JPH0466347B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a focused ion beam processing apparatus, and particularly to an ion beam processing method and method suitable for minimizing damage to a base substrate due to processing when repairing photomask defects. Regarding equipment.

[Background of the invention]

As shown in FIG. 1, the photomask has white dot defects 4, which are gaps where the pattern 2 should originally exist, and black dot defects 3, where excess pattern forming material has adhered. If this continues, these defects will be transferred to all wafers, so they must be corrected before transfer. The present invention relates to the correction of black spot defects among these defects.

Traditionally, lasers have been used to repair black spot defects in masks. For example, an example is shown in Electronic Materials, March 1978, page 49, and FIG. 2 shows the configuration of the optical system of the laser photomask correction device. In this device, as laser 5
Beam expander 8 using Nd:YAG laser
After expanding the beam with
A method is adopted in which the pattern forming material within the slit image is removed. In the past, this was sufficient to achieve a sufficient effect, but in recent years, as patterns have become increasingly finer, lasers have become increasingly fine due to the focusing limit due to the diffraction phenomenon of laser light and the fact that the processing process is thermal processing. It is becoming impossible to cope with the situation. Therefore, in recent years, ion beam processing, which focuses an ion beam extracted from a liquid metal ion source into a spot of 1 μm or less, has been attracting attention as an alternative processing method to laser processing. For example, see pages 22-23 of NIKKEI MICRO DEVICES, Spring 1985 Special Edition.

FIG. 3 shows a schematic configuration of the ion beam processing apparatus. The ion beam 33 is extracted from the source 20 by the extraction electrode 21, the beam is focused by the lens 22, the beam shape is corrected by the stigmator 23, the beam is deflected by the deflector 24, and the target photomask 25 is irradiated to remove sunspot defects. . At this time, the position to be processed is determined by detecting the secondary electrons 29 generated from the target by beam irradiation.
Secondary electron images are converted to CRT using the same principle as a scanning electron microscope.
32 and set it. The main parts of the apparatus are housed in a vacuum chamber 19 and evacuated to a constant vacuum pressure by a vacuum pump 31. Furthermore, the vacuum chamber 19 is installed on a surface plate 27 and supported by an air servo mount 28, thereby eliminating electric power from the floor.

In ion beam processing equipment, a beam focused to a spot diameter of 1 μm or less is scanned within the area to be removed, and black spot defects are removed by sputter processing. For example, when a black spot defect 35 exists next to a vertical line pattern 34 as shown in FIG. 4A,
From left to right within the beam scanning area 36 surrounded by the broken line,
Processing is performed by scanning the beam from top to bottom. Figure 4B
is the section A, AA in Fig. 4. FIG. 4C shows the state when the machining is completed. One of the differences between ion beam processing and laser processing is the non-selectivity of processing. In laser processing, direct processing occurs only in substances that absorb laser light, but in ion beam processing, processing proceeds with any material, although there are differences in processing speed due to differences in spatter rate. For this reason, when processing with an ion beam, processing is performed up to the base substrate 38 that is not processed using the laser, and the base substrate 38 is placed at the processing end.
A step 39 of 8 is generated. When the black spot defect 35 shown in FIG. 4A is actually removed by an ion beam and transferred onto a wafer, a hollow pattern 44 as shown in FIG. 5 is transferred. This occurs because the light is refracted and scattered by the step in the base substrate, and this new black spot defect is unavoidable in the machining marks as shown in Figure 4C.
This is a major obstacle in applying ion beam processing to mask correction.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an ion beam processing method and apparatus that can reduce new black spot defects that occur from the base substrate processing marks after mask correction using an ion beam.

[Summary of the invention]

Processing of the base substrate can be minimized by limiting the processing area to only areas with sunspot defects, but during processing, the sunspot defects gradually become smaller.
Since it is necessary to reset the processing area each time,
If an actual device were to be manufactured, it would be complicated, including pattern recognition, and would be impractical in terms of cost and operability.

Therefore, in the present invention, an attempt has been made to practically solve this problem using a simpler method.Actually, as shown in FIG. The beam shape is changed to avoid shadows.

