JP2961919B2 - Position detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position detecting device, and more particularly to a position detecting device for projecting and transferring an electronic circuit pattern on a reticle surface (first object surface) onto a wafer surface (second object surface) by a projection lens. The present invention relates to a position detecting apparatus suitable for an exposure apparatus for manufacturing a semiconductor element, which has an optically conjugate relationship with a wafer and detects a relative position between the reticle and an imaging unit which has been pre-aligned. .

[0002]

2. Description of the Related Art Conventionally, in an exposure apparatus for manufacturing a semiconductor device, a method of detecting a relative position (alignment) between a reticle and a wafer through a projection lens is one method.
There is a TL method.

[0003] Of these, a reference position (reference mark) on a predetermined surface and an alignment mark provided on the wafer surface are illuminated by using a light beam having a wavelength different from the exposure light used to illuminate the pattern on the reticle surface and print it on the wafer surface. There have been proposed various position detecting devices for detecting a relative position with respect to the position.

[0004] The applicant of the present invention has disclosed, for example, Japanese Patent Application No. 1-198261.
The publication proposes an observation method and an observation apparatus capable of performing high-accuracy position detection while observing an alignment mark image on a predetermined surface, for example, an imaging means surface using an imaging means such as a CCD camera.

In general, the illumination light of the alignment mark on the wafer surface, ie, the alignment light, is selected from a monochromatic laser light or a light from a white light source such as a halogen lamp using a filter. ~
(A luminous flux of about 60 nm).

[0006]

Generally, when a laser beam is used as the alignment beam, an alignment signal having a high S / N ratio can be easily obtained due to the high brightness and the light collecting property of the laser beam. On the other hand, the laser light has good coherence. (A) During the wafer process, the S / N ratio of the alignment signal is deteriorated due to speckle noise accompanying the surface roughness particularly of a metal layer on the wafer surface. A large position detection error occurs. (B) The asymmetry of the applied resist film, the non-uniformity of sputtering, and the like cause an asymmetric distortion in the alignment signal due to the interference of the laser beam, thereby lowering the alignment accuracy. (C) The interference between the reflected light from the resist surface applied to the wafer surface and the reflected light from the wafer surface changes with a change in the resist film thickness. As a result, the relative intensity of the alignment signal changes sinusoidally. Will come. In particular, when the interference condition is poor in a process in which the step of the alignment mark is small, the alignment mark cannot be detected. And so on.

FIG. 2 shows that the relative intensity I of the output signal varies sinusoidally according to the resist film thickness when the He—Ne laser beam is applied to the alignment mark on the silicon wafer surface with the resist.

Such a decrease in position detection accuracy due to laser light interference can be improved by using a light beam having a sufficiently wide wavelength width (for example, 200 nm) instead of laser light as alignment light.

However, in general, when a polychromatic light beam having a wide wavelength width is used, a large amount of chromatic aberration occurs in a projection lens. This chromatic aberration can be corrected by an observation system, and a high transmittance to non-exposure light can be obtained over a wide wavelength band. There are various problems such as difficulty in applying a coated coating (anti-reflection film).

For this reason, at present, the multicolor luminous flux is 50 to
The wavelength width of about 60 nm was the limit. 50-60 nm
When a polychromatic light beam having the above wavelength width is used as the alignment light, an extreme decrease in signal intensity due to speckle noise and a resist film thickness is improved. However, when the contrast of the alignment mark image is reduced due to the residual aberration of the projection lens and the entire observation system, and the wavelength width is not enough, the influence of interference remains to some extent, and the signal distortion due to the asymmetry of the resist film or the like has poor film thickness conditions. This causes a problem that the alignment accuracy is deteriorated due to the above problem.

