ProfilometerFrom Wikipedia, the free encyclopedia • Ten things you may not know about Wikipedia •Jump to: navigation, searchA profilometer is a measuring instrument used to measure a features length or depth,usually in the micrometre or nanometre level.While the historical notion of a profilometer was a device similar to a phonograph thatmeasures a surface as the surface is moved relative to the contact profilometers stylus,this notion is changing along with the emergence of numerous non-contact profilometerytechniques. Contact profilometers:A diamond stylus is moved vertically in contact with a sample and then moved laterallyacross the sample for a specified distance and specified contact force. A profilometer canmeasure small surface variations in vertical stylus displacement as a function of position.A typical profilometer can measure small vertical features ranging in height from 10 to65,000 nanometres. The height position of the diamond stylus generates an analog signalwhich is converted into a digital signal stored, analyzed and displayed. The radius ofdiamond stylus ranges from 5 μm to about 25 μm, and the horizontal resolution iscontrolled by the scan speed and scan length. There is a horizontal broadening factorwhich is a function of stylus radius and of step height. This broadening factor is added tothe horizontal dimensions of the steps. The stylus tracking force is factory-set to anequivalent of 50 milligrams (~500 mN).Advantages of contact profilometers: • Acceptance: Most of the worlds surface finish standards are written for contact profilometers. To follow the prescribed methodology, this type of profilometer is often required. • Surface Independence: Due to the fact that the stylus is in contact with the surface, this method is not sensitive to surface reflectance or color. Also, contacting the surface is often an advantage in dirty environments where non- contact methods can end up measuring surface contaminants instead of the surface itself. Non-contact profilometers:An optical profilometer is a non-contact method for providing much of the sameinformation as a stylus based profilometer. There are many different techniques whichare currently being employed, such as laser triangulation (triangulation sensor), confocal
microscopy and digital holography.Advantages of optical profilometers: • Speed: Because the non-contact profilometer does not touch the surface the scan speeds are dictated by the light reflected from the surface and the speed of the acquisition electronics. • Reliability: Optical profilometers do not touch the surface and therefore cannot be damaged by surface wear or careless operators. Many non-contact profilometers are solid-state which tends to reduce the required maintenance significantly. • Spot size: The spot size, or lateral resolution, of optical methods ranges from a few micrometres down to sub micrometre. On the small end, this is roughly an order of magnitude smaller than typical stylus tips.One special application is road pavement profilometers. These are of non-contact type,most of them use laser triangulation in combination with an inertial unit that establishes alarge reference plane to which the laser readings are related. The inertial compensationmakes the profile data more or less independant of what speed the profilometer vehiclehad during the measurements.
Method of thin film process control and calibration standard for opticalprofilometry step height measurementDocument Type and Number:United States Patent 6490033Link to this page:http://www.freepatentsonline.com/6490033.htmlAbstract:A method of calibrating an interferometer system and a multilayer thin film used forcalibrating the interferometer system. The method including measuring the step height ofa gold step with the interferometer system, the multilayer thin film comprising a goldlayer that defines the gold step. The multilayer thin film having an optical flat, a firstlayer on the surface of the optical flat, a second layer on the first layer, a test layer on apart of the second layer, and a gold layer on the test layer and on a part of the secondlayer uncovered by the test layer. The test layer having a test layer step, and the goldlayer having a gold step over the test layer step. Also, a reference standard and a methodof making the reference standard for a thin film sample with one or more componentthin film layers, the reference standard having a gold layer over the surface of the thinfilm sample.1. A method of calibrating an interferometer system comprising: measuring the height ofa gold step with the interferometer system, the gold step being in a gold layer of amultilayer thin film for use as a calibration standard, the multilayer thin filmcomprising:an optical flat;a first layer on the surface of the optical flat;a second layer on the first layer, the second layer having a first part and a second part;a test layer on the first part of the second layer, the test layer having a test layer step; and,a gold layer on the test layer and on the second part of the second layer, such that the goldlayer has said gold step over said test layer step.2. The method of claim 1 wherein the first layer has a thickness of 50 nm or less, thesecond layer has a thickness of 50 nm or less, and the gold layer has a thickness between15nm and 65 nm.3. The method of claim 2 wherein the first layer has a thickness of about 30 nm or less,the second layer has a thickness of about 30 nm or less, and the gold layer has a thicknessbetween about 30 nm and about 50 nm.4. The method of claim 3 wherein the optical flat has a .lambda./20 smooth surface ofamorphous material.
