JPH0616477B2 - Projection optics - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a projection optical apparatus capable of highly accurately correcting the imaging performance of a projection optical system.

(Background of the Invention) A reduction projection type exposure apparatus (hereinafter referred to as a stepper) has recently been a super L type.
It has been introduced to many SI production sites and has produced great results, but one of its important performances is overlay matching accuracy. An important factor that affects the matching accuracy is a magnification error of the projection optical system.
The size of the pattern used in the VLSI is becoming finer year by year, and accordingly, the need for improving the matching accuracy is also increasing. Therefore, the necessity of keeping the projection magnification at a predetermined value has become extremely high. At present, the magnification of the projection optical system is adjusted to such an extent that the magnification error can be neglected by adjusting the magnification when the apparatus is installed. However, in order to sufficiently cope with the high density of VLSI, it is necessary to correct the magnification error when the environmental conditions change, such as a slight change in atmospheric pressure in the clean room during the operation of the device. It is also necessary to correct magnification fluctuations that occur when the lens system itself changes in temperature due to absorption of exposure energy. Moreover, in general, changes in the image plane are accompanied by changes in environmental conditions such as atmospheric pressure fluctuations and changes in magnification due to temperature rise of the projection lens system itself. In a projection objective lens that requires high resolution, NA. Is large and the depth of focus is small, so even slight variations in the image plane must be sufficiently corrected.

In the projection optical system other than the conventional stepper, in order to correct the projection magnification, the object area mechanically changes the distance between the object surface and the projection lens, or moves the lens element in the projection lens in the optical axis direction. The method was taken. However, if the method of changing the optical member in the optical axis direction as described above is adopted in a device such as a stepper that requires extremely high-precision magnification and image plane setting, the mechanical eccentricity (shift, tilt) of the movable part is adopted. ), It is difficult to give a displacement while keeping the optical axis correct. As a result, the optical system including the object becomes non-coaxial, and there arises a disadvantage that a magnification distribution asymmetric with respect to the optical axis occurs on the image plane. In order to accurately set the magnification so that only an error of 0.05 μm or less occurs on the wafer, it is necessary to control the variation amount of the optical member to several μm to 1 μm or less including eccentricity (shift, tilt). There are many difficulties in realizing.

(Object of the Invention) The present invention has an object to provide a projection optical device which can correct the fluctuations of the magnification and the image plane with high accuracy without generating asymmetry of the optical performance, except for these drawbacks. .

(Summary of the Invention) Prior to the present invention, the present inventor firstly provided in a projection optical apparatus having a projection objective lens for projecting and exposing a pattern on a reticle onto a wafer, at least a lens interval in the projection objective lens. An air chamber isolated from the outside air is provided at one place, and a pressure controller for controlling the pressure of the air chamber is provided, and the pressure of the air chamber in the projection objective lens is changed by the pressure controller. An apparatus constructed so that the optical performance of the projection objective lens can be adjusted is disclosed in Japanese Patent Application No.
-137377. The present invention is based on the above-mentioned projection optical apparatus proposed above, and the value of the ratio between the magnification change amount and the image plane change amount of the projection objective lens by the air chamber whose pressure is controlled by the pressure controller, By configuring the projection objective lens to be approximately equal to the ratio value of the amount of change in magnification and the amount of change in image plane due to a predetermined factor, one air chamber having at least one lens interval is pressure-controlled by this. Then, the fluctuations of both the magnification and the image plane due to a predetermined factor are simultaneously corrected with high accuracy.

