Patent Application
20060192153
The present invention relates to extreme ultraviolet (”EUV”) light sources which provide EUV light from a plasma that is created from a source material and collected and directed to a focus for utilization outside of the EUV light source chamber, e.g., for semiconductor integrated circuit manufacturing photolithography e.g., at wavelengths of around 50 nm and below.
Extreme ultraviolet (“EUV”) light, e.g., electromagnetic radiation having wavelengths of around 50 nm or less (also sometimes referred to as soft x-rays), and including light at a wavelength of about 13.5 nm, can be used in photolithography processes to produce extremely small features in substrates, e.g., silicon wafers.
Methods to produce EUV light include, but are not necessarily limited to, converting a material into a plasma state that has an element, e.g., xenon, lithium or tin, with an emission line in the EUV range. In one such method, often termed laser produced plasma (“LPP”) the required plasma can be produced by irradiating a target material, such as a droplet, stream or cluster of material having the required line-emitting element, with a laser beam. For example, for Sn and Li source materials, the source material may be heating above its respective melting point and held in a capillary tube formed with an orifice, e.g. nozzle, at one end. When a droplet is required, an electro-actuatable element, e.g. piezoelectric (PZT) material, may be used to squeeze the capillary tube and generate a droplet at or downstream of the nozzle. With this technique, a relatively uniform stream of droplets as small as about 20-30 μm can be obtained.
As used herein, the term “electro-actuatable element” and its derivatives, means a material or structure which undergoes a dimensional change when subjected to a voltage, electric field, magnetic field, or combinations thereof and includes but is not limited to piezoelectric materials, electrostrictive materials and magnetostrictive materials. Typically, electro-actuatable elements operate efficiently and dependably within and range of temperatures, with some PZT materials having a maximum operational temperature of about 250 degrees Celsius.
Once generated, the droplet may travel, e.g. under the influence of gravity or some other force, and within a vacuum chamber, to an irradiation site where the droplet is irradiated, e.g. by a laser beam. For this process, the plasma is typically produced in a sealed vessel, e.g., vacuum chamber, and monitored using various types of metrology equipment. In addition to generating EUV radiation, these plasma processes also typically generate undesirable by-products in the plasma chamber (e.g debris) which can potentially damage or reduce the operational efficiency of the various plasma chamber optical elements. This debris can include heat, high energy ions and scattered debris from the plasma formation, e.g., atoms and/or clumps/microdroplets of source material. For this reason, it is often desirable to use so-called “mass limited” droplets of source material to reduce or eliminate the formation of debris. The use of “mass limited” droplets also may result in a reduction in source material consumption.
Another factor that must be considered is nozzle clogging. This may be caused by several mechanisms, operating alone or in combination. These can include impurities, e.g. oxides and nitrides, in the molten source material, and/or freezing of the source material. Clogging can disturb the flow of source material through the nozzle, in some cases causing droplets to move along a path that is at an angle to the desired droplet trajectory. Manually accessing the nozzle for the purpose of unclogging it can be expensive, labor intensive and time-consuming. In particular, these systems typically require a rather complicated and time consuming purging and vacuum pump-down of the plasma chamber prior to a re-start after the plasma chamber has been opened. This lengthy process can adversely affect production schedules and decrease the overall efficiency of light sources for which it is typically desirable to operate with little or no downtime.
With the above in mind, Applicants disclose systems and methods for effectively delivering a stream of droplets to a selected location in an EUV light source.
In a first aspect, a source material dispenser for an EUV light source is disclosed that comprises a source material reservoir, e.g. tube, that has a wall and is formed with an orifice. The dispenser may further comprise an electro-actuatable element that is spaced from the wall and operable to deform the wall and modulate a release of source material from the dispenser. A heat source heating a source material in the reservoir may be provided. Also, the dispenser may comprise a heat insulator reducing the flow of heat from the heat source to the electro-actuatable element.
In a particular embodiment, the heat insulator, e.g. silica, may be disposed between the electro-actuatable element and the wall to transmit forces therebetween. In one implementation, the heat source may comprise a resistive material that may be interposed between the wall and the insulator, for example, the heat source may comprise a resistive material, e.g. Mo, that is coated on the wall of the reservoir. In one arrangement, a cooling system for cooling the electro-actuatable element may be provided.
