JP2672052B2 - Step pattern detection method and apparatus - Google Patents

Description

BACKGROUND OF THE INVENTION [0001] Field of the Invention The present invention relates to a stepped pattern detecting method and apparatus for detecting the position of the step pattern formed on a sample such as a wafer is there. [0002] As a conventional technique for detecting a step pattern, alignment pattern detection by a reduction projection exposure apparatus is known . That is, with the progress of miniaturization of semiconductor integrated circuits, it is the current situation that the alignment accuracy between the reticle and the wafer during exposure by the reduction projection exposure apparatus is required to be higher and higher. Therefore, it is possible to perform alignment for each chip so as to cope with an array error of chips in a wafer, and to perform T through a reduction projection lens.
It is considered that the TL alignment method will become the mainstream in the future manufacturing of highly integrated circuits. FIG. 13 shows an example of the TTL alignment method. In this case, the circuit pattern previously formed on the reticle 1 is transferred to the wafer 3 mounted on the wafer stage 4 through the reduction projection lens 2 and
~ Several chips 16 are exposed, but prior to this exposure, the positions of the reticle initial setting patterns 15, 15 'are first detected by the reticle alignment optical systems 5, 5', so that the reticle 1 is exposed. Is set to the initial position. Next, on the wafer 3, the alignment patterns 14, 14 'near the chip 16 are imaged on the alignment patterns (window patterns) 13, 13' on the reticle 1 via the reduction projection lens 2, and both patterns are detected for wafer alignment. It is designed to be detected by an optical system. The wafer alignment detection optical system includes mirrors 6 and 6 ', relay lenses 7 and 7',
In addition to the magnifying lenses 8 and 8 ', the movable slits 9 and 9', the photomultiplier tubes (photomultipliers) 10 and 10 ', an optical fiber 1 for emitting alignment illumination light having the same wavelength as the exposure light
It is composed of 1, 11 ', etc. Illumination light from the optical fibers 11 and 11 'illuminates the alignment patterns 13 and 13' through half mirrors, relay lenses 7 and 7 ', and mirrors 6 and 6', while reflected light from the mirrors 6 and 6 '. ', Relay lens 7, 7', half mirror,
It is designed to be detected by the photomultiplier tubes 10 and 10 'through the magnifying lenses 8 and 8', the mirror, and the movable slits 9 and 9 '. By the way, if the detected wafer alignment patterns 14 and 14 'and the reticle alignment pattern are detected,
If the positions of 13 and 13 'do not match, the wafer 3
The position of both patterns 14, 14 ', 13, 13' is made to coincide by moving the wafer stage 4 carrying the wafers in the X and Y directions according to the displacement direction and the amount thereof. There is something. In this way, after the alignment is completed, the exposure system 12 irradiates the reticle 1 with exposure light. Note that, as one related to this type of alignment method, there is, for example, JP-A-55-41739. By the way, in this TTL alignment method, a problem that has been pointed out in the past but has not yet been solved is a decrease in alignment accuracy due to uneven coating of photoresist on the wafer. This problem has become an extremely serious problem in recent years as semiconductor circuits are highly integrated. Here, the method of applying the photoresist to the wafer will be described. As shown in FIG. 14, the photoresist 3 is rotated by the spin coater (rotational coating machine) at a high speed in the R direction while the wafer 3 is rotated by centrifugal force. 1 to the whole surface
It is adapted to be applied in a thickness of 2 μm (in the case of a single layer resist). In this case, the flow direction of the photoresist is a direction that spreads radially from the center of the wafer 3, as shown by arrows A, B, C, and D, but FIG.
3 is an enlarged view of the directional alignment pattern 19. In this example, the alignment pattern is formed by forming the SiO ₂ layer 22 as a concave or convex step pattern on the Si substrate 21 as shown in FIG. The film thickness of the formed photoresist 23 draws a gentle curve according to the shape of the step. In this way, the alignment pattern is Si
It is formed on the substrate 21, but the problem is as shown in FIG.
