Upload
lenard-cole
View
236
Download
0
Tags:
Embed Size (px)
Citation preview
Taklimat UniMAP
Universiti Malaysia Perlis
WAFER FABRICATION
Hasnizah Aris, 2008
Lecture 4
Photolithography
Taklimat UniMAP
Universiti Malaysia Perlis
WAFER FABRICATION
Hasnizah Aris, 2008
Introduction
The aim is to produce the features on the
mask with the highest possible resolution
using photoresist onto the wafer surface.
Taklimat UniMAP
Universiti Malaysia Perlis
WAFER FABRICATION
Hasnizah Aris, 2008
Photolithography Process Steps
1. Dehydration Bake
2. HMDS Priming and Cool Down Wafer
3. Photoresist Coating
4. Softbake
5. Align and Expose
6. Post Exposure Bake and Cool Down Wafer
7. Photoresist Development
8. Hardbake
Taklimat UniMAP
Universiti Malaysia Perlis
WAFER FABRICATION
Hasnizah Aris, 2008
Step 1: Dehydration bake
• To remove moisture from the wafer surface
• Moisture on wafer surface reduces resist adhesion
• Wafer on an oxide surface will allow wet etchants to penetrate easily between the resist and the wafer surface
• Parameters : Temperature
Taklimat UniMAP
Universiti Malaysia Perlis
WAFER FABRICATION
Hasnizah Aris, 2008
Step 2: HMDS PRIME• To promote adhesion of the photoresist to the wafer
surface• Hexamethyldisilazane• Parameters:
1. Temperature
2. Time
Taklimat UniMAP
Universiti Malaysia Perlis
WAFER FABRICATION
Hasnizah Aris, 2008
Step 3: Cool plate• To cool down a wafer to the ambient
temperature after HMDS baking process and before resist coating process
• Parameters :
1. Cool down rate
2. Temperature uniformity
3. Substrate temperature
Taklimat UniMAP
Universiti Malaysia Perlis
WAFER FABRICATION
Hasnizah Aris, 2008
Step 4: PHOTORESIST COATING• To coat a resist onto the Si wafer for patterning with a required resist thickness and
uniformity• Parameters :
1. Resist viscosity2. Resist dispense method3. Resist dispense velocity4. Resist dispense volume5. Resist dispense time6. Nozzle position7. Spin speed8. Spread time9. Acceleration / deceleration10. Final spin speed11. Final spin time12. Chuck diameter13. Chuck vacuum14. Controlled exhaust15. Ambient atmosphere (RH & Temperature)16. Cup ambient (RH & Temperature)17. Wafer centering18. Machine and chuck leveling19. Resist temperature control
Taklimat UniMAP
Universiti Malaysia Perlis
WAFER FABRICATION
Hasnizah Aris, 2008
Step 5: SOFTBAKE• To remove a solvent from photoresist and activates
photoactive compound• To remove stress in the photoresist• To improve photoresist adhesion• Parameters
1. Type of heat transfer (Hot plate or convection)2. Temperature3. Temperature uniformity4. Time5. Exhaust6. Cool down rate
Taklimat UniMAP
Universiti Malaysia Perlis
WAFER FABRICATION
Hasnizah Aris, 2008
Step 6: Align and exposure
• Si wafer with a layer of photoresist on its top will be aligned to the mask and exposed to the UV light.
