Patent Application
20110216395
The present invention relates generally to grazing-incidence collectors (GICs), and in particular to adjustable clips used to secure a GIC shell to a spider.
EUV lithography is anticipated to be the lithographic process of choice for producing future generations of semiconductor devices having linewidths on the order of 32 nm and smaller. The wavelength of the EUV radiation is nominally 13.5 nm, which calls for the use of specialized optics to collect and image the EUV radiation.
One type of EUV optical system used to collect the radiation from the light source is a grazing-incidence collector (GIC). A GIC typically comprises one or more concentrically arranged GIC shell mirrors (“GIC shells”). The GIC shells are configured to receive light from the EUV source at grazing incidence and reflect the light to form a focused illumination beam that first forms an intermediate focus and then creates an illumination region in the far field that is preferably uniform to within a specification set by the overall system optical design.
GICs typically require a “spider” that maintains the GIC shells in a secured position relative to one another. In some GICs, the GIC shells are secured to the spider using clips that engage the edge or outer surface of the shell and one of the spider spokes. To date, such clips have minimal or no adjustability, which makes optically aligning or adjusting the GIC shells problematic.
An aspect of the invention is an adjustable clip for securing a grazing-incident collector (GIC) shell to a spider having spokes. The adjustable clip includes a base having an upper surface, wherein the base is adapted to be secured to a spider spoke. The clip includes a fork member having two prongs each with end pads at respective prong ends. The fork member has, at an opposite end of the prong ends, a first hinge portion. A hinge leaf is secured to the base upper surface and has a second hinge portion that operably engages the first hinge portion to form a hinge that allows for rotatable adjustment of the fork member relative to the base. Alternatively, the base includes the second hinge portion formed integrally therewith. Movement of the GIC shell when performing optical alignment is accommodated by the rotation of the fork member, which allows the end pads to slide over the GIC shell outer surface. When GIC shell alignment is achieved, the end pads are laser welded to GIC shell outer surface, which fixes the clip in a rigid configuration that holds the GIC shell in place relative to the spider.
Another aspect of the invention is a method of aligning and securing a GIC shell having an outer surface and an edge to a spider having spokes each with an upper edge. The method includes arranging the GIC shell on the spider, with the GIC shell edge resting on portions of the upper edges of the spokes. The method also includes securing a base portion of an adjustable clip to one of the spoke upper edges. The method further includes securing a fork member to the base so that the fork member can rotate relative thereto, with the fork member having end pads that rest against the GIC outer shell. The method then includes optically aligning the GIC shell relative to the spider, which includes, for example, moving the GIC shell so that the fork member rotates and the end pads move relative to the GIC shell outer surface. The method then includes securing the end pads (e.g., via laser welding) to the GIC shell outer surface so that the adjustable clip becomes a rigid support member. Typically, a number of adjustable clips, such as three or more, are used to secure each GIC shell to the spider.
Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description present embodiments of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments of the invention and together with the description serve to explain the principles and operations of the invention.
The various elements depicted in the drawing are merely representational and are not necessarily drawn to scale. Certain sections thereof may be exaggerated, while others may be minimized. For ease of illustration, not all like elements are necessarily labeled. The drawing is intended to illustrate an example embodiment of the invention that can be understood and appropriately carried out by those of ordinary skill in the art.
Fork member 20 also has an opposite end 26 that includes a first hinge portion 38 that by way of example comprises a hinge knuckle 40. Hinge knuckle 40 has a hole 42 sized to accommodate a pin 50.
With reference also to
Clip 10 further includes a base 100 having an upper surface 102 and opposite sides 104 and 106. A set screw 120 with a head 122 having a screwing feature (shown as an Allen-type feature) is shown adjacent base 100. Set screw 120 also includes a shaft 124 with a threaded end 126. Base 100 includes a slot 110 having a cross-sectional shape that accommodates screw head 122 and a portion of shaft 124 (i.e., the head shank) adjacent thereto. Base upper surface 102 includes a central hole 130 in that reaches slot 110. In an example embodiment, base upper surface also includes a ledge 103 that accommodates knuckles 70.
Hinge leaf 60 is secured to base 100 so that holes 86 and 130 are aligned so that when set screw 120 is slid into slot 110, screwing feature 124 can be accessed through the leaf and the base from above.
In another example embodiment, second hinge portion 61 is formed integrally with base 100, thereby obviating the need for a separate hinge leaf 60 to be secured to base upper surface 102.