Now, in a pressure control air chamber formed by cutting off at least one lens interval in the projection objective lens from the atmosphere, the amount of change in magnification caused by a unit pressure change is determined by the lens interval that is integrally pressure controlled. Is the sum of the magnification change amounts at, and is represented by ΣΔX _c . Further, the amount of change in the image plane caused by the unit pressure change in this air chamber is also the sum of the amount of change in the image plane at each lens interval under pressure control, and is represented by ΣΔZ _c . Now, in the case of correcting the magnification of the projection objective lens and the fluctuation of the image plane caused by the atmospheric pressure fluctuation, the fluctuation generated in the entire system is from the reticle as the projection original plate to the wafer as the photosensitive object surface. Out of all air intervals of the above, which is equal to the fluctuation that occurs in the remaining air intervals other than the lens interval forming the above-mentioned air chamber that is shut off from the outside air and integrally pressure-controlled. The amount of change in magnification ΔX (P) that occurs in the remaining total air interval due to the unit pressure change of atmospheric pressure is the sum of the amount of change in magnification in each of the remaining total air intervals, and is expressed as ΔX (P) = ΣΔX _R. Be done. The image plane change amount ΔZ (P) is also the sum of the image plane change amounts at each of these total air intervals, and is represented by ΔZ (P) = ΣΔZ _R. Therefore, the ratio of the magnification variation due to atmospheric pressure variation and the imaging plane variation is defined as the variation ratio V (P), and V (P) = ΔZ (P) / ΔX (P) (1) is defined. On the other hand, C = ΣΔZ _c / ΣΔX _c (2) is defined as the correction ratio C, which is the ratio of the magnification change amount and the image plane change amount that can be changed by the air chamber that performs the integrated pressure control. Then, the variation ratio V (P) due to the atmospheric pressure variation
By providing the air chamber having the correction ratio C equal to, it is possible to simultaneously correct both the magnification change and the image plane change due to the atmospheric pressure fluctuation. That is, (1) (2)
From the formula, Therefore, the lens space in the projection objective lens may be combined to form an integrated pressure control air chamber.

Here, if the above equation (3) is rewritten, Therefore, this value α represents the ratio of the amount of change to the pressure change and the correction amount, and it suffices to apply the opposite pressure change to the atmospheric pressure change amount by the pressure that is α times the integral pressure control air chamber. It is meant and should also be called a control rate. That is, if the pressure in the control air chamber is inversely reduced or increased by α · ΔP with respect to the atmospheric pressure fluctuation amount ΔP, the resulting magnification change amount ΔX is ΔX = ΔP · ΔX (P) − α · ΔP · ΣΔX _c (5) = ΔP · {ΔX (P) −α · ΣΔX _c } From the equation (4), since α · ΣΔX _c = ΔX (P), ΔX = ΔP · {ΔX (P) −ΔX (P)}, so ΔX = 0 (5 ′), and the change in magnification is complete. Is corrected to.

Similarly, the corrected image plane change amount ΔZ is given as ΔZ = ΔP · ΔZ (P) −α · ΔP · ΣΔZ _c (6), and α · ΣΔZ _c = ΔZ (P) from the equation (4). Therefore, ΔZ = 0 (6 ′), and the fluctuation of the image plane is also corrected at the same time.

In the above description, the magnification and the imaging surface are corrected by the atmospheric pressure fluctuation. However, as described above, the factors causing the magnification and the imaging surface of the projection objective lens are not limited to the atmospheric pressure fluctuation. There is a change in temperature of the lens itself due to a change in environmental temperature or absorption of exposure energy. Regarding the environmental temperature of the projection optical device, it is possible to maintain a steady state with considerable accuracy, but it is difficult to compensate for the temperature change of the lens itself due to absorption of exposure energy.
According to the present invention, it is possible to accurately and simultaneously correct the fluctuations of the magnification and the image plane caused by the temperature change of the lens itself caused by the exposure energy irradiation.

That is, the magnification change amount per unit incident energy of the entire projection objective lens system is ΔX (E), and the image plane change amount is ΔZ.
Assuming that (E), the variation ratio V (E), which is the ratio of the amount of change in magnification due to the temperature change due to the absorption of the exposure energy of the lens and the amount of change in the image plane, is V (E) = ΔZ (E) / ΔX (E) Defined as (7). Therefore, the lens spacing is combined so that the correction ratio C by the integrated pressure control air chamber shown in the formula (2) becomes equal to the fluctuation ratio V (E) due to the exposure energy absorption of the lens shown in the formula (7). Just do it.

That is, It is sufficient to form the pressure-controlled air chamber so that Here, by rewriting by multiplying the denominator numerator on the left side of the equation (8) by ΔE and the denominator numerator on the right side by ΔP, Therefore, this value α'is also to be called a control rate, like α in Eq. (4).

