JPH0447807B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a projection exposure method and a projection exposure apparatus used for manufacturing semiconductor devices.

[Prior Art] In recent years, there has been remarkable progress in increasing the degree of integration of semiconductor devices such as ICs and LSIs, and the line width of the circuit patterns of these devices is becoming less than 1 micrometer.

It is difficult to manufacture these elements using the conventional contact exposure apparatus or proximity exposure apparatus as disclosed in Japanese Patent Application Laid-Open No. 51-126071.

On the other hand, a reduction projection exposure apparatus has been developed as an apparatus capable of printing a circuit pattern of about 1 micrometer.

In this projection exposure apparatus, the projection lens system has a large F number and a shallow depth of focus, so that, as shown in US Pat. A focusing mechanism is installed to precisely match the surfaces. This mechanism detects the deviation of the wafer surface from the image plane using the air pressure sensor and optical sensor described in this US patent, and corrects this deviation by moving the wafer up and down in the direction of the optical axis of the projection lens system. be.

However, conventional focusing mechanisms assume that the image plane does not move and adjust the position of the wafer, so if the image plane shifts for some reason, the surface on the wafer cannot be positioned at the image plane. occurs.

In a projection exposure apparatus, each time a circuit pattern image is projected, light from the illumination system enters the projection lens system, so the projection lens system absorbs a portion of the incident light and its temperature changes. A temperature change accompanying light absorption by a lens causes a change in the refractive index of the lens, as described in OPTIK 33. No. 4, pages 437 to 439 (1971).

This paper only shows that when a beam with a non-uniform cross-sectional intensity distribution is incident on a thin lens, a refractive index distribution occurs inside the lens and aberrations occur in the lens. The image plane shifts due to temperature changes, and we realized that this shift in the image plane cannot be ignored, especially in devices that project minute circuit pattern images of 1 micrometer or less.

In particular, projection exposure equipment for semiconductor manufacturing repeatedly performs exposure, so light from the illumination system enters the projection lens system intermittently, and when the photomask is irradiated with light, the temperature of the projection lens system increases. When the temperature rises and light irradiation is interrupted, the temperature of the projection lens system decreases, so the image plane of the projection lens system shifts vertically during work. Therefore, the problem of image plane shift in this device is serious.

[Summary of the Invention] An object of the present invention is to provide a projection exposure method and a projection exposure apparatus for semiconductor manufacturing, which can accurately align the surface of a wafer with the image plane, that is, the focus position of a projection lens system. .

In order to achieve this objective, the present invention uses the amount of light per unit time that enters the projection lens system via the photomask, the light irradiation time and the light irradiation interval time on the photomask by the illumination system, The amount of change in the focus position of the projection lens system due to the incidence of light into the projection lens system is calculated, and the focus position of the projection lens system is made to coincide with the surface of the wafer in consideration of this calculation result.

The amount of change in the focus position caused by the temperature of the projection lens system rising as the light enters the projection lens system is determined by the amount of light that enters the projection lens system through the mask (the amount of light per unit time and the amount of light per unit time). By detecting this amount of light, the amount of change in the focus position due to the incidence of light on the projection lens system can be determined with a certain degree of accuracy.

However, there is a time period after the end of the previous exposure and until the start of the next exposure in which no light enters the projection lens system, and during this time period the projection lens system radiates heat and its temperature drops. Therefore, simply considering the amount of light incident on the projection lens system to calculate the amount of change in the focus position will limit the accuracy of detecting the amount of change in the focus position due to the change in focus position caused by this temperature drop. I end up.

Therefore, in the present invention, the light irradiation interval time is also used to calculate the amount of change in the focus position due to the incidence of light on the projection lens, and the amount of change in the focus position is calculated by taking into account the rise and fall of the temperature of the projection lens system. I'm looking for more accuracy. Therefore, the wafer can be accurately focused, and a clear circuit pattern can be projected and transferred onto the wafer.

[Example] The present invention will be described below based on an example shown in the drawings.

In FIG. 1, 1 is the main body base, and 2 is the XY stage. The XY stage 2 is mounted on the main body base 1 and makes a desired in-plane movement by a well-known mechanism. A wafer 3 has a photosensitive layer, and is fixed on the XY stage 2 by a chuck (not shown). A projection lens barrel 4 accommodates a reduction type projection lens 5. 6 is a photomask, which includes a pattern for manufacturing a semiconductor circuit. Reference numeral 7 denotes a photomask stage, which is fixed to the upper part of the lens barrel 4 and has the function of fixing the photomask 6.

Next, reference numeral 8 denotes a column, which is fixedly installed on the main body base 1, and the fixed side of the focus adjustment mechanism 9 is provided on the upper part of the column. The focus adjustment mechanism 9 is composed of, for example, a rack and pinion or a helicoid, and the movable side is connected to the lens barrel 4. When the mechanism 9 is operated, the lens barrel 4 moves along the projection path. Reference numeral 10 denotes a lighting unit, which is fixed to the upper part of the pillar 8 via another pillar. The lighting unit 10 is a light source 1
1. Contains a shutter 12, a condenser lens 13, and an optical path bending mirror 14. The shutter 12 moves under the action of a rotary solenoid activated by a drive signal to block or open the illumination optical path. When the illumination optical path is opened, the light beam emitted from the illumination light source 11 passes through the condenser lens 13. converge,
After being reflected by the mirror 14, the photomask 6 is irradiated with the light.

