Information
-
Patent Grant
-
6809328
-
Patent Number
6,809,328
-
Date Filed
Friday, December 20, 200221 years ago
-
Date Issued
Tuesday, October 26, 200419 years ago
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Inventors
-
Original Assignees
-
Examiners
- Lee; John R.
- Gurzo; Paul M.
Agents
- Schwabe, Williamson & Wyatt, P.C.
-
CPC
-
US Classifications
Field of Search
US
- 250 4931
- 250 504 R
- 378 119
-
International Classifications
-
Abstract
Erosion-resistive coatings are provided on critical plasma-facing surfaces of an electrical gas plasma head for an EUV source. The erosion-resistive coatings comprise diamond and diamond-like materials deposited onto the critical plasma-facing surfaces. A pure diamond coating is deposited onto the plasma exposed insulator surfaces using, for example, a chemical vapor deposition processes. The diamond coating is made conductive by selective doping with p-type material, such as, but not limited to, boron and graphite.
Description
FIELD OF THE INVENTION
The present invention relates to extreme ultraviolet lithography, and more particularly, to erosion resistant coatings for components of EUV sources.
BACKGROUND OF INVENTION
Optical lithography is a key element in integrated circuit (IC) production. It involves passing radiation (light) through a mask of a circuit design and projecting it onto a substrate, commonly a silicon wafer. The light exposes special photoresist chemicals on the surface of the wafer which is used to protect unetched circuit details. Integrated circuit feature resolution is directly related to the wavelength of the radiation. The demand for ever smaller IC features is driving the development of illumination sources that produce radiation having ever smaller wavelengths. Extreme ultraviolet light (EUV) has shorter wavelengths than visible and UV light and can therefore be used to resolve smaller and more numerous features.
Extreme ultraviolet lithography is a promising technology for resolving feature size of 50 nm and below. There are many problems in order to realize EUV lithography and the most serious problem is to develop the EUV radiation source. An EUV source with a collectable radiation power of 50 W to 150 W at over 5 kHz in the spectral range of 13-14 nm will be required to achieve requirements for high volume manufacturing of 300 mm wafers.
Electrical discharge gas plasma devices (EUV lamps) are under investigation as promising EUV sources. The principle consists of heating up certain materials into a plasma to such a level that the material emits EUV radiation. Potential source materials which emit EUV radiation at excited energy levels include xenon, oxygen, and lithium. The aim is to produce as many photons as possible in the required wavelength range. A pulsed discharge of electrically stored energy across a gap between a cathode and an anode is used in the presence of the gas for the creation of plasma with temperatures of several 100,000 C. This plasma emits thermal radiation in the spectral range of around 10 nm to 20 nm.
FIG. 1
is a cross-sectional view of one possible configuration of an electrical discharge gas plasma head
10
capable of producing an EUV-emitting plasma
20
. The plasma head
10
comprises a plurality of closely positioned electrodes, in this example represented as a cathode
12
and anode
14
, separated by an insulator base
16
or ring separator. The area between the cathode
12
and anode
14
is filled with an ionizing gas
22
. A plasma discharge
17
initiated near the base
19
travels along the cathode
12
and anode
14
through self-induced electromagnetic forces. Upon reaching the cathode tip
18
and anode tip
15
, the discharge
17
compresses upon itself densifying, heating, and emitting EUV excitations.
Other electrode/insulator geometries are possible but all share the property of producing a pinched plasma in close proximity to one of more surfaces of the plasma head.
In operation, a tremendous heat load, on the order of 5 kW/cm
2
, is experienced by the components of the plasma head
10
. The plasma-facing components (PFCs) include: an inner cathode surface
11
of the cathode
12
, an outer anode surface
13
of the anode
14
, and exposed insulator base surfaces
13
of the insulator base
16
. Regardless of the specific component configuration and arrangement, there will be at least some PFCs that are susceptible to the effects of the operation of the plasma head
10
.
