Abstract:
An apparatus for adjusting an orientation of an optical component mounted within a laser resonator with suppressed hysteresis includes an electromechanical device, a drive element, and a mechano-optical device coupled to the mounted optical component. The drive element is configured to contact and apply a force to the mechano-optical device in such a way as to adjust the orientation of the mechano-optical device, and thereby that of the optical component, to a known orientation within the laser resonator. The optical component is mounted such that stresses applied by the mount to the optical component are homogeneous and substantially thermally-independent.

Description:
PRIORITY 
     This application claims the benefit of priority to United States provisional patent application No. 60/327,568, filed Jun. 7, 2001. 
    
    
     BACKGROUND OF INVENTION 
     1. Field of Invention 
     The present invention relates to an apparatus for adjusting the spectrum and bandwidth of a laser light source. 
     2. Description of Related Art 
     Excimer lasers are currently used as light sources for the integrated circuit lithography industry. These lasers produce a beam having a narrowband spectrum with a bandwidth of less than 1 pm at deep ultraviolet (DUV) wavelengths of 248 nm for a KrF laser or 193 nm for an ArF laser. Molecular fluorine lasers emit around 157 nm and will become more widely used for vacuum ultraviolet (VUV) lithography for producing even smaller structures on silicon wafers. There also exist semi-narrowband excimer lasers with bandwidths of more than 10 pm, for which the same principles hold. To produce extremely narrow-band UV light of low divergence and of a high spectral purity, a multitude of dispersive optical components may be utilized such as prisms, optical diffraction gratings and etalons or other interferometric devices. In general, adjustments to the wavelength and/or bandwidth of UV light emitted by these lasers may be made by using an electromechanical device (“EMD”), which in some way moves the position or changes the surface curvature of an optical component (“OC”) in the resonator of the excimer or molecular flourine laser. The EMD is coupled to a mechano-optical device (“MOD”) which transfers the motion of the EMD to the optical component, wherein the OC may be typically fixed to the MOD. Thus, when the optical component is moved, characteristics of the UV light output from the laser are changed. 
     In the normal operation mode of a DUV or VUV lithography laser system, it is desired to keep the laser wavelength substantially constant and the bandwidth (or another spectral property like full width at 1/e 2 , spectral purity, or an integral or differential quantity) below a specified value. These quantities can be monitored and controlled using a spectrometer such as an etalon spectrometer, grating spectrometer, prism spectrometer or other optical spectrometers in conjunction with a processor in a feedback loop including means for adjusting spectral parameters to desired values. 
     The typical temporal exposure pattern for the production of semiconductor chips is produced with pulse bursts of, e.g., 200 laser pulses and short breaks of 100 ms between them. A complete sequence may include 60 bursts and breaks, which is followed by a more or less long burst break of, e.g., 5 seconds. For lithography systems it is desired to keep the quality of the laser radiation under control for each pulse of the burst sequence. It is desired to have a lithography system wherein the wavelength of emission may be changed, particularly within a long burst break, over a wide range of up to 300 pm. This is to adapt the lithography system to environmental conditions like pressure and temperature. Furthermore, changes of wavelength in a small range of up to 0.6 pm without any laser pulses being emitted from the laser during that wavelength change are desired within short burst breaks, i.e. with an open feedback loop. This is to keep the quality of the lithography process under control, as changes in temperature of stepper optics can otherwise result in changes in exposure wavelength at an application process. 
     The desired tolerance limit of such componentry is extremely low in respect of hysteresis. Maintaining a stable and invariable position of optical elements and mechanical componentry within a defined range is, therefore, greatly desired. 