5. The method of claim 1 wherein the first layer is titanium with a thickness of about 20nm, the second layer is platinum with a thickness of about 20 nm, the test layer isplatinum with a thickness of about 6 nm, and the gold layer has a thickness of about 50nm.6. The method of claim 5 wherein the optical flat has a .lambda./20 smooth surface ofamorphous material.7. The method of claim 1 wherein two or more measurements of the step height of thecalibration standard are taken with the interferometer system for calibrating theinterferometer system.8. A multilayer thin film for use in calibrating an interferometer system comprising:a. a first layer on the surface of an optical flat;b. a second layer on the first layer, the second layer having a first part and a second part;c. a test layer on the first part of the second layer, the test layer having a step; and,d. a layer of gold on the test layer and on the second part of the second layer, so that thelayer of gold has a step over the step in the test layer.9. The multilayer thin film of claim 8 wherein the first layer has a thickness of 50 nm orless, the second layer has a thickness of 50 nm or less, and the gold layer has a thicknessbetween 15 nm and 65 nm.10. The multilayer thin film of claim 9 wherein the first layer has a thickness of about 30nm or less, the second layer has a thickness of about 30 nm or less, and the gold layer hasa thickness between about 30 nm and about 50 nm.11. The multilayer thin film of claim 10 wherein the optical flat has a .lambda./20smooth surface of amorphous material.12. The multilayer thin film of claim 8 wherein the first layer is titanium with a thicknessof about 20 nm, the second layer is platinum with a thickness of about 20 nm, the testlayer is platinum with a thickness of about 6 nm, and the gold layer has a thickness ofabout 50 nm.13. The multilayer thin film of claim 12 wherein the optical flat has a .lambda./20smooth surface of amorphous material.14. A method of making a multilayer thin film for use in calibrating an interferometersystem comprising:
a. depositing a first layer on the surface of an optical flat;b. depositing a second layer on the first layer, the second layer having a first part and asecond part;c. depositing a test layer on the first part of the second layer, the second layer having astep; and,d. depositing a layer of gold on the test layer and on the second part of the second layer,so that the layer of gold has a step over the step in the test layer.15. The method of claim 14 wherein the first layer has a thickness of 50 nm or less, thesecond layer has a thickness of 50 nm or less, and the gold layer has a thickness between15 nm and 65 nm.16. The method of claim 15 wherein the first layer has a thickness of about 30 nm or less,the second layer has a thickness of about 30 nm or less, and the gold layer has a thicknessbetween about 30 nm and about 50 nm.17. The method of claim 16 wherein the optical flat has a .lambda./20 smooth surface ofamorphous material.18. The method of claim 14 wherein the first layer is titanium with a thickness of about20 nm, the second layer is platinum with a thickness of about 20 nm, the test layer isplatinum with a thickness of about 6 nm, and the gold layer has a thickness of about 50nm.19. The method of claim 18 wherein the optical flat has a .lambda./20 smooth surface ofamorphous material.20. A method of making a reference standard for a thin film sample with one or morecomponent thin film layers, the thin film sample having a surface, the surface defining astep with a step height, the method comprising depositing a layer of gold on the surfaceof the thin film sample.21. The method of claim 20 wherein the gold layer has a thickness between about 30 nmand about 50 nm.22. The method of claim 20 wherein two or more measurements are taken with theinterferometer system for obtaining a mean value of the height of the step.23. A reference standard for use in thin film process control, the standard comprising alayer of gold deposited on the surface of a thin film sample in manufacture formeasurement by an interferometer system.24. The reference standard of claim 23 wherein the gold has a thickness between about 30