Therefore, in this case, when the exposure energy to the lens changes by ΔE, the pressure in the pressure control air chamber is changed to −α ′ ·
By changing only ΔP, the corrected magnification change amount ΔX is expressed as ΔX = ΔE · ΔX (E) −α ′ · ΔP · ΣΔX _c, and from Equation (9), α ′ · ΔP · ΣΔX _{Since c} = ΔE · ΔX (E), ΔX = 0 and the magnification change is completely corrected.

Similarly, the corrected image plane change amount ΔZ is expressed as ΔZ = ΔE · ΔZ (E) −α ′ · ΔP · ΣΔZ _c, and ΔZ = 0 is obtained by using the equation (9). Obviously, the image plane can also be corrected at the same time.

(Example) Hereinafter, the present invention will be described based on Examples of the present invention. FIG. 1 is a lens arrangement view showing an example of a projection objective lens used for a stepper, and a predetermined pattern on a reticle (R) is reduced and projected onto a wafer (W) by this objective lens. In the figure, rays showing the conjugate relation of the on-axis object point between the wafer and the reticle are shown. This objective lens is a reticle
It is composed of a total of 14 lenses L ₁ , L ₂ , ... L _{14 in} order from the (R) side, and the distance between each lens, the reticle (R), and the wafer.
Between (W) and a, b, c, ..., from the reticle side in order
There are a total of 15 air intervals of o. Table 1 shows the specifications of this objective lens. Where r is the radius of curvature of each lens surface, D is the center thickness and air gap of each lens, and N is the refractive index of each lens with respect to the i-line (λ = 365.0 nm), and the leftmost number in the table is the reticle side. It represents the order from. Further, D ₀ represents the distance between the reticle (R) and the frontmost lens surface, and D ₃₁ represents the distance between the final lens surface and the wafer (W).

Now, in this objective lens, air intervals a, b, ... O
If the atmospheric pressure of each is changed by +137.5 mmHg, the relative refractive index of each air space changes to 1.00005, the magnification change at this time, and the image plane or reticle.
The change in the conjugate plane with (R) is shown in Table 2. However,
The change in magnification ΔX is expressed by the amount of movement μm after the change in atmospheric pressure at each air interval when the image point that forms an image at a position 5.66 mm away from the optical axis when there is no change in atmospheric pressure on the image plane, and the change in atmospheric pressure The case where there is no image formation, that is, the case where the image is projected larger on a predetermined wafer surface (enlargement) is shown as a plus sign.
Further, the change ΔZ of the image plane is shown as the change of the image formation point on the axis, and the case of moving away from the objective lens is shown as a positive sign. Both values are in μm.

The projection optical apparatus according to the first embodiment of the present invention, which uses the projection objective lens having the above characteristics, blocks four continuous lens intervals from the tenth space j to the thirteenth space m from the atmosphere and communicates with each other. To control the pressure integrally,
Thus, the fluctuations of both the magnification and the image plane due to the fluctuation of the atmospheric pressure are corrected at the same time.

Here, in four lens intervals j, k, l, and m as air chambers for performing pressure control, the magnification change amount ΣΔX _c , the imaging plane change amount ΣΔZ _c, and the unit pressure of atmospheric pressure that occur with respect to the unit pressure change. The respective values of the magnification change amount ΔX (P) and the image plane change amount ΔΣ (P) that occur with respect to the change in the air space of the entire system excluding the pressure control air chamber are calculated from Table 2, and are as shown in Table 3 below. . In the table, the correction ratio C by the pressure controlled air chamber and the fluctuation ratio V (P) by the atmospheric pressure fluctuation are also shown.

In such a configuration, the correction ratio C is 0.929 [= C / V (P)] with respect to the fluctuation ratio V (P), which are substantially equal to each other, and the equations (5) and (5 ′) and As shown in equations (6) and (6 '), both the magnification variation and the image plane variation should be corrected at the same time. Here, the control rate α shown in the equation (4) is the control rate for the image plane variation given on the left side of the equation (4) and the control rate for the magnification variation given on the middle side of the equation (4). The average value of and is α = 0.62. Therefore, the atmospheric pressure fluctuation amount is +137.5 mmH as in the state shown in Table 2.
Substituting each value into the equation (5) for the case of g, ΔX = 0.374−0.62 × 0.63 = −0.017. This value is 2% or less with respect to the magnification change amount +1.004 when no correction is made in the entire system, and it can be seen that the value can be sufficiently corrected. On the other hand, substituting each value into the equation (6), ΔZ = 5.78−0.62 × 9.05 = 0.169. This value is about 1% with respect to the image plane change amount +14.83 in the case where no correction is made in the entire system, and it is clear that the correction can be performed extremely well.