     It is further desired that the mounting of the OC be independent of environmental conditions, in particular of possible temperature gradients within the optical component. The demands set out above apply also to elements and componentry in motion during operation. These linear and rotary motions can be very small (e.g., &lt;100 nm:x rad) and are essentially designed to fine tune the entire optical system to a desired wavelength of the UV light. This may result in high acceleration values and it is desired that such values be free of negative influence on the positional stability of the optical elements. Merest inaccuracies already prove undesirable during repeated starts at pre-defined set-points. These set-points can be reference coordinates at which the reference wavelength, for exampled 248.3271 nm, is found. To calculate various operating positions, it is desired that this value be recorded precisely and be maintained reliably. It is further desired that the hysteresis of such motional process be kept very small ensuring that the wavelength drift of the optical assembly is kept as minute as possible. 
     Spring mount contact pressure plates may be used for securely positioning OCs. A disadvantage is that there is a pointlike exerting of force into the substrates of OCs using this method. Consequently, this may lead to the development of partially irreversible strain birefringence. This causes severe wavefront deformation and striation in the beam profile. Optically acting gratings and etalons having adjustable orientations for controlling the wavelength and bandwidth of emission of the laser may be supported between high surface quality bearings which permit rotation of the OCs. Such systems are susceptible to hysteresis, and it is recognized herein that special consideration should be given to the design of bearing components. Important quantities are diameter of balls, surface quality of bearing components as well as sizing of pressure forces. In general small quantities of silicone-free lubricants are used for lubrication. 
     When designing components to support OC&#39;s, it is recognized herein that special consideration should be given for temperature gradient-dependent changes in length. Such assemblies may be generally very sensitive to temperature fluctuations reacting with play in bearings and thus producing hysteresis effects when adjusting positions and/or orientations of OC&#39;s. To a certain degree this is influenced by the breakaway friction of bearing components. This is the force necessary to leave the zone of elastic deformation of the bearing components and to proceed into a rotary, progressive motion. 
     SUMMARY OF THE INVENTION 
     The present invention relates to an apparatus for adjusting, with low hysteresis and high repeatability, the wavelength and/or bandwidth of a laser beam by moving an optical component. 
     In a particular embodiment, an apparatus for adjusting a position of an optical component within a laser resonator with suppressed hysteresis includes an electromechanical device comprising a drive element including a first contact surface, and a mechano-optical device for supporting the optical component including a second contact surface for contacting the first contact surface. The drive element permits adjustment of an orientation of the mechano-optical device by applying a force to the first contact surface, and thereby for adjusting an orientation of the optical component. The first and second contact surfaces are configured such that the drive element transmits a change of position to the mechano-optical device through a rolling contact between the first contact surface and the second contact surface. 
     In another embodiment, an apparatus for adjusting a position of an optical component within a laser resonator includes an electromechanical device comprising a drive element including a first contact surface, and a mechano-optical device for supporting the optical component including a second contact surface for contacting the first contact surface. The drive element permits adjustment of the position of the mechano-optical device by applying a force to the first contact surface, and thereby the mechano-optical device adjusts the position of the optical component. The apparatus also includes a controller for error correction of the position of the drive element which controls the electromechanical device, and a position measuring device which measures the position of the drive element. A signal feedback loop provides a signal indicative of the position of the drive element to the controller from the position measuring device. The controller controls the electromechanical device which adjusts the drive element based on the signal provided by the feed back loop. 
     In another embodiment, an apparatus for adjusting a position of an optical component within a laser resonator includes an electromechanical device comprising a drive element including a first contact surface, and a mechano-optical device for supporting the optical component including a second contact surface for contacting the first contact surface. The drive element permits adjustment the position of the mechano-optical device by applying a force to the first contact surface. The mechano-optical device adjusts the position of the optical component. The apparatus further includes a controller for error correction of the position of the mechano-optical device for controlling the electromechanical device, and a position measuring device which measures the position of the mechano-optical device. The controller and the position measuring device are connected in a feedback loop. The position measuring device provides a signal indicative of a position of the mechano-optical device. The controller controls the electromechanical device based on the signal from the position measuring device, such that the electromechanical device adjusts a position of the drive element and the drive element adjusts a position of the mechano-optical device based on a control signal from the controller. 
