Chapter 7 Measurement Optics
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1. the higher frequency from the laser head is in the reference path that is the path going to the reference mirror and 3 the measurement optics are moving away from each other the fringe counts will be INCREASING 7 6 User s Manual Chapter 7 Measurement Optics Measurement Direction Sense Interchanging f and fp will reverse the direction sense resulting in the fringe counts DECREASING as measurement optics move away from each other In this manual f and f2 have been used to identify the two frequency components of the laser beam H owever because the components that left the laser head having horizontal and vertical orientations can have the opposite orientations when they arrive at an interferometer fa and fg are used to identify the beam paths through the interferometers Figure 7 1 shows how two parallel beams derived from the same source can have different polarization orientations at interferometer inputs An interferometer using one of these beams will produce increasing counts as its measurement mirror moves away from it an identical interferometer parallel to the first but using the second beam will produce decreasing counts as its measurement mirror moves away User s Manual 7 7 Chapter 7 Measurement Optics Measurement Direction Sense VERTICAL AND HORIZONTAL POLARIZATION Notes 1 Shaded ovals represent laser beam cross section enlarged 2 V Vertical Polarization Com2. When making differential measurements both reflectors reference and measurement should be of the same type cube corner or plane mirror this minimizes thermal drift problems with ambient temperature changes To use the Agilent 10702A Agilent 10705A or Agilent 10766A ina differential configuration the reference cube corner can simply be detached from the interferometer housing and attached to the reference surface of interest This is shown in Figure 7A 7 in the Linear Interferometers subchapter subchapter 7A of this manual Be aware that all installation and alignment requirements for the measurement reflector now apply also to the reference reflector To use the Agilent 10706A or Agilent 10706B interferometer in a differential configuration a plane mirror is recommended as the reference reflector Simply replace the reference cube corner or high stability adapter with the Agilent 10722A Plane Mirror Converter and attach the reference plane mirror to the reference surface of interest This is shown in Figure 7C 4 in the plane mirror subchapter Subchapter 7C of this manual Again install and align the reference reflector the same as you would the measurement reflector User s Manual 7 11 Chapter 7 Measurement Optics Moving Interferometer Instead of Reflector Moving Interferometer Instead of Reflector When moving the interferometer instead of the measurement reflector is required the Agilent 10702A 001 or Agilent 10766
3. Bender 3 Linear Plane Mirror Measurements Displacement Pitch 2 128 5 nm 0 05 arcsec 0 24 urad See Specifications Turned only custom custom custom Agilent 10737L R Compact Three axis Interfero meters 3 Linear Plane Mirror Measurements Displacement Yaw Pitch See Specs Plane mirror or cube corners Customer determined Agilent 10711A P through U Reserved 7 4 User s Manual Chapter 7 Measurement Optics General Table 7 1 Measurement Optics Summary Continued Manual Model Number Application Typical Beam Config Reflector Reflector Sub and Name System Separation uration Weight chapter Resolution A Agilent 10766A General Purpose A 64 10 nm 11 mm Straight Agilent 224 g Agilent Linear 0 43 in through or 10767A 0 5 Ib 10785A Interferometer Turned V Agilent 10770A High Accuracy 1 64 10 nm 11 mm Agilent 650 g Agilent Angular Plane Mirror 0 43 in 10771A 1 5 Ib 10785A Interferometer W X Reserved Y Agilent 10774A High Resolution Not Included 800 g Agilent Short Range Plane Mirror Applicable 1 8 Ib 10776A Straightness Optics Y Agilent 10775A High Resolution Not Included 800 g Agilent Long Range Plane Mirror _ Applicable 1 8 Ib 10776A Straightness Optics User s Manual 7 5 Chapter 7 Measurement Optics Resolution Reso
4. If the laser beam has to go through a window for example into a vacuum chamber the window must meet the following requirements e A minimum window aperture of 25 4 mm 1 inch with a minimum thickness of 8 mm 0 3 inch If a larger window is used it must be proportionally thicker to assure no distortion in the window when under differential pressures e Transmitted wavefront distortion less than 4 10 peak valley single pass over a 23 mm 0 9 inch diameter e Parallelism of faces less than arc minutes to reduce beam steering e Surface quality 60 40 or better per Mil 0 13830 e The window must be strain free Differential Measurements with I nterferometers Several interferometers have the capability to make differential measurements A differential measurement is one in which both the reference beam and the measurement beam travel to external mirrors outside the interferometer housing This allows measurement of the relative positions of the two external mirrors either or both of which may be moving Viewed another way this allows measuring the motion of one reflector relative to a reference datum elsewhere in the machine external to the interferometer itself This is unlike the typical interferometer configuration because usually the reference beam path length does not change in differential configurations it can 7 10 User s Manual Chapter 7 Measurement Optics Differential Measurements with Interferometers On
