JP2555051B2 - Pattern detection method and device - Google Patents

Description

The present invention relates to a method and a device for detecting a pattern having a layered structure such as a semiconductor wafer, and more particularly, to an asymmetrical detection waveform due to uneven thickness of a resist coating layer. For the pattern
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pattern detection method and device suitable for improving symmetry.

[Conventional technology]

For exposure of fine patterns of micron or submicron, light with narrow spectrum width (eg mercury g-line or i-line) is used as exposure light source, and reduction lens that resolves with one wavelength (light with narrow spectrum width) It is done by. This resist causes chromatic aberration with respect to light having a wavelength different from that of the exposure light, or light having a wide spectrum width at the exposure wavelength or another wavelength. In the former case, images are formed for the respective wavelengths of light on different image planes, and in the latter case, the resolution is remarkably reduced. Using such a reduction lens, the dozens of masks (reticles) that are the original images are changed one after another, and the pattern on the chip on the wafer is reduced to 0.
To perform overexposure with accuracy of 5 to 0.2 μm, through the reduction lens (TTL), the alignment mark formed on the chip on the wafer is detected, the relative position with the reticle is determined, and the wafer or reticle is finely moved, The high-precision overlay exposure described above cannot be realized unless alignment is performed.

Even if such a TTL alignment method is adopted, it becomes difficult to apply the resist film applied on the wafer with a uniform thickness as the diameter of the wafer increases.
Since it becomes difficult to apply symmetrically to the alignment mark pattern due to the flow of the resist material during resist application, when detecting with monochromatic light that is resolved by this reduction lens, the detection waveform is The phenomenon that the shape changes and the asymmetry of the detected waveform occurs is inevitable. Although such a phenomenon has existed in the past, as the miniaturization of LSI progressed, the precision required for overlay became stricter, which became a major technical issue.

As a solution to this problem, there has been disclosed a method in which a signal obtained by detecting the e-line or d-line which is the emission line spectrum of a conventional mercury lamp and combining the detected waveforms as a new detection signal is disclosed.
It is shown in the publication. This method is more effective than the case of detecting with a single wavelength.

[Problems to be solved by the invention]

The above-mentioned conventional technique is such that the coating resist thickness on the wafer (usually 1 to
3 μm) does not have sufficient effect in all ranges,
There is a problem that it is effective only for a limited film thickness. FIG. 2A shows the conventional e-line (λ ₁ = 546 nm) and d-line (λ ₂ = 577 nm) when the resist film thickness d (μm) is changed.
It shows how the interference detection intensity changes due to the synthesis of the detection signals of. From this figure 0.8-1.5 μm and
It is effective only for the change of the resist film thickness of 3.0 to 3.8 μm, and it can be seen that the interference intensity greatly changes in other regions.
If such a large interference intensity amplitude exists, the asymmetry of the detected waveform will appear largely even if the film thickness varies slightly due to coating unevenness in this region. FIG. 2 (C) shows a detection waveform obtained by simulation for coating unevenness Δd1 = 0.1 μm accompanying the flow of the resist (arrow F) shown in FIG. 2 (B). When the symmetrical center position (dotted line) of the detected waveform is obtained, Δx, that is, 0.16 μm or more, deviates from the true center position (dotted line), and accurate superposition becomes impossible.

An object of the present invention is to solve the above-mentioned conventional problems, and to provide a method and an apparatus capable of accurately detecting the center of an alignment mark over a wide range of ordinary resist coating film thickness even if resist coating unevenness occurs. is there.

[Means for solving problems]

The purpose is to irradiate the surface of the substrate having a step pattern covered with a transparent film on the surface with light of different wavelengths from different directions, and to reflect the light of different wavelengths reflected on the surface of the step pattern and the transparent film. Detecting the reflected light for each of the different wavelengths of light, adding the detection signals corresponding to the detected reflected light for each of the different wavelengths of light, and detecting the position or shape of the pattern based on the result of the addition. And a device for detecting the same, and at least two or more different wavelengths of light having different wavelengths are applied to the surface of a substrate having a stepped pattern covered with a transparent film on the surface. The reflected light for each of the different wavelengths of the different wavelengths of light radiated from the direction and reflected on the surface of the step pattern and the transparent film is detected, and the detected difference is detected. Sum that the wavelength of the detection signal corresponding to the reflected light of each light respectively, is achieved by the pattern detection method and apparatus and detecting the position or shape of the pattern on the basis of the sum combined results.

