JPH03215929A - Alignment device - Google Patents

Abstract

PURPOSE:To cut down the length of an optical path in the air thereby enabling an alignment to be made with high precision by a method wherein the effect of color aberation in a projection optical system is averted by making use of multiple reflection members arranged in the space on the reticle side of the projection optical system so that an wafer surface and a reticle surface may have an almost cooperative relation through the intermediary of the multiple reflection members. CONSTITUTION:An image of a wafer alignment mark 10 is made on the part near a reticle alignment mark 2a on a reticle surface while the image of relative positions of both marks or the wafer alignment mark 10 is made on a reference mark arranged on the space on the reticle 2 side of a projection lens system 1 or an image pick-up element 12 surface to detect said relative positions. In order to make an alignment of a wafer 3, multiple reflection members 7 are arranged in the space on the reticle 2 side so that the wafer alignment mark 10 and the reticle alignment mark 2a or the wafer alignment mark 10 and the reference mark or the image pick-up element 12 may have a substantially conjugated relation to each other. Through these procedures, the image of the wafer alignment mark 10 can be successfully made on the part near the reticle alignment mark 2a thereby enabling the alignment to be made with high precision.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an alignment device for aligning a reticle and a wafer in semiconductor manufacturing equipment, and in particular to an alignment device that is illuminated with first wavelength light as exposure light. Through a projection lens system that reduces and projects the pattern on the reticle surface onto the wafer surface, a second wavelength light having a different wavelength from the first wavelength light is used to place the pattern between the reticle and the wafer or in the semiconductor manufacturing equipment. The present invention relates to an alignment device that detects the positional relationship between a reference mark and a wafer.

(Conventional Technique m) Recently, as semiconductor devices have become highly integrated, there has been a strong demand for miniaturization of electronic circuit patterns formed on wafer surfaces. Among these, reduction projection exposure equipment (steppers), which are promising for finer patterns, require finer projection resolution line widths and higher precision alignment of the reticle and wafer to achieve this. has been done.

The present applicant has previously proposed a highly accurate alignment device, for example, in Japanese Patent Laid-Open Nos. 58-25638 and 63-32303.

There are various methods for aligning the reticle and wafer, but in principle the alignment pattern of both the reticle and wafer is observed simultaneously within the exposure area using exposure light through a projection lens system. This is the most preferable method as it does not cause any measurement errors since the exposure conditions are reproduced as they are.

(Problems to be Solved by the Invention) In general, when exposing a pattern on a reticle surface onto a wafer, it is necessary to prevent standing waves from being generated within the resist layer and to prevent deterioration of resolution. is set so that the reflectance for the exposure wavelength is low. Furthermore, if alignment is performed using the exposure wavelength, the alignment mark will be exposed, so generally a wavelength light different from the exposure wavelength is used as the alignment light.

In order to achieve high resolution, the exposure wavelength is usually in the ultraviolet region or a wavelength shorter than the ultraviolet region, and the longer wavelength in the visible region is used as the alignment wavelength.

The projection lens system at the crotch is designed to provide the best aberration correction when using the exposure wavelength when projecting the pattern on the reticle surface onto the wafer surface. Therefore, if alignment is performed through a projection optical system using alignment wavelength light, which generally has a long wavelength different from the exposure wavelength light, the wafer alignment mark on the wafer surface will be placed above the reticle surface (projection lens The image will be formed in a direction that is farther away than the system. This makes it difficult to observe both the reticle alignment mark and the wafer alignment mark on the reticle surface at the same time.
There was a problem that alignment accuracy decreased.

In addition, a wafer alignment mark image is formed at a position other than the reticle surface to detect the positional relationship with the reference mark, or a wafer alignment mark is formed on the image sensor surface and the wafer alignment mark image is formed on the image sensor surface. Even when alignment is performed by detecting the position, the optical path length to the imaging point is long, so it is susceptible to the adverse effects of, for example, air fluctuations, and there is a problem in that alignment accuracy decreases.

In addition, the influence of chromatic aberration of the projection lens system not only affects the difference in the imaging point of the wafer alignment mark, but also adversely affects various aberrations such as chromatic spherical aberration, which deteriorates the optical performance at the imaging point at the alignment wavelength. There was a problem with letting it work.

