JPS5840820B2 - Electron beam automatic axis adjustment device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic electron beam axis adjustment device for an apparatus using an electron beam, such as an electron beam lithography apparatus.

In an apparatus using an electron beam, an aperture extracts only the central portion of the electron beam generated from an electron gun, which has the maximum current density, and then irradiates the electron beam onto a predetermined position on the sample surface.

However, in reality, the axial alignment between the electron gun and the aperture cannot be completed by mechanical axial adjustment alone; it is necessary to perform the adjustment while passing the electron beam.

A related art related to this will be explained using drawings.

FIG. 1 is a schematic explanatory diagram of a conventional electron beam axis adjustment device.

In the figure, a portion of an electron beam 2 generated from an electron gun 1 is taken out by an aperture 3 and used as a probe beam 4.

Here, the current density distribution 5 of the electron beam 2 on the surface of the aperture 3 has a mountain-like shape with a peak at a certain point on the x-y plane.

Therefore, in order to extract the electron beam 2 having the maximum brightness as the probe beam 4, the peak position must match the position of the aperture 3.

Therefore, as shown in the figure, there are two pairs of deflection coils 6 facing each other.
．． 7 are arranged perpendicular to each other, and the peak position of the electron beam 2 from the electron gun 1 is made to coincide with the aperture 3 by deflecting it.

The adjustment sequence begins with the terminal 17 of the deflection coil 6.7.
, 18, the current value of the probe beam 4 passing through the aperture 3 is measured by a measuring device (not shown) connected to the terminal 19 of the Faraday cup 14 provided behind the aperture 3. Measure.

Next, individually deflect the X-axis and Y-axis on the three aperture surfaces (that is, change the DC current value)
Find the position (optimal current value) where the maximum probe current can be obtained for each.

In this way, the peak position and the aperture 3 can be aligned, and the sample surface can be irradiated with the probe beam 4 having the maximum current density.

Although not shown in Figure 1, the sample is a Faraday cup 14
Both are placed on a horizontally movable sample stage.

During normal work (for example, drawing work), the sample is at the position where the probe beam 4 is irradiated, and only when performing axis adjustment work is the sample stage moved so that the probe beam 4 enters the Faraday cup 14. There is.

However, the above-mentioned conventional shaft adjustment device has a drawback in that the adjustment must be performed completely manually.

In other words, it takes several minutes to adjust the axis manually, and even if it is adjusted once, there is a risk that the set point may shift over time, and it is necessary to constantly monitor it at regular intervals. There was something special about it.

Furthermore, during adjustment, beam irradiation to the sample is completely interrupted, resulting in a reduction in sample processing efficiency.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a novel electron beam automatic axis adjustment device that can eliminate the drawbacks of the conventional devices as described above.

In order to achieve the above object, the present invention superimposes an AC deflection signal component having a relatively small amplitude on a DC deflection signal component in each of two pairs of deflection coils arranged orthogonally to each other, and The electron beam is deflected by applying a current with a phase difference of 90 degrees to the signal components, and the electron beam passing through the aperture is detected by a detector. Adjust the axis by changing the value.

This kind of shaft adjustment device for stealing has the following features: (1) automatic shaft adjustment is possible, (2) shaft adjustment time is 100 m or less, (
3) Since automatic adjustment can be performed in a short time, it can be done during sample processing free time (online), that is, without interrupting the work. (4) Also, monitoring operations can be performed constantly during free time. It has characteristics such as being able to

Hereinafter, the present invention will be explained in detail using the drawings.

2 to 5 are diagrams for explaining the principle operation of the present invention.

In FIG. 2, an electron beam 2 generated from an electron source 1 passes through an aperture 3 and becomes a probe beam 4. During axis adjustment, it is deflected by a deflection means (such as an electromagnetic coil) 21, and a detector (Faraday cup) 14 is deflected. The beam is incident on the surface of the sample 20 during sample processing.

Note that in FIG. 2, a deflection means (for example, an electromagnetic coil) for deflecting the electron beam 2 is omitted for convenience of drawing.

Here, let us assume that the electron beam 2 draws a trajectory 2' because the axis has not been adjusted.

In this case, it can be easily imagined that the electron beam current density distribution on the surface of the aperture 3 has a peak at a position slightly shifted to the right from the center of the aperture 3.

Therefore, since the axis cannot be aligned, the current value of the probe beam 4 irradiated onto the surface of the sample 20 becomes low.

This is also clear from looking at the detection signal from the detector (Faraday cup) 14.

