JPS60195509A - Projection optical device - Google Patents

Abstract

PURPOSE:To correct a magnification variation of a projection objective lens, and to maintain a sufficient magnification accuracy for practical use by cutting off a part or the whole of an air chamber formed between lens surfaces in the projection objective lens, from the open air, and controlling this air chamber to a prescribed constant pressure. CONSTITUTION:An internal lens barrel is formed substantially by piling up 14 supporting cylinders, and they are contained and supported as one body by an external lens barrel 20, and fixed by a holding ring 21. Air chambers B-N or 13 pieces are formed by the first supporting cylinder 1 - the fourth supporting cylinder 14 for supporting the first lens L1 through the fourtheenth lens L14, respectively. Through-holes 2a-13a for making the respective adjacent air chambers communicate are formed, and the fourteenth cylinder 14 and the first supporting cylinder support airtightly the lens, respectively. A pipe 22 is inserted into a through-hole 1a formed in the first supporting cylinder 1, and a pressure control device 23 controls a pressure of the unified air chambers B-N through the pipe 22.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a projection optical device that can easily correct the optical characteristics of a projection optical system.

(Background of the invention) In recent years, reduction projection exposure devices (hereinafter referred to as steppers) have
It has been introduced in many SI production sites and has brought great results, but one of its important performances is the accuracy of car matching. There is a magnification error in the optical system.

The size of patterns used in ultra-L8I is becoming increasingly finer year by year, and along with this, the need for improved matching accuracy is also becoming stronger. Therefore, it is becoming increasingly necessary to maintain the projection magnification at a predetermined value of 1. Currently, the @ ratio of the projection optical system is adjusted at the time of equipment installation, so that the magnification error can be ignored. It is also necessary to correct magnification errors caused by changes in environmental conditions, such as slight pressure fluctuations in a clean room.In conventional projection optical systems other than steppers, the distance between the object (reticle) and the projection lens is adjusted to correct the projection magnification. 1) by moving the lens element of the projection lens in the direction of the optical axis. The method used was to make paper. However, if the above method of changing the optical member in the direction of the optical axis is adopted for a device such as a stepper that requires extremely high-precision magnification setting, the optical axis will be distorted due to mechanical eccentricity (tilt) of the moving part. It is difficult to give the correct displacement. As a result, the optical system including the object is no longer coaxial, resulting in a disadvantage that a magnification distribution asymmetrical with respect to the optical axis occurs on the image plane. In addition, in order to accurately set the magnification so that an error of 0.05 μm or less occurs on the wafer, the amount of change in the optical member must be controlled to be within a few μm or 1 μm, including eccentricity (/7 and tilt). This is necessary, and the realization of these things will be accompanied by great difficulties.

(Object of the Invention) An object of the present invention is to eliminate these drawbacks and provide a projection optical device that can easily correct variations in optical characteristics such as magnification and image plane position without causing an asymmetric magnification distribution. purpose.

(Summary of the invention) In the present invention, it was discovered that one of the causes of variations in the projection magnification of the projection objective lens is atmospheric pressure fluctuations (7. Pressure fluctuations alone can change the projection magnification to a non-ignorable degree. It turns out that there are cases.

Therefore, among the air spaces within the projection objective, the space between the projection objective and the projection original plate (reticle), and the space between the projection objective and the photosensitive object (urchin...), the projection objective By shielding (sealing) part or all of the air chamber formed between the lens surfaces in the lens from the outside air and controlling this air chamber to a predetermined constant pressure, it is possible to correct magnification fluctuations of the projection objective lens, which is sufficient for practical use. This makes it possible to maintain high magnification accuracy.

According to the present invention, the projection objective lens does not need to be involved in any way with the projection original plate (reticle) which is replaceably mounted at the exposure-A position, or the photosensitive object (wafer) which frequently moves during each exposure and alignment. This is an extremely simple configuration because magnification correction is performed only in this case.

Further, since the correction does not require mechanical movement such as moving the projection objective lens, and is a so-called static correction, there is no possibility of eccentricity occurring, and there is no asymmetrical deterioration of the first-band performance.

