JPS5954908A - Surface position detecting method - Google Patents

Abstract

PURPOSE:To eliminate positioning errors in focusing, by projecting a plurality of light beams having different wave lengths at specified angles from the side of the surface of a sample, detecting the respective positions, and performing computation. CONSTITUTION:A light path L10, which is inputted at an incident angle theta1 is divided into a light path L11, which is reflected by the surface of a resist film, and a light path, which is transmitted through a resist film 11 and reflected by the surface of an SiO2 film of a semiconductor wafer 4 (the bottom surface of the resist film). Refractive indexes are different in the resist film in response to the wavelengths of light. Therefore, the light having the wavelength of lambda is refracted at a refractive index theta, passes through a light path L12, and is reflected. The light having the wavelength lambda' is refracted at a refractive index theta', passes through a light path L13, and is reflected. The positions of the reflected light beams, which are actually detected, are based on the combined light paths of the light paths L11, L12 and L13. In this way, the position of the light path L11 from the surface of the resist film, which is not affected by the reflection intensity can be accurately corrected and obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field of the Invention The present invention relates to a surface position detection method, such as automatic/dynamic focusing (autofocus) in a reduction projection exposure apparatus.
Concerning improvements in law.

(c) Conventional technology and problems □Recently, with the advancement of exposure technology, the conventional technology is closely adhered to! Instead of using light, a reduction exposure method, in which a mask pattern is projected in a reduced size onto a semiconductor wafer and exposed to light, has come to be used. This method is based on the same principle as the conventional photorepeater, which creates photomasks by reducing the size of the μ mask. This is a method that has many advantages, such as not being affected.

In an exposure apparatus that performs such reduction exposure, in addition to the conventional AF point mechanism that adjusts the X and Y axes to align the Focusing to form a clear image on the bar, <
The four structures are important elements.

Therefore, as shown in the partial resonance diagram of the reduction projection exposure device which is the real cause of chopsticks, the emission source 2 of the LED light is placed around the lens column 1, and the emission plate 8 is used at the bottom. The light is projected onto the semiconductor wafer 4, and the reflected light is received by the photodetector 6 using a reflector 5, which continuously focuses the light on the surface of the semiconductor wafer 4 according to the fixed position instruction of the detector. An automatic focusing mechanism is provided that finely adjusts the stage 7 in the Z direction so that the images are aligned. .

By the way, the wavelength (λ) of the light beam projected for this focusing must naturally be a non-photosensitive wavelength that does not sensitize the resist film coated on the semiconductor wafer surface. Human far ultraviolet (UV)
) light is used, the focusing beam is a wave 995
Infrared light of about 00λ is used.

However, a resist film with a thickness of 1 μm or several μm is coated on the surface of the semiconductor wafer, which is the object to be executed, and as shown in FIG. As a synthesis of the optical path Lll of the surface reflected light reflected from the surface of the semiconductor wafer 11 and the optical path TJ12 of the resist bottom surface reflected light from the silicon dioxide (SJLO,) film 12 surface formed on the semiconductor wafer 4,
The light will be reflected to the photodetector, and the combined optical path will also vary due to the difference in the reflection intensity ratio between the two reflected lights, resulting in a focusing error. That is, there is a problem that the reflectance of the 33.0 m film and the aluminum (1') film coated on the surface of the semiconductor wafer is greatly different, and the focusing distance is also different.

(C) Object of the Invention An object of the present invention is to propose a surface position detection method that eliminates the above-mentioned focusing position error and is not affected by reflection intensity.

((1) Number of grooves of the invention This [] target projects a plurality of light beams with different wavelengths from the side, and each of the reflected light beams (light beams that are insensitive to the resist film) This is achieved by a surface position detection method in which an accurate surface position is detected by detecting the position of the object and calculating the detected position, and will be described in detail below.

(e) Embodiment of the Invention Figure 3 shows an embodiment of the present invention, in which the optical path of two wavelengths (λ, λ') is shown, and the optical path LIO incident at an incident angle of 0 is a resist film. Optical path L reflected on the surface 1.1
, the S of the semiconductor wafer 4 passes through the resist film 11.
iO, and an optical path that is reflected at the film surface (bottom surface of the resist film), but since the refractive index within the resist film differs depending on the wavelength of the light, the light with the wavelength λ is refracted with the refractive index θ8, and the optical path is L12.
The light with the wavelength λ' is refracted by the refractive index θ'2 and reflected through the optical path TJ13, and the position of the reflected light that is actually detected is along these optical paths Lll, L12, T, -+
13 combined optical paths.

