JPS63213927A - Exposure system - Google Patents

Abstract

PURPOSE:To enable stable exposure with appropriate quantity of light for a long time by increasing or reducing the diameter of a laser light beam by monitoring the variation of the quantity of laser light from the set quantity of light according to the detected output of the laser light. CONSTITUTION:When laser light is transmitted from an excimer laser equipment 10, the laser light is detected by a photodetector 100 provided behind a reflecting mirror 42 and the information of the light is sent to a quantity-of-light monitor 110. When the monitored quantity of light by the quantity of light monitor 110 is less than a set value, a controller 120 sends an instruction to reduce the diameter of a laser beam to a beam diameter increasing or reducing unit 20 and the diameter of the laser beam is reduced according to the instruction. When the diameter of the laser beam is reduced, the density of the quantity of light is increased. When the quantity of light by the quantity of light monitor 110 is more than the set value, the diameter of the laser beam is increased by the beam diameter increasing or reducing unit 20, so the quantity of light is reduced.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an exposure apparatus used, for example, when printing a mask pattern onto a semiconductor wafer in the manufacturing process of semiconductor integrated circuits, and particularly relates to an improvement of the light source thereof. It is related to.

[Prior Art] In a photolithography process, which is one of the manufacturing processes for semiconductor integrated circuits, a circuit pattern on a photomask is transferred onto a semiconductor wafer using an exposure device. 2. Description of the Related Art In recent years, semiconductor integrated circuits have become increasingly highly integrated, and exposure devices are now required to print fine patterns with high precision.

Therefore, recently, a reduction projection type exposure apparatus that reduces a mask pattern and exposes it to light has come into use. In this reduction projection type exposure apparatus, the resolution R of the projection lens is approximately determined by o, 61λ/N,A. Here, N is the wavelength of the exposure light, and N and A are the numerical apertures.

Therefore, in order to improve the resolution R, it is sufficient to reduce the exposure wavelength λ or increase the numerical apertures N and A.

On the other hand, the depth of focus is expressed as FD=±(1/2)λ/(N, A,) 2. The deeper the depth of focus, that is, the larger its value, the easier it is to form an image.

For this reason, if the numerical aperture NA is increased in order to improve resolution, the depth of focus FD becomes shallow and imaging becomes difficult. Therefore, in order to improve resolution while maintaining a deep depth of focus, it is necessary to use short wavelength light as a light source.

For this reason, at present, ultraviolet light such as g-line (wavelength 436 nm) or i-line (wavelength 365 nm) from an Hg (mercury) lamp, which has a relatively short wavelength, is generally used as a light source. Recently, lasers, especially excimer lasers, which output ultraviolet light with a shorter wavelength and much higher intensity than the above-mentioned ultraviolet light, have been attracting attention as light Z sources.

[Problems to be Solved by the Invention] Excimer laser devices emit laser light by applying energy to a laser medium of a mixture of halogen and rare gas through electric discharge, but the laser is excited by high voltage electric discharge. Therefore, it is theoretically difficult to stabilize the output for each pulse.

For this reason, a power lock mechanism (a mechanism that controls the applied voltage of the laser) is generally used, but even with this, ±5
There is a variation in light intensity of about 10%.

On the other hand, on semiconductor wafers, the error in the required exposure amount is ±1%.
It is necessary to control the following. Therefore, in order to ensure an appropriate amount of exposure, it is necessary to control the exposure amount by performing exposure with multiple shot pulses while adjusting the laser output (light amount), but even with this method, it is not possible to obtain a sufficient amount of light with sufficient precision. There was a problem in that adjustments could not be made.

Further, when an excimer laser device is used for a long time, the laser output decreases due to gas deterioration or the like.

Normally, when the gas used is XeC1, the laser oscillation is
After about 106 shots in the case of KrF, the output drops to about 50%. For this reason, there was a problem in that stable exposure could not be performed for a long period of time.

The present invention has been made to solve these problems, and provides an exposure apparatus that can perform stable exposure over a long period of time with an appropriate amount of light even when using a laser light source with unstable output such as an excimer laser. The purpose is to

[Means for Solving the Problems] The present invention includes a light detection means for detecting laser light output from a laser light source; a light amount monitoring means for monitoring fluctuations in the amount of light; a light amount changing means for changing the amount of laser light by expanding or contracting the beam diameter of the laser light output from the laser light source; 1) Control the beam diameter of the light amount changing means so that the laser light amount becomes the set light amount value. The technical point is that the system is equipped with a control means.

