JP2556559B2 - Interval measuring device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a distance measuring device for measuring a distance between two objects with high accuracy. For example, in a semiconductor manufacturing apparatus, a distance between a mask and a wafer is measured, It is suitable when controlling to a predetermined value.

[Conventional technology]

2. Description of the Related Art Conventionally, in a semiconductor manufacturing apparatus, a distance between a mask and a wafer is measured by a distance measuring device or the like, and a pattern on the mask surface is exposed and transferred onto the wafer surface after controlling the distance to be a predetermined distance. This allows highly accurate exposure and transfer.

FIG. 17 is a schematic view of a distance measuring device proposed in Japanese Patent Laid-Open No. 61-111402. In the same figure, a mask M as a first object and a wafer W as a second object are arranged so as to face each other, and a light flux is condensed at a point P _S between the mask M and the wafer W by a lens L1.

At this time, they are reflected on the surface of the light flux mask M and on the surface of the wafer W, respectively, and are focused and projected onto the points P _W and P _M on the surface of the screen S via the lens L2. The distance between the mask M and the wafer W is measured by detecting the distance between the light converging points P _W and P _M on the screen S surface.

[Problems that the invention is trying to solve]

However, if the mask M and the wafer W are parallel to each other, the apparatus shown in the figure can accurately measure the distance between them, but one of them is tilted, for example, the mask M is tilted and becomes non-parallel as shown by a dotted line. In this case, the incident point of the light flux on the screen surface S changes from the point P _M to the point P _N , which causes a measurement error.

In view of the drawbacks of the above-mentioned conventional example, the present application aims to provide a distance measuring device that can always measure distance with high accuracy.

[Means for solving problems]

In the present invention, the spacing direction (the facing direction of the first object and the second object)
When the first object and the second object move relative to each other in the direction perpendicular to the (lateral direction), the incident positions move equally, and when the relative movement moves in the opposite direction, the two incident light positions move differently. Highly accurate interval measurement is always achieved by measuring the interval.

〔Example〕

FIG. 1 and FIG. 2 are a schematic diagram of an optical system and a schematic diagram of an apparatus configuration of an embodiment when the present invention is applied to an apparatus for measuring a distance between a mask and a wafer of a semiconductor manufacturing apparatus.

In FIGS. 1 and 2, 1 is a light beam from a light source 1a such as a He-Ne laser, a semiconductor laser, or an LED, 2 is a first object such as a mask, and 3 is a second object such as a wafer. The mask and the wafer are opposed to each other with a gap g _m therebetween. Reference numerals 8 and 8'represent physical optical elements provided on a part of the mask 2 surface, and reference numerals 9 and 9'represent physical optical elements provided on a part of the wafer 3, respectively. ,
9,9 'are Fresnel zone plates (hereinafter referred to as FZPs) that diffract the light so that it converges or diverges. In the figure, the mask 2 and the wafer 3 are FZ for simplification.
It is displayed as if it consists of only P8,8 'and FZP8,8'. 4 is a light receiving means, 10 is a CPU which receives a signal from the light receiving means 4, measures the distance between the mask 2 and the wafer 3, and issues a command signal based on the result, 100 A stage for supporting and carrying the wafer 3, 101 is a CPU 10 Stage 10 based on the command signal of
This is a stage driver that drives 0 in the gap direction (Z direction) between the mask and the wafer.

The light receiving means 4 is placed at a position apart from the wafer 3 by L ₀ .

Incidentally, FIG. 1 shows a state of reflected and diffracted light from the wafer 3 shown in FIG. 2, and the wafer 3 is shown as a transmissive diffraction element equivalent to a reflective type for convenience of explanation.

Reference numeral 4 is composed of a line sensor, an area sensor, a PSD, or the like, and can detect the position of the center of gravity of the incident light flux on the sensor surface, the spot shape, and the like.

Here, the center of gravity of the light flux is the point in the light flux cross section at which the integrated value becomes 0 vector when the position vector of each point in the cross section is multiplied by the light intensity at that point and integrated over the entire cross section. However, as another example, the position of the point where the light intensity reaches a peak may be detected. The CPU 10 obtains the position of the center of gravity and the spot shape of the light beam incident on the surface of the light receiving means 4 using the signal from the light receiving means 4, and calculates the distance g _m between the mask 2 and the wafer 3 as described later. There is.