The X-direction alignment pattern 19 near the chip 17 is parallel to the resist flow direction B, but for example, the X-direction alignment pattern 20 near the chip 18 is the resist flow direction C.
Means that they are almost orthogonal. As a result, as shown in FIG.
The photoresist film thickness distribution in the pattern width direction in the portion is symmetrical, but as shown in FIG. 16B, the photoresist film thickness distribution in the alignment pattern 20 portion is largely disturbed by the flow of the photoresist at the pattern edge portion. It is asymmetrical. Now, these alignment patterns 19 and 20
Is illuminated by pattern illumination light 24a, 25a, but the reflected light from the pattern is approximately reflected light 24b, 25b from the photoresist surface and reflected light 24c, 25c from the Si substrate 21 or the SiO ₂ layer 22 surface. Is obtained as interference light. That is, as can be seen from the interference intensity curve 28 shown in FIG. 18, the interference light intensity I changes periodically according to the film thickness d of the photoresist 23. From the above, the reflected light intensity distribution 26 from the alignment pattern 19 is shown in FIG.
As shown in (a), it is symmetrical, but the reflected light intensity distribution 27 from the alignment pattern 20 is asymmetric, as shown in FIG. 17 (b). Therefore, in the conventional alignment method in which the symmetry of the detection signal waveform is used to set the symmetry center of the waveform as the center position of the alignment pattern, as shown in FIG. 17B, the true pattern center position x _w
On the other hand, x _d may be regarded as the center position of the pattern and an error ex may occur, and the deterioration of the alignment accuracy cannot be neglected. Also, the TTL so far
In the alignment method, not only uneven application,
Problem that the contrast of the pattern detection signal is largely changed by the coating thickness of the photoresist is also circumstances that have been pointed out previously. [0007] In THE INVENTION to be solved INVENTION The above prior art, the position of the step pattern formed on a sample in the stable and against challenges to be detected with high accuracy, sufficient consideration Was not done. An object of the present invention is to solve the above problems of the prior art, the position of the step pattern formed on a sample in the stable with a light interference, moreover a step pattern detection method which can detect in the accuracy better The equipment is provided. The above object is to illuminate a step pattern formed on a sample with coherent illumination light.
In addition, it can be used as a position near the step pattern.
Coherent illumination light Coherent illumination branched from the midway position of the optical path
A reference light is created separately from the light, and the reference light is reflected from the above step pattern.
The two-dimensional display is caused by the interference between the coherent illumination light and the reference light.
In addition to generating the interference pattern, it is detected photoelectrically as an interference signal.
From the interference signal, the step depth in the step pattern
Signal level change due to corresponding phase change detected
The position of the step pattern is changed based on the signal level change.
This is achieved by detecting the position . Further, as the step pattern detection device, a coherent illumination light source that illuminates the step pattern formed on the sample, and a non-neighborhood of the step pattern are provided.
Coherent illumination light as a position
Separate reference light is created by a reflecting mirror from the coherent illumination light
Reference light creating means and the reflection from the step pattern
Interfering means for interfering the coherent illumination light and the reference light,
The two-dimensional interference pattern from the interference means is used as an interference signal.
Interference pattern detecting means for photoelectrically detecting the interference pattern
By processing the interfering signal from the lane detection means,
Due to the phase change corresponding to the step depth in the above step pattern
After detecting the signal level change,
Processing means for detecting the position of the step pattern
And is configured to include at least . If the step pattern formed on the sample such as the wafer is illuminated with the coherent illumination light and the reflected light from the step pattern interferes with the reference light, two-dimensional interference is caused. Although a pattern is generated, the interference pattern has a large signal change due to the phase change in the step portion of the step pattern by the step depth. Then
The upper interference pattern photoelectrically converted, by detecting the signal change, in which the position of the step pattern formed on a sample, such as a wafer can be detected with high accuracy. The coherent illumination light is not limited to monochromatic light and may be white light. Embodiments of the step pattern detection of the present invention will be described below.