[Action]

By implementing the above-mentioned means, it is possible to significantly reduce the fluctuation of the detection intensity due to the interference with the film thickness, as compared with the case where the light of two wavelengths is vertically incident, and the detection waveform due to the coating unevenness is obtained. The asymmetry of is significantly reduced, and the pattern position detection accuracy is significantly improved.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 (A), (B),
This will be described with reference to (C) and (D). A circuit pattern 31 and window patterns 30, 30 'are drawn on the lower surface of the reticle 3. The circuit pattern 31 on the reticle is aligned with the chip 41 on the wafer 4 by the reduction lens 5. When the wafer pattern detection described below is performed, the position of the wafer is known.
Therefore, the reticle is slightly moved, the alignment marks 35 and 35 'drawn on the reticle are illuminated by the reticle illumination system 25 and 25', and the reticle position is controlled while reading the position by the reticle position detection systems 65 and 65 '. As a result, the reticle image is superimposed on the circuit pattern on the wafer with desired positional accuracy. At this point, the exposure illumination system (not shown) above the reticle irradiates the reticle with the exposure illumination light, and the overexposure is completed.

An embodiment of the wafer pattern detection of the present invention will be described here. Narrow spectrum light having wavelengths λ ₁ and λ ₂ is emitted from the light sources 11 and 12, and by driving the shutters 221 and 222 by the control circuit 60, light having wavelengths λ ₁ and λ ₂ can be obtained at desired times. It is possible to take out. Wavelength selective mirror 21 transmits light in a wavelength lambda _1, it reflects the lambda ₂ light and allowed incident on the light deflector (galvano mirror) 2. The light reflected by the optical deflector is reflected by the beam splitter 21 and the lens 22
After passing through the window pattern 30 via the mirror 23, the light enters the reduction lens 5. When the light sources 11 and 12 are lasers, the laser light incident on the reduction lens illuminates a region sufficiently smaller than this pupil diameter on the entrance pupil 51 of the reduction lens.
The directivity of the incident light on the wafer is high. Since the mirror surface of the galvano mirror 2 is arranged in a conjugate positional relationship with the wafer surface by the lens 22 and the reduction lens, when the galvano mirror is deflected, the position of the laser beam on the pupil changes, and the alignment mark on the wafer 4 is changed. The incident angle to 401 (402) changes as θ ₀ and θ ₁ as shown in FIG. 1 (B). At this time, since the above-described conjugate relationship is established, the irradiation position of the alignment mark 401 on the wafer remains unchanged. The light reflected by the alignment mark 401 on the wafer passes through the reduction lens 5, the reticle upper window pattern 30, the mirror 23, and the lens 22 in the direction opposite to the outward path, then passes through the beam splitter 21, and is formed by the imaging lens 61. The image of the alignment mark on the wafer is formed on the image pickup surface of the image pickup device 6. The lens 22 and the imaging lens 61 correct the chromatic aberration of the reduction lens with respect to λ ₁ and λ ₂ . The electric signal obtained by the image pickup device 6 is sent to the control circuit 60.

Next, the detection method of the present invention using two wavelengths and a plurality of irradiation angles will be described with reference to FIGS. 1 (C) and 1 (D). The graph in the figure shows the temporal change of the incident angle (swing angle) of the light (laser light) of λ ₁ and λ ₂ on the alignment mark 401 on the wafer. That is, the galvano mirror 2 and the shutters 221 and 222 are used to sequentially irradiate the wafer at two incident angles of θ = θ ₀ and θ ₁ . The order of irradiating the light of λ _{1 and} the light of λ ₂ is arbitrary, and it is also possible to detect the light at the same time when the image forming magnifications of the both lights completely match. In this way, the images of the marks irradiated at the incident angles θ ₀ and θ ₁ with respect to the two wavelengths λ ₁ and λ ₂ are obtained by the processing circuit 60 as the respective four pattern signals. By taking the sum of the signals obtained in this way, the resist coating unevenness as shown in FIG.
(Thickness), a signal waveform that is symmetric, that is, faithful to the pattern shape of the base 42 can be obtained. Here, the reason why the above-mentioned symmetrical waveform is obtained will be described with reference to FIG. Light having a wavelength λ _j that enters the resist 43 at an incident angle θ _i is refracted at point A at a refraction angle determined by the refraction index n of the resist,
After being reflected by the surface B of the base 42, it passes through the resist surface C and again escapes into the atmosphere. The light passing through this optical path and directly incident on C,
The light reflected by C causes interference, but these two rays, AB
The difference Δlλ _{j in} the optical path between C and A′C (A ′ is a foot dropped from A to a ray passing through A ′) affects the interference intensity I _ij of both lights. The optical path length difference Δlλ is given by the following equation.

