JP2778231B2 - Position detection device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a position detecting device, for example, in an exposure apparatus for manufacturing a semiconductor element, on a first object surface such as a mask or a reticle (hereinafter, referred to as a “mask”). When exposing and transferring the fine electronic circuit pattern formed on the second object surface such as a wafer, the distance between the mask and the wafer is measured and controlled to a predetermined value (interval setting). The present invention relates to a position detection device suitable for performing positioning (alignment) in a relative plane.

(Prior Art) Conventionally, in an exposure apparatus for manufacturing a semiconductor element, relative spacing and alignment between a mask and a wafer are important factors for improving performance. Especially in the interval setting and alignment in a recent exposure apparatus,
For high integration of semiconductor devices, devices having an accuracy of, for example, submicron or less are required.

At that time, the distance between the mask and the wafer is measured by a plane distance measuring device or the like, and after controlling the distance to be a predetermined distance, position information obtained from a so-called alignment pattern for positioning provided on the mask and the wafer surface is obtained. Utilization is used to perform both alignments. As an alignment method at this time, for example, the amount of deviation between the two alignment patterns is detected by performing image processing, or alignment is proposed as proposed in U.S. Pat. No. 4,037,969 or Japanese Patent Application Laid-Open No. 56-157033. This is performed by using a zone plate as a pattern, irradiating the zone plate with a light beam, and detecting the position of a light-converging point on a predetermined surface of the light beam emitted from the zone plate.

Generally, an alignment method using a zone plate has a feature that relatively high-precision alignment can be performed without being affected by a defect of an alignment mark, as compared with a method using a simple alignment mark.

FIG. 8 is a schematic view of a conventional position detecting device using a zone plate.

In the same figure, a parallel light beam emitted from a light source 72 passes through a half mirror 74 and is condensed at a converging point 78 by a converging lens 76, and is then placed on a mask alignment pattern 68a on a mask 68 and a support 62. The wafer alignment pattern 60a on the surface of the wafer 60 is irradiated. These alignment patterns 68a and 60a are constituted by reflection type zone plates,
Focus points are formed on planes orthogonal to the optical axis each including the focus point 78. At this time, the amount of shift of the condensing point position on the plane is detected by guiding the light onto the detection surface 82 by the condensing lenses 76 and 80.

Then, based on the output signal from the detector 82, the control circuit 84
Drives the drive circuit 64 to position the mask 68 relative to the wafer 60.

FIG. 9 shows the mask alignment pattern shown in FIG.
FIG. 8 is an explanatory diagram showing an image forming relationship of a light beam from 68a and a wafer alignment pattern 60a.

In the figure, a part of the luminous flux diverging from the converging point 78 is diffracted from the mask alignment pattern 68a to form a converging point 78a indicating the mask position near the converging point 78.
Further, some other light beams pass through the mask 68 as zero-order transmission light and enter the wafer alignment pattern 60a on the wafer 60 without changing the wavefront. At this time, after the light beam is diffracted by the wafer alignment pattern 60a, the light beam is transmitted again through the mask 68 as zero-order transmission light, condensed in the vicinity of the converging point 78, and forms a converging point 78b representing the wafer position. In the figure, when the light beam diffracted by the wafer 60 forms a converging point, the mask 68 acts as a simple transparent state.

The position of the focal point 78b by the wafer alignment pattern 60a formed in this way is determined by the amount of deviation Δσ in the direction (lateral direction) along the mask / wafer surface with respect to the mask 78 of the wafer 60. It is formed as a shift amount Δσ ′ of an amount corresponding to the shift amount Δσ along a plane orthogonal to the included optical axis.

FIG. 10 is a schematic view of an interval measuring device proposed in Japanese Patent Application Laid-Open No. 61-111402. In the figure, a mask M as a first object and a wafer W as a second object are arranged to face each other, and a light beam is focused on a point Ps between the mask M and the wafer W by a lens L1.

In this case the light beam is respectively reflected by the above mask M surface and the wafer W surface, a point P _W on the screen S surface through the lens L2, the are converged projected to P _M. The distance between the mask M and the wafer W focal point P _W of the light beam on the screen S surface is measured by detecting the distance between the P _M.