The PFCs are commonly only a few millimeters from the plasma
20
and in an erosive environment that quickly damages the PFC's. This erosion severely effects performance, lifetime and reliability of the discharge head
10
. In particular, the anode
14
tends to erode more quickly than the cathode
12
, which puts severe limitations on the lifetime of the discharge head
10
as well as producing debris that can impinge upon and harm the other components of the plasma head and overall system, as well as harm the exposed target
34
being illuminated.
The cathode
12
and anode
14
are commonly made from refractory metals, such as tungsten or molybdenum which are more resistant to the effects of extreme heat. These materials are expensive, difficult to machine, and are prone to cracking when structurally loaded under sever heating conditions. These materials, none the less, erode over time in this environment.
The insulator components, namely the insulator base
16
, comprise various ceramic materials, all of which suffer to some extent, from thermal cracking and erosion in these environments.
In order for the electric discharge plasma EUV sources to meet commercial requirements and demands, including reliability and productivity, lifetime-extending improvements will have to be made for the components of the discharge heat
10
.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1
is a cross-sectional view of an electric discharge gas plasma EUV source;
FIG. 2
is a cross-sectional view of a plasma head in accordance with an embodiment of the present invention;
FIG. 3
is a cross-sectional view of a plasma head in accordance with an embodiment of the present invention;
FIG. 4
is a cross-sectional view of a plasma head in accordance with an embodiment of the present invention; and
FIG. 5
is a table of candidate insulator materials used to electrically insulate conductive components of the discharge head in accordance with embodiments of the present invention.
DESCRIPTION
In the following detailed description, reference is made to the accompanying drawings which form a part hereof wherein like numerals designate like parts throughout, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. Therefore, the following detailed description is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims and their equivalents.
Embodiments of apparatus and methods of the present invention provide diamond and diamond-like coatings on critical plasma and electrical discharge-exposed surfaces of an electrical discharge gas plasma head
10
. Referring again to
FIG. 1
, the electrical discharge gas plasma head
10
comprises an electrically conductive annular nozzle
12
electrically insulated from a centrally-positioned anode
14
by an insulator base
16
or ring separator. Of particular interest are the plasma-facing components (PFCs) which include: an inner cathode surface
11
of the cathode
12
, an outer anode surface
13
of the anode
14
, and exposed insulator surfaces
13
of the insulator base
16
.
Diamond and diamond-like coatings are used as an erosion-resistant coating for both the anode and cathode, as well as the insulator. Diamond has a high thermal conductivity, 20 W/cm-K (5× better than Copper), and is extremely erosion and thermal shock resistant. Continuous, high quality diamond coatings, or films, can be deposited on various materials by plasma enhanced chemical vapor deposition (CVD) techniques. The thickness of the coating depends on the intended use, but a thickness in the range of about 1-100 μm is indicated for most applications.
FIG. 2
is a cross-sectional view of a plasma head
2
coated with two types of diamond coatings, one electrically conductive
40
and one electrically insulating
44
, in accordance with the present invention. The cathode
12
and the anode
14
is provided with a conductive diamond coating
40
on the inner cathode surface
11
and on the outer anode surface
13
.
Diamond can be made conductive by doping the diamond material with a p-type material. Suitable p-type materials include, but are not limited to, Boron and graphite. Boron doping provides a resistivity of 0.1 Ω-cm. Though the resistivity is higher than the cathode
12
and anode
14
materials, the conductive diamond coating
40
will be extremely thin and spread over a large area resulting in a low resistance, for example, 1e
−3
Ω. The thermal load due to passage of large currents through the conductive diamond coating
40
will be conducted away. Also, diamond is a photoconductor, and therefore, the electrical resistivity of the conductive diamond coating
40
decrease in the presence of a bright plasma.
Matching the thermal expansion co-efficient of the conductive diamond coating
40
and the substrate reduces the potential for delamination failure.
Referring again to
FIG. 2
, an insulating diamond coating
44
is deposited on the insulator base
16
. In an embodiment in accordance with the present invention, the insulator base
16
is coated with an insulating diamond coating
44
comprising pure diamond. Pure diamond has a breakdown voltage of 10{circumflex over ( )}7 V/cm, making it a good electrical insulator.
