1. IC工艺技术系列讲座 第二讲
PHOTOLITHOGRAPHY 光刻

2. 讲座提要 1. General 2. Facility (动力环境) 3. Mask (掩膜版)
4. Process step highlight (光刻工艺概述)
5. BCD 正胶工艺
6. History and 未来的光刻工艺

3. MASKING Process (光刻工艺)
1. General
MASKING Process (光刻工艺)
Photolithography (光学光刻) ----Transfer a temporary pattern (resist)
Defect control
Critical dimension control
Alignment accuracy
Cross section profile
Etch (腐蚀) ----Transfer a permanent pattern (Oxide, Nitride, Metal…)

4. 2.0 Facility requirement Temperature (温度) 70 oF Humidity (湿度) 45%
Positive pressure (正压) >0.02in/H2O
Particle control (微粒) Class 100
Vibration (震动)
Yellow light environment (黄光区)
DI water (去离子水) 17mhom
Compress air and Nitrogen (加压空气,氮气)
In house vacuum(真空管道)

5. 3.0 Mask (掩膜版) Design PG tape Mask making
Plate --- quartz, LE glass, Soda line glass
Coating --- Chrome, Ion oxide, Emulsion
Equipment --- E-beam, Pattern generator
Mask storage ---Anti static Box

6. Pellicle

7. Pellicle protection

8. 5. Develop inspection (显检)
4.0 光刻工艺概述
Prebake and HMDS (前烘)
Resist coating (涂胶)
EBR (去胶边), soft bake,
3. Exposure (曝光)
Alignment (校正)
4. Develop (显影)
Post e-bake, Hard bake, backside rinse
5. Develop inspection (显检)

9. 4.1 Prebake and HMDS treatment
Purpose of Pre-bake and HMDS treatment is to improve the resist adhesion on oxide wafer. HMDS is adhesion promoter especially designed for positive resist.
HMDS (Hexamethyldisilane) can be applied on the wafers by
1. Vapor in a bucket
2. vapor in a vacuum box
3. Directly dispense on wafer
4. YES system --- in a hot vacuum system
5. Vapor in a hot plate (with exhaust)
Too much HMDS will cause poor spin, vice versa will cause resist lifting

10. 4.2 Resist Coating (涂胶) Resist coating specification (指标）
Thickness（厚度）0.7u – 2.0u (3.0以上for Pad layer)
Uniformity（均匀度）+ 50A – +200A
Size of EBR （去胶边尺寸）
Particle（颗粒）<20 per wafer
Backside contamination(背后污染）
三个主要因数影响涂胶的结果
Resist Product (产品）
Viscosity （粘度）
Spinner Dispense method （涂胶方法）
Spinner speed (RPM) （转速）
Exhaust （排气）
Soft bake temperature （烘温）
Facility Temperature （室温）
Humility （湿度）

11. 4.2.1 Coater (涂胶机） Equipment module and special feature
Pre-bake and HMDS --- Hot/Cold plate
Resist dispense --- Resist pump
RPM accuracy --- Motor
EBR --- Top/bottom
Hot plate --- soft bake temperature accuracy
Exhaust
Waste collection
Temperature/Humidity control hood
Transfer system --- Particle and reliability
Process step and process program --- Flexible

12. 4.2.2 Coater (涂胶机）combination
SVG 8800
升降机 涂胶 热板
升降机
升降机 涂胶 热板 热板
升降机
升降机
HMDS 冷板 涂胶 热板 冷板
升降机
升降机
HMDS 冷板 涂胶 热板 热板 冷板
升降机
升降机 热板 冷板 显影 热板 热板 冷板
升降机

13. 4.2.3 Coater (涂胶机） Resist dispense methods
Static
Dynamic
Radial
Reverse radial
Resist pump (Volume control --- 2cc/wafer and dripping)
Barrel pump ---Tritek
Diaphragm pump --- Millipore
N2 pressure control pump --- IDL
Step motor control pump --- Cybot
size of dispense head

14. rpm (转速） and acceleration （加速）
Coater (涂胶机）
rpm (转速） and acceleration （加速）
Maximum speed --- Up to rpm
Stability --- day to day
Acceleration --- controllable number of steps
Reliability --- time to replacement
EBR (Edge bead removal)（清边）
Method --- Top EBR or Bottom EBR or Top and bottom EBR
Problem --- Dripping
Chemical ---- Acetone, EGMEA, PGMEA, ETHLY-LACTATE