On the other hand, 17 is an air nozzle, which is held at the bottom of the lens barrel 4 and can be arranged at the periphery of the projection optical path, or can freely move into and out of the optical path. Air nozzle 1
7 is connected to an air micrometer main body (not shown), which serves to precisely measure the distance between the upper surface of the wafer 3 and the final surface of the projection lens 5. Note that other methods can also be used to measure the spacing.

Further, a photodetector 18 is fixed on the XY stage 2, and can be caused to enter the illumination area by operating the XY stage 2. The photodetector 18 measures the pattern projection light transmitted through the photomask 6 and detects the intensity of the projection light. In this way, the transmittance of the photomask can be measured. Furthermore, for a photomask whose transmittance is already known or a mask whose transmittance is known from another measuring device, the conditions may be set using a transmittance setting switch 21 provided in the controller 20, and this switch 21 can be set by the photodetector. It would be better to have 18 attached.
A cable 22 has a function of transmitting signals from the controller 20 to the main body of the apparatus.

As mentioned above, if the printing process is repeated in the apparatus with the above structure, the focus of the projection lens 5 will shift. To △
It can be expressed as =K·τ·E·to/t. Here, K is the unique focus change coefficient of the projection lens 5, τ is the transmittance of the photomask 6, E is the amount of light irradiated from the illumination unit 10 per unit time, to is the total open time of the shutter 12, and t is the exposure interval time. It is the total. Note that if the focus change coefficient K of the projection lens 5 is experimentally measured for one projection lens, the same K can be used in devices incorporating the same projection lens.

A microprocessor 20' in FIG. 2 constitutes the core of the controller 20, and the conditional expression regarding Δ and the focus change coefficient K described above are stored in the storage device M in advance. Note that, in addition to electrical means, mechanical means such as a cam can also be used as a storage method. Then,
The photomask 6 used in this process is set on the mask stage 7, the XY stage 2 is moved, the photodetector 18 is positioned within the projection exposure, the shutter 12 is opened, and the printing light transmitted through the photomask 6 is measured by the photodetector 18. , a signal corresponding to the amount of transmitted light τ·E is input from the detection circuit 18' to the microprocessor 20'. After that, the shutter 12 is closed, the XY stage 2 is moved to set the wafer 3 at the printing position, and the shutter 12 is closed again.
is opened and the pattern of the mask 6 is printed onto the wafer 3. At this time, since the amount of focus change △ during the first printing is "0", the projection lens 5 and the wafer 3 measured by air injection from the air nozzle 17
The distance from the lens to the lens corresponds to the design value, and the focus adjustment mechanism 9 is operated to set the focus position so that the distance corresponds to the design value.

When the baking of wafer 3 is completed, the XY stage 2
is moved and this wafer is replaced with another wafer,
The XY stage 2 moves again to set the next new wafer 3 at the printing position. On the other hand, the shutter drive control circuit 12' inputs the opening time (light irradiation time) of the shutter 12 and the exposure interval time (light irradiation interval time) to the microprocessor 20'. The microprocessor 20' separately integrates the shutter opening and the exposure interval each time it occurs, and stores it in the storage device M as an exposure history to/t. Prior to exposing the next wafer 3, the microprocessor 20'
The value of Δ is calculated by calculation based on E·to/t. This value of △ is input to the focus adjustment control circuit 9', the focus adjustment mechanism 9 operates, and the lens barrel 4
Move the air micrometer (not shown)
The adjustment operation continues until the amount of change detected by the focus change amount becomes equal to the calculated amount of change in focus. Therefore, the wafer 3 is automatically positioned at the best imaging position of the projection lens 5 at all times. In this example, the lens barrel 4 is moved to simplify the mechanism, but a structure in which the wafer 3 or the photomask 6 is moved in the optical axis direction may be adopted.

[Effects of the Invention] As described above, in the present invention, since the amount of change in the focus position due to the incidence of light on the projection lens is determined by taking into account the rise and fall of the temperature of the projection lens system, it is possible to accurately determine the focus position. Can be detected. Therefore, accurate focusing can be performed at all times during work, and a clear circuit pattern can be projected and transferred onto the wafer.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of a projection exposure apparatus according to the present invention, and FIG. 2 is a diagram showing a signal processing system of the apparatus shown in FIG. 2... XY stage, 3... Wafer, 5... Projection lens, 6... Photo mask, 9... Focus adjustment mechanism, 10... Lighting unit, 17... Air nozzle, 18... Photo detector, 20... Controller , 20'...microprocessor.

Claims (1)

[Scope of Claims] 1. In a projection exposure method for semiconductor manufacturing in which a photomask is irradiated with light and an image of a circuit pattern of the photomask is projected onto a wafer by a projection lens system, the light is incident on the projection lens system through the photomask. The amount of change in the focus position of the projection lens system is calculated using the amount of light per unit time, the light irradiation time for the photomask, and the light irradiation interval time, and the focus position of the projection lens system is calculated based on the calculation. A projection exposure method for semiconductor manufacturing, characterized in that the surface of the wafer is made to coincide with the surface of the wafer. 2. An illumination system that irradiates light onto a photomask, a projection lens system that projects an image of the circuit pattern of the photomask onto a wafer, and detects the amount of light per unit time that enters the projection lens system via the photomask. irradiation history detection means for detecting a light irradiation time and a light irradiation interval time by the illumination system, and calculating an amount of change in a focus position of the projection lens system using the light amount and each time. 1. A projection exposure apparatus for semiconductor manufacturing, comprising means for aligning the focus position of the projection lens system with the surface of the wafer based on the calculation.