JPH043662B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a projection optical device and method thereof that can maintain high accuracy in the magnification of a projection optical system.

(Background of the invention) Reduction projection exposure devices (hereinafter referred to as steppers) have been introduced to many VLSI production sites in recent years and have brought great results, but one of their important performances is overlay matching accuracy. It will be done. Among the factors that affect this matching accuracy, an important one is the magnification error of the projection optical system. The size of patterns used in VLSIs is becoming smaller and smaller year by year, and the need for improved matching accuracy is also growing. Therefore, the need to maintain the projection magnification at a predetermined value has become extremely high. Currently, the magnification of the projection optical system is adjusted at the time of installation of the apparatus, so that the magnification error can be ignored. However, there is an increasing demand to prevent magnification errors from occurring even when environmental conditions change, such as slight temperature changes during operation of the device or slight pressure fluctuations in a clean room.

As a result of various experiments, the projection magnification Y of the projection lens is determined by atmospheric pressure PA, atmospheric temperature TA, and lens temperature.
According to the function f, which is a function of TL, it turns out that Y=f(PA, TA, TL) ...(1), and the position F of the imaging plane of the projection lens is also determined by the function g, F =g(PA, TA, TL)...(2) It turned out that. On the other hand, this type of exposure equipment is normally installed in a clean room that only allows temperature fluctuations within ±0.1°C, but in some cases, it is installed in clean rooms where temperature fluctuations of about ±1°C occur. It may be installed. Furthermore, since the clean room is not sealed against atmospheric pressure, the pressure of the projection lens fluctuates with the atmospheric pressure. Furthermore, in this type of exposure apparatus, the lens temperature increases because exposure light with strong energy is used to transfer the circuit pattern to the photoresist on the wafer. Therefore, it can be said that the exposure apparatus is installed in an environment where the optical characteristics (projection magnification, image plane position) of the projection lens vary.

Therefore, it is conceivable to house the exposure equipment in a constant temperature and constant pressure chamber, but this method would require a constant temperature and constant pressure chamber to become large-scale, making it unsuitable for actual IC production sites.

(Object of the Invention) The present invention solves the above-mentioned drawbacks, and an object of the present invention is to provide an exposure apparatus that can make the optical characteristics of a projection lens constant without increasing the size of the exposure apparatus.

(Summary of the Invention) The present invention prevents thermal changes in the projection lens due to exposure energy by flowing gas with controlled temperature and pressure into the projection lens chamber, and also prevents thermal changes in the projection lens from changes in atmospheric pressure and outside temperature. The projection magnification or imaging position is stabilized by monitoring the pressure of the inflowing gas and controlling the pressure of the inflowing gas.

(Examples) Hereinafter, the present invention will be described based on Examples. FIG. 1 is an explanatory diagram of an embodiment of the present invention. In FIG. 1, a projection lens 1 includes a reticle (mask) R
This is for projecting an original pattern (for example, an integrated circuit pattern) formed on the wafer W onto the wafer W. An optical image of the original pattern illuminated by the illumination device 2 is formed onto the wafer W by the projection lens 1. A stage 3 for two-dimensionally moving the wafer W includes a wafer holder 3a. The wafer holder 3a vacuum-chucks the wafer and can move the wafer up and down in the optical axis direction of the projection lens 1. The stage drive unit SD drives the stage 3 two-dimensionally and also drives the wafer holder in the vertical direction.

The projection lens 1 includes a lens barrel 1a and a plurality of lenses arranged at a predetermined gap (air chamber).
It consists of L ₁ , L ₂ , L ₃ , L ₄ and L ₅ . Lens L ₁ and L ₂
A first gap 8 between the lens barrel 1a and the lens barrel 1a is opened to the outside of the lens barrel 1a through a ventilation hole 7. with lens L ₂
A second gap 10 between L ₃ and L 3 is communicated with the first gap 8 via a ventilation hole 9 . The gap 12 between lenses L ₃ and L ₄ is connected to the second gap 10 through the ventilation hole 11.
It is communicated with. The fourth between lenses L ₄ and L ₅
The gap 14 is communicated with the third gap 12 via the ventilation hole 13. The fourth gap 14 is connected to the outside of the lens barrel 1a via a ventilation hole 15. These ventilation holes 9, 11, and 13 are formed, for example, at the lens support ratio. In addition, the first to fourth gaps 8, 1
0, 12, and 14 are sealed so as to be isolated from the outside of the lens barrel 1a, except for the ventilation holes 7 and 15.