FIG. 2 simultaneously achieves magnification correction and image plane correction by controlling the pressure of the integrally formed air chamber by blocking the four lens intervals in the projection objective lens from the atmosphere as described above. FIG. 1 is a schematic configuration diagram of a projection optical device according to a first example which is capable of performing. The projection objective lens (1) projects the pattern on the reticle (R) uniformly illuminated by the illuminating device (2) onto the wafer (W) placed on the stage (3) in a reduced scale. In the projection objective lens (1),
Space j, 11th space k, 12th space 1 and 13th space m
The four air chambers (J, K, L, M) corresponding to (1) are cut off from the atmosphere connected by the communication part (11a), and the pressure is controlled through the pipe (11) as a pressure control space. The space where the pressure changes with the atmospheric pressure is omitted from FIG. 2 in order to avoid complication of the drawing. The pressure control space is connected by a pipe (11) to a pressure controller (12) provided outside the objective lens. And the pressure controller (1
Air having a constant pressure is constantly supplied from the pressurized air supply unit (4) to the unit (2) through the filter (13), and is exhausted by the exhaust unit (8) as necessary. On the other hand, a pressure sensor (14) for detecting the internal pressure of the air chamber is provided on the side surface of the air chamber, and the output signal is sent to the calculator (5). A measured value of atmospheric pressure is input to the computing unit (5) from the measuring unit (6). The calculator (5) has a magnification change amount Σ per unit pressure in the air chamber in the pressure control space.
ΔX _c , the image plane change amount ΣΔZ _c, and the magnification change amount ΔX (P) and the image plane change amount ΔZ (P) per unit pressure in the entire system excluding the pressure control space are stored. The value determines the control rate α shown in equation (4).
Then, the computing unit (5) calculates the variation amount ΔP of the atmospheric pressure with respect to the reference state based on the input signal from the measuring unit (6), and sets the pressure control amount necessary for this, that is, the control ratio of the opposite sign to the atmospheric pressure variation amount. A pressure control signal corresponding to the multiplied value −k · ΔP is sent to the pressure controller (12). Then, the pressure controller (12) appropriately changes the amount of inflow of air from the pressurized air supplier (4) and the amount of outflow to the exhaust device (8) according to the signal from the computing unit (5) to control the pressure. The pressure in the air chamber is -k
Change P only. By such a series of operations, the pressure of the pressure control air chamber is controlled according to the change of atmospheric pressure fluctuation with time, and the magnification of the projection objective lens and the image plane are always kept constant.

In the above-described first embodiment, four continuous lens intervals from the tenth space to the thirteenth space are integrated pressure control air chambers, and the other lens intervals are all configured to be capable of changing the pressure together with the atmospheric pressure. It is also possible to shield some or all of the lens spacing without pressure control from the atmosphere and seal. For example, in the configuration of the first embodiment, the lens interval corresponding to the fourteenth space n can be sealed from the atmosphere. In the case of the second embodiment as described above, each change amount, the correction ratio, and the variation ratio are shown in Table 4 as in Table 3.
Shown in.

As shown in Table 4, since the pressure controlled air chamber is the same as in the first embodiment, ΣΔX _c , ΣΔZ _c and the correction ratio C are the same as those in Table 3, and are caused by the atmospheric pressure change in the entire system. The respective values of the magnification variation amount ΔX (P) and the imaging plane variation amount ΔZ (P) differ from the respective values in Table 3 by the respective variation amounts in the fourteenth space n. Therefore, the variation ratio V (P) is also different from that in Table 3. In this case, the correction ratio C is 1.063 [= C / V (P)] with respect to the fluctuation ratio V (P), and the ratio of the fluctuation ratio to the correction ratio is 1 as compared with the case of the first embodiment. It is approaching. Here, if the control rate α shown in the equation (4) is the average value of the control rate for each variation, then α = 0.59. Therefore, similarly to the case of the first embodiment, if the respective values are substituted into the equations (5) and (6) and the resulting variation amount is calculated, ΔX = 0.382−0.59 × 0. 63 = 0.010 ΔZ = 5.16−0.59 × 9.05 = −0.18. This magnification variation ΔX is 1% without correction, and the image plane variation ΔZ is only about 1% without correction, and it is clear that both are extremely well corrected.