In the present invention, when aligning a wafer and a reticle through a projection lens system, a multiple reflection member is placed in a space on the reticle side of the projection optical system, and by using the multiple reflection member, chromatic aberration of the projection optical system can be reduced. (axial chromatic aberration), the wafer surface and reticle surface are brought into a substantially conjugate relationship via the multiple reflection member, and the optical path length in the air is shortened. The purpose of the present invention is to provide an alignment device that reduces the amount of stress and enables highly accurate alignment.

(Means for Solving the Problems) The alignment apparatus of the present invention projects a pattern on a reticle surface illuminated with light of a first wavelength onto a wafer surface. An image of the wafer alignment mark of the wafer is formed near the reticle alignment mark on the reticle surface using second wavelength light, and the positional relationship between the two or the image of the wafer alignment mark is formed on the reticle side of the projection lens system. When aligning the wafer by detecting the positional relationship between the reference marks or the image sensor surface, a multiple reflection member is placed in the space on the reticle side of the projection lens system. the wafer alignment mark and the reticle alignment mark are in a substantially conjugate relationship via the multiple reflection member, or the wafer alignment mark and the reference mark or the imaging device are in a substantially conjugate relationship via the multiple reflection member. It is characterized by the fact that

In addition, the present invention is characterized in that the wafer alignment mark is composed of a diffraction grating, and a set of diffracted lights of orders having the same absolute value and different signs among the diffracted lights from the wafer alignment mark are used.

(Embodiment) FIG. 1 is a schematic front view of an embodiment of the present invention applied to a reduced projection type exposure apparatus (stepper). FIG. 2 is a schematic side view of FIG. 1.

In the figure, numeral 2 denotes a reticle, and reticle alignment marks 2a for alignment with the wafer 3 are formed on an electronic circuit pattern and a part of its periphery. 1 is a projection lens system, which provides good aberration correction when reducing and projecting the pattern on the 2nd surface of the reticle onto the 3rd surface of the wafer using exposure wavelength light (for example, G-line, wavelength 436 nm), which is the first wavelength light. is designed to be done.

That is, the projection lens system 1 has aberrations corrected so that the reticle 2 and the wafer 3 have a good conjugate relationship with respect to the exposure wavelength. 4 is an XYZ stage on which wafer 3 is placed;
The drive is controlled in a predetermined direction. 5 is a surface plate on which the XYZ stage 4 is placed.

Reference numeral 6 denotes an illumination device that emits exposure light, which is disposed above the reticle 2 and illuminates the electronic circuit pattern on the surface of the reticle 2.

Each of the above elements 1 to 6 constitutes one element of the stepper.

Next, the alignment system will be explained.

11 is an alignment light source that emits long wavelength light (second wavelength light) different from the exposure wavelength light, for example, He-Ne.
A laser (wavelength: 632.8 nm) is used. 2l is a light splitter having a half mirror surface, and 22 is a mirror. Reference numeral 8 denotes an objective lens, which causes the alignment light 1 to emitted from the alignment light source 11 to be incident on a multiple reflection member 7 made of a glass block via a light splitter 21, a mirror 22, and a reticle 2. The multiple reflection member 7 has reflection surfaces 7a and 7b (thick lined portions in the figure) on part of the entrance surface and the exit surface, and is arranged in an area that does not block the exposure light flux shown by the dotted line ' in FIG. 2. . The multiple reflection member 7 reflects the alignment light from the wafer at least twice on at least one surface of the reflectors 7a and 7b. The alignment light incident on the multiple reflection member 7 is reflected multiple times on the reflection surfaces 7a and 7b and then exits, illuminating the wafer alignment mark 10 on the surface of the wafer 3 via the projection lens l. The alignment light incident on the wafer alignment mark 10 is reflected, and the reflected light reverses the original optical path and enters the projection lens system 1.

At this time, the image of the wafer alignment mark 1o is formed in two directions of the reticle 2 (in the direction away from the projection lens system I) due to the influence of the chromatic aberration of the projection lens system 1; however, in this embodiment, the image of the wafer alignment mark 1o is The alignment light is multiple-reflected through a multi-reflection member 7 having an appropriately configured shape, and then emitted, whereby an image 10a of the wafer alignment mask 10 is focused near the reticle alignment mark 2a on the reticle 2 surface. I try to visualize myself.

