JPS6231119A - Electron beam exposure - Google Patents

Abstract

PURPOSE:To improve the stability of a control system by a method wherein the amount of exposure in relation to the variation of the current density of an electron beam is compensated by maintaining the cycle of the system clock constant and by increasing and decreasing the blanking time so as to operate the whole system with a constant clock cycle. CONSTITUTION:The amount of exposure in relation to the variation of the current density of an electron beam is compensated by adjusting the exposure time. At that time, the cycle of the system clock that is a sum of the exposure time and the blanking time is held at a constant value, and the blanking time of an electron beam is increased and decreased. The variation of the current density of the electron beam is not so large and generally remains within a few %, and there will be no problem even if the blanking time of the electron beam is increased and decreased in such amount. Then, it is made possible to allow a series of exposure processes with a system clock with a constant cycle, thereby improving the stability of the control system.

Description

[Detailed Description of the Invention] [Summary] The present invention provides an electron beam exposure method in which the exposure amount is corrected for fluctuations in the electron beam current density by increasing or decreasing the blanking time while keeping the system clock cycle constant. The entire system operates at a constant clock cycle, improving its stability and performance.

[Industrial application field]

The present invention relates to an electron beam exposure method, and relates to an improvement of a system control method to improve the stability and performance of the electron beam exposure method.

Microfabrication technology that realizes fine, high-density patterns for semiconductor integrated circuit devices (hereinafter referred to as IC) is a combination of resist patterning technology and etching technology for semiconductor substrates, etc. using this resist pattern as a mask. It's technology.

As an exposure method for patterning a resist, the electron beam exposure method not only has high resolution, but also has a pattern generator function and has the advantage of shortening production time. Although it is applicable to both mask and wafer direct writing, further improvement of the system is desired.

[Conventional technology]

Electron beam exposure processing based on design data of each pattern of an IC or the like is carried out, for example, as shown in the block diagram shown in FIG.

That is, the design data recorded on the magnetic disk 11 is transferred to the buffer memory 13 by the processor 712, and decomposed by the pattern generator 14 into usually rectangular pixel combinations as units of exposure processing. A correction calculation circuit 15 performs coordinate transformation on the decomposed data of each pixel to eliminate pattern distortion, and determines the main deflection, sub-deflection, and rectangular side length that determine the coordinates of each pixel. A set of beam shaping deflection data is determined.

These data are then transferred by a driver 16 and a receiver 17, respectively, and converted into analog signals by a digital/analog converter 19 via a switching circuit 18. The analog signal is amplified by an amplifier 20 and inputted to a main deflector 21a, a sub-deflector 21b, and a beam forming deflector 21c, respectively.

In direct wafer exposure of semiconductor devices, the electron beam is normally deflected by the main deflector 21a to the center of a square subfield of, for example, 100 μm on a side, and then deflected to the irradiation position within the subfield by the sub deflector 21b with this center as a reference. be done. Note that during the output settling time from when the deflection signal is input until the transient phenomenon converges, the electron beam is blocked by the blanking electrode 23, and when the blanking signal is released, electron beam exposure is started.

The required exposure amount of the electron beam is determined by the sensitivity, thickness, etc. of the resist, but to achieve this, the exposure Ml (C/cm"
) = Current density (A/cm”) X Exposure time (sec)
The exposure time is determined for the set current density based on the relationship. The current density is set according to the required exposure amount, but since slight fluctuations occur due to misalignment of the electron optical system, dirt, etc., the current density is periodically measured to absorb fluctuations.

That is, for example, the required exposure amount is I x 1O-5C/c
m'' and the exposure time T when the current density is set to 10.OA/cm''. is, Tso= I X10-'/10=1.0OX10-6
sec, but when the current density changes to 9.9 A/am''.

is the exposure time T3, Ts = I Xl0-'/9.9'', 1.01
Adjust 8 times in 10-6 seconds.

As shown in FIG. 3 (al, (bl), this exposure time T3 and the blanking time TBO (conventionally set to a pre-selected constant value) during which the electron beam is blocked by the blanking electrode 23 are cycled alternately. The sum T of the exposure time T and the blanking time T''ao is the cycle of the system clock.

The system clock with period T is sent out from system clock generator 2, and the blanking time TBO is sent out from blanking time generator 3 in synchronization with the system clock, based on the main clock pulse (given by main clock generator 1). Ru.