In another aspect, a source material dispenser for an EUV light source is disclosed that comprises a source material reservoir having a wall and formed with an orifice, and a plurality of electro-actuatable elements. For this aspect, each element may be positioned to deform a different portion of the wall to modulate a release of source material from the dispenser. The dispenser may further comprise a plurality of heat insulators, with each insulator disposed between a respective the electro-actuatable element and the wall to transmit forces therebetween. A heat source comprising a resistive material may be interposed between the wall and the insulator(s).
In one embodiment, a clamp may be used to clamp the electro-actuatable elements on the reservoir. In one implementation, the dispenser may further comprise a controller for generating a first signal to actuate the electro-actuatable elements to modulate a release of source material from the reservoir and a second signal, different from the first signal, for unclogging the orifice.
A method of dispensing a source material for an EUV light source is also described. The method may comprise the acts/steps of: providing a source material reservoir having a wall and formed with an orifice; providing a plurality of electro-actuatable elements, each element positioned to deform a different portion of the wall; and actuating the elements to modulate a release of source material from the dispenser.
One particular method may also comprise the act/step of providing a plurality of heat insulators, each insulator disposed between a respective electro-actuatable element and the wall to transmit forces therebetween.
In one method, the act/step of providing a heat source, wherein the heat source comprising a resistive material interposed between the wall and the insulator(s), may be completed.
In one or more of the above described methods, a first drive signal may be provided to actuate the electro-actuatable elements to modulate a release of source material from the reservoir for plasma production and a second drive signal, different from the first drive signal, may be provided to actuate the electro-actuatable elements to unclog the orifice.
With initial reference to
The light source 20 may also include a target delivery system 24, e.g., delivering targets, e.g. targets of a source material including tin, lithium, xenon or combinations thereof, in the form of liquid droplets, a liquid stream, solid particles or clusters, solid particles contained within liquid droplets or solid particles contained within a liquid stream. The targets may be delivered by the target delivery system 24, e.g., into the interior of a chamber 26 to an irradiation site 28 where the target will be irradiated and produce a plasma. In some cases, the targets may include an electrical charge allowing the targets to be selectively steered toward or away from the irradiation site 28.
Continuing with
The light source 20 may also include an EUV light source controller system 60, which may also include a laser firing control system 65, along with, e.g., a laser beam positioning system (not shown). The light source 20 may also include a target position detection system which may include one or more droplet imagers 70 that provide an output indicative of the position of a target droplet, e.g., relative to the irradiation site 28 and provide this output to a target position detection feedback system 62, which can, e.g., compute a target position and trajectory, from which a target error can be computed, e.g. on a droplet by droplet basis or on average. The target error may then be provided as an input to the light source controller 60, which can, e.g., provide a laser position, direction and timing correction signal, e.g., to a laser beam positioning controller (not shown) that the laser beam positioning system can use, e.g., to control the laser timing circuit and/or to control a laser beam position and shaping system (not shown), e.g., to change the location and/or focal power of the laser beam focal spot within the chamber 26.
As shown in
Continuing now with reference to
An electrical current may then be selectively passed through the resistive material via wires 216a,b to supply heat to the source material 208. With this arrangement, the insulators 210a-h are positioned to reduce the flow of heat from the heat source 214 to the electro-actuatable element.
As best seen in
As previously indicated, a separate pair of control wires may be provided for each element 206 to allow the elements 206 to be selectively expanded or contracted by a drive signal either independently, or in cooperative association with one or more other elements 206. As used herein, the term “drive signal” and its derivatives means one or more individual signals which may, in turn, include one or more drive control voltages, currents, etc for selectively expanding or contracting one or more electro-actuatable elements. For example, the drive signal may be generated by the controller 90 (see
With the above described structural arrangement, the dispenser 148 may be operated in one of several different control modes, to include an operational mode in which a first drive signal is utilized to modulate a release of source material from the reservoir for subsequent plasma production, and a cleaning control mode in which a second drive signal, different from the first drive signal is used for unclogging a clogged dispenser orifice. For example, an operational mode may be implemented using a drive signal in which a sine wave of the same phase is applied to all electro-actuatable elements 206. Thus, in this particular implementation, all electro-actuatable elements 206 may be compressed and expanded simultaneously.
