JP2902172B2 - Exposure equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure apparatus using a pulse laser, and more particularly to an improvement in exposure control of a high-output pulse laser.

[0002]

2. Description of the Related Art As semiconductor technology continues to be highly integrated and miniaturized, a pulse laser such as an excimer laser has recently been used in an exposure apparatus as a light source in the far ultraviolet region. However, the pulse energy of the excimer laser fluctuates by about 5% for each shot with respect to the set energy.
For this reason, the exposure energy for each chip is also affected by this variation. Therefore, in order to obtain reproducibility of resolution and line width, exposure was performed using pulse light of several hundred pulses or more to reduce the amount of relative variation, thereby suppressing variation in exposure energy.

On the other hand, in recent years, the sensitivity of a resist applied to a wafer has been improved, and the number of pulses required for exposing one chip to tens to hundreds of pulses has become sufficient. However, when the number of pulses per chip is reduced, the problem arises that the exposure amount for one chip does not fall within a predetermined allowable range unless the energy applied to the wafer is controlled for each laser pulse. . Various methods have been proposed for controlling the pulse energy for each pulse, such as controlling the output energy of the laser and using an interference filter or a neutral density filter.

[0004]

There are various methods for controlling the pulse energy for each pulse, but the method of controlling the pulse energy of the laser device for each pulse is the simplest method because of the structure of the apparatus. And the response is excellent.

[0005] However, the current laser device cannot output the set output as set under any condition. For example, in the case of a gas laser such as an excimer laser, the laser gas used deteriorates with time,
Even if the same setting parameters are used, the output energy changes depending on the state of the laser due to deterioration or contamination of the optical components used for the laser. For this reason, even if the pulse energy is controlled for each pulse by changing the setting parameter in order to control the exposure amount, the pulse energy does not always become the set energy. Therefore, it is difficult to accurately control the exposure amount by simply changing the setting parameters in order to obtain a predetermined exposure amount. Further, a method has been proposed in which the pre-exposure amount is controlled by changing the set pulse energy in the last few pulses of the exposure. Control was required and was not always a sufficient method.

As a method of determining the exposure amount of the next pulse, there is a method of obtaining an average value of the energy of several to several tens of pulses from the previous pulse and determining the energy from the value. However, as a characteristic of the laser device, the energy is slightly larger in the initial several tens to one hundred pulses, so that when the total number of exposure pulses is several tens to several hundreds, satisfactory accuracy is not always obtained by this method. That is, when the remaining exposure is performed with the average pulse energy obtained from the initial several tens of pulses, the actual exposure often becomes larger than the target exposure.

In view of the above-mentioned problems in the prior art, the present invention provides an exposure apparatus that projects a pattern on an original plate onto a substrate by emitting a pulsed laser beam a plurality of times. It is an object of the present invention to provide an exposure apparatus capable of performing the above.

[0008]

According to the present invention, there is provided an exposure apparatus for projecting and exposing a pattern on an original to a substrate by causing a pulse laser to emit a plurality of pulses. Pulse laser output control means for causing the pulse laser to emit pulse light at an emission intensity according to the control parameter, an exposure amount detection means for detecting an exposure amount for each pulse of the pulse laser, and a pulse output for each pulse detected by the exposure amount detection means. An exposure amount integrating means for integrating the exposure amount; and a preset total exposure amount (Eto
tal) and the remaining exposure amount (Ntot) obtained by using the difference between the integrated exposure amount (SUM) integrated by the exposure amount integrating means.
al) and the number of remaining exposures (N) to calculate the average remaining pulse energy (Eave), and compares the average remaining pulse energy with the amount of one-pulse exposure at the time of the previous exposure for each pulse. By changing the control parameter so that the one pulse exposure amount becomes equal to the remaining pulse average energy, highly accurate exposure amount control is performed.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a schematic configuration of a stepper as a reduction projection type exposure apparatus according to an embodiment of the present invention. In FIG. 1, a laser light source (pulse laser) 1 is a light source that emits a laser beam in which, for example, KrF is sealed. This light source emits light having a wavelength in the far ultraviolet region of 248 nm. The illumination optical system 2 includes a beam shaping optical system, an optical integrator, a collimator, and a mirror (all not shown). These members are formed of a material that efficiently transmits or reflects light in the far ultraviolet region. The beam shaping optical system is for shaping a beam into a desired shape, and the optical integrator is for uniforming the orientation characteristics of a light beam. A reticle R (or a mask) on which an integrated circuit pattern is formed is arranged along the optical path of the illumination optical system 2, and a projection optical system 3 and a wafer W are further arranged.

A mirror 4 is provided on the optical path from the illumination optical system 2.
Are arranged, and a photosensor 5 for ultraviolet light is arranged on an optical path reflected by the mirror 4. The output of the photo sensor 5 is converted into an exposure amount per pulse via an integration circuit 6 and input to a controller 7 for calculating an integrated exposure amount. The laser output control unit 8 drives the excimer laser light source 1 based on the calculation result of the controller 7. This allows the output light to be controlled as needed for each pulse,
The pattern of reticle R is exposed on wafer W.