An example of the alignment pattern detection of the reduction projection exposure apparatus will be described with reference to FIGS. 1 to 9. First, the principle when the step pattern detection of the present invention is applied to the alignment pattern detection of a reduction projection exposure apparatus will be described with reference to FIGS. Assuming an Si step pattern as the alignment pattern, the reflectance at the photoresist / air interface is usually 5.5% (refractive index of air
1.0, refractive index of photoresist 1.61 (when wavelength is 514 nm))
On the other hand, the reflectance at the photoresist alignment pattern (step pattern) interface shows a high value of 24% (Si refractive index 4.75 (wavelength 514 nm)). As shown in FIG. 1, a coherent light source 40 such as a laser light source.
The illumination light 41 from the above is separated into two directions by the beam splitter 42, and one of them is adapted to illuminate the alignment pattern 48 on the wafer as the alignment illumination light 43 via the reduction projection lens 2. Alignment pattern 48 is S
The i substrate 45 is formed as a step pattern, and a photoresist 46 is applied thereon. On the other hand, the other is incident on a semitransparent mirror (transmission factor 0 in this case) 51. Here, the optical path length lr from the beam splitter 42 to the semitransparent mirror (reflecting mirror) 51 is changed to the beam splitter 42.
From the surface of the photoresist 46 to almost the same as the optical path length l _w (x), and setting the optical path length difference within the coherence length of the coherent light source 40, the reflected light 49 from the surface of the photoresist 46,
Interface 47 between step pattern of Si substrate 45 and photoresist 46
The reflected light 50 from the light interferes with the reflected light 52 from the semitransparent mirror 51, and as a result, an interference pattern 53 is obtained. Although details will be described later, in the interference pattern 53, the reflected light 50 mainly from the interface 47 between the step pattern and the photoresist 46 and the semi-transparent mirror 51 from the reflectance at each interface. Of the alignment pattern 48
The interference pattern 53 is obtained as a signal having a large signal change due to the change of the phase by the step depth e at the step. That is, the influence of interference caused by the film thickness d (x) of the photoresist 46 is relatively small. Then, the interference pattern 53 and the alignment pattern (not shown) on the reticle are detected by an alignment optical system (not shown) equipped with a magnifying lens and an image pickup device, and the alignment amount is determined from the center position of both patterns. If required, the reticle and the wafer can be aligned with relatively good accuracy. Note that FIG. 2 shows an incident state of the illumination light 43 which is a parallel beam incident on the alignment pattern 48. By the way, the semitransparent mirror on which the illumination light is incident is a mirror in a broad sense, and has a transmittance of 0 as in the optical system shown in FIG.
The case of is also included. This semitransparent mirror can be provided outside the alignment pattern illumination light path on the wafer including the reduction projection lens, or can be provided inside the illumination light path as described later. Further, desirably, a wavefront correction optical system is provided in the optical path provided with the semitransparent mirror. Further, in this embodiment, the light from the coherent light source is coherent in time and space. Now, the above-mentioned interference pattern will be described in detail. In the optical system shown in FIG. 1, the intensity of the reflected light 49 from the surface of the photoresist 46 is I ₁ , and the Si substrate 4 is
Assuming that the intensity of the reflected light 50 from the interface 47 between the step pattern of 5 and the photoresist 46 is I ₂ and the intensity of the reflected light 52 from the semitransparent mirror 51 is Ir, the intensity of the interference pattern 53 by these three reflected lights. The distribution I (x) is approximately represented by the following mathematical formula. I (x) = (I ₁ + I ₂ + Ir) +2 (I ₁ · I ₂ ) ^1/2 cos {4πn _r d (x) / λ} +2 (I ₁ · Ir) ^1/2 cos {4πn _a (l _w (x) -lr) / λ} +2 (I ₂ · Ir) ^1/2 cos [4π {n _a (l _w (x) -lr) + n _r d (x)} / λ] [0014 ] However, λ is the wavelength of the alignment illumination light,
n _a represents the refractive index of air, and n _r represents the refractive index of the photoresist. The first term in the equation gives the direct current component of the interference intensity, the second term is the modulation component of the interference intensity between the reflected light 49 and the reflected light 50, and the third term is the reflected light 49 and the reflected light. The modulation component of the interference intensity with 52 and the fourth term give the modulation component of the interference intensity between the reflected light 50 and the reflected light 52, respectively. Here, the intensity of the illumination light 41 is 1, the ratio of the reflectance and the transmittance at the beam splitter 42 is 1, n _a = 1 and n.