nm and about 50 nm.Description:FIELD OF THE INVENTIONThe invention relates generally to thin films and the interference microscope andspecifically to techniques for calibrating an optical profilometer and for measuring athin film surface profile.BACKGROUND OF THE INVENTIONOptical profilometry is a non-contact method of measuring the surface characteristics of athin film sample in three dimensions. Optical profilometry is often preferred to contactmethods, such as atomic force microscopy and surface contact profilometry, because thelatter are intrinsically less accurate and can destroy features of the sample duringmeasurement.An optical profilometer is one type of interference microscope (interferometer). Aninterference microscope generally is used either to measure or to visualize the phasedifferences between two or more beams of electromagnetic radiation, when directed to athin film it measures the surface features of the thin film sample under investigation.When the microscope measures the phase differences, it generates an interference patternwhich a computer can analyze to derive a surface profile of the sample. The microscopeand computer together comprise an interferometer system.Several beams of the radiation used to measure surface features of a thin film maypenetrate slightly beneath the surface of the thin film before they are scattered. Thispenetration depth changes the distance traveled by a beam and may affect the phasedifference between the beam and another beam with which it interferes, creating noise inthe interference pattern and decreasing the accuracy of the measurement. The noisebecomes more significant when the profilometer is used to measure thin film stepheights that fall below 10 nanometers, because at this height the penetration depth is onthe same order of magnitude as the step height. If radiation with a smaller wavelengthand higher energy is used, the noise becomes even greater because this radiationpenetrates even deeper into the thin film. Moreover, the smaller the wavelength, themore dramatically a slight difference in the path traveled by the radiation affects theresulting phase difference as well as the interference pattern.The penetration depth of the beam introduces additional inaccuracies into the process ofcalibrating the optical profilometer, especially when the profilometer must be calibratedfor taking measurements of thin film step heights in the sub-10 nanometer range.Previously the best technique of calibration for these step heights was to calibrate to amuch higher step and then extrapolate blindly to a step that is an order of magnitudelower. Alternately, a contacting measuring method might have been used instead of non-contact optical profilometry.Unfortunately, the technique of calibrating to a higher step may yield imprecise
measurements. Alternately, contacting measuring methods may damage the surfacefeatures of a thin film sample. Further, these methods are generally less accurate andmay be more costly.Another drawback of measuring a step height with an optical profilometer arises whenthe step does not have an identical composition in its upper and next lower levels. Inparticular, if the upper level of the step comprises one metal with one penetration depthwhile the next lower level comprises a different metal with a different penetration depth,the step might create even more noise in the interference pattern.SUMMARY OF THE INVENTIONAccordingly, an object of one embodiment of the invention is to provide a technique forcalibrating an optical profilometer to measure very small step heights. Another object ofan embodiment of the invention is to provide a calibration standard for opticalprofilometry step height measurements. Another object of an embodiment of theinvention is to provide a technique for measuring very small step heights. Another objectof an embodiment of the invention is to provide a reference standard for thin filmprocess control.Briefly described, and in accordance with one embodiment thereof, the inventionprovides a method of calibrating an interferometer system including measuring the stepheight of a gold step with the interferometer system. The gold step is in a gold layer of amultilayer thin film which acts as a calibration standard. The multilayer thin film(calibration standard) has an optical flat, a first layer on the surface of the optical flat, asecond layer on the first layer, a test layer on a part of the second layer, and a gold layeron the test layer and on a part of the second layer uncovered by the test layer. The testlayer has a test layer step, and the gold layer has the gold step over the test layer step. Thegold step is equivalent in height to the test layer step and exhibits a lower penetrationdepth than the test layer step beneath it. The gold step also has a uniform (gold)composition in its upper level and next lower level.In accordance with another embodiment thereof, the invention provides a calibrationstandard for optical profilometry step height measurements. The calibration standard hasa multilayer structure comprising an optical flat, a first layer on the surface of the opticalflat, a second layer on the first layer, a test layer on a part of the second layer, and a goldlayer on the test layer and on a part of the second layer uncovered by the test layer. Thetest layer has a test layer step, and the gold layer has a gold step over the test layer step.In accordance with another embodiment thereof, the invention provides a method ofmaking a reference standard for a thin film sample with one or more component thinfilm layers. The method includes depositing a layer of gold over the surface of the thinfilm sample.In accordance with another embodiment thereof, the invention provides a referencestandard for a thin film sample with one or more component thin film layers. The