In some instances, clips 10 with two prongs 30 cannot be used in certain locations due to mechanical interference with other elements. To avoid mechanical interference, in some locations, clips with one prong 30 may be employed. A single-prong clip 10 is not as stiff in the circumferential direction as the two-prong clip and is not recommended for sustaining lateral loads. However, this embodiment is acceptable when is used in appropriate combination with two-prong clips 10 where the latter absorb lateral loads.
Spider 200 includes an outer ring 210, an inner ring 220, and a plurality of spokes 230 (six are shown by way of illustration) that mechanically connect the inner and outer rings to provide structural support to the spider. In an example where spider 200 is a cooled spider, outer ring 210, inner ring 220, and plurality of spokes 230 are fluidly connected by cooling channels 240 that are fluidly connected to input and output cooling fluid manifolds 250A and 250B, thereby forming a cooling fluid flow path through the spider.
Spokes 230 each include an edge 234 configured support two or more GIC shells 200 in a spaced apart configuration. In an example embodiment, edge 234 includes a number of steps 236 that are used to support clips 10 as well as GIC shells 200 at GIC shell edge 304, as show in
When base 100 is secured to step 236, fork 20 is adjusted so that end pads 36 rest against GIC shell outer surface 302. However, fork member 20 rotates around hinge 80 so that the position of GIC shell 300 relative to spider 10 can be moved, e.g., for optical alignment of the GIC shell, while end pads 36 continue to rest against GIC shell outer surface 302. In particular, when adjusting the position of GIC shell 200 relative to spider 200, end pads 36 move relative to (e.g., slide over) GIC shell outer surface 302.
When GIC shell 300 is optically aligned, then as shown in
Also, as shown in
Spider with GIC Shells
An EUV light source LS is also shown as arranged along GIC mirror axis A1 and relative to GIC mirror 400. Spider 300 is configured to operably support one or more GIC shells 300 in a spaced-apart and concentric configuration while not substantially blocking EUV radiation from being relayed from EUV light source LS to a GIC mirror intermediate focus.
In forming the GIC mirror 400, the innermost GIC shell 300 is arranged on spider 100 with the GIC shell edge 304 placed on the corresponding inner steps 236 of spokes 230. Steps 236 support GIC shell 300 at respective portions of the GIC shell edge 304. Other GIC shells 300 are then added from the inside direction to the outside direction until the completed GIC mirror 400 is formed, as shown in
In 701, the base 100 of a clip 10 is secured (e.g., screwed) onto spider 200 at one of the innermost steps 236 of spokes 230. In an example, this is done for at least three clips 10.
In 702, GIC shell 300 is positioned (e.g., aligned) relative to spider 200, and during this positioning, clips 10 “self-adjust” by fork members 20 rotating relative to their respective bases 100 at their respective hinges 80. Once GIC shell 300 is in an optically aligned position on spider 200, then in 703, hinge leafs 60 are laser welded to their respective bases 100. Then in 704, end pads 36 are laser welded to GIC shell outer surface 302, whereby clips 10 become rigid support members.
In the aforementioned embodiment where second hinge portion 61 is formed integrally with base 100, step 702 is eliminated.
In 705, the next outermost GIC shell 300 is arranged on spider 200 on the next outermost spoke steps 236, and process 700 is repeated in the direction from the innermost GIC shell to the outermost GIC shell until GIC mirror 400 is formed, such as shown in
Clip with Actuator Mechanism
In an additional aspect of the present invention, the use of one or more clips 10 allow for optimization of the optical performance of GIC mirror 400, not only by self-adjustment of the clips as described above, but also through controlled manipulation of at least of one the shape (via stressing and deformation), the orientation, and the position (via translation and rotation) of the GIC shell 300. Such controlled manipulation is beneficial as it allows to correct for astigmatism (i.e., deviations of perfect cylindrical symmetry), or to correct orientation and placement errors of the GIC shell.
By adjusting the positions of screws 510 relative to support member 502, a small but controllable amount of pressure is exerted against GIC shell 300 through end pads 36, leading to at least one of a small displacement, a small deformation, or a small change in orientation of the GIC shell. This makes clips 10 adjustable, and therefore makes GIC shells 300 adjustable. In this embodiment, screws 510 serve as manually adjustable actuators.
Besides using screws 510 as adjustable actuators, other actuators can be used, such piezo electric, electromagnetic, etc. However, given that a GIC mirror is intended to be operated in a very aggressive plasma environment, and that adjustments are not often required, it is preferable to have a robust and stable actuation mechanism. Example actuation distances are between about 50 microns and 500 microns. Such adjustments, along with the preferred robustness, can satisfactorily be done using one or more screw-based actuators mechanisms as described above.
It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Thus it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.
