JPH0512849B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a projection exposure apparatus and method used, for example, in manufacturing semiconductor devices.

In recent years, semiconductor devices such as IC, LSI, VLSI
Progress in miniaturization and high integration of patterns such as these has been remarkable, and we are moving toward an era in which pattern line widths are 1 to 2 μm or less. In order to advance the miniaturization and higher integration of patterns, what is required is printing performance that allows printing of fine patterns of 1 to 2 μm or less, and alignment performance that accurately aligns each pattern across multiple processes. An object of the present invention is to provide a projection exposure apparatus that has the following properties and causes fewer defects on wafers.

In order to meet these demands, various projection exposure apparatuses (reduction lens projection method, equal-magnification lens projection method, mirror projection method, etc.) have been developed. These 1~
The resolution of a projection exposure system that can print fine patterns of 2 μm or less is the effective F number of the projection optical system.
It is determined by Fe and the wavelength λ of the printing light, and its depth of focus is generally defined as ΔZ=±2λFe ² . Currently, in the case of reduction projection exposure equipment with a resolution (printing performance) of about 1 μm, the wavelength of the printing light is 0.436 μm, and Fe=
It is equipped with an optical system of about 1.4. Therefore, the corresponding depth of focus is approximately ±1.7 μm. For this reason, it is essential for these projection exposure apparatuses to have a focus adjustment mechanism to reliably image the pattern formed on the photomask onto the wafer surface, and various methods are available. has been done.

There are two main focus adjustment mechanisms currently available:
It is classified as The first is the TTL method, which detects the position of the wafer through the projection optical system and always adjusts the wafer to the best imaging position of the projection optical system.The second is the fixed distance method, which always adjusts the wafer to a constant distance from the projection optical system. It is a method. Since the first TTL method requires a complicated optical system and also imposes various restrictions on the design of the projection optical system, most projection exposure apparatuses currently employ the second constant distance method. Fixed distance method uses air nozzle,
There are methods using non-contact electric micro and optical methods, etc., and both have a wafer position detection accuracy of about ±0.3 μm, and when combined with a position adjustment mechanism, always satisfy the depth of focus for the projection optical system. This makes it possible to set the wafer at a certain distance that is possible.

By the way, in the constant distance method, the wafer is always set at a constant distance from the projection optical system, so in order to guarantee the accuracy of setting the wafer at the best imaging position of the projection optical system, it is necessary to set the wafer at the best imaging position of the projection optical system. The prerequisite is that it does not change. However, when the projection optical system is irradiated with printing light to print a mask pattern onto the wafer, the projection optical system absorbs a portion of the printing light, and the heat generated thereby causes temperature changes in the projection optical system. This causes a change in optical performance such as refractive power of the projection optical system. Therefore, the optical characteristics of the projection optical system change, such as the best imaging position of the projection optical system moving.

The present invention has been made in view of the above circumstances, and its purpose is to provide a semiconductor manufacturing method and an exposure apparatus that can compensate for changes in the optical characteristics of a projection optical system. ,
In a semiconductor manufacturing method in which a photomask is irradiated with light and an image of a circuit pattern of the photomask is printed onto a wafer by a projection lens system, the wafer and a photodetector are selectively inserted into a projection optical path of the projection lens system. a step of detecting, with the photodetector, information on the amount of irradiation light per unit time that enters the projection lens system via the photomask when the photodetector is inserted into the projection optical path; detecting time information regarding the time when the system is irradiated with light and the time when the system is not irradiated with light, and the optical arrangement of the projection lens system with respect to the wafer or the projection with respect to the photomask based on the detected light amount information and the time information. It is characterized by having a step of adjusting the optical arrangement of the lens system. A second invention of the present application also provides an illumination system for irradiating light onto a photomask, a projection lens system for projecting an image of a pattern of the photomask onto an object to be exposed, a moving stage on which the object to be exposed is placed, and the stage. a light amount detection means provided above for detecting the amount of light irradiated per unit time of light incident on the projection lens system via the photomask; and irradiation for detecting the light irradiation time and the light irradiation interval time to the projection lens system. The method further comprises a history detection means, and an adjustment means for adjusting an optical arrangement of the projection lens system with respect to the wafer or an optical arrangement of the projection lens system with respect to the photomask based on detection outputs of the light amount detection means and the irradiation history detection means. It is characterized by

Hereinafter, the present invention will be explained based on embodiments shown in the drawings.