The light receiving means 4 (and the CPU 10 if necessary) is movable relative to the mask 2 and the wafer 3.

In the present embodiment, the luminous flux 1 from the semiconductor laser is
(Wavelength λ = 8300Å) is incident on the Fresnel zone plate on the mask 2 surface as a plane wave at an angle θ in the y _z plane with respect to the normal to the mask surface. FIG. 1 shows the situation of FIG.
The Fresnel zone plates 9 and 9'of the wafer 3 are shown as a transmissive diffraction element equivalent to the reflection diffraction in the diffraction state of the light ray viewed from the direction (y direction) perpendicular to the longitudinal direction of the. The luminous flux shown on the right side of the wafer 3 is
_{The Z} direction component is emitted in the direction opposite to the drawing. In FIG. 2, the distance between the spots 7 and 7 '(distance between the centers of gravity of 7 and 7') serves as information about the surface distance g _m . Therefore, the CPU measuring the distance between the spots 7 and 7'in the light receiving means 4 detects g _m . The principle will be described later. In FIG. 1, FZPs 8 and 8'on the surface of the mask 2 have focal points at F ₁ and F ₂ , and the first-order diffracted light having the same diffracting action as a so-called concave lens that diverges the incident light flux with this point as the divergence origin is used. There is a pattern to have. This first-order diffracted light strikes the wafer surface 3 and is reflected and diffracted to a predetermined position on the detecting means 4 which is further separated from the wafer by L ₀ + g _m to form a spot.
And 9'patterns are provided on the wafer 3. Conversely speaking, the detecting means 4 is arranged at a position where the light diffracted by the FZPs 8,8 ', 9,9' is focused. The light reflected and diffracted from the wafer 3 actually reaches the detecting means 4 through the mass 2 as shown in FIG. 2 before reaching the detecting means 4 from the FZPs 9 and 9 ', but when passing through the mask 2, it is diffracted. It is passed as so-called zero-order direct-passing light.

Incidentally, as the procedure for measuring the gear gap in the present embodiment, for example, the following method can be adopted. As a first method, a signal of the distance between the centers of gravity of the two light fluxes is obtained on the detection surface of the light receiving means 4 with respect to the distance ΔZ between the two objects, and the CPU 10 calculates the distance ΔZ from the distance between the two bodies from the center distance signal. Is calculated, and the stage driver 101 moves the stage 100 by an amount corresponding to the positional displacement amount ΔZ at that time.

As a second method, the CPU 10 finds the direction in which the distance deviation amount ΔZ is canceled from the signal from the light receiving means 4, and the stage driver 101 moves the stage 100 in that direction, and repeats until the distance deviation amount ΔZ falls within the allowable range. Do it.

Flow charts of the above alignment procedure are shown in FIGS. 2 (B) and 2 (c), respectively.

The principle of measuring the surface spacing g _{m in the} apparatus configured as described above will be described in detail with reference to FIGS. 1 and 2.

In FIG. 1, it is assumed that the optical axis of the FZP8 on the mask 2 is 5, the optical axis of the FZP9 is 6, and the optical axes of the two are offset by Δ _{1 in the} x direction. If the optical axis of the FZP8 'is 5'and the optical axis of the FZP9' is 6 ', the optical axes of these are also deviated by Δ _{2 in the} x direction, and the deviating direction is as shown in FIG. . or,
The distance between F ₁ and the mask 2 (focal length of the FZP8 as a concave lens) is f _M1 , and the distance between F ₂ and mask 2 (focal length of the FZP8 ′ as a concave lens) is f _M2 .