Although FIG. 2 describes the y-axis, the same can be said about the y-axis.

FIG. 3a shows the distribution of current density I on the X-axis on the aperture 3 plane in FIG.

In Figure 3a, a point on the surface of the aperture 3 where the current density peaks, the center of the aperture 3, and the electron source 1
If the angles that lines 2' and 2 make with the perpendicular line from the electron source 1 are θ and θO, respectively, then when θ is changed by the deflection means, the change in the beam current Ip passing through the aperture 3 is θ The distribution curve 2 in Figure 3b as a function of
3.

Therefore, this distribution has a peak at θ2θ0, which indicates the angle at which alignment is perfect.

The example shown by distribution curve 22 in FIG. 3a is θ−θ+〉θ0
The beam current IP at this time is indicated by point R on the distribution curve 23 in the same figure.

Also, the beam current IP when θ=θ−θ0 is indicated by a dot on the curve 23.

Now, the procedure for automatic axis adjustment will be explained using FIGS. 3a and 3b.

First, it is determined whether the peak position of the current density distribution 22 on the X-axis is on the left or right side of the aperture 3.

For this purpose, as shown by point R in the same figure, a current in which an AC deflection signal component 24 (preferably a sine wave) having a relatively small amplitude is superimposed on a DC deflection signal component is applied to the X-axis deflection means. Apply.

That is, the DC deflection signal component causes a deflection by an angle θ0, and the AC deflection signal component causes a minute angle deflection (oscillatory) around this point.

When the probe beam in this state is detected by a detector (Faraday cup), an AC component signal 25 is obtained.

It can be seen that the phases of the AC deflection signal component 24 and the signal 25 are exactly inverted.

When this signal 25 is detected using the AC deflection signal component 24 as a synchronization signal, a signal 28 is obtained.

Signal 29 is obtained by further smoothing this signal.

That is, the peak position of the current density distribution 22 on the X-axis (
When the point (corresponding to point R) is on the right side of the center of the aperture 3, the value is negative as shown by the signal 29.

The amplitude of the signal 29 becomes smaller as the point R approaches the point P (that is, as the peak position of the current density distribution 22 on the X-axis approaches the center position of the aperture 3), and complete axis alignment is achieved. Sometimes it becomes zero.

Here, if the peak position of the current density distribution 22 on the Then, the center, that is, point P
The same effect can be achieved by controlling the value to decrease as it approaches .

Now, the case where the peak position is to the left of the center of the aperture 3 will be explained.

As can be easily imagined from the explanation of the case on the right, the same AC deflection signal component 26 causes a minute angle deflection to obtain a signal 27, which becomes a synchronous detection signal 30 and a signal 31 when smoothed.

That is, when the peak position (corresponding to a dot) is on the left side of the aperture 3, the value is positive as shown by the signal 31.

The amplitude of the signal 31 becomes smaller as the dot approaches the point P, and reaches O when the alignment is complete.

Of course, if it is too thick, you can do the same thing as when it is on the right side.

Although only the procedure for the y-axis has been described above, exactly the same procedure is performed for the y-axis as well.

This process is illustrated in Figure 4, which shows A-'? C
-')D-)E The shaft adjustment is completed through the process.

However, if the following method is used without performing the above-mentioned axis alignment in the x and y directions alone, the axis alignment can be performed in - times of operations.

The phases of the AC deflection signals applied to the deflection coils in the X direction and the Y direction are shifted by 90 degrees, and the output signals of the Faraday cup obtained at this time are synchronously detected with the respective AC deflection signals.

In this way, changes in the probe beam current caused by each AC deflection signal can be obtained independently in the X and X directions as synchronous detection outputs, so by feeding these back to each DC deflection signal simultaneously, the -dimensional In exactly the same way as in the above case, two-dimensional alignment can be performed once.

For example, as in the case of FIG. 4, assume that the aperture is located at the initial point A in FIG.

At this time, sinwt 33 in the X direction, and 9 in the X direction
When applying a cosine wave coswt34 with a different phase of 0°,
The aperture will make a circular movement 35 about point A.

Also, the gradient vector of current density at point A is r, y
Assuming that the angle between the axis and the vector r is θ, and that the vector r is constant within the range of the circular motion, the output of the Faraday cup is cos(wt-θ)36.

If the outputs of synchronous detection using sinwt 33 and coswt34 are respectively I, , I, these are given by the average values of 37 and 38, respectively, and the following equation is given. Since these are fed back to the DC deflection current, the aperture The position moves from point A in the direction of the vector r, and finally reaches the peak position where the current density gradient vector r becomes zero along the trajectory 39.