Since the output of the excimer laser is large, exposure of several pulses may be sufficient depending on the resist sensitivity. However, the variation in the output of each pulse of the excimer laser usually reaches ± 5% or more.
For this reason, in the process of performing the finest processing with a stepper or the like, the amount of variation also poses a problem if only a few pulses are exposed per shot. Therefore, the exposure is performed by increasing the number of pulses to several tens of pulses such that the influence of the variation can be ignored. At this time, the exposure apparatus of this embodiment measures the exposure amount for each pulse and calculates the integrated exposure amount. Then, the average value of the remaining exposure amount obtained by subtracting the integrated exposure amount from the total exposure amount to be exposed is calculated. Then, the set voltage is changed so that the value of one pulse energy at that time approaches the average value.

FIG. 2 shows an exposure sequence of the exposure apparatus of the above embodiment in detail.

First, in step S1, a total exposure amount Etotal to be exposed first is set. In step S2, the total exposure amount
From Etotal and standard pulse energy Estd, the total number of exposures Ntotal
Is set, and in step S3, the integrated exposure amount SUM, the number of remaining exposures (number of times of pulse emission) N, and the average pulse energy Eave
Set. The integrated exposure amount SUM is set to “0” and the number of times is Ntot
al, the average pulse energy is “the value of Etotal / Ntotal”. In step S4, a set voltage for first exposure is set by a relational expression V = f (E) between voltage and energy. In step S5, exposure is performed at the set voltage Vave, and the actual exposure EN is measured (step S6). The exposure EN measured in step S7 is added to the accumulated exposure amount SUM up to that time to obtain a new accumulated exposure amount SUM, and the remaining number N is decremented. In step S8, the total exposure amount Etotal is used to calculate the integrated exposure amount SU.
The value obtained by subtracting M, that is, the sum of the remaining exposure amounts is obtained and the remaining number of times N
Find the value Eave divided by. Eave obtained here is the average exposure energy per one pulse of the remaining exposure.

In step S9, the average exposure energy is compared with the exposed one-pulse exposure energy EN. If the difference is smaller than the determination condition Eε, the flow advances to step S13.
If the difference is larger than the judgment condition Eε, the step S1 is executed.
At 0, it is determined whether the value Eave-EN is larger or smaller than 0. When Eave-EN> 0, in step S11, a predetermined change amount ΔV is added to the set voltage Vave to obtain a new Vave.

When Eave-EN <0, in step S12, the change amount ΔV is subtracted from the set voltage Vave to obtain a new Vave. In step S12, it is determined whether or not the number N of remaining exposures is 0. If it is not 0, the process returns to step S5, and if it is 0, the process ends.

FIG. 3 shows the change in the integrated exposure. As the number of exposures increases, the actual exposure approaches the target exposure. As described above, if the sequence shown in FIG. 2 is used, the fluctuation due to the variation between the laser pulses can be eliminated as much as possible, and the laser-specific laser gas or optical component for changing the target set value for each pulse. Not only deterioration but also temporal fluctuation due to the optical transmission optical system inside the stepper is removed, and stable exposure amount control can be performed.

In the above embodiment, the difference between the remaining exposure average energy Eave and the actual exposure EN was used as a criterion. However, the actual exposure EN to be compared is set to a plurality of exposures EN + 1 and EN + 2 up to several times before. Average or weighted average (3EN + 2EN +
It is also an effective method to prevent abrupt change of the condition by using 1 + EN + 2) / 6 and stabilize the exposure to a target amount.

[0019]

As described above, according to the present invention, an appropriate exposure amount can be obtained stably even with respect to variations among pulse lasers such as excimer lasers, deterioration of laser gas, and deterioration of optical components. .

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an exposure apparatus according to an embodiment of the present invention.

FIG. 2 is a flowchart showing an exposure sequence in the exposure apparatus of FIG.

FIG. 3 is an explanatory diagram showing a change in an integrated exposure amount in the embodiment of FIG.

[Explanation of symbols]

1; excimer laser, 2; illumination optical system, 3; reduction optical system, 4; mirror, 5; photosensor, 6;
7: controller, 8: laser output control unit, R: reticle, W: wafer.

Claims (2)

(57) [Claims] 1. An exposure apparatus for projecting and exposing a pattern on an original onto a substrate by causing a pulse laser to emit a plurality of pulses, wherein a pulse laser output for emitting the pulse laser with a light emission intensity according to a set control parameter is provided. and control means, the exposure value detecting means for detecting an exposure amount for each pulse of the pulsed laser, the exposure amount integrating means for integrating the exposure amount for each detected pulse by the exposure detecting means,
The total exposure amount (Etotal) set in advance and the exposure
The difference of the integrated exposure amount (SUM) integrated by the light amount integration means
Exposure (Ntotal) and Remaining Exposure Time
The number comprises a computing means from (N) calculates the residual pulse average energy (Eave), one pulse exposure amount when the residual pulse average energy and pre-exposure compared to each pulse, 1 pulse exposure of the next exposure An exposure apparatus, wherein the control parameter is changed so as to match the residual pulse average energy. 2. A compares the average one pulse exposure to the residual pulse average energy and a plurality of times before each pulse, the system <br/> control as follows exposure coincides with the remaining pulse average energy The exposure apparatus according to claim 1, wherein the parameter is changed.