JPS60120343A - Optical projecting device - Google Patents

Abstract

PURPOSE:To facilitate adjustment and to improve the precision of image formation by isolating gaps of lens groups consisting of plural lenses between a reticle and a wafer from atmospheric pressure partially, and preventing variation in refractive index due to the influence of the atmospheric pressure. CONSTITUTION:Lens groups consisting of plural lenses L1-L14 are provided between the reticle and wafer W, and an image of the pattern of the reticle R is formed on the wafer W. There are gaps (a)-(o) present among the reticle R, lenses L1-L14, and wafer W. Sic gaps (c) and (g)-(l) among those gaps are isolated from the atmosphere and variation in the refractive indexes of the lenses with the atmospheric pressure is prevented. Consequently, the magnification of a projection objective lens is corrected to simplify the constitution, thereby preventing eccentricity and improve image forming peformance.

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 magnification accuracy of a projection optical system.

(Background of the Invention) In recent years, reduction projection exposure devices (hereinafter referred to as steppers) have become
It has been introduced in many SI production sites and has brought great results, and one of its important features is overlay matching accuracy. 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 increasingly smaller year by year, and the need for improved matching accuracy is also becoming stronger. 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 when installing the device)
The magnification error is at least negligible. However, in order to adequately cope with the increasing density of VLSIs, it is also necessary to correct magnification errors caused by changes in environmental conditions, such as slight pressure fluctuations in the clean room during operation of the device.

Conventionally, in projection optical systems other than Temper, methods have been used to correct the projection magnification by mechanically changing the distance between the object (reticle) and the projection lens, or by moving the lens element in the projection lens in the optical axis direction. was. However, if the method of changing the optical member in the optical axis direction as described above is adopted for a device such as a stepper that requires extremely high-precision magnification setting, the optical axis It is difficult to apply displacement while maintaining the correct position. 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 does not occur on the wafer, it is necessary to control the amount of change in the optical member to within a few μm or 1 μm, including eccentricity (shift, tilt). Achieving these goals involves great difficulties.

(Objective of the Invention) An object of the present invention is to eliminate these drawbacks and provide a projection optical device that can accurately and easily correct magnification without generating an asymmetrical magnification distribution. (Summary of the Invention) In developing the present invention, we discovered that one of the factors that cause variations in the projection magnification of a projection objective lens is atmospheric pressure fluctuations, and as a result of intensive study, we found that pressure fluctuations alone can cause projection magnification to change to a degree that cannot be ignored. found. and,
In the present invention, each air space formed between the lens surfaces in 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 (wafer) It has been found that the amount of magnification variation caused by one or more air gaps within the projection objective may be approximately equal to the magnification variation caused by the entire system. That is, there are cases where it can be considered that the magnification change of the entire system is caused only by one or more such spaces. Therefore, by shielding and sealing only this one or more spaces from the atmosphere, it is possible to substantially correct the magnification fluctuation of the entire system.

To be more specific, the air space formed in the optical path from the projection original plate to the photosensitive object surface, that is, (3) all the air spaces formed between each lens surface in the projection objective lens, and the projection distance. If the pressure in all the spaces between the objective lens and the projection original plate and the space between the projection objective lens and the photosensitive object surface changes with the atmospheric pressure, the amount of change in magnification ΔTx that occurs in these entire systems is the magnification change in all air gaps. It is expressed as the sum of the amount of change, and becomes ΔTx - ΣΔxi.

If one or more air spaces formed in the projection objective are sealed and sealed from atmospheric pressure, if the pressure in these sealed spaces or spaces changes with the atmospheric pressure, When the amount of change in magnification caused by space is Δ8x, with respect to the amount of change in magnification ΔTx of the entire system,
The change can be corrected by ΔSX. Therefore, ΔTx - ΔS The magnification fluctuation of the entire system is corrected by selecting one or more spaces such that the amount of magnification fluctuation ΔSX caused by these spaces is approximately equal to the amount of magnification fluctuation ΔTX caused by the entire system when the space fluctuates, and sealing the space. can do. In other words, it is sufficient to seal one or more air gaps in the projection objective such that ΔTx ΔSx (2). If there is only one space to be sealed, Δ8x=ΔXj, and if multiple spaces are sealed, ΔSx=Σx
j”.

Note that when there are multiple air gaps to be sealed within the projection objective lens, it is easier to seal them and the structure is simpler by combining adjacent air gaps, but in order to better satisfy equation (2), It is also possible to integrally seal non-adjacent spaces. In addition, although the present invention focuses on correction of magnification fluctuations as described above, in general, changes in the imaging plane due to pressure changes Δ
Since Z also occurs, it is possible to select a space to be sealed taking into consideration not only the magnification but also the fluctuation of the imaging plane. Note that spaces other than the sealed space within the projection objective lens may be configured to communicate with the atmosphere so that the pressure within each space changes with atmospheric pressure fluctuations.