The projection optical apparatus according to the second embodiment is not particularly shown because it is different from the apparatus according to the first embodiment shown in FIG. 2 only in that the fourteenth space is sealed off from the atmosphere. Further, in the case of the second embodiment, since the values of the fluctuation amounts and control rates occurring in the entire system are different, the stored values and calculated values in the calculator (5) are naturally different, but the operation of each member is substantially the same. is there.

In the first and second embodiments, the fluctuation of the magnification and the image plane due to only the atmospheric pressure fluctuation is corrected, but in reality, the projection objective lens itself absorbs the exposure energy as described above. Since the temperature changes, the magnification and the image plane may change accordingly. For this purpose, in addition to the exposure energy required for exposing the wafer, it is desirable to give a constant exposure energy to the projection objective lens itself. That is, by keeping the energy incident on the projection objective lens constant in a unit time, it is possible to eliminate the fluctuation of the magnification and the image plane caused by the exposure energy.

Here, a method of keeping the exposure energy applied to the projection objective lens constant per unit time will be described in detail. As a unit time, in practice, a sufficiently short time compared with the saturation time of the magnification change and the image plane change may be set. The shorter the unit time, the higher the magnification and the accuracy of the image plane tend to be. Although the saturation time varies depending on the device, it is approximately several minutes to several tens of minutes, so it is sufficient to select a value between several tens of seconds and several minutes as the unit time. In the above method, the magnification and the image plane change due to the incident energy, and it is used after it is in a saturated state.Therefore, when operating a stepper that is not in use again, it is necessary to wait until the magnification is saturated. Become. In order to reduce this waiting time, it is convenient to first give more incident energy per unit time as the warm-up time than when using it, and to change the magnification and the image plane in a short time.

The energy that enters the projection optical system in a unit time is affected by the brightness of the light source, the transmittance of the reticle, the reflectance of the wafer, etc., but the most fluctuating time is that the shutter opens within the unit time and the illumination light It is the ratio of the time of incidence on the projection optical system (hereinafter represented by τ). Therefore, it is most important to keep this τ value constant in order to compensate the magnification error. For example, the time τ for processing one wafer during the standard operation of the stepper is used as the unit time. Τ at the time of steady exposure operation is given by the following equation.

Here, t1 is a time required for wafer exchange, t2 is a wafer alignment time, t0 is an exposure time per one shot, tc is a stepping time, and N is a number of shots per one wafer. Since the shutter is opened and the exposure energy is incident on the projection objective lens only during the exposure time, Nt0 per wafer is obtained. Whenever the wafers are being processed one after the other, the repetition is always the same and τ does not change. However, if the wafer is not continuously supplied for some reason or if the device fails, τ will be small because the time will usually remain with the shutter closed, and the magnification will be reduced when wafer exposure is restarted. And a change in the image plane occurs. Therefore, when the normal exposure operation is stopped, the shutter is opened at a constant ratio to prevent the reduction of τ so that the exposure energy is incident on the projection objective lens. Here, the opening / closing operation of the shutter may be determined as follows in order to maintain τ in equation (10). That is, the time for determining that the apparatus has stopped the steady exposure operation is t3. During this time, the shutter is closed. Next, a time t4 for keeping the shutter in the open state is necessary to prevent the decrease of τ. Then, the shutter is operated so as to satisfy τ = t4 / (t3 + t4). Therefore, t4 is given by t4 = τ · t3 / (1−τ). At this time, if τ in Eq. (10) is used, a decrease in τ can be avoided.

