JPH07122693B2 - Exposure equipment for VLSI manufacturing - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure apparatus for manufacturing a VLSI which can correct the magnification of a projection optical system with high accuracy and easily.

[0002]

2. Description of the Related Art A reduction projection type exposure apparatus (hereinafter referred to as a stepper) has been introduced to many production sites of VLSI devices in recent years and has brought great results. One of its important performances is overlay matching accuracy. can give. An important factor that affects the matching accuracy is a magnification error of the projection optical system. The pattern line width used in VLSI is becoming finer year by year, and along with this, there is a strong need for improvement in matching accuracy. Therefore, the need to maintain the projection magnification at a predetermined value has become extremely high. At present, the magnification of the projection optical system is adjusted to such a degree that the magnification error can be ignored once it is adjusted when the apparatus is installed. However, due to a magnification error when environmental conditions change, such as a slight temperature change during operation of the device or a slight atmospheric pressure change in the clean room, or the projection optical system absorbs a part of the exposure energy during the exposure operation. There is an increasing demand for fine adjustment of the magnification in order to correct the magnification error that occurs or to obtain higher matching accuracy than in the initial setting.

Conventionally, in a projection optical system other than a stepper, the distance between an object (reticle) and a projection lens is mechanically changed to change the projection magnification, or the lens element in the projection lens is moved in the optical axis direction. The method was taken.

[0004]

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 which requires extremely high-precision magnification setting, a mechanical movable part is used. Due to the eccentricity (shift, tilt), it is difficult to give a displacement while keeping the optical axis correct. Therefore, the optical system including the object is not coaxial, and there is a drawback that a magnification distribution asymmetric with respect to the optical axis occurs on the image plane. Also, 0.0 on the wafer
In order to accurately set the magnification so that only an error of 5 μm or less occurs, it is necessary to control the change amount of the optical member to several μm to 1 μm or less including eccentricity (shift, tilt). A great deal of difficulty is involved.

Therefore, the present invention provides an exposure apparatus for manufacturing a VLSI, which can correct a magnification error caused by partial absorption of exposure energy with high precision and easily without generating an asymmetric magnification distribution. The purpose is to

[0006]

In order to solve the above problems, the present invention provides an illumination means (2) for uniformly illuminating a reticle (R) having a pattern to be projected, and a plurality of optical elements (L _{1 to} L). ₁₄ ) and a plurality of air gaps (a to o), and a projection optical system (1) for imaging and projecting the pattern of the reticle, and a photosensitive substrate (W) exposed by the projected pattern are placed. The stage (3) and a selected air space in the projection optical system are made into an airtight chamber that is shielded from the outside air, and the refractive index of the gas in the airtight chamber is forcibly changed to slightly change the imaging characteristics of the projection optical system. And an adjusting device (12) for controlling the ultra LS for exposing the VLSI device on the photosensitive substrate.
I It is applied to an exposure apparatus for manufacturing.

In the present invention, the rate of change in magnification of the projection optical system, which occurs when the refractive index is changed by the adjuster (12) among a plurality of air intervals (a to o) in the projection optical system (1). Is relatively large and the rate of change of the image plane position is relatively small, the air gap (h) is set to the airtight chamber (1
A projection optical system set as 0), and means for detecting information regarding exposure energy accumulated in the projection optical system during projection exposure of the reticle pattern, and correction of magnification variation of the projection optical system caused by the exposure energy. The calculation means (5) for calculating a value corresponding to the refractive index of the gas in the airtight chamber (10) necessary for the operation based on the detected information, and the refractive index of the gas in the airtight chamber (10) are A control system (feedback system including the pressure sensor 14) that feedback-controls the regulator (12) is provided so as to be equivalent to the calculated value.