(Examples) Hereinafter, the present invention will be described based on Examples of the present invention. FIG. 1 is a lens arrangement diagram showing an example of a projection objective lens used in a stepper, and a predetermined pattern on a reticle (R) is reduced and projected onto a wafer (T) by this objective lens. 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 arranged in order from the reticle (TL) side: Ll + "2 r...L,
There are a total of 14 lenses 9, the distance between each lens, the reticle (R), and the wafer (5), in order from the reticle side, a and b.

A total of 15 air intervals, C1..., 0, are formed. Table 1 shows the specifications of this objective lens. however,
r is the radius of curvature of each lens, D [center thickness and air gap of each lens, Nld i-line of each lens (λ-365.0 nm)
The numbers at the left end of the table represent the order from the reticle side. Also, Do is the reticle (
D3□ represents the distance between the final lens surface and the wafer (W).

Now, in this objective lens, the air distance is a.

b,...0 atmospheric pressure +137.5 mmHg respectively
, the relative refractive index of each air gap is 1
. However, the magnification change ΔX is the amount by which an image point formed at a position 5 to 66 mm away from the optical axis when there is no change in air pressure on the imaging plane moves after changes in air pressure in each air interval.
Expressed in units of m, when there is no atmospheric pressure fluctuation, the image plane is projected larger onto a predetermined wafer surface (enlargement)
is shown as a positive sign. Further, the change ΔZ in the imaging plane is shown as a change in the axial imaging point, and the case where it moves away from the objective lens is shown as a positive sign. Both values are in μm.

FIG. 2 is a graph showing the values of each space for the amount of change in magnification ΔX shown in Table 2 above. The vertical axis of the graph in Figure 2 is the magnification change ΔX, the horizontal axis is the pressure change ΔP,
The symbols shown on each straight line in the figure correspond to each space. 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 of FIG. 2, it can be seen that the magnification fluctuation amount caused by the third space C alone is the closest value to the magnification fluctuation amount S = 1.004 due to the entire system.

Therefore, by sealing only this third space C, it is possible to substantially correct the magnification fluctuation of the entire system. In other words, the amount of magnification variation of 1.164 due to the third space C can be reduced to zero by shielding this space from the atmosphere and sealing it, 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 magnification change is -016, which is 1
It is clear that this decreases to 6%. 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 magnification changes due to atmospheric pressure fluctuations not only by one space but also by sealing a combination of a plurality of spaces to block them from the atmosphere. For example, in the above objective lens, if six consecutive lens intervals from the 7th space g to the 12th space t are sealed from the atmosphere and are integrally sealed, the sum of the magnification fluctuations occurring in these six spaces is 0935. Since it can be made zero, it is possible to correct the variation to a small value of only 0.069, which is the difference from the magnification variation of 1.004 that occurs in the entire system. That is, the magnification variation in the entire system is corrected to 6.9%. Also,
If the 13th space m is also sealed off from the atmosphere in addition to these six spaces, the magnification variation amount in the entire system can be corrected well to -0,067. Furthermore, if the 14th space n is also sealed and sealed from the atmosphere to form a total of 8 sealed spaces, these 8
The correction amount for magnification variation due to two spaces is 1.063,
It is possible to correct the magnification variation amount of the entire system to be as small as -0059.

Of the above embodiments, the configuration in which only the third space C is sealed off from the atmosphere and sealed is the simplest, but by sealing this third space C, the fluctuations due to the entire system of the image forming plane become larger. . On the other hand, when eight consecutive spaces from the 7th space g to the 14th space n are sealed, the image forming surface fluctuation of the entire system is the total amount of image forming surface fluctuation due to these eight spaces 3
91 are corrected at the same time, which is somewhat advantageous.

As described above, according to the present invention, the projection original plate (reticle), which is replaceably mounted in the exposure apparatus, and the photosensitive object (wafer), which is frequently moved during each exposure and alignment, are not involved in any way, but only in the projection objective lens. Since magnification correction is performed, the configuration is extremely simple.

Further, since no mechanical movement is required for the correction, and it is a so-called static correction, there is no possibility of eccentricity occurring, and there is no asymmetrical deterioration of the imaging performance.

[Brief explanation of the drawing]

FIG. 1 is a lens configuration diagram of a projection objective lens used in an embodiment according to the present invention, and FIG. 2 is a graph showing changes in magnification with respect to pressure changes at each zoom interval. Applicant: Nippon Kogaku Kogyo Co., Ltd. Agent: Takashi Watanabe

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, an air interval formed between each lens surface in the projection objective lens;
and the pressure in the space between the projection objective and the projection original, and in the space between the projection objective and the photosensitive object, producing a magnification variation approximately equal to the magnification variation that would occur if the pressures in the space between the projection objective and the projection original plate all varied with atmospheric pressure. A single lens in the projection objective
Alternatively, a projection optical device characterized in that a plurality of lens spaces are sealed and sealed from the atmosphere, and the remaining space is communicated with the atmosphere so that the pressure can fluctuate according to atmospheric pressure.