(Problems to be Solved by the Invention) In the above-described position detecting device and interval measuring device, a laser light source having a large light output and good directivity is used as a light source means.

On the other hand, since the laser light source has good coherence, the detection surface is affected by noise light such as interference fringes due to multiple reflections between the mask and the wafer and interference fringes due to speckle scattered light from fine irregularities between the mask and the wafer. There is a problem in that the light intensity distribution of the laser beam incident on the laser beam or the light beam cross-sectional shape changes for each incident position on the detection surface. If the incident position of the noise light on the detection surface is constant, it is often spatially fixed, so the detection signal does not change even after a lapse of time,
Even if the light intensity distribution of the incident light beam is averaged over time, this noise light cannot be canceled out. Therefore, when trying to detect the movement of the converging point (for example, the center of a circular light beam) or the reference point (for example, the point where the light intensity is a peak) based on the light intensity on the detection surface, the light beam cross-sectional shape or light Since the intensity fluctuates, the amount of movement of the incident point of the laser beam does not match the actual amount of movement of the converging point of the laser beam, and as a result, a detection error occurs in position shift detection and interval shift detection. There was a problem.

The present invention reduces a detection error due to speckle scattered light when a laser beam having good coherence is used as a light source means, and reduces a relative displacement or a relative displacement between a first object and a second object arranged opposite to each other. It is an object of the present invention to provide a position detecting device capable of detecting with high accuracy.

(Means for Solving the Problems) The position detecting device of the present invention provides a position shift and / or a relative distance between a first object surface and a second object surface which are opposed to each other. An alignment mark for detecting a shift is provided, and among the light beams from the light projecting means, the light beams which have been subjected to the wavefront conversion by the alignment marks on the first object surface and the second object surface are guided to a predetermined surface. When detecting the relative position shift and / or relative distance shift between the first object and the second object by detecting the incident position of the light beam on the predetermined surface by the detecting means, At least one of the object and the second object is slightly vibrated by the driving means in a direction insensitive to the direction of detecting the relative displacement or relative displacement.

For example, the present invention is characterized in that at least one of the first object and the second object is slightly vibrated in a direction orthogonal to the relative displacement detection plane. The exposure apparatus of the present invention performs relative alignment between a first object and a second object using the above-described position detection apparatus, and transfers a pattern on the first object surface onto a second object surface by exposure and transfer. It is characterized by having.

(Embodiment) FIG. 1 (A) is a sectional view of a main part of a first embodiment of the present invention, and FIG. 1 (B) is a schematic view in which main parts of FIG. 1 (A) are developed. FIG. 1 (B) shows a case in which a positional shift in the XY plane is detected.

This embodiment shows a case where the present invention is applied to an exposure apparatus for manufacturing a proximity type semiconductor element.

Reference numeral 1 denotes a mask as a first object, on which an electronic circuit pattern is formed. Reference numeral 2 denotes a wafer as a second object. Reference numeral 5 denotes an alignment mark provided on the mask 1 surface, and reference numeral 3 denotes an alignment mark provided on the wafer 2 surface. Alignment marks 3 and 5 are each one-dimensional or two
It consists of a physical optical element such as a grating lens, a Fresnel zone plate, or a diffraction grating without a lens function that performs a two-dimensional lens function.

In the present embodiment, the relative positional deviation between the mask 1 and the wafer 2 in the XY plane is detected using the light beam that has undergone the wavefront conversion action by the alignment marks 5 and 3. FIG. 2 shows an example of a pattern when the alignment marks 3 and (5) are constituted by Fresnel zone plates.

Reference numeral 10 denotes a laser light source which emits a coherent light beam having good directivity. Reference numeral 12 denotes a projection lens, which is a laser light source.
The laser beam from 10 is emitted as a parallel light beam onto the alignment mark 5 on the mask 1 surface. 11 is a detection unit,
For example, it is composed of a line sensor such as a CCD. Reference numeral 13 denotes a light receiving lens which receives a light beam from the mask 1 surface, and
The light is guided. Reference numeral 17 denotes a wafer stage, and a wafer 2
Is placed. Reference numeral 18 denotes a stage driving means which drives and vibrates the wafer stage 17 with a small stroke as described later. E is an exposure area.