[Embodiments of the invention]

Examples of the present invention will be described below.

FIG. 7 shows the existence form of the sunspot defect 52 divided into five cases. A is the edge of the pattern 51 in all four directions, and sharp processing edges are required there. B has pattern edges in three directions, and the base substrate is exposed in one direction, so sharp processing edges are required for the top and bottom left, but sharp processing edges in the right direction will cause edge shadows on the transferred pattern, so The machining edge in this direction must be smooth. Furthermore, C requires machining with sharp edges in two directions and gentle edges in two directions, D requires sharp edges in one direction and gentle edges in three directions, and E requires machining with gentle edges in all directions. Become. FIG. 8 summarizes how the beam diameter dx in the X direction and the beam diameter dy in the Y direction are changed for each case in FIG. 7. Let's take case C as an example. As shown in FIG. 7, in C, the upper and left directions correspond to the edges of the pattern, so the processed edges in the upper and left directions of the beam scanning area 52 indicated by broken lines are made so that the edges of the transferred pattern do not sag. It has to be sharp. On the other hand, in the downward and right directions, the processed edges must be smooth so as not to cast shadows on the transferred pattern. Therefore, as shown in the left diagram of case C in FIG. 8, the processing beam diameter is the minimum beam diameter at the upper left end of the scanning area, and as it goes to the right, the beam diameter dx in the X direction increases. Further, the beam diameter dy in the Y direction is expanded as it goes downward, so that the beam diameter becomes the maximum at the lower right of the scanning area. The minimum beam diameter is the focused beam diameter of the lens itself, and the maximum beam diameter varies depending on the size of the processing area and the surrounding conditions of the processing area, but is usually 2 μmφ to 5 μmφ or 1/4 to 1 of the shorter width of the processing area. /3. The center and right figures of Figure 8 Case C show the beam diameter dx in the X direction and the beam diameter dy in the Y direction.
Change as a function of Y as shown in the figure. Next, how to actually change the beam diameter and beam shape will be explained. FIG. 9 shows electrodes related to this example. Diagram A mainly shows lenses 57 and 5.
The applied voltages are shown at 8 and 59, where V ₀ is called the accelerating voltage, V ₁ is called the extraction voltage, and V ₂ is called the lens voltage.
Figure B is a BB cross-sectional view seen from the source direction in Figure A, and the beam is scanned by applying the deflection voltages V _x+ , V _x- ·V _y+ , and V _y- to the deflector 65, respectively. Figure C is viewed from the source direction of Figure A.
It is a CC cross-sectional view, showing the voltage applied to the stigmator 66, and applying the same voltage to the opposite electrode,
Squeeze or stretch the beam shape. Normally, it is used to correct astigmatism of the optical systems 56 to 64, but in the present invention, it is used to actively change the beam shape. Let the voltages applied to each electrode be V〓, V〓, V〓, V〓. At this time, the applied voltages for realizing the beam change in case C of FIG. 8 are as shown in FIG. 10. In this example, the acceleration voltage V ₀ and the extraction voltage V ₁ are constant because processing is performed with the ion acceleration energy and current constant. The beam diameter is changed by the lens voltage _V2 , and the beam shape is changed by the stigmator applied voltages V〓, V〓,
I have V〓, V〓 in charge. However, since the beam shape is changed in the X and Y directions but not in the diagonal direction, V〓 and V〓 are not output. Further, the deflector voltages V _x+ , V _x- , V _y+ , and V _y- give normal scanning waveforms. Now, as shown in the upper right of Figure 10.
V ₂ is changed from the just focus voltage V _2j in synchronization with beam scanning. Since the beam diameter increases as it deviates from V _2j , the beam diameter changes as shown in FIG. 11A. Points a to h in FIGS. 10 V and V correspond to points a to h in FIG. 11B, and the beam shape change will be explained using this. At point a, both V〓 and V〓 are 0, and there is no beam deformation. At point b
With V〓 and V〓, the beam is elongated in the X direction. At point C, the beam is elongated in the Y direction because of V〓 and V〓. After this d, e, f
Continuing in the same way, at point g the beam diameter is the same as at point b.
Since the signs of V〓 and V〓 are opposite, the beam shape at point b becomes an XY-inverted beam shape. At the final point h, both V〓 and V〓 are 0, the beam shape does not change, and the maximum beam diameter remains the same. In this way, the beam change of case C in FIG. 8 can be realized. Actually the 12th
When a sunspot defect 70 on a photomask as shown in Figure A is processed within the scanning area 71 using the beam change in Case C in Figure 8, Figures 12B and C (Figure 12B is a cross section taken along arrow C in Figure A) As shown in Fig. 12 (C is a sectional view taken along arrow B CC' in Fig. A), the processed edge on the pattern 72 side has a sharp edge, and the processed edge of the base substrate portion 73 without the pattern 72 is smooth. When transferred to a wafer, no shadows were produced at the processed edge, making it possible to effectively correct black spot defects.

