JPH0469660A - Exposing device - Google Patents

Abstract

PURPOSE:To accurately control exposure by measuring exposing energy with respect to each laser output pulse, obtaining remaining exposure based on target exposure and exposing energy integrated till previous time, calculating the energy of next one pulse and controlling the exposing energy of each pulse. CONSTITUTION:The target exposure is set and the total number P of pulses required for exposure is calculated. Next, the set energy of the first one pulse is calculated, the energy is set and a command for generating one pulse is given. Then, the number of light emitting times is counted up and the energy per one pulse is detected. The remaining exposure is calculated and the set energy of the next one pulse is calculated. Then, the number P of pulses is compared with the number of times (m) of the pulses and when they become the same, exposure is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an exposure apparatus, and particularly to a semiconductor exposure apparatus.

[Prior Art] Semiconductor technology continues to become highly integrated and miniaturized, and optical exposure methods are also expanding their scope with the development of high-resolution lenses. When using such exposure equipment to transfer and print a circuit pattern on a mask or reticle onto a wafer, the resolution line width of the circuit pattern printed on the wafer is proportional to the wavelength of the light source. A short wavelength light source in the UV) region is used. However, these light sources have low output in the deep UV region, and the photoresist material applied to the wafer has low photosensitivity, resulting in long exposure times.
Throughput becomes smaller.

On the other hand, in recent years, it has been learned that excimer lasers, which are high-output light sources in the deep UV region, are effective means for exposure apparatuses. However, excimer lasers cannot be used with conventional deuterium lamps or Xe-Hg lamps.
Unlike a lamp, it uses a pulse oscillation method, and therefore, the conventional analog exposure control method, that is, the method of controlling the time set by a timer using a shutter, etc. cannot be used.

Therefore, an exposure control method using pulse exposure has been proposed for some time.

For example, Japanese Patent Application Laid-Open No. 169136/1984 proposes a method of controlling the energy of exposure light so that the final exposure light has smaller energy than other exposure lights.

[Problem to be Solved by the Invention] However, in the case of an excimer laser, the variation in the output of one pulse reaches ±5% or more.

Therefore, in the case of JP-A-60-169136, it is necessary to greatly change the energy of the last pulse, but when using a method of changing the output energy of the laser itself, if the laser excitation voltage is too large, the laser Alternatively, the excitation circuit may be destroyed, and conversely, if the excitation voltage is gradually reduced, the laser will no longer oscillate. Therefore, it is generally very difficult to significantly change the output energy of the laser itself. In addition, even if a method of controlling the laser output energy with a filter etc. is used, the laser output energy can be
In the case of attenuation, there is a problem that the absorption of energy by a filter or the like increases and the filter deteriorates.

In view of the problems of the prior art, an object of the present invention is to
It is an object of the present invention to enable more accurate exposure control to be performed easily in an exposure apparatus that performs exposure using pulsed laser light.

[Means for Solving the Problems] In order to achieve the above object, the exposure apparatus of the present invention includes a laser generating means that generates pulsed laser light, and a pattern of one shot of an original using multiple pulses of the laser light. an optical means for exposure-transferring the image onto a substrate; an exposure-amount detection means for integrating and detecting the amount of exposure during this exposure-transferring at least every pulse; and an optical means for detecting the amount of exposure by integrating the amount of exposure during this exposure-transfer at least every pulse; Based on the detection results by the exposure amount variable means and the exposure amount detection means, the remaining exposure amount after subtracting the amount of exposure already exposed from the total amount of exposure required for exposure transfer of one shot is calculated for each pulse from the first pulse. and control means for calculating the exposure amount of the next one pulse from the amount and controlling the exposure amount variable means based on the result.

When calculating the exposure amount, it is preferable that the control means further consider data on the past usage state of the laser generating means. Alternatively, first calculate the number of pulses necessary to obtain exposure with uniform light distribution characteristics, and then calculate the energy of one pulse and the number of exposures necessary for one shot so that one shot of exposure ends at an integral multiple of that number. Calculate the total number of pulses. Furthermore, it has a means that can charge the energy of the laser generating means before setting the laser output energy through the exposure amount variable means.

As the laser generating means, for example, one using an excimer laser can be used.

[Operation] According to the present invention, the exposure energy is measured for each laser output pulse, the remaining exposure amount is determined from the target exposure amount and the cumulative exposure energy up to the previous time, and the next one pulse is calculated from this remaining exposure amount. Since the energy is calculated and the exposure energy is controlled for each pulse, there is no need to greatly change the energy of the last few pulses, and the exposure amount can be easily and accurately controlled for each shot.