[0008]

According to the present invention, at least one space shielded from the outside air is formed in a portion of the projection optical system through which light rays pass, and the projection magnification is changed by changing the atmospheric pressure of the space. I am trying. That is, it is found that a space that is shielded from the outside air is formed in a portion where the light rays of the projection optical system pass, and that the projection magnification can be accurately changed by changing the atmospheric pressure of the space, and based on this technology, It is possible to correct various magnification errors.
However, the relationship between the change in atmospheric pressure and the change in magnification in the space also differs depending on the projection magnification and the lens type, and also in a certain lens system depending on in which space the pressure is changed. Also, when the atmospheric pressure of the space is changed, not only the magnification changes but also the image plane position generally changes,
The degree of the influence also differs depending on the space.

Therefore, one of the lens intervals of the existing projection objective lens is constructed as an air chamber which is shielded from the outside air, and when the pressure in the air chamber changes by a unit pressure from the time when the initial magnification is set, the magnification is changed. It is assumed that the amount, that is, the amount of displacement of the predetermined off-axis image point on the image plane is ΔX ₁ . Further, it is assumed that the pressure in the air interval other than this air chamber changes approximately equal to the atmospheric pressure, and the magnification change amount is ΔX with respect to the change in the unit pressure of the atmospheric pressure in the entire interval excluding this one air chamber. Suppose At this time, if there is a change in the atmospheric pressure by ΔP, the pressure in the sealed air chamber is ΔP ₁
However, the magnification change can be corrected by satisfying the relationship of ΔP ₁ · ΔX ₁ + ΔP · ΔX = 0 (1).

However, even if the magnification can be corrected by the pressure change in only one air chamber, it is difficult to simultaneously correct the fluctuation of the image plane. Therefore, it is desirable to newly provide a second air chamber that is shielded from the outside air. In this case, if the image plane change amount by the first air chamber with respect to the change of the unit pressure is ΔZ ₁ , the magnification change amount by the second air chamber is ΔX ₂ , and the image plane change amount is ΔZ ₂ , then ΔP ₁ · ΔX ₁ + ΔP ₂ · ΔX ₂ + ΔP · ΔX = 0 ··· (2) ΔP ₁ · ΔZ ₁ + ΔP ₂ · ΔZ ₂ + ΔP · ΔZ = 0 to meet the two conditions at the same time By changing the pressure in the air chamber by ΔP _{1 and} the pressure in the second air chamber by ΔP _2, it is easy to correct the fluctuations of both the magnification and the image plane position that occur in the remaining air chamber. It will be possible.

With respect to the variation of the image plane position, for example, if the automatic focus detection device is always operated to move the stage for supporting the wafer precisely up and down, the variation of the image plane position should be taken into consideration. Instead, as described above, only one air chamber is provided and the pressure control of this air chamber is performed, so that only the magnification correction is performed.

[0012]

EXAMPLES The present invention will be described below 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 (W) by this projection objective lens. In the figure, light rays are shown which represent the conjugate relationship of the on-axis object point between the wafer and the reticle. This projection objective lens has L ₁ , L ₂ , and
It is composed of a total of 14 lens elements L ₁₄ , and the distance between each lens element and the reticle (R) and the wafer (W),
A total of 15 air intervals a, b, c, ..., O are formed from the reticle side. Table 1 shows the specifications of this projection 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 i-line (λ
= 365.0 nm), the leftmost number in the table indicates the order from the reticle side. Also, 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 projection lens, if the atmospheric pressures of the air intervals a, b, ... O are changed by +137.5 mmHg, the relative refractive index of each air interval is 1.00.
The change in magnification and the change in position of the imaging plane, that is, the conjugate plane with the reticle (R), are as shown in Table 2. However, the change in magnification ΔX is the moving amount of the image point, which is imaged at a position 5.66 mm away from the optical axis when there is no change in atmospheric pressure on the image forming plane, in μm after the change in atmospheric pressure at each air interval.
It is expressed in units, and the case where there is no fluctuation in the atmospheric pressure, that is, the case where the projection is larger on the image plane, that is, the predetermined wafer surface (enlargement) is shown as a positive 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 projection lens is shown as a positive sign. Both values are in μm.

