Stage Metrology Concepts: Application Specific Testing. Hans Hansen Sr. Systems Design Engineer BSME, MSE 2/28/2008

Transcription

1 Stage Metrology Concepts: Application Specific Testing Hans Hansen Sr. Systems Design Engineer BSME, MSE 2/28/2008

2 Topics Review of Stage Error Definitions Setting Stage Specifications for Applications Application-Specific Ways of Providing Stage Specifications

3 Basic Definitions Accuracy- the degree to which a system produces the correct result compared to a standard reference Repeatability- the degree to which a system produces the same result from run to run By definition, accuracy can not be better than repeatability, but repeatability can be better than accuracy. Precision- the resolution/ fineness to which a system can position.

4 Stage Errors Single Axis Degrees of Freedom Translation Stage 3 Translations : 2 fixed, 1 free 3 Rotations : All fixed Rotary Stage 3 Translations : All fixed 3 Rotations : 2 fixed, 1 free Errors Motions that are supposed to be fixed, but aren t Motions that are supposed to be free but are inaccurate Both have repeatable and non-repeatable terms

5 Accuracy, Repeatability & Resolution Low Accuracy Low Repeatability Low Accuracy High Repeatability High Accuracy High Repeatability Fine Resolution Coarse Resolution

6 Linear Stage Definitions X Direction Free: Positioning Accuracy & Repeatability Y Direction Fixed: Horizontal Straightness Error, Repeatable and Non-repeatable Z Direction Fixed: Vertical Straightness, Repeatable and Non-repeatable Ө x Fixed: Roll Error Ө y Fixed: Pitch Error Ө z Fixed: Yaw Error

7 Stage Errors - Linear

8 Stage Errors - Angular

9 Abbe Error Linear Errors are affected by rotation errors an amount that depends upon where the error is measured. Horizontal Straightness Measured at A Given Height is the sum of the straightness at the center of roll + product of the roll and the height from the roll center to the point of measurement Height Abbe distance Error Component from roll Abbe error

10 Abbe Error

11 Bidirectional vs. Unidirectional Positioning Repeatability Unidirectional- target always approached from one direction Bidirectional- target approached from both directions. Applies to both linear and rotary systems

12 Unidirectional Repeatability

13 Bidirectional Repeatability

14 Squareness Arises when we combine axes Example: Squareness of XY Stage System Measured using a square and indicator Need to take measure at appropriate height Combines rotation and linear errors

15 Fixed vs. Moving Sensitive Direction Affects appropriate orientation of indicator and reference surface when measuring straightness Example- Single axis microscope Sample Fixed Sample Moving Indicator should always be mounted where the objective is mounted.

16 Rotary Stage Definitions X Direction Fixed: Radial Motion, Repeatable and Non-repeatable Y Direction Fixed: Radial Motion, Repeatable and Non-repeatable Z Direction Fixed: Axial, Repeatable and Nonrepeatable Ө x Fixed: Tilt Error in XZ plane Ө y Fixed: Tilt Error in YZ plane Ө z Free: Positioning Accuracy and Repeatability

17 Rotary Stage Errors Axial Radial Tilt/Wobble

18 Error Correction- Mapping Errors measured and stored in computer as a lookup table or function Mapping data must travel with stage Only as accurate as repeatability of system as measured and in use. Meaningful only if done at appropriate Abbe height

19 2D Accuracy Renishaw lasers used with an optical square to calibrate out accuracy, straightness, yaw, and orthogonality in one test Laser outputs are read into two free encoder inputs of an A3200 system. Need to do this to synchronize the encoder and laser information Matlab is used to post process the results and generate 2D calibration files Courtesy of Aerotech

20 Difficulty in Specifying Stages Given All The Error Terms Stages typically specified in terms of the classical individual stage errors. Performance we are interested in result from the combination of these errors

21 Proposal Define performance in terms of applicationspecific tests Specify individual errors only as necessary

22 Example Simple 1 Axis System Requirement to Position Sample Under Objective in X,Y & Z to Specific Accuracy & Repeatability Specify X Positioning Specify Y&Z Straightness Both need to be at height of sample and take into consideration moving vs. stationary objective

23 Example 2 Axis XY System Requirement to Position Sample Under Objective in X,Y & Z to Specific Accuracy & Repeatability Specify X&Y Positioning Test Specify Combined Z Straightness Test Both need to be at height of sample and take into consideration moving vs. stationary objective

24 4 Axis System Brushless DC Drives, 20 nm Resolution

25 Example 3 Axis RӨZ System Requirement to Position Sample Under Objective in R,Ө & Z to Specific Accuracy & Repeatability Specify R,Ө Positioning Test Specify Combined Z Straightness Test Both need to be at height of sample and take into consideration moving vs. stationary objective

26 3 Axis RӨZ System (nanomotion motors)

27 Conclusion Defining stage specifications in terms of individual stage errors can be cumbersome. Consider defining your own specifications that are unique to your application

28 Backup

29 Linear vs. Mechanical Bearings Parameter Units Linear Motors Linear Bearings Linear Motors Air Bearings accuracy microns ±5 ±0.5 accuracy, mapped microns ±1 ±0.25 repeatibility, bi-directional microns ±0.5 ±0.2 positional stability microns +/ /-0.04 encoder resolution microns straightness and flatness microns roll,pitch,yaw arc-sec 10 2 speed, no load mm/sec acceleration, no load mm/sec^ settling time sec <0.2 <0.2

30 Measurement Techniques Straightedge Reversal Technique Place straightedge on the carriage, parallel to the axis that is being tested Mount gage on a stationary part of the tool, with the sensitive contact positioned against the straightedge and scan axis of interest Repeat scan with the straightedge flipped 180 degrees around its long axis, and the gage head repositioned on the opposite side of the machine scanning the same surface. The gage head's direction of motion is reversed, so that a "bump" on the straightedge should read as a positive number on both trials. The results of one trace are subtracted from the other. Because the gage head was reversed, carriage errors cancel each other out, so any remaining deviation from zero reflects error in the straightedge. (assumes that carriage errors are repeatable.) The results can be used as correction factors for all future uses of the straightedge.

31 Reversal- Setup 1

32 Reversal Setup 2

33 Reversal- Math T 1 (Z) = P(Z) + S(Z) T 2 (Z) = P(Z) - S(Z) T= Indicator Reading P= Stage Straightness Error S= Straightedge Straightness Error