Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2000-04-25
2002-01-22
Rosasco, S. (Department: 2811)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C250S492220
Reexamination Certificate
active
06340543
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for repairing opaque defects (remaining defects) in metal film patterns on a photomask used as an original form in a photomechanical process during manufacture of semiconductor devices (LSIs), and to the structure of the metal film patterns repaired on the photomask.
2. Description of the Background Art
A photomask is used as an original form when transferring resist patterns onto wafer surfaces with a transfer apparatus in a photomechanical process during manufacture of semiconductor devices, on which patterns corresponding to the resist patterns are formed with metal film of CrON etc. If the metal film pattern has residue of the metal film (opaque defects) or blanks of the metal film (clear defects or pinhole defects) differing from the originally designed pattern, then the pattern transferred to the wafer may, depending on the defect size, differ from the originally designed resist pattern or the dimensions of the transferred pattern may vary from those of the original pattern. Furthermore, with the size reduction of the integrated circuit patterns to be finally produced by using the resist as a mask, the dimensional precision required for the resist pattern is becoming more severe, and accordingly the defect size limit allowed on the mask is becoming smaller. When defects exist in the metal film pattern on a photomask, the allowable defect size is usually limited to one-fourth to one-third of the design pattern dimensions (on the mask) so that the defects are not transferred onto the wafer or so that the transferred defects will not cause variation in dimensions from those of the original resist pattern or integrated circuit pattern over a permissible range determined on the basis of the semiconductor product's quality. Accordingly, while the allowable defect size on a mask was about 1 &mgr;m in a semiconductor product with about 3-&mgr;m design pattern dimension, the allowable defect size is reduced to about 0.3 &mgr;m when the integrated circuit pattern is downsized and the design pattern dimension is reduced to about 1 &mgr;m.
A conventional method for repairing opaque defects on the photomask will now be described referring to the plane views of
FIGS. 28 and 29
. As shown in
FIG. 28
, the opaque defects include isolated defects (hereinafter referred to as isolated opaque defects) like that shown by
73
and defects continuous with one of the edges of the original metal film pattern
70
(hereinafter referred to as opaque extension defects) like that shown by
72
. A laser repair method using YAG (yttrium/aluminum/garnet) laser etc. is usually used to repair such opaque defects
72
and
73
. That is to say, as shown in
FIG. 29
, a laser light beam is shaped through an aperture (not shown) in accordance with the size and shape of the opaque defects
72
and
73
and applied to the opaque defect portions. Then the opaque defects
72
and
73
absorb energy of the laser light and they thus evaporate and disappear. Particularly, for repair of the isolated opaque defect
73
, a laser irradiation region
74
is set to sufficiently include the entire defect and the laser light beam is applied to the inside of the region
74
to completely remove the isolated opaque defect
73
. For repair of the opaque extension defect
72
, the laser light is applied in the same way as in the case of the repair of the isolated opaque defect
73
so that the opaque extension defect
72
can be completely removed. Particularly, for the opaque extension defect
72
, the optical system on the optical path is adjusted so that the boundary along which the opaque extension defect
72
is in contact with one edge of the pattern
70
can reproduce the original edge of the pattern defined in the absence of the opaque extension defect
72
, and the laser light is applied with one end of the laser irradiation region
74
aligned with the extension of the original pattern edge. That is to say, the original pattern edge is reproduced without allowing the metal film to remain in the repaired area after the opaque extension defect
72
is repaired with laser, or without causing the edge in the repaired area to be recessed from the position of the original pattern edge by excessively removing the metal film. The above-described repairing method is applied to common photomasks mainly using CrON film and also to phase shift photomasks mainly using CrON film or MoSiON film.
The methods for repairing opaque extension defects also include, as well as the laser repair method, a method using ion beam (ion beam etching method), where the beam can be positioned more accurately than in the laser light repair method. In this repair method, as in the case of the laser repair method, the defects are repaired to reproduce the original pattern edges without allowing the metal film to remain in areas where opaque extension defects have been repaired and without causing the repaired areas to be recessed by excessive repair.
The conventional laser repair method or ion beam etching method raise the following problem in the repair of opaque defects. The problem will now be described referring to the plane views of
FIGS. 30 and 31
.
That is to say, in the areas
75
in
FIG. 30
in which the opaque defects have been repaired (opaque defect repaired portions), a very thin film of light-shielding metal remains or the surface of the quartz glass is roughed by the irradiation of beam. Accordingly, the transmittance in the opaque defect repaired portions
75
is lower than that in the original quartz glass portions
71
(
FIG. 28
) where no opaque defect exists. Hence, when the metal film pattern is transferred onto a semiconductor wafer after the photomask is repaired to form a resist pattern, the exposure to the resist areas located right under the opaque defect repaired portions differs from (is smaller than) the exposure to the other resist areas located right under the original quartz glass portions free of opaque defect. Then, as shown in
FIG. 31
, parts of the edges of the resist pattern
76
on the semiconductor wafer swell, which raises the problem of dimensional variation of the pattern
76
. Such dimensional variation does not cause serious problem in device quality if the devices have such large design pattern dimensions on photomasks, e.g. about 3 &mgr;m, as would allow large dimensional variation. However, when the design pattern dimension on photomasks is reduced to about 1 &mgr;m, for example, the dimensional variation of the resist pattern due to the transmittance reduction in areas where opaque defects have been repaired by the conventional method seriously affect the device quality over the permissible range. This problem is likely to happen in areas in which isolated opaque defects existing near the metal film pattern have been repaired or in areas where opaque extension defects continuous with edges of the metal film patterns have been repaired. Especially, this problem is very likely to occur in memory cells in DRAM etc. where finest patterns are formed densely.
SUMMARY OF THE INVENTION
A first aspect of the present invention is directed to a method for manufacturing a photomask comprising a quartz glass and a pattern composed of a metal film formed on a surface of the quartz glass. According to the present invention, the method comprises the steps of: detecting whether the pattern has an opaque defect continuous with or proximate to the pattern and having a first width in a first direction and a second width in a second direction, the second direction being perpendicular to the first direction and corresponding to a direction in which an edge of the pattern is extended; and when the opaque defect is detected in the step of detecting, removing the opaque defect by applying a given beam onto a beam irradiation region obtained by correcting in the first direction an irradiation region on the surface of the quartz glass which contains the opaque defect and has third and fourth widths respectively in the first
Hosono Kunihiro
Nagamura Yoshikazu
Suzuki Kazuhito
Yoshioka Nobuyuki
Mitsubishi Denki & Kabushiki Kaisha
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Rosasco S.
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