FIG. 3 is a diagram showing an example of a change with time of opening and closing of such a shutter. The open state of the shutter is shown at a high level, and the closed state of the shutter is shown at a low level. This is an example in which the unit time T is set to the wafer exchange time t1, the wafer alignment time t2, and the exposure time t0 repeated N times and the stepping time tc. Since (t3 + t4) is the unit time T for calculating τ, the shorter the processing time, the higher the accuracy as described above.
There is no problem if it is set below the value of the denominator of equation (10). (N3
If the exposure operation does not return to the steady state even after the lapse of + t4) time, the decrease of τ can be prevented by repeating (t3 + t4) n times. In this example, the calculation of t3, t4, τ and the determination that the steady operation has stopped may be performed by an electronic circuit, or the operator may determine and input the respective numerical values. Further, since τ = t4 / (t3 + t4) is a term to be controlled, it goes without saying that the same effect can be obtained by dividing t3 and t4 into i pieces. The example shown in the lower part of FIG. 3 is a case of being divided into two.

That is, when the shutter closing time t3i and the shutter opening time t4i for each divided part are Should be satisfied. The value of this denominator is equal to the unit time T.

Now, FIG. 4 is a schematic configuration diagram of the third embodiment according to the present invention, and the inside of the projection objective lens is shown as a sectional view. In the figure, members having the same functions as those in the first embodiment are designated by the same reference numerals. In this third embodiment, by controlling the pressure of a part of the lens spacing in the projection objective lens,
The magnification and the image plane are simultaneously corrected due to the temperature change of the projection objective lens and the environmental temperature change caused by the absorption of the exposure energy. The fourteen lenses L ₁ , L ₂ , ..., L ₁₄ constituting the objective lens system are respectively the first
Support lens barrel (101), second support lens barrel (102), ...
It is supported by a fourteenth support lens barrel (114). By stacking these 14 support lens barrels, the inner lens barrel is substantially formed, and these are formed into the outer lens barrel (20).
Are integrally housed and supported by and are fixed by a retaining ring (21). 1st lens L ₁ to 14th lens L
The first support barrel for supporting _14, respectively (101) - 14
The support lens barrel (114) forms 13 lens spaces B to N in the lens barrel, and these lens spaces B to N are formed.
Correspond to the air intervals b to n shown in FIG. 1, respectively. Here seventh support barrel for supporting a seventh lens L ₇ (1
07) and the eighth support barrel (10) for supporting the eighth lens.
In 8), through holes (107a) and (108a) for communicating the adjacent air chambers are formed. The sixth support barrel for supporting a sixth lens _{L 6} (10
6) and ninth support barrel for supporting a ninth lens _{L 9} (10
According to 9), the three lens spaces G, H and I are integrally shielded from the atmosphere to form one air chamber,
The pressure of the closed air chamber is controlled through the pipe (11) connected to the pressure controller (12). Also,
The other lens spaces B to F and J to N are defined by the first supporting lens barrel (101) to the seventh supporting lens barrel (107) and the ninth supporting lens barrel (109) to the fourteenth supporting lens barrel (114), respectively. It is sealed from the atmosphere and kept at a constant pressure.
Since the lens barrel structure is as described above, only the lens supporting lens barrels at both ends of the air chamber to be integrally sealed may be sealed with the outer lens barrel by a sealing member such as an O-ring.

In the structure of the third embodiment as described above, all the lens spaces other than the three lens spaces G, H, and I for performing integrated pressure control among the lens spaces in the projection objective lens are sealed to the atmosphere. Therefore, the changes in the magnification and the image plane caused by the atmospheric pressure fluctuation can be almost ignored.
Therefore, it is possible to correct other factors, for example, variations in magnification and image plane due to temperature change of the lens itself due to absorption of exposure energy. Therefore, the magnification change amount ΣΔX _{c, the} image plane change amount ΔΣZ _c , and the correction ratio C in the three lens spaces G, H, and I forming the pressure control air chamber are calculated from the above-described second value. It is as shown in Table 5.