_{When r} = 1.6 (λ = 436 nm), the reflectance of the semitransparent mirror 51 is 95%, the reflectance of the photoresist 46 / air interface is 5.5%, and the reflectance of the step pattern / photoresist 46 interface 47 is 24%. The first term in FIG. 3 is shown as a straight line 60 in FIG. 3, the second term is shown as a curve 61, the third term is shown as a curve 62, and the fourth term is shown as a curve 63. From FIG. 3, the intensity distribution of the interference pattern 53 is affected by the fourth term in the mathematical expression, that is, the interference between the reflected light 50 from the step pattern / resist 46 interface 47 and the reflected light 52 from the semitransparent mirror 51. It is known that it appears most strongly. As a result, the interference pattern 53 is obtained as a signal having a large signal change due to the change in phase at the step portion of the alignment pattern 48 by the step depth e. This reflectance at the interface 47 is higher than the reflectivity at the photoresist 46 surface. As a result, the influence of the interference (the second term and the third term in the above equation) due to the film thickness d (x) of the photoresist 46 becomes relatively small. Therefore, as shown in FIG. 4A, when the film thickness distribution of the photoresist 46 is left-right asymmetric at the step portion of the alignment pattern 48, the conventional alignment method causes the interference shown in FIG. As is clear from the light intensity curve, the reflected light intensity distribution 64 from the alignment pattern 48 is asymmetrical as shown in FIG. 4B, and x _d is regarded as the pattern center position with respect to the true pattern center position x _w. However, the detection error e _x is generated.
However, according to the present invention, as shown in FIG. 4 (c), the reflected light intensity distribution 65 has good symmetry without being significantly affected by the film thickness distribution of the photoresist 46, and has high contrast. It is possible to ideally detect the true pattern center position x _w . As a result, the decrease in alignment accuracy due to the photoresist film thickness and coating unevenness can be eliminated. According to the present invention, as shown in FIG. 5, the alignment pattern is SiO ₂ on the step pattern of the Si substrate 66.
It is also applicable to the case where each transparent layer of 67 and Si ₃ N ₄ 68 is formed. This is because when the incident light 74 is received, the surface of the photoresist 69 and the interfaces 72 and 7 of the respective layers.
Of the reflected light 75, 76, 77, 78 from each of 1 and 70, the one with the highest intensity is the interface 7 between the underlying Si substrate 66 and SiO ₂ 67.
This is because it is the reflected light 78 from 0. Therefore, since the obtained interference intensity distribution greatly changes at the stepped portion of the Si substrate 66, the film thickness of the photoresist 69 is not so affected, and the same effect as the above case can be obtained. An embodiment in which the step pattern detection of the present invention is applied to the alignment pattern detection of the reduced projection exposure apparatus will be described with reference to FIGS. 6 to 9. FIG. 6 shows an optical system in this embodiment. The optical system comprises a step pattern illumination system, a step pattern detection optical system, a reference optical path and an interference pattern detection signal processing system. In this case, a laser beam from an Ar laser (wavelength 514.5 nm) 80 as a coherent light source
The beam splitter 82 is divided into two beams 86 and 87 by a beam splitter 84 via a beam splitter 82 and a relay lens 83. Of these, beam 87 is mirror 85b-8
5f, guided to the reference optical path consisting of the wavefront correction optical system 88 and the reflection mirror 89, and reflected by the reflection mirror 89. At the same time, the wavefront correction optical system 88 adjusts the beam diameter of the beam 87 and forms an image on the reduction projection lens. The wavefront phase is adjusted according to the characteristics. The other beam 86 is reflected by the mirror 85.