At this time, the positions 7 and 7 of the spots formed by the patterns FZP8 and 8'on the mask 2 and the patterns (FZP) 9 and 9'on the wafer 3 are the optical axis 5 of the FZP8 and the optical axis 5'of the FZP8 ', respectively. It is assumed that the positions can be shifted by g ₁ and g ₂ from. Patterns 9 and 9'on the wafer are _{1 so} that the positions of F ₁ and 7 and F ₂ and 7'are in a conjugate relationship.
Design so that the next diffracted light is generated. This time The relationship is established. The directions of g ₁ and g ₂ with respect to the optical axes 5 and 5'are as shown in FIG. If the mask 2 and the wafer 3 are displaced from each other along the xy plane while the gap g _m is kept constant, the value of Δ ₁ and Δ ₂
It can be expressed by an equation corresponding to the case where the shift amount δ is added to the value of. When the wafer shifts upward by δ in the plane of Fig. 1, the deviation of the spots 7,7 'from the optical axes 5,5'g ₁ ′, g ₂ ′ (the deviation direction is the same as g ₁ , g ₂ ). Is Can be represented by That is, the spots on the detecting means 4 of the light flux condensed by the FZPs 8 and 9 are in the direction of decreasing g ₁ , that is, in the upward direction of FIG. The spots on the detecting means 4 for the luminous flux which is moved by only the distance and is condensed by the FZPs 8 ', 9'are in the direction of increasing g ₂ , that is, in the direction of FIG. Just move. Therefore, if each FZP is adjusted so that f _M1 = f _M2 , the distance between the spots 7 and 7 ′ can be found to be invariable from the equation even if the deviation δ occurs. Even if the wafer 3 is tilted, if f _M1 = f _M2 is set, the movement amounts of the spots 7 and 7 ′ are substantially the same amount in the same direction, so that the distance between 7 and 7 ′ is unchanged. Become.

On the other hand, as can be seen from the equation, if the surface spacing g _m changes, the values of g ₁ and g ₂ change accordingly. For example, if L ₀ is larger than _{f M1, f M2, g 1} , g 2 decreases with increasing g _m, g _1, g ₂ if g _m decreases increases. Therefore, the distance between the spot 7 and the spot 7'changes according to g _m . This means that by measuring the distance between the spots 7 and 7'on the detecting means 4, even if the mask and the wafer move or tilt in the plane, the surface distance information between the mask and the wafer is not affected by the influence. It means that it can be detected. Distance between mask 2 and wafer 3 g _m and spot
The relational expression with the distance l _{1 of} 7,7 ′ is as follows.

Where l _M is the optical axis distance between FZP8 and FZP8 ′, and f _M1 = f _M2
It is said that.

 The following is a numerical example.

For example, when L ₀ = 18345.94 μm, f _M1 = f _M2 = 114.535 μm, the relationship between the surface spacing g _m and g ₁ / Δ ₁ , g ₂ / Δ ₂ is When Δ ₁ = Δ ₂ = 10 μm The distance between spots 7 and 7'is 71.5μ for the gear
When it changes by 10 μm from m to 61.5 μm, it changes by 111.34 μm (= 1055.67 × 2-1000 × 2). Therefore, if the gear gap fluctuates by 1 μm, the fluctuation of the spot distance between 7 and 7'is 11.1
It becomes 3 μm, and a one-dimensional line sensor or PSD is used as the detection means 4.
If the variation in the distance between the spots 7 and 7'can be detected by using, for example, with a resolution of 1 .mu.m, the change in the surface distance between the mask 2 and the wafer 3 can be detected with a resolution of 0.09 .mu.m.

If each parameter in the relational expression between the distance value between the mask 2 and the wafer 3 and the distance value of the spots 7 and 7'is obtained in advance, this relational expression is obtained from the obtained measured value of the distance of the spots 7 and 7 '. Based on this, the surface distance between the mask 2 and the wafer 3 is obtained.

Incidentally, FIG. 3 shows the relationship between the optical axes of the FZP pattern on the mask and the FZP pattern on the wafer shown in FIG. 2 as viewed from above the mask and wafer surfaces. In the figure, FZP8,8 'and FZP9,9' are shown side by side in the y direction for the sake of clarity, but in reality they are in a state of overlapping in the vertical direction of the paper (z direction). In the figure, 8a, 8'a, 9a, 9'a are lines parallel to the y-axis including the optical axis of each FZP.

Further, the spots 7 projected on the light receiving means 4 in FIG.
FIG. 4 (A) shows the relationship of 7 '. Thus, when the light receiving means 4 is used as one line sensor and two spots 7 and 7'are formed on the line sensor 4 to directly measure the distance between them, masks and wafers that can be considered in the normal case Set each parameter of the mask and the relational expression of the wafer interval g _m and the spot interval l _{1 so} that the spot interval does not become 0 within the interval range. As a result, for each value of l ₁ , only one value of g _m can be found.

