# US 7,611,610 B2 · Method and apparatus for controlling topographical variation on a milled cross-section of a structure > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,611,610 B2 - Document ID: US7611610B2 - Status: Granted - Kind: B2 - Application number: 10/716,181 - Filed: 2003-11-18 - Published: 2005-05-19 - Granted: 2009-11-03 - Earliest claimed: 2003-11-18 - Assignees: FEI Company - Inventors: James P. Nadeau; Pei Zou; Jason H. Arjavac - Web page: https://patentgrep.com/patent/US7611610B2 ## CPC - G11B 5/3163: {Fabrication methods or processes specially adapted for a particular head structure, e.g. using base layers for electroplating, using functional layers for masking, using energy or particle beams for shaping the structure or modifying the properties of the basic layers} - H01J 2237/3114: Machining - G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R) - H01J: ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS (spark-gaps H01T; electric arc lamps H05B31/00; particle accelerators H05H) ## Abstract An improved method of controlling topographical variations when milling a cross-section of a structure, which can be used to reduce topographical variation on a cross-section of a write-head in order to improve the accuracy of metrology applications. Topographical variation is reduced by using a protective layer that comprises a material having mill rates at higher incidence angles that closely approximate the mill rates of the structure at those higher incidence angles. Topographical variation can be intentionally introduced by using a protective layer that comprises a material having mill rates at higher incidence angles that do not closely approximate the mill rates of the structure at those higher incidence angles. ## Claims ### Claim 1 A method of exposing a planar cross-section of a structure composed of a first material, the method comprising: depositing a layer of a second material on said structure, said second material having mill rates at higher incidence angles that match the mill rates of the first material at those incidence angles; directing an ion beam at the structure; milling the structure in order to expose a cross-section of the structure thereby producing a uniformly planar face on said exposed cross-section. ### Claim 2 (depends on 1) The method of claim 1 in which said second material has mill rates at incidence angles greater than 75 degrees that match the mill rates of the first material at incidence angles greater than 75 degrees. ### Claim 3 (depends on 2) The method of claim 2 in which said second material has mill rates at incidence angles greater than 75 degrees that that are equal to or greater than the mill rates of the first material at incidence angles greater than 75 degrees. ### Claim 4 (depends on 1) The method of claim 1 in which said second material has mill rates at incidence angles greater than 45 degrees that match the mill rates of the first material at incidence angles greater than 45 degrees. ### Claim 5 (depends on 4) The method of claim 4 in which said second material has mill rates at incidence angles greater than 45 degrees that that are equal to or greater than the mill rates of the first material at incidence angles greater than 45 degrees. ### Claim 6 (depends on 1) The method of claim 1 in which said structure comprises a write-head for a magnetic disk system. ### Claim 7 (depends on 1) The method of claim 1 in which said first material comprises an alloy of Ni and Fe. ### Claim 8 (depends on 1) The method of claim 1 in which said second material comprises carbon. ### Claim 9 A method of measuring a dimension of a cross-section of a structure composed of a first material, the method comprising: depositing a layer of a second material on said structure, said second material having mill rates at higher incidence angles that matches the mill rates of the first material at those incidence angles; directing an ion beam at the structure in order to expose a planar cross-section of the structure and said layer of a second material; directing an electron beam at the planar cross section; determining the edge positions for the desired dimensions of the cross-section; and determining the distance between said edge positions. ### Claim 10 (depends on 9) The method of claim 9 in which said second material has mill rates at incidence angles greater than 75 degrees that matches the mill rates of the first material at incidence angles greater than 75 degrees. ### Claim 11 (depends on 10) The method of claim 10 in which said second material has mill rates at incidence angles greater than 45 degrees that are equal to or greater than the mill rates of the first material at incidence angles greater than 45 degrees. ### Claim 12 (depends on 9) The method of claim 9 in which said second material has mill rates at incidence angles greater than 45 degrees that matches the mill rates of the first material at incidence angles greater than 45 degrees. ### Claim 13 (depends on 12) The method of claim 12 in which said second material has mill rates at incidence angles greater than 45 degrees that are equal to or greater than the mill rates of the first material at incidence angles greater than 45 degrees. ### Claim 14 (depends on 9) The method of claim 9 in which said first material comprises an alloy of Ni and Fe. ### Claim 15 (depends on 9) The method of claim 9 in which said second material is carbon. ### Claim 16 (depends on 9) The method of claim 9 in which directing an ion beam at the structure in order to expose a planar cross-section of the structure and said layer of a second material, comprises focused ion beam milling. ### Claim 17 (depends on 9) The method of claim 9 in which determining the edge positions on cross-section comprises forming an image of said cross-section on an image forming device and applying an algorithm to assign an edge position based upon gray-level variations. ### Claim 18 A method of choosing a first material to be deposited as a protective layer on a structure composed of a second material prior to milling in order to control topological variation of a cross-section of said structure, the method comprising: determining whether a planar or non-planar cross-section topography is desired; determining the approximate mill rate of the second material at higher incidence angles; if a planar cross-section is desired, selecting a first material from known materials having a mill rate at higher incidence angles that match the mill rates of the first material at those incidence angles; and if a non-planar cross-section is desired, selecting a first material from known materials having a mill rate at higher incidence angles that does not match the mill rates of the first material at those incidence angles. ### Claim 19 (depends on 18) The method of claim 18 in which a planar cross-section is desired and in which selecting a first material from known materials comprises selecting a first material having mill rates at incidence angles greater than 75 degrees that match the mill rates of the first material at incidence angles greater than 75 degrees. ### Claim 20 (depends on 19) The method of claim 19 in which selecting a first material from known materials comprises selecting a first material having mill rates at incidence angles greater than 75 degrees that are equal to or greater than the mill rates of said second material at incidence angles greater than 75 degrees. ### Claim 21 (depends on 18) The method of claim 18 in which a planar cross-section is desired and in which selecting a first material from known materials comprises selecting a first material having mill rates at incidence angles greater than 45 degrees that match the mill rates of the first material at incidence angles greater than 45 degrees. ### Claim 22 (depends on 21) The method of claim 21 in which selecting a first material from known materials comprises selecting a first material having mill rates at incidence angles greater than 45 degrees that are equal to or greater than the mill rates of said second material at incidence angles greater than 45 degrees. ### Claim 23 (depends on 18) The method of claim 18 in which selecting a first material from known materials comprises: selecting a preliminary group of materials from known materials with mill rates at higher incidence angles that match the mill rates of said second material at higher incidence angles; determining the electron emission coefficient of said second material; determining the electron emission coefficient of each selected preliminary material; and selecting from said preliminary group, an appropriate first material having the greatest relative difference in electron emission coefficient as compared to said second material. ### Claim 24 (depends on 23) The method of claim 23 in which selecting a first material from known materials comprises selecting a first material having mill rates at incidence angles greater than 45 degrees that match the mill rates of the second material at incidence angles greater than 45 degrees. ### Claim 25 (depends on 23) The method of claim 23 in which selecting a first material from known materials comprises selecting a first material having mill rates at incidence angles greater than 75 degrees that match the mill rates of the second material at incidence angles greater than 75 degrees. ### Claim 26 (depends on 18) The method of claim 18 in which a non-planar cross-section is desired and in which selecting a first material from known materials comprises selecting a first material having mill rates at incidence angles greater than 45 degrees that do not match the mill rates of the first material at incidence angles greater than 45 degrees. ### Claim 27 (depends on 18) The method of claim 18 in which a non-planar cross-section is desired and in which selecting a first material from known materials comprises selecting a first material having mill rates at incidence angles greater than 75 degrees that do not match the mill rates of the first material at incidence angles greater than 75 degrees. ### Claim 28 (depends on 26) The method of claim 26 in which the desired cross-section topography comprises a recessed cross-section face. ### Claim 29 (depends on 28) The method of claim 28 in which selecting a first material from known materials comprises selecting a first material having mill rates at incidence angles greater than 45 degrees that are that are substantially lower than the mill rates of said second material at incidence angles greater than 45 degrees. ### Claim 30 (depends on 28) The method of claim 28 in which selecting a first material from known materials comprises selecting a first material having mill rates at incidence angles greater than 75 degrees that are that are substantially lower than the mill rates of said second material at incidence angles greater than 75 degrees.