Radiation imagery chemistry: process – composition – or product th – Effecting frontal radiation modification during exposure,...
Reexamination Certificate
1995-08-23
2004-01-06
Angebranndt, Martin (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Effecting frontal radiation modification during exposure,...
C430S005000, C355S053000, C355S077000
Reexamination Certificate
active
06673526
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pattern formation method and a method and apparatus for production of a semiconductor device using that method, more particularly relates to a method of exposure which enables a pattern to be formed without the problem of a secondary peak even if using a phase shifting mask.
2. Description of the Related Art
At present, in the research and development of semiconductor integrated circuits, effort is being made to develop devices of a design rule of the sub-half micron order. In developing such devices, photolithography is indispensable. It is not too much to say that the resolution performance of the exposure devices used in photolithography, the so-called “reduction, projection, and exposure devices”, determines the success or failure of research and development into semiconductor devices and the feasibility of mass production.
Conventionally, the resolution performance of reduced projection and exposure devices has been improved by enlarging the numerical aperture of the reduction projection lens or shortening the exposure wavelength based on the following Rayleigh criterion:
R=k
1
×&lgr;/
NA
where, R: resolution
&lgr;: Exposure wavelength
NA: Numerical aperture
k1: Process coefficient
However, in the fabrication of a semiconductor device, there are step differences caused by the topography, wafer flatness, etc. of the semiconductor device, and therefore securing of the depth of focus is also an important parameter at the same time as the resolution performance. The dimensional precision of the resist pattern in the photolithography step at the time of fabrication of a semiconductor device is generally ±5 percent. In an actual device, as shown in
FIG. 1
, there is always unevenness in the surface of the semiconductor substrate S. For example, there is a convex portion In of polycrystalline silicon etc. As a result, the pattern of the resist PR is not formed on the same focal plane. For this reason, the dimensions of the pattern of the resist PR differ between the upper portion and the lower portion of a step difference. Of course, this becomes more conspicuous the finer the pattern in a case where a stepper of the same wavelength and same numerical aperture is used. This tendency is seen in common for all types of resist.
The depth of focus becomes smaller in primary proportion to the exposure wavelength and in inverse proportion to the square of the numerical aperture. At the mass production stage, a depth of focus of about 1.5 &mgr;m is necessary. For this reason, there are restrictions in order to satisfy both of the resolution performance and the depth of focus considered necessary.
FIGS. 2A and 2B
show the dependency on the numerical aperture when the resolution performance of the depth of focus (D.O.F) in KrF excimer laser lithography, which is the most advanced exposure, is used as a parameter. As will be understood from the figures, the highest resolution which is obtained while satisfying the needed depth of focus of 1.5 &mgr;m is about 0.35 &mgr;m. Accordingly, it is extremely difficult to resolve a line width of 0.35 &mgr;m or less with a depth of focus of 1.5 &mgr;m or more. Some sort of technique for enlarging the depth of focus is necessary.
In response to such a request, in recent years, the halftone type phase shift method has been proposed. This exposure method is an extremely powerful method for improving the resolution and depth of focus of an isolated pattern such as a contact hole. In the halftone type phase shift method, as shown in
FIG. 3
, a semitransparent Cr, Si
x
N
y
, SiO
x
, N
y
, Mo
x
, Si
y
film, or the like having a transmittance with respect to the exposure light of about several percent to about 20 percent, that is, allowing passage of a fine amount of exposure light therethrough, is used as the halftone film
2
corresponding to the dark portions
1
. In the bright portions
3
, both the film
2
and the transparent substrate (with a concave portion
5
formed therein) or only the film
2
is etched and made to act as a mask. At this time, by setting the phase difference between the bright portions
3
and the dark portions
1
formed by the semitransparent film to 180°, as shown in
FIG. 4B
, the gradient of the distribution of the intensity of the light in an isolated pattern (for example, a hole pattern of 0.6 &lgr;/NA) can be made sharp. Note that,
FIG. 4A
shows the distribution of the intensity of the light in an isolated pattern using a conventional chromium mask.
In the design of this phase shifting mask, the transmittance of the halftone film
2
is an important factor. Namely, so as to make the gradient of the distribution of the intensity of the light in an isolated pattern sharper, it is sufficient to raise the transmittance of the halftone film
2
. However, by raising the transmittance, the light shielding effect by the halftone film
2
is weakened, and the resist ends up exposed over its entire surface.
Also, usually, at the time of formation of a pattern, as shown in
FIG. 5A
, a secondary peak called a side lobe is generated due to the adjacency effect on both sides of the desired pattern position in the distribution of the intensity of the light irrespective of the light shielding position. The secondary peak becomes stronger by raising the halftone transmittance. As shown in
FIG. 5B
, even in a so-called completely isolated contact hole wherein, for example, when the design dimension of the hole pattern
6
is defined as W, the distance between the adjoining patterns is 3W or more, the peripheral portion becomes “gouged” in shape (numeral
8
part). With a shape as shown in
FIG. 5B
, there is concern that the diameter of the contact hole will be enlarged in the etching step.
Further, when it is intended to apply the halftone phase shifting mask method to a so-called periodic pattern portion having a high pattern density, the secondary peak becomes stronger due to interference between adjoining patterns, that is, the mutual adjacency effect, at the periodic pattern portion having the high pattern density.
Accordingly, when it is intended to form a device pattern by using the halftone phase shifting mask method, the design and a CAD process must be carried out with sufficient consideration given to the distance between patterns. This places a tremendous load on the design and CAD process and prevents practical application.
So as to solve the above-mentioned problems, intensive study is currently underway in various areas on how to enlarge the depth of focus without making the adjacency effect more conspicuous and without placing a heavy load on the design of the mask. However, no effective exposure method for enlarging the depth of focus without suffering from the above-described problems has yet been found. Accordingly, it is essential to quickly establish an exposure technique for enlarging the depth of focus without making the adjacency effect conspicuous and without placing a heavy load on the design of the mask.
At the present time, when a practical depth of focus cannot be obtained in the fabrication of a device, pattern formation has been carried out by using the multilayer resist method, electron beam exposure method, and the like. However, a sufficiently satisfactory effect has not been obtained.
Accordingly, it is essential to quickly establish an exposure technique for enlarging the depth of focus without making the adjacency effect conspicuous, without placing a heavy load on the design of the mask, and without exerting an advance influence on the aberration and other imaging characteristics by a method other than that mentioned above.
SUMMARY OF THE INVENTION
The present invention was made in consideration of the above-described situation and has as an object thereof to provide a pattern formation method and a method and apparatus for production of a semiconductor device using the same which, when fabricating a semiconductor device or the like, decides on the method of enlarging the depth of foc
Ogawa Tohru
Uematsu Masaya
Angebranndt Martin
Kananen, Esq. Ronald P.
Sony Corporation
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