reference standard has a layer of gold that is measured by the profilometer, but isotherwise essentially the same as the thin film sample.BRIEF DESCRIPTION OF THE DRAWINGSThe foregoing and other features of the invention will be described in more detail in thefollowing Detailed Description of the Preferred Embodiment, taken in conjunction withthe accompanying drawings wherein:FIG. 1 is a cross-sectional view showing the multilayer structure of the first embodimentof the invention;FIG. 2 is a cross-sectional view showing the multilayer structure of another embodimentof the invention;FIG. 3 is a top view illustrating the process of preparing the multilayer thin film of theinvention; andFIG. 4 is a cross-sectional view showing the structure of the reference standard of anotherembodiment of the invention.DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTSFIG. 1 shows a first embodiment of the invention. A multilayer thin film 10, used tocalibrate an interferometer system, has an optical flat 12 preferably with a .lambda./20smooth surface 14 of amorphous material. On the optical flat 12 is a first layer 16 whichadheres strongly to the surface 14 of the optical flat 12. On the first layer 16 there is asecond layer 20 which adheres strongly to the first layer 16. The second layer 20 has afirst part 22 and a second part 24 that are generally coplanar with each other and adjacentto each other. On the first part 22 of the second layer 20 there is a test layer 30 whichadheres strongly to the first part 22 of the second layer 20. A gold layer 40 is located bothon the second part 24 of the second layer 20, and on the test layer 30.The test layer 30 defines a test layer step 32, with a height of a generally known value, atthe boundary 34 of the test layer 30. The gold layer 40 defines a gold step 42 over the testlayer step 32. The gold step 42 is equivalent in height to the test layer step 32. Theinterferometer system is calibrated by measuring the height of the gold step 42 severaltimes with the interferometer system, and then calculating the mean value, median value,and standard deviation of the measurements.FIG. 2 shows another embodiment of the invention. A multilayer thin film 50, which islocated on optical flat 12, comprises a first layer 60 with a thickness of about 30 nm orless, a second layer 70 with a thickness of about 30 nm or less, a test layer 80, and a goldlayer 90 with a thickness of about 50 nm or less. The test layer 80 creates a step 82 whichis reflected in the gold layer 90 as step 92. A particular example of the multilayer thinfilm 50 has a first layer 60 of titanium with a thickness of 20 nm, a second layer 70 of
platinum with a thickness of 20 nm, a test layer 80 of platinum with a thickness of 6 nm,and a gold layer 90 with a thickness of 50 nm. A multilayer thin film with thisconstruction can act as a calibration standard for calibrating an interferometer system.A multilayer thin film sample with the foregoing construction is formed first bydepositing a titanium and platinum bilayer on the optical flat 12. The sample is thenremoved from a thin film depositing system. As shown in FIG. 3, half 110 of the sample100 is then masked with aluminum foil 120 before the sample 100 is reloaded into thedepositing system for depositing a test layer of platinum thereon. The sample 100 is thenonce again removed from the depositing system, the aluminum foil 120 is removed fromthe sample, and the sample 100 is reloaded into the depositing system for depositing agold layer thereon.FIG. 4 shows another embodiment of the invention, a reference standard 140 for a thinfilm sample with one or more component thin film layers. The thin film sample has asurface 150 upon which is deposited a test layer 160 that defines a step 162. Thereference standard 140 comprises a gold layer 170 on the surface 150 of the thin filmsample, which as a result of step 162 creates a step 172. Because gold has a small knownbeam penetration, and the top and bottom of the steps 42 (FIG. 1), 92 (FIG. 2) and 172(FIG. 4) are of gold, these structures can be used as accurate calibration standards for aninterferometer (profilometer) system. These structures provide accuracy for steps whichare at least 10 nanometers or less. The gold layer 170 may have a thickness no greaterthan 50 nm.While the foregoing embodiments of the present invention have been set forth inconsiderable detail for the purposes of making a complete disclosure of the invention, itshould be apparent to those of skill in the art that numerous changes may be made in suchdetail without departing from the spirit and principles of the invention.
