionally by hardware regardless of the operations of ASX and ASY.

Specify a predetermined x-y eI region (the region where the length of the X axis is ASX and the length of the y axis is ASY) using ASX and ASY, and scan the sample 18 while scanning this region two-dimensionally.
The amount of secondary electrons is monitored, and the peak value of the electrical signal S2 corresponding to the amount of secondary electrons is detected by the peak hold circuit 31. When a large peak value exceeding a predetermined reference value is detected, the peak hold circuit 31 outputs a signal S4, and the alignment coil control circuit 26 outputs a signal S4.
The values of ASX and ASY at that time are held.

A large peak value is detected when a significant portion of the electron beam reaches the sample, and when the electron beam passes through a complex electron optical system.

Therefore, by retaining the values of the deflection signals (ASX, ASY) at that time as x-y parameters and using these as the initial values for gun alignment described below, you can smoothly go from rough optical axis adjustment to precise adjustment. can be moved to.

Figure 2 is an overall flowchart of the optical axis adjustment process including the above-mentioned peak detection process, where (a) is the peak detection processing section, (b)
(c) is a rough alignment processing section, and (c) is a fine alignment processing section.

ASX held in the peak detection processing unit (a).

The value of ASY is passed to the rough alignment processing section (b).

In the rough alignment processing section, after bringing the crossover image to the center of the CRT screen using ATX and ATV, the filament current of the electron gun 11 (abbreviated as GUN) is reduced, and the ASX and ASY passed from the peak detection processing section A are A series of processes are performed, such as equalizing the symmetry of the crossover image, terminating the alignment scan, and restoring the GUN filament current.

The reason for reducing the filament current is as follows.

By adjusting ATX and ATV of the alignment coil, a crossover image can be displayed on the CRT screen. The deviation of the optical axis can be determined from the symmetry of this crossover image. When observing this symmetry, precise observation becomes possible by lowering the filament current. That is, in FIG. 3, (a), (b), and (c)
) When the filament current is lowered in the order of (c) in the same figure,
, a separated image of the crossover image is observed. Symmetry appears in the area balance of each separated part. If the balance is good, the degree of coincidence of the optical axes is high. Therefore, the accuracy of optical axis adjustment can be improved by finely adjusting ASX and ASY passed from the peak detection processing unit A to improve symmetry.

FIGS. 4 and 5 are detailed flowcharts of the rough alignment process.

First, the four alignment coil control parameters ASX
, ASY, ATX, and ATV are set (step 5ho). Here, the initial value of the variable range is set to the full range.

Next, start the alignment scan in step S++
), image data at the initial values of the coil control parameters is acquired (step S1□). FIG. 6 shows an example of image data, where a square frame is an image acquisition range, and a shape close to a circle within the acquisition range is an image including a crossover image. The peripheral distribution of the image corresponds to the current density distribution of the electron beam, and gradually decreases toward the periphery of the image. FIG. 7 shows the image data of FIG. 6 converted into map data. The numbers in the squares represent the strength of the image (the amount of secondary electrons), and the PR
F (Y) and PRF (X) are marginal distribution data.

The barycentric coordinates of the image can be determined from this peripheral distribution (step 513). For example, if the center of gravity position (coordinate) on the X axis is Px, and the center of gravity position (coordinate) on the Y axis is py, it can be determined as follows.

Here, an evaluation amount T (ATV) is introduced as a function of ATV. However, it is assumed that the evaluation amount T (ATV) when no crossover image appears on the CRT screen is equal to the value at the farthest position from the center coordinates of the CRT screen. The evaluation quantity T (ATX, ATV) is given by T (ATX, ATV) = (Xo-PRF (x))" + (Yo-PRF O') ) 2...■. Here, Xo and Yo are the center coordinates of the CRT screen.

Next, the difference between the CRT screen center position and the center of gravity position of the crossover image is calculated as the current evaluation amount T (ATV) (step 314), ATV is updated (step S1), and the image data is read again. Step 516)
, this is repeated until ATV-a (ATV scanning ends) (step Sl?).

Next, find the minimum value of the evaluation amount T (ATV) obtained for each iteration, and calculate this minimum value and ATX, AT which gives this value.
Save the value of V in T, , v (ATX, ATV) (step S's).

Next, ATX is updated (step 319), and ATY is scanned to obtain T, , v (ATX, ATV).

After completing the ATX scan (step 528), T...
Find the minimum value Tm1n of v (ATX, ATV) (Step 7 52I), and if the Tm1n is larger than the predetermined convergence value TSo (Step S2□), reduce the update step (Step 523) or higher. Step (crossover image search operation) is repeated.

The search operation is rough in the initial state and is set to be performed over a full range, and the ATX and ATV acquired for each search are
Narrow the search range around the value of , and at the same time make the update steps more detailed (Step 7, 524). This makes it possible to shorten the search time.

The above processing is completed when Tm1n falls below the convergence value TSo, and the values of ATX and ATV at that time are saved (
Step 525), the process proceeds to the next ASX and Asy search process.