     According to another embodiment, an apparatus for adjusting a position of an optical component within a laser resonator with suppressed hysteresis includes a housing for mounting the optical component therein, and an electromechanical device including a drive member configured to travel in an approximately linear direction, a mechano-optical device rotatably coupled to the housing, and a contact point where the drive member and the mechano-optical device are in contact with each other. The drive member and mechano-optical device are configured for directing the contact point to follow a substantially tangential path relative to the rotation of the mechano-optical device. 
     In another embodiment, an apparatus for adjusting a position of an optical component within a laser resonator with suppressed hysteresis includes a mechano-optical device for supporting an optical component, and an electromechanical device comprising a drive element coupled to the mechano-optical device by an elastic material. The drive element is moved by the electromechanical device for adjusting an orientation of the mechano-optical device and thereby for adjusting an orientation of the optical component. 
     According to a further embodiment, an apparatus for adjusting an orientation of an optical component mounted within a laser resonator includes an optical mount for mounting the optical component thereon; and a mechano-optical device coupled by an elastic material to the optical mount. The mechano-optical device is rotationally adjustable for adjusting the orientation of the optical component within the laser resonator. 
     In another embodiment, an apparatus for adjusting an orientation of an optical component mounted within a laser resonator includes a mechano-optical device for mounting the optical component thereon. The mechano-optical device is rotationally adjustable for adjusting the orientation of the optical component within the laser resonator. The mechano-optical device is rotatable at least approximately about a center of gravity of the combination of the optical component and mechano-optical device. 
     In a further embodiment, an apparatus for adjusting a position of an optical component within a laser resonator with suppressed hysteresis includes a mechano-optical device for supporting the optical component and having a contact segment, an electromechanical device comprising a drive element coupled to the mechano-optical device, wherein the drive element is moved by the electromechanical device for adjusting an orientation of the mechano-optical device and thereby for adjusting an orientation of the optical component, and at least one spring for coupling the drive element to the contact segment of the mechano-optical device. 
     In another embodiment, an apparatus for adjusting a position of an optical component within a laser resonator with suppressed hysteresis includes a mechano-optical device for supporting an optical component, and an electromechanical device comprising a drive element magnetically coupled to the mechano-optical device. The drive element is moved by the electromechanical device for adjusting an orientation of the mechano-optical device and thereby for adjusting an orientation of the optical component. 
     In a further embodiment, an apparatus for adjusting a position of an optical component within a laser resonator with suppressed hysteresis includes a mechano-optical device for supporting the optical component and having an adjustable orientation for adjusting an orientation of the optical component. The optical component is supported on the mechano-optical device by a roller bearing comprising a ruby ball bearing. 
     In another embodiment, an apparatus for mounting an optical component within a laser resonator includes a housing disposed within the laser resonator and having the optical component mounted therein, the optical component having an axis of rotation defined therethrough, a first ball bearing coupled to a first surface of the optical component, a second ball bearing coupled to a second surface of the optical component, the first and second ball bearings being substantially aligned along said axis of rotation, and a leaf spring coupled to the housing and also to one of the first and second ball bearings for controlling a spacing between the first and second ball bearings such that the spacing is adjustable to a changing dimension of the optical component as a temperature of the optical component changes. 
     In another embodiment, an apparatus for mounting an optical component within a laser resonator includes a housing disposed within the laser resonator and having the optical component mounted therein, the optical component having an axis of rotation defined therethrough, a first ball bearing coupled to a first surface of the optical component, a second ball bearing coupled to a second surface of the optical component, the first and second ball bearings being substantially aligned along the axis of rotation, and at least one spring coupled to the housing and also to one of the first and second ball bearings for controlling a spacing between the first and second ball bearings such that the spacing is adjustable to a changing dimension of the optical component as a temperature of the optical component changes. 