[0014]

[Table 1]

[0015]

[Table 2]

From Table 2 above, the rate of change in the image plane position due to the eighth space h is the smallest, and the eighth space h is optimal for setting the air space for magnification correction, and the fourteenth space n It can be seen that the change in magnification due to is the smallest and is most suitable for the correction of the image plane position. Therefore, the eighth space h and the fourteenth space n
Are defined as air chambers that are shielded from the outside air, and magnification control and image plane correction are performed by controlling the pressure in these air chambers. Then, the eighth space h and the fourteenth space n
Spaces other than the above shall not change from the atmosphere and change with atmospheric pressure. Rewriting equation (2) above, the conditions for correcting the magnification and the image plane due to atmospheric pressure changes in the projection lens are: ΔPh · ΔXh + ΔPn · ΔXn + ΔP · ΔX = 0 .. 3) ΔPh · ΔZh + ΔPn · ΔZn + ΔP · ΔZ = 0. Where ΔPh is the pressure change in the eighth space h, ΔXh
Is the amount of change in magnification with respect to the unit pressure change in the eighth space h, ΔZ
h is the change in the image plane with respect to the unit pressure change in the eighth space h, ΔPn is the pressure change in the fourteenth space n, and ΔXn is the fourteenth space.
Magnification change per unit pressure change of space n, ΔZn is the first
4 is a change in image plane with respect to a unit pressure change in the four spaces n.
Further, ΔP is a change in atmospheric pressure, ΔX is a change in magnification with respect to a unit pressure change in all spaces other than the space h · n, and ΔZ is a space h ·
It is a change in the image plane with respect to a unit pressure change in all spaces other than n. The unit of pressure change is mmHg, and the unit of magnification change, image plane change, and image plane change is μm / mmHg.

Table 2 shows that the pressure change in each space is +137.5 mm.
Since the magnification change and the image plane change at Hg are described, ΔXh, ΔXn, ΔX, ΔZh, ΔZ in the equation (3) are described.
When n and ΔZ are obtained by this, the formula (3) can be rewritten into the following form. 9.53 × 10 ^-4 × ΔPh−5.82 × 10 ⁻⁵ × ΔPn + 6.41 × 10 ⁻³ × ΔP = 0 (4) −2.19 × 10 ⁻⁴ × ΔPh + 4.51 × 10 ⁻³ × ΔPn + 1 .04 × 10 ⁻¹ × ΔP = 0 When ΔPh and ΔPn satisfying the expression (4) are obtained, ΔPh = −8.2 ΔP and ΔPn = −23.5ΔP are obtained. As a more specific example, when the atmospheric pressure fluctuates by -10 mmHg, the eighth space is pressurized by 82 mmHg and the 14th space is pressurized by 235 mmHg. Both can be corrected.

FIG. 2 shows the pressure control of the air chamber as described above.
The projection light enables magnification correction and image plane correction by
It is a schematic block diagram of a learning device. The projection objective (1) is illuminated
On the reticle (R) uniformly illuminated by the light device (2)
The pattern and the photosensitive substrate placed on the stage (3)
Then, reduction projection is performed on the wafer (W). Projection objective
In (1), the eighth air gap h and the 14th air gap shown in FIG.
Two independent air chambers (10) corresponding to air spacing n
(20) is formed, and each air chamber (10, 20) is
Pipes (11, 21) to the outside of the objective lens
Connected to the pressure controllers (12) and (22) provided
ing. And each pressure controller (12, 22) has a filter
Pressurized air supply through filters (13) and (23)
(4) Air with a constant pressure is constantly supplied. one
On the side of each air chamber, the pressure
Sensors (14) and (24) are provided and output
The signal is sent to the calculator (5). The calculator (5) has a total
A measurement value signal of atmospheric pressure is also input from the measuring instrument (6). Calculation
As described above, the air chamber (10, 2,
Magnification change ΔX per unit pressure in 0)₁, ΔX₂
And image plane change amount ΔZ₁, ΔZ ₂And unit pressure of atmospheric pressure
The amount of change in magnification ΔX per force and the amount of change in image plane ΔX are
It is remembered. And the computing unit (5) is a measuring instrument
The atmospheric pressure change amount ΔP is detected by the signal from (6),
In order to satisfy both conditions of equation (2), each air chamber
Required pressure change ΔP₁, ΔP₂Calculate each pressure controller
Signals for making these pressure changes at (12, 22)
Emit. In each pressure controller (12, 22), a calculator
Based on the signal from (5), flow through a needle valve, etc.
Amount control is performed and ΔP is applied to each air chamber.₁, ΔP₂Pressure change
give. In addition, the atmospheric pressure measuring instrument is equipped with the stepper.
Can also be used as a barometer for light wave interferometer (not shown)
Noh.

