JPS63229305A - Pattern detector - Google Patents

Abstract

PURPOSE:To enhance the utilization efficiency or S/N ratio of illumination beam by markedly reducing the reflected light returning to a light source, by providing a plane-of-polarization rotary member between a polarizing beam splitter and a detection optical system to limit incident illumination beam to a specific polarized beam component. CONSTITUTION:The laser beam incident on a polarizing beam splitter 9 from a laser beam source 4 is limited to P-polarized beam, and the splitter 9 permits the transmission of the almost whole quantity of said incident beam. When the laser beam passes through the next lambda/4 plate 10, a plane-of-polarization rotates by pi/4 to become circular polarized beam. Therefore, the spot beam LAy formed on a wafer W is also circular polarized beam and, at the same time, the reflected beam from the wafer W is preserved as circular polarized beam. When this reflected beam again reversely advances through the plate 10 with respect to illumination beam, linear polarized beam (S polarized beam) wherein the plane of polarization is further rotated by pi/4 is obtained. Therefore, the reflected beam from the water W is almost entirely reflected by the splitter 9 to reach a space filter 14. As a result, the reflected beam from the wafer W returning to the beam source is reduced to an almost negligible value and the generation of back talk is prevented.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a pattern detection device that optically detects or observes a pattern formed on a substrate by self-illumination.
In particular, mask patterns used in the manufacturing process of semiconductor devices (
The present invention relates to a pattern detection device suitable for an apparatus (for example, an exposure apparatus) that detects marks) or wafer patterns (marks) and performs mask or wafer alignment (for example, an exposure apparatus).

(Prior Art) Conventionally, as an alignment optical system or device to which this type of pattern detection device is applied, for example,
One disclosed in Japanese Patent No. 262423 is known.

In this alignment optical system, laser light is used as illumination light for the marks in order to improve the S/N ratio and accuracy of detecting patterns, especially alignment marks.

Further, in general, a telecentric optical system is used as an alignment optical system in view of the significance of mark position detection and measurement. In particular, projection exposure equipment uses a projection optical system that is telecentric at least on the wafer (exit pupil) side in order to print the circuit pattern of the mask (reticle) onto the wafer. Even in the case of detection, telecentricity as a system is guaranteed. Now, when detecting marks on a wafer through such a projection optical system, the illumination light for alignment that reaches the wafer through the projection optical system is reflected on the wafer surface and becomes specularly reflected light, diffracted light, and scattered light. It becomes light and travels back to the projection optical system. In this case, since the system is a telescopic link, even if it is off-axis, the regularly reflected light and some of the diffracted and scattered light travel backwards along the same optical path as the illumination optical path. Therefore, in order to extract the optical information from the mark, a method is adopted in which an amplitude divider such as a half mirror 1 or a half prism is installed in the illumination optical path to separate the illumination light and the optical information from the mark. .

(Problem to be Solved by the Invention) However, in such conventional methods, part of the optical information from the wafer mark or the wafer surface itself returns to the laser light source via the amplitude splitter, and the laser This method has the disadvantage of causing so-called backtalk, a phenomenon that makes the oscillation of light unstable. This drawback can be somewhat improved by changing the ratio of reflectance and transmittance of the amplitude splitter, but if the ratio is other than l:1, there will be a loss in detection of optical information from the wafer, or a loss of illumination light to the wafer. A new problem arises, such as strength reduction, and the ratio is usually set at 1:1.

(Means for solving the problem) In the present invention, the light transmission path of illumination light (especially laser light) and the detection path of optical information from the pattern on the substrate are separated by a polarizing beam splitter (wavefront splitter). A wavefront rotating plate (for example, a λ/4 plate) that changes the polarization state is provided between this polarizing beam splitter and a detection optical system (for example, a projection optical system of an exposure device or an objective lens for observation), and The polarization state of the incident illumination light is limited to a specific component (linearly polarized light).

(Function) Therefore, the polarization state of the illumination light that reaches the substrate and the polarization state of the reflected light (regular reflection light, diffracted light, scattered light) from the substrate are the same as the polarization state of the illumination light that enters the polarizing beam splitter from the light source. Therefore, almost all of the reflected light is separated into the detection path by the polarizing beam splitter, and the reflected light that returns to the light source is significantly reduced. There is also less light loss (equivalent to or greater than conventional SZN)
You can get the ratio.

