JPS63147320A - Formation of pattern for alignment - Google Patents

Abstract

PURPOSE:To obtain a diffracted-light signal with a high SN ratio by a method wherein, when a pattern, for alignment use, on a first object is illuminated by a first beam of coherent light and is then transcribed to a prescribed part of a photosensitive layer on a second object, the prescribed part of the photosensitive layer is illuminated simultaneously by a second beam of coherent light at an illuminating angle which is different from the angle of the first beam of coherent light. CONSTITUTION:When a pattern 6, for alignment use, on a first object 3 is illuminated by a first beam SIGMA1 of coherent light and is then transcribed to a prescribed part of a photosensitive layer 7 on a second object 4, the prescribed part is illuminated by a second beam SIGMA2 of coherent light at an angle which is different from the angle of the first beam SIGMA1 of coherent light; this second beam of coherent light is made to interfere with the first beam SIGMA1 of coherent light; as a result, a pattern, for alignment use, in the form of a latent image of the first object 3 is formed three-dimensionally on the photosensitive layer 7 on the second object 4. For example, if the pattern 6, for alignment use, on a reticle 3 is illuminated from an illuminating device 2, the pattern 6, for alignment use, is transcribed onto a wafer 4 through an image-forming device 5. During this process, the distribution showing the refractive index and the transmissivity corresponding to the distribution of an interference fringe formed by the beam SIGMA1 and SIGMA2 is formed inside the resist layer 7 of the wafer 4.

Description

[Detailed description of the invention] [Field of invention] The present invention relates to a method for forming alignment patterns.

[Prior Art] Conventionally, one of the methods for aligning a wafer and a reticle in a semiconductor exposure apparatus uses a latent image.

To align using this method, first, as shown in FIG. 3, the alignment pattern 14 on the reticle 11 is
The imaging system 12 is illuminated by the printing light emitted from the illumination system 10.
The image is transferred to a resist, which is a photosensitive layer, on the wafer 13 through the wafer 13. At that time, the printing light is irradiated so that the resist is fully saturated. Then, a latent image as shown in FIG. 4 is formed. Next, this latent image and the mark previously formed on the Unihachi substrate 15 are scanned with a laser beam other than the printing light, and the diffracted light is detected to determine the relationship between the latent image and the mark. Find the distance and perform alignment. This is an alignment method using latent images.

As shown in FIG. 4, the latent image has different refractive index nl+n2 and transmittance T, , T between the portions irradiated with the printing light (shaded portions) and the portions that are not. Its distribution is one-dimensional in the horizontal direction of the sea urchin eight substrates.

[Problems to be Solved by the Invention] However, when scanning a laser over such a latent image pattern and detecting the diffracted light, the intensity of the diffracted light depends on the thickness of the resist when the laser light is perpendicularly incident. In the case of oblique incidence, the diffraction intensity decreases compared to normal incidence, and a sufficient S/N ratio cannot be obtained.

The present invention eliminates the drawbacks of the conventional example described above and at the same time improves the S/N ratio.
It is an object of the present invention to provide a method for forming an alignment pattern that can obtain a high diffraction light signal.

[Means for Solving the Problems] In order to solve the above problems, the present invention illuminates the alignment pattern on the first object with the first coherent light to illuminate the photosensitive layer on the second object. When transferring to a predetermined portion, the second coherent light is simultaneously applied to the predetermined portion of the photosensitive layer at an irradiation angle different from that of the first coherent light.

[Function] When the second coherent light is irradiated with the first coherent light at different angles as described above, interference fringes due to interference between the first and second coherent lights are formed in the photosensitive layer. A layered three-dimensional pattern is formed. At this time, the angle formed by each layer of the layered pattern with respect to the surface of the photosensitive layer can be suitably determined by the irradiation angle of the first and second coherent lights.

[Example] Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a diagram showing a latent image forming method according to an embodiment of the present invention. In the figure, 1 is a laser light source that outputs illumination light of the same wavelength as the printing light, 2 is an illumination system, 3 is a reticle,
4 is a wafer, 5 is an imaging system, and 6 is an alignment pattern. The illumination system 2 emits coherent parallel light flux Σ1 and light flux Σ1 only when illuminating the alignment pattern 6 on the reticle 3.
It is illuminated with two light beams, a second parallel light beam Σ2, which has a different irradiation angle from that of the second parallel light beam Σ2. In order to simplify the explanation later, here we use the parallel light flux Σ
, is vertically incident on the resist 7.

In this configuration, when the alignment pattern 6 on the reticle 3 is irradiated by the illumination system 2, the alignment pattern 6 is transferred onto the wafer 4 via the imaging system 5. At that time,
In the resist 7 of the wafer 4, a refractive index and transmittance distribution is formed that corresponds to the distribution of interference fringes (intensities) formed by the light beams Σ1 and Σ2. This is the so-called latent image.