[Example code] Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a block diagram of an exposure apparatus that best represents the features of the present invention. In the figure, reference numeral 1 denotes an excimer laser light source that is filled with, for example, KrF or ArF and emits pulsed laser light. 2 is an illumination system that shapes the laser beam emitted by the excimer laser light source into a desired beam shape, uniformizes the light distribution characteristics of the luminous flux, and emits the beam, and is composed of a beam shaping optical system, an optical integrator, a collimator lens, a mirror, etc. Ru. M is a mask or reticle which is interlayered on the output optical path of the illumination system 2 and has an integrated circuit pattern formed thereon, 3 is a projection optical system, W is a wafer, and the integrated circuit pattern formed on the mask M is a projection optical system. 3 and onto the wafer W for projection exposure. 4 is a mirror,
5 is a sensor, and a part of the luminous flux emitted by the illumination system 2 is incident on the photoelectric conversion surface of the sensor 5 by the mirror 4. 6
is a light amount integrating circuit that integrates one pulse of light incident on the sensor 5. The sensor 5 and the light amount integration circuit 6 are calibrated to detect the correct energy. Reference numeral 7 denotes a CPU, which receives a one-pulse energy signal from the light amount integrating circuit 6 each time the excimer laser 1 emits light. CPU
7 issues control commands such as a light emission command to the excimer laser 1 via a laser control section 8 and sets light emission energy.

Here, the illumination system 2 will be explained in detail using FIG. In this figure, 501 is a beam shaping module that shapes the laser beam from the excimer laser 1, 502 is an incoherent module that gives an optical path difference to the laser beam, and the laser beam from the incoherent module 502 passes through a fly-eye lens 503. After passing through the filter 504
Focus the light upward. The laser light once focused on the filter 504 passes through a condenser lens 505 and is then deflected by two wedge-shaped prisms 506. The laser beam then passes through a condenser lens 507 and forms a point light source (laser lens) 509 on an aperture 508 . The two wedge-shaped prisms 506 rotate in opposite directions about an axis 511, and the position of the point light source 509 formed on the aperture 508 changes depending on the rotational position. For example, when the two wedge-shaped prisms 506 are rotated in opposite directions at a speed ratio of 3-2, the locus of the point light source 509 draws a serge shape on the surface of the aperture 508 as shown in FIG. Thereafter, the laser beam passes through a condenser lens 510, a masking blade (not shown), and an imaging lens (not shown) and is irradiated onto the mask M.

Next, exposure amount control in this configuration will be explained based on FIG. 2. FIG. 2 is a flowchart of exposure amount control by the CPU 7. When exposure starts for a certain shot, first in step 100, the number of light emitting pulses m is set to 0.
At the same time, the remaining exposure amount Jafm-11 is set to an initial value (target exposure amount Ja), and in step 101, the target exposure amount JR is divided by the standard exposure amount 56 per pulse to determine the total number of pulses required for exposure. Calculate P. The remainder of this division is the theoretical insufficient number of pulses (0≦L<1) when exposed under the above conditions.

Next, in step 102, the target exposure amount J8 is divided by the total number of pulses P to determine the set energy JIl of the first pulse.
Calculate. Theoretically, if exposure is performed by this number of pulses P with this set energy JIl, the target exposure amount Ja will be exactly achieved.

Next, in step 103, the setting energy Ja for one pulse is
is set, and in step 104, a one-pulse light emission command is issued through the excimer laser control section 8.

Next, in step 105, the number of times the excimer laser 10 emits light is counted up, and in step 106, the energy Jt per pulse is detected through the sensor 5 and the light amount integrating circuit 6.

Finally, in step 107, the remaining exposure amount up to the previous time J8.
. -1) and the current energy Jt per pulse to calculate the current remaining exposure amount JaII.

Next, in step 108, the set energy Je for the next one pulse is calculated from the remaining exposure amount J-, the total number of pulses P, and the number m of light emission pulses after the start of exposure.

In the next step 109, the total number of pulses P required for exposure is compared with the number of light emitting pulses m after starting exposure, and if the number is the same, the process moves to exposure at the next shot position, and if the total number of pulses P is less than P. If so, the process returns to step 103. In this way, steps 103 to 10B are repeated until the number m of light emission pulses reaches the total number P of pulses.

According to this embodiment, not only highly accurate exposure control is possible, but also the amount of change in the charging voltage of the excimer laser 1 can be kept small. This can prevent deterioration of the excimer laser.

If it is thought that the energy fluctuation of the excimer laser is large, it is preferable not only to compare the number of pulses in step 1.09, but also to adjust the exposure energy and change the total number of pulses P depending on the amount. In addition, when specifying the energy to the excimer laser 1 by the laser control unit 8, the amount of energy may be sent by serial communication or parallel communication, but in order to shorten the exposure time, the oscillation frequency of the excimer laser will be changed in the future. It is thought that it will rise. Therefore, it seems better to specify energy using analog voltage. Furthermore, as the oscillation frequency increases, a function that allows the excimer laser 1 to be charged with energy for emitting light even before specifying the emitted light energy is essential.