However, from the combined optical path of the lights having different wavelengths λ and λ', it is possible to correctly correct and determine the position of the optical path TJ 11 from the resist film surface, which is not affected by the reflection intensity. This will be explained below as shown in Figure 4 (a).
The optical path of light with wavelength λ is shown in a model diagram, and the refractive index of the resist film n=-fiηit, S, Ln 02 , and the distance DI between optical path TJ 11 and optical path L12 is 2X (
ltan 02 X (!O8θ1.

Therefore, when two wavelengths (λ, S') are used, the optical path 11 and L12 and the distance D1 between the optical path 11 and L13. D2 is DI = 2a tan 02 ×OO801D2 =
2(1, tan θ' x cos θ1 (d,; resist film thickness) (see Figure 4(b)).
12 and TJ l If the intensity ratio detected as the combined optical path of 1 and l113 is a:b, and the optical path of TJ 11 is taken as a reference, the combined optical path of Lll and LIs is D'l = - from the optical path position of Lll. ”--X 2 a tan
θ2Cosθ1a+b Also, the combined optical path of Lll and Ll, 3 is also r from the optical path position of Lll, /2 = 't) X 2d tanθ'ya coS
O1+i+L) (see FIG. 4(c)). L 1 l and T,
The difference between the combined optical path of No. 12 and the combined optical paths of Lll and Ll3 is (D'2-Dl) (see # in FIG. 4(d)). What we are trying to find is ordinary = Hiiragiho p 2, D'] = Shuguchi D1, and Ma holds true, eventually, a''+'b (
D2-Dl)Id, is a relational value that can be actually measured, and tanθ'2, tanθ2 depends on the refractive index, and the refraction n x 1,7 jl,n', = 1. ．． 7
．． Q. If the case is 2-01 mllo, then the combination of L11+L11--i device and IJ Ll.

becomes.

Difference aEb from +L1B combined optical path position (D2-01)
When , for example, b 1) can be obtained, and if the reflected light is corrected so that it comes to a position shifted by 1D2, accurate surface position detection can be performed. .

Practically speaking, one light emitting source emits light onto the film surface at a constant angle of incidence, and the reflected light is divided into two parts, each of which transmits single wavelength light with wavelengths λ and λ'. Through the top,
A method is adopted in which the light is simultaneously received by separate photodetectors and its position is detected, the position of reflection from the resist film surface is calculated by a computer from that value, and the stage is moved up and down based on the calculated value.

g) Effect of invention 　　　　　　　　　　□.

As can be seen from the explanation of the above embodiments, when multiple light beams with different wavelengths are detected, regardless of the reflection intensity ratio,
It is possible to accurately detect the position of the 'i' surface of a sample with a semi-transparent film. Therefore, if the present invention is applied to, for example, a reduction exposure apparatus, it will be possible to form a pattern with even higher precision without compromising exposure accuracy.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of the automatic focusing mechanism of a reduction projection exposure apparatus, and Figure 2 is a diagram of the optical path of a light beam from a single conventional light source.
Fig. 3 is an optical path diagram of light beams of two wavelengths according to the present invention, and Fig. 4 <a) to frog) are reference optical path diagrams for calculating the correction distance from the detection optical path position according to the present invention. It is. In the figure, 1 is a lens column, 2 is a light emitting source, 3 and 5 are reflective plates, 4 is a semiconductor wafer, and 6 is a photodetector. 7 is a stage, 11 is a resist film, 12 is a Si, 0g film, Llo is an optical path of incident light, Lll is an optical path of reflected light from the resist film surface, Lll! , LlB indicate the optical path of light transmitted through the resist film and reflected from the semiconductor wafer surface.

Claims (1)

[Claims] When detecting the surface position of a sample surface covered with a semi-transparent film, electric light beams with different wavelengths are beamed onto the sample surface at a predetermined angle from the side of the mortar surface, and the 1. A surface position detection method, comprising: calibrating each position of reflected light of a light beam, and calculating the detected position to accurately detect a surface device.