Optical: systems and elements – Lens
Reexamination Certificate
2002-06-28
2003-12-09
Ben, Loha (Department: 2873)
Optical: systems and elements
Lens
C359S351000, C359S355000, C359S365000, C359S385000, C359S566000, C359S823000, C355S053000, C355S067000, C356S237400, C250S492200
Reexamination Certificate
active
06661580
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to optical inspection systems, and more specifically to auto-focusing techniques for optical inspection systems.
BACKGROUND OF THE INVENTION
Generally, the industry of semiconductor manufacturing involves highly complex techniques for integrating circuits into semiconductor materials. Due to the large number of processing steps and the decreasing size of semiconductor devices, the semiconductor manufacturing process is prone to processing defects that decrease device yields. Testing procedures to eliminate these processing defects from the processing steps are therefore critical for maintaining high yielding production facilities. Since the testing procedures are an integral and significant part of the manufacturing process, the semiconductor industry constantly seeks more sensitive and efficient testing procedures.
FIG. 1
is a diagrammatic view of a typical optical semiconductor inspection system
100
that includes an integrated auto-focus mechanism
114
.
FIG. 1
illustrates only the components of an optical inspection system that are relevant to the description of the present invention, therefore various components necessary for operation of the inspection system are not shown.
FIG. 1
shows an illumination source
102
that directs light or photons through one or more sets of optical lenses
104
so that a semiconductor wafer specimen
106
can be illuminated and inspected. Optical lens set
104
illustrated in
FIG. 1
is an objective lens set. Photons reflected off of specimen
106
are directed back to an inspection detector
108
through beam splitter
110
. Inspection detector
108
detects photons reflected off of specimen
106
for inspection purposes. In order for inspection system
100
to produce accurate inspection results, specimen
106
should be positioned within a very small depth of field
112
. Otherwise, sensitivity of inspection system
100
will be lost.
To ensure that specimen
106
is within the depth of field
112
, auto-focus mechanism
114
is used. Auto-focus mechanism
114
includes a light emitting diode (LED)
116
that directs an auto-focusing light beam
118
into optical lenses
104
such that light beam
118
hits specimen
106
, then is directed back into auto-focusing detector
120
via beam splitters
122
and
124
. Gratings
126
and
128
, which are offset slightly from each other, are placed respectively in front of LED
116
and auto-focusing detector
120
. Grating images
126
(
a
) and
128
(
a
) are shown to illustrate the their respective orientations. The position of specimen
106
with respect to field of view
112
affects the intensity of light detected at auto-focus detector
120
. Therefore, the focus of optical system
100
can be monitored through auto-focus mechanism
114
. Auto-focus device uses at least some of the same optical lens elements in the system as illumination source
102
.
FIG. 1
illustrates an embodiment where illumination source
102
and auto-focus device
114
both direct light beams through objective lens section
104
. Specifically, auto-focus light beam
118
is directed through the field of view of objective lens section
104
.
As is commonly known, anti-reflective coatings (AR coatings) are formed on the surfaces of the optical lenses of an optical inspection system. AR coatings beneficially reduce reflections off of the lens surfaces, however, they also tend to reduce the amount of light that can be transmitted through the lenses. As will be described in further detail below, these AR coatings also cause undesirable effects such as reducing the sensitivity of an optical inspection system.
BRIEF SUMMARY OF THE INVENTION
In general, the present invention pertains to techniques for increasing the percentage of light that is transmitted through optical inspection systems that operate in or near the ultraviolet and deep ultraviolet electromagnetic spectrums. Along with increasing the amount of light transmission, the techniques of the present invention also provide additional advantages such as reduction of ripple, increased ability to match inspection systems, and improving manufacturability. The techniques of the present invention involve using an auto-focus light source near the operational range of the inspection system and slightly raising the lower end of the operational range.
One aspect of the present invention pertains to a microscope optical inspection system that includes at least one set of inspection optical lens elements, an illumination source that directs light into the set of inspection optical lens elements, wherein the operational bandwidth of light used for inspection is approximately within the ultraviolet and deep ultraviolet range or within portions thereof, and an auto-focus device that directs an auto-focusing light beam into at least some of the set of inspection optical lens elements, wherein the wavelength of the auto-focusing light beam is proximate to or within the operational bandwidth.
Another aspect of the present invention pertains to a microscope optical inspection system that includes at least one set of inspection optical lens elements, an illumination source that directs light into the set of inspection optical lens elements, and an auto-focus device that directs an auto-focusing light beam into at least some of the set of inspection optical lens elements, wherein the auto-focus device uses a light emitting diode or semiconductor laser made of gallium and nitride.
REFERENCES:
patent: 5999310 (1999-12-01), Shafer et al.
patent: 6115175 (2000-09-01), Maruyama et al.
patent: 6320697 (2001-11-01), Takeuchi
patent: 6483638 (2002-11-01), Shafer et al.
patent: 6486940 (2002-11-01), Williamson
patent: 6512631 (2003-01-01), Shafer et al.
Ben Loha
Beyer Weaver & Thomas LLP
KLA-Tencor Technologies Corporation
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