Therefore, the interference intensity I of both lights is given by the following equation.

Here, α is a positive number of 1 or less, and is a value determined by the complex refractive index of the resist and the base material. From the formula (2), when light of one kind of wavelength λ ₁ is incident from the fixed −direction θ ₁ , the following formula is applied to the resist thickness d. Since a detection signal determined by is obtained, the detection signal level greatly changes due to a slight change in d as shown in FIG. However, the detection signal I obtained by the present invention is the first
If two types of incident angles shown in FIGS. (C) and (D) are used,
It becomes the following formula.

If this is illustrated under the following conditions, the interference detection signal level (proportional to the interference intensity) shown in FIG.

Therefore, even when the resist coating film thickness differs between the left and right edge portions of the wafer alignment mark (Δd = 0.1 μm), the asymmetry of the waveform is significantly reduced as shown in FIG. 4 (B).
The error Δx between the center position of the waveform and the true center position is 0.04 μm
Becomes FIG. 2C (Δx = 0.16 μm) when two wavelengths are vertically incident on the same pattern, and FIG. 5B (Δx = 0) when two-angle illumination is performed using only one wavelength of light. .
This effect is clear when compared with 25 μm). The fifth
In the figure (A), light of 515 nm has two tilt angles (θ ₁ = 0 °, θ ₂ = 2
2 °) This is the interference intensity that occurs when illuminated.

Next, one embodiment of the present invention will be described with reference to FIG. In FIG. 6, the optical system is the same as that in FIG. 1, and the deflection of the galvanometer mirror is changed by the control circuit 60 from the above-described embodiment as shown in FIGS. 6 (A) and 6 (B). That is, the irradiation times at the incident angles of θ ₁ and θ ₂ of the wavelength of λ ₁ are changed and added with different weights. If the weight of the incident angle θ _i of the wavelength λ _j is w (i, j), then w (1,1) = 1 w (1,2) = 2 w (2,1) = 2 w (2,2) = 1. As a result, the detection signal level (interference intensity) I resulting from the change in the resist thickness is in the range of the practical resist thickness 1 μm to 4 μm as shown in FIG. 6 (C). It can be seen that the change in the signal level is made uniform over a wider range than in the case of FIG. 5 (B) described above. FIG. 6 (D) shows the unevenness of the resist coating film thickness Δd.
Is the detected waveform when 0.1 μm, and the symmetry of the detected waveform is significantly improved compared to FIG. 2 (C), and the error Δx is
It turns out that it becomes 0.04 μm.

FIG. 7 shows an embodiment of the present invention, in which the incident angle θ is 532 nm.
₂ shows the relationship between the resist thickness d and the interference intensity in the case of illumination at ₂ (θ ₂ = θ) and 0 ° at 543.5 nm. In this case the 7th
At θ = 0 ° in Figure (A), the resist thickness is 2.2 μm to 3.2 μm.
The change in the interference intensity is small in the range. There 53
When the incident angle of 2 nm is changed, the resist thickness d in which the change in interference intensity becomes small changes as shown in FIGS. 7 (B) to 7 (E).
That is, in this embodiment, if the resist thickness d is known in advance, it is possible to reduce the interference intensity by changing the incident angle of light of one wavelength according to this thickness.