Both the image 10a of the wafer alignment mark 10 and the reticule alignment mark 2a formed on the two surfaces of the reticle are viewed by the imaging lens 8 via the mirror 22 and the light splitter 21, forming part of an observation system. An image is formed on the surface of the image sensor 12.

The wafer 3 and reticle 2 are aligned by observing both alignment marks 10a and 2a.

As described above, in this embodiment, the image 10a of the wafer alignment mark 10 is caused by the chromatic aberration of the projection lens system l.
By using the multiple reflection member 7 to form an image in the vicinity of the reticle alignment mark 2a on the two surfaces of the reticle instead of focusing the image at a position away from the surface, both alignment marks 10a and 2a can be observed well. This enables highly accurate alignment.

11 In particular, in this embodiment, when the aberration of the imaging light beam of the wafer alignment mark 10 becomes large due to the influence of the chromatic spherical aberration of the projection lens system l caused by the alignment light, the wafer alignment mark 10 is constructed from a diffraction grating. It's good to do that. It is preferable that the shape of the multiple reflection member 7 is configured so that the first-order diffracted lights (for example, ±1st-order diffracted lights) having the same absolute value and different sign from the diffraction grating intersect on the two surfaces of the reticle.

At this time, since one diffraction grating generates diffraction targets only in one-dimensional direction, only one-dimensional information can be obtained. Therefore, the third
As shown in the figure, patterns of diffraction gratings fob and 10c are arranged within the wafer shot region 13 on two lines that pass through the optical axis 1a of the projection lens system 1 and are perpendicular to each other. At this time, a diffraction grating fob is used to generate diffracted light in the sagittal direction of the projection lens thread 1. The longitudinal direction of the pattern 10c is aligned with the optical axis 1 of the projection lens system 1 as shown in FIG.
It is preferable to configure it so that it is parallel to a line perpendicular to a.

I2 Also, in this embodiment, when the wafer alignment mark 10 is composed of a diffraction grating, the reticle alignment mark 2a on the second surface of the reticle 12 has a pitch equal to the pitch of the diffraction grating of the wafer alignment mark 10 multiplied by the imaging magnification. It may also be composed of a diffraction grating. According to this, reticle 2
Since the intensity of the light passing through the reticle changes with a period corresponding to the pitch of the diffraction grating, alignment can be performed within the range below the pitch of the diffraction grating simply by detecting the light intensity of the light passing through the reticle alignment mark. can.

At this time, by moving the XYZ stage 4 or scanning the light receiving element to scan the image of the diffraction grating in the pitch direction of the diffraction grating, for example, if the position where the light intensity is maximum is detected, the relative change can be further detected. It can be detected with high precision.

Note that the direction of light incidence on the wafer alignment mark 10 may be as shown in FIG. 1, in which O-order light (light along the optical axis 1a direction) is made incident and ±1st-order light is detected. Conversely, the O-order light may be detected by inputting the ±1st-order light.

In this embodiment, if a glass block is used as the multiple reflection member 1, the imaging magnification between the wafer reticles of the alignment light and the imaging magnification of the exposure light between the wafer reticles may differ greatly. In this case, for example, as shown in FIG. 1, a magnification correction member l6 that performs a refraction action at an arbitrary position in the space on the reticle 2 side of the projection lens system 1.
It would be better to arrange a positive lens or a negative lens to match the imaging magnification of both the exposure light and the alignment light.

In particular, when the wafer alignment mark 10 is composed of a diffraction grating as described above, only two beams need to be corrected, so a single lens can be used as the magnification correction member 15, and prisms, mirrors, etc. can also be used for this purpose.

The above explanation shows the case where alignment is performed by simultaneously observing both the image 10a of the wafer alignment mark 10 on the wafer 3 surface and the reticle alignment mark 2a on the reticle 2 surface.

The present invention is not limited to this method; for example, as shown in FIG. It can be similarly applied to an alignment system that performs the following.

In the figure, an image 10a of the wafer alignment mark 10 is formed on the surface of the reference mark 14 whose positional relationship with the reticle 2 has been determined in advance, and the image 10a of the wafer alignment mark 10 is
The positional relationship with a is imaged on the surface of the image sensor 12 by the imaging lens 8, and alignment is performed while observing both sides.
From this, alignment between the mask 3 and the reticle 2 is performed indirectly.

