Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
2000-11-01
2002-11-12
Berman, Jack (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S492200, C250S492220, C430S311000, C430S322000, C378S119000
Reexamination Certificate
active
06479830
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an extreme ultraviolet lithography system and, more specifically, to an extreme ultraviolet lithography system that utilizes protective diamond thin film coatings to reduce the erosive effects on hardware components as a result of energetic particles emitted from a laser-produced plasma light source.
2. Description of the Prior Art
In extreme ultraviolet lithography (EUVL), a next-generation microchip fabrication process, a laser-produced plasma (LPP) light source or “fireball” generates extremely short wavelength radiation (the shorter the wavelength, the smaller, denser and faster the transistors on the microchip) that is the result of high density clusters of material introduced by a nozzle interacting with high-intensity long-wavelength radiation from a pulsed laser.
Referring to
FIG. 1
, a material
10
, such as xenon, is introduced through a nozzle
12
. As it leaves the nozzle
12
, the material
10
is in the form of extremely small high-density clusters that absorb the high-intensity long-wavelength radiation
14
from a pulsed laser (not shown). A highly Ionized energetic plasma forms and emits copious amounts of short wavelength radiation to form the LPP light source
16
. Essentially, the plasma converts long-wavelength laser power into short wavelength extreme ultraviolet (EUV) power. As a practical matter, a nearby “diffuser” may be used to collect and re-circulate the unused material
10
so that the gas load on the EUVL system's vacuum pumps is reduced. Not shown, is nearby hardware for supporting both the nozzle
12
and the diffuser
18
. This hardware is very compact. For example, the gap between the nozzle
12
and the diffuser
18
Is typically less than a centimeter and the distance from the nozzle to the plasma fireball is typically 1.5 to 5 millimeters.
Referring to
FIG. 2
, the laser-produced plasma (LPP) light source or “fireball”
16
generates extremely short wavelength radiation which is the result of the jet of material
10
from nozzle
12
interacting with high-intensity long-wavelength radiation from the pulsed laser, as previously described. Next, a condenser optics assembly
20
projects the radiation
22
onto a mask
24
that collects the radiation
22
. As with standard lithography techniques, a projection optics assembly
26
collects the light reflected from the mask
24
and images features of the mask
24
onto a water
28
, exposing a photoresist. The mask
24
and the wafer
28
are moved together so the entire pattern on the mask
24
is replicated on the wafer
28
.
Because the fireball
16
emits many kilowatts of power, with roughly half of the absorbed power going into radiation and the other half into kinetic energy of plasma ions and electrons, a sizable fraction of each half is eventually intercepted by source hardware components contained within the EUVL chamber, causing the hardware components to structurally erode and/or their functional capabilities to degrade. Structural erosion occurs as a result of a hardware component losing material through the sputtering by the plasma ions or neutral atoms. And a functional degradation occurs as a result of the sputtered material collecting on the surface of a hardware component. For example, because of its close proximity to the plasma light source, a first mirror (not shown) of the condenser optics assembly
20
typically becomes contaminated and loses its reflectivity, necessitating its frequent replacement. These frequent replacements can have an unacceptable impact on the maintenance and cost of ownership of an EUVL system.
By covering the relevant hardware with a low-sputter yield material such as graphite, conventional EUVL systems have reduced hardware material losses that are the consequence of ion sputtering, but mirror contamination issues still remain. Additionally, because the thermal contact between conventional protective covers and the surfaces of the hardware components is poor, the temperature of the cover tends to rise. And since sputter yield is the number of particles released from or near the hardware surface, per Incident particle, the attendant rise in temperature of the protective cover increases the sputter yield as the surface of the hardware approaches melting or sublimation temperatures. Thermal management and erosion problems are closely related since most materials that have low sputter yield do not have acceptable thermal properties. For example, conventional nozzles (see
FIG. 1
, numeral
12
) are typically made from solid graphite, which has very low sputter yield but poor thermal conductivity, or copper, which has excellent thermal conductivity but a high sputter yield.
Therefore, based on the shortcomings of the prior art, an extreme ultraviolet lithography system that reduces the erosive effects of ion sputtering under thermally managed conditions by utilizing thin film, low-sputter yield protective coatings on high-thermal conductive hardware component materials is highly desirable.
SUMMARY OF THE INVENTION
The present invention provides an extreme ultraviolet lithography system including a laser-produced plasma light source for generating short wavelength radiation and a plurality of hardware components located near the laser-produced plasma light source. Each hardware component is formed of a high-thermal conductive material and a layer of thin film material is deposited over the outer surface of the hardware element. The thin film layer protects the hardware component from the erosive effects of a plasma of the short wavelength radiation without decreasing the thermal contact between the layer and the outer surface of the hardware component.
REFERENCES:
patent: 5374318 (1994-12-01), Rabalais et al.
patent: 6011267 (2000-01-01), Kubiak et al.
patent: 6190835 (2001-02-01), Haas et al.
patent: 6285737 (2001-09-01), Sweatt et al.
Fornaca Steven W.
Talmadge Samuel
Berman Jack
Fernandez Kalimah
TRW Inc.
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