JPH04177717A - Charged particle beam aligner and exposing method - Google Patents

Abstract

PURPOSE:To make possible an accurate clock correction for every pattern on an actual block mask by a method wherein an aligner is provided with a block mask clock memory for storing a clock correction amount for every pattern, which is obtained by actually measuring, of basic irradiation time for each pattern on the block mask. CONSTITUTION:A control part 25 of a charged particle beam aligner 10, by which a block exposure is performed, is provided with a block mask clock memory 28. A clock correction amount for each mask NO (each pattern on a block mask 15) is stored in this memory 28. The clock correction amount is a correction amount of basic irradiation time for each pattern, which is decided by the beam current density of the image of each pattern and the photosensitivity of a photosensitive resist on a matter to be irradiated, and is determined through measurement. Thereby, an accurate clock correction can be performed for every pattern on the actual block mask 15 and a calibration becomes possible.

Description

[Detailed Description of the Invention] [Summary of the Invention] Regarding a charged particle beam exposure apparatus and exposure method that perform block exposure, it is an object of the present invention to enable accurate lock correction and calibration for each pattern of an actual block mask. In a charged particle beam exposure apparatus equipped with a block mask having an aperture group for shaping a charged particle beam into one of a plurality of basic patterns or a variable rectangular pattern, the basic irradiation time for each pattern on the block mask is
The structure includes a block mask clock memory that stores clock correction amounts for each pattern obtained through actual measurements, and a block mask that has a group of apertures that shapes the charged particle beam into one of a plurality of basic patterns or a variable rectangular pattern. In an exposure method using a charged particle beam exposure apparatus, a reference irradiation time is given to each pattern on the block mask, and the reference irradiation is performed using a measured clock correction amount for each pattern on the block mask. The configuration is such that the exposure time for the pattern is determined by correcting the time.

[Industrial application field]

The present invention relates to a charged particle beam exposure apparatus and an exposure method that perform block exposure.

In recent years, with the increase in the density of integrated circuits, new exposure techniques using electron beams have been studied and put into practical use in place of photolithography, which has been the mainstream method for forming fine patterns for many years.

[Conventional technology]

A conventional electron beam lithography system that is in practical use is one that generates arbitrary shots using a variable rectangular beam to draw a pattern on an irradiated object. Such a device has a pattern generator function that decomposes pattern data, which is the minimum unit on the design side, into shots in an arbitrary variable rectangular beam.

However, as integration progresses, the pattern data becomes smaller and the number of patterns increases, resulting in an increase in the number of beam shots resolved by the pattern generator, resulting in a problem of lower throughput. Therefore, in order to obtain a realistic throughput even in the generation of ultra-fine patterns, a block exposure method has been proposed.

Semiconductor devices that require ultra-fine patterns are, for example, 6
Like a 4 mega DRAM, most of the area to be drawn is a repetition of an arbitrary basic pattern, although it is small. If the repetition of this basic pattern can be processed in one shot, throughput will improve. Therefore, block exposure is a method in which the basic pattern as described above is held on a transmission mask and is irradiated with an electron beam to generate the basic pattern in one shot.

FIG. 6 shows an example of a block exposure method. The main part is a block mask 15, on which a plurality of basic patterns (15b, etc.) are formed, and a rectangular pattern 15a for a variable rectangular beam is also formed in the center. Electrons emitted from the electron gun II pass through the shaping aperture 12, and are selectively irradiated to an arbitrary pattern portion of the block mask 15 by the mask deflector 14 placed at the image point of the crossover formed by the electromagnetic lens 13. . In addition, for a single pattern without a repeating pattern, block mask 15 is used.
A rectangular pattern 15a is selected from among the patterns, and the method is similar to the conventional variable rectangular beam exposure method. The patterned image is returned to the optical axis by the converging action of the lens, the pattern image is reduced by the reduction lens 16, and is irradiated onto an arbitrary part of the object 20 by the projection lens 17, deflection coil, etc.

In order to obtain a highly accurate pattern by irradiating the pattern image of the electron beam onto the irradiated object, various elemental technologies are necessary, but whether or not the desired pattern can be obtained depends on the irradiated object.
- It is determined by setting the pattern irradiation time determined by the photosensitivity of the electron beam photoresist and the current density of the electron beam pattern image. In the variable rectangular beam exposure method, this is used as the basic irradiation time, and clock correction is applied to each pattern data in order to take into account proximity effects caused by pattern arrangement and high density. Clock correction is to correct the exposure amount (irradiation time), and the shot time of each pattern is determined by the ratio to the basic irradiation time, thereby making all patterns highly accurate in exposure.