However, in the present invention, since the manufacturing location of the projection objective lens and the usage location of the projection exposure apparatus incorporating it are different, there is basically a difference in atmospheric pressure due to differences in altitude, etc., and the pressure inside the objective lens is used. Optimal depending on the location environment. In order to change the pressure in the sealed air chamber of the projection objective lens depending on the environment at the place of use, the pressure is controlled to an optimum pressure by a pressure control means. In particular, maintaining the pressure in the sealed air chamber of the projection objective lens at an optimal pressure that adapts to the environment of the place of use is advantageous in the following points because the pressure difference between the inside and outside of the sealed air chamber can be reduced. . (1) There is little risk that the outermost lens surface of the lens elements constituting the sealed air chamber of the projection objective will be deformed or displaced due to the pressure difference between atmospheric pressure and the pressure inside the lens; Even if there is a leak of gas in the air chamber, the pressure is controlled to the optimum pressure by the pressure control means, so there is little chance of fluctuations in optical performance such as magnification.

(Examples) The present invention will be described below based on Examples. FIG. 1 is a lens arrangement diagram showing an example of a projection objective lens used in a stepper.
The above predetermined pattern is reduced and projected onto the wafer (W). In the figure, light rays representing the conjugate relationship between on-axis object points between the wafer and the reticle are shown. This objective lens is a reticle (R)
Consists of a total of 14 lenses, L+, Ls, ...Le+ in order from the side, and the distance between each lens and reticle (R)
, aX b in order from the reticle side between the wafer (W) and the wafer (W).
, c, ..., 0, a total of 15 air intervals are formed. The specifications of this objective lens are shown in Table IK. however,
r is the radius of curvature of the valley lens surface, D is the center thickness and air spacing of each lens, and N is the staff of the valley lens (λ = 365.Or+
m), and the leftmost number in the table represents the order from the reticle side. Also, D.

represents the distance between the reticle (R) and the foremost lens surface, and represents the distance between the final lens surface and the wafer (W).

Now, in this objective lens, the air intervals a, bl...
・If the atmospheric pressure at 0 is changed by +137.5 rrrnHg, the relative refractive index of each air gap is 1.0
Table 2 shows the change in magnification and the change in the imaging plane, that is, the conjugate plane with the reticle (R). However, the magnification change ΔX is the amount by which the image point, which is imaged at a position 5 or 66 mm away from the optical axis when there is no change in air pressure on the imaging plane, moves after the air pressure changes in each air interval in μm.
It is expressed in units, and a positive sign indicates a case where the image is projected larger (enlargement) on the image forming plane when there is no atmospheric pressure fluctuation, that is, on a predetermined wafer surface. Further, the change ΔZ in the imaging plane is shown as a change in the imaging point on the axis, and the case where it moves away from the objective lens is indicated with a positive sign. Both values are in μm.

Table 1 Table 2 First Example: From Table 2 above, the double 4f motion in the first space a, that is, the space between the reticle and the projection objective lens, and the fifteenth space 0, that is, the space between the wafer and the projection objective lens, are both positive. is the value of
The total is 0.043. Therefore, by cutting off all the spaces formed within the projection objective lens, that is, the second space b to the fourteenth space n, from atmospheric pressure and integrally sealing them, There is no change in magnification due to the space within the projection objective lens, and only the change in magnification is due to the first space a and the fifteenth space 0, which is about 4% of the change in magnification that can occur due to all the threads.
By shielding the entire space formed within the projection objective lens from atmospheric pressure, the change in the image plane can also be reduced to 1.02μ.
Figure 2 is a diagram showing the lens barrel structure and pressure control means of the projection objective shown in Table 1.
The lenses L1, L2, ..., L12 are the first support tube (1), the second support tube (2), ..., respectively.
, supported by a fourteenth support tube (14).