Next, an embodiment of the present invention is shown in FIG. In this embodiment, a mercury lamp or Xe lamp 10 is used as the illumination light. Parts in FIG. 8 which coincide with those in FIG. 1 represent the same item. In the embodiment shown in the figure, the chrome surface 30 on the reticle surface is a full-face chrome mirror surface 37 at the center and the hyperbolic grating 36 is provided at the periphery as shown in FIG.
Is provided. The mirror surface 37 plays a role of reflecting the reflected light from the wafer downward and guiding it to the detection system. On the other hand, the hyperbolic grating, which the present inventors have shown in detail in Japanese Patent Application No. 58-205817, forms a diffraction image almost at the wafer image position when it is irradiated with the laser illumination light 211. Therefore, by detecting the wafer image and the reticle diffraction image with the same detection optical system, the wafer or the reticle can be finely moved and relative alignment can be realized. This embodiment will be described in more detail with reference to FIG.

The light emitted from the Xe lamp 10 becomes light of two narrow spectra (about 5 nm width) having different wavelengths λ ₁ and λ ₂ by the interference filters 24 and 24 ′, and enters the fibers 11 and 11 ′. At the exit of the fiber is a movable aperture 20 in which apertures of various shapes are arranged. FIG. 8B shows an example of the movable aperture 20 in which two circular apertures 100 and 101 are irradiated with light 251 having a wavelength λ ₁ . This aperture is imaged by the lens 22 on the pupil of the reduction lens 5. Therefore, as shown in FIG. 8 (C), the illumination lights 200 and 201 pass through points A and B of the pupil 51 with a certain spread. Therefore, FIG. 8 (D)
After passing through the reduction lens 5, the light 200 passing through the center A of the pupil illuminates the wafer 4 perpendicularly and the light 201 passing through B illuminates the wafer 4 with an inclination as shown in FIG. That is, in this embodiment, illumination having two incident angles is performed at the same time. Movable opening
If the right side aperture of FIG. 8 (B) is installed at the exit of the fiber by moving 20, the illumination of one place will be on the pupil of the reduction lens, and the wafer will be irradiated from one direction. (Strictly speaking, irradiate from one direction and a direction in the vicinity of that direction). By deflecting the galvanometer mirror 2 or moving the movable aperture 20 as shown in FIG. 8 (A), the incident angle to this wafer can be controlled and a plurality of incident angles can be obtained in time series.

Although the structure described in the above embodiments uses two wavelengths, the effect is large even if illumination is performed at a plurality of incident angles using three or more wavelengths. However, if a large number of wavelengths are used, it is difficult to construct an optical system for correcting chromatic aberration such as a reduction lens and an optical system for generating light of a large number of wavelengths, resulting in high cost. Therefore, as shown in the above embodiment, by using two wavelengths, one is vertical, and the other is selected as an optimum angle within the maximum possible incident angle, thereby effectively using four wavelengths. Is relatively advantageous.

In the above-described embodiment, the reflective pattern is used as the detection target pattern, but it is clear that the transmissive pattern can also obtain the same operation and effect.

〔The invention's effect〕

According to the present invention, since the resolution is corrected only for a single wavelength such as a reduction lens for exposure of an LSI, it is difficult to configure a detection system for light having a continuous spectrum component or a large number of spectra. In the above, since it is not affected by the transparent coating of the test object covering the pattern, it is very effective in accurately detecting the position of the pattern and the two-dimensional (planar) shape. For example, when it is used for alignment of a reduction exposure apparatus, a detection deviation of about 0.1 to 0.3 μm may occur in the conventional method, but this method suppresses the detection deviation of about 0.05 μm.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, and FIG.
FIG. 3 is a diagram showing an example of wavelength detection, FIG. 3 is a diagram for explaining the principle of interference detection light, FIG. 4 is a diagram for explaining an embodiment of the present invention, and FIG. 5 is a conventional two-tilt illumination method. FIG. 6 is a diagram for explaining a case where weighting is applied to each of the two tilt angles in another embodiment of the present invention, and FIG. 7 is one wavelength in another embodiment of the present invention. Is vertical and other wavelengths are tilted, and the tilt is optimized according to the resist thickness. FIG. 8 is a mercury lamp according to another embodiment of the present invention, which is different from FIG. It is the figure which showed the case where was used. 11, 12 is a light source (laser), 2 is a deflector, 3 is a reticle,
4 is a wafer, 401 and 402 are alignment marks, 5 is a reduction lens,
6 is a detector, 60 is a control circuit, 20 and 20 'are movable apertures, 10 is a lamp, 24 and 24' are interference filters, and 51 is a pupil of a reduction lens.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication location G03F 9/00 H01L 21/30 502M (56) Reference JP-A-63-172905 (JP, A) JP-A-63-128205 (JP, A) JP-A-62-149129 (JP, A)