[Operation] In the present invention, first, the laser beam is detected by the photodetecting means, and its fluctuation is monitored by the light amount monitoring means.

This monitoring is performed, for example, by taking the average value of the light amount of a plurality of shots.

The monitoring results are sent to the control means. In the control means,
The monitor results are compared with the set value, and a control command is issued to the light amount changing means.

The light amount changing means expands or reduces the beam diameter of the incident laser light based on the control command, and changes the light amount so that the light amount of the laser light becomes the set value.

[Example] Hereinafter, an example of the present invention will be described with reference to the accompanying drawings.

First, the configuration of this embodiment will be explained with reference to FIG. In the figure, 10 is an excimer laser device, 20
is the beam diameter expansion/reduction part. The beam diameter enlarging/reducing section 20 enlarges or reduces the beam diameter of the laser beam oscillated and output from the excimer laser device 10, and is constituted by, for example, a zoom expander shown in FIG. 2.

Next, 30 is an aperture that limits the spread of the beam to an appropriate diameter, 40 and 41 are reflecting mirrors, and 42 is a reflecting mirror made of, for example, a beam splitter with low transmittance through which a portion of the light passes.

Further, 50 and 51 are illumination system lenses, 60 is a reticle on which a circuit pattern to be projected and exposed is formed, 70 is a projection lens, 80 is a semiconductor wafer, and 90 is an exposure stage.

Here, the optical path of the laser beam in the above optical system will be explained. The pulsed laser beam oscillated and output from the excimer laser device 10 is transmitted to a beam diameter expansion/reduction unit 20.
The beam diameter is expanded or decreased depending on the size of the beam.

The enlarged or reduced laser beam passes through the aperture 30 and its spread is regulated to a constant value,
Further, the light is reflected by reflection mirrors 40 and 41 and enters the illumination system lens 50.

Further, the laser beam is sent by the reflecting mirror 42 to an illumination system lens 51 composed of, for example, a cylindrical lens or a fly's eye lens. The laser beam then passes through the reticle 60, passes through the projection lens 70, and reaches the semiconductor wafer (30), whereupon the circuit pattern of the reticle is transferred onto the semiconductor wafer 80.

Next, 100 is a photodetector, 110 is a light amount monitor, 120
is the control section. A portion of the laser light is incident on the photodetector 100 after passing through the above-mentioned reflecting mirror 42, and the light intensity of the laser light is monitored by a light intensity monitor 110, and the result is sent to the control unit 120. It is configured to be manually operated. This control section 120 has a function of controlling the degree of beam diameter change by the beam diameter enlarging/reducing section 20 in accordance with a predetermined set light amount value and fluctuations in the light amount of the laser beam.

Note that the laser output varies between each pulse, so
It is convenient for the light amount monitor 110 to monitor the amount of light by taking the average value of a plurality of shots. Further, it is convenient if the control unit 120 is able to expand or reduce the beam diameter independently of the set light amount value.

Next, an example of the configuration of the beam diameter enlargement and small part 20 described above is as follows.
This will be explained with reference to FIG.

In this example, the beam diameter enlarging/reducing section 20 is, for example, a zoom expander, and the figure is a schematic configuration diagram thereof. In the figure, reference numerals 21, 22, and 23 are convex lenses made of, for example, quartz or fluorite, and among these, the convex lens 21 constitutes a zoom lens section. 24 is a driving motor, and 25 is a position detection encoder. By changing the beam diameter in such a system, the power (light energy) per unit area can be varied over a wide range.

To explain the operation of the device as described above, the optical axis direction is shifted from the above-mentioned control section 120 to the motor 24. thI
Information regarding the amount is sent, and the motor 24 is rotated for the corresponding time or number of rotations while monitoring the amount of rotation by the encoder 25. The motor 24 moves the zoom lens section including the convex lens 21 in the optical axis direction to enlarge or reduce the diameter of the incident laser beam. With this configuration,
It is possible to quickly make fine adjustments to enlarge or reduce the beam diameter.