FIG. 5 is a flowchart of the search process. ATX above
, By adjusting the ATV, a crossover image appears on the CRT screen, so in order to observe the symmetry of this image, the filament current is gradually lowered (Step S
3o). When a separated image of the lossover image as shown in FIG. 3 is observed, adjust ASX and ASY to improve the symmetry of the image. Specifically, in the same way as the previous ATX and ATV processing (corresponding steps are given the same number with a dash), ASX and ASY are finely adjusted so that the center of gravity position and the center of the screen match. Evaluation amount Ss, (A
SX, ASY) is a predetermined convergence value TS.

When it is determined that the following has been achieved, the adjustment is completed (step 531) - As described above, ASX, ASY, ATX.

After performing rough adjustment of the ATV, the next fine alignment process is performed.

FIG. 8 is a process flow diagram of the process. First, the filament current is returned to its original state (step 541), and the alignment scan is completed (step S4□). Next, the four parameters obtained in the rough alignment, that is, the ASX ,
,,,ASY,,,v,ATXsav + ATY
smv is set to an initial value (step 543), and while finely adjusting these parameters, an algorithm is executed to find the maximum point of the beam current that reaches the sample surface (step 544).

As described above, according to this embodiment, prior to rough alignment, the amount of secondary electrons from the sample 18 is monitored while scanning ASX and ASY two-dimensionally, and the amount of secondary electrons is adjusted accordingly. The peak hold circuit 31 detects the peak value of the electrical signal S2, and when a large peak value exceeding a predetermined reference value is detected, the peak hold circuit 3
1 outputs the signal S4, and the alignment coil control circuit 26 holds the ASX and ASY values at that time. Therefore, when a large peak value appears, a large portion of the electron beam will fall onto the sample. This is the case when a complex electron optical system (
Since this is a case where the deflection signal (AS
By using the values of X, ASY) as initial values for rough alignment, it is possible to smoothly transition from rough optical axis adjustment to precise adjustment. Good optical axis adjustment results can be obtained even when the deviation is large.

〔Effect of the invention〕

According to the present invention, when adjusting the optical axis of the electron beam,
A predetermined X-y area is designated, and while scanning the area, an electron beam passing through the electron optical system is detected, and the x-y area of the area at the time of detecting the passing electron beam is detected.
Since the y parameter is used as the initial value for optical axis adjustment, it is possible to smoothly transition from rough optical axis adjustment to precise adjustment, especially when there is a large deviation of the optical axis such as when starting up the equipment. Good optical axis adjustment results can be quickly obtained.

[Brief explanation of the drawing]

1 to 8 are diagrams showing an embodiment of the optical axis adjustment method for an electron beam device according to the present invention, in which FIG. 1 is a configuration diagram thereof, FIG. 2 is a flow diagram of the entire alignment adjustment, Fig. 3 shows the change in crossover image when the filament current is lowered, and Fig. 4 shows the ATX of the rough alignment. Adjustment flow diagram by ATV, Figure 5 shows ASX of the rough alignment. FIG. 6 is a diagram showing the captured image data, FIG. 7 is a map of the image data, and FIG. 8 is a fine adjustment flowchart. FIG. 9 is an explanatory diagram of two modes of gun alignment showing a conventional example. 1O...Electron beam device, 11...Electron gun, 12...Optical axis adjustment coil, 13...Pre-aperture, 14... Blanking plate, 15...
...objective aperture, 16...Faraday cup, 17...deflection coil, 18...sample, 19...stage, 20... Analyzer, ゛21...Detector, 22...Control computer, 23...Display device, 24...Electron gun control circuit, 25... ...Alignment coil drive circuit, 26.
...-.Alignment coil control circuit, 27...
...Blanking plate system all HB, 28...
...Faraday cup control circuit, 29...
Deflector control circuit, 30... Signal processing circuit, 31... Peak hold circuit, 32...
-Memory device, 33... Analyzer drive device.ゝ-Mini-' Crossover image (a) (b) (c) Third drawing image Figure 6 showing captured image data of one embodiment PRF (X) Map diagram of image data of one embodiment Figure 7 Figure 1: Fine adjustment flowchart of the embodiment Figure 8: Explanatory diagram of two modes of gun alignment showing a conventional example Figure 9:

Claims (2)

[Claims] (1) In an electron beam device in which an electron optical system is interposed between an electron beam generation source and a predetermined sample, and the electron beam is deflected and scanned by the electron optical system, when adjusting the optical axis of the electron beam, a predetermined step is performed. specifying an x-y region of the region, detecting an electron beam passing through the electron optical system while scanning the region, and detecting the x-y region of the region at the time of detecting the passing electron beam;
- An optical axis adjustment method for an electron beam device, characterized in that the y parameter is used as an initial value for optical axis adjustment. (2) Claim (1) characterized in that the amount of electron beam irradiation on the sample is converted into an amount of electricity, and when the peak value of the amount of electricity exceeds a predetermined value, the passing electron beam is detected. A method for adjusting the optical axis of the described electron beam device.