JPH0562876A - Exposure equipment - Google Patents

Abstract

(57) [Abstract] [Purpose] In an exposure apparatus that projects and exposes a pattern on an original plate onto a substrate by making a pulsed laser emit multiple pulses, stable exposure is always performed with an appropriate exposure amount. In an exposure apparatus that projects and exposes a pattern on an original plate R onto a substrate W by causing a pulsed laser to emit a plurality of pulses, a pulsed laser that causes a pulsed laser 1 to emit a pulsed light with an emission intensity according to a set control parameter. The output control means 8, the exposure amount detecting means for detecting the exposure amount of each pulse of the palace laser 1, the exposure amount integrating means for integrating the exposure amount of the pulse amount detected by the exposure amount detecting means, and the integrated exposure And a calculation means for calculating the residual pulse exposure energy and the average energy of the residual pulse from the pulse exposure amount. The average energy per pulse of the residual pulse exposure amount and the pulse exposure amount during the pre-exposure are compared for each pulse, and the next exposure is performed. The control parameter is changed by the pulse energy output control means so that the 1 pulse exposure amount at that time matches the average energy.

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 improvement of exposure control of a high power pulse laser.

[0002]

2. Description of the Related Art The semiconductor technology has been highly integrated and miniaturized, and in recent years, a pulse laser such as an excimer laser has been used in an exposure apparatus as a light source in the far ultraviolet region. However, the pulse energy of the excimer laser varies by about 5% with respect to the set energy for each shot.
Therefore, the exposure energy on each chip is also affected by this fluctuation. Therefore, in order to obtain the resolving power and the reproducibility of the line width, exposure is performed by using pulsed light of several hundreds of pulses or more to reduce the amount of relative variation and suppress the variation of exposure energy.

On the other hand, in recent years, the sensitivity of the resist applied to the wafer has been improved, and the number of pulses required for exposure for one chip has become sufficient to be several tens to several hundreds of pulses. However, when the number of pulses per chip decreases, 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. .. As a method of controlling the pulse energy for each pulse, various methods such as controlling the output energy of a laser and using an interference filter or a neutral density filter have been proposed.

[0004]

There are various methods of 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 because of the configuration of the device. And the responsiveness is excellent.

However, it cannot be said that the current laser device outputs the set output as set under any condition. For example, in the case of a gas laser such as an excimer laser, deterioration of the laser gas used over time,
Due to deterioration or contamination of the optical components used in the laser, the output energy changes depending on the laser state even with the same setting parameters. Therefore, even if the setting parameter is changed to control the pulse energy for each pulse in order to control the exposure amount, the setting energy does not always become the setting energy. Therefore, it is difficult to accurately control the exposure amount only by simply changing the setting parameters to obtain the predetermined exposure amount. Also, a method of controlling the pre-exposure amount by changing the set pulse energy in the last few pulses of exposure has been proposed, but the one that cannot be set within the range of 0 to 100% like the set voltage of the excimer laser is special. However, it was not always a sufficient method because various controls were required.

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

In view of the above-mentioned problems in the conventional example, the present invention is an exposure apparatus which projects and exposes a pattern on an original plate onto a substrate by causing a pulsed laser to emit a plurality of pulses, and the exposure is always stable with an appropriate exposure amount. It is an object of the present invention to provide an exposure apparatus capable of performing.

[0008]

In order to achieve the above object, in the present invention, the average residual exposure energy is calculated for each pulse during exposure, and the pulse energy for the next exposure is made to match this average energy. By doing so, 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 structure of a stepper which is a reduction projection type exposure apparatus according to an embodiment of the present invention. In the figure, a laser light source (pulse laser) 1 is a light source that emits laser light in which, for example, KrF is enclosed. 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 (none of which is shown). These members are made of a material that efficiently transmits or reflects light in the far ultraviolet region. The beam shaping optical system is for shaping the beam into a desired shape, and the optical integrator is for making the orientation characteristics of the light flux uniform. A reticle R (or 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.
And a photosensor 5 for ultraviolet light is arranged in the optical path reflected by the mirror 4. The output of the photo sensor 5 is converted into an exposure amount per pulse through an integrating circuit 6 and is input to a controller 7 which calculates 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. With this, the output light controlled as required for each pulse,
The pattern of the reticle R is exposed on the wafer W.