In the embodiment shown in FIG. 4, the wafer alignment mark 10 may be composed of a diffraction grating, and a magnification correction member 16 may be arranged as required.

In addition, the base mark l4 may be composed of a diffraction grating with a predetermined pitch6.In this embodiment, the mirror 22 is arranged above the reticle 215, and together with the alignment light source 1l, the light splitter 21, and the imaging The lens 8, the reference mark 14, and the image pickup device 12 may also be arranged on both sides of the reticle 2 -J.

At this time, it is preferable to form a transparent part in a part of the reticule 2 and allow the alignment light to pass through the transparent part.

In addition, in this embodiment, the reference mark 14 is omitted, and the image sensor 12 whose positional relationship with the reticle 2 is determined in advance.
Alignment may be performed by directly forming an image of the wafer alignment mark IO on the surface and detecting the position of the image.

In this embodiment, the present invention can be applied even if a mirror system having a concave mirror and a convex mirror is used instead of the projection lens.

(Effects of the Invention) According to the present invention, when aligning a wafer and a reticle through a projection lens system using alignment wavelength light having a wavelength different from that of exposure wavelength light, the space on the reticle side of the projection lens system By arranging the multi-reflection member having the shape described above within the reticle, the image of the wafer alignment mark can be formed near the reticle alignment mark on the reticle surface while maintaining good optical performance, allowing for highly accurate alignment. It is possible to achieve an alignment device that makes it possible.

Furthermore, if a diffraction grating is used as an alignment mark, it is possible to easily achieve an alignment device capable of highly accurate alignment.

[Brief explanation of drawings]

Figure 1 is a schematic front view of an embodiment of the present invention applied to a stepper, Figure 2 is a schematic side view of Figure 1, and Figure 3 is the arrangement of wafer alignment marks in a wafer shot according to the present invention. The explanatory diagram, FIG. 4, is a schematic diagram of a main part of another embodiment of the present invention. In the figure, 1 is a projection lens system, 2 is a reticle, 2a is a reticle alignment mark, 3 is a wafer, 4 is an XYZ stage, 5 is a surface plate, 6 is an illumination device, 7 is a multiple reflection member, 8 is an imaging lens, 10 17 is a wafer alignment mark, 11 is an alignment light source, 12 is an image sensor, 16 is a magnification correction member, 21 is a light splitter, and 22 is a mirror.

Claims (7)

[Claims] (1) The wafer on the wafer surface is illuminated with a second wavelength light having a longer wavelength than the first wavelength light through a projection lens system that projects the pattern on the reticle surface illuminated with the first wavelength light onto the wafer surface. An image of an alignment mark is formed near the reticle alignment mark on the reticle surface, and the positional relationship between the two or an image of the wafer alignment mark is placed on a reference mark or image sensor surface arranged in a space on the reticle side of the projection lens system. the positional relationship between the two is detected by a detection means,
When aligning the wafer, a multiple reflection member is provided in a space on the reticle side of the projection lens system, and the wafer alignment mark and the reticle alignment mark are in a substantially conjugate relationship via the multiple reflection member, or the wafer alignment An alignment device characterized in that a mark and the reference mark or the image pickup device are in a substantially conjugate relationship via the multiple reflection member. (2) The alignment apparatus according to claim 1, wherein the wafer alignment mark is composed of a diffraction grating. (3) The alignment apparatus according to claim 2, wherein among the diffracted lights from the wafer alignment mark, a set of diffracted lights having the same absolute value and different signs are used. (4) The alignment apparatus according to claim 3, wherein the set of diffracted lights of orders having the same absolute value and different signs are ±1st order diffracted lights. (5) The pattern of the diffraction grating is arranged so that the longitudinal direction of the pattern coincides with two directions that pass through the optical axis of the projection lens system and are orthogonal to each other within the plane of the wafer. alignment device. (6) Claim 2 characterized in that the reticle alignment mark or the reference mark is composed of a diffraction grating.
The alignment device described. (7) Claim 1, characterized in that a magnification correction member is disposed in the optical path between the projection lens system and the detection means.
7. The alignment device according to 2, 3, 4, 5 or 6.