Radiant energy – Radiation controlling means
Reexamination Certificate
2000-02-16
2003-09-09
Anderson, Bruce (Department: 2881)
Radiant energy
Radiation controlling means
C250S515100
Reexamination Certificate
active
06617600
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to radiation shields, and in particular to such shields for protecting a tool from being damaged by high-irradiance radiation when processing a workpiece with the tool.
BACKGROUND OF THE INVENTION
In many modern-day manufacturing applications, such as semiconductor manufacturing or materials processing, it is desirable to process an object (“workpiece”), with a beam of high-irradiance radiation to modify the chemical, physical or electrical properties of the workpiece. In semiconductor manufacturing, the substrate is often a silicon wafer, and in materials processing, the substrate can be a metal plate. For most applications, the radiation source is a high-irradiance (units: J/cm
2
) laser. Efficient manufacturing techniques typically require that a robotically controlled tool deliver this high-irradiance radiation to the workpiece, preferably with little user intervention.
With reference to
FIG. 1
, prior art processing tool
10
comprises, in order along axis A
1
, a workpiece support member
14
(i.e., a “chuck”) and a tool portion
20
. The latter includes a variety of components such as vacuum lines, electrical cables, mechanical apparatus, metal surfaces, and the like. Workpiece support member
14
supports a workpiece
24
having an upper surface
26
, a lower surface
28
and an outer edge
30
. A source of radiation (not shown) irradiates upper surface
26
of workpiece
24
with high-irradiance radiation
34
.
A problem often encountered in radiation-based processing tools such as processing tool
10
is that a portion
38
of high-irradiance radiation
34
incident workpiece
24
spills over onto tool portion
20
, or even onto workpiece support member
14
. Portion
38
is referred to herein as “spillover radiation.” This happens most often when a region on surface
26
near the edge of workpiece
24
is being processed. Since spillover radiation
38
has sufficiently high irradiance to modify the surface properties of workpiece
24
, it also typically has sufficient irradiance to modify the surface properties of tool portion
20
. In time, spillover radiation
38
can damage tool portion
20
, can cause unwanted heating problems within processing tool
10
, and can result in potentially harmful reflections.
Unfortunately, it is not possible to simply shield the tool from spillover radiation using conventional shields made of metal or plastic, because the high irradiance beam would damage such a shield. For instance, simply extending workpiece support member
14
to capture spillover radiation is not a practical solution because the workpiece support member typically needs to be made of a light, machinable metal such as aluminum, which is susceptible to damage from high-irradiance radiation.
Ideally, it is desirable to intercept spillover radiation
38
with a shield capable of rendering the radiation harmless before it irradiates the tool. If, for example, a metallic shield is placed between workpiece
24
and tool portion
20
to intercept spillover radiation
38
, the metallic shield will, in all likelihood, ablate or be damaged by the radiation. Further, a metallic shield may reflect radiation onto other portions of processing tool
10
. Generally, speaking, any shielding material that relies primarily upon surface absorption of radiation will probably be damaged.
There are several prior art shields designed to intercept radiation and render it harmless. For example, U.S. Pat. No. 5,153,425, entitled “Broadband Optical Limiter with Sacrificial Mirror to Prevent Irradiation of a Sensor System by High Intensity Laser Radiation,” describes a broadband optical limiter for use in combination with a sensor system operative to prevent irradiation of the sensor system by laser radiation of unknown wavelengths having intensity levels sufficient to damage or disable the sensor system. The broadband optical limiter is further operative to throughput, with minimal optical distortion at wide-angle fields of view, electromagnetic radiation in the operating spectral band(s) of the sensor system. The broadband optical limiter includes a flat or spherically shaped sacrificial mirror that is operative to reflect electromagnetic radiation in the operating spectral band(s) of the sensor system and to be optically machined, i.e., vaporized, by focused laser radiation of unknown wavelengths having intensity levels sufficient to damage or disable the sensor system to create reflective dead spot. The reflective dead spot prevents the focused laser radiation from being throughputted to the sensor system. The broadband optical limiter further includes optical components to focus incident electromagnetic and laser radiation onto the sacrificial mirror, to turn incident electromagnetic and laser radiation out of the field of view of the sensor system, and to turn electromagnetic radiation reflected by the sacrificial mirror back into the field of view of the sensor system. A major disadvantage of this type of shield, however, is that it is sacrificial, and changes due to the irradiation. Such shields tend to need to be replaced frequently.
U.S. Pat. No. 4,114,985, entitled “Shield for High Power Infrared Laser Beam,” describes shielding from and the termination of high power infrared laser beams by interception of the beam by one of two spaced, juxtaposed, ceramic (i.e., clay-based) sheet members. The beam-intercepting member has a thickness to beam power density relationship that allows opaque to translucent conversion of the portion thereof illuminated by the beam. The translucent portion subsequently diffuses the beam. The second ceramic sheet member then absorbs the diffused beam. A major shortcoming of this shield, however, is that it requires two clay-based, opaque sheet members, with the first sheet having to be of sufficient strength to cause a transformation from opaque to translucent by virtue of the incident radiation.
U.S. Pat. No. 4,575,610, entitled “Laser Shielding Device,” describes a laser-shielding device having two spaced-apart layers of shielding material defining a sealed chamber between the two layers. At least one layer degrades in the presence of an impinging laser beam, creating a hole through the layer. A pressure change in the chamber is sensed and signaled to a machine controller to stop the lasing operation. Unfortunately, this shield device is not well-suited for protecting a tool from spillover radiation, since the shield is sacrificial and thus would need to be replaced often. Further, the shield is pressurized, which adds to its complexity.
SUMMARY OF THE INVENTION
The present invention relates to radiation shields, and in particular such shields for protecting a tool from being damaged by high-irradiance radiation when processing a workpiece with the tool using high-irradiance radiation.
A first aspect of the invention is a shield for protecting a tool portion having an irradiance damage threshold from high-irradiance radiation from a light source when irradiating a workpiece, said shield arranged between the light source and the tool portion and having an irradiance damage threshold, an absorption coefficient, a volume and a thickness, and designed to absorb in said volume, a portion of said high-irradiance radiation that would otherwise be incident the tool portion, wherein the shield maintains said absorbed high-irradiance radiation below said shield irradiance damage threshold, and wherein radiation exiting the shield and incident the tool portion and incident the tool portion has an irradiance below the irradiance damage threshold of the tool portion.
A second aspect of the invention is a shield for protecting a tool portion having an irradiance damage threshold from high-irradiance radiation from a light source when irradiating a workpiece, said shield arranged between the light source and the tool portion and having an irradiance damage threshold, a scattering coefficient, a volume and a thickness, and designed to scatter in said volume a portion of said high-irradiance radiation that would oth
Fong Yu Chue
Gortych Joe
Hawryluk Andrew M.
Anderson Bruce
Jones Allston L.
Ultratech Stepper, Inc.
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