Profilometer stylus assembly insensitive to vibrationDocument Type and Number:United States Patent 5309755Link to this page:http://www.freepatentsonline.com/5309755.htmlAbstract:A stylus profilometer having a counterbalanced stylus with a motion transducer using avane moving between parallel, spaced-apart, conductive plates which damp the motion ofthe vane by means of trapped air. The vane forms an electrode with the plates so that thecombination is a pair of capacitors in a balanced bridge arrangement. Motion of thestylus causes an unbalance of the bridge indicative of the extent of stylus motion. A leverarm associated with the stylus has a tip influenced by a magnetic field which biases thestylus or controls force on a surface to be measured. The entire assembly has a very lowmoment of inertia to reduce the effects of vibration on the stylus and thereby increaseresolution of the device and reduce damage to the substrate.A profilometer assembly comprising,an elongated stylus arm and counterbalance having a first end with a hard stylus mountedfor contact with a substrate disposed below the arm and a second end, opposite the firstend having a vane for motion between two parallel plates, the stylus arm having a pivotbetween the first and second ends, said parallel plates forming a stylus displacementmeasurement transducer with said vane, anda variable force member associated with the first end of the stylus arm for urging the firstend into contact with said substrate.2. The apparatus of claim 1 wherein said variable force member comprises a coil having aferromagnetic core located a spaced distance from a lever connected to the first end of thestylus arm and having a ferromagnetic tip which can be magnetically actuated from adistance by said core.3. The apparatus of claim 1 wherein said pivot is seated in a pivot member having a pairof opposed ends, one end supporting the stylus arm and the opposite end supporting saidvane.4. The apparatus of claim 1 wherein said parallel plates are disposed in air and have anareawise extent shielding the vane from outside air.5. A profilometer assembly comprising,a measurement stylus mounted at the end of an arm for contact with a substrate,a pivot member having opposed forward and rearward sides and a central regiontherebetween mounted for turning on an axis defined from a relatively massive member,the pivot member supporting said arm on the forward side and a counterweight memberon the rearward side, the counterweight including a force transducer having means for
signaling motion of the pivot member, andmeans for adjustably biasing the forward side of the pivot member, thereby urging saidstylus into contact with the substrate, having a coil spaced from said pivot member, aferromagnetic core extending through the coil and a lever in magnetic communicationwith the core, transmitting force induced by the coil, to the forward side of the pivotmember, the lever connected to the pivot member but spaced from said coil and core.6. The apparatus of claim 5 wherein said arm, lever and vane have a rotational moment ofinertia about the pivot member, said moment of inertia less than 0.5 gm-cm.sup.2.7. The apparatus of claim 5 wherein said pivot member has a rearwardly extendingpaddle, said vane being connected to said paddle.8. A profilometer assembly comprising,a measurement stylus mounted at the end of an arm for contact with a substrate,a pivot member having opposed forward and rearward sides and a central regiontherebetween mounted for turning on an axis defined from a relatively massive member,the pivot member supporting said arm on the forward side and a counterweight memberon the rearward side, the counterweight including a force transducer having means forsignaling motion of the pivot member, andmeans for adjustably biasing the forward side of the pivot member, thereby urging saidstylus into contact with the substrate.wherein the force transducer means comprises a pair of spaced-apart, parallel plates witha movable vane therebetween, the vane connected to the rearward side of the pivotmember whereby motion of the stylus member is transmitted through the pivot memberto the vane.9. The apparatus of claim 8, wherein said vane and said parallel plates form a bridgecircuit.10. A profilometer assembly comprising,a stylus arm for step-height measurements of a substrate,a pivot member supporting the stylus arm,a vane supported by the pivot member, rearwardly of the stylus arm, partiallycounterbalancing the stylus arm and having a mass-radius squared product incombination with the stylus arm not exceeding 0.5 gm-cm.sup.2, wherein the vane movesin air between and generally parallel to two parallel plates, the air between the parallelplates damping motion of the vane,
