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Questions and Answers
What characterizes a chip scale package?
What characterizes a chip scale package?
Which of the following IC package types is solder-mounted and has no leads?
Which of the following IC package types is solder-mounted and has no leads?
In semiconductor chip fabrication, which step is crucial for ensuring the accuracy of the design before manufacturing?
In semiconductor chip fabrication, which step is crucial for ensuring the accuracy of the design before manufacturing?
What is the primary purpose of the masks used in the photolithography process?
What is the primary purpose of the masks used in the photolithography process?
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Which IC package type allows the maximum performance while conserving space on the chip surface?
Which IC package type allows the maximum performance while conserving space on the chip surface?
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What do multichip packages typically resemble?
What do multichip packages typically resemble?
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During the fabrication process, which rule is NOT commonly considered?
During the fabrication process, which rule is NOT commonly considered?
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What are pin-grid arrays primarily used for in terms of assembly?
What are pin-grid arrays primarily used for in terms of assembly?
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What is a primary disadvantage of ion implantation compared to diffusion?
What is a primary disadvantage of ion implantation compared to diffusion?
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What is the main aim of the diffusion process in IC fabrication?
What is the main aim of the diffusion process in IC fabrication?
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Which method is NOT commonly used for diffusion in silicon wafer doping?
Which method is NOT commonly used for diffusion in silicon wafer doping?
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What is a key benefit of ion implantation technology in semiconductor manufacturing?
What is a key benefit of ion implantation technology in semiconductor manufacturing?
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Which of the following statements is TRUE regarding ion implantation?
Which of the following statements is TRUE regarding ion implantation?
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Why is diffusion still used in certain applications despite the advantages of ion implantation?
Why is diffusion still used in certain applications despite the advantages of ion implantation?
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What happens to impurity atoms during the ion implantation process?
What happens to impurity atoms during the ion implantation process?
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In the context of semiconductor devices, how are regions for MOSFET transistors created?
In the context of semiconductor devices, how are regions for MOSFET transistors created?
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What is the purpose of the oxide layer in the fabrication process of the n-well?
What is the purpose of the oxide layer in the fabrication process of the n-well?
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Which method involves placing the wafer in a furnace with gas to add dopants?
Which method involves placing the wafer in a furnace with gas to add dopants?
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In the fabrication process, what occurs immediately after the photoresist is exposed to light?
In the fabrication process, what occurs immediately after the photoresist is exposed to light?
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What is used to strip away the remaining photoresist after the etching process?
What is used to strip away the remaining photoresist after the etching process?
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What characterizes the n-well after the etching and dopant implantation processes?
What characterizes the n-well after the etching and dopant implantation processes?
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What material are the transistor gates primarily made of in the cross-section process?
What material are the transistor gates primarily made of in the cross-section process?
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During the fabrication process, what is the role of high temperatures (900–1200 °C) in the wafer processing?
During the fabrication process, what is the role of high temperatures (900–1200 °C) in the wafer processing?
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What is the effect of lateral diffusion observed in the fabrication of the n-well?
What is the effect of lateral diffusion observed in the fabrication of the n-well?
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How are the nMOS and pMOS transistors connected in a typical cell design?
How are the nMOS and pMOS transistors connected in a typical cell design?
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What is the total height of a typical cell when including the separation space between it and adjacent structures?
What is the total height of a typical cell when including the separation space between it and adjacent structures?
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What factor increases the size of the cell in contemporary designs?
What factor increases the size of the cell in contemporary designs?
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Which layers are involved in bringing terminals into contact with gates in modern standard cells?
Which layers are involved in bringing terminals into contact with gates in modern standard cells?
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What is one design rule satisfied by the separation of adjacent gates?
What is one design rule satisfied by the separation of adjacent gates?
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What parameter, λ, characterizes the resolution of a manufacturing process?
What parameter, λ, characterizes the resolution of a manufacturing process?
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Why is it difficult to migrate from one manufacturing process to another?
Why is it difficult to migrate from one manufacturing process to another?
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What is the minimum width and spacing requirement for metal and diffusion in a layout with two metal layers in an n-well process?
What is the minimum width and spacing requirement for metal and diffusion in a layout with two metal layers in an n-well process?
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How must contacts be arranged in relation to adjacent layers in an n-well process?
How must contacts be arranged in relation to adjacent layers in an n-well process?
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What is the connection between feature size and λ in layout design?
What is the connection between feature size and λ in layout design?
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What is indicated by a feature size of 180 nm in a manufacturing process?
What is indicated by a feature size of 180 nm in a manufacturing process?
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Which of the following describes the MOSIS service?
Which of the following describes the MOSIS service?
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What is the minimum overlap required for polysilicon over diffusion where a transistor is desired?
What is the minimum overlap required for polysilicon over diffusion where a transistor is desired?
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What is the primary reason that pMOS transistors are designed to be wider than nMOS transistors?
What is the primary reason that pMOS transistors are designed to be wider than nMOS transistors?
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What layout rule is commonly used for standard cells in automated layout systems?
What layout rule is commonly used for standard cells in automated layout systems?
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What is the layout spacing between polysilicon and contacts?
What is the layout spacing between polysilicon and contacts?
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What is the main advantage of using short-channel transistors in digital systems?
What is the main advantage of using short-channel transistors in digital systems?
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In a standard inverter layout, how is the size of an nMOS transistor typically presented?
In a standard inverter layout, how is the size of an nMOS transistor typically presented?
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What do the horizontal strips in a standard cell layout typically consist of?
What do the horizontal strips in a standard cell layout typically consist of?
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What is the distance by which the N-well surrounds pMOS transistors?
What is the distance by which the N-well surrounds pMOS transistors?
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Which of the following describes the typical connection of power and ground lines in the layout?
Which of the following describes the typical connection of power and ground lines in the layout?
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Study Notes
Semiconductor Manufacturing Process
- Semiconductor fabrication is a crucial process
- Fabrication is based on CMOS technology
- CMOS transistors are fabricated on silicon wafers
- Silicon is economical, provides better conductivity, less noise, and easier formatting for MOSFET transistors
- Silicon is the base material for MOS fabrication
Step-by-Step Fabrication Process
- From silicon wafers to functional chips
- Wafer manufacturing is a crucial process in the semiconductor industry
- Raw materials are processed to create thin, flat disks called wafers, which serve as the substrate for integrated circuits (ICs), sensors, and other microelectronic components.
- Wafer Manufacturing process includes: Raw Material Preparation (Si Ingot Production), Ingot Slicing, Wafer Polishing, and Wafer Cleaning
Oxidation
- Oxidation creates an oxide layer (SiO2)
- SiO2 (insulating layer) is used to control current flow, isolate components, and improve device performance
- Oxidation process uses an oxidation furnace at 900-1200 degrees Celsius with H2O or O2
- In bipolar and MOS transistors, SiO2 isolates one device from another
- Provides surface passivation
- Acts as a barrier or mask against the diffusion or implantation of impurity dopant in substrate
- SiO2 acts as a component in MOS devices
- Serves as a dielectric isolation between multilevel inter connect layers
- Different techniques to form SiO2 layer: Thermal Oxidation (used in IC fabrication, used when charge density level is low), Wet anodization, Vapor phase oxidation (also known as chemical vapor deposition, used in multilevel structures), Plasma oxidation
Lithography
- Lithography is the process of transferring patterns of geometric shapes from a mask to a thin layer of radiation-sensitive material (resist)
- Photolithography uses E-beam and includes various further steps such as
- Oxidation Layering
- Photoresist Coating
- Stepper Exposure
- Development and Bake
- Acid Etching, Spin, Rinse, and Dry
Photomask Design
- Photomask is a "master template" for IC design
- Masks come in different sizes, a common size is 6x6 inches
- They typically have quartz or glass substrate coated with opaque film, for more complex designs other materials are also used
- IC design is translated into file format, then a photomask is created in a photomask facility
- Masks are inserted into a lithography scanner, which applies light patterns through projection optics, to precisely pattern the wafer
Full Mask
- One layer equates to one mask
- Number of layers equals the number of masks
MLM (Multiple Layers per Mask)
- Layers are applied to one mask
- Reduces the number of masks used
Etching
- Etching removes unusual materials from the wafer using chemicals or plasma, performed after lithography
- Two types:
- Wet Etching: Selective material removal from a substrate using liquid etchants (acids, bases, or solvents)
- Dry Etching: Selective material removal using plasma (highly reactive gas)
Deposition
- Deposition deposits a blanket of materials onto a surface.
- Methods include selective deposition, atomic-layer deposition, chemical vapor deposition, and physical vapor deposition
- Choice of method depends on the process node, type of chip, and deposition time
- Conductive layers (poly-silicon, aluminum) and protective/insulating layers (silicon oxide) are deposited using CVD or PVD (high-temperature chamber).
- Deposition must be uniform throughout the wafer
Doping
- Ion implantation and diffusion introduce dopants into semiconductor materials
- Ion implantation: Bombards semiconductor wafers with high-energy dopant ions using electrical fields
- Applications: Used in advanced semiconductor devices (ICs) where precise doping is essential (e.g., CMOS technology)
- Diffusion: Places the semiconductor wafer in a furnace with dopant sources, like gases or solid dopants.
- Applications: Used in older semiconductor technologies where precise control of doping profiles is less critical
Diffusion vs. Ion Implantation
- Ion implantation: Precise dopant control, but damages the material and is expensive
- Diffusion: Simpler, inexpensive, but less control over dopant profile and more gradual doping
Diffusion
- Adding impurities to the silicon wafer to create regions for MOSFET transistors.
- The wafer is placed in a furnace with materials needed for N-well and P-well
- Aims to change the conductivity of silicon substrate over a depth
- Used in bipolar and MOS device technologies to form bases, emitters, and collectors, and source/drain regions in MOS devices
Ion Implantation
- Involves accelerating impurity ions to high velocity, injecting them into a single crystal substrate. This changes the electronic properties of the substrate.
- Dopant atoms are vaporized, accelerated, and directed at the silicon substrate
- Enters the crystal lattice, collides with silicon atoms, and gradually loses energy until coming to rest at a certain depth within the lattice
Metal Wiring
- Creates electrical connections between components on a semiconductor. Different parts of an integrated circuit (IC) can communicate
- Involves depositing, patterning, and etching metal layers using metal deposition, lithography techniques, and etching.
- Includes annealing (improves properties), testing to verify quality
- Critical process for semiconductor device performance and reliability
Wafer Dicing
- Cutting a silicon wafer into individual components known as dies or chips
- Enables manufacturers of integrated circuits (ICs) and other semiconductor devices to harvest many individual dice from a single wafer.
- Requires high-quality, high-precision machinery and skilled operators.
IC Packaging
- Protection of the semiconductor device from corrosion or physical damage, and for allowing mounting of electrical contacts to the printed circuit board (PCB).
- The last stage of semiconductor device production
- Package protects the internal components from external elements (like potential damage from the environment, as well as aging).
Common IC Package Types
- Pin-grid array(PGA): For socketing electrical connections
- Lead-frame and dual-inline packages (DIL): For assembling components where pins go through holes
- Chip scale package (CSP): Single-die, direct surface-mountable package, smaller than 1.2 times the die's area
- Quad flat pack (QFP): Leadless variety of lead-frame package
- Quad flat no-lead (QFN): Tiny package (size of a chip), for surface mounting
- Multichip package(MCP)/Multichip modules (MCMs): Integrates multiple ICs, discrete components, and dies onto a substrate to resemble a larger IC
- Area array package: Offers maximum performance with conserved space, allowing any part of the chip surface to be used for interconnection
Testing
- Testing functionality of fabricated semiconductor chips
- Following various rules and considerations during fabrication
- Design Rule Check (DRC)
- Scalable-Design Rule
- Micron-Rules Process
- Circuit-Under Test
- Packaging ICs Rules
- Cleanroom Environment
Fabrication Process: Inverter
- VLSI Fabrication sequence of steps.
- Involves a series of layers in chip, defined through photolithography
- Hypothetical set of six masks: n-well, polysilicon, n+ diffusion, p+ diffusion, contacts, and metal
- Masks specify the locations of the components
Inverter Cross-section
- Shows the regions of the inverter
- Components like n+ diffusion, p+ diffusion, polysilicon, and metal layers.
Fabrication Process: Inverter Mask Set
- Masks for the inverter's fabrication process are shown. Each section corresponds to a specific layer
- n-well, Polysilicon, n+ Diffusion, p+ Diffusion
Fabrication Process: Cross-sections while manufacturing the n-well
- Oxidation of the wafer substrate, before fabrication process, in a high temperature process
- Photoresist is spun onto the wafer, followed by the exposure and then removing the photoresist to reveal oxide (HF etching)
- Dopants are added via diffusion or implantation
Fabrication Process: Cross-sections while manufacturing polysilicon and n-diffusion
- Creating transistor gates from polycrystalline silicon (polysilicon).
- The polysilicon masks are used to determine the locations for the gates, atop thin gate oxides
- Processes to introduce n+ regions for the transistor's active area
- The protective oxide layer is stripped
Fabrication Process: Cross-sections while manufacturing p-diffusion, contacts, and metal
- Creating the p-diffusion mask to form the structure of Figure (a), followed by masking; also using oxide masking and etching
- Sputtering aluminum over the whole wafer to fill the contact cuts
- Using a metal mask to pattern the remaining metal layers
- Finally, the protective oxide is removed to complete the fabrication process.
Layout Design Rules
- Describes how small features are packed reliably.
- Often specified in microns, and scaling rules from one process to the next are challenging because rules do not always scale in the same way.
- Using the parameter lambda (λ), which is half the minimum drawn transistor channel length.
- Describes the minimum width and spacing for transistors, contacts, and polysilicon to avoid breaks in the process
- For example, an 180nm process uses design rules with λ = 0.09 μm
Layout Design Rules: Inverter
- PMOS transistors are often wider than nMOS transistors due to the slower movement of holes compared to electrons.
- Unit inverter layouts are often used with a larger pMOS transistor and a unit nMOS transistor
- In digital systems, transistor length is often minimized due to its positive correlation with speed, smaller sizes, and lower power consumption.
Gate Layouts
- "Line of diffusion” rule is commonly used for standard cells in automated layout systems.
- Four horizontal strips: metal ground, n-diffusion, p-diffusion, and metal power
- Power and ground lines, often called supply rails, are commonly vertically formed from polysilicon
- The transistors, and their appropriate connections, are made within the cell.
- Examples of an inverter layout with well and substrate taps are illustrated
Gate Layouts
- 3-input NAND gate transistors: nMOS transistors are connected in series, and pMOS transistors are in parallel
- Power/ground extends in the cell by 2λ
- Cell height is 36λ or 40λ
- Wire connections typically are from polysilicon to either top or bottom
- Cell layouts use 4λ transistors
Know More
- Videos for additional knowledge about MOSFETs and semiconductor industry
What to Learn Next
- Next topics to study
Reminder
- Prepare for participation in class.
Thank You for Listening
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Description
Explore the crucial steps of semiconductor fabrication based on CMOS technology, from silicon wafers to functional chips. Understand the importance of materials like silicon and the oxidation process in creating an effective oxide layer for device performance. This quiz will deepen your knowledge of semiconductor manufacturing techniques.