Therefore, according to the third embodiment, it is possible to correct the factors that cause the magnification and the image plane variation with a variation ratio of about -13. For example, in general, when the projection objective lens absorbs the exposure energy and the temperature rises, the image plane moves toward the objective lens, that is, the image plane changes in the negative direction, and the magnification is a small positive or negative value. Although it tends to fluctuate, in the third embodiment, by decreasing the pressure in the pressure control air chamber, a positive magnification change and a negative image plane change occur at a ratio of −1: 13. Therefore, it is possible to equally correct the negative image plane change and the positive magnification change due to the temperature rise of the objective lens due to the absorption of the exposure energy.

It should be noted that changes in the magnification and the image plane when the projection objective lens itself absorbs the exposure energy and rises in temperature are largely different depending on the material of the objective lens. It is necessary to measure accurately, and it is desirable to configure the pressure controlled air chamber by combining the lens spaces so as to have the correction ratio C closest to the fluctuation ratio V (E) obtained by this. Further, the control rates α and α ′ are not necessarily the average values of the respective control rates for the magnification and the image plane as in the first and second embodiments described above. It is considered effective to adopt the control rate of. Furthermore, in the third embodiment described above, all lens spaces except the lens space for pressure control are sealed, but the entire lens system may be structured so that only a part of the lens space is sealed and the rest can change in pressure with atmospheric pressure. Magnification and imaging plane variations due to atmospheric pressure fluctuations in N may be negligible, and it is appropriate within the scope of the present invention to find an optimal combination of pressure control space and sealed space for each individual lens type. It could easily be done by a trader.

By the way, N ₂ contained in air as atmospheric pressure so far,
Only the total pressure has been handled without considering the partial pressure of each gas such as O ₂ , CO ₂ , H ₂ O .... However, since it is important to control the refractive index of air in the present invention, normally, only N ₂ is used instead of air, or the partial pressure of each gas is controlled under a constant total pressure to change the refractive index of air. It is naturally included in the present invention to do so.

(Effects of the Invention) As described above, according to the present invention, the projection objective and the projection surface of the stepper are prevented from fluctuating due to a change in atmospheric pressure or a temperature change of the lens itself due to absorption of exposure energy. It is possible to perform correction with high accuracy without giving mechanical movement to members in the system and thus without causing asymmetric optical performance. Further, since the exposure of the wafer surface is always stably performed and the overlay matching is performed with high accuracy, it greatly contributes to the manufacture of semiconductor elements such as VLSIs, which are becoming higher in density.

[Brief description of drawings]

FIG. 1 is a lens configuration diagram of a projection objective lens for a stepper according to an embodiment of the present invention, FIG. 2 is a schematic configuration diagram of a first embodiment of a projection optical apparatus according to the present invention, and FIG.
FIG. 4 is a diagram showing opening / closing of a shutter for exposure energy control applicable to the second embodiment, and FIG. 4 is a schematic configuration diagram of the third embodiment. (Explanation of symbols of main parts) R: projection original plate (reticle) W: photosensitive object (wafer) L ₁ , L _{2 to} L ₁₄ ... Lenses a, b to o ... Air spacing B, C to N ... … Lens space 1 …… Projection objective lens 12 …… Pressure controller

Claims (1)

[Claims] 1. An illumination system for illuminating a reticle on which a pattern to be projected and exposed is formed, and a projection optical system in which each of a plurality of optical elements is incorporated in a lens barrel with a predetermined air gap in the optical axis direction. And a stage for holding a photosensitive substrate onto which a projection image of the reticle pattern projected by the projection optical system is held, wherein the projection optical system communicates some air spaces therein. Correction unit ΣΔ between the amount of change in magnification ΣΔXc of the projection optical system and the amount of change in image plane ΣΔZc caused by a unit change in pressure inside the air chamber.
Zc / ΣΔXc is a change amount of magnification ΔX and a change amount of image plane ΔZ caused by a change in environmental conditions around the projection optical system or a temperature change due to partial absorption of exposure energy of the projection optical system. To be almost equal to the ratio ΔZ / ΔX,
Both of the air gaps constituting the air chamber are combined; further, both the magnification variation and the image plane variation of the projection optical system caused depending on the change of the environmental condition or the absorption state of the exposure energy. The projection optical apparatus is provided with a pressure controller for controlling the pressure in the sealed air chamber based on a change in the environmental condition or an absorption state of exposure energy so as to simultaneously correct the above.