Air from the air supply source AS is supplied to a first control valve 6 for flow rate adjustment after dust is removed by a filter 5 such as a dust-proof HEPA filter. Air whose flow rate is regulated by the control valve 6 flows into the first gap 8 via the pipe PP1 and the vent hole 7. The fourth lens chamber 14 has a ventilation hole 15 and a pipe PP
2 to a second control valve 16 for flow rate adjustment. The second control valve 16 is connected to an exhaust device 17. Therefore, the air supplied from the air supply source AS flows from the first gap 8 to the fourth gap 14 after being adjusted in flow rate by the first control valve 6.
Next, the flow rate is adjusted by the second control valve 16, and the gas is discharged to the outside world by the exhaust device 17. At this time,
Adjusting the pressure within the lens barrel 1a (in the first to fourth gaps 8, 10, 12, 14) according to the resistance values that the first and second control valves 6, 16 give to the air flow. I can do it. Pressure detector 2
0 detects the pressure within the lens barrel 1a, for example, detects the pressure within the fourth gap 14. The temperature detector 21 measures the lens temperature, e.g.
Detect the temperature of L ₅ . The environmental sensor 19 detects the external pressure (atmospheric pressure) and the temperature of the atmosphere, which determine the refractive index of the air. The microcomputer (CPU) 18 has a pressure detector 20 and a temperature detector 21
and interface the output of the environmental sensor 19.
Read via IF. The CPU 18 also controls the lighting device 2, the first and second lights via the interface IF.
Controls the control valves 6 and 16 and the stage drive unit SD.

Now, when an operation start command is input from the keyboard KB (step P1), the CPU 18
The air supply source AS, exhaust device 17, and stage drive unit SD are operated as follows. First, turn on the mercury lamp in the lighting device 2 (step P2),
Next, the air supply source AS and the exhaust device 17 are operated to cause air to flow from the first gap 8 to the fourth gap 14 (step P3). Next, position the reticle R,
That is, alignment is performed (step P4), and a command is sent to the stage drive unit SD to drive the stage 3 so that the circuit pattern of the reticle R is imaged on the local area S1 (shown in the second diagram) of the wafer W (step P5). ). Next, the shutter in the illumination device is opened to expose the photoresist coated on the wafer W, and after a predetermined period of time, the shutter is closed (step P6). Thereafter, the stage 3 is moved and the shutter is opened and closed so that similar operations are performed from local area S2 to S11 (step-and-repeat exposure operation). When it is detected that this operation has been repeated N times (11 times for the wafer shown in Figure 2) (step P7), the stage 3 is moved to the wafer exchange position and the wafer is exchanged (step P8). . Thereafter, the same operation is repeated according to the number of wafers (step P9), and when a predetermined number of wafers have been exposed, the operation is ended (step P10).
FIG. 3 shows a flowchart of this operational step.

During such a step-and-repeat exposure operation, a portion of the exposure energy incident on the projection lens 1 is absorbed by the lenses _L1 to _L5 .
On the other hand, since air is being sent from the air supply source AS during this time, the lenses L ₁ to _{L 5} are air-cooled. However, since it is not possible to perfectly match the temperature of the air for cooling and the temperature of the lens,
It is difficult to completely suppress variations in magnification of a projection lens. Additionally, if the temperature of the clean room where the exposure equipment is installed fluctuates by about ±1°C, the temperature of the cooling air will also fluctuate, which can also cause magnification fluctuations. (This can be solved by keeping the air temperature constant.) Furthermore, if the refractive index of air changes due to changes in atmospheric pressure or the like, the optical characteristics of the optical system from the reticle R to the wafer W change, which also causes a change in magnification.

When the lens barrel 1a is sealed as shown in FIG. 1, the projection magnification and the imaging plane position vary as follows. That is, the projection magnification Y is the atmospheric pressure PA, the atmospheric temperature
TA, lens temperature TL, and lens barrel 1a
It is a function of the internal pressure (internal pressure of the first to fourth gaps) PL, and using the function f ₁ , it can be expressed as Y=f ₁ (PA, TA, TL, PL) (3). From the state expressed by equation (3), the atmospheric pressure is △PA, the atmospheric temperature is TA, the lens temperature is △TL, and the internal pressure of the lens barrel is △PL.
If the amount of each change is small, use the coefficients C ₁ , C ₂ , C ₃ , and C ₄ to calculate the change in projection magnification △Y as △Y=C ₁・△PA+C ₂ △TA+C ₃・It can be approximated as △TL＋C ₄・△PL ……(4). The coefficients C ₁ to C ₄ are measured or calculated in advance. Therefore, in order to make the magnification change zero, that is, △Y=0, the internal pressure of the lens barrel should be △PL'=-(C ₁ △PA+C ₂ △TA +C ₃ △TL)/C ₄ ...( It turns out that you only need to change 5).

