Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2002-08-05
2004-12-28
Rosasco, S. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
Reexamination Certificate
active
06835507
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to photolithography. More particularly, the present invention relates to a projection lens of an exposure apparatus of a photolithography system, and to the associated phenomenon of flare that causes defects in a pattern formed on a wafer by light focused on the wafer by the projection lens.
2. Description of the Related Art
In general, flare is a phenomenon that produces a bad exposure in a photolithographic process due to defects of a projection lens of the exposure apparatus of the photolithography system. More specifically, when a portion of the surface of the lens is defective, the exposure light is dispersed at the defective portions, and photoresist patterns are formed incorrectly by the exposure light. Here, the defects at the surface of the lens which may produce flare-include contaminants, scratches, or a difference in refractory indices between portions of the lens. Light passing through such defective portions of the lens during exposure scatters and thus, the light does not focus properly on the photoresist layer.
The flare phenomenon will be described more fully with reference to
FIGS. 1 and 2
. Referring to
FIGS. 1A and 1B
, an exposure apparatus for performing a photolithographic process includes a lens
14
for scaling down and projecting a light shielding pattern
11
of a mask
10
onto a predetermined portion of a wafer
12
. The lens
14
is interposed between the mask
10
and the wafer
12
. The top surface of the wafer
12
is coated with a photoresist layer (not shown).
As shown in
FIG. 1A
, if no defect occurs at the surface of the lens
14
, the shielding pattern
11
on the mask
10
is projected on a reduced scale onto the photoresist layer. Accordingly, photoresist patterns
12
a
are formed on the wafer
12
.
On the other hand, as shown in
FIG. 1B
, if defects occur at the surface of the lens
14
, light disperses at the defective portions
15
of the lens
14
. The dispersion of light results in an irregular distribution of light on the photoresist layer during the exposure, and decreases the contrast of the image. In addition, portions of the wafer
12
corresponding to and adjacent to the defective portions
15
may become excessively exposed. As a result, an on chip variation phenomenon occurs in which photoresist patterns
12
b
on the wafer
12
are deformed, or the widths of photoresist patterns
12
b
formed in one field vary. As the photolithographic process is repeated, the lens
14
of the exposure apparatus becomes more severely defective, and the amount of flare varies.
Accordingly, in photolithography, the amount of flare of a lens and the position on the wafer which is affected by flare must be measured and determined for every exposure process if the photoresist patterns are to be formed as desired.
However, conventional photolithography systems do not have tools for identifying whether flare is produced by a projection lens, for identifying whether a wafer is affected by flare, and/or for determining the extent of a flare-affected region on a wafer. Thus, it is difficult to correct for the flare, i.e., to avoid bad exposures.
SUMMARY OF THE INVENTION
An object of the present is to solve the above-described problems related to flare in the photolithography process.
More specifically, it is a first object of the present invention to provide a mask which is capable of being used in a photolithography system to identify whether flare is being produced by the projection lens of the system and to quantify the amount of flare.
It is a second object of the present invention to provide a method of manufacturing such a mask.
It is a third object of the present invention to provide a method of identifying a flare-affected region on a wafer.
It is a fourth object of the present invention to provide a method of correcting for the flare to produce the photoresist patterns having desired line widths in a region that would otherwise be affected by the flare.
It is a fifth object of the present invention to provide a method of designing the line width of transmission patterns (or shielding patterns) of a mask to compensate for the flare produced by the lens of the photolithography system with which the mask is to be used.
The mask according to the present invention includes a mask substrate having a light shielding region and a light transmission region, and a plurality of alternating line and space patterns formed in each of the light shielding region and the light transmission region. The line and space patterns formed in the light shielding region correspond to the line and space patterns formed in the light transmission region.
The plurality of line patterns all have the same line width, and the plurality of space patterns all have the same line width. The space patterns may be light transmission patterns in the form of grooves interposed between the line patterns.
A main light shielding layer formed on a predetermined portion of the mask substrate may divide the mask substrate into the light shielding region and the light transmission region. The main light shielding layer defines at least one group (row, for example) of light transmission patterns. At least one sub light shielding layer is formed in the light transmission region of the mask substrate, and defines at least one group of light transmission patterns corresponding to those defined by the main light shielding layer.
A plurality of rows of the light transmission patterns are formed in the main light shielding layer as spaced from one another in a longitudinal direction of the mask. Likewise, a plurality of rows of light transmission patterns are formed in the at least one sub light shielding layer as spaced form one another in the longitudinal direction.
The light transmission patterns all have the same size. In addition, the (latitudinal) spacing of the light transmission patterns in the rows thereof is uniform, and the longitudinal spacing of the rows of the light transmission patterns is also uniform.
The boundary between the main light shielding layer and the light transmission region is preferably linear and extends at a right angle to a line passing through the centers of longitudinally aligned ones of the light transmission patterns. The light shielding region and the light transmission region may have the same size, and the light transmission patterns are located along a longitudinal area of the mask substrate.
In order to manufacture the mask, a light shielding layer of a light-blocking material is first formed on the mask substrate (transparent). At least one light transmission pattern is formed in the light shielding layer. Subsequently, the main light shielding layer is formed by removing one portion of the light shielding layer from the light transmission region, and the at least one sub light shielding layer is formed by leaving a portion of the light shielding layer in the light transmission region around the light transmission patterns.
In forming the light transmission pattern and forming the main light shielding layer, portions of the main light shielding layer may be removed such that the light transmission patterns join the boundary between the main light shielding layer and the light transmission region.
In order to identify a flare-affected region on a wafer, photoresist patterns are formed on the wafer using the mask to carry out a photolithography process. The line widths of photoresist patterns formed by the line and space patterns of the light shielding region of the mask, and the line widths of the photoresist patterns formed by the line and space patterns of the light transmission region of the mask are measured. Next, the line widths of the photoresist patterns are compared. If the difference in the line widths of the photoresist patterns differ by more than a predetermined value, such as the calibrated precision of the measuring apparatus, it is determined that the projection lens is producing flare. The amount of flare is calculated based on the difference in lin
Choi Seong-Woon
Han Woo-Sung
Jeong Tae-Moon
Ki Won-Tai
Sohn Jung-Min
Rosasco S.
Samsung Electronics Co,. Ltd.
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