Furthermore, in this example, the beam diameter and beam shape were changed by changing the lens voltage and stigmator voltage. However, although the optical system itself is complicated, the voltage application is a little simpler, as shown in FIG. 13.
A similar effect can be obtained by adding the pole-opposed flat electric plates 80 into the optical system. At this time, lens electrode 7
Since the final stage of 7 is at the ground level, the beam diameter can be changed by changing the voltage applied to the disk electrode 78 above and below the ground level, and the just focus lens voltage, which is a high voltage like the lens voltage, can be changed.
There is no need to change the voltage above and below V _2j . Also,
Since the stigmator 79 is responsible for adjusting the original beam shape, it is sufficient to apply the same voltage to the opposite electrode of the four-pole plate electrode and change it as necessary. In addition to the role of , the voltage application method is simpler than the conventional method, which required complicated changes in the applied voltage because it was responsible for changing the beam shape. Note that the beam diameter changing disc electrode 78 can also be used as a final stage lens electrode, which is normally used at ground level, by applying a voltage to it. Furthermore, whether a dedicated electrode is provided or a shared electrode is used, a design that minimizes disturbances in the electric field is required, such as by providing an earth shield to prevent the beam shape from being distorted between that electrode and the next electrode. be.

〔Effect of the invention〕

According to the present invention, a new black spot defect caused by a step at the edge of a processed base substrate, which has always been a problem when conventionally focusing an ion beam to correct a black spot defect on a photomask, is not generated. Therefore, photomask sunspot defect correction using an ion beam is effective and has the effect of further improving practicality.

[Brief explanation of drawings]

Figure 1 is a plan view of a photomask, Figure 2 is a configuration diagram of a laser photomask repair device, Figure 3 is a configuration diagram of an ion beam processing device, Figure 4 is an explanatory diagram of mask modification using an ion beam, and Figure 5 is a plan view of the wafer transfer pattern after mask correction, FIG. 6 is a cross-sectional view of the corrected mask targeted by the present invention, FIG. 7 is a classification diagram of the existence forms of sunspot defects, and FIG. 8 is a diagram of each sunspot defect type. 9 is an explanatory diagram of the voltage applied to each electrode of the ion optical system, and FIG. 10 is a voltage-time graph of each applied voltage.
Figure 11 is an explanatory diagram of the beam change due to the applied voltage in Figure 10, Figure 12 is a plan view and cross-sectional view of the mask after processing, and Figure 13 is a schematic diagram of the ion optical system equipped with an electrode dedicated to beam change. . Explanation of symbols, 1...Base substrate, 2...Pattern, 3...Black spot defect, 4...White spot defect, 5...Laser, 6...Laser beam, 7...Mirror, 8...Beam expander , 9...Mirror, 10...Slit, 11...Mirror, 12...Objective lens, 1
3...Photomask, 14...Table, 15...
...Illumination light source, 16...Illumination optical system, 17...Filter, 18...Observation optical system, 19...Vacuum chamber, 20...Source, 21...Extraction electrode, 2
2... Focusing lens, 23... Stigmator,
24...Deflector, 25...Photomask, 2
6...Table, 27...Surface plate, 28...Air servo mount, 29...Secondary electron, 30...Secondary electron detector, 31...Vacuum pump, 32...
CRT, 33...Ion beam, 34...Pattern, 35...Sunspot defect, 36...Beam scanning area, 37...Ion beam, 38...Beam scanning area, 39...Step, 40...Spattered Atom, 41...Pattern, 42...Base substrate, 43
...pattern, 44...wax pattern, 48...
... Pattern, 49 ... Base substrate, 50 ... Machining trace, 51 ... Pattern, 52 ... Black spot defect, 53
...Beam scanning area, 54...Beam spot,
55... Beam scanning area, 56... Source, 57
...first lens electrode, 58...second lens electrode,
59...Third lens electrode, 60...Photomask, 61...Table, 62...Ion beam,
63... Stigmator, 64... Deflector, 65... Deflector electrode, 66... Stigmator electrode, 67... Beam scanning area, 68...
...Beam spot, 69...Pattern, 70...
Black spot defect, 71...Beam scanning area, 72...Pattern, 73...Base substrate, 74...Source, 7
6... Extraction electrode, 77... Focusing lens, 78
... Beam diameter adjustment electrode, 79 ... Stigmator, 80 ... Beam shape adjustment electrode, 81 ... Deflector, 82 ... Photomask, 83 ... Ion beam, 84 ... Table.