     In a further embodiment, an optical mount for mounting an optical component thereon and having an adjustable orientation within a laser resonator with suppressed hysteresis includes a housing for mounting the optical component thereto, a leaf spring and a leaf spring clamp coupled to the housing, and a first ball bearing and a second ball bearing for rotatably supporting the optical component therebetween. The first ball bearing is supported between the leaf spring and the leaf spring clamp in a direction offset from an axis of rotation of the optical component substantially defined through the first and second ball bearings. 
     In a further embodiment, a hysteresis reducing optical apparatus for a laser system includes an optical component coupled to an upper roller ball and to a lower roller ball, and a housing including a base, a leaf spring clamp and a clamp. The leaf spring attaches the upper rollerball in a sideways fashion to the housing. The clamp attaches the lower rollerball to the housing in a sideways fashion. The clamp fixes the lower bearing in a stationary manner. 
     According to another embodiment, an optical mount for mounting an optical component thereon within a laser resonator includes a base for supporting the optical component at a first surface, a plano-curved segment for supporting the optical component at a second surface opposite the first surface, the plano-curved segment supporting the optical component by contacting the second surface of the optical component with a planar surface of the plano-curved segment, a leaf spring contacting a curved surface of the plano-concave segment for controlling a force exerted on the optical component by the planar surface of the plano-curved segment, and at least one spring for coupling the leaf spring to the base for controlling a spacing between the first and second ball bearings such that the spacing is adjustable to a changing dimension of the optical component as a temperature of the optical component changes. 
     An apparatus for adjusting an orientation of an optical component mounted within a laser resonator with suppressed hysteresis includes an optical mount for mounting the optical component thereon, and an electro-mechanical device coupled by a solid link to the optical mount for adjusting an orientation of the optical component within the laser resonator. The solid link is elastically deformable for providing the suppressed hysteresis. 
     The features mentioned in the subclaims relate to further developments of the solution according to the invention. Further advantages of the invention are found in the following detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Below, the present invention will be described in greater detail based on embodiments, with reference to the attached drawings. 
     FIG. 1 schematically illustrates an arrangement for adjusting an orientation of an optical component according to a preferred embodiment; 
     FIG. 2 is an illustration of the movement of the drive element of the EMD; 
     FIG. 3 is an illustration of the movement the drive element of the EMD; 
     FIG. 4 is a schematic illustrating a PMD measuring the position of the EMD; 
     FIG. 5 is a schematic illustrating a PMD measuring the position of the MOD; 
     FIG. 6 is a schematic illustrating the linear movement of the drive element and the rotary movement of the EMD; 
     FIGS. 7 a  through  7   f  are drawings illustrating the various contact surface geometries between the drive element and the MOD; 
     FIG. 8 is an illustration of a solid coupling between the drive element and the MOD; 
     FIG. 9 is an illustration of a solid coupling between the MOD and the OC; 
     FIGS. 10 a  and  10   b  schematically illustrate a spring coupling between the drive element and the MOD; 
     FIG. 11 schematically illustrate a magnetic coupling between the drive element and the MOD; 
     FIG. 12 schematically illustrates a leaf spring element of the design; 
     FIG. 13 schematically illustrates a spherical segment table element of the design; 
     FIGS. 14 a  and  14   b  schematically illustrate a side mounted leaf spring design; 
     FIG. 15 schematically illustrates a low tension mounting aspect of the invention. 
     FIG. 16 a  shows an example of a device including a solid coupling between optics module housing and MOD. 
     FIG. 16 b  shows a side view of the device of FIG. 16 a.    
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Those of ordinary skill in the art will realize that the following description of the present invention is illustrative only and not in any way limiting. Other embodiments of the invention will readily suggest themselves to such skilled persons. 