a, after being sequentially reflected by the surface of the mirror 1m on the reticle 1, it is incident on the center of the entrance pupil 2p of the reduction projection lens 2 and illuminates the alignment pattern (step pattern) 48 on the wafer 3. . FIG. 7 is an enlarged view of the illumination state in this case. The beam 86 is a parallel beam and functions as stepped pattern illumination light. Here, from the beam splitter 84 to the reflecting mirror 89
Up to the optical path length from the beam splitter 84 to the alignment pattern (step pattern) 48 on the wafer 3 by finely moving the reflecting mirror 89 in the optical axis direction. By setting within the interference distance, the reflected light from the reflecting mirror 89 and the reflected light from the alignment pattern (step pattern) 48 interfere with each other by the same principle as the Twyman-Green interferometer, and the beam splitter 84 The interference pattern can be obtained. This interference pattern is sequentially passed through the relay lens 83, the beam splitter 82, the mirror 85g, and the magnifying lens 90.
The two-dimensional solid-state image pickup device 91 takes an image, but the photoelectrically converted interference pattern from the two-dimensional solid-state image pickup device 91 is subsequently subjected to noise removal and AD conversion by the preprocessing circuit 92, and further, depending on the vertical direction compression circuit 93, a pattern. It is designed to be electrically compressed in a direction orthogonal to the detection direction. The computer 94 performs a predetermined process on the signal converted into the one-dimensional information by this compression, whereby the alignment pattern (step pattern) 48
The center position of is required. The processing by the computer 94 at that time will be described. FIGS. 8A and 8B show examples of interference patterns picked up by the solid-state image pickup device 91, respectively. The detection area 95 of the step pattern detection optical system for the alignment pattern (step pattern) 48 is as shown in the figure. First, referring to FIG. 8 (a), this shows the case where the reflecting mirror 89 and the alignment pattern (step pattern) 48 are relatively inclined in the direction of the arrow, and depending on the size and direction of the inclination. Thin interference fringes 96 are generated. In such a case, as shown in FIG.
The dimensional signal 98 is obtained as a low contrast signal.
Therefore, it is necessary to set in advance the reflecting mirror 89 and the alignment pattern (step pattern) 48, that is, the wafer to be completely parallel. By the way, if the size of one chip on the wafer is 20 mm × 20 mm, the tilt of the wafer within one chip is about 1 μm at most. Therefore, once the reflecting mirror 89 is finely adjusted, this is always No need to monitor. Next, referring to FIG. 8B, this shows an interference pattern in the case where the reflecting mirror 89 and the wafer are completely parallel to each other, and an alignment pattern (step pattern) is shown. An image 97 having a large change in intensity is obtained at the stepped portion of. The one-dimensional signal 99 shown in FIG. 9 (b) is also obtained with high contrast accordingly. The computer 94 obtains the center position x _w (X-direction center position) of the alignment pattern (step pattern) on the wafer from the one-dimensional signal 99 using the symmetry of the waveform. The alignment amount Δ and the alignment direction can be obtained from the misalignment with the center position x _r of the alignment pattern (not shown) on the reticle obtained separately. The stage 4 is finely moved in the x direction based on the alignment amount Δ and the alignment direction, and the situation is exactly the same for the alignment in the y direction. After the alignment in the x and y directions is completed in this way,
The circuit pattern on the reticle 1 is printed on the chips on the wafer 3 by being irradiated with exposure light from an exposure system (not shown). By repeating the above alignment and printing operations for each chip, reduction projection exposure is performed on the wafer 3. According to the embodiment described above, the alignment pattern (step pattern) detection signal can be obtained with good symmetry without being affected by the photoresist film thickness distribution as described above. It is possible to eliminate a decrease in alignment accuracy caused by uneven coating.
Further, in the case of the conventional alignment method, the contrast of the alignment pattern (step pattern) detection signal largely changes not only due to the coating unevenness but also due to the coating thickness of the photoresist itself. By slightly moving the mirror 89 in the optical axis direction, the interference intensity can always be set to the inclined portion of the curve 63 shown in FIG.