The operation of the entire system described above proceeds according to system clock pulses, the period T of which is the fundamental period of electron beam exposure.

[Problem that the invention seeks to solve]

In the conventional electron beam exposure method, the system clock frequency '#J4'1' increases or decreases as the exposure time T increases or decreases.

In electron beam exposure processing, the multi-stage data processing and transfer as described above is performed according to this system clock, and the clock cycle of the entire system fluctuates, which not only complicates the control system but also causes data errors. The probability of this occurring is increasing.

In order to promote the miniaturization of patterns and at the same time improve the capabilities of exposure systems such as increasing the degree of integration and improving throughput, there is a strong demand for a solution to this problem related to the basics of system control.

[Means for solving problems]

The above-mentioned problem can be solved by the present invention, which maintains the system clock cycle at a constant value and makes the adjustment by increasing or decreasing the electron beam blanking time when correcting the exposure amount for fluctuations in the electron beam current density by adjusting the exposure time. This problem is solved by an electron beam exposure method.

[For production]

According to the present invention, the exposure amount is corrected for fluctuations in the electron beam current density by increasing or decreasing the exposure time as in the conventional method, but the system clock period, which is the sum of the exposure time and the blanking time, is maintained at a constant value. , increase or decrease the electron beam blanking time.

Fluctuations in the electron beam current density are not so large, usually only a few percent, and no particular problem occurs even if the electron beam blanking time is increased or decreased by this amount.

According to the present invention, it is possible to operate a series of exposure processes using a system clock having a constant cycle, and a great effect can be obtained in solving the above-mentioned problems.

〔Example〕

The present invention will be specifically explained below using examples.

For example, when the required exposure amount is I x 10-SC7cm'' and the current density is set to 10.0^/cm'', the standard exposure time T. =1. If the electron beam blanking time Ti+o=0.30 μSec, the system clock period T0 becomes To=Tso+Tgo=1.30 μsec as shown in FIG. 1 (al).

If the current density fluctuates to, for example, 9.9 A/cm'' during the continuation of the electron beam exposure started in this state, it is necessary to adjust the exposure time to Ts ``1.01 μsec.

According to the present invention, the system clock period T0 is not changed;
The electron beam blanking time is 'r' as shown in the figure).
By adjusting I = 0.29 μsec, the exposure time T, Ts = To - Tm = 1.30 - 0.29 = 1.01
Let it be μsec.

In this embodiment, the system clock pulse generation circuit 2 shown in FIG. 2 has a reference exposure time T. and blanking time T,.

For example, the clock pulse with the period T0 of the sum of the period #J]
It is generated by counting 130 main clock pulses of 10 ns each, and this initial setting is not changed while a series of exposure processing continues.

For example, the aforementioned exposure time T = 1.01 μsec can be easily realized by giving a command to the blanking time generator 3 to increase the number of main clock pulses to be counted from 30 to 29.

〔Effect of the invention〕

As explained above, according to the present invention, even if the exposure time is adjusted in electron beam exposure, the system clock cycle is kept at a constant value, and the entire system including data processing, transfer, etc. proceeds at a constant clock cycle. Second, the stability of the control system is improved, the probability of data errors occurring is reduced, and the system performance is improved.

[Brief explanation of drawings]

FIG. 1 is a time chart of an embodiment of the present invention, FIG. 2 is a block diagram of an electron beam exposure system, and FIG. 3 is a time chart of a conventional example. In the figure, 1 is a main clock pulse generator, 2 is a system clock pulse generator, 3 is a blanking time generator, 11 is a magnetic disk, 12 is a processor, 13 is a buffer memory, 14 is a pattern generator, and 15 is a correction calculation circuit. , 16 is a driver, 17 is a receiver, 1
8 is a latching circuit, 19 is a digital/analog converter, 20 and 22 are amplifiers, 21a is a main deflector, 2
1b is a sub-deflector, 21c is a beam shaping deflector, 2
3 indicates a blanking electrode. Part 1: The game of death in Thailand (child 1)

Claims (1)

[Claims] Electron beam exposure characterized in that when correcting the exposure amount for fluctuations in the electron beam current density by adjusting the exposure time, the system clock cycle is held at a constant value and the adjustment is made by increasing or decreasing the electron beam blanking time. Method.