(Embodiment) FIG. 1 is a diagram showing a schematic configuration of a reduction projection type exposure apparatus suitable for an embodiment of the present invention. A reduction projection optical system (hereinafter simply referred to as a projection lens) 1 which also functions as a detection optical system of the present invention reduces an image of a circuit pattern etc. formed on a reticle R onto a wafer W by 115 or 1/10. Expose. The reticle R is placed on a reticle stage (not shown),
This reticle stage is moved in the X and Y directions by a drive unit (not shown).
direction, and the θ (rotation) direction. Then, the reticle R is aligned (positioned or positioned) at a predetermined position, for example, with respect to the optical axis AX of the projection lens 1 using an alignment microscope (not shown). Further, the reticle R is illuminated with exposure light containing a wavelength effective for exposing the resist applied to the wafer W (eg, g-line or i-line). Due to the illumination of this exposure light, a light beam EL forming a pattern image of the reticle R is imaged on the surface of the wafer W.

On the other hand, this wafer W is placed on a stage 2 that moves two-dimensionally in the X and Y directions. Although the stage 2 is not shown, it has a Z stage section for vertically moving the wafer W, and an e-table provided on the Z stage section for slightly rotating the wafer W. The two-dimensional movement of the stage 2 is performed by a drive unit (motor etc.) 20, and the stage 2
The position (coordinate values) in the XY coordinate system is constantly detected by a length measuring device 3 such as a laser interferometer with a resolution of, for example, 0.02 μm.

Next, the alignment detection optical system (alignment optical system) for the wafer W will be explained. A linearly polarized laser beam from a laser light source 4 is expanded to a predetermined beam diameter by a beam expander 5, and shaped by a cylindrical lens 6 into an elliptical beam with an elongated cross section.

This shaped laser beam is reflected by a mirror 7, passes through a lens 8, a polarizing beam splitter 9, a λ/4 plate 1 serving as a phase rotation member, and an objective lens 11 forming a part of the detection optical system. Reticle R by mirror 12
is reflected upward from the bottom surface of the After the laser beam from the mirror 12 is partially converged into a slit shape, it reaches the mirror 13 which has a reflection plane parallel to the reticle R below the reticle R, where the laser beam is directed toward the entrance pupil 1a of the projection lens 1. reflected. The reticle side of this projection lens l is non-telecentric, but the wafer side (ie exit pupil side) is a telecentric system. Of course, the same applies to a double-sided telecentric system. Furthermore, the objective lens 11 is also designed as a telecentric system in this embodiment.

Now, the laser beam that has passed through the projection lens 1 is imaged onto the wafer W by the action of the cylindrical lens 6 into an elongated strip-shaped spot light LAy. The wavelength of this spot light is determined so as not to expose the resist on the wafer W.

On the wafer W, marks for positioning (alignment marks) are formed in advance with minute irregularities, so when the spot light LAy irradiates this mark, scattered light and diffracted light are emitted from the mark in addition to specularly reflected light. arise. The optical information from these marks enters the projection lens 1 back, passes through the entrance pupil 1a, is reflected by the mirror 13.12, and is reflected by the objective lens 11, λ/
It passes through the four plates lO and is reflected by the polarizing beam splitter 9,
A spatial filter 14 is reached. The spatial filter 14 is conjugate with the aperture position (pupil plane) of the objective lens 11, that is, the entrance pupil 1a or the exit pupil of the projection lens 1, and blocks only specularly reflected light (0th order diffracted light) from the surface of the wafer W.

The diffracted light (scattered light) from the surface (mark) of the wafer W is displaced with respect to the optical path of the specularly reflected light on the pupil plane depending on the spatial frequency. Therefore, the spatial filter 14 passes only the diffracted light and scattered light, and the condenser lens 15 focuses the diffracted light and scattered light onto a light receiving element 16 serving as a photoelectric detector. The light receiving element 16 outputs a photoelectric signal SA corresponding to the intensity of the diffracted light or scattered light, and this photoelectric signal SA is input to an alignment signal processing circuit (hereinafter simply referred to as a processing circuit) 17 .

The processing circuit 17 also inputs the position information (time-series up/down pulse signals or parallel digital signals) PD from the length measuring device 3, and generates a photoelectric signal SA according to the diffracted light and scattered light from the mark. Detect the occurrence position (scanning position). Specifically, the photoelectric signal SA was sampled using up and down pulse signals generated every unit movement distance (0.02 μm) of stage 4, and each sampling value was converted into a digital value and stored in memory in address order. After that, the scanning position of the mark is detected by predetermined calculation processing. The control device 1B controls the drive unit 20 based on the position information of the detected mark. If marks on the wafer W are provided to accompany each of a plurality of chips on the wafer, by detecting the position of each mark, the center of each chip and the optical axis AX (pattern of the reticle R) can be determined. center)
and can be aligned accurately.