In FIG. 1, 1 is the main body base, and 2 is the XY stage. The XY stage 2 is mounted on the main body base 1 and moves within a desired plane by a well-known mechanism. A wafer 3 has a photosensitive layer, and is fixed on the XY stage 2 by a chuck (not shown). 4 is a projection lens barrel, and a reduction type projection lens 5
to accommodate. 6 is a photomask, which includes a pattern for manufacturing a semiconductor circuit. Reference numeral 7 denotes a photomask stage, which is fixedly installed at the top of the lens barrel 4 and has the function of fixing the photomask 6.

Next, reference numeral 8 denotes a column, which is fixed to the main body base 1, and has a fixed side of the focus adjustment mechanism 9 on its upper part. The focus adjustment mechanism 9 is composed of, for example, a rack and pinion or a helicoid, and the movable side is connected to the lens barrel 4, so that when the mechanism 9 is operated, the lens barrel 4 moves along the projection optical path. Reference numeral 10 denotes a lighting unit, which is fixed to the upper part of the pillar 8 via another pillar. The lighting unit 10 includes a light source 11,
It houses a shutter 12, a condenser lens 13, and an optical path bending mirror 14. The shutter 12 is moved by the action of a rotary solenoid activated by a drive signal to block or open the illumination optical path.
When the illumination optical path is opened, the light beam emitted from the illumination light source 11 is converged by the condenser lens 13 and reflected by the mirror 14.
After being reflected, the photomask 6 is irradiated with the light.

On the other hand, 17 is an air nozzle, which is held at the lower end of the lens barrel 4 and can be arranged at the periphery of the projection optical path, or can freely move into and out of the optical path. Air nozzle 1
7 is connected to an air micrometer main body (not shown), which serves to precisely measure the distance between the upper surface of the wafer 3 and the final surface of the projection lens 5. Note that other methods mentioned earlier in the specification can also be used to measure the distance.

Further, 18 is a photodetector, which is fixed on the XY stage 2, and can be caused to enter the illumination area by operating the XY stage 2. The photodetector 18 has a function of measuring the pattern projection light transmitted through the photomask 6 to measure the transmittance of the photomask. Note that for a photomask whose transmittance is already known or a mask whose transmittance is known from another measuring device, the conditions may be set using a transmittance setting switch 21 provided in the controller 20, and this switch 21 It is preferable to install it alongside 18.
A cable 22 has a function of transmitting signals from the controller 20 to the main body of the apparatus.

In the apparatus having the above structure, when the printing process is repeated, the focus of the projection lens 5 shifts. That is, when the pattern printing light from the illumination unit 10 passes through the projection lens 5, the projection lens 5 absorbs a part of the printing light and heat is generated in the projection lens 5.

The refractive index of the projection lens has temperature dependence, and as heat is generated in the projection lens 5, the temperature of the projection lens 5 changes, and accordingly, the temperature of the projection lens 5 changes.
The refractive index of changes. For this reason, the refractive power of the projection lens 5 changes and the pin position of the projection lens 5 moves. The amount of change in focus over time Δl due to the irradiation of the projection lens 5 with printing light is experimentally determined as Δl=K・τ・
It can be expressed as E・to/t. Here, K is the inherent focus change coefficient of the projection lens 5, and τ is the photomask 6.
, E is the amount of light emitted from the illumination unit 10 per unit time, to is the total open time of the shutter 12, and t is the total exposure interval time. Note that if the focus change coefficient K of the projection lens 5 is experimentally measured for one projection lens, the same K can be used in devices incorporating the same projection lens.

Reference numeral 20' in FIG. 2 is a microprocessor, which constitutes the core of the controller 20, and stores the above-mentioned conditional expression regarding Δl and the focus change coefficient K in the storage device M in advance. Note that, in addition to electrical means, mechanical means such as a cam can also be used as a storage method. Then,
The photomask 6 used in this process is set on the mask stage 7, the XY stage 2 is moved, the photodetector 18 is positioned in the projection optical path, the shutter 12 is opened, and the printing light transmitted through the photomask 6 is measured by the photodetector 18. , a signal corresponding to the amount of transmitted light τ·E is input from the detection circuit 18' to the microprocessor 20'. After that, the shutter 12 is closed, the XY stage 2 is moved to set the wafer 3 at the printing position, and the shutter 12 is closed again.
is opened and the pattern of the mask 6 is printed onto the wafer 3. At this time, since the focus change amount Δl during the first printing is "O", the distance between the projection lens 5 and the wafer 3 measured by the air jet from the air nozzle 17 matches the design value, and The focus adjustment mechanism 9 is operated to set the focus position so that the value is reached.