It is possible to keep the signal contrast high. Next, a second embodiment in which the step pattern detection of the present invention is applied to the alignment pattern detection of the reduced projection exposure apparatus will be described with reference to FIGS. FIG. 10 shows an optical system in the second embodiment. In this alignment optical system, the reference optical path is removed from the optical system shown in FIG. 6, and a semitransparent mirror 100 as a dichroic mirror is added to the lower end of the reduction projection lens 2,
The difference is that the stepped pattern illumination light path itself is used as a reference light path. As in the previous embodiment, first the beam 81 from the Ar laser 80 is reflected by the beam splitter 82, the relay lens 83.
After being sequentially reflected by the mirror 85a and the mirror 1m surface on the reticle 1 through the light, the light is incident on the center of the entrance pupil 2p of the reduction projection lens 2, and further passes through the semitransparent mirror 100. (Step pattern) 48 is incident as illumination light. In this case, on the upper surface of the semitransparent mirror 100, an antireflection film (wavelength 514.5n
m), and the lower surface 101 is coated with a thin film having the reflectance / transmittance spectral characteristics shown in FIG. 12, but the lower surface 101 and the alignment pattern (step pattern) 4
When the optical path length up to 8 is set within the coherence length of the Ar laser 80 by finely moving the semitransparent mirror 100 in the optical axis direction, from the lower surface 101 of the semitransparent mirror 100 by the same principle as the Fizeau interferometer. And the reflected light from the alignment pattern (step pattern) 48 interfere with each other to obtain an interference pattern. This interference pattern follows the same optical path in reverse through the reduction projection lens 2 and then the beam splitter
An image is picked up by the two-dimensional solid-state image pickup device 91 via the mirror 82, the mirror 85g, and the magnifying lens 90, and the subsequent signal processing and alignment procedures are performed in exactly the same manner as in the previous embodiment. Is. The bottom surface 1 of the semitransparent mirror 100
As shown in Fig. 12, the thin film coated with 01 has an extremely high transmittance for the exposure wavelength of 436 nm (g-line of a mercury lamp), and no particular problems occur during exposure. ing. Further, reference numeral 111 indicates an imaging position of the interference pattern. The fine movement mechanism of the semitransparent mirror 100 will be briefly described. FIGS. 11A and 11B show the fine movement mechanism of the semitransparent mirror 100. The semitransparent mirror 100 is supported by the reduction projection lens 2 by a leaf spring or the like (not shown), and the fine movement mechanism is, for example, three wedge-shaped bases 102a fixed to the upper surface of the semitransparent mirror 100. , 103a, 104a
On the other hand, the wedge-shaped movable spacers 102b, 103b, 104b are realized by finely moving the three piezo elements 102c, 103c, 104c independently. Piezo elements 102c, 103c,
One end of 104c is attached to the wedge-shaped movable spacers 102b, 103b, 104b, while the other end is fixed to the reduction projection lens 2. Therefore, the piezo elements 102c, 103c, 10
When a voltage signal is applied to 4c, they expand and contract according to the voltage signal, and as a result, the semitransparent mirror 100 can finely move in the vertical direction. Therefore, according to the present embodiment, not only the same effect as in the case of the previous embodiment can be obtained, but also by using the alignment optical path itself as the reference optical path, the disturbance in the reference optical path or the reduction projection lens The effect of the imaging characteristic itself on the interference pattern is removed, and at the same time, the alignment optical system is simplified. The present invention has been described above. However, the present invention is not limited to the above-described alignment pattern detection, and line width measurement of a step pattern such as a resist pattern formed on a semiconductor wafer can be performed. Obviously, it can be applied to detect geometric information. As described above, according to claims 1 and 2, it becomes possible to detect a fine step pattern formed on a sample such as a wafer with high contrast, and as a result, the position of the step pattern in the stable and can be detected with high accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing an optical system for explaining a step pattern detection principle of the present invention. FIG. 2 is an illumination light for an alignment pattern (step pattern). FIG. 3 is a diagram showing the relationship between the optical path length difference and the interference intensity. FIG. 4 (a) is an alignment pattern (step pattern) showing the state of uneven photoresist coating. 