5. A should be used In practice for alignment reasons these are the only interferometers except the straightness interferometers that can be moved while making measurements For a detailed explanation of why this option is required see Figure 7A 2 in the Linear I nterferometers subchapter subchapter 7A of this manual Product specifications and descriptions in this document subject to change without notice Copyright C 2002 Agilent Technologies Printed in U S A 07 02 This is a chapter from the manual titled Laser and Optics User s Manual For complete manual order Paper version p n 05517 90045 CD version p n 05517 90063 This chapter is p n 05517 90107 7 12 User s Manual
6. Measurement Optics Chapter 7 Measurement Optics General General Each laser measurement system s measurement axis must have an interferometer and a reflector Machine design considerations determine which type of interferometer is best The choice of the interferometer for each axis usually determines the reflector for that axis This chapter describes the Agilent Technologies measurement optics available for Agilent Technologies laser measurement systems The first part of this chapter presents material that should be useful to the user of any of the interferometers Following this introductory material the chapter is divided into subchapters that describe individual interferometer types including characteristics and specifications Table 7 1 lists the measurement optics in order by Agilent M odel Number It also 1 identifies the subchapter in which each measurement optic is described 2 provides summary descriptions of the measurement optics and 3 lists the reflectors and Agilent adjustable optics mounts with which the optics may be used The mounts are described in Chapter 9 Accessories of this manual Agilent Technologies beam directing optics are described in Chapter 6 Beam Directing Optics of this manual Other Agilent optics that are neither 1 interferometers nor 2 beam directing optics are described in Chapter 9 Accessories of this manual 7 2 User s Manual Manual Sub chapter C
7. e useful example of a differential measurement in a lithography application is for measuring the motion of the X Y stage relative tothe optical column The Agilent 10719A One Axis Differential Interferometer and the Agilent 10721A Two Axis Differential Interferometer are ideally suited to this type of measurement because they provide parallel reference and measurement paths which are offset vertically by 19 mm 0 750 inch For such an application a user supplied reference plane mirror is required in addition to the measurement reflector on the X Y stage Differential measurements that can be made using an Agilent 10719A interferometer are shown in Figure 7J 2 Differential measurements that can be made using an Agilent 10721A interferometer are shown in Figure 7K 2 The Agilent 10715A Differential Interferometer instead of having an offset spacing as in the Agilent 10719A or Agilent 10721A interferometers permits the reference beams and the measurement beams to be aligned essentially coaxially A specially shaped reference plane mirror Shown in Figure 7G 7 is supplied with the Agilent 10715A For moreinformation about the Agilent 10715A see subchapter 7G of this manual Customized differential configurations are possible with several other interferometers However considerable care should be exercised during design and layout to avoid introduction of alignment errors thermal or mechanical instabilities and potential deadpath problems
8. hapter 7 Measurement Optics General Table 7 1 Measurement Optics Summary Model Number and Name Agilent 10702A Linear Interferometer Application General Purpose Typical System Resolution 1 64 10 nm Beam Separation 12 7 mm 0 5 in Config uration Straight through or Turned Reflector Agilent 10703A Reflector Weight Agilent 10711A Agilent 10705A Single Beam Interferometer Low mass Limited space 1 64 10 nm Not Applicable single beam Straight through or Turned Agilent 10704A Agilent 10710B Agilent 10706A Plane Mirror Interferometer Plane Mirror 1 128 5 nm 12 7 mm 0 5 in Straight through or Turned Agilent 10724A or user supplied Agilent 10711A Agilent 10706B High Stability Plane Mirror Interferometer Plane Mirror 1 128 5 nm Straight through or Turned Agilent 10724A or user supplied Agilent 10711A Reserved Agilent 10715A Differential Interferometer High Accuracy Plane Mirror 12 7 mm 0 5 in Straight through or Turned Agilent 10724A or user supplied Agilent 10711A Agilent 10716A High Resolution Interferometer High Resolution Plane Mirror 12 7 mm 0 5 in Straight through or Turned Agilent 10724A or user supplied Agilent 10711A Agilent 10717A Wavelength Tracker Wavelength of light compensation Not Applicable Not Applicab