     Referring to FIG. 1, the EMD  10  is coupled to a drive element  20 . A non-limiting example of an EMD  10  includes an electric motor that has an output element that moves in a linear direction. The EMD  10  is configured to move the drive element  20  back and forth in a linear direction illustrated by the arrow  30 . Non-limiting examples of a drive element would be the output element of the EMD  10  and a shaft coupled to the output element of the EMD  10 . In FIG. 1, reference numeral  40  indicates the outward direction of the EMD  10  and reference numeral  50  indicates the inward direction of the EMD  10 . The drive element  20  is coupled to the MOD  60 . The MOD  60  is a device which transfers the motion of the EMD  10  to the OC  70 , wherein the OC  70  is preferably contained in MOD  60  and is fixed to the MOD  60 . The MOD  60  is coupled to the OC  70  such that the MOD  60  may be rotated by the EMD  10  to rotate the OC  70  preferably about an axis of rotation  75  through a center of gravity of the OC  70 . Non-limiting examples of OCs  70  that may be used in these types of optical systems are prisms, optical diffraction gratings and etalons or other interferometric devices having non-parallel and/or non-planar inner reflecting surfaces (see, e.g., U.S. patent application Ser. No. 09/715,803, which is assigned to the same assignee as the present application and is hereby incorporated by reference). The linear movement of the drive element  20  rotates the MOD  60  which in turn rotates the OC  70 . The rotation of the MOD  60  and OC  70  are illustrated by arrow  80 . Thus, the optical properties of the OC may be tuned according to the rotative position of the OC. 
     In a preferred embodiment herein, the OC  70  may be adjusted by having the drive element  20  approach the desired OC  70  position from the same direction. Referring to FIG. 2, reference numeral  100  indicates the target position of the drive element which corresponds to a desired rotation of the OC  70 . It is preferred herein to always approach a target position by moving the drive element  20  in the outward direction indicated by the pointing direction of the arrow  120 . Thus, reference numeral  110  indicates the starting position of the drive element  20 , and in order to approach the target position  100 , the drive element moves in an outward direction  120 . 
     Referring to FIG. 3, if the starting position  130  of the drive element is already outward of the target position  100 , then the drive element is preferably first moved in an inward direction as indicated by the pointing direction of the arrow  140  towards and past the target position  100  to an intermediate position  150 , where the drive element then moves in an outward direction  160  to the target position where it stops. 
     This aspect of approaching the target position from the same relative direction, advantageously suppresses positional uncertainty associated with hysteresis in the system, thus allowing for greater accuracy in positioning the OC  70  of FIG. 1 which in turn increases the accuracy in tuning the light source. 
     Referring to FIG. 4, a position measuring device (“PMD”)  400  measures the position of the drive element  410 . The PMD  400  provides an electronic signal corresponding to the position of the drive element  410  to a controller  420 . The controller controls the EMD  430 . The controller  420 , thereby through the feedback loop illustrated by the connection  440  controls the EMD  430  and adjusts the position of the drive element  410  to more accurately position the drive element  410 , and thereby more accurately positions the MOD  450 . Non-limiting examples of controllers include state machines and microcontrollers. 
     Referring to FIG. 5, the PMD  500  measures the position of the MOD  510 . The PMD  500  provides an electronic signal corresponding to the position of the MOD  510  to a controller  520 . The controller controls the EMD  530 . The controller  520 , thereby through the feedback loop illustrated by connection  540  controls the EMD  530  which adjusts the position of the drive element  550 , which in turn more accurately positions the MOD  510 . 
     Referring to FIG. 6, the contact point  600  between the drive element  610  and the MOD  620  is positioned to maximize tangential travel, illustrated by the directional arrow  630 , of the contact point  600 , thereby reducing side to side sliding of the MOD  620  with respect to the drive element  610  at the contact point  600  about a circumference of travel of the MOD  620  indicated by arc  640 . According to a preferred embodiment herein, materials are selected for the contact surfaces that are stiff and have a low surface roughness, thereby reducing the friction at the contact point between the drive element  610  and the MOD  620 . It is further preferred to reduce the contact area and sliding between the drive element  610  and the MOD  620  by use of various shapes of the components  610  and  620  at the contact point  600 . 
