JPS6198314A - Automatic focusing mechanism - Google Patents

Abstract

PURPOSE:To compensate focus variation due to environmental variation without a printing test by moving a reference surface for focusing in the optical axis direction on the basis of an output of a sensor means for detecting the environmental conditions of a pattern transfer device. CONSTITUTION:An offset compensating function part of an automatic focusing means is constituted so that the outputs of an atmospheric pressure sensor 31, a temperature sensor 32, a humidity sensor 33, and a focus detector 34 are inputted to a microprocessor 35, and after executing operation, the miroprocessor 35 calculates a distance from the original point of the coordinates of an air sensor to a wafer surface and inputs the moving distance of a Z axis to a Z axis driver 36. An offset value for indicating the reference position of focusing is set up in an air sensor. The offset value is set up so that a best focusing position found by a printing test is the reference focusing position. When a fixed offset value is determined, an automatic focusing function part moves an wafer in the optical axis (Z axis) direction by the device 36 so that an offset reading value is set up to a required value on the basis of the output of the air sensor 34.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to an autofocus mechanism that automatically corrects a focus position according to environmental conditions such as atmospheric pressure. This mechanism is suitable for application to, for example, an IC pattern printing and transfer apparatus, particularly a projection type printing apparatus that uses a projection optical system to transfer a mask pattern onto a wafer.

[Description of Prior Art] A projection type printing device is a printing device that prints a pattern image formed on an original plate (for example, an IC drawn on a reticle).
A projection optical system transfers a pattern (pattern) onto a photoreceptor (for example, a wafer coated with a photosensitive agent), and the resolution line width is determined by the brightness (hereinafter referred to as FNO) of the projection optical system.

In recent years, as IC patterns have become finer, IC pattern printing and transfer equipment has also progressed from the conventional contact and proximity methods to projection methods.
There is a shift toward lens projection optical systems (with small NO values).

Normally, the critical resolution (L) and depth of focus (D) of the projection method are L=1.6λF, where λ is the printing wavelength.
NO D = ±λFN, O' (based on λ/8), but as shown in the above equation, in order to increase the resolution, the wavelength must be shortened or the FNO value must be decreased, which increases the resolution. The depth of focus becomes shallow.

For example, the projiexi (°＞”
:0I0"11°"*Ma! ! ! &LyTGl”
(436 nm) and FNO of 1.43 is the mainstream, but the depth of focus at this time is only ±0.9 μm. Various autofocus methods have been devised to place the wafer within this small depth of focus, and the accuracy is as high as ±0.1 μm to ±0.5 μm.

However, most current autofocus systems set a reference plane at a certain distance from the end face of the lens barrel of the projection optical system, and maintain a constant distance from this reference plane to the wafer surface. When the focus position (focus reference plane) is constant, it is possible to place the wafer surface at the focus position with extremely high accuracy, but if the focus position changes for some reason, the wafer surface cannot be placed at the focus plane. Put it away.

Factors that can be considered to change the focus position of the projection optical system are ■ changes in the temperature of the air between the reticle and the wafer and changes in the temperature of the glass material in the projection optical system, ■ atmospheric pressure of the air between the reticle and the wafer, and (2) the humidity of the air between the reticle and the wafer.
Among the components of the projection optical system that can change due to the temperature change of the air and glass material described in 1. The focus position of the projection optical system changes as the components change. The change in focus position due to such a temperature change is coefficient-wise the largest among the above three factors. Conventionally, the amount of change in the focus position has been suppressed by controlling the environment of the device and the temperature inside the device by means such as near conditioning.

On the other hand, for changes in the atmospheric pressure of the air (■) and the humidity of the air (■),
ens) has conducted detailed research on Abride Obedix 19
1967 No. 1 (APPLiEDOPT I C819
As published in 67 No. 1), it is known that the refractive index of the air changes when the atmospheric pressure or humidity of the air changes - in this case, the refractive index of the glass material does not substantially change. The relative refractive index at the refractive surface changes from .

