JPH0652650B2 - Alignment method of charged beam - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method of aligning a charged beam in a charged beam apparatus such as an electron beam drawing apparatus.

[Technical background of the invention and its problems]

In recent years, an electron beam drawing apparatus has been used as an apparatus for forming a fine and high-density pattern of a VLSI or the like. Among the electron beam drawing apparatuses, particularly the variable size beam method is capable of drawing with high accuracy and high throughput. Therefore, it is impossible to transfer by light 0.5
It is suitable as an apparatus for directly drawing a VLSI pattern having a design rule of [μm] or less on a wafer.

FIG. 5 shows an example of an electron optical system of a conventional device of this type.
In the figure, 1 is an electron gun, 2 is a first shaping aperture mask having a rectangular aperture (aperture) 2a, 3 and 4 are condenser lenses for illuminating the mask 2, 5 is a second shaping aperture mask, and 6 is a mask. A projection lens for projecting the image of the aperture 2a of 2 onto the mask 5 to form a combined aperture image, 7 is the aperture image of the mask 2 and the mask 5
Of the variable size deflector for changing the size of the synthesized aperture image by changing the overlap with the aperture 5a of
Is a reduction lens, 9 is an objective lens for projecting the reduced synthetic aperture image onto the sample surface 12, and 10 is the sample surface 1.
A scanning deflector for positioning the beam position on the two,
Reference numeral 11 is an objective aperture mask for defining the aperture angle of the lens 9.

In the optical system having this configuration, the electron gun crossover P, which is the light source, is imaged at the positions P ₁ , P ₂ , P ₃ , and P ₄ , respectively, and separated from the aperture image. Here, the crossover image P ₂ needs to be accurately focused on the deflection center of the deflector 7 by the condenser lens 3 or 4. When the crossover image P ₂ deviates from the deflection center of the deflector 7, the beam moves in the radial direction with respect to the objective aperture mask 11 in accordance with the deflection of the deflector 7, and a dose error of the drawing pattern occurs. However, no matter how precisely the condenser lenses 3 and 4 are focused, the above-mentioned beam movement with respect to the objective aperture mask 11 may occur, and it is clear that the cause is the axis shift of the beam with respect to the projection lens 6. did.

FIG. 6 is a schematic diagram for explaining the mechanism of the above beam movement. When the range in which the beam is deflected by the deflection of the deflector 7 is the region sandwiched by the optical paths b and c about the optical axis a of the lens 6, the crossover image P _{2 at} the deflection center of the deflector 7 is formed at the point A. To be imaged. At this time, the point A does not move with respect to the deflection by the deflector 7, and a dose error does not occur. On the other hand, when the range in which the beam is deflected by the deflection of the deflector 7 is the area sandwiched between the optical paths e and f with the optical path d as the center,
Since the optical paths e, d, and f are largely deviated from the optical axis, the beam moves to E, D, and F due to the spherical aberration of the projection lens 6. This movement is magnified by the reduction lens 8 and projected on the objective aperture mask 11 to cause a dose error. The amount of movement increases in proportion to the cube of the deviation from the optical axis. Therefore, it is necessary to align the center optical path of the deflection with the optical axis of the lens 6.

Conventionally, such axial alignment is performed by arranging a limiting aperture mask having a circular aperture smaller than the beam diameter in or near the lens so that the center of the aperture coincides with the axis of the lens to maximize the beam current passing through the aperture. The coil for axis alignment was adjusted so that

However, when a limiting aperture mask is placed in or near the projection lens, as is clear from FIG. 7, the optical path of the beam 17 is aligned with the optical axis of the lens 6 as the deflector 7 deflects the beam size. On the other hand, move vertically. Therefore, the amount of the beam cut by the limiting aperture mask 15 changes depending on the beam size,
It causes the fluctuation of the beam current. In addition, 16 in FIG. 7 has shown the coil for axis alignment. Further, in the optical configuration as shown in FIG. 5, when the limiting aperture mask is placed near the projection lens 6, a penumbra of the limiting aperture mask is generated in the shaped beam image on the sample surface 12, and the current density is uniform. It is not desirable because it may damage the sex.

[Object of the Invention]

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to align a charged beam without causing fluctuations in the beam current and without impairing the uniformity of the beam current density. An object of the present invention is to provide a charged beam axis alignment method that can be accurately performed.

[Outline of Invention]

The gist of the present invention is to use an axis-aligning aperture mask having an aperture diameter larger than the beam diameter, and detect the edge position of the aperture of this aperture mask to align the beam axis.