     FIGS. 7 a - 7   f  show several embodiments wherein a drive element  700  and a MOD  710  (the reference numbers with respect to the drive element  700  and MOD  710  are the same in FIGS. 7 a  through  7   f ) contact each other by a rolling contact enabled by advantageous shapes of contact surfaces of the MOD  710  and/or the drive element  700 . The drive element  700  shown in FIG. 7 a  has a planar contact surface  721 , and the MOD  710  has a spherical contact surface  722 . FIG. 7 b  shows a drive element with a concave contact surface  723  along with a spherical contact surface  724  on the MOD  710 . FIG. 7 c  illustrates a contact surface wherein the rounded contact surface  726  of the MOD  710  acts to unroll off the contact surface  725  of the drive element  700 . FIG. 7 d  shows a drive element  700  with a spherical contact surface  727  along with a MOD  710  with a planar contact surface  728 . In FIG. 7 e , the drive element  700  has a spherical contact surface  729 , whereas the MOD  710  has a concave contact surface  730 . FIG. 7 f  shows a rounded contact surface  731  on the drive element  700  which unrolls of the contact surface  732  of the MOD  710 . 
     FIG. 8 shows a coupling  800  between the MOD  810  and the drive element  820 . The coupling  800  is a stiff connection with elastic properties. The coupling  800  has some elastic properties in order to compensate for the difference between the linear motion of the drive element  820  and the circular motion of the MOD  810 . The coupling  800  may be a wire, a piece of sheet metal or a twisted piece of sheet metal. Using the solid coupling  800  advantageously eliminates friction due to sliding between the contact surfaces of the drive element  820  and the MOD  810 . 
     FIG. 9 illustrates another embodiment of a MOD  900  and a solid coupling  910  between the MOD  900  and the housing  920  of the optics module. The solid coupling  910  between the MOD  900  and optics module housing  920  eliminates friction due to bearings that may otherwise be used to hold the OC  930 . 
     It is preferred herein to align the rotation axis of the MOD  900  with the center of gravity of the MOD  900 . This prevents unbalance in the system when the MOD  900  is rotated. 
     In FIG. 10 a , a top view of a EMD  1005  and MOD  1010  system is shown. Drive element  1000  of the EMD  1005  is forced against MOD  1010  by a set of springs  1030  which are attached to both the drive element  1000  and the MOD  1010 . The MOD  1010  shown has a specially configured end  1040  for coupling with the spring  1030 . In FIG. 10 b , a side view of the system of FIG. 10 a  is shown, where it may be seen that the set of springs  1030  includes an upper and a lower spring, thereby avoiding unbalance caused by the springs  1030  exerting force on the components. Irrespective of what position the drive element  1000  and MOD  1010  are in, the springs exert a constant force on both the drive element  1000  and the MOD  1010 , thus suppressing hysteresis as the position of the MOD  1010  is changed. 
     FIG. 11 shows a drive element  1100  and a MOD  1110 . The contact surfaces of the drive element  1100  and the MOD  1110  are kept together by a magnetic coupling between a pair of magnets or a magnet and a magnetic material  1120  and  1130 . The elements  1120  and  1130  of this embodiment allow for an equal force above and below and on both sides of the drive element  1100  and MOD  1110 , thus avoiding unbalance. The magnetic coupling force is approximately constant despite the position of the drive element  1100  and the MOD  1110 , thereby suppressing hysteresis. 
     The OC of any of the embodiments described herein may be typically supported by a bearing, such as a roller bearing. This roller bearing may be advantageously made of ruby, which is extremely hard and has a very low coefficient of friction, thereby suppressing hysteresis in the system, due to the lack of friction from the roller bearing. It is also advantageous to fix one end of the ruby roller element because due to the hardness and low coefficient of friction of the ruby, the friction in the system is suppressed and mechanical stability of the system is enhanced. 
