Patent Application
20060066197
1). Field of the Invention
Embodiments of this invention relate to a method and apparatus for producing electromagnetic radiation, particularly for use in semiconductor substrate processing.
2). Discussion of Related Art
Integrated circuits are formed on semiconductor wafers. The wafers are then sawed (or “singulated” or “diced”) into microelectronic dice, also known as semiconductor chips, with each chip carrying a respective integrated circuit. Each semiconductor chip is then mounted to a package, or carrier, substrate. Often the packages are then mounted to a motherboard, which may then be installed into a computing system.
Numerous steps may be involved in the creation of the integrated circuits, such as the formation and etching of various semiconductor, insulator, and conductive layers. Before the various layers may be etched, a layer of light-sensitive photoresist is formed on the substrate to protect the portions of the substrate that are not to be etched.
Machines referred to as photolithography steppers are used to expose the desired pattern in the photoresist layer. In order to achieve the desired pattern, light, or electromagnetic radiation, is directed through a reticle, or “mask,” and focused onto the substrate.
As the features on the semiconductor substrates become smaller, shorter wavelength electromagnetic radiation is required to expose the photoresist. One form of such electromagnetic radiation is known as “extreme ultraviolet” (EUV) light. EUV light is often produced in plasma chambers by applying a voltage across a cathode and an anode, which are held within a plasma emission gas, such as xenon.
As the plasma is generated between the cathode and anode, tremendous heat often builds up on the anode, which can lead to the anode becoming permanently damaged, such as by melting.
Embodiments of the invention are described by way of example with reference to the accompanying drawings, wherein:
In the following description, various aspects of the present invention will be described, and various details set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced with only some or all of the aspects of the present invention, and the present invention may be practiced without the specific details. In other instances, well-known features are admitted or simplified in order not to obscure the present invention.
It should be understood that
The substrate transport subsystem 14 may be attached to and located at a lower portion of the frame 12 and may include a substrate support 20 and a substrate track 22. The substrate support 20 may be sized to support semiconductor substrates, such as wafers with diameters of, for example, 200 or 300 mm. Although not illustrated in detail, the substrate support 20 may include various actuators and motors to move the substrate support 20 in an X/Y coordinate system which may be substantially perpendicular to the sheet, or page, on which
The exposure subsystem 16 may be connected to the frame and suspended substantially over the substrate support 20. The exposure subsystem 16 may include an electromagnetic radiation source 24, a collector 28, a reticle 30, and imaging optics 32.
As illustrated in
The electrode subsystem 28 may be secured to an upper section of the chamber wall 26, or the frame 12, and may include at least one first electrode 36, and at least one, or a plurality, of second electrodes 38, as well as heat exchangers 40. The first electrode 36 may be a cathode and have a trapezoidal cross-section. The first electrode 36 (hereinafter referred to as “the cathode”) may have a central axis 42, which extends through a central portion of the plasma emission chamber, and may be made of a conductive material, such as copper.
The second electrodes 38 (hereinafter referred to as “the anodes), as illustrated in
The anodes 38 may be positioned so that the central axis 44 of each anode 38 is orthogonal to the central axis 42 of the cathode 36. The anodes 38 may be made of an electrically conductive material, with a first thermal conductivity, such as a titanium alloy. The anodes 38 may also be made of other metals with high melting temperatures, such as molybdenum and tungsten.
Although not illustrated, the plasma emission chamber 24 may also include actuators connected to the anodes 38 to rotate the anodes 38 about the central axes 44 thereof.
Still referring to
The heat exchangers 40 may connect each anode 38 to the chamber wall 26. The heat exchangers 40 may be rectangular in shape and have a rectangular cross-section when viewed in a direction parallel to the central axis 42 of the cathode 36.
As illustrated in
Referring again to
The computer control console 18 may be in the form a computer having memory for storing a set of instructions and a processor connected to the memory for executing the instructions, as is commonly understood in the art. The computer control console 18 may be electrically connected to both the substrate transport subsystem 14 and the exposure subsystem 16, as well as all of the various components thereof, and may control and coordinate the various operations of the stepper 10.
In use, a semiconductor substrate 62, such as a wafer having a diameter of, for example, 200 or 300 mm, may be placed on the substrate support 20 by the substrate track 22. The substrate 62 may have a plurality of integrated circuits, divided amongst multiple microelectronic dice, formed thereon and a layer of photoresist deposited over the dice.
Referring to
As is commonly understood in the art, when the voltage between the anodes 38 and the cathode reaches the “discharge voltage” for the particular plasma gas used, a plasma may be generated between the anodes 38 and the cathode 36. In particular, a plasma may be generated from the plasma gas between the exposed portions 52 of the anodes and the cathode 36. The plasma may emit electromagnetic radiation, such as extreme ultraviolet radiation. The electromagnetic radiation 64 may have a wavelength of, for example, between 2 and 200 nanometers (nm), depending on the particular plasma gas used. In one embodiment, in which xenon gas is used, the electromagnetic radiation 64 may have a wavelength of approximately 13.5 nm.
During the generation of the plasma, the exposed portions 52 of the anodes 38 may be subjected to extreme temperatures, such as over 1000° C. The cooling liquid supply 58 may be activated to supply the cooling liquid, such as liquid nitrogen (at 77° K), through the fluid channel within the cooling portion 48 of each of the heat exchangers 40, and thus cool the heat exchanger 40.
Because of the rotation of the anodes 38, the heat generated during the plasma generation is distributed evenly along the outer edges of the anodes 38. Additionally, the exposed portions 52 of the anodes 38 may be subjected to the high plasma temperatures for only a brief period before being rotated into the anode chamber 46 of the heat exchangers 40. As the exposed portions 52 are rotated into the anode chamber 46, because the thermal conductivity of the heat exchangers 40 may be higher than the thermal conductivity of the anodes 38, and due to the cooling of the heat exchangers 40, heat from the anodes 38 may be transferred to the heat exchangers 40 through conduction and radiation.
Still referring to
Referring to
The wafer support 20 may move the semiconductor substrate 62 in the X/Y coordinate system so that individual sections of the semiconductor substrate 62, which may correspond with one or more of the dice, may be exposed one at a time, as is common understood in the art. When the entire photoresist layer has been exposed, the substrate track 22 may remove the semiconductor substrate 62 from the substrate support 22, and replace it with a second semiconductor substrate to be exposed as described above.
One advantage is that because of the rotation of the anodes during the generation of the plasma, the heat generated is distributed around the anodes, preventing any one portion of the anodes from becoming too hot and becoming permanently damaged. Another advantage is that because the heat exchangers have a thermal conductivity that is higher than the thermal conductivity of the anodes, heat is more easily transferred from the anodes and into the heat exchangers, thus further increasing the cooling of the anodes. A further advantage is that the cooling fluid keeps the temperature of the heat exchangers very low, thus increasing the cooling of the anodes even further. A further advantage is that the heating on bearings within the anodes is minimized thus provided the anodes with improved reliability and longevity. A further advantage is that because of the heat exchanger, there is no need to have a liquid cooling system within the anode itself, thus reducing the costs of manufacturing the anodes.
Other embodiments may use a different number of anodes, such as six, which may or may not be symmetrically arranged about the central axis of the cathode, or any other axis. The heat exchangers may not be required as the rotation of the electrodes may sufficiently distribute the heat generated across the surface of the electrode to prevent the electrodes from being damaged. The cathode may rotate instead of the anode, or both electrodes may rotate during the plasma generation.
While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative and not restrictive of the current invention, and that this invention is not restricted to the specific constructions and arrangements shown and described since modifications may occur to those ordinarily skilled in the art