Note that the relationship between the value related to the amount of movement in the optical axis direction obtained by the encoder 25 and the light amount value on the light amount monitor 110 is preferably linear for light amount value setting control.

Next, the overall light weight adjustment operation in the above embodiment will be explained. When a laser beam is output from the excimer laser device 10, the laser beam is detected by a photodetector placed behind the reflecting mirror 42, and its optical information (intensity value) is detected.
is sent to the light amount monitor 110.

Then, the light intensity of the laser beam is calculated by the light intensity monitor 110, and the light intensity information is sent to the control section 120. The control section 120 compares the information from the light amount monitor 110 with a preset light amount value to determine whether the light amount is appropriate, and sends a command corresponding to the result to the beam diameter expansion/reduction section 20. The beam diameter enlarging/reducing section 20 enlarges or reduces the beam diameter based on a command from the control section 120.

For example, when the light amount monitor value of the light amount monitor 110 is less than the set value, the control section 120 sends a command to reduce the beam diameter to the beam diameter enlargement/reduction section 20, and the beam diameter enlargement/reduction section 20: Based on this, the laser beam diameter is reduced.

When the beam diameter is reduced, the light density, that is, the light amount (light energy) per unit area increases. On the other hand, the diameter of the laser beam irradiated onto the reticle 60 is determined by the diameter of the aperture 3.
It is kept constant by 0. Therefore, the amount of light supplied to the exposure section increases.

Further, if the light amount of the light amount monitor 110 is greater than the set value, the beam diameter enlarging/reducing section 20 expands the beam diameter by the operation opposite to the above, so that the light amount is reduced.

As described above, a predetermined light amount can be obtained by repeating the feedback of expanding or reducing the beam diameter until the light amount of the light amount monitor 110 reaches the set value.

By the way, when expanding or contracting the beam diameter, considering a certain region within the beam diameter, the light intensity distribution of the beam changes. Generally, this type of laser light has a Gaussian distribution, so the uniformity of the intensity distribution becomes a problem if left as is. However, if the beam diameter is expanded and a very narrow area of the beam is used as in the present invention, a luminous flux area that can be considered to be almost uniform can be obtained. Therefore, there is an advantage that poor resolution is less likely to occur during exposure.

Note that the present invention is not limited to the above-mentioned embodiments. For example, if the laser output decreases due to long-term use of the excimer laser device 10, the beam diameter expansion magnification may be initialized by the above-described operation. It goes without saying that an appropriate amount of light can be obtained by lowering it further (reducing the beam diameter) and maintaining the set light amount value.

Furthermore, it is clear that if the diameter of the aperture 30 is made variable, the light amount adjustment area can be further expanded by using it in combination with the beam diameter expansion/reduction unit 20 described above. It is.

Further, the optical system shown in FIG. 2 may be used when adjusting or correcting the appropriate exposure amount to the semiconductor wafer by sequentially expanding or contracting the beam diameter during exposure of the semiconductor wafer. In this case, the light detection by the photodetector 100 is omitted,
For example, the beam diameter may be changed by time control based on the period of the laser pulse.

[Effects of the Invention] As explained above, the present invention provides feedback control of the amount of laser beam from the light source by means of a light amount adjusting means that is disposed outside the laser oscillator and is capable of controlling the amount of light by expanding and contracting the beam diameter. Therefore, even if the laser output fluctuates, the laser light supplied to the exposure section will have an appropriate amount of light, resulting in the effect that stable exposure can be performed for a long time under good light amount conditions.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG.
FIG. 3 is a configuration diagram showing an example of the beam diameter expansion/reduction section shown in the figure. [Explanation code for symbols of main parts]

Claims (2)

[Claims] (1) An exposure apparatus that projects and exposes a circuit pattern of a mask onto a photosensitive substrate using pulsed laser light output from a laser light source, comprising: a light detection means for detecting the laser light; and a detection output of the light detection means. a light amount monitoring means for monitoring fluctuations in the amount of laser light with respect to a predetermined set light amount value based on the amount of light emitted from the laser light source; and a control means for controlling the beam diameter of the light amount changing means so that the laser light amount becomes the set light amount value based on the monitoring result of the light amount monitoring means. An exposure device featuring: (2) The exposure apparatus according to claim 1, wherein the light amount changing means includes a zoom expander.