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VLSI System Design LEC3.1 CMOS FABRICATION REVIEW
Engr. Anees ul Husnain ( ) Department of Computer Systems Engineering, College of Engineering & Technology, IUB
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A review up till now… Cross Sectional views of a transistor
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Fabricating one transistor
Oxidation (Field oxide) Silicon substrate Silicon dioxide oxygen Photoresist Develop oxide Coating photoresist Mask-Wafer Alignment and Exposure Mask UV light Exposed exposed Polysilicon Deposition polysilicon Silane gas Dopant gas Oxidation (Gate oxide) gate oxide oxygen Photoresist Remove oxide RF Power Ionized oxygen gas Oxide Etch photoresist Ionized CF4 gas Mask and Etch Ionized CCl4 gas poly gate G S D Active Regions top nitride silicon nitride Nitride Deposition Contact holes Etch Ion Implantation resist ox Scanning ion beam Metal Deposition and Etch drain Metal contacts
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Top view
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Wafer preparation
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Start with P substrate Start Target structure
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1. Spin Resist Coating Target structure
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2. Expose N Well Mask to UV light
Target structure
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3. Develop resist Target structure
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4. Implant N Well Target structure
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Anneal wafer to diffuses N well (heal lattice) and grow new oxide layer
Target structure
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5. Remove Resist Target structure
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Remove oxide from anneal
Target structure
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1. Spin Resist Target structure
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2. Expose resist with active diffusion mask
Target structure
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3. Develop resist Target structure
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4. Grow oxide on exposed surface
Target structure
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5. Strip resist Target structure
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Grown thin oxide over silicon surfaces
Target structure
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1. Deposit poly using Chemical Vapor Deposition (CVD)
Target structure
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2. Spin resist 3. expose resist using the GATE mask 4. develop resist 5. etch poly
Target structure
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Remove thin oxide layer where exposed
Target structure
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1. Spin resist 2. expose with P implant mask 3. develop resist 4
1. Spin resist 2. expose with P implant mask 3. develop resist 4. implant P 5. strip resist Target structure
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1. Spin resist 2. expose with N implant mask 3. develop resist 4
1. Spin resist 2. expose with N implant mask 3. develop resist 4. implant N 5. strip resist Target structure
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Remove resist – anneal wafer – oxide etch
Target structure
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Grow oxide 1. spin resist 2. expose Contact mask 3. develop resist 4
Grow oxide 1. spin resist 2. expose Contact mask 3. develop resist 4. etch contacts 5. strip resist Target structure
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1. Deposit metal L1 2. spin resist 3. expose metal L1 mask 4
1. Deposit metal L1 2. spin resist 3. expose metal L1 mask 4. develop resist 5. etch metal 6. strip resist Target structure
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Rest of metal layers follow similarly
Target structure
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