According to the present invention, when an alignment mark on a wafer surface is projected onto a predetermined surface with non-exposure light via a projection lens and observed, and the position of the alignment mark image on the predetermined surface is detected, a preset value is set. Within the wavelength range ,
From among the plurality of light beams having a spectral characteristic of and different center wavelength each other has a width, by illuminating the alignment marks in the light beam by selecting a certain one of said light beam,
It is an object of the present invention to provide a position detection device and a position detection method that enable observation in a good interference condition and enable highly accurate position detection.

[0012]

According to a first aspect of the present invention, there is provided a position detecting apparatus for projecting a pattern on a first object plane onto a second object plane via a projection lens. (2) In a position detection device that detects an image of an alignment mark provided on an object surface and detects a position of the alignment mark based on the image, the position detection device detects a position of the alignment mark in a polychromatic light that does not include a wavelength of exposure light in a light flux from a light source unit . One of a plurality of luminous fluxes having a wavelength width and different spectral characteristics having different center wavelengths from each other
Of the light beam, the selection means is selected based on the symmetry of the image formed by the light beams, the alignment with the light flux forming a good image of the selected pair <br/> symmetries in said selection means The feature is that the mark is illuminated. Further, the second aspect of the present invention
The position detecting method according to the present invention includes the steps of:
On the second object plane via a projection lens for projecting on the object plane
Detects the image of the alignment mark provided in
Position detection method to detect the position of the alignment mark based on
The wavelength of the exposure light in the light flux
It has a wavelength width within the polychromatic light that does not contain
Among a plurality of light beams having different spectral characteristics from each other,
One of the light beams is formed by each light beam by the selecting means.
Selected based on the symmetry of the image to be selected, and selected by the selecting means.
The light beam forming the selected image with good symmetry
The feature is that the mark is illuminated.

[0013]

FIG. 1 is a schematic view of a main part of a first embodiment of the present invention. In the figure, a projection lens 2 projects an electronic circuit pattern on the reticle 11 surface illuminated with exposure light from an illumination system (not shown) onto the wafer 1 surface. Reference numeral 12 denotes a θZ stage on which the wafer 1 is placed. Reference numeral 13 denotes an XY stage on which the θZ stage 12 is mounted. The θZ stage 12 and the XY stage 13 drive and control the wafer 1 in an arbitrary direction. 1a is an alignment mark formed on the wafer 1 surface.

FIG. 5 is an explanatory diagram showing an example of the pattern of the alignment mark 1a. Reference numeral 8a denotes light source means, which comprises a halogen lamp or the like and emits polychromatic light having a wide wavelength width. Reference numeral 9 denotes a wavelength selection member, which is configured by arranging a plurality of color filters in a turret type, for example. The plurality of color filters have spectral characteristics of a narrow wavelength width different from the wavelength of the exposure light and different from each other at the center wavelength.
At this time, the center wavelength of each of the plurality of color filters is set so as to be located within a wavelength region not including the wavelength of the exposure light whose chromatic aberration has been properly corrected by an observation system described later.

A driving means 14 rotates the wavelength selection member 9 so that a predetermined color filter is positioned on the optical path. Reference numeral 5 denotes a half mirror, and a wavelength selection member 9
A light beam having a specific spectral characteristic that has passed through one of the color filters is reflected toward the erector lens 4c. 4b is a relay lens and 4a is an objective lens.
In the present embodiment, the objective lens 4a, the relay lens 4b, and the erector lens 4c constitute one element of the observation system 4.

Reference numeral 4d denotes a correction system, which is arranged as necessary, and corrects various aberrations generated in the projection lens 2. 3 is a mirror. Reference numeral 8b denotes a laser which emits light having a wavelength different from that of the exposure light. Reference numeral 6 denotes a half mirror that reflects light from the laser 8b. In the present embodiment, the wavelength selecting member 9, the light source means 8a, the laser 8b, and the like constitute one element of the selecting means 15.