A better understanding of an implementation of a cleaning control mode may be obtained with reference now to
In one implementation of a cleaning mode, the phase and shape of driving voltages used to actuate opposed, electro-actuatable element pairs, such as pair 206a, 206e shown in
In another implementation, a circular motion may be imparted to the dispenser tip to shake deposits loose, for example, by applying a sine wave with phase shift equal to 360/2n, where n is the number of pairs of electro-actuators. For example, if two electro-actuator pairs are employed, a phase shift of about 90 degrees may be used.
It will be understood by those skilled in the art that the aspects of embodiments of the present invention disclosed above are intended to be preferred embodiments only and not to limit the disclosure of the present invention(s) in any way and particularly not to a specific preferred embodiment alone. Many changes and modification can be made to the disclosed aspects of embodiments of the disclosed invention(s) that will be understood and appreciated by those skilled in the art. The appended claims are intended in scope and meaning to cover not only the disclosed aspects of embodiments of the present invention(s) but also such equivalents and other modifications and changes that would be apparent to those skilled in the art. While the particular aspects of embodiment(s) described and illustrated in this patent application in the detail required to satisfy 35 U.S.C. § 112 are fully capable of attaining any above-described purposes for, problems to be solved by or any other reasons for or objects of the aspects of an embodiment(s) above described, it is to be understood by those skilled in the art that it is the presently described aspects of the described embodiment(s) of the present invention are merely exemplary, illustrative and representative of the subject matter which is broadly contemplated by the present invention. The scope of the presently described and claimed aspects of embodiments fully encompasses other embodiments which may now be or may become obvious to those skilled in the art based on the teachings of the Specification. The scope of the present invention is solely and completely limited by only the appended claims and nothing beyond the recitations of the appended claims. Reference to an element in such claims in the singular is not intended to mean nor shall it mean in interpreting such claim element “one and only one” unless explicitly so stated, but rather “one or more”. All structural and functional equivalents to any of the elements of the above-described aspects of an embodiment(s) that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Any term used in the specification and/or in the claims and expressly given a meaning in the Specification and/or claims in the present application shall have that meaning, regardless of any dictionary or other commonly used meaning for such a term. It is not intended or necessary for a device or method discussed in the Specification as any aspect of an embodiment to address each and every problem sought to be solved by the aspects of embodiments disclosed in this application, for it to be encompassed by the present claims. No element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element in the appended claims is to be construed under the provisions of 35 U.S.C. § 112, sixth paragraph, unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited as a ”step” instead of an ”act”.
The present application is a continuation-in-part application of co-pending U.S. patent application Ser. No. 11/067,124 filed on Feb. 25, 2005, entitled METHOD AND APPARATUS FOR EUV PLASMA SOURCE TARGET DELIVERY, attorney docket number 2004-0008-01, the entire contents of which are hereby incorporated by reference herein. The present application is also a continuation-in-part application of co-pending U.S. patent application Ser. No. 11/174,443 filed on Jun. 29, 2005, entitled LPP EUV PLASMA SOURCE MATERIAL TARGET DELIVERY SYSTEM, attorney docket number 2005-0003-01, the entire contents of which are hereby incorporated by reference herein. The present application is also related to co-pending U.S. non-provisional patent application entitled LASER PRODUCED PLASMA EUV LIGHT SOURCE WITH PRE-PULSE filed concurrently herewith, attorney docket number 2005-0085-01, the entire contents of which are hereby incorporated by reference herein. The present application is also related to co-pending U.S. nonprovisional patent application entitled LASER PRODUCED PLASMA EUV LIGHT SOURCE filed concurrently herewith, attorney docket number 2005-0081-01, the entire contents of which are hereby incorporated by reference herein. The present application is also related to co-pending U.S. provisional patent application entitled EXTREME ULTRAVIOLET LIGHT SOURCE filed concurrently herewith, attorney docket number 2006-0010-01, the entire contents of which are hereby incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11067124 | Feb 2005 | US |
| Child | 11358983 | Feb 2006 | US |
| Parent | 11174443 | Jun 2005 | US |
| Child | 11358983 | Feb 2006 | US |