FIG. 4 (B) shows the relationship between the spots 7 and 7'projected onto the light receiving means 4 in another embodiment of the present invention. In this way, spots 4a and 4b are formed on the two line sensors 4a and 4b, respectively, which are provided at positions displaced in the y-direction, and the x-direction component interval l ₁ between them is obtained to obtain the mask 2 and the wafer 3
You may ask for the interval. In this case, even if the x-direction component interval l ₁ is set to 0 when the mask 2 and the wafer 3 are at the set interval, whether the interval is larger or smaller than the set interval depends on whether the spots 7 and 7 ′ are on the left or right of the drawing. You can tell which side you are on.

Here, since the FZPs 8, 8 ', 9, 9'shown in FIG. 2 have a lens function in both the x and y directions, the mask 2 and the wafer 3 are y-shaped.
When moving considerably in the direction, spot 7,
7'moves in the width direction of the line sensor 4. Therefore, the line sensor 4 has a sufficient width so that the spots 7 and 7'are located on the sensor even if the mask 2 and the wafer 3 are displaced in the maximum possible y direction. Instead of a line sensor, an area sensor with a sufficient width in the y direction is used for spot 7,
7'may be detected. The FZP on the mask and the wafer may be a diffraction pattern having a power (refractive power) in at least one direction (here, the x direction), and may not have the power in the y direction in FIG. In FIG. 2, the mask and the wafer have a power only in the alignment direction (x direction) and no power in the direction perpendicular to the alignment direction (y direction) and the incident angle θ is set to 17.5 °. FZ on
An example of the pattern of P is shown in FIG.

Further, there is no particular limitation on the method of dividing the area of the pattern setting on the mask and the wafer, as long as the relationship between the optical axes derived from the power setting of the pattern is clearly set.

FIG. 6 shows another example of area division of the one shown in FIG. In this embodiment, FZP8 and 8'and FZP9 and 9'are provided in parallel in the y direction. The optical axes of the FZPs 8 and 8'are located at the same position in the x direction, and the optical axes of the FZPs 9 and 9'are provided so as to be offset from each other by Δ ₁ and Δ _{2 in the} x direction. Even when the parallel direction is changed in this way, the same effect as the above-described embodiment can be obtained by adjusting the incident angle of the incident light and the refraction angle of the diffracted light by the pattern so that the diffracted light is condensed on the light receiving means 4. .

Further, the power (refractive power) of the FZP of the mask and the wafer need not be a combination of unevenness when compared to a lens as shown in FIG. 1, but a combination of unevenness as shown in FIG. May be

In FIG. 7, the spots 7 and 7'are the same as in FIG.
From the optical axis 5, 5'of Is shown, Becomes Here, the focal length of FZP of _M1 and _M2 masks, g _m
Mask and wafer spacing, Are the optical axes of the mask FZP8 and 8'and the wafer FZP9 and 9 ', respectively.
This is the amount of axis shift. Even in this case, it is possible to detect the surface distance between the mask and the wafer by measuring the distance between the spots 7 and 7 ', regardless of the xy plane shift of the mask and the wafer and the occurrence of the tilt of the wafer. Is the same as.

The above changes the gap between the mask and the wafer, and the two light fluxes that move along the xy plane of the mask and the wafer without changing the gap due to the relative shift or the wafer tilt cause the optical axis shift between the mask and the wafer. This is the case of being formed by two different FZP sets. Next, a case will be described in which the two light fluxes are formed by causing two FZPs on the mask side to have a light flux refracting action in different directions.

FIG. 8 is an optical path diagram showing one embodiment when different refractive angles are given to the FZPs 8 and 8'of the mask. In Figure 8, FZP
The luminous fluxes incident on 8,8 ′ are Δ ₁ ′,
It is emitted as a divergent light beam with focal points F ₁ and F ₂ separated by Δ ₂ ′ as the divergence origin, and is incident on FZPs 9 and 9 ′ whose optical axes are deviated from ΔZ ₁ and Δ ₂ from FZPs 8 and 8 ′, respectively. Then, the light receiving means 4
Focus on the top to form spots 7,7 '.