Reference numeral 7 denotes an image pickup means, which comprises, for example, a CCD camera or the like. Reference numeral 21 denotes a bar mirror for the interferometer, which is mounted on the XY stage 13. Reference numeral 22 denotes an interferometer, which measures the amount of movement of the XY stage 13. Reference numeral 10 denotes a control device which drives and controls the XY stage 13 based on a signal from the interferometer 22. Further, the control device 10 controls the selection unit 15 to emit a light beam having a specific spectral characteristic based on a signal from the imaging unit 7 or based on an external input signal (not shown).

In this embodiment, the selecting means 15 controls the laser 8
One of the laser beams from b or the polychromatic light from the light source means 8a selected from the light beams selected by the color filter of the wavelength selection member 9 is guided to the observation system 4. Then, the alignment mark 1a on the surface of the wafer 1 is irradiated via the mirror 3 and the projection lens 2. The reflected light from the alignment mark 1a on the surface of the wafer 1 returns to the original optical path,
That is, the light passes through the projection lens 2, the mirror 3, the observation system 4 and the half mirrors 5 and 6, is incident on the imaging means 7, and forms an alignment mark image on its surface. Thus, the positional relationship between the reference mark and the alignment mark image on the surface of the imaging means 7 is detected.

In this embodiment, the positional relationship between the reticle 11 and the reference mark of the image pickup means 7 is determined in advance, and the positional relation between the alignment mark 1a on the wafer 1 and the reference mark of the image pickup means 7 is detected. Thus, the relative position between the reticle 11 and the wafer 1 is detected.

Next, each component of this embodiment will be described.

FIG. 3 shows a wavelength shift amount for changing from a condition observed dark to a condition observed bright due to interference between a resist surface and a wafer surface when He-Ne laser light (wavelength 633 nm) is used as alignment light. Δλ
With respect to the resist thickness. The range of the resist thickness commonly used in the current semiconductor device manufacturing process is about 1.0 to 2.5 μm. Assuming that the refractive index n of the resist material is n ≒ 1.6, the wavelength shift amount Δλ for changing the dark state of the interference condition to the bright state is about 12 to 2
9 nm.

In this embodiment, the wavelength shift amount Δλ is set to 18 nm at the center thereof, and the wavelength bands of two light beams for illuminating the alignment mark are set as follows. Example 1 (i) Center wavelength 633 nm, wavelength width 20 nm (ii) Center wavelength 615 nm, wavelength width 20 nm FIG. 4 is a waveform signal when an alignment mark on a wafer surface is observed using light beams in these two wavelength bands. is there. In (i), the asymmetry of one alignment mark is strongly shown, whereas in (ii), the asymmetry due to interference is reduced. This indicates that the interference condition changes by changing the center wavelength of the illumination light, and the signal waveform can be improved to be faithful to the alignment mark.

In selecting a plurality of wavelength bands,
The control device 10 having a CPU calculates and evaluates the symmetry and contrast of the waveform signal of the alignment mark by each illumination light, or an evaluation amount such as template matching for matching a predetermined waveform, and selects a better waveform signal. Is aligned.

In this embodiment, a procedure for detecting an alignment mark having good symmetry from a plurality of alignment marks by utilizing the high coherence of a laser beam is to select one light beam from the plurality of light beams. If performed before, higher precision alignment is possible.

As a specific means for detecting an alignment mark having a good waveform signal, for example, video signals of a plurality of alignment marks as shown in FIG. 5 are taken out, and an evaluation function Z (x) is calculated and evaluated for each alignment mark. Then, an alignment mark may be selected from the result.

FIG. 6 shows a video signal of a predetermined alignment mark (one of the alignment marks in FIG. 5) and a calculation result of an evaluation function Z (x _i ) value. Various evaluation functions have been proposed, but in this embodiment,

[0027]

(Equation 1) The calculated value is shown.

Next, another embodiment in which a procedure for selecting an alignment mark having a good waveform signal is added will be described. Example 2 The wavelength bands of the two light beams for illuminating the alignment mark are set as follows.

(I) He-Ne laser having a center wavelength of 633 nm (ii) Halogen lamp having a center wavelength of 615 nm and a wavelength width of 20 nm FIG. 7 is a flowchart of an alignment procedure in this embodiment. The alignment procedure of this embodiment is set as follows.

