Optics: measuring and testing – By polarized light examination – With birefringent element
Patent
1990-12-14
1993-07-13
Turner, Samuel A.
Optics: measuring and testing
By polarized light examination
With birefringent element
356349, 356351, 356358, G01B 902
Patent
active
052278620
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a projection exposure apparatus and method used for a fine pattern such as a semiconductor circuit pattern or a liquid crystal display device pattern, or more in particular to a projection exposure apparatus capable of exposing the whole surface of an exposure area with high resolution by detecting the inclination and height of an object to be exposed to light.
BACKGROUND ART
In the exposure of a fine pattern of a semiconductor integrated circuit or the exposure of a drive circuit pattern in a large vision field of a display device as represented by a TFT (Thin Film Transistor) liquid crystal television or the like, it is necessary to expose a pattern faithfully to the original image with a small line width variation over the whole surface in the exposure area. Especially in the field of the semiconductor integrated circuit, a pattern with a line width of 0.5 .mu.m or less will be required to be exposed over the whole surface of a region of approximately 15 mm in the future. With the increase in the fineness of the pattern, however, the range of forming an image (depth of focus) will become .+-.1 .mu.m or less. For this reason, it is essential that the photoresist surface on a wafer accurately coincides with the surface where a pattern image is to be formed. In order to realize this, it is necessary to detect the inclination and height of the wafer surface (photoresist surface) in the exposure area accurately.
In a first well-known example disclosed in JP-A-63-7626, a laser diode beam is converged from a diagonal direction on the wafer surface and the height is detected by detecting the position of convergence. Also, according to this well-known example, the multiple reflection accompanying a multilayered structure of a wafer is handled by use of a three-wavelength semiconductor laser with the convergence point changed along the direction perpendicular to the diagonal incident direction thereby to determine heights of different places on the wafer. This well-known example, which is primarily intended to detect the height, is capable of detecting an inclination by taking measurements at positions changed along the direction perpendicular to the diagonal incident direction. An accurate value of an inclination is difficult to obtain, however, even if two positions are measured in a narrow area of about 20 mm in diameter. If the height detection of high accuracy is to be realized in this well-known example, it is necessary to attain sufficient convergence on the wafer, that is to say, to reduce the diameter of convergence as far as possible. The reduction in the diameter of convergence, however, requires an increased convergence angle of the convergence beam (the angle formed by the outermost beam of the convergence light fluxes to the main light beam), with the result that the incident angle of the principal ray would be unavoidably reduced. This reduction in angle (which reduces the angle from a line perpendicular to the wafer surface) increases the effect of the multiple interference due to the multilayered structure of the wafer for the reason mentioned below. This well-known example uses three wavelengths to cope with the problem. Since each wavelength is affected by the interference, however, the problem has yet to be basically solved.
According to a second well-known example disclosed in JP-A-63-199420 as a conventional method of inclination detection, on the other hand, a light beam for inclination detection having a different wavelength from the exposure wavelength is irradiated through a projection lens, the reflected light beam is converged and the inclination is detected from the convergence position. Since the light beam is applied to the wafer in a substantially perpendicular direction or at a small incident angle, however, the effect of interference with the light beam reflected from the base is not negligible, thereby making accurate detection difficult for the reason mentioned below.
Further, in a third well-known example disclosed in JP-A-6
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Oshida Yoshitada
Tanaka Minoru
Tanimoto Tetsuzo
Hitachi , Ltd.
Turner Samuel A.
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