15. Resist Type Negative resist Positive resist G-line i –line
reverse image
TAC --- top anti-reflective coating
BARLI --- bottom anti-reflective coating
Chemical amplification resist
X ray resist

16. Transfer a pattern from the mask (reticle) to resist
Exposure (曝光)
Transfer a pattern from the mask (reticle) to resist
Goal
1. Critical Dimension control (CD)条宽
2. Alignment 校准--- Mis-alignment, run in/out
3. Pattern distortion 图样变形--- Astigmatism
4. Cross section profile 侧面形貌--- side wall angle
5. Defect free无缺陷
Equipment/mask/resist selection
1. Resolution 分辨率--- Expose character, Light source (wavelength), N/A,
2. Auto-alignment skill 自动校准技术--- Light field, dark field, laser
3. Mask掩膜版--- e-beam master, sub-master, spot size, quartz plate, defect density, CD requirement
4. Resist selection 胶选择

17. 4.3.2 Exposure (曝光) Aligner Technology 1:1 1. Contact print (接触）
Soft contact, hard contact, proximity
2. Scanner (扫描）
3. Stepper (重复）
1X, 2X , 4X, 5X, 10X
4. Step – Scan (重复扫描)
4X --- reticle move, wafer move, reticle/wafer move
5. X ray (X光）
1:1
6. E-beam (电子束）--- Direct write

18. 4.3.3 Exposure (曝光) Contact print (接触）
1. Most of use for negative resist process --- for 5u process and can be push to 3u.
2. Positive resist can print smaller than 3u, and deepUV can push to 1u, but very high defect
3. Equipment:
--- Canon PLA 501
--- Cobilt
--- Kasper
--- K&S

19. Contact print ---Canon 501

20. Scanner (扫描） 4.3.4 Exposure (曝光)
1. Most of use for G –line Positive resist process --- for 3u process and can be push to 2u.
2. Negative resist can print smaller than 4u
3. Equipment:
--- Canon MPA 500, 600
--- Perkin Elmer 100, 200, 300, 600, 700, 900

21. PE 240 Scanner

22. Canon 600 Scanner

23. 4.3.5 Exposure (曝光) Stepper (重复）
1. G line positive resist --- for <0.8u process
2. i line positive resist --- <0.5u process
3. i line resist plus phase-shift mask --- can be pushed to 0.35
4. deepUV resist process u and below
5. Equipment:
--- Ultratech
--- Canon
--- Nikon
--- ASML

24. 4.3.6 Exposure (曝光) 6 ASML Stepper list Model Wavelength Resolution
ASML g 0.8
ASML 5000
ASML 5500 – 20,22,25,60,60B,80,80B i 0.55
ASML 5500 – 100,100C,100D,150 i 0.45
ASML 5000 – 200,200B,250,250B UV 0.35
ASML 5500 – 300,300B,C,D,TFH UV 0.25
ASML Step-Scan UV

25. 4.4.1 Develop (显影） Develop process 1. Post expose bake
2. Resist Develop
3. DI water rinse
4. Hard Bake
Develop equipment
1. Batch develop
2. Track develop　
Develop chemical
1. KOH
2. Metal free (TMAH) Tetramethylamoniahydroxide
3. Wetting agent --- with/without
4. Concentration %TMAH
Track develop method
1. Spray
2. Steam
3. Signal-Paddle
4. Double-Paddle

26. 4.4.2 Develop (显影） Develop Track
1. Temperature control water jacket for Develop line
2. Develop pump/develop pressure canister
3. Exhaust
4. Hot plate temperature control
5. Pre-wet --- process program

27. CD control in developing
1. Post bake process
2. Develop Time
3. Concentration of developer chemical (Higher fast)
4. Developer temperature (lower faster ~ 1o C/0.1u)
5. Develop recipe --- pre-wet, paddle, rotation
6. Age of the develop chemical
7. Rinse --- DI water pressure
8. Hard bake temperature

28. 4.5.1 Develop Inspection Tool for inspection 1. Microscope
Manually loading
Automatic loading
2. UV lamp
3. CD measurement equipment
Manually measuring system --- Vicker,
Automatic measuring system --- Nanoline
CD SEM

29. Inspection items 4.5.2 Develop Inspection 1. Layer name 2. Alignment
3. Run in/out
4. Pattern distortion
5. Pattern integrity
6. Defects
lifting, particle, discoloration, scumming, bridging, excess resist, scratch
7. CD (critical dimension)

30. Nanoline --- for CD measurement

31. Hitachi CD SEM

32. Leitz Microscope inspect station

33. Autoload UV inspection system

34. 5.0 BCD 正胶工艺 Resist coating Equipment SSI, SVG8800, SVG 90
Process step pre-bake/HMDS/cold plate
spin (<5000rpm) ---dynamic dispense
---top (bottom) side EBR(2mm)
soft bake (100oC)/cold/palte
Resist/spec Shipley (1.2u)
1818 (1.8u 1st metal)
6818 (2.4u 2nd metal)
6118 (2.9u Pad)
6124 (3.6u-4.5u ST)
Everlight 533(1.2)
Uniformity A
升降机
HMDS 冷板 涂胶 热板 冷板
升降机

35. SVG 90

36. SVG 8800

37. 5.1.1 Positive Resist (正胶） Component (成分） Manufacturing (制造商）
Resin （树脂）
Diazonaphthoquinone(DNQ)/novolak
Photo-sensitizer （感光剂）
Solvent （溶剂）
Dye （染料）
Manufacturing (制造商）
Kodak – Hunt – Ash chemical (USA)
TOK (Japan)
JSR (Japan)
Shipley (USA)
AZ (USA, Germany)
Sumitomo (Japan)
Everlight (Taiwan)

38. 5.1.2 Positive Resist (正胶） Product Name and feature (产品称与特性）
以everlight (永光）正胶为例
Product Series EPG 510 Series
Expose wavelength G-Line (435nm)
Thickness
Name rpm 5000rpm
Viscosity （粘度） EPG cp 1.25u 0.80u
EPG cp 2.00u 1.25u
EPG cp 3.25u 2.00u
EPG cp 4.50u 2.75u
EPG cp 9.00u 5.5u
Resolution (分辨率） 0.8u (0.55u --- the smallest)
Depth of Focus (聚焦深度）+ 1.4u (1.0u line/space)
Sensitivity (感光度） Eth = 60 mj/cm2
Eop = 90 mj/cm2

39. Select a positive resist
1. Resolution （分辨率）
2. Resist thickness --- Spin curve （厚度）
3. Photo speed (曝光速度)
4. Expose latitude (曝光宽容度)
5. Adhesion （粘附性）
6. Reflective notch （反射缺口）
6. Metallic content （金属含量）
7. Thermal stability （热稳定性）
8. Plasma resistance （抗腐蚀能力）
9. How easy to be removed （清除能力）
10. Price （價格）

40. Equipment 5.2 Expose Ultratech stepper 1100 – (6”)
Canon – (6”)
Perkin Elmer 240 – (4”)

41. Positive Resist reaction during expose

42. Positive Resist reaction during expose

43. 5.2.1 Ultratech Stepper Ultratech stepper G-line N/A --- 0.24 and 0.31
1:1 print ratio
3 X 5 inch reticle --- 3, 4, 5, 7 field
4u depth of focus
Blind step can be push to <5u (no spec)
Center of array < + 50u
Dark field alignment
Site by Site alignment
Alignment target
*oat --- 4mm X 4mm
*K/T u X 200u

44. Ultratech Stepper 1100

45. Ultratech Stepper 1500/1700

46. 5.2.2 Ultratch stepper specification

47. UTS---Reticle and Job file
Fiducials
Guide

48. UTS---primary lens

49. UTS Alignment Optic

50. Ulratech stepper site by site alignment

51. UT alignment procedure
Load job file into computer
Load reticle
　　　　Start
Ｆiducials alignment --- Guide, rotation(1500)
OAT alignment
OAT size = 4mmX4mm
Fast and slow scan 1000u
Side by side alignment
Key and target size 200uX200u
shot scan 20u
long scan 100u (80u)
Auto-focus
Goble or local
Failure alignment
Skip
Expose
Zmode

52. 5.3 Perkin Elmer aligner Micalign PE 100 Micalign PE 200, 220, 240
Micalign PE 300, 340, 340HT
Micalign PE 500
Micalign PE 600
Micalign PE 700
Micalign PE 900
Micscan 100
Micscan 200
Micscan 300
Micscan 400

53. PE 240 Specification

54. PE 240

55. PE 240 PM Facility Center of curvature Vibration from environment
Parallelism
Light intensity
Focus
Distortion
Mask/wafer centering
View optic
HPC rebuild
Cooling air flow rate
Vibration from HPC
Facility
Vibration from environment
Temperature control hood
Process
Reference wafer
Aperture selection
Resist build up on XYO pins
Roof mirror cleaning
Mask heat up during expose

56. PE --- Focus wedge mask

57. PE --- distortion

58. PE --- Projection optic

59. PE Mercury lamp

60. PE --- Adjustable slit

61. PE alignment procedure
Set scan
Load mask
Load wafer
Switch to mask
Use microscope and carriage movement to find the alignment mark on mask (Test die)
Move mask only to align the wafer
Switch to wafer
Move wafer align to mask

62. 5.4.1 Resist develop Equipment SSI, SVG8800, SVG 90
Process step pose-e bake/cold plate
develop --- double paddle
--- DI water rinse
--- back N2/rinse
hard bake ( oC)/cold/palte
Developer TMAH 2.35%
升降机 热板 冷板 显影 热板 冷板
升降机

63. SVG 8800

64. SVG 90

65. 5.4.2 Resist develop Equipment Develop sink
Equipment set up Temperature
N2 blanket
Filter size
Filter change
Developer TMAH 2.38%
Develop change
Process step
batch develop --- immerse (1’ & 15”)
QDR DI water rinse (8 cycles)
hard bake ( oC)/cold/palte

66. Will imprint technology replace photolithography?
6. History and 未来的光刻工艺
Will imprint technology replace photolithography?
In 1798, image was transferred by stone plate
1940, Bell Lab used resist developed by Eastman Kodak
1960, San Francisco bay area becomes the silicon valley --- AT &T, Raytheon, Fairchild, Negative resist – contact print process wildly was used.
End of 1970-early of 1980, positive resist – Projection print (Perkin Elmer Micalign) started to be used in production. Bay area became cloudy --- National, Intel and AMD. Outside bay area had Motolora, TI, IBM.
From 1970 to early 2000, the technology of semiconductor is developed very fast. The smallest feature size from 10u reduced to 0.09u u and 0.35u products were running mass production every where ---USA, Europe, Japan, Taiwan, Korea… i-line,and deepUV --- 5X stepper and step-scan (4X) aligner became the major tools.
Now, 0.09u technology become mature u, 0.045u and 0.035u technology are being developed. Immersion lithography and imprint technology will be used to print these nano feature.
Imprint technology claims that it is able to print 0.01u (10nm) --- It may be the future masking.

67. 6.1 History
Lithography, as used in the manufacture of the integrated circuit, is the process of transferring geometric shapes on a mask to the surface of a silicon wafer. These shapes make up the parts of the circuit, such as gate electrodes, contact windows, metal interconnections, and so on. Although most lithography techniques used today were developed in the past 40 years, the process was actually invented in 1798; in this first process, the pattern, or image, was transferred from a stone plate (the word litho comes from).
The first practical two dimensional device patterning on a silicon wafer was actually carried out in the late 1940s at the Bell Lab. At that time, polyvinylcinnamate, developed by Eastman Kodak, was used as a resist. However, device yields were low because of the poor adhesion of the polyvinylcinnamate to the silicon and oxide surface. The Kodak chemists then turned to a synthetic rubber based material---a partially cyclized isoprene and added a UV active sensitizer---a bis-aryl-azide into it to crosslink the rubber matrix and created a new class of photoresist material. Since the unexposed area of the new material was the only part of the polymer matrix that will dissolve in an organic solvent and yielding a negative image of the mask plate, therefore, the new material was then referred as the negative resist.
The cyclized rubber/bisazide resist was widely used in the contact printing age. However, the contact mode of printing created severe wear of the mask plate and the defect density of the photomask and the wafer was very high. The industry therefore decided to switch to contactless projection printing in 1972 for producing the 16k DRAM.
Projection printing, however, was carried out in the Fraunhoffer or the so called far field diffraction region and the aerial image was much poorer than the contact or proximity method of printing. In order to preserve the same quality of image structure, the contrast of the image material must be increased.

68. Lithographic lore has it that the diazonaphthoquinone/novolak resist (the term novolak is derived from the Swedish word lak, meaning lacquer or resin and prefixed by the Latin word novo, meaning new) made their way from the blue print paper industry to the microelectronic through family ties: at that times, the offices of Azoplate, the American outlet for Kalle printing plate, was located at Murray Hill, NJ, just across the street from the famous Bell Labs. The father of a technician at Azoplate worked as a technician at Bell Labs. Apparently the father had complained one day about the poor resolution quality of the solvent developed resist system used at the Bell Labs and the son had boasted the properties of the Azoplate DNQ/novolak material; anyway, one day the father took a bottle of the material with him to the Bell Labs, and the age of the DNQ/novolak resist began.
The new material was marketed by Azoplate under the trade name of AZ photoresist. It was always referred as the positive resist for a positive tone of image would be reproduced by the new material. The use of DNQ/novolak system increased rapidly after the introduction of the projection lithography. By 1980s, the DNQ resist had completely supplanted the old negative resist as the workhorse of the semiconductor industry in the high-end applications.
The DNQ/novolak resist has held sway for 6 device generations, from the introduction of the 16K DRAM to the large scale production of the 64M DRAM in 1994 to The success of such material was the indicative of it supreme performance and potential.
Today, it appears that it is not really the resolution which defines the limit of the DNQ/novolak resist application, but rather the loss in the depth of focus with the ever increasing NA of the stepper. Deep UV and chemical amplification negative tone resist slowly erode the market place of the DNQ/novolak resist. By the end of the 1990s, the DNQ/novolak resist was no longer be used in the technologically most advanced applications---the printing of the critical levels of the 256M DRAM.

69. Introduction of nanoimprint technology
6.2 Future
Introduction of nanoimprint technology
Fabricating microstructures and nanostructure is important in many fields of science and technology, including electronics, data storage, flexible displays, microelectromechanical systems, microfluidics, photonics and biosensors. Traditionally, optical or electron beam lithography systems are used to print the relevant structures. However, new printing methods such as imprint lithography and soft lithography have recently been explored in some detail to lower the costs of fabricating low volumes of structures with very small features and to increase the range of printing application.
The soft lithography schemes, in general, use a soft template pattern made of silicone elastomer, polydimethylsiloxane (PDMS), which is placed into contact with the substrate in a variety of ways, to pattern a surface film, to transfer a material, or for direct integration into the final part, with a range of innovative applications. Challenges in this area are generally concerned with the inherent limitations of the PDMS material including resolution limitations when curing due to differences in thermal expansion between the master and mold; adhesion to common master materials like silicon; significant time, about an hour, to fabricate a mold; elasticity of the mold, which may impact multilevel alignment; insolubility with common solvents; contamination issues and incompatibility with some organic materials.

70. The imprint methods utilize heat or UV curable liquids to mold patterns onto a substrate from a rigid template. Research groups have demonstrated sub-100nm resolution, some have down to 10nm. Imprint process; however, do not transfer materials from the template to the substrate like the soft lithography schemes. Another hesitation with the imprint technique concerns the lifetime of the master pattern. The problem is similar to that encountered in the contact photolithography, where it has been found that the defect free lifetime is only limited to less than 1000 passes, despite the application of coatings and lubricants. This concern arises from the important requirements that the substrate must undergo significant contact and removal forces, that a rigid master pattern is used and that a tool is required to achieve good imprints.
In Stanford University, a new class of high resolution pattern formation and materials transfer printing strategy has been developed. This new method is collectively referred to as molecular transfer lithography. The new approach is based on the room temperature fabrication of water soluble polymer templates by spin casting a polyvinyl alcohol film forming solution to replicate surface patterns. It is different than the imprint lithography and soft lithography by employing a water soluble template. The template dissolves at the conclusion of the image transfer, whereas in the alternative approaches, the template is reused. The use of the water soluble template for patterning microstructure and nanostructure features enables a true contact printing method wherein the master template does not actually contact the substrate and the possibility of substrate to mask damage is eliminated and the integrity of the master pattern is preserved during the replication process.