whereby the momentum of the arm is minimized in order to reduce damage to substrates.11. The apparatus of claim 10, wherein the vane and said parallel plates define twocapacitors arranged for differential sensing of the amount of turning of said pivot therebysensing the deflection of said stylus arm.12. The apparatus of claim 10 further comprising a solenoidal coil generating a magneticfield spaced a distance from said arm and a lever having one end connected to said pivotmember and a free end having a ferromagnetic tip in communication with said magneticfield whereby said magnetic field can bias said arm relative the substrate.13. The apparatus of claim 10, wherein said vane moves between two fixed parallel plateelectrodes.Description:TECHNICAL FIELDThe invention relates to instruments for measuring profiles of surface features of apatterned semiconductor wafer or measuring fine texture on soft substrates.BACKGROUND ARTProfiling instruments were first developed in the 1930s for the purpose of characterizingsurfaces in terms of roughness, waviness and form. In recent years, they have beenrefined for precise metrology in the measurement and production control of the thin filmartifacts which are the building blocks of semiconductor devices. As the semiconductorindustry has progressed to smaller dimensions with each new generation of product, theneed for more sensitive and precise profiling instruments has grown. As artifacts becomesmaller, a smaller radius stylus must be used to fully resolve them. But a smaller radiusproduces higher contact pressure and necessitates use of lower stylus force. The use ofvery low stylus force renders the instrument more vulnerable to noise generation fromroughness of the measured surface and also from environmental sources of vibration. Thepresence of noise in the output reduces the effective sensitivity of the instrument andcompromises the fidelity of its traces. Fidelity is also lost whenever the ratio of styluspressure to surface yield strength rises to the degree that plastic deformation of thesurface occurs and detail of the surface variations is obliterated. Reduction of stylus forceis the only solution to this problem.In U.S. Pat. No. 4,103,542 Wheeler et al., assigned to the assignee of the presentinvention, disclose a counterbalanced stylus arm, pivoted about a bearing, in whichstylus force may be adjusted by moving the counterbalance. Force is measured using alinear variable differential transformer having a core associated with the stylus arm and acoil, through which the core moves, supported independently of the arm. In U.S. Pat. No.4,391,044 Wheeler discloses a similar stylus arm supported for linear scanning.It is evident that operation of profilers at very low stylus force is desirable. The present
state of the art in commercial profilers allows operation down to 1.0 mg. of force.However, a relatively quiet environment is necessary for good results at that force andsuch conditions are not always available in the users environment. What is needed is areduced reaction of the stylus/sensor assembly to the vibration or shock energy pulseswhich reach it from whatever source.An object of the invention was to devise a stylus assembly for a profilometer withimproved vibration and shock insulation properties.SUMMARY OF INVENTIONThe above object has been achieved in a profilometer stylus assembly which reduces theeffects of vibration and shock energy pulses by means of a substantial decrease in themoment of inertia of the assembly. For, as an energy pulse comes to the stylus armstructure, it will generate an accelerating force which will tend to raise the stylus fromthe sample surface either at the leading edge of the pulse or upon the rebound if theaccelerating force exceeds the set stylus force. The acceleration force developed is inproportion to the moment of inertia of the stylus arm structure, hence its reduction allowsthe use of lower stylus force.Conventional practice in existing designs is to locate the measurement sensor, sometimesa core working with a coil, close to the stylus on a pivoted stylus arm. A counterweightis frequently employed on the opposite end of the arm to achieve a static balance. Thisdesign approach assures that the sensor will precisely track the stylus motion and alsothat some momentum effects are avoided when a motion pulse is introduced through thestylus arm pivot.Contrary to standard designs, the stylus support arm and the measurement sensor of thepresent invention are in opposed positions about the pivot. A vane, supported by thepivot, opposite the stylus, moves in air between two larger parallel capacitor plates. Thetrapped air between the plates damps the motion of the vane, thereby providing clampingof large stylus motions, while the two plates with the vane form a differential capacitorfor the measurement of motion. An important feature is that the moment of inertia about arotational axis can be made very small. Mass reduction at a maximum distance from thepivot is most important.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 is a side perspective view of a profilometer stylus assembly of the presentinvention.FIG. 2 is a front perspective view of the profilometer stylus assembly shown in FIG. 1.FIG. 3 is a top plan view of the profilometer stylus assembly shown in FIG. 1.FIG. 4 is a side plan view of the profilometer stylus assembly shown in FIG. 1.