In the present embodiment, the laser beam from the laser light source 10 is incident on the alignment mark 5 on the surface of the wafer 1 as a parallel light beam by the light projecting lens 11 so that the light beam that has undergone a wavefront conversion action, for example, a transmission diffraction action, is applied to the alignment mark 5. The light is incident on the alignment mark 3 on the surface of the wafer 2. A light beam that has been subjected to an optical action, for example, reflection / diffraction action, at the alignment mark 3 is transmitted without undergoing a diffraction action at the alignment mark of the mask 1 and condensed by the light receiving lens 13 to be incident on the surface of the detection unit 11 as an alignment light flux. I do.

FIG. 3 is an explanatory diagram of the intensity distribution of the alignment light incident on the surface of the detection unit 11. The alignment light beam incident on the detection unit 11 is photoelectrically converted, and a signal having a waveform similar to that shown in FIG. 3 is obtained, for example. The output signal from the detection unit 11 is A / D-converted by the AD conversion unit 19 and sent to the arithmetic unit 20. Then, the relative displacement between the mask 1 and the wafer 2 in the plane (XY plane) is obtained from the incident position (center of gravity) of the alignment light beam to the detection unit 11 by the calculating means 20.

Now, as shown in FIG. 1 (B), the mask 1 and the wafer 2 are displaced by Δσ in the parallel direction, and the distance from the wafer 2 to the focal point of the light beam reflected by the alignment mark 3 on the wafer 2 is a, Assuming that the distance from the converging point of the light beam that has passed through the alignment mark 5 of the mask 1 is b, the center-of-gravity shift amount Δδ of the converging point of the alignment light beam on the detection unit 11 surface is Becomes That is, the center-of-gravity shift amount Δδ is enlarged by (b / a + 1) times.

For example, if a = 0.5 mm and b = 50 mm, the center of gravity shift amount Δδ
Is magnified 101 times from the equation (a).

It should be noted that the center-of-gravity shift amount Δδ and the positional shift amount Δσ at this time are in a proportional relationship as apparent from the equation (a). Assuming that the resolution of the detection unit 11 is 0.1 μm, the displacement Δσ is 0.001
A position resolution of μm is obtained.

In the present embodiment, the center of gravity of the light beam is a point on the light receiving surface of the detection unit where a value obtained by multiplying the position vector of each point in the light receiving surface by the light intensity at the point is integrated into a zero vector when integrated over the entire cross section. However, a point having the highest light intensity may be used as a representative point.

The principle of the method for detecting the displacement in this embodiment has been proposed by the present applicant in, for example, Japanese Patent Application Laid-Open Nos. 1-233305 and 2-1506.

 Next, features of the present embodiment will be described.

In general, when a laser beam is incident on fine irregularities on the mask surface or fine irregularities (up to 1000 mm) on the surface of the wafer on which Al is coated, speckle scattered light is generated by these irregularities and noise light is generated. As a result, it is superimposed on the alignment light beam on the detection unit surface. The intensity of the noise light due to the speckle scattered light increases as the coherence of the laser light source increases. The incident position and size of the noise light vary depending on the relative positions and intervals of the mask and the wafer. If the laser light source, the mask, the wafer, and the like do not relatively change, the noise light does not change over time, so that even if the time average is electrically performed, the noise light cannot be removed.

Further, since the spot diameter of the noise light is substantially equal to the diameter of the alignment light beam, when it overlaps with the alignment light beam on the detection unit surface, it cannot be spatially separated or separated on the spatial frequency axis.

As a result, for example, as shown in FIG. 4, the waveform of the output signal from the detection unit is disturbed, and the position of the center of gravity of the incident light beam on the detection unit surface fluctuates. As a result, a position shift detection error occurs. Since this detection error is generated at the position of the light spot on the detection unit surface, even if it is converted to an electric signal and then averaged, the error in detecting the displacement cannot be reduced.

Therefore, in the present embodiment, the mask 1 or the wafer 2 is slightly vibrated in an insensitive direction at the time of detecting a position shift in order to average spatially noise light caused by speckle scattered light superimposed on the locally concentrated alignment light beam. ing.

For example, the wafer 2 is slightly vibrated in the direction (Z direction) between the mask and the wafer within the range of 1000 to 2000 ° by the wafer driving means 18.

