PERPENDICULAR FILM HEAD PROCESSING PERSPECTIVES FOR AREAL DENSITY INCREASES

Transcription

1 PERPENDICULAR FILM HEAD PROCESSING PERSPECTIVES FOR AREAL DENSITY INCREASES R. E. Fontana, Jr., N. Robertson, M.C. Cyrille, J. Li, J. Katine San Jose Research Center Hitachi Global Storage Technologies San Jose, CA R. E. Fontana, Jr. Perpendicular Film Head Processing Perspectives for Areal Density Increases 1

2 Processing Overview As with any solid state device, lithography and patterning are the central challenges in forming memory cells or transducers Lithography Minimum feature size F Alignment control (3σ) 20% F Patterning Sensor and pole tip ion milling Sensor CMP R. E. Fontana, Jr. Perpendicular Film Head Processing Perspectives for Areal Density Increases 2

3 Some Observations Lithography: Recording head processing will track the traditional International Technology Roadmap for Semiconductors (ITRS) trends. It is doubtful that head lithography will exceed the IC roadmap goals for gate resist dimensions (i.e. isolated features). Patterning: Because of the isolated geometry of head structures (1 minimum feature per 0.3 mm²) head patterning for pole tips and sensors uses non mainstream IC techniques like ion milling and subtractive CMP pattern removal to form sensor and pole tip minimum features. Bit Aspect Ratio (BAR): Magnetic recording areal density improvements of 40% per year are required to match IC improvements in bit cell efficiency. For constant BAR an annual minimum feature reduction of 20% is required in comparison to IC roadmap reductions of 16%. It is unlikely that constant BAR can be sustained due to the thickness of sensor structures. This BAR issue, together with the inability to scale fly height, leads to hyper scaling in lithography (trackwidth) to sustain annual areal density increases. R. E. Fontana, Jr. Perpendicular Film Head Processing Perspectives for Areal Density Increases 3

4 The Head Structure The perpendicular head structure Trailing Shield Write Pole Tip MR Sensor ABS View Cross Section View R. E. Fontana, Jr. Perpendicular Film Head Processing Perspectives for Areal Density Increases 4

5 The Bit Cell Bit cell area = 4F²/BAR. F is MR sensor width and BAR is bit aspect ratio MR width 1.0 F Pole Width 1.6 F Guard Band 0.4 F Track Pitch 2.0 F Bit Length 0.5 Read Gap Bit Length 2F/BAR R. E. Fontana, Jr. Perpendicular Film Head Processing Perspectives for Areal Density Increases 5

6 The IC Environment IC minimum features, F, are printed on a 2F pitch (equal line and space) The smallest IC feature is the gate resist, about 0.6F, and printed on a 4F pitch In 2005 the ITRS expanded the concept of lithography nodes to set distinct roadmap goals to the main IC technologies of DRAM, Microprocessors, and FLASH. FLASH is now considering printing equal line and space lithography using 2 mask processing, i.e. 2 masks with minimum feature F printed on a 4F pitch and anticipating increase alignment capability of tools to create the equal line and space final structure R. E. Fontana, Jr. Perpendicular Film Head Processing Perspectives for Areal Density Increases 6

7 The IC Environment Feature and Alignment Comparisons (ITRS 2005) DRAM (F) 80 nm 70 nm 65 nm 57 nm 50 nm 45 nm μprocessor (F) 90 nm 78 nm 68 nm 59 nm 52 nm 45 nm FLASH (F) 76 nm 64 nm 57 nm 51 nm 45 nm 40 nm Isolated Gate 54 nm 48 nm 42 nm 38 nm 34 nm 30 nm Film Head Sensor¹ 110 nm 98 nm 82 nm 70 nm 51 nm 35 nm 3σ Alignment (IC) 15 nm 13 nm 11 nm 10 nm 9 nm 8 nm 1. Assumes 40% annual areal density with minimum bit length of 15 nm Workable solution exists Research solution exists No solution exists R. E. Fontana, Jr. Perpendicular Film Head Processing Perspectives for Areal Density Increases 7

8 IC Minimum Feature Landscape Gate resist dimension is ~ 60% of half pitch dimension Feature Size (nm) International Technology Roadmap for Semiconductors (ITRS) 11% to 16% annual reduction in feature size DRAM NAND Flash MPU Gate (resist) Gate (physical) Year R. E. Fontana, Jr. Perpendicular Film Head Processing Perspectives for Areal Density Increases 8

9 IC Minimum Feature Changing Landscape 4F Pitch Lithography Half pitch of metal 1 line in the IC industry has been defined as the minimum feature, F. This is the most difficult lithography step since equal line and space resist features are produced on a 2F pitch. The narrowest IC feature is the gate structure. This is a less difficult lithography step since isolated line resist features are produced on a 4F pitch. Example gate structures are ~ 60% of half pitch structures. In the future, half pitch structures with minimum feature F may be formed with two mask levels, each level having isolated feature F on a pitch of 4F. R. E. Fontana, Jr. Perpendicular Film Head Processing Perspectives for Areal Density Increases 9