FIG. 5 a side view of a capacitor plate used in the profilometer stylus assembly shownin FIG. 1.BEST MODE FOR CARRYING OUT THE INVENTIONWith reference to FIGS. 1-4, a diamond tip 11 having a radius of 0.01 mm. is adhered toan end of a slender stainless steel wire 13 which is bent at a right angle. The wire radiusis about 0.25 mm. The diamond tip is adhesively mounted to a squared-off end of thewire, while the opposite end of the wire is inserted into a hollow aluminum arm 15 whichhas a length of approximately 2 cm and a wall inside radius of approximately 0.018 cm.The aluminum arm is sufficiently rigid that it will not bend when sensing step heights, yetsufficiently low mass that its moment of inertia can be kept low. The overall mass of thearm, wire and diamond tip should not exceed approximately 0.05 grams. Arm 15 fits intoa groove 17 in pivot member 19. Washer 21 holds the arm in place in the groove 17,while a tiny screw 23 holds the washer in place against the wall of the pivot member 19.Support beam 25 has a downwardly extending column 27 to which a flexural pivot 29 ismounted, connecting the pivot member 19 to the column 27. In this manner, thealuminum arm 15 has a center of rotation about the flexural pivot 29. The flexural pivot29 has enough torsion to lightly hold the stylus tip 11 downwardly against a surface to bemeasured. The entire mass on the stylus side of the pivot should not exceed 0.50 grams,including a lever described below.A frame 31 may be connected to a tilt compensation or leveling mechanism as describedin the prior patents to Wheeler. The underside of frame 31 supports a connector block 33which acts as an elevational adjustment for a pair of spaced apart parallel capacitor plates35 and 37. The spacing between the plates is approximately 0.7 mm., with an air gapbetween the plates.FIG. 5 shows the detail of a single capacitor plate. Such plate features a planar ceramicmember 61 having a pair of conductive films which are silkscreened and then fired on theceramic member to form a capacitor plate. The two plates are identical and so only one isshown. A conductive metal film 63 is shown extending through a via hole 65, in theceramic member. The upper surface of the drawing represents the side of the plate facingthe movable vane 41 in FIG. 1. The purpose of the via hole 65 is to provide electricalconnection to a thin wire which is soldered on an outer surface solder pad and carries thesignal from the capacitor plate to associated electronics. Wire 39 in FIG. 4 is such a wire.A second conductive metal layer 71 is in insulative relationship with respect to metallayer 63, but is also deposited on the ceramic member 61. The layer is plated through asecond via 73 and has a bonding ring 75 on the backside of the capacitor plate. Layer 71serves to terminate the shield of the wire which is terminated in via 65. The shieldreduces electrical noise pickup.Returning to FIGS. 1-4, a small insulative spacer, not shown, separates plate 35 fromplate 37 and a screw fastens the two plates to frame 31. The area extent of the platesshould be large enough to shield the vane from outside air, so that the vane experiences
resistance to motion due to compression of air momentarily trapped between the closelyspaced plates. A pair of electrical leads 39 is connected to the parallel plates, one lead toeach plate. Between the parallel plates, a low mass of electrically conductive vane 41 isspaced, forming a capacitor with respect to each of the parallel plates 35 and 37. Therange of motion of the vane, indicated by arrows A in FIG. 4, is plus or minus 0.16 mm.Moreover, vane 41, being connected to the pivot member 19, damps pivoting motion asthe vane attempts to compress air between the parallel plates. This damping motion of thevane serves to isolate vibration and shock which may be transmitted into arm 15.Vane 41 is connected to a paddle 43 which is the rearward extension of pivot