The absolute refractive index of air is nA, and the absolute refractive index of 111 particles is nG.
, where n is the relative refractive index of glass and air, n = n c
/ n A − , and when nA changes by ΔnA, the change in n ωΔn is given by Δn−=n(,・ΔnA from nA key 1. Normally, n(, is about 1.5, so Δn= 1.5ΔnA, and the effect that the change in the refractive index of air has on the relative refractive index change between glass and air is 1.5 times the change in the refractive index of the air itself.For example, if the atmospheric pressure changes by 5 mmHg, the refractive index of air will change. changes by approximately i, ax io, which corresponds to the relative refractive index of glass and air of 2.7X 10, and varies depending on the individual properties of the projection optical system, but the focus change is 0.5 to 1. This value corresponds to .5 μm.As can be seen from the above-mentioned depth of focus value of ±0.9 μm, this value is a sufficient amount of change to cause problems in terms of the performance of the apparatus.

As mentioned above, in projection printing devices, changes in focus occur due to changes in the external environment (temperature, atmospheric pressure, humidity, etc.), but conventionally, focus changes are corrected by performing a printing test about once every three days. Was.

[Object of the Invention] An object of the present invention is to automatically correct changes in focus of the projection optical system in a so-called constant distance autofocus mechanism that adjusts the distance from the projection optical system to the surface of the photoreceptor to a predetermined value. By doing so, it is possible to correct changes in focus due to environmental changes without performing a burn-in test.

In addition to being caused by the external environment, the temperature change described above also occurs due to a temperature increase in the projection optical system due to burning light or a temperature increase due to heat generation in the device including the projection optical system, and may occur during transient conditions such as when the device starts operating. However, in order to automatically correct changes in the focus position due to changes in the temperature of the projection optical system, the applicant stores the relationship between temperature and focus position in advance in memory, and the projection optical system He previously proposed an exposure device that detects the temperature of ::i, reads out the focus position corresponding to that temperature from memory, and corrects the focus position (Japanese Patent Application No. 58-230578).
issue). The present invention differs from the above-described prior application in that it does not directly detect temperature changes in the projection optical system, but instead detects external environmental conditions including temperature.

[Explanation of Examples] Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 shows a cross section of an optical system portion of a printing apparatus to which an autofocus mechanism according to an embodiment of the present invention is applied. In the figure, 1 is a reticle, 2 is a projection optical system, and 3 is an autofocus mechanism. In the figure, autofocus mechanism 3
An air sensor is used as the focus detector (34 in FIG. 2), 4 is the nozzle end face of the air sensor, 5 is the wafer, and 6 is the coordinate origin of the air sensor.

FIG. 2 is a block diagram of the offset correction function section of the autofocus mechanism 3 shown in FIG.
The output is inputted to the microprocessor 35, and the microprocessor 35 executes the calculations described below.
1, the distance from the air sensor coordinate origin 6 to the surface of the wafer 5 is calculated, and the Z-axis movement distance is input to the Z-axis drive device 36.

Next, the present invention will be explained in detail using FIGS. 1 and 2. The light that passes through the reticle 1 and is diffracted is transmitted to the projection optical system 2.
A reticle pattern is imaged on the 5 surface of the wafer. The air sensor 34 senses the back pressure of the air blown out from the air nozzle 4, and moves the air sensor 34 from the air sensor coordinate origin 6 to the wafer 5.
The distance to the surface is determined by electrical processing (hereinafter, this distance measurement value is referred to as an offset read value). On the other hand, an offset value indicating a focus reference position is set in the air sensor. Typically, this offset value is
The best focus position found by performing . . . is set as the focus reference position.

Once a certain offset value is determined, the autofocus function section shown in FIG.
The wafer 5 is moved in the direction of the optical axis (two axes). When the focus position of the projection optical system 2 is constant, the wafer 5 surface can be maintained at the focus position of the projection optical system 2 by the above autofocus function. However, as mentioned above, when the temperature, air pressure, and humidity change, the focus position of the projection optical system 2 changes, so even if the offset value is kept constant, the surface of the wafer 5 and the focus plane of the projection optical system 2 do not match.