When the baking of wafer 3 is completed, the XY stage 2
is moved and this wafer is replaced with another wafer,
The XY stage 2 moves again to set the next new wafer 3 at the printing position. On the other hand, the shutter drive control circuit 12' inputs the opening time of the shutter 12 and the exposure interval time to the microprocessor 20'.
The microprocessor 20' separately integrates the sums each time the shutter is opened and the exposure interval occurs, and stores them in the storage device M as an exposure history to/t. Prior to exposing the next wafer 3, the microprocessor 20 calculates the value of Δl by calculations based on K, τ·E, and to/t. This value of Δl is input to the focus adjustment control circuit 9', and the focus adjustment mechanism 9 operates.
The adjustment operation is continued by slightly moving the lens barrel 4 until the amount of change detected by an air micrometer (not shown) becomes equal to the calculated amount of change in focus. Therefore, the wafer 3 is automatically positioned at the best imaging position of the projection lens 5 at all times. In addition,
In this example, the lens barrel 4 is moved to simplify the mechanism, but a structure in which the wafer 3 or photomask 6 is moved in the optical axis direction may also be adopted.

As described above, according to the present invention, inconveniences caused by fluctuations in optical characteristics that occur when a projection optical system is used continuously can be corrected without requiring complicated equipment such as the TTL system. Further, according to the present invention, not only can such a device be realized at low cost, but also no major changes are required to other parts of the device. Note that the present invention is applicable not only to projection exposure apparatuses for semiconductor manufacturing, but also to projection exposure apparatuses in other fields.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of a projection exposure apparatus according to the present invention, and FIG. 2 is a diagram showing a signal processing system of the apparatus shown in FIG. 2... XY stage, 3... Wafer, 5... Projection lens, 6... Photo mask, 9... Focus adjustment mechanism, 10... Lighting unit, 17... Air nozzle, 18... Photo detector, 20... Controller , 20'...microprocessor.

Claims (1)

[Scope of Claims] 1. In a semiconductor manufacturing method in which a photomask is irradiated with light and an image of a circuit pattern of the photomask is printed onto a wafer by a projection lens system, the wafer and a photodetector are placed in the projection optical path of the projection lens system. selectively inserting the photodetector into the projection optical path, and detecting, by the photodetector, information on the amount of irradiation light per unit time that enters the projection lens system via the photomask when the photodetector is inserted into the projection optical path. a step of detecting time information regarding a time when the projection lens system is irradiated with light and a time when the projection lens system is not irradiated with light; and a step of detecting time information regarding a time when the projection lens system is irradiated with light and a time when the projection lens system is not irradiated with light; A semiconductor manufacturing method, comprising the step of adjusting the arrangement or the optical arrangement of the projection lens system with respect to the photomask. 2. An illumination system that irradiates the photomask with light, a projection lens system that projects an image of the pattern of the photomask onto the illumination object, a movable stage on which the illumination object is placed, and a movable stage that is provided on the stage and that displays the photomask. a light amount detection means for detecting the amount of irradiated light per unit time of light incident on the projection lens system through the projection lens system; an irradiation history detecting means for detecting the light irradiation time and the light irradiation interval time for the projection lens system; and the light amount An exposure apparatus comprising an adjusting means for adjusting an optical arrangement of the projection lens system with respect to the wafer or an optical arrangement of the projection lens system with respect to the photomask based on detection outputs of the detection means and the irradiation history detection means. 3. The exposure apparatus according to claim 2, wherein the adjusting means includes means for moving the projection lens system in the optical axis direction. 4. The exposure apparatus according to claim 2, wherein the adjusting means includes means for moving the wafer in the optical axis direction. 5. The exposure apparatus according to claim 2, wherein the adjusting means includes means for moving the photomask in the optical axis direction.