According to (a) and (i), an alignment mark having a good evaluation amount of the waveform signal is selected.

(B) When the signal waveform is good in (i), alignment is performed according to (i).

The alignment is performed by switching to (ii) when the signal waveforms of (c) and (i) are bad (due to speckle noise and interference conditions). Example 3 The wavelength bands of the three light beams for illuminating the alignment mark are set as follows.

(I) He-Ne laser having a center wavelength of 633 nm (ii) Halogen lamp having a center wavelength of 633 nm and a wavelength width of 20 nm (iii) Halogen lamp having a center wavelength of 615 nm and a wavelength width of 20 nm FIG. 8 shows an alignment procedure in this embodiment. It is a flowchart figure.

According to (a) and (i), an alignment mark having a good evaluation amount of the waveform signal is selected.

When the signal waveforms of (b) and (i) are good, alignment is performed according to (i).

When the signal waveforms of (c) and (i) are bad (due to speckle noise and interference conditions), (ii) and (ii)
Switching to the illumination of i), the symmetry and contrast of each signal waveform are compared, and the better one is selected to perform alignment.

[0037]

According to the present invention, when an alignment mark on a wafer surface is formed on a predetermined surface with non-exposure light through a projection lens and observed for position detection as described above, the alignment mark is set in advance. Within the wavelength range, the wavelength
Prevention from among the plurality of light beams having spectral properties with and different center wavelength each other has a width, by illuminating select a certain one of said light beam, a decrease in signal intensity due to signal degradation and interference caused by speckle noise In addition, it is possible to achieve a position detection device and a position detection method that can reduce asymmetric distortion of an alignment signal, enable observation in a state where interference conditions are good, and enable highly accurate position detection.

[Brief description of the drawings]

FIG. 1 is a schematic view of a main part of a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a relationship between a photoresist thickness and a relative reflection intensity.

FIG. 3 is an explanatory diagram showing a relationship between a resist thickness and a wavelength shift amount for changing from a dark condition to a bright condition.

FIG. 4 is an explanatory diagram of a mark signal waveform of an alignment mark image based on a center wavelength.

FIG. 5 is a schematic view of an alignment mark.

FIG. 6 is an explanatory diagram showing a video signal of an alignment mark and a symmetry relationship.

FIG. 7 is a flowchart of a second embodiment of the present invention.

FIG. 8 is a flowchart of a third embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Wafer 2 Projection lens 3 Mirror 4 Observation system 5 Half mirror 6 Half mirror 7 Imaging means 8a Light source means 8b Laser 9 Wavelength selection member 10 Controller 11 Reticle 15 Selection means

Claims (2)

(57) [Claims] 1. An image of an alignment mark provided on a second object plane is detected via a projection lens for projecting a pattern on a first object plane onto a second object plane, and an alignment mark is formed based on the image. In the position detecting device that detects the position of the light beam, the light beam from the light source means has a wavelength width in the polychromatic light that does not include the wavelength of the exposure light and has a central wavelength different from a plurality of light beams having spectral characteristics different from each other. One
Of the light beam, the selection means is selected based on the symmetry of the image formed by the light beams, the alignment with the light flux forming a good image of the selected pair <br/> symmetries in said selection means A position detection device characterized by illuminating a mark. 2. A pattern on a first object plane is defined on a second object plane.
Provided on the second object plane via a projection lens for projecting
An image of the alignment mark is detected, and an
Position detection method for detecting the position of the alignment mark
Does not include the wavelength of the exposure light in the luminous flux from the light source means.
Within the polychromatic light, they have wavelength widths and different center wavelengths.
One of a plurality of light beams having different spectral characteristics
The light flux formed by each light flux by the selecting means.
The pair selected based on the symmetry of the image and selected by the selecting means
The alignment mark is formed with a light beam that forms an image with good
A position detection method characterized by being illuminated.