4B and 4C are views for explaining a difference in reflected light intensity distribution between the conventional method and the alignment method according to the present invention. [FIG. 5] FIG. FIG. 6 is a diagram showing a cross section of another alignment pattern (step pattern) portion to which the present invention is applicable. FIG. 6 is a diagram showing an alignment optical system according to the first embodiment of the present invention. 7] FIG. 7 shows the illumination light to the alignment pattern (step pattern) in that case. FIG. 8A and FIG. 8B are diagrams showing an incident state, and FIG. 8A and FIG. 8B are diagrams showing examples of interference patterns captured respectively. FIG. 9A and FIG. FIG. 10 is a diagram showing a compressed one-dimensional signal waveform of the interference patterns shown in FIGS. 10A and 10B. FIG. 10 is a diagram showing an alignment optical system according to a second embodiment of the present invention. 11 (a) and 11 (b) are diagrams showing the fine movement mechanism of the semitransparent mirror and its part in the optical system. [FIG. 12] FIG. 12 is the reflectance of the thin film coated on the lower surface of the semitransparent mirror. FIG. 13 is a diagram showing a transmittance spectral characteristic. FIG. 13 is a diagram showing an example of a conventional TTL alignment method. FIG. 14 is a diagram showing a method of applying photoresist to a wafer. FIG. 15 is a diagram showing an enlarged wafer alignment pattern (step pattern). FIGS. 16A and 16B are alignment diagrams. FIG. 17A and FIG. 17B are diagrams showing the difference in photoresist film thickness distribution depending on the direction of the pattern (step pattern). FIGS. 17A and 17B show the intensity of reflected light from the alignment pattern (step pattern) due to the difference in film thickness distribution. FIG. 18 is a diagram showing the difference in distribution. FIG. 18 is a diagram showing the relationship between the photoresist film thickness and the interference intensity. [Explanation of symbols] 1 ... Reticle, 2 ... Reduction projection lens, 3 ... Wafer, 4 ...
Wafer stage, 40 ... Coherent light source, 42, 82, 84 ... Beam splitter, 48 ... Alignment pattern (step pattern), 51, 100 ... Semi-transparent mirror, 53 ... Interference pattern, 80 ... Ar
Laser, 88 ... Wavefront correction optical system, 89 ... Reflector, 91 ... Two-dimensional solid-state imaging device

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location H01L 21/30 522B (72) Inventor Masataka Shiba 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Hitachi, Ltd. (56) References JP-A-59-27527 (JP, A) JP-A-60-169703 (JP, A)

Claims (1)

(57) [Claims] The step pattern formed on the sample is illuminated with coherent illumination light , and
The coherent illumination light as a stand is branched from the midway position of the optical path.
A reference beam is created separately from the coherent illumination light, and the step pattern
The interference between the coherent illumination light reflected from the lamp and the reference light
Generates a more two-dimensional interference pattern and photoelectrically interferes
Signal, and from the interference signal, the step pattern
The signal level change due to the phase change corresponding to the step depth at
After being detected, the step pattern is detected based on the signal level change.
A step pattern detection method that detects the position of a turn . 2. The coherent illumination light reflected from the step pattern is
Interfering with the reference light whose length and inclination can be set variably
The step pattern detection method according to claim 1, wherein 3. Interferable to illuminate the step pattern formed on the sample
Illuminating light source and the non-proximal position of the step pattern
Coherent illumination light Coherent illumination branched from the midway position of the optical path
Create a reference beam by creating a reference beam separately from light using a reflector
Means and reflected coherent illumination light from the step pattern
Interference means for interfering with the reference light, and from the interference means
Photoelectrically detects the two-dimensional interference pattern of
Interference pattern detecting means and the interference pattern detecting means
By processing the interference signal from
Signal level change due to phase change corresponding to step depth
Is detected, the step pattern is detected based on the signal level change.
Processing means for detecting the position of the
Step pattern detection device including. 4. In the reference light creating means, the reflection mirror itself in the direction of the reference light optical axis is used.
The reference light is created by adjusting the body movement and tilt.
The step pattern detection device according to claim 3.