17 Resists 10

17 Resists 10 - Resists This lecture covers the pattern...

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So far we have been concerned with layer deposition, i.e., z-axis features - Now we’ll deal with x,y ! Same concept has driven lithography for 40 years Resists This lecture covers the pattern transfer materials, photoresists , used in lithography…
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Circuit design layout Create mask Image Replicate onto resist Create device/circuit feature Overall transfer scheme Pattern generation Photolithography Etch, implant, etc. Decompose into layers You should be familiar with this
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Basic lithography process Thermal oxide on silicon Silicon wafer Spin photoresist UV light Mask/reticle Developed pattern Etch oxide Remove resist Positive resist Negative resist
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0.01 0.1 1 10 100 1960 1970 1980 1990 2000 2010 2020 Year CD (microns) Lithography as a technology driver Note: It has taken about 7 generations of equipment to achieve this effect We could not achieve any shrink in CD without advancements in lithography!
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Lithography goals: Print images on whole wafer Minimum CD Overlay < 0.2 CD Good uniformity of CD ( ± 10%) High wafer throughput Repeatable (24x7x52) High reliability Good matching between machines Allow for circuit topography Maintain cleanliness Pattern transfer = Lithography + Etch
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Photoresist requirements Good adhesion to many surfaces Sensitivity tuned to one wavelength High sensitivity, high contrast High purity Long shelf-life Low cost of ALL materials Uniform thickness across wafer Uniform exposure through resist Resistant to acids, plasmas, ions Easily removed etc. Mask Resist Oxide Silicon
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1. Matrix Provides mechanical and chemical stability 2. Sensitizer or photo- active compound (PAC) Determines exposure effect 3. Solvent Determines viscosity for spin coating and thickness uniformity Three basic components of all resists
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Positive resist components 1. Matrix: “Novolac” - Low molecular weight (1000 - 3000) resin - Good chemical barrier (important since it will be used as an etch barrier) Reminder - positive resist will give a positive image of the features on the mask – dissolves when exposed to light
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2. Sensitizer or photo active compound (PAC): DNQ (Diazonaphthaquinone) - Insoluble in aqueous solutions - 1:1 resin : PAC mix is also insoluble - Hydrolysis occurs on exposure carboxylic acid - Resin + acid is soluble in base Positive resist components
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17 Resists 10 - Resists This lecture covers the pattern...

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