member 19,opposite arm 15, serving to counterbalance the arm. The total mass of the vane, paddleand pivot member on the vane side of the pivot should not exceed about 0.6 g. The vane41 is grounded so that a differential pair of capacitors may be formed with respect toparallel plates 35 and 37 with their respective electrical leads 39. Such a pair ofcapacitors may be arranged in a balanced bridge configuration. Movement of the vanebetween plates 35 and 37 upsets the balance of the bridge, with the change of capacitanceindicative of stylus tip motion.An electrical solenoidal coil 51 has a central ferromagnetic core 53 which becomesmagnetized on application of current to the coil 51 by means of wires 55. The magnetizedcentral ferromagnetic core 53 attracts a ferromagnetic tip 57 of a lever 59 having an endopposite the ferromagnetic tip which is affixed to the pivot member 19. By applyingcurrent to the wires 55 and magnetizing the core 53, magnetic force is exerted on thelever 59 causing a bias in the form of a rotation, indicated by the arrow B in FIG. 4. Thelever 59 should be light weight, yet stiff so that the lever will not bend on the applicationof magnetic force.In operation, the stylus tip 11 scans a surface to be measured, such as a patternedsemiconductor wafer. Scanning may be achieved either by moving the frame 31 withrespect to a fixed wafer position or alternatively moving the wafer, on an X-Y waferstage with the position of the stylus fixed, or a combination of the two motions. In thelatter instance, the stylus arm may be moved linearly in the X direction while the wafer isadvanced in the Y direction after each lengthwise X direction scan. The stylus tip 11 ismaintained in contact with the surface of the wafer by an appropriate bias applied throughthe coil 51 and the core 53 into the lever 59. The bias should be great enough to maintaincontact, but yet not damage the surface being measured. Deflections of the tip 11 arecaused by topological variances in the surface being measured and these are translatedrearwardly through the pivot member 19 to the vane 41, but which resists undesirablelarge amplitude motion due to vibration because of the air displacement between theparallel plates 35 and 37. However, as the air is compressed and displaced, the vane 41moves slightly causing a signal in electrical leads 39 reflecting a change in an electricalbridge circuit connected to these wires. At the end of a scan, the tip 11 is raised to protectit from damage in the event that a wafer is changed.In building arm 15, wire 13 and tip 11, it is important to maintain the moment of inertiaas small as possible. The mass-radius squared product should not exceed about 0.5 g-
cm.sup.2 and we have achieved a mass-radius squared product of 0.42 g-cm.sup.2. Theradius is measured with respect to the center of the spring pivot 29 to the furthest radialextent of the steel wire 13. A similar moment of inertia is calculated with respect to thevane 41 and the lever 59. The sum of the moments is termed the moment of inertia for theentire stylus arm. By maintaining a low moment of inertia, the stylus arm is less sensitiveto vibration and greater resolution in profile measurements of thin films, and the like,may be achieved.Profilometers Veeco Dektak Stylus Profilometer The stylus profilometer uses a diamond tipped stylus to scan across the sample surface and measures the surface topography of thin and thick films. The vertical movements of the stylus is measured and recorded simultaneously during the scanning, which reveals the topographical structure of the surface. The instrument has vertical resolution in nanometers and horizontal resolution as small as twenty nanometers and measures the film thicknesses from 5 nm and over 500 µm.Tài liệu tham khảoPossibilities and limitations of the stylus method for thin film thickness measurementsThin Solid Films, Volume 21, Issue 2, April 1974, Pages 237-243