JPS6332303A - Alignment device - Google Patents

Abstract

PURPOSE:To perform high-accuracy alignment when the alignment is performed by using light reflected by a reflection mirror by correcting an error in return position generated when the reflection mirror is returned after a wafer surface is shot by using the signal of a detecting means. CONSTITUTION:When the reflection mirror 13 is at its normal position as shown by a solid line, two alignment light beams of different wavelength forming images at a point P2 on the surface of the wafer 4 form images on points P1 and P2 on straight lines P1 and P0. Then, when the mirror 13 shifts from the normal position by an angle theta/2 and returns, one of two light beams of different wavelength forming an image at a point P'0 on the surface of the wafer 4 forms an image at a point P'1 on the surface of a reticle 1 and the other light beam forms an image at a point P'0. The difference in length between those segments P1P'1 and P0P'0 causes variation in offset value between the two light beams. For the purpose, the reflection position D' of, for example, luminous flux from a light source 14 based on the mirror 13 is detected 15 and the output of the detecting means 15 is utilized to adjust the offset between the two wavelengths. Consequently, the position error of the mirror 13 is corrected to prevent alignment accuracy from deteriorating owing to chromatic aberration at the time of use of plural wavelengths.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to an alignment device that aligns two objects in a predetermined relationship, and particularly in semiconductor manufacturing equipment, a first object such as a reticle or mask and a first object such as a wafer. 2
The present invention relates to an alignment device suitable for performing alignment with an object by providing a certain amount of gap or via a projection optical system.

(Conventional technology) Recent semiconductor manufacturing equipment has increased the density of integrated circuits.
There is a growing demand for finer electronic circuit patterns formed on wafer surfaces. Along with this, there is an increasing demand for highly accurate alignment between a reticle or mask (hereinafter referred to as a "mask") on which an electronic circuit pattern is formed and a wafer.

The present applicant has proposed an alignment device using an observation device in Japanese Unexamined Patent Publication No. 58-25638.

The same bulletin describes the projection optical system for projection exposure on the wafer surface.
He-
Light of a wavelength (442 nm) emitted from a Cd laser is used. Since the two wavelengths used at this time are approximately equal, by configuring the projection optical system mainly, approximately equal optical performance is obtained for light of both wavelengths.

In many cases, the diffracted scattered light signal obtained from the alignment mark on the wafer surface tends to become unstable due to the effects of uneven resist coating, variations in the step structure of the alignment mark, and the like.

Also, the distance between the wavelength for projection exposure and the wavelength for alignment.
When a multilayer resist is used as the resist applied on the wafer surface, the multilayer resist absorbs the alignment light and reduces the reflected light from the alignment mark on the wafer surface, resulting in a decrease in S/N ratio and a decrease in alignment accuracy. There were times when I did.

Therefore, in order to improve these drawbacks, it has been considered to perform alignment using a plurality of wavelengths to improve alignment accuracy.

In many exposure systems for semiconductor manufacturing, light beams of multiple wavelengths from an alignment illumination system are reflected by an optical element, such as a reflector, placed above the mask surface, and then incident on the mask surface via a projection optical system. . And in these devices,
The reflecting mirror is removed from the optical path of the alignment illumination system for each shot toward the surface of the sea urchin. However, since chromatic aberration generally remains in the projection optical system, errors in the return position of the reflecting mirror, such as angular errors, are the cause of deteriorating alignment accuracy even when a plurality of wavelengths are used.

(Problems to be Solved by the Invention) When performing alignment using light of a plurality of wavelengths and reflected by a reflecting mirror disposed above the reticle surface, the present invention aims to move the reflecting mirror to each part of the surface of the reticle. The purpose of the present invention is to provide an alignment device that always enables good alignment by correcting errors in the return position that occur when the lens is removed from the alignment optical path for each shot and returned after each shot using a signal from the detection means. do.

(Means for solving the problem) When projecting the first object illuminated by the illumination system onto the second object plane via the projection optical system, for alignment between the first object and the second object. In an alignment apparatus that illuminates an alignment mark provided on the first object through some optical elements of an alignment illumination system provided between the illumination system and the first object or in the illumination system, the optical The element is installed so as to be removable from the optical path of the alignment illumination system, and the first object and the second object are aligned using a signal from a detection means that detects the attitude of the optical element.

(Embodiment) FIG. 1 is a schematic diagram of a part of an optical system when the present invention is applied to an exposure apparatus for semiconductor manufacturing using a reduction projection optical system.

In the figure, 1 is a reticle, 2 is a projection optical system, 3 is a wavelength plate, and 4 is a wafer. Numerals 16 and 17 are light sources for alignment, and 16 of these are He-Ne lasers that emit light with a wavelength of 632.8 nm. Also, 17 is He-
It is a Cd laser and emits light with a wavelength of 442 nm. Reference numeral 13 denotes an optical element detachably provided in the alignment optical path above the reticle 1, and is made of, for example, a reflecting mirror.

In this embodiment, the reticle 1 is illuminated by an illumination system (not shown), and the circuit pattern on the reticle surface is projected and exposed onto the wafer surface at a predetermined magnification by the projection optical system 2.

In addition, the two lights with different wavelengths from the lights [16 and 17] were reflected by a half mirror 18, and further reflected by a reflecting mirror 13 which was designed to be removed from the optical path of the alignment illumination system when working on the surface of the sea urchin. The alignment mark on one side of the rear reticle is illuminated. The alignment mark on the reticle 1 is then reduced and projected onto the wafer surface by the projection optical system 2.