On the other hand, in order to make the light distribution characteristics of the luminous flux uniform, there are cases where a point light source (light source image) 509 is arranged on the circumference or in a Lissajous shape, which is created for each pulse by swinging the laser light one pulse at a time. be. In this case, 5 point light sources placed at one time
It may be necessary to determine the number of 09's (the number of pulses required to complete a circle or Lissajous shape) and the number of times to place them. Therefore, in the above embodiment, the total number of pulses is determined first and exposure is performed to achieve that number of pulses, so it is also possible to slightly modify this and determine the number of pulses as follows. .

That is, step 101 shown in FIG. 2 is replaced with steps 201 and 202 shown in FIG.
In 01, the point light sources are arranged by dividing the target exposure amount Ja by the standard exposure amount J5 per pulse and the number S of point light sources to be arranged at one time (for example, one cycle from the start point to the end point in FIG. 6). Calculate the number of times N. In this case, the theoretical number of insufficient placements (0≦L<1.) when exposed under the above conditions
The number S of point light sources to be placed at one time and the number N of point light sources to be placed at one time are determined so that L is minimized. And step 2
In step 02, the total number of pulses P is calculated by multiplying the number S of point light sources arranged at one time by the number N of point light sources arranged.

In the above description, the output energy of the excimer laser 1 is directly changed, but instead of changing the output energy of the excimer laser 1, a filter or the like is placed in the optical path of the laser beam to change the output energy of the laser. It's okay.

FIG. 4 is a graph showing the relationship between the time after gas exchange of the laser and the laser output energy when the charging voltage of the laser is kept constant. In this way, the CPU 7 sets 1 to the excimer laser 1 through the laser control unit 8.
The relationship between the set energy JIl of the pulse and the actual energy Jt detected by the CPU 7 through the sensor 5 and the light amount integration circuit 6 may change over time.

This is due to a change in the output energy of the excimer laser 1, and the causes include deterioration of the filling gas, clouding of the window, deterioration of the electrodes, etc. Therefore, in this case, the time since the laser gas exchange, the number of times the laser has started since the gas exchange, the cloudiness of the window, the deterioration of the laser electrode,
Previous setting energy JIl and actual energy J
It is essential to have a function of converting the relationship with t into data and using those data to determine the set energy Je so that the actual energy Jt matches the required energy.

[Effects of the Invention] As explained above, the laser output energy of the next pulse is calculated from the remaining exposure amount after subtracting the already exposed amount from the predetermined exposure amount, and the exposure is performed with that energy amount. Exposure amount control can be performed with ease and with high precision.

FIG. 4 is a graph showing the relationship between time and laser output energy when the charging voltage is kept constant; FIG. 5 is a diagram showing the illumination system of this embodiment in detail; FIG. 6 is a diagram showing an example of arrangement of point light sources.

1: Excimer laser, 2. Illumination system, 3: Projection optical system, 4
: Mirror, 5. Photo sensor, 6. Light amount integration circuit, 7:
CPU, 8. Laser control unit, M: mask, W: wafer.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a reduction projection type exposure apparatus, ie, a so-called stepper, according to an embodiment of the present invention; FIG. 2 is a flowchart of exposure amount control of the apparatus of FIG. 1;

Claims (5)

[Claims] (1) a laser generating means that generates a pulsed laser beam; an optical means that exposes and transfers one shot of the pattern of the original onto a substrate using a plurality of pulses of the laser beam;
an exposure amount detection means for integrating and detecting the exposure amount during this exposure transfer at least for each pulse; an exposure amount variable means for changing the amount of exposure by the laser beam emitted by the laser generating means at least for each pulse; Based on the detection result by the amount detection means, for each pulse from the first pulse, the next one is calculated from the remaining exposure amount, which is obtained by subtracting the already exposed amount from the total exposure amount required for one shot of exposure transfer.
An exposure apparatus comprising: a control means for calculating a pulse exposure amount and controlling the exposure amount variable means based on the result. (2) The exposure apparatus according to claim 1, wherein the control means further takes into consideration data on past usage conditions of the laser generating means when calculating the exposure amount. (3) When calculating the exposure amount, the control means first calculates the number of pulses necessary to obtain exposure with uniform light distribution characteristics, and so that one shot of exposure ends at an integral multiple of that number. 2. The exposure apparatus according to claim 1, wherein the energy of one pulse and the total number of pulses required for one shot of exposure are calculated. (4) The control means has means capable of charging the energy of the laser generation means even before setting the laser output energy via the exposure amount variable means.
The exposure apparatus described. (5) The exposure apparatus according to claim 1, wherein the laser generating means includes an excimer laser.