Next, the imaging plane position F is expressed using the function g ₁ as F=g ₁ (PA, TA, TL, PL) (6). Similarly to equation (4), the above-mentioned minute changes in pressure and temperature can be approximated as △F=C ₅・△PA+C ₆・△TA +C ₇・△TL+C ₈・△PL ……(7). Here, the coefficients C ₅ to C ₈ are measured or calculated in advance. Therefore, if the change in the position of the image plane cannot be ignored compared to the depth of focus of the projection lens, the distance between the projection lens 1 and the wafer W is changed to obtain good image formation on the wafer. .

When the command to start operating the exposure apparatus is input from the keyboard KB in step P1, the CPU 18 resets address M1 of the memory for storing atmospheric pressure (built into the CPU 18) to zero (step P21), and then resets the atmospheric pressure memory to zero. Address M2 of the memory for storage is reset to zero (step P22), then address M3 of the memory for lens temperature storage is reset to zero (step P22).
P23), and address M4 of the memory for storing the internal pressure of the lens barrel 1a is reset to zero (step P24). Subsequently, the atmospheric pressure detection force from the environmental sensor 19 is written to address P1 of the calculation register (built-in CPU 18) (step P25), and then the atmospheric temperature detection force from the environment sensor 19 is written to address R2 of the register. write (step P26), write the lens temperature detection force from the temperature detector 21 to address R3 of the register (step P27), and
Write the internal pressure of the lens barrel 1a from the pressure detector 20 to address R4 of the register (step P28).
When this is completed, subtract the data at address M1 in memory from the data at address R1 in the register to find △PA, and write it to address M5 in memory (step
P29), then subtract the data at address M2 of the memory from the data at address R2 of the register to find △TA and write it to address M6 of the memory (step P30), then subtract the data at address M3 of the memory from the data at address R3 of the register. Subtract the data to find △TL and write it to memory address M7 (step P31), then subtract the data at memory address M4 from the data at register R4 to find △PL and write it to memory address M8. Write (Step P32). Next, write the data at address R1 of the register to address M1 in memory (step P33), then write the data at address R2 of the register to address M2 in memory (step P34), and then write the data at address R3 of the register to memory. The data at address M3 of the register is written (step P35), and the data at address R4 of the register is written to address M4 of the memory (step P36). When this is completed, the timer circuit TC measures a predetermined time ts (step P37). This time determines the sampling period for sampling pressure and temperature.

Next, the data at addresses M5 to M8 in the memory is read (step P38), △PL' is calculated from equations (4) and (5) (step P39), and the first and second The control valves 6 and 16 are controlled to increase or decrease the internal pressure of the lens barrel 1a (step P40). At this time, the first and second control valves 6 and 16 are independently controlled to make the amount of air flowing into the lens barrel more than a fixed amount per unit time, and to independently control the resistance value to the air under these conditions. Adjust, △
The internal pressure of the lens barrel is increased or decreased so that Y=0. When this operation is finished, the CPU 18 will move from memory M5 to
Read the data at address M8 again (step
P41), calculate ΔF from equation (7) (step P42).
Then, it is determined whether ΔF can be ignored compared to the depth of focus of the projection lens 1 by comparing the constant α and ΔF (step P43). The result of this determination is △
If F>α, the fluctuation in the position of the imaging plane cannot be ignored, so the wafer holder 3a is moved up and down via the stage drive unit SD. On the other hand, if △F<α, step
Jump to P45. In step P45, the timer circuit TC monitors whether the time ts has been counted, and when ts has elapsed, the process returns to step P25. Here, the time ts is set so as to ensure the operating time of the first and second control valves and the operating time of the stage drive unit SD. FIG. 4 shows a flowchart of this operation.

Next, a second embodiment of the present invention will be described using FIG. In the second embodiment, the air passing through the filter 5 and the control valve 6 passes through the branched pipe PP1' to the first to fourth gaps 8, 10, 1.
2 and 14 in parallel, and is discharged via a branched pipe PP2', differing only in this respect from the serial piping of the first embodiment. The first embodiment has the characteristic that the same level of temperature stabilization can be achieved with a smaller flow rate than the second embodiment, but when there is no restriction on the flow rate, the second embodiment has a better effect on the fluid. The resistance is small, which is advantageous for stabilizing the temperature of the lens.