     It is also preferred herein to improve characteristics of the ball bearing system which supports the optical component by using a limited, constant vertical contact pressure force on the bearing system to reduce play in the bearing, and allow for temperature dependant changes of size in the system. FIG. 12 shows an OC  1200  supported by an upper roller ball  1210 , and a lower roller ball  1220 . A leaf spring  1230 , attached at both a right side and left side to a housing  1240 , applies a force to the roller ball  1210  at an upper bearing upper shell  1250 , which holds roller ball  1210 , through upper bearing lower shell  1260 , which holds OC  1200 , through lower bearing upper shell  1270 , through lower roller ball  1220 , and through lower bearing lower shell  1280 , as shown. Thermal growth of the OC is illustrated by arrows  1290 . Ideally, the rotational axis of the OC  1200  is co-linear with the center of mass of the entire OC/bearing assembly. Further, the axes of the upper and lower bearing elements are substantially aligned to each other to prevent elliptic rather than circular line pressure of the roller balls  1210  and  1220 . 
     FIG. 13 shows a spherical segment  1320  which serves as a combined bearing and optical support of an OC  1310 . The device permits precise adjustment of the OC  1310  around an operating point  1300 . The circular portion  1325  shown in FIG. 13 may be a physical shell, e.g., connecting an upper bearing (not shown) that is similar to that described with respect to FIG. 12, or that may be similar to the spherical segment  1320  of FIG. 13, wherein portions of the circular portion  1325  between upper and lower surfaces of the OC  1310  may serve as the housing  1240  of FIG.  12 . Alternatively, the circular portion  1325  may be only shown in FIG. 13 to illustrate that the center of curvature of the spherical segment  1320  is at the operating point  1300  approximately centered on the OC  1300 . Any desired rotary motion may be executed around the operating point  1300 . The OC  1310  to be rotated is mounted on a spherical segment  1320  which doubles as performing a bearing function. As indicated above, the operating point  1300  of the OC  1310  is preferably at, or at least near, a center of curvature of the spherical segment  1320 . Rotational adjustment of the OC  1310  about the rotational axis  1328  extending vertically through the operating point  1300  may be achieved by rotating the OC  1310  via the MOD (not shown here, but see FIGS. 1-11 and description thereof above) and the drive element (again, not shown here, but see FIGS. 1-11 and description above) in the direction indicated by the circular arrow  1330 . Rotational adjustment in the plane of the paper, or about a rotational axis perpendicular to the plane of the drawing in FIG.  13  and extending through the operating point  1300  may also be achieved by tilting the spherical segment  1320  relative to the horizontal plane upon which the OC  1310  rests in FIG.  13 . The rotary motion about the axis  1328  is facilitated by a ring-shaped bearing  1340 . As a result of being able to adjust the OC  1310  with each of these degrees of freedom, a light beam traversing the OC  1310  and remaining within an acceptance angle of a laser resonator within which the OC  1310  is being used may have a selected wavelength and its alignment with respect to the optical axis of the resonator can be properly set. 
     FIGS. 14 a  and  14   b  schematically illustrate an alternative embodiment to those shown and described with respect to FIGS. 12 and 13. The ball bearings  1400  and  1410  are similar to those shown and described with respect to FIG.  12 . However, the ball bearings  1400  and  1410  are coupled to the housing  1420 , not by top and bottom bearing shells such as top bearing shell  1240  and bottom bearing shell  1260  of FIG. 12, but rather by a side-oriented leaf spring  1430  and a side oriented clamp  1440 . The OC  1450  is therefore positioned by bearing  1400  and bearing  1410  along the vertical axis  1428 , while the bearings  1400  and  1410  are supported by forces from the spring  1430  and clamp  1440  that are perpendicular to the axis  1428 , such that these forces coupling the bearings  1400  and  1410  to the housing  1420  do not put tremendous compression stress on the OC  1450 . 