In general, the detecting unit 11 is configured by arranging a plurality of elements (11a, 11b, 11c,...) In a direction of detecting a displacement (X direction) as shown in FIG. For this reason, in the present embodiment, the wafer 2 is vibrated in an insensitive direction, for example, in the Z direction when detecting the positional deviation. (Furthermore, fine vibration may be performed in the Y direction.) At this time, noise light due to speckle scattered light appears at an average period of the fine structure of the wafer from the mask. The position of the center of gravity of the alignment light in the direction of displacement detection does not change, and the waveform of the output signal from the detection unit is averaged over time to reduce fluctuations in the center of gravity of the alignment light beam due to speckle scattered light, thereby reducing misregistration detection errors. Has been reduced.

FIG. 6 shows the voltage applied to the piezoelectric element when the wafer stage 17 is slightly vibrated in the XY plane using the piezoelectric element as the wafer driving means 18 and the output signal from the detecting section when the CCD is used as the detecting section 11. FIG. 4 is an explanatory diagram of a timing chart showing a relationship with the above.

In this embodiment, the same effect can be obtained even if a bimorph is used as the wafer driving means 18.

In the above embodiment, the case where the positional deviation between the mask and the wafer is detected in the XY plane is described. However, the relative positional deviation detection for calculating the amount of positional deviation from a preset distance between the mask and the wafer is described. The present invention can be similarly applied.

FIG. 7 (A) is a schematic view of an optical system according to an embodiment when the present invention is applied to an apparatus for measuring the distance between a mask and a wafer in a semiconductor manufacturing apparatus, and FIGS. 7 (B) and (C) are Figure (A)
FIG. 3 is a schematic diagram of a main part showing an optical path of a part of FIG.

Light beam from 71, for example H _e -N _e laser or a semiconductor laser LD, etc. In the figure, 72 is a first object, for example a mask, 73
Is a second object, for example, a wafer, and the mask 72 and the wafer 73
Are initially opposed to each other at a position separated by a distance d _O. 7
Reference numerals 4 and 75 denote first and second physical optical elements as alignment marks provided in a part of the surface of the mask 72, for example, a scribe line. These physical optical elements 74 and 75 are, for example, a diffraction grating or a zone plate Fresnel lens. Etc.

Reference numeral 78 denotes a light receiving means, which is composed of, for example, a line sensor or a PSD, and detects the position of the center of gravity of the incident light beam. Reference numeral 79 denotes a signal processing circuit which calculates the center of gravity of the light beam incident on the surface of the light receiving means 78 by using a signal from the light receiving means 8 and calculates the distance between the mask 72 and the wafer 73 as described later. . Reference numeral 80 denotes an optical probe, which includes a light receiving means 78 and, if necessary, a signal processing circuit 79.
73 is relatively movable.

In this embodiment, the light beam 71 from the semiconductor laser LD is used.
(Wavelength λ = 830 nm) is a Fresnel zone plate (hereinafter abbreviated as FZP) 7 as the first physical optical element on the surface of the mask 72.
It is incident on point A on four surfaces. The diffracted light of a predetermined order diffracted at an angle θ1 from the first FZP 74 is reflected at a point B (point C when the wafer 73 is at the position P2) on the surface of the wafer 73. Reflected light when these reflected light 31 is the wafer 73 is positioned at the reference position P1 near the mask 72, the reflected light 32 reflected light when the wafer 73 is from the position P1 at a distance d _G only displaced position P2 It is. In this embodiment, the alignment mark on the surface of the wafer 73 is constituted by a simple reflection surface.

Next, the reflected light from the wafer 73 is transferred to the second object on the first object 72 surface.
At the point D on the FZP75 surface (point E when the wafer 73 is at the position P2). The second FZP 75 has an optical function of changing the exit angle of the output diffracted light according to the incident position of the incident light beam.

A predetermined order diffracted light 61 diffracted at an angle θ2 from the second FZP 75 (a diffracted light 62 when the wafer 73 is at the position P2)
Is guided on the surface of the light receiving means 78.

Then, the incident light beam on the light receiving means 78 surface at this time
The distance between the mask 72 and the wafer 73 is calculated using the position of the center of gravity of 61 (the incident light 62 when the wafer 73 is at the position P2).