Note that for convenience of explanation, the aperture position has been described as being moved to the peak position, but this is relative and is not different from moving the peak position to the aperture position. Not even.

FIG. 6 shows a schematic explanatory diagram of an automatic axis adjustment device for providing electronic beams based on the operating principle described above.

In the figure, the X-axis circumferential deflection coil 6 and the Y-axis side deflection coil 7 are supplied with a current obtained by adding the output of a sine wave current oscillator 8 and the output of a constant current source 9 for X-axis deflection by an adder 10, and a sine wave The phase of the output of the current oscillator 8 is set by the phase shifter 1.
A current obtained by adding the current delayed by 90 degrees by 1 to the output of the constant current source 13 for y-axis deflection is applied by an adder 12, and the electron beam 2 is caused to vibrate two-dimensionally with respect to the aperture 3.

At this time, the current value of the probe beam 4 that has passed through the aperture 3 is detected by a detector (Faraday cup) 14, and this signal is synchronized with the outputs of the oscillator 8 and the phase shifter 11, and is detected by the synchronous detectors 15 and 16, respectively. Negative feedback is applied to the constant current source 9 for X-axis deflection and the constant current power source 13 for Y-axis deflection, respectively, so that these output signals become zero through synchronous detection.

By performing the above operations, the peak position of the current density of the electron beam 2 can be located at the center of the aperture 3.

The time required for this operation was less than 100 msec.

Further, the higher the oscillation frequency of the oscillator, the faster the operating speed.

However, if it becomes too high, problems will arise in other aspects, so 1 in 10 KHz to 100 (Z is an appropriate value).

Therefore, it is possible to sufficiently adjust the axis by utilizing the free time during sample processing, so that the sample processing efficiency can be improved.

Note that when the device to which the device according to the present invention is installed is used for its original purpose, the outputs of the constant current power source 9 for X-axis deflection and the constant current power source 13 for Y-axis deflection are held constant by memory. It continues.

Furthermore, it goes without saying that the AC deflection signal is not superimposed on the deflection electrodes at times other than when adjusting the pongee.

As described above, by using the automatic electron beam axis adjustment device according to the present invention, it is possible to consistently obtain an electron beam containing the highest current density and perform efficient sample processing, and its industrial value is extremely high. It's a dog.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a conventional electron beam axis adjustment device, FIGS. 2 to 5 are explanatory diagrams of the operating principle of the present invention, and FIG. 6 is a schematic configuration diagram of an electron beam automatic axis adjustment device according to the present invention. It is. 3...Aperture, 6,7...x,
y-axis deflection coil, 14...detector (Faraday cup).

Claims (1)

[Scope of Claims] 1. Electron beam deflection means disposed between an electron source and an aperture for passing the electron beam from the electron source, and a direct current deflection signal component and an alternating current deflection signal to the electron beam deflection means. means for detecting the electron beam that has passed through the aperture; means for synchronously detecting the output signal from the detection means with the output of the AC deflection signal component; An automatic electron beam axis adjustment device comprising means for controlling the value of the DC deflection signal component so that the output signal of the synchronous detection means becomes zero. 2. The electron beam deflection means is an electromagnetic deflection coil, and the deflection signal application means includes a constant current source, a sinusoidal current source, and an adder for adding the outputs of both types of current sources. The electron beam automatic axis adjustment device according to scope 1. 3 a first electron beam deflection means disposed between an electron source and an aperture for passing the electron beam from the electron source; and a first electron beam deflection means also disposed between the electron source and the aperture; a second electron beam deflection means for deflecting the electron beam in a direction perpendicular to the electron beam deflection means; and a first DC deflection signal component and a first AC deflection signal component to the first electron beam deflection means. The first
a second direct current deflection signal component and a second alternating current deflection signal component having a phase difference of 90 degrees from the first alternating current deflection signal component on the second electron beam deflecting means; means for detecting the electron beam that has passed through the aperture; and a first deflection signal applying means for synchronously detecting the output signal from the detection means with the output of the first alternating current deflection signal component. A second synchronous detection means for synchronously detecting the output signal from the detection means using the output of the second AC deflection signal component; means for controlling the value of the first DC deflection signal component so that the signal value becomes zero; and means for controlling the value of the first DC deflection signal component so that the value of the output signal becomes zero by the output signal of the second synchronous detection means and means for controlling the value of the DC deflection signal component.