Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
1999-10-13
2001-10-09
Young, Christopher G. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C430S030000, C430S311000
Reexamination Certificate
active
06300019
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pellicle that prevents a particle from directly lying on a mask used for exposing a wafer, to thereby defocus the particle.
2. Description of the Related Art
Pellicles have been widely used in semiconductor manufacturing in order to reduce the influence of foreign particles when exposing wafers using a mask.
FIG. 1
shows a structure of a conventional pellicle. The pellicle principally incorporates a pellicle frame
20
and a pellicle membrane
30
. A typical pellicle membrane
30
may include, for example, nitrocellulose and fluoropolymers. Because the pellicle membrane
30
has a thickness of approximate 1 micron it has very little strength to resist external forces. In addition to the pellicle frame
20
and the pellicle membrane
30
, the pellicle incorporates a first adhesive
40
and a second adhesive
50
. The pellicle frame
20
supports the pellicle membrane
30
, wherein they are adhered to each other by the second adhesive
50
. In the process of manufacturing semiconductors, a mask
10
is first prepared. The mask
10
is then cleaned and thereafter the surface of the mask
10
is inspected to detect any particles lying on the mask
10
. After it has been confirmed that the surface satisfies given criteria, the pellicle is mounted onto the mask
10
. Thereafter, the surface of the mask
10
is checked again. When the mask
10
is in good condition, a light source (not shown) placed at a side of the mask
10
irradiates a ray toward the mask
10
, whereby a wafer (not shown) placed at another side thereof is exposed to the ray through the mask
10
.
In mounting the pellicle onto the mask
10
, the pellicle is pressed to the mask
10
using the pellicle mounting system
60
. This pressing and the first adhesive
40
enables the pellicle to be fixed on the mask
10
. The first adhesive
40
may preferably be covered with a liner (not shown) for ease of handling. Such a liner is then removed before the pellicle is mounted.
As shown in
FIG. 1
, pressure is applied with the contact of the pellicle membrane
30
and the pellicle mounting system
60
. In other words, the pellicle mounting system
60
directly presses the pellicle membrane
30
. Because the pellicle membrane
30
is thin and therefore weak to external force, this pressing may damage the pellicle membrane
30
. Such damage, if severe, might cause foreign particles to invade the space surrounded by the mask
10
and the pellicle. Alternatively, the pellicle membrane
30
may peel away from the pellicle frame
20
.
To detect a particle on the mask
10
, a method is used wherein a light source obliquely irradiates a ray toward the mask
10
and a light detector detects a ray scattered by the particle. However, a conventional pellicle frame
20
might block a ray scattered by a particle lying near the pellicle frame
20
from reaching the detector, thereby blocking detection of such a particle.
Related to this, the size of such pellicle membranes
30
has increased and as a result, there are instances where the pellicle membrane
30
bends to its own weight. As a result, the exposure of the wafer fails, that is, the pattern on the mask
10
cannot be accurately copied to the wafer.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide a pelicle which overcomes the above issues in the related art. This object is achieved by combinations described in the independent claims. The dependent claims define further advantageous and exemplary combinations of the present invention.
According to an aspect of the present invention, there is provided a pellicle used for preventing a first particle from lying on a mask used for exposing a wafer and defocusing a second particle lying on the pellicle, the pellicle being mounted onto the mask by pressing the pellicle to the mask using a pellicle mounting system, the pellicle comprising: a pellicle membrane; and a pellicle frame including a first portion on which the pellicle membrane is attached and a second portion with which the pellicle mounting system establishes contact.
The distance between the surface of the first portion on which the pellicle membrane is attached and the surface of the mask on which the pellicle is mounted is preferably equivalent to the distance between a surface of the second portion with which the pellicle mounting system establishes contact and the surface of the mask.
A first distance between the surface of the first portion on which the pellicle membrane is attached and the surface of the mask on which the pellicle is mounted is preferably longer than a second distance between the surface of the second portion with which the pellicle mounting system establishes contact and the surface of the mask.
The second portion preferably has a mechanism for preventing the pellicle mounting system from slipping on the second portion in a direction in parallel with the surface of the mask. The mechanism preferably has a surface that resists the sliding of the pellicle mounting system.
A first distance between the surface of the first portion on which the pellicle membrane is attached and the surface of the mask on which the pellicle is mounted is preferably shorter than a second distance between the surface of the second portion with which the pellicle mounting system establishes contact and the surface of the mask.
The second distance is preferably longer than a third distance necessary for defocusing the second particle. The pellicle frame includes a contact portion that has an inclined surface and that guides the pellicle mounting system to the establishment of contact with the pellicle frame. The inclined surface is preferably directed outward. The inclined surface is directed inward.
According to another aspect of the present invention, there is provided a pellicle that prevents a particle from lying on a mask used for exposing a wafer, comprising: a pellicle membrane; a pellicle frame on which the pellicle membrane is attached; and a supporting member that prevents the pellicle membrane from bending.
The pellicle frame preferably includes a fixing mechanism that fixes the supporting member on the pellicle frame. The supporting member preferably lies under the pellicle membrane. The supporting member preferably lies over the pellicle membrane. The supporting member and the pellicle membrane are preferably adhered to each other.
The supporting member is preferably a string. The fixing mechanism preferably has a hook for fixing the string. The mechanism preferably has a defined recess for fixing the string. The fixing mechanism preferably has solder for fixing the string.
The supporting member is preferably a net. The fixing mechanism preferably uses solder to fix the net.
The pellicle frame preferably includes a thick portion thicker than other portions, wherein the supporting member is the thick portion.
According to further another aspect of the present invention, there is provided a method of detecting a particle on a mask used for exposing a semiconductor wafer, comprising: applying a ray to the mask on which a pellicle is mounted using a pellicle mounting system, the pellicle including a pellicle membrane and a pellicle frame having a first portion on which the pellicle membrane is attached and a second portion establishing contact with the pellicle mounting system, a surface of the first portion on which the pellicle membrane is attached being lower than a surface of the second portion with which the pellicle mounting system establishes contact, and being higher than the height of the pellicle membrane necessary for defocusing the particle, and receiving a scattering ray produced by the particle from the applied ray.
According to still another aspect of the present invention, there is provided a method of mounting a pellicle on a mask comprising: mounting the pellicle on the mask using a pellicle mounting system, the pellicle including a pellicle frame comprising a first contact portion having a first inclined surface, the pelli
Funatsu Hiroyuki
Ikeda Shigeru
Jones Volentine PLLC
OKI Electric Industry Co., Ltd.
Young Christopher G.
LandOfFree
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