The distances g ₁ and g ₂ from the pattern axis of the FZPs 8 and 8'of the spots 7 and 7'of the mask and wafer FZP are given by the following equations.

, If the deviation amount δ is added to the value of Δ _{1 and} the value of Δ _{2 in} the equation, the deviation g ₁ ′ of the optical axis 7, 5 ′ from the optical axis 5, 5 ′,
g ₂ ′ is If f _M1 = f _M2 , the spot 7,
The 7'distance does not depend on the xy plane shift of the mask and wafer. This distance does not change even if the wafer tilts,
Therefore, by measuring the distance between the spots 7 and 7'as in the previous embodiment, it is possible to measure the mask and wafer intervals that are not affected by the xy in-plane deviation and the wafer inclination. Although FIG. 8 shows the case where the combination of the powers of the FZP of the mask wafer is uneven, this may be uneven as in the above-mentioned embodiment. 、、、
As can be seen from the equation, the same effect can be obtained even if the axial deviation amounts Δ ₁ and Δ _{2 of the} FZPs of the mask and the wafer are both 0.

Up to now, the example in which the FZP is provided on both the mask and the wafer has been described, but the case where the FZP is provided only on the mask and the specular reflection surface without a pattern is used for the wafer will be described next. FIG. 9 illustrates the device configuration of this example. FIG. 10 shows the relationship between the setting of the pattern area on the mask and the optical axis of the FZP in FIG. 23 and 23 'are incident side FZPs, 23a and 23a' are y-axis parallel lines including the optical axes of the incident side FZPs 23 and 23 ', and 24a and 24a'.
Is a y-axis parallel line including the optical axis of the FZP on the emission side FZP 24, 24 'on the mask 2 for re-diffracting the light 25, 25' reflected by the wafer 3 in the 0th order. As shown in this figure, the incident side FZP23,23 '
And the output side FZPs 24 and 24 'have their optical axes shifted in the x direction by Δ ₁ ^* and Δ ₁ ^* , respectively. FIG. 11 shows the situation shown in FIG. 9 as an optical path diagram in which specular reflection of the wafer is replaced with an equivalent transmitted light beam. In Fig. 11, the distance of the spot position 20 from the mask FZP optical axis 21, 21 'on the incident side.
g ₁ ^* and g ₂ ^* are expressed as follows. (F _M1 ^* , f _M2
^* Is the focal length of FZP23, 23 ') As described above, in this case as well, the distance g _m between the mask 2 and the wafer 3 is not affected by the xy in-plane deviation and the wafer inclination by detecting the distance between the spots 20 and 20 'as in the previous embodiment. Can be obtained.

Although the embodiment shown in FIGS. 9, 10, and 11 was the case where the 0th-order specular reflection of the wafer was used, a linear grating 33 is provided on the wafer 3 to change the diffraction direction on the wafer 3. FIG. 12 shows an embodiment in which the above is provided. The FZPs 31, 31 ', 32, 32' in the figure are provided so as to focus the luminous flux diffracted by the linear grating 33 on the light receiving means 4, except for the FZPs 21, 21 ', 2 in FIG.
Similar to 2,22 ', y-axis parallel line including each optical axis
31a, 31a ', 32a, 32a' are also Δ ₁ ^* , Δ ₂ respectively as shown in the figure.
Only ^* is shifted in the x direction. FIG. 13 shows in detail the relationship between the mask, the pattern area of the wafer and the optical axis in the example of FIG. Similar to FIG. 3, the mask 2 and the wafer 3 are viewed from above, and the mask 2 and the wafer 3 are displaced in the x direction for easy understanding. In the case of this embodiment, the same effect as that of the embodiment of FIG. 9 can be obtained.

Although all of the above have described the case of the proxy used in X-ray lithography, an example applied to the case of a reduction type optical stepper or a stepper using excimer light is shown below.