Taklimat UniMAP
Universiti Malaysia Perlis
WAFER FABRICATION
Hasnizah Aris, 2008
Step 7: POST EXPOSURE BAKE
– To reduce the effect of standing waves which occur during exposure
– To increase the resistance of the resist prior to the etching process
– Parameters :1. Type of plate (hot plate or convection oven)2. Temperature3. Temperature uniformity4. Time5. Exhaust6. Cool down rate
Taklimat UniMAP
Universiti Malaysia Perlis
WAFER FABRICATION
Hasnizah Aris, 2008
Step 8: Cool plate• To cool down a wafer to the ambient
temperature before development process
• Parameters :
1. Cool down rate
2. Temperature uniformity
3. Substrate temperature
Taklimat UniMAP
Universiti Malaysia Perlis
WAFER FABRICATION
Hasnizah Aris, 2008
Step 9: Development process– To remove area of resists that have been exposed/unexposed
to form a pattern– The development rate for positive resist much less than
negative resist– Parameters :
1. Development technique (Immersion/Spray/Puddle)2. Developer type (Metal Ion/metal ion free)3. Developer concentration4. Developer temperature5. Development time6. Carbon dioxide absorption7. Agitation8. Time between exposure and develop9. Time between develop and rinse10.Resist thickness11.Post exposure bake temperature12.Exposure energy
Taklimat UniMAP
Universiti Malaysia Perlis
WAFER FABRICATION
Hasnizah Aris, 2008
Step 10: Hardbake– To increase the resistance of the resist– To remove any residual solvent– Parameters :
1. Type of plate (conduction or convection)
2. Temperature
3. Temperature uniformity
4. Time
5. Exhaust
6. Cool down rate
Taklimat UniMAP
Universiti Malaysia Perlis
WAFER FABRICATION
Hasnizah Aris, 2008
Photolithography equipment: Exposure tools
Taklimat UniMAP
Universiti Malaysia Perlis
WAFER FABRICATION
Hasnizah Aris, 2008
Photolithography equipment: Printing methods
Taklimat UniMAP
Universiti Malaysia Perlis
WAFER FABRICATION
Hasnizah Aris, 2008
Taklimat UniMAP
Universiti Malaysia Perlis
WAFER FABRICATION
Hasnizah Aris, 2008
Taklimat UniMAP
Universiti Malaysia Perlis
WAFER FABRICATION
Hasnizah Aris, 2008
MASK
– A glass plate with a thin film of chromium
– Contain complete pattern for the whole wafer
– Same feature size on the wafer
– The pattern is transferred by using mask aligner
Taklimat UniMAP
Universiti Malaysia Perlis
WAFER FABRICATION
Hasnizah Aris, 2008
Taklimat UniMAP
Universiti Malaysia Perlis
WAFER FABRICATION
Hasnizah Aris, 2008
Taklimat UniMAP
Universiti Malaysia Perlis
WAFER FABRICATION
Hasnizah Aris, 2008
RETICLE– A glass plate with a thin film of
chromium
– Contains multiple image fields (two or three) and each field contains numerous die patterned
– Images on the reticles are protected by a pellicle
Taklimat UniMAP
Universiti Malaysia Perlis
WAFER FABRICATION
Hasnizah Aris, 2008
Reticle
Chrome Pattern
Quartz Substrate
Pellicle
Taklimat UniMAP
Universiti Malaysia Perlis
WAFER FABRICATION
Hasnizah Aris, 2008
Mask vs. ReticlesMask Reticles
Chrome glass has an image that covers the entire wafer
Chrome glass image covers only a part of the wafer
A mask normally transfers the image to the wafer surface in 1:1 ratio
A reticle has a larger image and feature size than image it projects on the wafer surface (usually with 4:1. 5:1 or 10:1 reduction ratios)
Exposure systems such as projection printers, proximity printers, and contact printers
Exposure systems need to expose several times to cover the whole wafer. The step and repeat processes need an exposure system called steppers.
Taklimat UniMAP
Universiti Malaysia Perlis
WAFER FABRICATION
Hasnizah Aris, 2008
Photoresist Components
Polymer• Phenol-formaldehyde• React when exposed to energy (Photosolublization)• Dark
Solvent• Vehide for polymers and sensitizers• Ethoxyethylacetate & methoxyethylacetate• -Determine the thickness of resist
Sensitizers• Control / modify chemical reaction
Taklimat UniMAP
Universiti Malaysia Perlis
WAFER FABRICATION
Hasnizah Aris, 2008
Photoresist Performance FactorsResolution• Smallest opening can be resolved in photoresistlayer• Positive resist > negative resist
Adhesion• Ability to adhere to the variety of surface• Negative resist > positive resist
Exposure Speed• The speed with which resist react to exposure• Negative resist > positive resist
Pinhole count• Pinhole increase –layer thickness decrease• Negative resist has fewer pinholes than negative photoresist
Taklimat UniMAP
Universiti Malaysia Perlis
WAFER FABRICATION
Hasnizah Aris, 2008
Negative PR vs. Positive PR
Taklimat UniMAP
Universiti Malaysia Perlis
WAFER FABRICATION
Hasnizah Aris, 2008
Storage and Handling of Photoresist
– Photoresist should be contained in the dark bottle
– Photoresist should be operated in the yellow or gold lighting area
– Photoresist must be stored under constant temperature condition
– Photoresist bottles should be tightly closed– Photoresist should be filtered before use