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

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

First, in step S1, the total exposure amount Etotal to be exposed first is set. Also, in step S2, the total exposure amount
Total number of exposures Ntotal from Etotal and standard pulse energy Estd
Is set, and the cumulative exposure amount SUM, the number of remaining exposures (the number of pulsed light emission) N, and the average pulse energy Eave
To set. The total exposure amount SUM is set to "0" and the number of times is Ntot
al, the average pulse energy is “Etotal / Ntotal value”. In step S4, the set voltage for the first exposure is set by the relational expression V = f (E) of voltage and energy. In step S5, exposure is performed with the set voltage Vave, and the actual exposure amount EN is measured (step S6). The exposure EN measured in step S7 is added to the accumulated exposure amount SUM up to that point to obtain a new accumulated exposure amount SUM, and the remaining number N is decremented. In step S8, the total exposure amount Etotal is changed to the integrated exposure amount SU
The value obtained by subtracting M, that is, the total amount of remaining exposure is calculated, and the remaining number N
Calculate Eave divided by. The Eave obtained here is the average exposure energy per pulse of the remaining exposure.

In step S9, the average exposure energy is compared with the exposed one-pulse exposure energy EN, and if the difference is smaller than the judgment condition Eε, the process proceeds to step S12. If the difference is larger than the judgment condition Eε, it is judged in step S10 whether the value Eave-EN is larger or smaller than 0. When Eave−EN> 0, in step S11, a preset 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 of remaining exposures N 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. When the number of exposures increases, the actual exposure approaches the target exposure. As described above, if the sequence shown in FIG. 2 is used, fluctuations due to variations between laser pulses can be eliminated as much as possible, and the target setting value is changed for each pulse, so that the laser gas unique to the laser and optical components Not only the deterioration but also the temporal fluctuation due to the optical transmission optical system inside the stepper is removed, and the stable exposure amount control can be performed.

In the above embodiment, the difference between the average remaining exposure energy Eave and the actual exposure amount EN was used as the judgment condition, but the actual exposure amount EN to be compared is the exposure amount EN + 1, EN + 2 up to a plurality of times before. Average value or weighted average value (3EN + 2EN +
It is also an effective method to prevent sudden changes in conditions by using 1 + EN +2) / 6, etc., and stabilize and converge to the target exposure amount.

[0019]

As described above, according to the present invention, it is possible to stably obtain an appropriate exposure amount against variations among pulse lasers such as excimer lasers, deterioration of laser gas, and deterioration of optical parts. ..

[Brief description of drawings]

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

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

FIG. 3 is an explanatory diagram showing a change in 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; integrating circuit,
7: controller, 8: laser output controller, R: reticle, W: wafer.

Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location H01S 3/00 A 8934-4M 7352-4M H01L 21/30 311 S

Claims (2)

[Claims] 1. An exposure apparatus for projecting and exposing a pattern on an original plate onto a substrate by causing a pulsed laser to emit a pulsed light a plurality of times, and a pulsed laser output that causes the pulsed laser to emit a pulsed light with an emission intensity according to a set control parameter. Control means, exposure amount detection means for detecting the exposure amount for each pulse of the pulse laser, exposure amount integration means for integrating the exposure amount of the pulse amount detected by this exposure amount detection means,
An arithmetic means for calculating the residual exposure amount and the residual pulse average energy from the accumulated exposure amount is provided, and the average energy per pulse of the residual exposure amount and the 1-pulse exposure amount at the time of pre-exposure are compared for each pulse. Then, the exposure apparatus is characterized in that the control parameter is changed by the pulse energy output control means so that one pulse exposure amount at the time of the next exposure coincides with the average energy. 2. The average energy per pulse of the remaining exposure amount and the average one pulse exposure amount up to a plurality of times are compared for each pulse, and the next exposure amount is the average energy per pulse of the remaining exposure amount. The exposure apparatus according to claim 1, wherein the control parameters are changed so as to match.