FIG. 14 is a schematic configuration diagram showing an example in which the present invention is applied to an optical stepper or an excimer reduction stepper. 40 is a reticle, 45 is a wafer, 41 is a projection optical system, 43, 43 ', 47, 4
Reference numeral 7'denotes an FZP provided on the reticle. In this example, the linear grating 51 on the wafer changes the emission angle of the light beam 1.
The distance between the spots 48 and 48 'changes according to the amount of change .delta. When the position of the wafer 45 approaches or moves away from the reticle. In principle, the optical system 41 is provided between the reticle 40 and the wafer 45, which is the same as that of the embodiment shown in FIG. 12, and therefore the same effect as described above can be obtained. Like FIG. 14, FIG. 15 is also a structural schematic diagram showing an example in which the present invention is applied to a stepper. 63,6
3'is an FZP on the reticle, and 64, 64 'are FZPs on the wafer. By measuring the distance between the optical spots 65, 65' formed on the detecting means 4, the optical axis of the imaging lens 61 of the wafer 68 is measured. It is possible to measure the deviation of the direction, that is, the reticle 60 and the distance. This is the same as the embodiment of FIG. 2 in principle.

FIG. 16 shows an example of application to a mirror reduction type stepper. The reticle 40 and the wafer 45 have a conjugate (imaging) relationship with respect to the three groups of mirrors 72, 73, and 74. 76,76 ′ is F on the reticle
ZP pattern areas, 78 and 78 'are FZP pattern areas on the wafer. The deviation of the wafer in the optical axis direction is detected by measuring the distance between the spots 81 and 81 'by the light receiving means of No. 4. This is also similar in principle to the embodiment shown in FIG. The mask and the FZP of the wafer are shown as an example of a combination of convex and concave, or a combination of concave and convex when compared to a lens, but if a spot that can be made on the detecting means is obtained, convex and convex or concave and concave. May be Even if the spot has a little space, it will be okay if the center of gravity can be detected.

〔The invention's effect〕

As described above, according to the present invention, the space between the mask and the wafer is
It is now possible to measure highly accurate distances without being affected by relative displacement along the xy plane or wafer tilt.

[Brief description of drawings]

1 is an optical path diagram of the first embodiment of the present invention, FIG. 2 (A) is a device configuration diagram of the embodiment of FIG. 1, and FIGS. 2 (B) and 2 (C) are the embodiments of FIG. FIG. 3 is an FZP optical axis relational diagram of the embodiment of FIG. 1, FIG. 4A is a relational diagram of the spot and the light receiving means of the embodiment of FIG. 1, and FIG. 4B. Is a relationship diagram of the spot and the light receiving means of the second embodiment of the present invention, FIG. 5 is an example of FZP pattern of the embodiment of FIG. 1, and FIG. 6 is an FZP optical axis relationship diagram of the third embodiment of the present invention. FIG. 7 is an optical path diagram of a fourth embodiment of the present invention, FIG. 8 is an optical path diagram of a fifth embodiment of the present invention, FIG. 9 is a device configuration diagram of a sixth embodiment of the present invention, and FIG. Is an optical axis relation diagram of the FZP of the embodiment of FIG. 9, FIG. 11 is an optical path diagram of the embodiment of FIG. 9, FIG. 12 is a device configuration diagram of the seventh embodiment of the present invention, and FIG. 12 is an optical axis relation diagram of the FZP of the embodiment of FIG. 8 is an apparatus configuration diagram of the embodiment, FIG. 15 is an apparatus configuration diagram of the ninth embodiment of the present invention, FIG. 16 is an apparatus configuration diagram of the tenth embodiment of the present invention, and FIG. 17 is a diagram of a conventional example. is there. In the figure, 1a ... light source, 8, 9, 8 ', 9' ... FZP 4 ... light receiving means, 10 ... CPU.

Claims (1)

(57) [Claims] 1. Light source means for emitting at least a first light flux and a second light flux in the direction of a first object and a second object facing each other for position detection, and a predetermined direction by the first object and the second object. The incident position of the first light flux whose incident position on the first light-receiving surface changes in accordance with the relative position of the first object and the second object facing each other and along the direction orthogonal to the facing direction. A first light detecting means for detecting the second light receiving surface, which is deflected in a predetermined direction by the first object and the second object and changes in relative position along the facing direction of the first object and the second object. The incident position on the second light receiving surface is different from that of the first light beam, and the incident position on the second light receiving surface is the same as that of the first light beam according to the relative position change along the direction orthogonal to the facing direction. Second optical detector for detecting the incident position of the second light flux Means a detection result to the first object Zui and means for detecting the facing direction relative change in position of the second object, a distance measuring apparatus characterized by having a said first and second light detecting means.