FIG. 5
is a table of insulating materials suitable for accepting an insulating diamond coating
44
. Nitroxyceram and IRBAS exhibit good thermal shock resistance, and then coating with an insulating diamond coating
44
for erosion resistance exhibits a very good combination of desirable properties.
FIG. 3
is a cross-sectional view of a plasma head
3
coated with two types of diamond coatings, one electrically conductive
40
and one electrically insulating
44
, in accordance with the present invention. The cathode
12
and the anode
14
is provided with a conductive diamond coating
40
on the inner cathode surface
11
and on the outer anode surface
13
. A thin cone
46
adapted to advance over and onto the anode base
41
of the anode
14
. The thin cone
46
is coated with an electrically insulating diamond coating
44
, wherein, upon installation, the anode base
41
of the anode
14
is electrically insulated. The anode top portion
43
is provided with a conductive diamond coating
40
after the insulating cone
46
is assembled.
FIG. 4
is a cross-sectional view of a plasma head
4
coated with two types of diamond coatings, one electrically conductive
40
and one electrically insulating
44
, in accordance with the present invention. The anode base
41
is provided with an electrically insulating diamond coating
44
. The anode top portion
43
and the cathode
12
is provided with a conductive diamond coating
40
on the inner cathode surface
11
and on the outer anode surface
13
. In another embodiment, the anode outer surface
13
is coated with an insulating diamond coating
44
, and subsequently, the top portion
43
is coated with a conductive diamond coating
40
. In yet another embodiment, the anode
14
comprises an anode base
41
and a separate anode top portion
43
. The anode base
41
is processed to receive an insulating diamond coating
44
and the top portion
43
is provided with a conductive diamond layer
40
. The top portion
43
is coupled with the anode base
41
using a coupling means, such as welding and brazing.
Although specific embodiments have been illustrated and described herein for purposes of description of the preferred embodiment, it will be appreciated by those of ordinary skill in the art that a wide variety of alternate and/or equivalent implementations calculated to achieve the same purposes may be substituted for the specific embodiment shown and described without departing from the scope of the present invention. Those with skill in the art will readily appreciate that the present invention may be implemented in a very wide variety of embodiments. This application is intended to cover any adaptations or variations of the embodiments discussed herein. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.
Claims
- 1. A diamond coated EUV source, comprising:a cathode comprising an electrically conductive diamond coating on a plasma facing surface; an anode comprising an electrically conductive diamond coating on a plasma facing surface; and a base insulator having a non-electrically conductive diamond coating on a plasma facing surface, the cathode and anode being spaced apart and electrically insulated by the insulator.
- 2. The diamond coated EUV source of claim 1, wherein the electrically conductive diamond coating is a p-doped diamond coating, and the non-electrically conductive diamond coating is pure diamond.
- 3. The diamond coated EUV source of claim 1, wherein the electrically conductive diamond coating is a boron-doped diamond coating, and the non-electrically conductive diamond coating is pure.
- 4. The diamond coated EUV source of claim 1, wherein the electrically conductive diamond coating is a graphite-doped diamond coating, and the non-electrically conductive diamond coating is pure diamond.
- 5. An extreme ultraviolet source, comprising:an annular cathode having an electrically conductive diamond coating on a plasma facing surface; an anode axially located with the annular cathode, the anode having an electrically conductive diamond coating on a plasma facing surface, the anode having a gas discharge tip; a base insulator having a non-electrically conductive diamond coating on a plasma facing surface, the cathode and anode being spaced apart and electrically insulated by the base insulator; a gas source adapted to provide gas to the gas discharge tip; and a voltage source adapted to drive a plasma discharge between the anode to the cathode in the presence of the gas.
- 6. The extreme ultraviolet source of claim 5, wherein the electrically conductive diamond coating is a p-doped diamond coating, and the non-electrically conductive diamond coating is pure diamond.
- 7. The extreme ultraviolet source of claim 5, wherein the electrically conductive diamond coating is a boron-doped diamond coating, and the non-electrically conductive diamond coating is pure.
- 8. The diamond coated EUV source of claim 5, wherein the electrically conductive diamond coating is a graphite-doped diamond coating, and the non-electrically conductive diamond coating is pure diamond.
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