Claims (13)

(57) [Claims] 1. A substrate having a stepped pattern covered with a transparent film on the surface thereof is irradiated with light having different wavelengths from different directions, and is reflected by the stepped pattern and the surface of the transparent film. The reflected light of each of the different wavelengths of light of different wavelengths is detected, the detection signals corresponding to the detected reflected light of each of the different wavelengths of light are respectively added, and the pattern is based on the result of the addition. A pattern detection method characterized by detecting the position or shape of a pattern. 2. The substrate is a semiconductor wafer, the transparent film is a resist, and the light having different wavelengths is light generated from a light source of a mercury lamp or a Xe lamp. The pattern detection method according to the first item of the range. 3. A stepped pattern and a stepped pattern covered with a transparent film are irradiated onto the surface of the substrate with light of different wavelengths from at least two different directions for each of the light of different wavelengths. Detecting reflected light for each of the different wavelengths of light of the different wavelengths reflected on the surface of the transparent coating, adding detection signals respectively corresponding to the detected reflected light for each of the different wavelengths of light, A pattern detection method comprising detecting the position or shape of the pattern based on the result of the addition. 4. The irradiation of light of different wavelengths to the pattern from at least two or more different directions for each of the different wavelengths of light is performed by changing the irradiation time in the different directions. Item 3 pattern detection method 5. The pattern detection method according to claim 4, wherein the detection signals corresponding to the different directions of the light of different wavelengths are weighted corresponding to the irradiation time and added. 6. The pattern detection method according to claim 3, wherein the irradiation from at least two or more different directions includes irradiation from a direction perpendicular to the substrate. 7. The substrate is a semiconductor wafer, the transparent film is a resist, and the light having different wavelengths is light generated from a light source of a mercury lamp or a Xe lamp. The pattern detection method according to the third aspect. 8. An irradiating means for irradiating the surface of a substrate having a stepped pattern covered with a transparent film on the surface with different wavelengths from different directions, and the stepped pattern radiated by the irradiating means. Detection means for detecting the reflected light of each of the different wavelengths of the light of the different wavelengths reflected by the surface of the transparent film, and detection corresponding to the reflected light of each of the different wavelengths of light detected by the detecting means A pattern detecting apparatus comprising: an arithmetic means for adding the respective signals; and a processing means for detecting the position or shape of the pattern based on the result of adding the detection signals by the arithmetic means. . 9. The method according to claim 1, wherein the substrate is a semiconductor wafer, the transparent film is a resist, and the irradiation means has a light source section equipped with a mercury lamp or a Xe lamp. 8. The pattern detection device according to item 8. 10. An irradiation means for irradiating the surface of a substrate having a stepped pattern covered with a transparent film on its surface with light of different wavelengths from at least two or more different directions for each light of different wavelengths, Detecting means for detecting reflected light of each of the different wavelengths of light of the different wavelengths that is irradiated by the irradiating means and reflected on the surface of the step pattern and the transparent coating, and the different wavelengths detected by the detecting means Calculation means for adding the detection signals corresponding to the reflected light for each light, and processing means for performing processing for detecting the position or shape of the pattern based on the result of adding the detection signals by the calculation means. A pattern detection device characterized by being provided. 11. The irradiation unit according to claim 10, further comprising a control unit for controlling irradiation time of the light of the different wavelengths to the pattern for each of the different directions. Pattern detector. 12. The pattern detecting apparatus according to claim 10, wherein the irradiating means irradiates the light beams having different wavelengths from a direction perpendicular to the substrate and a direction inclined to the substrate, respectively. . 13. The substrate is a semiconductor wafer, the transparent film is a resist, and the irradiation means has a light source section equipped with a mercury lamp or a Xe lamp. The pattern detection device according to item 10.