That is, according to the present invention, in the method of aligning a charged beam in a charged beam apparatus, the aperture center is arranged so as to match the axis on which the charged beam is to be aligned, and the aperture diameter is larger than the diameter of the beam at that position. Using the formed aperture alignment mask and the alignment deflector that is arranged closer to the beam radiation source side than the aperture mask and that deflects the beam to the aperture center of the aperture mask, the beam is deflected by the deflector. While scanning on the aperture mask, the intensity or amount of the beam reflected from the mask, the beam passing through the mask, or the beam flowing into the mask is continuously detected to measure the edge position of the aperture. The aperture center position is obtained from the edge position, and the beam axis is obtained by the deflector. It was a method to match the aperture center position.

Especially when aligning the beam axis with the aperture center,
The beam is scanned in the X direction by the deflector to scan the X of the aperture.
After detecting the two edge positions in the X-direction, the deflector sets the axis of the beam to the center position of each edge in the X-direction, and then the deflector scans the beam in the Y-direction to detect the two edges in the Y-direction of the aperture. After detecting the position, the beam axis is set to the center position of each edge in the Y direction by the deflector, and when the deviation between the beam axis and the aperture center position at this time is outside the allowable range, the above operation is repeated. It is characterized by

〔The invention's effect〕

According to the present invention, since a part of the beam is not cut by the limiting aperture or the like, accurate beam axis alignment is performed without causing beam current fluctuations and reduction in uniformity of the current density distribution of the shaped beam. be able to. Furthermore, since the beam after axis alignment does not scatter from the limiting aperture, charge-up of scattered electrons does not occur, so that the effect of improving the beam stability can be obtained.

Example of Invention

 Hereinafter, details of the present invention will be described with reference to illustrated embodiments.

FIG. 1 is a schematic configuration diagram showing an electron beam drawing apparatus used in a method of an embodiment of the present invention. The same parts as those in FIG. 5 are designated by the same reference numerals, and detailed description thereof will be omitted.
The configuration from the electron gun 1 to the objective aperture 11 is the same as that of the apparatus shown in FIG. 5, and the points that this apparatus is different are the aperture mask 21 for axis alignment, the deflection coil 2 for axis alignment.
2, the backscattered electron detector 23 and the control power supply 20 for driving them are provided. That is, the main surface of the projection lens 6 has an aperture 2 having a diameter larger than the beam diameter at this position.
An axis alignment aperture mask 21 having 1a is arranged. The center of the aperture of this mask 21 is the lens 6
It is arranged so as to coincide with the center (optical axis) of. Between the shaping aperture mask 2 and the deflector 7, an axis-aligning deflection coil 22 for deflecting the beam at the center of the aperture of the axis-aligning aperture mask 21 is arranged.
A backscattered electron detector 23 that detects backscattered electrons from the aperture mask 21 is disposed between the axis alignment aperture mask 21 and the deflector 7.

Next, the axis alignment method used in the above apparatus will be described.

First, the deflection signal supplied to the size varying deflector 7 is set to zero so that the beam is not deflected by the deflector 7. Then, as shown in FIG. 2, the electron detector 23 detects the reflected electron signal from the axis alignment aperture mask 21 in synchronization with the scanning of the X coil of the axis alignment deflection coil 22.

Here, as shown in FIG. 3A, the detection signal obtained when the beam is scanned in the X direction so as to traverse the aperture 21a of the aperture mask 21 for axis alignment is shown in FIG.
As shown in. I ₀ is a backscattered electron signal when the beam is completely stopped by the aperture mask 21. Set the threshold level, for example, in I _0/2, I =
The deflection coordinates corresponding to I _0/2, each X _B, and X _C.
X _B and X _C correspond to the edges B and C of the aperture 21a of the aperture mask 21 for axis alignment. X _B , X _C midpoint X
_D is obtained, and the beam is set to X _D by the X coil, that is, the midpoint D of each of the edges B and C.

Then, similarly, the Y coil of the deflection coil 22 is scanned, edge coordinates Y _E and Y _F are detected as shown in FIG. 3C, and the coil is set to the center point coordinate Y _G. Where Y _E , Y
_F corresponds to the edges E and G of the aperture 21a, and Y _G corresponds to the position of the midpoint G of the edges E and F. Then X again
By scanning the coil, the edge coordinates X _J (corresponding to the edge J), X _K (corresponding to the edge K) and the midpoint coordinates X _M (edges J and K) of the aperture 21a are scanned as shown in FIG. 3 (d).
(Corresponding to the middle point M) and set the beam to the value of X _M. By repeating such an operation several times, it becomes possible to accurately align the electron beam with the aperture center of the aperture mask 21 for alignment. It is usually sufficient to perform the operation of the flowchart shown in FIG.
With such a method, it was possible to perform axis alignment with an accuracy of 5 [μm] on an aperture having a diameter of 600 [μm].