[Problem to be solved by the invention]

In the block exposure method, a repeating pattern is created in one shot.
・Since the exposure is performed using the variable beam exposure method, the absolute number of clock corrections for each pattern used in the variable beam exposure method is reduced, but
It is necessary. However, clock correction in conventional block exposure is based on design data. In other words, the clock correction amount for each pattern on the block mask is
It is determined based on the size and shape of the pattern (both are design values). The correction for the proximity effect is similar, and the manufacturing error of the block mask, the position of each pattern on the block mask, the characteristics of each exposure device, etc. are not taken into consideration.

It is an object of the present invention to improve the above-mentioned problems and to enable accurate lock correction and calibration for each pattern of an actual block mask.

[Means to solve the problem]

As shown in FIG. 1, in the present invention, a block mask clock memory 28 is provided in a control section 25 of a charged particle beam exposure apparatus 10 that performs block exposure.

As shown in FIG. 1(C), this memory 28 stores clock correction amounts for each mask number (pro, mask 15, pattern 2). The clock correction amount is
The amount of correction for the basic irradiation time of the pattern is determined by the beam current density of the pattern image and the sensitivity of the beam-sensitive resists 1 to 1 on the object to be irradiated, and is determined by actual measurement.

During exposure, the clock correction amount for the pattern is obtained by reading out the block mask clock memory 28, and the basic irradiation time of the pattern generation circuit section 27 is corrected, and the result is used as the exposure time.

[Effect]

According to this exposure apparatus and method, each pattern can be exposed accurately for an appropriate exposure time. That is, the pattern information read out from the magnetic drum 22 or magnetic tape 23 by the processor 21 and expanded into the data memory 26 is as shown in FIG. 1(b), and includes shape codes 1, 2. 0.・・・・・・
・The pattern start point, pattern start point, and clock correction amount are... Conventionally, exposure is performed based on these, or the clock correction amount is determined based on design data. It does not correspond to actual exposure equipment or block masks. In contrast, in the present invention, the clock correction amount is calculated by measuring the sample current based on the actual exposure apparatus and the block mask, and this is stored in the block mask clock memory 28, and is used during exposure. Since the exposure time is obtained by reading and correcting the basic irradiation time, correct exposure can be performed.

〔Example〕

To explain FIG. 1 in detail, exposure data is stored in a magnetic disk 22 or a magnetic tape 23, and is stored in a processor 2.
1 via an interface 24 to a data memory 26
will be forwarded to. As shown in the figure (b), the data memory 26 stores shape coats 1°2 (these are variable beam patterns), their pattern starting points (coordinates XI, Yll), pattern starting points (lengths of two sides of a rectangle), X2.Y2), clock correction (CLK; numerical value of 1.112), and 7
Trix information (pitch PX of this repeated shape 1.

PY, number NX, NY, etc.) are stored. For the shape code 0 (this is a block pattern), the pattern starting point (XI, Yl), mask number, clock correction, and matrix information are stored.

The clock correction data stored in the data memory 26 is at the design stage. The clock correction data for shape code 0, the block pattern, is located in the memory 26 in its general value CLK, and in the block mask clock memory 28 in its modified value for the individual pattern. This memory 28
The contents are as shown in FIG. That is, the memory 28
is the corresponding mask (block pattern) 15 by mask NO.
b, . . . clock correction amount CL K 1 ,
CLK2.

. Read out the memory 26, shape code O, mask NO.
When the mask N is obtained, the memory 28 is read out and the mask N is obtained.
A clock correction amount CLKx of O is obtained and used by adding or multiplying it to the clock correction amount in the memory 26.

The clock correction data and pattern information thus obtained are sent to the block exposure device 1 via the pattern generation circuit section 27.
0, forming a pattern.

Note that a basic irradiation time is set in advance in the pattern generation circuit block 27 by the processor 21, and the basic irradiation time is corrected using the clock correction data or becomes the actual exposure time.

FIG. 2 shows the relationship among the data memory, block mask clock memory, and pattern generation circuit section. data memory 26
The pattern data X1, Yl, etc. read from the are sent to the pattern generation circuit section 27, and the clock correction amount CLK is
The mask NO is sent to the multiplier 31, and the mask NO is sent to the memory 28.
The clock correction amount CLK2 read from the memory 28 with this mask NO is sent to the adder/multiplier 31.

The pattern generation circuit section 27 sends pattern information to a D/A converter such as a deflector according to the pattern data from the memory 26, and also sends the basic irradiation time CL (.) to the second adder/multiplier 32. The addition/multiplication result CLK3 of the multiplier 31 is also sent to the addition/multiplier 32, and the addition/multiplier 32 outputs the addition/multiplication result CLK of these CLKo and CLK3 to the exposure apparatus.