In this way, a constant projection magnification is always maintained with respect to atmospheric pressure fluctuations, and highly accurate matching as a stepper is stably achieved. In the above embodiment,
The signal from the pressure sensor provided in each air chamber is fed back to the pressure controller via the arithmetic unit, and the pressure controller is always operated.However, a human reads the measured value by the pressure sensor and the measuring instrument, The pressure change required for each air chamber may be calculated, and each pressure controller may be manually operated as needed.

Further, a temperature sensor (7) is provided near or inside the lens barrel of the projection objective lens (1), and this output signal is sent to the arithmetic unit (5) so that the arithmetic unit only changes the atmospheric pressure. Of course, it is possible to correct the variation around the projection objective lens or the temperature change of the projection objective lens itself. As described above, if there are at least two spaces in the optical path of the projection optical system in which the atmospheric pressure can be independently controlled, changes in both the projection magnification and the image plane position can be controlled. At this time, if the method of moving the lens element in the projection lens in the optical axis direction or changing the distance between the reticle and the projection lens is used, it is not always necessary to provide two or more spaces for controlling the atmospheric pressure. When the stepper has a function of detecting and following a change in the position of the image plane, the atmospheric pressure control of the space may be performed only for one space by paying attention to only the change in magnification. When it is desired to limit the space for controlling the atmospheric pressure to a single stepper that does not have the ability to detect the position of the image plane, it is advisable to select a space with a small change in the image plane, such as the eighth space h shown in FIG. Be done. For a space where the atmospheric pressure is not controlled, it may be better to make a hole in the lens barrel so that the same fluctuation as the atmospheric pressure fluctuation of the outside air occurs, and in some cases a completely sealed air chamber should be provided. Is possible.

As in the embodiment shown in FIG. 2, a specific lens interval in the projection objective lens is formed in an air chamber which is shielded from the outside air, and the pressure in this air chamber is controlled to finely adjust the magnification. However, there are various methods of operating such a magnification fine adjustment means. First, as in the embodiment shown in FIG. 2, the factors affecting the stepper magnification change and the extent of the influence are investigated in advance, and the variation amount of each element (for example, the ambient temperature is measured without directly measuring the projection magnification). This is a method in which the change amount and the fluctuation amount of the atmospheric pressure) are measured to predict the amount of change in the magnification, and the magnification fine adjustment means is activated. In this case, it is desirable to configure a servo system that measures each influencing element in real time and automatically adjusts the magnification immediately as shown in FIG. 2, but it is also possible to manually adjust the magnification based on the measured value. .

Further, in general, the projection lens of the stepper absorbs a part of the exposure energy and its temperature rises. For this reason, the projection lens continues to be exposed to exposure light for a long time,
If the exposure operation is continuously performed for a long time, the magnification may slightly change. Therefore, the energy stored in the projection lens is directly measured to finely adjust the magnification (pressure controller 12).
It is desirable to provide feedback to the air chamber 10).
It should be noted that, instead of directly measuring the accumulated energy in the projection lens, the relationship between the exposure time and the continuous operating time and the change in magnification is previously checked by experiments and calculations, and the information of the exposure time and the continuous operating time is used to finely adjust the magnification. It is preferable to use a servo system that feeds back to and corrects the magnification error.