FIG. 2 is a cross-sectional view of the wafer 4 on which this latent image is formed. Assuming that the refractive index of the resist 7 before exposure is nI, the wavelength of the printing light is λ, and the angle between the luminous fluxes Σ1 and Σ2 is 20, according to Snell's law, the luminous fluxes Σ1. Σ2 is s + mouth 2θ
=n, forming an angle of 2θ' that satisfies 5in2θ'. At this time, the fringe of the latent image consists of two light beams Σ1. This occurs at the portion connecting the intersection points of the wavefronts W, , W2 of Σ2, that is, the shaded area in the drawing. As is clear from the figure, the fringe of the latent image is made up of a half angle of the angle formed by both light beams. In other words, the angle between the stripes and the normal to the wafer substrate 8 is θ'. Further, the fringe pitch is λ/2rzsin(θ').

Next, a method for detecting a latent image will be described with reference to FIG. In the figure, 21 is a laser light source having a wavelength λ' different from that of the printing light, z2 is a polarizing beam splitter, 23 is a λ/4 plate, 24 is a condenser lens, and 25 is a photodetector.

In this configuration, when linearly polarized light is supplied from the laser light source 21 (wavelength λ'), the light flux first passes through the polarizing beam splitter 22 . After that, roughly λ/4 plate 2
By passing through the sheet metal 3, the light becomes circularly polarized light and enters the wafer 4 on which a latent image is formed.

At this time, θ' with respect to the normal to the wafer 4 (however, si port 2
Assuming that the incident angle is 0''=n, sin (π/2-θ'), the light beam reverses the original optical path due to the refractive index distribution and hits the λ/4 plate 2 sheet metal 3, resulting in linearly polarized light. This luminous flux is then reflected by the polarizing beam splitter 22 toward the condenser lens 24 and enters the photodetector 25. At this time, the luminous flux that enters each section in the figure from the laser light source 21 is 'l+ 12+ 13, the optical path difference of each beam to the detector is λ/sin θ'. Therefore, if θ' is determined so that the following holds true, the signal strength of the latent image will be maximized. Most of the surface reflection of the wafer 4 goes to the side opposite to the laser light source 21, so the S/N is
It also becomes more expensive.

As described above, by illuminating the alignment pattern on the reticle 3 with two coherent beams with the same wavelength as the printing light, while appropriately selecting the angle formed by these beams, the alignment pattern on the reticle 3 can be illuminated with a laser beam with a wavelength different from that of the printing light. A detectable latent image can be formed efficiently regardless of the resist thickness.

However, since the refractive index of the resist differs depending on the wavelength, it is necessary to adjust the incident angle of the illumination light when detecting a latent image to correspond to the wavelength.

[Modification of Embodiment] In the above description, the alignment pattern 6 on the reticle 3 is formed using two light beams Σ3. Although the wafer 4 is illuminated with Σ2 and both light beams are irradiated to the wafer 4 via the imaging system 5, either one of them may be irradiated directly onto the wafer 4 without passing through the pattern 6 or the imaging system 5.

Further, when detecting a latent image, although the incident light and the diffracted light have the same path in the above example, a certain angle may be provided between the two edge paths.

[Effects of the Invention] As explained above, according to the present invention, a latent image pattern for positioning is formed that can be detected very efficiently as a diffracted light signal with a high S/N ratio, regardless of the thickness of the photosensitive layer. can do.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a latent image forming method according to an embodiment of the present invention, FIG. 2 is a cross-sectional view of a latent image pattern formed by the method of FIG. 1, and FIG. 3 is a diagram of a conventional apparatus. 4 is a sectional view of a conventional latent image pattern, and FIG. 5 is a diagram showing a method of detecting a latent image formed by the method of FIG. 1. 1: laser light source, 2: illumination system, 3 reticle, 4: wafer, 5: imaging system, 6: alignment pattern, 21: latent image detection laser light source, 22: polarizing beam splitter, 23: λ/4 plate, 24: condenser lens, 25: photodetector. Patent Applicant Canon Co., Ltd. Agent Patent Attorney Tatsuo Ito Agent Patent Attorney Tetsuya Ito Figure 1 Figure 2 Figure 4

Claims (1)

[Claims] 1. When the alignment pattern on the first object is illuminated with the first coherent light and transferred to a predetermined portion of the photosensitive layer on the second object, a second light is applied to the predetermined portion. By irradiating coherent light at a different angle from the first coherent light and causing it to interfere with the first coherent light, a latent image pattern for alignment of the first object is three-dimensionally formed on the photosensitive layer on the second object. 1. A method for forming an alignment pattern, the method comprising forming an alignment pattern. 2. The method for forming an alignment pattern according to claim 1, wherein the first and second coherent lights are obtained by dividing output light from one light source. 3. The alignment pattern according to claim 1, wherein the second coherent light illuminates the alignment pattern on the first object in the same way as the first coherent light. Formation method. 4. Alignment according to claim 1, wherein the first object is a reticle, the second object is a wafer, and the photosensitive layer is a layer of photoresist coated on the wafer. How to form a pattern for use.