In the present invention, an air pressure sensor 31 and a temperature sensor 32 are provided on the device.
A humidity sensor 33 is arranged to sense changes in atmospheric pressure, temperature, and humidity, and a microprocessor 35 calculates the amount of change in the focus position. The amount of change in the focus position ΔS is calculated as follows, where ΔSp, ΔST, and ΔSv are the amount of change in the focus position due to atmospheric pressure, temperature, and humidity, respectively. do. Here, ΔP, ΔT, and ΔV are atmospheric pressure and temperature i!, respectively. Ii1 degree change, A, B, and C are constants. Although the constants A, B, and C may be determined by calculation, it is more practical to determine them by experiment. Also, in the above formula, ΔP,
ΔS is determined by a linear equation of ΔT and ΔV. Theoretically, the influence of higher-order terms can be considered, but ΔP, Δ
Since the values of T and ΔV are actually small, a linear equation is sufficient.

The microprocessor 35 calculates an offset value to correct the measured focus position change, and controls the Z-axis drive device 3 so that the offset read value becomes the offset value.
6, the wafer 5 is moved in two axial directions. Focus detector 34 detects the offset read value and inputs it to microprocessor 35. The microprocessor 35 compares the offset read value and the offset value, and if the difference is greater than the allowable amount, the Z-axis drive device 36 moves the wafer 5 again, and the same operation is repeated thereafter.

[Modifications of Examples] Note that the present invention is limited to the above-mentioned Examples.
It can be implemented with appropriate modifications. for example,
j In the above embodiment, an air sensor is used as a device for detecting the vertical position of the wafer surface, but a non-contact electric micrometer may be used for this, or an optical method such as a method using laser beam scanning or television image processing may be used. A device using a conventional detection method may also be used. Furthermore, in the embodiment described above, a predetermined calculation formula is used to determine the focus position or focus position correction, but the focus position corresponding to environmental conditions such as atmospheric pressure, temperature, humidity, etc. is stored in memory in advance. , the focus position may be read using environmental condition information.

Further, in the above description, the case where the present invention is applied to a semiconductor printing device is explained, but the present invention can also be applied to other pattern transfer devices such as a hologram creation device and a copying machine. Of course.

[Effects of the Invention] As described above, according to the present invention, the set position of the pattern transfer surface such as the wafer surface is corrected according to changes in atmospheric pressure, temperature, or humidity. picture,
Yo□(7)! (t:, l, m force, ka, wa, a, o
j, the pattern transfer surface can be made to match the focal plane of the projection optical system.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an optical system portion of a printing apparatus to which an autofocus mechanism according to an embodiment of the present invention is applied, and FIG. 2 is a block diagram of an offset correction function section of the autofocus mechanism in FIG. 1. be. 1 reticle, 2: projection optical system, 3: autofocus mechanism, 4: air nozzle end face, 5: wafer, 6: air sensor coordinate origin, 31: atmospheric pressure sensor, 32: temperature sensor, 33: humidity sensor, 34: focus Detector (air sensor), 35: Microprocessor, 36: Z-axis drive device.

Claims (1)

[Scope of Claims] 1. An autofocus mechanism that is used in a projection-type pattern transfer device using a projection optical system and focuses by aligning a pattern transfer surface of a photoreceptor with a predetermined focus reference surface, A sensor means arranged on the pattern transfer device to detect environmental conditions of the pattern transfer device, and a means for moving the focus reference plane in the optical axis direction based on the output of the sensor means to correct the focus position. An autofocus mechanism that is characterized by: 2. The autofocus mechanism according to claim 1, wherein the sensor means is one or both of an air pressure sensor and a humidity sensor. 3. The autofocus mechanism according to claim 1 or 2, wherein the focus position correction means calculates the position or movement amount of the focus reference plane based on a predetermined calculation formula. 4. A patent claim in which the focus position correction means includes means for storing in advance the position of the focus plane corresponding to the environmental condition, and means for reading out the focus plane corresponding to the output of the sensor means as the focus reference plane. Range 1 or 2
Autofocus mechanism as described in section.