Further, the stepper may be provided with a projection magnification measuring function, and the measurement result may be fed back to the magnification fine adjusting means. If the magnification can be measured in real time, it is possible to use a servo system that immediately adjusts the magnification. If the measurement takes time, display the measured value once,
The magnification may be finely adjusted manually based on the value. It is also easy to set up a sequence in which the magnification is adjusted based on the measured value and the magnification is checked again. Since the projection magnification can be known by actually exposing the wafer with a stepper and measuring the wafer, this information can also be fed back to the magnification adjusting means.

By the way, up to now, only the total pressure has been handled without considering the partial pressure of each gas such as N ₂ , O ₂ , CO ₂ , H ₂ O, etc. contained in air as atmospheric pressure. However, since it is important to control the refractive index of air in the present invention,
It is naturally included in the present invention that 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.

Since the present invention provides a method that enables fine adjustment of the magnification, it is obvious that it is useful not only for keeping the magnification constant but also for intentionally changing the magnification. is there.

[0026]

As described above, according to the present invention, since the projection magnification can be adjusted with high accuracy and easily, the magnification error caused by the absorption of the exposure energy by the projection optical system during the exposure operation can be prevented. Since the correction can be sequentially performed, a high matching accuracy can be maintained, and it is possible to provide an exposure apparatus for manufacturing a VLSI, which greatly contributes to improvement in the productivity of the VLSI.

[Brief description of drawings]

FIG. 1 is a lens configuration diagram of a projection objective lens used in an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of an embodiment of an exposure apparatus for manufacturing VLSI according to the present invention.

[Explanation of symbols]

 1 Projection Objective Lens 10, 20 Air Chamber 12, 22 Pressure Controller R Reticle W Wafer

Claims (2)

[Claims] 1. A projection optical system, which comprises an illuminating means for uniformly illuminating a reticle having a pattern to be projected, a plurality of optical elements and a plurality of air gaps, and a projection optical system for image-projecting the pattern of the reticle. And a stage on which the photosensitive substrate exposed by the pattern is placed and an airtight chamber in which the selected air gap in the projection optical system is shielded from the outside air, and the refractive index of the gas in the airtight chamber is forcibly changed. An ultra-LSI for exposing an ultra-LSI element on the photosensitive substrate, which comprises an adjuster for minutely changing the image formation characteristic of the projection optical system.
In the manufacturing exposure apparatus, the information corresponding to the exposure energy accumulated in the projection optical system during the projection exposure of the reticle pattern is directly detected or previously obtained by experiment and calculation.
Accumulated exposure energy and variation in magnification of the projection optical system
Of the projections that may occur during the projection exposure,
Means for detecting information corresponding to a magnification error of the shadow optical system ; magnification of the projection optical system generated by the exposure energy
Calculating means for calculating a value corresponding to the refractive index of the gas in the airtight chamber necessary to correct an error based on the detected information; and a refractive index of the gas in the airtight chamber for the calculated value And a control system for feedback-controlling the adjuster so as to be equivalent to the exposure apparatus for VLSI manufacturing. 2. A projection optical system, which comprises an illuminating means for uniformly illuminating a reticle having a pattern to be projected, a plurality of optical elements and a plurality of air gaps, and a projection optical system for image-projecting the reticle pattern. And a stage on which the photosensitive substrate exposed by the pattern is placed, and an airtight chamber in which the selected air space in the projection optical system is shielded from the outside air, and the pressure of the gas in the airtight chamber is forcibly changed to A VLSI manufacturing exposure apparatus for exposing a VLSI element onto the photosensitive substrate, comprising: an adjuster for minutely changing an image forming characteristic of a projection optical system, wherein the projection optical system is used during projection exposure of the reticle pattern. the information corresponding to the error of the projection magnification changes due to exposure energy stored in the system, determined in advance by experiments and calculations
Accumulated exposure energy and double the projection optical system
Means for detecting based on the relationship with the rate fluctuation ; a value corresponding to the pressure of the gas in the hermetic chamber necessary to correct the magnification error of the projection optical system due to the exposure energy, And a control system that performs feedback control of the regulator so that the pressure of the gas in the airtight chamber becomes equivalent to the calculated value. Exposure equipment for VLSI manufacturing.