Note that if the laser light source 4 is always turned on in the above configuration and the laser beam is sent to the projection lens 1, the spot light LAy will always be reflected if the wafer W is at that position. This also applies during exposure operation.
This means that reflected light from the surface of the wafer W (reflected light of laser light, reflected light of exposure light) returns to the alignment optical system.

In the above configuration, the illumination light (laser light) that enters the polarization beam splitter 9 from the laser light source 4 is limited to, for example, P-polarized light, which is a component in one direction of linearly polarized light. Therefore, the polarizing beam splitter 9 transmits almost all of the incident laser light. When this P-polarized laser beam hits the next λ/4 plate 1 sheet metal 0, the plane of polarization rotates by π/4 and becomes circularly polarized light. Therefore, the spot light LAy formed on the wafer W is also circularly polarized light, and at the same time, the reflected light from the wafer W is also preserved as circularly polarized light. When this reflected light travels backwards again with respect to the λ/4 plate 1 sheet metal 0 bright light, it becomes linearly polarized light whose polarization plane has been further rotated by π/4, here S
Becomes polarized light. Therefore, almost all of the reflected light from the wafer W is reflected by the polarizing beam splitter 9, and the spatial filter 1
It will reach 4. Therefore, the reflected light from the wafer W that returns to the laser light source 4 is reduced to an almost negligible level, and backtalk is prevented from occurring. In order to make the illumination light incident on the polarizing beam splitter 9 into a linearly polarized light component in one direction, some kind of polarization means is required, but the utilization efficiency of the illumination light that has reached the wafer W is determined by the reflectance of the wafer W. Depending on the circumstances, it can be quite large.

Furthermore, the illumination light incident on the polarization beam splitter 9 is P,
Even in the case of linearly polarized light that includes both S and S polarization components, almost all of the S polarization component is reflected by the polarization beam splitter 9 in the direction of arrow J in FIG. 1, and only the P polarization component reaches the λ/4 plate 10. Therefore, it can be implemented in the same way. In this case as well, the ratio of the illumination light reaching the wafer W to the reflected light reaching the spatial filter 14, that is, the utilization efficiency, is as large as in the previous case.

Next, a second embodiment of the present invention will be described based on FIG. 2. This embodiment is also exemplified by an alignment optical system of a projection exposure apparatus, but here the projection lens 1 is a double-sided telesend link system. Other members having the same functions as those in the embodiment shown in FIG. 1 are given the same part numbers and symbols. The alignment optical system of this embodiment is provided above the reticle R, and performs photoelectric detection by scanning marks on the reticle R and marks on the wafer W with a spot light of a laser beam. A linearly polarized laser beam from the laser light source 4 enters the polarization beam splitter 9 via the lens system 8 as S-polarized light. This laser beam is polarized by a polarizing beam splitter 9.
Almost all of the light is reflected, enters the λ/4 plate 10a, and is converted into circularly polarized light.

Thereafter, the laser beam is vertically reflected by the plane mirror M, enters the λ/4 plate 10a again, is converted into P-polarized light (linearly polarized light), and enters the polarizing beam splitter 9. At this time, since the laser beam is P-polarized light, almost all of the laser beam passes through, enters the telecentric objective lens 11 via the λ/4 plate 10b, and is imaged on the reticle R as a circularly polarized laser spot light. Entrance pupil 1a of projection lens 1
The spotlight LAy passes through the center of the wafer W and reappears on the wafer W.
imaged as. In this embodiment, since marks on the reticle R and marks on the wafer W are simultaneously detected through the objective lens 11, the wavelength of the laser beam is set to match the achromatic wavelength of the projection lens 1, for example, the wavelength of the exposure light. stipulated by. Of course, if the projection lens l is achromatic for two different wavelengths, the exposure wavelength and the wavelength of the laser beam can be matched to each of the achromatic wavelengths. It is also possible to use a laser beam with a wavelength that is not achromatized, and for that purpose, a chromatic aberration correction optical system may be provided in the light transmission path of the laser beam to the reticle R.

Now, the reflected light (regularly reflected light, diffracted light, scattered light) from the wafer W travels backward through the projection lens 1 and enters the objective lens 11 via the transparent portion of the reticle R.

