Detection Of Phase Defects On Photomasks By Differential Imaging
A Method For Detecting Phase Features Or Phase Defects On Photomasks For Optical Lithography Is Described. The Asymmetric Imaging Behavior Through Focus Of Defects Or Features With A Phase Other Than 0 Deg Or 180 Deg Is Used To Distinguish Them From Other Features On The Mask. The Mask Is Inspected At Equally Spaced Positions About An Optimum Focus In Both Positive And Negative Directions. The Images Are Subtracted From One Another To Produce A Differential Image Of The Mask. While Opaque Features As Well As Transmitting Features At 0 Deg And 180 Deg Behave Identically At Positive And Negative Defocus, Thus Leading To A Zero-Valued Differential Image, The Focus Asymmetry Of Phase Defects And Features Produces A Non-Zero Differential Image From Which These Phase Defects And Features Can Be Located. By Comparing The Locations On The Mask For Which A Non-Zero Differential Image Is Obtained With The Designed Data For The Mask, The Phase Defects Can Be Sorted From The Phase Features And The Absence Of Phase Features Can Be Detected. Additional Image Processing Can Be Applied To Verify The Integrity Of The Phase Features. The Differential Image Inspection Technique Can Be Implemented On Existing Optical Inspection Tools By Employing A Two-Pass Inspection Performed At Positive And Negative Defocus In Sequence. In Addition, A New Apparatus With Parallel Inspection Optics Is Described For Inspecting The Mask At Positive And Negative Focus Simultaneously.
Patent Number: US6327033B1
Application Number: US1999336445A
Inventor: Ferguson, Richard A. | Wong, Alfred K.
Priority Date: 21 Jun 1999
Priority Number: US6327033B1
Application Date: 21 Jun 1999
Publication Date: 4 Dec 2001
IPC Current: G01N0021956 | G03F000130 | G03F000184 | G03F000126
US Class: 356394
Assignee Applicant: International Business Machines Corporationmonk
Title: Detection of phase defects on photomasks by differential imaging
Usefulness: Detection of phase defects on photomasks by differential imaging
Summary: For detecting phase defects and other phase features on a photomask using differential imaging used in integrated circuit manufacture.
Novelty: Phase defects detection method for integrated circuit manufacture, involves collecting photomask images at multiple focal planes positioned in positive and negative directions about optimum focus position
Electronics
Circuit Design
Hong Kong