10 Minimum Feature and Bit Aspect Ratio Bit Cell Area = 4 F² / BAR (130 Gbit/in² F = 100 nm with BAR =8) MR Width F Track Pitch 2F Bit Length 2F / BAR (25 nm) Read Gap 4F / BAR (50 nm) Read gap is limited by minimum sensor stack thickness to ~ 35 nm Cap 5 nm Free Layer 6 nm Cap Free layer TV Barrier 1 nm Barrier AP Pinned Layer 8 nm AP pinned layer AFM 9 nm AFM layer Underlayer 5 nm Underlayer BAR < 0.12 F / nm) F = 66 nm Maximum BAR = 8 F = 50 nm Maximum BAR = 6 F = 33 nm Maximum BAR = 4 R. E. Fontana, Jr. Perpendicular Film Head Processing Perspectives for Areal Density Increases 10

11 Areal Density and BAR and Minimum Feature Critical challenge to minimize hyper scaling of trackwidth is to sustain BAR in future areal density targets F BAR Areal Density Read Gap 100 nm Gb/in² 50 nm 100 nm Gb/in² 66 nm 80 nm Gb/in² 40 nm 80 nm Gb/in² 53 nm 60 nm Gb/in² 30 nm 60 nm Gb/in² 40 nm 40 nm Gb/in² 20 nm 40 nm Gb/in² 26 nm 40 nm Gb/in² 40 nm R. E. Fontana, Jr. Perpendicular Film Head Processing Perspectives for Areal Density Increases 11

12 IC and Head Minimum Features A convergence to gate resist dimensions with decreasing BAR Feature Size (nm) BAR = 8 BAR = 6 BAR = 4 DRAM NAND Flash Gate (resist) Gate (physical) Disk (40%) Year R. E. Fontana, Jr. Perpendicular Film Head Processing Perspectives for Areal Density Increases 12

13 Alignment Perpendicular heads require the control of the relative placement of the back edge of the trailing shield with the flair point of the pole tip yoke. The write head feature placements are referenced to the back edge of the read sensor Yoke flair point Trailing shield back edge MR stripe back edge R. E. Fontana, Jr. Perpendicular Film Head Processing Perspectives for Areal Density Increases 13

14 ITRS Alignment For IC technology 4F pitch lithography has placed a greater emphasis on alignment Perpendicular head technology has also placed a greater emphasis on alignment 3σ alignment is set at ~20% of DRAM half pitch or 0.2 F The ITRS data is a vector sum of x and y alignment. Head structure alignment favors one vector only σ ~ 10 nm or 9% of head critical feature σ ~ 6 nm or 13% of head critical feature DRAM (F) 80 nm 70 nm 65 nm 57 nm 50 nm 45 nm FLASH (F) 76 nm 64 nm 57 nm 51 nm 45 nm 40 nm Isolated Gate 54 nm 48 nm 42 nm 38 nm 34 nm 30 nm Film Head Sensor¹ 110 nm 98 nm 82 nm 70 nm 51 nm 35 nm 3σ Alignment (IC) 15 nm 13 nm 11 nm 10 nm 9 nm 8 nm R. E. Fontana, Jr. Perpendicular Film Head Processing Perspectives for Areal Density Increases 14

15 Patterning Pole tip processing for perpendicular recording has become more ion mill intensive than for a comparable longitudinal recording head Perpendicular thin pole tip material ~ 100 nm Longitudinal thick plated pole tip material ~ 1000 nm Perpendicular ion milling to form re-entrant feature Longitudinal ion milling to form a notch and to tune trackwidth Sensor processing has now evolved to intensive ion milling for tunnel structures and CMP for liftoff Patterning processes for sensor and pole tip formation are converging!! R. E. Fontana, Jr. Perpendicular Film Head Processing Perspectives for Areal Density Increases 15

16 Patterning Pole tip and sensor similarities (Drawings to scale) CMP surface 50 nm Top shield Top lead Sensor Hard bias filler Insulation Bottom shield Trailing shield Trailing shield gap Pole tip Insulation R. E. Fontana, Jr. Perpendicular Film Head Processing Perspectives for Areal Density Increases 16

17 Patterning CMP and ion milling are now used for forming TV and GMR sensors Image Resist CMP stop layer Sensor Ion mill Deposition: Hard magnet & Leads CMP stop layer CMP Removal CMP stop layers TEM cross section of a 100 nm RW sensor defined by CMP and DUV photo and ion milling (M.C. Cyrille, J. Katine, J.Li ) R. E. Fontana, Jr. Perpendicular Film Head Processing Perspectives for Areal Density Increases 17

18 CMP Sensor Processing Process extendibility with e-beam with 50 nm and 40 nm dimensions (M. C. Cyrille, J. Katine, J.Li) R. E. Fontana, Jr. Perpendicular Film Head Processing Perspectives for Areal Density Increases 18

19 Summary and Final Observations from a Process Person Minimum feature formation will track the ITRS roadmaps. Head dimensions will approach the gate resist dimensions at 500 Gbit/in² areal densities Alignment is becoming the critical process issue. Alignment is a key concern for the IC industry and tooling will target delivering 3σ alignment at 20% of minimum feature. Alignment is a vector quantity and perpendicular head alignments rely on one component of the vector, i.e. x and not x and y. NAND Flash is driving both alignment and minimum feature As sensor and pole tip thicknesses converge, patterning strategies practiced for the sensor are now being leveraged and utilized for pole tip formation. A Caution Total sensor thickness and spacing do not scale with areal density placing limits on constant BAR recording system designs. The net result is hyper scaling in TW reduction. The write head is becoming more complex. Need to have head designs consistent with ITRS roadmap and not exceed it. R. E. Fontana, Jr. Perpendicular Film Head Processing Perspectives for Areal Density Increases 19