At the same time, reflected light (regular reflection, diffraction, scattered light) from the marks on the reticle R also enters the objective lens 11. Objective lens 1
1, the reflected light from the wafer W and the reflected light from the mark on the reticle R are both converted into linearly polarized S-polarized light via the λ/4 plate 10b, and almost all of them are reflected by the polarizing beam splitter 9. Only the diffracted light and scattered light are detected by the light receiving element 16 via the pupil-conjugate spatial filter 14 and the condensing lens 15.

As described above, in this embodiment, backtalk to the laser light source is similarly prevented, and the effect of high utilization efficiency of illumination light can be obtained.

Furthermore, in this embodiment, the size of the laser beam incident on the polarizing beam splitter 9 on the pupil plane is made smaller than the pupil diameter, and a vibrating mirror or a polygon mirror provided between the laser light source 4 and the lens system 8 is used. Alternatively, the spot light may be scanned. In this case, by making the origin of deflection of the laser beam conjugate with the pupil plane of the objective lens 11, that is, the exit surface (incidence surface 1a) of the projection lens 1, the spot light maintains a telescopic link on the reticle R and the wafer W. scanned.

On the other hand, in the case of this embodiment, since the light receiving element I6 is arranged on the extension line of the direction in which the laser beam enters the polarizing beam splitter 9, when both the S and P polarization components enter the polarizing beam splitter 9, There is a possibility that the P-polarized light component will reach the light receiving element 16 as is. However, even in such a case, in this embodiment, one polarized light component directly directed from the laser light source 4 to the light receiving element 16 is blocked by the light shielding part 14a of the spatial filter 14, so that the light receiving element 16 will never reach.

The light blocking portion 14a of the spatial filter 14 is provided at the center of the pupil image plane, and serves to block specularly reflected light.

In the case of a telecentric system, the shape and dimensions of the specularly reflected light on the pupil plane are the same as the shape and dimensions on the pupil plane of the laser beam that illuminates the reticle R1 or the wafer W. The light blocking portion 14a necessarily blocks all the light flux of the unidirectional polarized light component (S-polarized light) directly reaching the laser beam R4 via the polarizing beam splitter 9. This is the same even when the laser beam is swung at a pupil conjugate position as described above.

Therefore, in this embodiment as well, the illumination light incident on the polarization beam splitter 9 may be linearly polarized light including P polarized light and S polarized light. Note that if the light shielding part 14a of the spatial filter 14 is made of a material that is highly absorbent to the wavelength of the laser beam, the reflected light from the light shielding part 14a can be prevented from returning to the laser light source 4.

Furthermore, the plane mirror M and the λ/4 plate 10a of this embodiment may be attached together.

Further, in this embodiment, at the position of the spatial filter 14,
A photoelectric element having a light-receiving surface arranged so as to receive only the diffracted light and scattered light separated from the specularly reflected light within the pupil plane may be directly provided. In this case, one polarized light component (
P-polarized light) reaches a region other than the light-receiving surface of the photoelectric element, so if only that region is made an opening or a transparent part to escape to the rear, it can have the same function as the anti-reflection light shielding part 14a described above. This can be achieved and the occurrence of backtalk can be suppressed. Note that the objective lens 1 of the alignment optical system of this embodiment
It goes without saying that if a substrate having a pattern is placed under the device 1, it can be used as a beam scanning pattern detection device.

(Effects of the Invention) As described above, according to the present invention, the light returning to the lens light source etc. is significantly reduced, the oscillation of the laser light source can be stably maintained, and the utilization efficiency of illumination light is improved, and the pattern (
The S/N (signal light to stray light) ratio during mark) detection is improved,
Effects such as improved accuracy in pattern recognition and pattern position detection can be obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an exposure apparatus to which a pattern detection apparatus according to a first embodiment of the present invention is applied, and FIG. 2 is a diagram showing the configuration of an exposure apparatus to which a pattern detection apparatus according to a second embodiment of the invention is applied. FIG. [Explanation of symbols of main parts] ■... Projection lens 4... Laser light source 9... Polarizing beam splitter 10, ], Oa, 10b -
... λ/41 anti-11... Objective lens W... Wafer R... Reticle

Claims (1)

[Scope of Claims] A light source for irradiating illumination light onto a substrate having a predetermined pattern; a detection optical system disposed between the light source and the substrate; and between the detection optical system and the light source. a light splitter disposed in the pattern, the light splitter separates the optical path of the illumination light to the pattern and the optical path of the reflected light from the pattern, and detects the reflected light. The splitter is a polarizing beam splitter, a polarization plane rotating member for changing the polarization state is provided between the polarizing beam splitter and the detection optical system, and illumination light incident on the polarizing beam splitter is limited to a specific polarization component. A pattern detection device characterized by: