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Questions and Answers
How are nMOS transistors connected in the described design?
How are nMOS transistors connected in the described design?
What is the total height of the cell when accounting for spacing requirements?
What is the total height of the cell when accounting for spacing requirements?
Which layer is generally not used as a routing layer in contemporary standard cells?
Which layer is generally not used as a routing layer in contemporary standard cells?
What is the width of the transistors used in the cell designs mentioned?
What is the width of the transistors used in the cell designs mentioned?
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What component allows free access to all terminals on metal routing layers?
What component allows free access to all terminals on metal routing layers?
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What is the primary material used in the fabrication of MOSFET transistors?
What is the primary material used in the fabrication of MOSFET transistors?
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What does the oxidation process create in the semiconductor manufacturing process?
What does the oxidation process create in the semiconductor manufacturing process?
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Which step is NOT part of the wafer manufacturing process?
Which step is NOT part of the wafer manufacturing process?
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Why is silicon chosen as the base material for semiconductor fabrication?
Why is silicon chosen as the base material for semiconductor fabrication?
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At what temperature range does the oxidation process typically occur?
At what temperature range does the oxidation process typically occur?
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What is one of the roles of the SiO2 layer created during oxidation?
What is one of the roles of the SiO2 layer created during oxidation?
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What is the final purpose of creating silicon wafers in semiconductor manufacturing?
What is the final purpose of creating silicon wafers in semiconductor manufacturing?
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Which of the following processes is involved in wafer manufacturing?
Which of the following processes is involved in wafer manufacturing?
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What is the initial step in the fabrication process of an inverter?
What is the initial step in the fabrication process of an inverter?
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What material is used to define the n-well during the fabrication process?
What material is used to define the n-well during the fabrication process?
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Which method involves accelerating dopant ions through an electric field?
Which method involves accelerating dopant ions through an electric field?
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What happens to the oxide layer after the n-well is formed?
What happens to the oxide layer after the n-well is formed?
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What occurs to the photoresist during the exposure process?
What occurs to the photoresist during the exposure process?
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What is formed over the thin layer of oxide in transistor gates?
What is formed over the thin layer of oxide in transistor gates?
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What does lateral diffusion cause during the n-well fabrication?
What does lateral diffusion cause during the n-well fabrication?
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Which acid is used to etch the oxide layer during n-well formation?
Which acid is used to etch the oxide layer during n-well formation?
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What process is used to grow the polysilicon layer?
What process is used to grow the polysilicon layer?
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What is the purpose of doping the polysilicon?
What is the purpose of doping the polysilicon?
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What characterizes the self-aligned process in transistor fabrication?
What characterizes the self-aligned process in transistor fabrication?
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What is the role of the protective oxide layer during the fabrication process?
What is the role of the protective oxide layer during the fabrication process?
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What material is used to fill the contact cuts after the p-diffusion process?
What material is used to fill the contact cuts after the p-diffusion process?
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What method has historically been used to form n+ regions?
What method has historically been used to form n+ regions?
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How is aluminum applied to the wafer during the fabrication process?
How is aluminum applied to the wafer during the fabrication process?
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What does the term 'n-diffusion' refer to in transistor fabrication?
What does the term 'n-diffusion' refer to in transistor fabrication?
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What is the primary technique used for forming a SiO2 layer in IC fabrication?
What is the primary technique used for forming a SiO2 layer in IC fabrication?
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Which step is not part of the photolithography process?
Which step is not part of the photolithography process?
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What is a photomask primarily used for in semiconductor manufacturing?
What is a photomask primarily used for in semiconductor manufacturing?
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Which of the following best describes the etching process in semiconductor fabrication?
Which of the following best describes the etching process in semiconductor fabrication?
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What material is commonly used as a substrate for photomasks?
What material is commonly used as a substrate for photomasks?
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What does the scanner do in the photomask lithography process?
What does the scanner do in the photomask lithography process?
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Which of the following processes uses E-beams in lithography?
Which of the following processes uses E-beams in lithography?
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What is the purpose of photoresist in the lithography process?
What is the purpose of photoresist in the lithography process?
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What is the recommended spacing between polysilicon and contacts?
What is the recommended spacing between polysilicon and contacts?
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Why are pMOS transistors typically wider than nMOS transistors?
Why are pMOS transistors typically wider than nMOS transistors?
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What does the 'minimum possible length' refer to in digital systems?
What does the 'minimum possible length' refer to in digital systems?
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What are the supply rails in the standard cell layout?
What are the supply rails in the standard cell layout?
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What is the function of metal wires in the gate layout of an inverter?
What is the function of metal wires in the gate layout of an inverter?
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How does a 3-input NAND gate differ from a standard inverter in layout?
How does a 3-input NAND gate differ from a standard inverter in layout?
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In a typical layout, what is the position of the n-diffusion layer?
In a typical layout, what is the position of the n-diffusion layer?
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What design rule involves the use of four horizontal strips in the layout?
What design rule involves the use of four horizontal strips in the layout?
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Study Notes
Semiconductor Manufacturing Process
- The fabrication of semiconductors is a crucial process
- CMOS technology is used for fabrication
- Silicon wafers are used as the base material
- Silicon is economical, provides better conductivity, less noise and ease of formatting the MOSFET structure.
Step-By-Step Fabrication Process
- Raw Material Preparation (Si Ingot Production)
- Ingot Slicing
- Wafer Polishing
- Wafer Cleaning
- Oxidation
- Photolithography
- Etching
- Electrical Die Sorting
- Metal wiring
- Deposition & Ion implantation
- Packaging
Oxidation
- Oxidation creates an oxide layer (SiO2) or insulating layer on the wafer
- It controls current flow, isolates components, and improves device performance
- An oxidation furnace is used at 900-1200 degrees Celsius with H2O or O2
- SiO2 isolates devices in bipolar and MOS transistors
- Provides surface passivation
- Acts as a barrier/mask against impurity dopant diffusion or implantation in substrates
- Acts as a component in MOS devices
- Serves as a dielectric isolation between multilevel inter connect layers
Different Oxidation Techniques
- Thermal Oxidation: Basic process used in IC fabrication, used when low charge density is required at the silicon-oxide interface
- Wet Oxidation
- Vapor Phase Oxidation
- Plasma Oxidation
Lithography
- Lithography transfers geometric patterns from a mask to a sensitive material (resist) on a semiconductor wafer.
- Photolithography uses E-beam to transfer patterns
- Oxidation Layering
- Photoresist Coating
- Stepper Exposure
- Development and Bake
- Acid Etching
Photomask Design
- A photomask is a master template for IC design
- Commonly 6x6 inches in size
- Quartz or glass substrate
- Uses opaque film
- Involves translating the IC design into a file format and creating a photomask in the photomask facility
Full Mask
- 1 layer --> 1 mask
- Number of layers equals number of masks
Etching
- Etching removes unwanted material from the wafer, following lithography.
- Wet etching uses liquid etchants (mixture of chemicals such as acids, bases, or solvents) to selectively remove material.
- Dry etching uses plasma (highly reactive, energetic gas) to selectively remove material.
Deposition
- Deposition adds a blanket of material onto a surface
- Multiple methods exist such as selective deposition, atomic-layer deposition, chemical vapor deposition, and physical vapor deposition.
- The method used depends on chip type and time needed for deposition
- Creates conductive layers for Poly-silicon and aluminum
- Creates insulation and protection layers such as SiO2
- Process done in a high-temperature chamber.
- Must be uniform across the wafer
Ion Implantation
- Introduces dopants into the semiconductor material.
- High-energy ions bombard the wafer to embed dopants.
- Essential in creating precise doping profiles, and important for modern high-speed electronics.
Diffusion
- Dopants diffuse into the semiconductor at high temperatures.
- Used in older technologies where precise control of doping profiles wasn't crucial.
- Used in conjunction with thermal oxidation for creating doped regions.
Diffusion vs. Ion Implantation
- Ion implantation provides precise dopant concentration and depth control, but can damage the material and is more costly.
- Diffusion provides less control over dopant profiles, but is simpler and less damaging.
Wafer Dicing
- Cuts a silicon wafer into individual chips (dies)
- Enables the production of integrated circuits and semiconductor devices.
- Requires high quality, high precision machinery and precise operator skill
IC Packaging
- The material that encases a semiconductor device
- Protects the device from corrosion, physical damage, and external elements.
- Ensures the mounting of electrical contacts
- The final stage in the semiconductor manufacturing process
Common IC Package Types
- Pin-grid array (for socketing)
- Lead-frame and dual-inline packages
- Chip scale package
- Quad flat pack
- Quad flat no-lead
- Multichip packages (multichip modules)
- Area array package
Testing
- Design Rule Check (DRC)
- Scalable Design Rule
- Micron-Rules Process
- Circuit-Under Test (CUT)
- Packaging ICs Rules
- Cleanroom Environment
Fabrication Process: Inverter
- A series of steps that create an inverter (using photolithography)
- Uses six masks: n-well, polysilicon, n+ diffusion, p+ diffusion, contacts, and metal.
Inverter Cross Section
- Shows the components of the inverter
- Shows n-well and substrate contacts.
IC Fabrication Process: Inverter Mask Set
- Diagram showing the different masks required for inverter fabrication.
Fabrication Process: Cross-Sections while Manufacturing the n-well
- Shows the stages in creating the n-well
- Describes the use of high-temperature oxidation and photoresist for masking.
- Includes a description of the etching process using hydrofluoric acid
- Depicts the use of a piranha etch for removing remaining photoresist.
Fabrication Process: Cross-sections while manufacturing polysilicon and n-diffusion
- Creates the gates; involves polycrystalline silicon which is generally referred to as polysilicon
- The process of creating a thin gate oxide layer and growing a polysilicon layer using chemical vapor deployment (CVD)
Fabrication Process: Cross-sections while manufacturing p-diffusion, contacts, and metal
- Involves masking, sputtering, and plasma etching processes to form p-diffusion, contact, and metallization.
- Shows the cross-sections for the p-diffusion mask creating the structure
Layout Design Rules
- Describes the features and how closely packaged in a manufacturing process
- Uses lambda (λ) as a parameter for scalability - This is typically half the minimum width of a transistor channel
- Feature size often used to describe a process
Layout Design Rules (continued)
- Describes minimum widths, spacing for metals and diffusions, transistor design parameters (W/L)
Layout Design Rules: Inverter
- Explains the different sizes of PMOS and NMOS used in the layout of the inverter circuit.
Gate Layouts
- Shows the "line of diffusion" rule for automated layout systems and supply and ground rails and transistor gate arrangements
Gate Layouts (continued)
- Provides specifics for various transistor configurations.
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Description
Explore the crucial steps involved in semiconductor fabrication, focusing on CMOS technology and silicon wafers. Learn about each step from raw material preparation to packaging, and understand the significance of processes like oxidation and photolithography in enhancing device performance.
