Light exposure method

Details Light exposure method Light exposure method

1999-03-24

2001-11-27

Huff, Mark F. (Department: 1756)

Radiation imagery chemistry: process, composition, or product th

Plural exposure steps

C430S005000, C430S311000, C430S396000, C359S483010

Reexamination Certificate

active

06322957

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of light exposure applicable to semiconductor lithography, or a like process, particularly to a method of light exposure utilizing evanescent light.
2. Related Background Art
In recent years, techniques for making a fine semiconductor device are being developed rapidly. Demagnifying light projection methods are employed for transferring a pattern of IC (integrated circuit) or the like by light exposure. In such a method, a mask is prepared for pattern formation; this mask is illuminated by a light projection system; and the light penetrating through the mask is focused by a demagnification lens on a light-receiving base plate to transfer the pattern on the mask onto the light-receiving base plate.
In this method, the minimum dimension of the pattern is limited by occurrence of light diffraction. The limit is about 0.6 &lgr;/NA (where &lgr; is light wavelength, and NA is numerical aperture of the lens).
For obtaining a smaller pattern size, a phase shift light projection method is disclosed in Japanese Patent Application Laid-Open No. 62-50811. For lowering the resolution limit, an oblique light projection method is disclosed in Japanese Patent Application Laid-Open No. 4-267515.
Even with the above techniques and a stepper employing an excimer laser light source, the pattern size cannot be made smaller than about 0.15 &mgr;m at present.
For lowering the limit caused by light diffraction, a method is disclosed in Japanese Patent Publication Gazette No. 8-179493 (1987), in which so-called evanescent light leaking from a dielectric material is utilized to transfer a pattern of 0.15 &mgr;m or finer.
The light exposure employing the evanescent light is explained by reference to FIG.
1
. In
FIG. 1
, laser beam
30
is introduced at such an incident angle that the laser beam is totally reflected as reflected laser beam
31
at the bottom face of prism
32
. A mask
34
is provided on glass base plate
33
. This mask
34
is made from an electroconductive material such as chromium, and serves as a light-intercepting film. Photosensitive material (photoresist)
36
is applied onto transfer-receiving base plate
37
. Glass base plate
33
carrying mask
34
is closely attached to prism
32
with interposition of spacer
38
. Thereby, evanescent light
35
leaks through openings of mask
34
. When photosensitive material
36
applied on transfer-receiving base plate
37
is brought close thereto to expose it to leaking light
35
, a latent image is formed in the photosensitive material by photopolymerization, crosslinking reaction, or a like process. This latent image is developed and fixed to transfer the pattern of the openings of mask
34
to form a fine pattern of not larger than 0.2 &mgr;m.
The above prior art techniques, however, utilize a circularly polarized laser beam introduced in one direction, so that they have a disadvantage that the transfer accuracy differs between a vertical pattern and a lateral pattern. More specifically, the mask pattern for an IC or the like is generally constituted of slit-shaped openings arranged perpendicularly to each other, vertically and laterally. Therefore, when light is introduced to a fine slit of not more than the wavelength of the light, the behavior of the light leaking from the slit-shaped openings is different between the linearly polarized light introduced perpendicularly to the length direction of the opening and that introduced parallel thereto. The linearly polarized light introduced perpendicularly to the length direction of the slit leaks in the same shape as the slit, whereas the linear polarized light introduced parallel thereto leaks out along the edge of the opening, not to transfer precisely the pattern of the mask.
In the above prior art techniques, a triangular prism is used. In the triangular prism, the light reflected at the bottom face leaves the prism to the air through the prism face nearly perpendicular to the light path, so that a part of the light to be emitted outside is reflected by the prism face to return to the bottom to cause interference with the original incident light, thereby disturbing the uniform distribution of the evanescent light, disadvantageously.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method of light exposure which solves the aforementioned problems of prior art techniques and is capable of transferring optically a pattern containing strip-shaped portions extending in different directions with high precision.
In a first embodiment of the present invention, there is provided a method of exposure to a light pattern containing a first strip-shaped portion extending in a first direction and a second strip-shaped portion extending in a second direction, the method comprising steps of placing, on a light-receiving face, a first mask having a strip-shaped slit corresponding to the first strip-shaped portion extending in a first direction of the pattern; projecting, to the first mask, a first linearly polarized light beam polarized in the second direction to irradiate the light-receiving face through the slits of the first mask; removing the first mask from the light-receiving face, and placing, on the light-receiving face, a second mask having a strip-shaped slit corresponding to the second strip-shaped portion extending in a second direction of the pattern; and projecting, to the second mask, a second linearly polarized light beam polarized in the first direction to irradiate the light-receiving face through the slit of the second mask.
In a second embodiment of the present invention, there is provided a method of exposure to a light pattern containing a first strip-shaped portion extending in a first direction and a second strip-shaped portion extending in a second direction, the method comprising steps of placing, on a light-receiving face, a first mask having a strip-shaped slit corresponding to the first strip-shaped portion extending in a first direction of the pattern; projecting, to the first mask, a first linearly polarized light beam polarized in the first direction to irradiate the light-receiving face through the slit of the first mask; removing the first mask from the light-receiving face, and placing, on the light-receiving face, a second mask having a strip-shaped slit corresponding to the second strip-shaped portion extending in a second direction of the pattern; and projecting, to the second mask, a second linearly polarized light beam polarized in the second direction to irradiate the light-receiving face through the slits of the second mask.
In any of the above embodiments, preferably the first linearly polarized light beam and the second linearly polarized light beam are projected to the first mask or the second mask through an optical block having a bottom face in close con tact with the mask at an incident angle of the light beam to cause total reflection at the bottom face, and the light-receiving face is exposed to the evanescent light passing through the slit of the first or second mask.
The polarization direction of the linearly polarized light means the vibration direction of the electric field vector of the light. In the case where a linearly polarized light beam is introduced at a prescribed incident angle not perpendicular to the irradiated face as above, the linearly polarized light beam polarize d in a first direction means such a polarized light beam that the projected component of vibration direction of the electric field vector of the linearly polarized light is parallel to the above first direction. On the other hand, the linearly polarized light beam polarized in a second direction means such polarized light that the projected component of vibration direction of the electric field vector of the linearly polarized light is parallel to the above second direction.
In the case where the first and second linearly polarized light beams are introduced at a prescribed angle not perpendicular to an irradiated face, preferably a first imaginary

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