As described above, in the first and second embodiments, air is flowed by exhausting the air with the exhaust device 17, but air may be fed into the filter 5 with a compressor or blower, or air may be fed with air from a high-pressure cylinder. A gas or a liquefied or solidified gas may be returned to a gas and the temperature may be adjusted to a desired value for use.

Note that although air is most easily used as the gas to be flowed in the present invention, other gases such as N ₂ , He, CO ₂ , Freon gas, etc. may also be used.

Furthermore, in the description of the above embodiment, it is assumed that the gas is released into the flowing gas, but it may be made to flow into the filter 5 again without being released. In this case, it is necessary to insert a heat exchanger in the path through which the gas flows.

In addition, in the above embodiment, the pressure of the gas flowing out from the first control valve 6 is lower than the pressure of the gas flowing into the first control valve 6, and as a result, the temperature of the gas decreases due to adiabatic expansion, so the lens heats up. Increased absorption effect (higher cooling effect).

FIG. 6 shows a specific example of a control valve for flow rate adjustment. The gas entering from the passage PP10 in the base body 31 is subjected to resistance and the flow rate is controlled by the needle valve 32, and then exits from the passage PP11.
The needle valve 32 is provided with a rack 32a, which moves up and down when a pinion 33 is rotated by a motor or the like. This allows the resistance to gas and the flow rate to be adjusted.

(Effects of the Invention) According to the present invention as described above, when radiant energy for exposure passes through a projection lens, it is absorbed by the lens, and its influence on optical characteristics such as projection magnification and image plane position is reduced. can be significantly reduced. Furthermore, by controlling the air pressure inside the lens barrel (air pressure in the gap), it is possible to prevent fluctuations in the optical characteristics of the projection lens due to fluctuations in atmospheric pressure or external temperature.

Further, according to the present invention, since the lens cooling effect is high, good optical characteristics can be maintained even if the exposure amount per unit time is increased. Therefore, for example, it is possible to increase the illuminance of the mercury lamp and shorten the exposure time per exposure, thereby increasing the throughput. Further, according to the present invention, the lens is cooled by flowing gas into the lens barrel, but even if the lens cannot be completely cooled to the temperature of the gas, the pressure inside the lens barrel can be controlled. This makes it possible to correct variations in optical properties.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a first embodiment of the present invention.
FIG. 2 is a diagram showing the local exposure area of the wafer and the exposure order. 3 and 4 are flowcharts showing the operation of the first embodiment. FIG. 5 is an explanatory diagram of a second embodiment of the present invention. FIG. 6 is a diagram showing a specific example of a control valve for flow rate adjustment. (Signs of main parts) 1... Projection lens, 1a
... Lens barrel, AS ... Air supply source, 7,9,
11, 13, 15...Vent hole, 6, 16...Control valve, 17...Exhaust device, 18...Microcomputer.

Claims (1)

[Scope of Claims] 1. An apparatus for projecting and exposing a pattern formed on a reticle onto a photosensitive substrate with predetermined imaging characteristics via a projection optical system, comprising at least one optical element constituting the projection optical system. a lens barrel having a ventilation hole for shielding a space between from outside air and supplying a controlled gas into the space; supplying a controlled flow rate of gas into the space through the ventilation hole; a flow rate adjustment means; a pressure detector for detecting the pressure in the space; a detection means for detecting atmospheric pressure changes and temperature changes within the apparatus that cause fluctuations in the imaging characteristics; means for calculating the pressure in the space necessary to correct the variation from the predetermined imaging characteristic based on each amount of change;
A projection exposure apparatus comprising: a control means for controlling the flow rate adjusting means so that the calculated pressure is detected by the pressure detector. 2. The apparatus according to claim 1, wherein the detection means includes a temperature detector that detects temperature changes in the lens barrel of the projection optical system. 3. The apparatus according to claim 1, wherein the detection means includes an environmental sensor that monitors atmospheric pressure and temperature around the projection optical system. 4 the lens barrel has a first vent hole for inflowing the gas and a second vent hole for discharging the gas;
The flow rate regulating means includes a first control valve that controls the gas flow rate through the first vent hole, and a second control valve that controls the gas flow rate through the second vent hole; 4. The apparatus according to claim 2, wherein the means independently controls the opening amounts of the first and second control valves.