By stacking these 14 support tubes, an inner mirror section is essentially formed, and these are connected to the outer barrel (20).
It is integrally housed and supported, and is fixed by a presser foot 31k (21). The first support tube (1) to the fourteenth lens that supports the lens L+ to the fourteenth lens L+t, respectively.
Thirteen air chambers BN are formed by the support tube (14) K, and these air chambers BN correspond to the air intervals bn shown in FIG. 1, respectively. From the second support tube (2) that supports the second lens L2 to the thirteenth support tube (13) that supports the thirteenth lens, K denotes through holes (2a) to communicate the adjacent air chambers, respectively. (Zaa) is formed. In addition, the fourteenth support tube (14) that supports the fourteenth lens L++f located at the tip of the objective lens airtightly seals the fourteenth lens L+t so as to isolate the thirteenth air chamber N from the outside air via the fourteenth lens L+4. It is also supported in an airtight manner by an external lens barrel (2o). The first support tube supporting the second lens L+ is the second lens L+.
2 is airtightly supported. For this air-tight support, a Q-+) seal is used. A tube (22) is inserted into the through hole (la) formed in the first support cylinder 1. With the first support tube (1)! (22) is also provided with a gasket for airtightness.

A pressure control device (23) controls the pressure in the integral air chamber BN via the pipe (22). The pressure control device (23) is
When increasing the pressure in the air chamber B-H, pressurized air is sent from the pressurized air supply device (24) to the air chamber B-N via the pressurized air tube (22), and when decreasing it, the air chamber B-H is fed into the air chamber B-N. The air in B to N is exhausted through the exhaust device (26).

A filter (25) is arranged between the pressure control device t (23) and the pressurized air supply device (24) to purify the air sent into the air chamber BN. Pressure center length
(27) 9 This is for detecting the pressure in the air chamber, for example, the pressure in the air chamber H.

The pressure setting circuit (28) sets the atmospheric pressure according to the altitude of the place where the projection exposure apparatus is used. A comparison circuit (29) compares the output signal of the pressure sensor (27) and the output signal of the pressure setting circuit (28), and generates a signal indicating the difference or magnitude relationship between the two river force signals.

The pressure control device (23) inputs the output signal of the comparison circuit (29) and controls the pressure sensor (27) and the pressure setting circuit (2).
8) The pressure in the air chambers BN is controlled so that the outputs have a predetermined relationship (match).

In this way, the pressure Vi in the air chamber B-N is always maintained at an atmospheric pressure depending on the altitude, etc. of the location where the exposure apparatus is used, making it possible to precisely maintain the magnification of the projection objective lens.

Second Example: FIG. 3 is a graph showing the values of each space regarding the amount of change in magnification ΔX shown in Table 2 above. The vertical axis of the graph in Figure 3 is the magnification change amount ΔX, and the horizontal axis is the pressure change amount ΔP.
The symbols shown on each straight line in the figure correspond to the valleys 9. Further, the amount of change in magnification ΔTx in the entire system is shown by a thick solid line.

From the above Table 2 and the graph in Figure 3, it can be seen that the magnification fluctuation amount caused by the third air gap C alone is the closest value to the magnification fluctuation amount S = 1.004 due to the entire system.
Accordingly, by sealing only this third air gap C, the magnification variation of all yarns can be corrected by 1f. In other words, the amount of magnification variation of 1.164 due to the third air gap C can be reduced to zero by sealing off and sealing this space from the atmosphere, so that only the difference from the magnification variation due to the entire system becomes the actual amount of magnification variation. Therefore, in this case, the actual amount of change in magnification is 10,
16, and it is clear that the number decreases to 16. The magnification change ΔTx' of the entire system after this correction is shown by the dotted line in FIG.

Now, it is possible to correct the magnification change due to atmospheric pressure fluctuations not only by one air interval but also by sealing a plurality of air intervals in combination to isolate them from the atmosphere. For example, in the objective lens described above, the seventh air interval g
1 between six consecutive lenses from to the 12th air spacing l
If 4 is isolated from the atmosphere and sealed integrally, these 6
Since the sum of 0.935 of the magnification fluctuations occurring in the two air intervals can be reduced to zero, the difference from the magnification fluctuation of 1.004 occurring in the entire system is 0.935.
It is possible to correct for a small value variation of only 0.069.