In this embodiment, the first and second FZPs 74 provided on the surface of the mask 72,
The reference numeral 75 denotes a predetermined known pitch, and the diffraction angles θ1 and θ2 of the diffracted light having a predetermined order (for example, ± 1st order) of the light beam incident thereon are obtained in advance.

Now, let the focal length of the second FZP75 be fM2 (μm) (where fM2
Is applicable to either positive or negative), and assuming that the distance from the second FZP 75 to the luminous flux evaluation surface corresponding to the surface of the light receiving means 78 is l, in this case, the wafer 73 is displaced by the distance d _G from the reference position P1. The amount of movement S of the center of gravity position on the surface of the light receiving means 78 is Given by The position of the center of gravity (reference point) when the wafer 73 is at the reference position P1 is obtained in advance, and the deviation of the center of gravity from the reference point at the time of the interval measurement is obtained. As a result, the position P1 of the wafer 73 is
Distance deviation amount d _G from is determined.

The mask-wafer distance d _O at the position P1 is obtained in advance by another distance measuring means.

In the present embodiment, similarly to the first embodiment, in order to remove the adverse effect of noise light due to speckle scattered light, the mask or wafer 73 is moved by the driving means (not shown) in the gap detection direction (Z direction). A minute vibration is made in a non-sensing direction, for example, in the XY plane.

(Effects of the Invention) According to the present invention, as described above, at least one of the mask and the wafer is vibrated in a direction insensitive to the detection direction, so that a mask when a laser light source having good coherence is used as the light source means. It is possible to remove the adverse effect of noise light based on speckle scattered light generated by fine irregularities on the wafer, and to accurately detect relative displacement between the mask and wafer and relative displacement. A possible position detecting device can be achieved.

[Brief description of the drawings]

1 (A) and 1 (B) are schematic views of a main part of the first embodiment of the present invention and explanatory views showing a part of the development, FIG. 2 is a pattern diagram of an alignment mark of FIG. 1 (A), and FIG. FIG. 4 is an explanatory diagram of the intensity distribution of the alignment light beam on the detection unit surface in FIG. 1 (A), FIG. 5 is a schematic diagram of the detection unit in FIG. 1 (A), and FIG.
FIG. 7 is a timing chart showing the relationship between the voltage applied to the driving means and the output signal from the detection unit according to the first embodiment of the present invention, and FIGS. 7 (A), (B) and (C) show the timing chart of the present invention. 8 and 9 are schematic diagrams of a conventional position detecting device using a zone plate, and FIG. 10 is a schematic diagram of a conventional interval measuring device. In the figure, 1,72 is a first object (mask), 2,73 is a second object (wafer), 3,5,74,75 are alignment marks, 10 is a laser light source, 11 is a detection unit, and 12 is light projection Lens, 13 is a light receiving lens,
17 is a wafer stage, 18 is a wafer driving means, 19 is an A / D converter, and 20 is an arithmetic means.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-56-98829 (JP, A) JP-A-2-47822 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01B 11/00-11/30 H01L 21/31 501-531,561-5 79 G03F 7/20-7/24 G03F 9/00-9/02

Claims (3)

(57) [Claims] An alignment mark is provided on a first object surface and a second object surface which are opposed to each other to detect a relative displacement and / or a relative displacement in a relative surface of each of them. Of the light beams from the means, the light beams having undergone wavefront conversion by the alignment marks on the first object surface and the second object surface, respectively, are guided on a predetermined surface, and the incident position of the light beam on the predetermined surface Is detected by the detecting means, and when detecting the relative positional deviation and / or the relative distance deviation between the first object and the second object, at least one of the first object and the second object is relatively driven by the driving means. A position detecting device characterized in that it is slightly vibrated in a direction insensitive to a direction of detecting a target position deviation or a relative distance deviation. 2. The position detecting device according to claim 1, wherein at least one of the first object and the second object is slightly vibrated in a direction orthogonal to a relative position detection plane. 3. A relative position between a first object and a second object is adjusted by using the position detecting device according to claim 1, and a pattern on the first object surface is exposed on a second object surface. An exposure apparatus that performs transfer.