At this time, on the sea urchin surface 4, light with a wavelength of 442 nm and light with a wavelength of 6
The two lights of 32.8 nm are imaged together, that is, brought into focus. Further, the configuration is such that, for example, light having a wavelength of 442 nm is imaged on the reticle surface 1. In this case, the light with a wavelength of 632°8 nm will not form an image on the reticle surface 1 due to the chromatic aberration of the projection optical system.
The image will be focused on a point Po above.

In this embodiment, the alignment signal from the wafer surface 4 is detected using the aforementioned two wavelengths of light that are in focus,
The alignment signal from the reticle surface 1 is detected using one light beam having a focused wavelength (442 nm).

At this time, an e-wavelength plate 3 is placed near the pupil position of the projection optical system 2, and the reflected light for the reticle signal that is directly reflected from the reticle 1 and the reflected light for the wafer signal that has been reciprocated through the e-wavelength plate 3 are separated. The 90 degree linearly polarized light components are made different. As a result, each polarized light component is separated into two beams by the polarizing beam splitter 7, and a reticle signal and a wafer signal are detected independently.

That is, the reticle signal light is reflected by the polarizing beam splitter 7 and guided to the reticle signal charge detection system 10, and the wafer signal light having two wavelengths is transmitted through the polarizing beam splitter 7. Then divide it into two with half mirror 8,
One transmits light with a wavelength of 442 nm, and the other transmits light with a wavelength of 632.8 nm.
Wavelength 442 nm with filter 9 that does not transmit nm light.
The wafer signal photoelectric detection system 11 detects the light.

The other side is reflected by a half mirror 8, passes the light with a wavelength of 632.8 nm through a reflecting mirror 8°, and passes the light with a wavelength of 632.8 nm through a filter 9' that does not transmit the light with a wavelength of 442 nm. Detected. The alignment accuracy is improved by, for example, weighting the two signals from the wafer signal photoelectric detection systems 11 and 12, or by performing alignment using an average value.

By performing wafer signal detection at two wavelengths in this way, a stable signal can be obtained by averaging signals caused by variations in the step structure of the alignment mark 7 and the influence of diffracted and scattered light due to resist unevenness on the wafer surface. I have to.

Furthermore, in this embodiment, a certain amount of shift occurs between the two wavelengths due to axial chromatic aberration caused by the projection optical system. Therefore, by using a pre-prepared wafer at one wavelength or by using a reference mark, wafer signals are acquired separately at two wavelengths and offset is performed to correct the shift at this time.

In this embodiment, the reflecting mirror 13 is removed from the alignment illumination system for each shot of the wafer surface, and returned to its original position after the shot is completed.

For this reason, the angular error in the reproducibility of the reflecting mirror causes the offset value between the two wavelengths to change due to chromatic aberration caused by the projection optical system.

For example, if the reflecting mirror 13 is in the normal position as shown by the solid line in FIG. , direct aP
Image is formed on tPo. For example, if the projection optical system is a telecentric system, the points P1 and Po are imaged at equal distances from the optical axis of the projection optical system.

However, the position of the reflector 13 is at an angle θ from the normal position.
If it returns after shifting by
The light is focused on a point Pl° on the reticle surface 1, but the wavelength is 6.
The 32.8 nm light is focused on point P0.

At this time, if we calculate the distance between each point using the dimensions as shown in the figure, we get P, P,'=j2. tanθ1 P, Po'=uOtanθ1. This difference in length was calculated in advance as it is 2
This causes the offset value of two wavelengths to change.

Therefore, in this embodiment, the light source 14 and the detection means 5 are used to detect the angular error of the position of the reflecting mirror 13 from the normal position, for example, by detecting a mark provided on the back surface of the reflecting mirror 13, or The position of reflection of the light beam from the light source 14 by the reflecting mirror 13 is determined by detecting D' = 11 an θ.

Then, the output signal from the detection means 15 is used to adjust the offset between the two wavelengths. This causes reflection fi13
This corrects positional errors and prevents deterioration in alignment accuracy due to chromatic aberration when multiple wavelengths are used.

Although this example shows the case where light with two wavelengths is used, it is also possible to use light with two or more wavelengths and weight the signals obtained with the light of each wavelength, or to calculate the average value. Alignment may be performed by taking .

(Effects of the Invention) According to the present invention, when alignment is performed using a plurality of wavelengths via a removable reflector placed above the reticle surface, the return position, that is, the attitude of the reflector is detected, and the projection optical system is By properly correcting the offset caused by the return position error of the reflecting mirror due to the chromatic aberration of the system, an alignment device that enables highly accurate alignment has been achieved.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of a part of an optical system of an embodiment when applied to an exposure apparatus for semiconductor manufacturing using a projection optical system, and Fig. 2 shows the imaging position near the reticle surface of two wavelengths caused by chromatic aberration. FIG. In the figure, 1 is a reticle, 2 is a projection optical system, 3 is a wavelength plate, and 4 is a reticle.
is a wafer, 7 is a polarizing beam splitter 28, 18 is a half mirror, 9' is a filter, 10 is a reticle signal photoelectric detection system, 11° 12 is a wafer signal charge detection system, 1
3 is a reflecting mirror, 14 is a light source, and 15 is a detection means.

Claims (1)

[Claims] (1) When projecting the first object illuminated by the illumination system onto the second object plane via the projection optical system, a In an alignment apparatus that irradiates an alignment mark between the illumination system and a first object or through some optical elements of the alignment illumination system provided in the illumination system, the optical element is emitted from the optical path of the alignment illumination system. An alignment device, characterized in that the first object and the second object are aligned by using a signal from a detecting means that is removably installed and detects the attitude of the optical element.