9. icipate these effects and minimize them if necessary during the laser measurement system design process Certain interferometers are inherently less susceptible to vibration effects than others This is particularly true of differential style interferometers such as the Agilent 10715A Agilent 10719A and Agilent 10721A Thestability of theseinterferometers is dueto the fact that both their reference beams and their measurement beams travel to external mirrors Any motion of the interferometer itself that is common to both beams will not appear as a measurement Of course any vibration between the reference and mirrors will constitute real measurable displacements F asteners Any optical component that fits an adjustable mount is supplied with mounting screws to mount it on the appropriate adjustable mount User s Manual 7 9 Chapter 7 Measurement Optics Vacuum Applications Vacuum Applications Many of the optical components of the laser measurement system have vacuum options which are compatible with vacuum environments Contact Agilent Call Center for information telephone numbers of various call centers are listed on the Service and Support page at the back of this manual Typically these components have housings made of stainless steel and optical elements attached to the housings using a lower volatility vacuum grade adhesive See the specifications for a list of materials used in the optics Use Through Window
10. le Built in Not Applicable Agilent 10719A One axis Differential Interferometer One Linear Plane Mirror Measurement Differential or One Angular Measurement 1 128 5 nm 0 054 arcsec 0 26 urad See Specifications Straight through only custom custom custom Agilent 10721A Two axis Differential Interferometer Two Linear Plane Mirror Measurements Differential Linear 1 128 5 nm 0 08 arcsec 0 4 urad User s Manual See Specifications Straight through only custom custom custom 7 3 Manual Sub chapter Chapter 7 Measurement Optics General Table 7 1 Measurement Optics Summary Continued Model Number and Name Reserved Application Typical System Resolution Beam Separation Config uration Reflector Reflector Weight Agilent 10735A Three axis Interferometer 3 Linear Plane Mirror Measurements Displacement Yaw Pitch 2 128 5 nm 0 04 arcsec 0 2 urad 0 05 arcsec 0 24 urad See Specifications Turned only custom custom custom Agilent 10736A Three axis Interferometer 3 Linear Plane Mirror Measurements Displacement Yaw Pitch 2 128 5 nm 0 04 arcsec 0 2 urad 0 05 arcsec 0 24 urad See Specifications Turned only custom custom custom Agilent 10736A 001 Three axis Interferometer with Beam
11. lution The fundamental optical resolution for each interferometer type is listed in Table 7 2 Using electronic resolution extension the system resolution is increased significantly Depending on the system an additional resolution extension factor of 32 is usually available Table 7 2 Interferometer Resolutions Interferometer Type Fundamental Resolution Linear A 2 0 316 micron 12 44 microinches Plane Mirror A 4 0 158 micron 6 32 microinches High Resolution Plane Mirror 2 8 0 079 micron 3 12 microinches Range The nominal optical measurement range for an Agilent laser measurement system is usually 40 meters 130 feet for the sum of all axes In calibrator systems this range may be doubled with the Agilent 5519A B optional long range kit The 3 mm diameter beam of the Agilent 5517C 003 Laser Head allows a maximum range of 10 meters 32 feet for the sum of all axes Measurement Direction Sense Direction sense depends on the relation of the optical frequencies in the interferometer s reference and measurement paths This in turn depends on 1 the orientation of the laser head 2 the effect of any beam bending optics in the path between the laser head and the interferometer and 3 the interferometer s configuration straight through or turned For example if 1 f the lower frequency from the laser head is in the measurement path that is the path going to the measurement mirror and 2 f
12. ponent 3 H Horizontal Polarization Component 4 fa and fg represent beam paths in Interferometer Beam Splitter Interferometer fp t a Interferometer fA PS Figure 7 1 Effect of beam directing optics on laser beam polarization orientations 7 8 User s Manual Chapter 7 Measurement Optics Vibration Isolation Vibration Isolation Vibration of the optics along the laser beam can cause the fringe count in the laser measurement system electronics to fluctuate rapidly Vibrations along this axis constitute real measurable displacements you will have to decide if these fluctuating measurements are acceptable in your application In extreme cases however the velocity of the optics may momentarily exceed the velocity limitation of the laser measurement system causing an error When vibration occurs perpendicular to the beam the beam signal power can fluctuate If this fluctuation is too great insufficient beam signal will arrive at the receivers causing a measurement signal error Loose mounting can cause the optics to move inappropriately during a measurement causing a measurement error or loss of beam power Elastic mounting can have the same effect as loose mounting It can also be responsible for a sag offset in the optics positions If there is vibration in the machine an elastic mounting can transmit and amplify the vibration to the attached optic possibly causing more errors You should ant
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