In FIG. 3, A indicates the beam position when the deflection signals of the variable size deflector 7 and the axis alignment deflection coil 22 are set to zero, and a indicates the size of the beam on the aperture mask 21. .

As described above, according to the method of this embodiment, the edge position of the aperture 21a of the aperture mask 21 is detected by using the axis alignment aperture mask 21, the axis alignment deflection coil 22, the backscattered electron detector 23, etc. By measuring the coordinates, the electron beam can be accurately aligned with the center of the aperture. In this case, unlike the case where the limited aperture mask is used, there is no inconvenience that a part of the beam is cut by the aperture mask and the fluctuation of the beam current and the deterioration of the uniformity of the beam current density are prevented in advance. You can Further, since the scattered electrons are not charged up, there is an advantage that the stability of the beam can be improved.

The present invention is not limited to the method of the embodiment described above. For example, in order to detect the aperture edge of the aperture mask for alignment, the beam that has flowed into the aperture mask may be detected instead of detecting the reflected electrons. Furthermore, it is also possible to detect the beam that has passed through the aperture mask and use the reflected electron or beam current signal thereof. However, in this case, the characteristics of the detection signal are the opposite of those in FIG. Also,
The configuration of the electron beam drawing apparatus is not limited to that shown in FIG. 1, and the present invention can be applied to various electron beam apparatuses that require axial alignment. Further, the invention is not limited to the electron beam, but can be applied to the axis alignment of the ion beam. In addition, various modifications can be made without departing from the scope of the present invention.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an electron beam drawing apparatus used in an embodiment method of the present invention, and FIGS. 2 and 3 are schematic diagrams for explaining a method of detecting an aperture edge to obtain an aperture center. 4 and 5 are flowcharts for explaining the axial alignment procedure, FIG. 5 is a schematic configuration diagram showing a conventional device, FIG. 6 is a schematic diagram for explaining axial alignment of the projection lens, and FIG. 7 is a restriction. It is a schematic diagram for demonstrating the conventional axial alignment method using an aperture. 1 ... Electron gun, 2, 5 ... Molding aperture mask, 3, 4 ...
Condenser lens, 6 ... Projection lens, 7 ... Dimension variable deflector, 8 ... Reduction lens, 9 ... Objective lens, 10 ... Scan deflector, 11 ... Objective aperture mask, 12 ... Sample surface,
20 ... Control power source, 21 ... Axis alignment aperture mask,
21a ... Aperture, 22 ... Deflection coil for axis alignment, 2
3 ... Backscattered electron detector.

Claims (3)

[Claims] 1. A method for aligning a charged beam emitted from a charged beam radiation source in a charged beam apparatus for focusing and irradiating the charged beam onto a sample, wherein an aperture center is aligned with an axis to be aligned. And an aperture mask for alignment with an aperture diameter larger than the diameter of the beam at that position, and a beam radiation source side that is closer to the aperture mask than the aperture mask. Using an axis-aligning deflector that deflects to the center of the aperture, while scanning the beam on the aperture mask by the deflector, the intensity of the beam reflected from the mask, the beam passing through the mask, or the beam flowing into the mask, or The edge position of the aperture is continuously measured by continuously detecting the Is a method of determining the aperture center position from the edge position, and causing the deflector to match the axis of the beam with the determined aperture center position, wherein the deflector is used when the beam axis is aligned with the aperture center. The beam is scanned in the X direction by means of the above to detect the two edge positions in the X direction of the aperture, and then the axis of the beam is set by the deflector to the center position of each edge in the X direction. The beam is scanned in the Y direction by means of to detect the two edge positions of the aperture in the Y direction, and then the axis of the beam is set by the deflector to the center position of each edge in the Y direction. A method of axially aligning a charged beam, wherein the above operation is repeated when the deviation between the beam axis and the center position of the aperture is out of the allowable range. 2. The method of axial alignment of a charged beam according to claim 1, wherein the aperture of the aperture alignment mask is formed in a circular shape. 3. The charged beam apparatus is a variable dimension type charged beam drawing apparatus comprising two beam shaping aperture masks and a beam dimension varying deflector between the aperture masks, and the axis aligning apparatus is for aligning the axes. The method for aligning a charged beam according to claim 1, wherein a deflector is arranged between the beam size varying deflector and the beam shaping aperture mask on the sample side.