     FIG. 14 b  shows a top cross sectional view through A—A of FIG. 14 a . In FIG. 14 b , the bottom bearing  1410  is not shown. The surfaces  1460  for contacting the ball bearings  1400  and  1410 , can be machined into the housing  1420  in one machining or chucking set up, thereby allowing for extremely high tolerances for aligning the ball bearings  1400  and  1410  along one axis. This will result in a reduction or elimination of hysteresis due to the upper bearing  1400  and the lower bearing  1410  not being properly aligned. 
     FIG. 15 shows a low-tension mount of a sensitive OC  1500 . If there is any strain on the OC  1500 , then there wavefront deformations may be caused to light traversing the OC  1500 , and it is therefore desired to minimize input forces to the OC  1500 . The embodiment shown in FIG. 15 provides an extensive load distribution on the OC  1500  which is preferable to a less extensive distribution, wherein a point-like load would exert the greatest force over a small area of the OC  1500 . The extensive load distribution is achieved by the use of a curved contact pressure clamp  1510  which is planar or otherwise shaped like the OC  1500  where the clamp contact the surface of the OC  1500  substantially along its entire area on one side such as its top surface, as shown. The opposite side of the clamp  1510  is preferably shaped like a partly-cylindrical or partly spherical cap. A leaf spring  1520  held by two columns  1530  is used to deliver a selected and adjustable pressure force F N  onto the OC  1500  is minimal exertion of pressure at any point. In this design, the influence of strain on the OC  1500  is substantially suppressed thereby suppressing wavefront deformations to the laser beam traversing the OC  1500  to better than λ/10 for combinations of two to three prisms for a KrF laser resonator or four prisms of an ArF laser resonator, such as may be included in a beam expander of a line-narrowing module of these lasers including a grating and/or an etalon. A prism or prisms of a beam expander used in a molecular fluorine laser resonator would also similarly benefit. 
     FIGS. 16 a - 16   b  illustrate another embodiment including a solid link  1600  to the module housing. The solid link  1600  has advantageous properties of elastic deformation, which allows for the rotary motion of the MOD and the linear motion of the drive element. Applying finite element analysis to the geometry of the solid link  1600  as well as knowing characteristics of the material used for the solid, such as E-module, allows for highly accurate prediction of the angular displacement, resilience and cross rigidity of the material. Referring to FIG. 16 a , the solid link  1600  system comprises a first part  1610 , a second part  1620  coupled to the OC  1630 , wherein the first part  1610  and second part  1620  are coupled at the solid link  1600  which acts something like a hinge and further also allows for rotating movements of the OC  1630 . Using such a solid link  1600  as a hinge member removes stick-slip effects caused by sliding friction of bearings used to support the MOD. The operating width of the slot  1650  between the first part  1610  and the second part  1620  may be adjusted prior to fabrication to allow for greater or lesser rotative action. The drive element preferably couples to the second part  1620 , while the first part couples to the optical module housing. 
     FIG. 16 b  shows a side view of this embodiment including the solid link  1600 . The EMD  10  and drive element  20  are configured for rotating the MOD  60 . An optical component ( 1630 ) would be positioned on surface  1660  of the second part  1620  and the first part  1610  would be preferably coupled to the optics module housing (as illustrated by elements  1670 ), when the system is in place in the optics module. The first part  1610  and second part  1620  are advantageously coupled together at the solid link  1600  and having slot  1650  between them which permits the hinging action between the first and second parts  1610 ,  1620 . 
     As already indicated above, while exemplary drawings and specific embodiments of the present invention have been described and illustrated, it is to be understood that that the scope of the present invention is not to be limited to the particular embodiments discussed. Thus, the embodiments shall be regarded as illustrative rather than restrictive, and it should be understood that variations may be made in those embodiments by workers skilled in the arts without departing from the scope of the present invention as set forth in the claims that follow, and structural and functional equivalents thereof.