The data stored in the block mask clock memory 28 is obtained by actual measurement. Specifically, this is done by measuring the sample current when each pattern of the block mask is irradiated with a beam. As shown in FIG. 3, the pattern 15a provided on the optical axis of the block mask 15 is a rectangular pattern used in variable rectangular beam exposure. The current density (sample current - area of the rectangular pattern 15a) determined using the rectangular pattern 15a provided on the front shaft portion is used to set the basic irradiation time.

Correction data for the basic patterns 15b, 15c, . . . are obtained as follows. That is, as shown in FIG. 4(a), a measurement mask 15A having a rectangular pattern 15a provided on the optical axis portion of the operational mask on the entire surface of the operational mask (block mask) of FIG. , set in place of the operational mask, each pattern O, I, 2.
The sample current when irradiated with... is measured, and the ratio of the optical axis portion to the current density of the mask pattern 15a is calculated. As a result, data as shown in FIG. 4(b) is obtained.

The correction factor for pattern N010 is 1.000, depending on the reference. Measurement mask pattern], +2. 3. The correction factor for . This measurement procedure is shown in FIG. 5(a). Select the pattern as shown and measure the sample current (■) to obtain the current density correction value for pattern 0 (■). This is done for all patterns on the mask (N is the number of patterns). This provides correction data for the position of the pattern on the mask. It should be noted that there may be differences between the measurement mask and the operational mask, changes in the state of the exposure device due to replacement if they cannot coexist, etc., but these are considered minor and will be ignored.

Next, as shown in FIG. 5(b), measure the sample current of each pattern of the operational mask. Rectangular pattern 15a of optical axis part
Also calculate the current density at , and estimate the current for each sample based on the aperture degree (beam irradiation area) of each pattern determined at the time of mask manufacturing. The current density used in calculating this estimated sample current is corrected using a current density map based on pattern selection obtained using the measurement mask. Final correction is then performed by comparing the measured sample current value and estimated sample current value for each pattern. This final correction involves a mixture of corrections based on mask manufacturing accuracy and pattern opening degree, but this can be determined through inspection processing. For example, when comparing sample currents of patterns with the same or similar apertures, the mask manufacturing precision becomes relevant, so the mask itself can be evaluated. The final clock correction amount is stored in the block mask clock memory (■).

This calibration is performed at appropriate intervals to update the block mask clock memory. In this way, the clock correction amount can always be maintained at the optimum value.

[Effects of the Invention] As explained above, according to the present invention, it is possible to eliminate non-uniformity in beam irradiation due to the selected pattern on the block mask, thereby making it possible to perform high-precision exposure. Furthermore, it is possible to deal with the manufacturing accuracy of each pattern on the block mask and the characteristics of the exposure apparatus, and the former also leads to an improvement in the throughput of manufacturing the block mask.

[Brief explanation of the drawing]

Fig. 1 is a diagram of the principle of the present invention, Fig. 2 is a block diagram showing the configuration of the control unit, Fig. 3 is an explanatory diagram of the operational mask, Fig. 4 is an explanatory diagram of the measurement mask and correction data, and Fig. 5 is an explanatory diagram of the operational mask. A flowchart showing the correction procedure. FIG. 6 is an explanatory diagram of an exposure apparatus equipped with a block mask. In FIG. 1, 28 is a block mask blocker memory, 14A in FIG. 4 is a measurement mask, and 15 in FIG. 6 is a block mask.

Claims (1)

[Claims] 1. In a charged particle beam exposure apparatus equipped with a block mask (15) having an aperture group for shaping a charged particle beam into one of a plurality of basic patterns or a variable rectangular pattern, each pattern on the block mask A charged particle beam exposure apparatus characterized by having a block mask clock memory (28) that stores clock correction amounts for each pattern obtained by actual measurement with respect to a basic irradiation time. 2. The clock correction amount to be stored in the block mask clock memory is determined using a measurement mask (15A) that has the same aperture arrangement as the block mask, and each aperture is the same as the rectangular aperture for the variable rectangular pattern in the center of the block mask. Measure the sample current, obtain the current density correction for each aperture with respect to the rectangular aperture from this result, then measure the sample current for each pattern using a block mask, and use the current density correction value to estimate each pattern. 2. The charged particle beam exposure apparatus according to claim 1, wherein the sample current is calculated and the sample current value of each measured pattern is used for calculation. 3. In an exposure method using a charged particle beam exposure apparatus equipped with a block mask having an aperture group for shaping a charged particle beam into one of a plurality of basic patterns or a variable rectangular pattern, the standard irradiation time for each pattern on the block mask is An exposure method characterized in that: the reference irradiation time is corrected using a measured clock correction amount for each pattern on the block mask, and the exposure time for the pattern is determined.