That is, the magnification variation in the entire system is corrected to 6.9 inches. In addition, if the 13th air interval m1 is also sealed off from the atmosphere in addition to these six air intervals, the amount of magnification variation in the entire system becomes -0,067, which allows for better correction. . Furthermore, the first
If 4 air intervals n are also sealed and sealed from the atmosphere to form a total of 8 sealed spaces, the correction amount for the magnification fluctuation due to these 8 spaces will be 1.063, and the magnification fluctuation it of the entire system will be - It is possible to make the correction as small as 0,059.

Of these embodiments, the configuration in which only the third air interval C is sealed and sealed from the atmosphere is the simplest, but by sealing the third air interval CL, fluctuations due to the entire system of the image forming surface become larger. . On the other hand, from the seventh air interval positive g to the first
When 8 consecutive air spaces up to 4 air spaces n are sealed, the fluctuation of the focal plane of the entire system is simultaneously corrected by the sum of 3.91 of the fluctuations of the imaging plane due to these 8 air spaces. Therefore, it is somewhat advantageous.

In this way, even when part of the air gap is sealed, the lens barrel structure shown in FIG. 2 can be used as is. That is, there is an O-IJ ring, etc. between the support tube that supports the lens on both sides of the air gap to be sealed and the external lens barrel (20). r: Just put it in. Further, the pressure control means shown in FIG. 2 can be used as is. That is, the closed air space is connected to the pressure control device (23), and the pressure sensor (27) is placed in the closed air space. This makes it possible to maintain the pressure in a part of the air space (air chamber) of the projection objective at an optimum pressure.

As described above, it is possible to maintain the air chamber pressure that is most suitable for the environment where the stepper is used, and projection exposure can be performed with less variation in magnification and less variation in the imaging plane even when atmospheric pressure changes. becomes possible. It goes without saying that it is also possible to completely correct magnification fluctuations in the same way by filling the air chamber in the projection objective lens with a specific gas such as nitrogen gas or carbon dioxide gas and maintaining the pressure at a predetermined level. do not have. Note that the pressure in the air chamber may be determined depending on the altitude, or may be the average atmospheric pressure of the area (annual, monthly, etc.). In addition, in the second embodiment, a slight variation in magnification may remain if only the air chamber is sealed, but if you want to eliminate this as well, close the other air chambers to reduce the pressure in the other air chambers. It may be controlled to change actively (change the refractive index of the other air chamber). Furthermore, even if the optical characteristics of the projection objective lens change due to partial absorption of the exposed light that passes through the projection objective lens during wafer exposure, the change in optical characteristics can be corrected by controlling the pressure in the other air chambers. .

(Effects of the Invention) As described above, according to the present invention, it is possible to statically correct magnification fluctuations without requiring mechanical operations such as moving the projection objective lens in the optical axis direction, and it is possible to asymmetric optical performance. This method consistently performs stable and highly accurate overlay matching without any deterioration, and greatly contributes to the production of high-density semiconductor devices such as VLSIs. Also, if the air chamber has a small communication with the outside and the pressure in the air chamber changes to a degree that cannot be ignored after a long period of time,
The optimum pressure can be maintained at all times by operating the pressure control means.

[Brief explanation of the drawing]

FIG. 1 is a lens configuration diagram of the projection objective lens, FIG. 2 is an explanatory diagram of the structure and pressure control means of the projection objective lens barrel in the first embodiment of the present invention, and FIG. 3 is a second embodiment of the present invention. This is a useless graph to explain. (Explanation of symbols of main parts) R...Projection original plate (lenacle) W...Photosensitive object (wafer) L+, l, t~Lu...lens a) b- o...
...Air interval 13, C-N...Air chamber 23...Pressure control device 27...Pressure sensor 28...Pressure setting circuit 29...・Comparison circuit applicant Takao Watanabe, agent of Nippon Kogaku Co., Ltd.

Claims (1)

[Claims] In a projection optical device having an objective lens for projecting and exposing a pattern on a projection original plate onto a photosensitive object surface, all or part of a plurality of air gaps formed between each lens surface in the projection objective lens are 1. A projection optical device comprising: means for connecting the air to outside air; and pressure control means for maintaining the pressure in the air gap at a predetermined pressure.