Claims (1)

[Claims] 1. Ion source, ion optical system, target,
Ion beam processing consists of a table, a vacuum evacuation system, a power supply control system, a vacuum chamber, and a stand, and the ion beam is pulled out from the ion source, focused and deflected by the ion optical system, and irradiated onto the target for processing. In the method,
An ion beam processing method characterized in that processing is performed by changing the diameter or shape of the spot of the ion beam on the target in synchronization with a deflector that deflects the ion beam. 2. When changing the diameter or shape of the ion beam spot, a microcircular spot or an elliptical spot whose major axis is parallel to the end surface at the edge of the processing area on the target that requires a sharp edge, or an end surface that requires a gentle edge. 2. The ion beam processing method according to claim 1, wherein processing is carried out using a beam having a large circular spot or an elliptical spot whose major axis is perpendicular to the end face. 3. The above-mentioned minute circular spot is a direct focus spot of the concentrating lens included in the above-mentioned ion optical system, the above-mentioned large circular spot is 1 μm to 10 μm or 1/4 to 1/2 of the short side of the above processing area, and the elliptical spot is used. 3. The ion beam processing method according to claim 2, characterized in that processing is carried out using a spot whose major axis and minor axis are between the diameters of the minute circular spot and the diameter of the large circular spot. 4. The ion beam processing method according to claim 1, wherein the spot diameter is changed by changing the lens voltage of the focusing lens in synchronization with the deflector. 5. The spot shape is changed by applying a predetermined voltage synchronized with the deflector to a stigmator included in the ion optical system and normally used to correct astigmatism of the ion beam. The ion beam processing method according to scope 1. 6. The ion beam according to claim 1, wherein the spot diameter is changed by applying a voltage synchronized with the deflector to a spot diameter adjusting electrode specially added to the ion optical system. Processing method. 7. A patent characterized in that the spot shape is changed by applying a voltage synchronized with the deflector to a spot shape adjusting electrode specially added to the ion optical system or to a final stage lens electrode of the focusing lens. An ion beam processing method according to claim 1. 8 Ion source, ion optical system, target,
In an ion beam processing device consisting of a table, a vacuum evacuation system, a power supply control system, a vacuum chamber, and a pedestal, it is used to adjust the lens voltage and beam shape applied to the focusing lens in synchronization with the ion beam deflector included in the ion optical system. An ion beam processing device characterized by being provided with a synchronous circuit and a power supply that change the voltage applied to a stigmator. 9. The ion beam processing apparatus according to claim 8, wherein the ion beam apparatus is provided with a synchronization circuit for the spot diameter adjusting electrode, the spot shape adjusting electrode, and the deflector, and a power supply. 10. The ion beam processing apparatus according to claim 9, wherein a circular hole disk electrode is provided below the focusing lens as the spot diameter adjusting electrode. 11. The ion beam processing apparatus according to claim 9, characterized in that the spot shape adjusting electrode is provided with four or eight opposed parallel plate electrodes.