Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2002-06-07
2004-03-16
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C430S311000
Reexamination Certificate
active
06706453
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for formation of a semiconductor device pattern, a method for designing a photo mask pattern, a photo mask and a process for a photo mask, in particular, to a method for formation of a semiconductor device pattern, a method for designing a photo mask pattern, a photo mask and a process for a photo mask by means of photolithographic technology for forming a microscopic pattern in a semiconductor device.
2. Description of the Background Art
In recent years semiconductor integration circuits have been achieved remarkably high levels of integration and miniaturization. Accompanying that, miniaturization of circuit patterns formed on a semiconductor substrate (hereinafter referred to simply as a wafer) has made rapid advances.
Above all, photolithographic technology is widely perceived as the basic technology in pattern formation. Accordingly, up until the present day a variety of developments and improvements have been achieved. However, the miniaturization of patterning shows no signs of abating and the requirements for the increase of resolution of patterns have become more stringent.
This photolithographic technology is a technology wherein a pattern of a photo mask (original layout) is copied onto the photoresist applied to a wafer so that the copied photoresist is used to pattern the lower layer film to be etched.
At the time of copying of this photoresist, development processing is applied to the photoresist and the type where the part of the photoresist to which light hits is removed through this development processing is called a positive type photoresist while the type where the part of the photoresist to which light does not hit is eliminated is called a negative type photoresist.
In general, a resolution limit R (nm) in photolithographic technology using a scaling down exposure method is represented as:
R=k
1
·&lgr;/(
NA
)
Here, the wavelength (nm) of the utilized light is denoted as &lgr;, numerical aperture of a projection optical system of the lens is denoted as NA and a constant depending on the resist process is denoted as k
1
.
As is known from the above equation, in order to increase the resolution limit R, that is to say, in order to gain an even smaller pattern a method for making the values of k
1
and &lgr; smaller while making the value of NA larger should be considered. That is to say, the constant depending on the resist process should be made smaller while proceeding to make the wavelength shorter and to make NA higher.
However, improvement of the light source or lenses are technically difficult and a problem arises, on the contrary, in proceeding to make the wavelength shorter and the NA higher so that the focal point depth &dgr; (&dgr;=k
2
·&lgr;/(NA)
2
) of light becomes shallower so as to induce the lowering of the resolution.
Under such circumstances, in manufacturing semiconductor integrated circuits it is necessary to form a microscopic pattern with a large process margin. A modified illumination method works effectively for formation of a concentrated pattern and is widely practiced. On the other hand, as for a method for formation of an isolated line pattern with a large process margin, there is the method of using a Levenson type phase shift mask.
However, in the case of the Levenson type phase shift mask, it is necessary to manufacture a phase shifter for converting the phase of the exposure light by 180° and there is the problem that the mask is difficult to manufacture. In addition, since the Levenson type phase shift mask attempts to increase the resolution by positively interfering with the transmission light of different phases, there is the problem that lens aberration of the projection exposure apparatus influences the resolution so that the excellent characteristics which are supposed to be gained in the case of no aberration cannot be gained. Therefore, the method of using the Levenson type phase shift mask is in the condition where the practical use thereof hasn't made progress.
In addition, a method for improving the process margin (so-called auxiliary pattern method) by arranging the lines of a line width which is not resolved on the mask along the originally patterned lines has been taken into consideration. However, in this method the dimension of the mask pattern becomes extremely small and there is a problem that inspection for defects of the mask is difficult.
SUMMARY OF THE INVENTION
The purpose of the present invention is to provide a method for the formation of a semiconductor device pattern, a method for designing a photo mask pattern, a photo mask and a process for a photo mask wherein it is possible to form a microscopic pattern without using an auxiliary pattern method, a phase shift mask or the like and wherein the defect inspection of a mask is easy.
A method for a semiconductor device pattern formation according to the present invention includes a first exposure step of exposing a first photoresist on a wafer surface by a projection exposure method through a first photo mask which has an aperture pattern for light transmission including a pair of lines with substantially same width which run parallel to each other with a gap and which are isolated from other aperture patterns for light transmission, and an exposure amount, defined by an energy given to the pattern which has a sufficiently large mask aperture when the first photoresist is exposed, is four or more times and twenty or less times as large as the exposure amount on the border where the first photoresist is converted from soluble to insoluble in a developer through exposure or the exposure amount on the border where the first photoresist is converted from insoluble to soluble in a developer through exposure.
According to a method for the formation of a semiconductor device pattern, the first photoresist is exposed through a so-called overexposure wherein the exposure amount is larger than an ordinary exposure via the first photo mask which has a pair of aperture patterns for light transmission. Thereby, a microscopic pattern can be formed wherein the fluctuation of the pattern dimension is small even when the focus is changed to a certain degree. In addition, the depth of focus (DOF), which is a focal range wherein a certain focusing performance can be maintained at a constant level, can be made large. Therefore, a microscopic pattern can be formed with a large process margin and with a high precision without using an auxiliary pattern method of a phase shift mask.
The above described method for a semiconductor device pattern formation preferably further includes a second exposure step wherein regions of the first photoresist corresponding to regions other than pairs of aperture patterns for light transmission are exposed after the first exposure step and before the development step of the first photoresist.
A complicated pattern can be dealt with by carrying out a double exposure in the above manner.
In the above described method for a semiconductor device pattern formation, the first exposure is preferably carried out by modified illumination.
Thereby, the resolution and the depth of focus can be further increased.
In the above described method for a semiconductor device pattern formation, the modified illumination is preferably carried out by using a ring band illumination stop in the illumination optical system.
Thereby, the resolution and the depth of focus can be increased.
In the above described method for a semiconductor device pattern formation, the modified illumination is preferably carried out by using a quadruple polar illumination stop in the illumination optical system.
Thereby, the resolution and the depth of focus can be increased.
In the above described method for a semiconductor device pattern formation, the first photo mask is preferably an attenuating phase shift mask including a semi-transmissive shielding film having the pair of aperture pattern, for light transmission. The semi-transmissive shielding film includes a mat
Huff Mark F.
Renesas Technology Corp.
Sagar Kripa
LandOfFree
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