Radiation imagery chemistry: process – composition – or product th – Registration or layout process other than color proofing
Reexamination Certificate
1999-01-22
2002-05-21
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Registration or layout process other than color proofing
C430S005000, C430S030000
Reexamination Certificate
active
06391501
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a mask pattern generating method and pattern generating apparatus suitable when desiring to form fine patterns on a wafer substrate at a high resolution from a transmittance light of a photo mask using an exposure device in the process of manufacturing a highly integrated semiconductor device etc.
2. Description of the Related Art
The photo masks used in the process of manufacturing semiconductor devices are comprised of a light blocking film formed on a glass substrate. In a pattern forming process of semiconductor elements, the light blocking pattern on the photo mask is projected on a photo resist coated on the wafer surface and then exposed. The light blocking pattern on the photo mask is obtained by converting designed CAD data to drawing apparatus data and faithfully patterning it. The photo mask pattern is precisely transferred onto the wafer by a semiconductor photolithographic process.
In the photolithographic process in the process of manufacturing a semiconductor device, a high resolution beyond the resolution limit determined by the wavelength of the light is required because it is necessary to form the pattern close to an exposure wavelength. Accordingly, the phase shift method has recently been used as a lithographic technique which can form finer patterns than the exposure wavelength.
Below, the principle of a spatial frequency modulation type phase shift method will be explained.
FIGS. 16A and 16B
are views of the principle of the phase shift method compared with a method of the prior art, and
FIGS. 17A and 17B
are views of Fourier spectrum of the phase shift method and the method of the prior art.
Here, assume that a period of light intensity transmittance is close to the resolution limit of a one-dimensional period pattern having 1/&ngr;
0
. Since the light transmitting object is the mask pattern whose size is close to the resolution limit, when considering only the sinusoidal basic frequency component, the amplitude of the light passing through the photo mask can be approximated as follows:
Mask of the related art:
T
(
x
)=|cos 2&pgr;&ngr;
0
x|
(1-1)
Phase shift mask:
T
(
x
)=cos 2&pgr;&ngr;
0
x
(1-2)
In the method of the related art shown in
FIG. 16A
, the light passing through the photo mask was divided into a 0-order diffracted light proceeding straight along the light axis and a ±1st-order diffracted light having an angle of &thgr; (sin &thgr;=&ngr;
0
&lgr;) with respect to the light axis and strikes a projection lens. On the other hand, as shown in
FIG. 16B
, in the phase shift method, the light passing through the phase shift mask is separated into a ±1st-order diffracted light having an angle of &thgr;/2 with respect to the light axis and strikes the projection lens. In both cases, only the refracted light passing through the inside of the projection lens contributes to form an image.
The Fourier spectrum formed on an iris plane of the projection lens is expressed as follows from the Fourier transform of the formulas 1-1 and 1-2.
Mask of the related art:
F
(&ngr;)=(4/&pgr;){&dgr;(&ngr;)/2+[&dgr;(&ngr;+&ngr;
0
)]+&dgr;(&ngr;−&ngr;
0
)]/2+ . . . } (2-1)
Phase shift mask:
F
(&ngr;)=(½)[&dgr;(&ngr;+&ngr;
0
/2)+&dgr;(&ngr;−&ngr;
0
/2)] (2-2)
As shown in
FIGS. 17A and 17B
, in a transmittance type mask of the related art not considering phases, there are spectrum components at &ngr;=0 and ±&ngr;
0
, while in a phase shift mask, this depend only on &ngr;=±&ngr;
0
/2. Namely, the basic spectrum obtained from the phase shift mask lies at a position of half of the spectrum obtained by the transmittance type mask. This is equivalent to the spatial frequency of the mask pattern becoming half. The projection lens of a stepper acts as a low-pass filter for transferring only the spatial frequency component smaller than a proper frequency (Eigen frequency) &ngr;c (=NA/&lgr;). When considering a case where the spatial frequency &ngr;
0
of a not transferred fine pattern is &ngr;c<&ngr;
0
≦284 c, in the case of a transmittance type mask, the spectrum component of ±&ngr;
0
does not pass, so no contrast of the image can be obtained. On the other hand, a phase shift mask transfers the basic spectrum &ngr;=±&ngr;
0
/2 so forms a pattern image on the image plane. This is the characteristic of a spatial frequency modulation type phase shift mask which has the largest effect of improving the resolution.
The basic layout structure of the spatial frequency modulation type phase shift mask uses, as shown in
FIG. 16B
, two phases of 0 degree and 180 degrees and arranges shifters in order that apertures of the mask alternately become inverse in phase. As a shifter, as shown in
FIG. 16B
, there are shifters stacked on films different from the light blocking film and shifters formed by etching a glass surface to impart a shifter function.
This shifter arrangement corresponds to a two-color problem of coloring a flat map by two colors. The shifter phases have to be arranged alternately. Therefore, in a complicated interconnection layout, in principal it is impossible to avoid an arrangement discrepancy (phase mismatch) where the shifter phases cannot be alternately inverted.
As a first prior art, Ohi et al. in the article “Method of Design of Phase-Shifting Mask Utilizing Compactor”, JJAP, Vol. 33 (1994), No. 12B, pp. 6774-6778, discusses a technique for avoiding phase mismatch using layout compression (compaction) in a phase shift method using the phase difference of transmittance light between patterns formed.
FIG. 18
is a view of the principle of a so-called Levenson type phase shift utilizing a negative resist—a premise of the first prior art.
In the photo mask shown in
FIG. 18
, chrome apertures provided at the pattern forming locations are alternately arranged with shifters (glass etching trenches) of a 180-degree phase and without trenches of a 0-degree phase. Accordingly, in this phase shift method, since the phase difference of the light passing through the pattern itself is utilized, a negative resist in which the pattern transferring locations remain without being dissolved in the developing solution is necessary. In addition to the fact that obtaining a practical negative resist is difficult, it is necessary that the pattern layout itself be a pattern which generates a phase difference. Therefore, while this is effective with simple lines and spaces, there is no phase shift effect with an isolated pattern. Accordingly, in the first prior art, even though it is possible to avoid a phase mismatch, there is the disadvantage that there are many constraints in the predicted resist materials and pattern preparation.
Therefore, in recent years, studies have been made on a technique based on multiple exposures including phase shift exposures by a mask giving a phase difference to the light passing through the two sides of the fine patterns to be formed and ordinary exposures for removing the unnecessary patterns generated due to the same (hereinafter referred to as the phase shift multiple exposure method). This second prior art is discussed by Tamechika et al. in the article “Automatic Generation of Phase-Shifting Mask Patterns Using Shifter-Edge Lines”, MICRO-AND-NANO-ENGINEERING '97”.
FIGS. 19A and 19B
are views of the principle of a Levenson type phase shift utilizing a negative resist in the phase shift multiple exposure method.
In the phase shift mask shown in
FIG. 19A
, apertures provided at the sides of fine patterns (chrome patterns) are alternately formed with shifters of 180-degree phase (glass etching trenches) and without trenches of 0-degree phase. The peripheries are covered with chrome because a positive resist is used. In the second exposure (ordinary exposure), not illustrated peripheral interconnection port
Huff Mark F.
Kananen, Esq. Ronald P.
Mohamedulla Saleha R.
Rader & Fishman & Grauer, PLLC
Sony Corporation
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