Photocopying – Projection printing and copying cameras – Illumination systems or details
Reexamination Certificate
1999-12-07
2001-10-16
Gray, David M. (Department: 2851)
Photocopying
Projection printing and copying cameras
Illumination systems or details
C355S053000, C355S077000
Reexamination Certificate
active
06304319
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposure apparatus for transferring a specific patter of image from a mask to a photosensitive substrate, a method of producing the exposure apparatus, and a method of producing device with the exposure apparatus, and particularly, to a technology for detecting the position of the photosensitive substrate while monitoring alignment mark on the mask and alignment mark on the photosensitive substrate.
2. Related Background Art
It is common, in an exposure apparatus applied for performing a lithography process in manufacturing semiconductor devices, liquid crystal devices, and other relevant devices, to monitor alignment marks on the mask and the photosensitive substrate with an alignment microscope viewing from above the mask for positioning the mask and photosensitive substrate (for example, a wafer or a glass coated with photosensitive material such as photoresist). Some of techniques for detecting the position of a photosensitive substrate are a TTL (through the lens) alignment method (laser step alignment or LSA) using non-exposure light and projection optics as disclosed in Japanese Patent Laid-open Publication (Sho)60-130742 (U.S. Pat. No. 4,677,301), an off-axis alignment method (field image alignment or FIA) using a wide band of non-exposure light as disclosed in Japanese Patent Laid-open Publication (Sho)62-171125, and a TTR (through the reticle) alignment method (auto step alignment or ASA) using exposure light through reticle.
SUMMARY OF THE INVENTION
We, the inventors, have found through reviewing the prior art methods that the following problems are not solved. Among the prior art method described above, the TTL alignment using non-exposure light enables to prevent the photoresist from being exposed to light and has an advantage that the detection of alignment mark on a substrate is facilitated because the photoresist has a higher transparency to non-exposure light. On contrary, this method is susceptible to aberration of non-exposure light in the optical projecting system. In general, the optical projecting system has only a narrow range of aberration compensation and thus requires an extra optics for the compensation which may complicate the overall arrangement. In addition, it is necessary to employ illumination light approximate to monochrome light having a narrow range of wavelengths as the non-exposure light for ease of the compensation, whereby the effect of resist interference will be inevitable.
In the off-axis alignment using a wide band of non-exposure light, alignment mark on a substrate is monitored with the light having a wide band for minimizing the effect of resist interference. However, an extra optics for monitoring the alignment mark is needed in addition to the optical projection system. If the relative relationship between the two optical systems is unstable, the accuracy of the detection of the position will be declined thus lowering the throughput.
The TTL alignment method and the off-axis alignment method require extra optics in addition to the optical projecting system. It is hence needed to prepare reference markings such as fiducial points for measuring offset values between respective optical systems, whereby the apparatus will be made intricate.
In the TTR alignment used when directly monitoring the alignment mark on a substrate through a reticle is needed while exposure light is applied, aberration in the optical projecting system is negligible because the exposure light is involved. However, this method employs a novolak organic material as the photoresist for the photosensitive substrate. The photoresist of such a material has a lower transparency to the exposure light before exposure, causing detection light from the alignment mark to be received at a less S/N ratio (signal noise ratio). Also, the photoresist of such a material possibly produces bleaching which increases the transparency during the exposure and a phenomenon that the refraction is gradually changed, hence causing distortion of an image of the alignment mark and increasing error in the detection of the position. For compensation, some modifications have been proposed; for example, a preparatory irradiation of the exposure light is applied before the main exposure action to increase the transparency of the photoresist (to expose a portion which covers the alignment mark and make the photoresist transparent to a degree) for making a stable state that change in the refraction does not occur or a portion which covers the alignment mark is removed to expose the alignment mark as disclosed in U.S. Pat. No. 5,656,229. This step will delay the detection of the position of the substrate thus lowering the throughput. Also, in case that the removal of the portion is carried out by etching, the protection of the alignment mark is needed as will be troublesome.
The present invention has been invented for eliminating the foregoing problems and its object is to provide an exposure apparatus having a simple arrangement capable of detecting the position of a substrate at higher accuracy without applying a preparatory irradiation over or removing a portion of the photoresist which covers alignment mark on the photoresist substrate, a method of producing the exposure apparatus, and a method of producing devices with the exposure apparatus.
A method of producing devices according to the present invention comprises: a first step of placing at a specific location a photosensitive substrate having a surface thereof provided with alignment marks and coated with a photoresist which is substantially transparent to detection light having a wavelength falling within a range where the wavelength of exposure light exists; a second step of detecting the position of the alignment marks with the detection light of the wavelength and adjusting the position of the photosensitive substrate in response to result of the detection; and a third step of illuminating a mask having a pattern of interest with the exposure light and transferring the pattern of interest via an optical projecting system to the photosensitive substrate. The wavelength of the detection light is within a range where the wavelength of the exposure light exists (&lgr;±100 nm when &lgr; being the wavelength of the exposure light).
The photosensitive substrate prepared at the first step may be a substrate having the alignment marks applied to the surface thereof and coated with the photoresist. The photoresist may be a transparent photoresist which is transparent to the exposure light and the detection light. The transparent photoresist may have a transparency of higher than 10% for one micrometer of thickness to the exposure light and the detection light and preferably may be of chemical magnification type.
In the method of producing devices according to the present invention, the second step is arranged for directing the detection light to the alignment marks on the photosensitive substrate while its amount is being controlled to be smaller than a desired level of the exposure light. The desired level of the exposure light may be an level enough to cause the transparent photoresist to respond to the exposure light. The amount of the detecting light may preferably be less than ⅓ the desired level of the exposure light for protecting the alignment marks. More preferably for avoiding the optical properties of the transparent photoresist from being affected, the amount of the detection light may be smaller than a threshold at which the transparent photoresist becomes susceptible to the detection light.
We, the inventors, made sure that when the surface of the substrate was protected with anti-reflection coating (BARC), the alignment marks could significantly be read with a level of the detection light which is substantially 10% of the desired level of the exposure light. Also, we, the inventors, made sure that when the substrate was not provided with anti-reflection coating, the detection light which is as small as 2% to 3% of the desire
Gray David M.
Nguyen Hung Henry
Nikon Corporation
Oliff & Berridg,e PLC
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