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Questions and Answers
What is the main purpose of using gettering in semiconductor manufacturing?
What is the main purpose of using gettering in semiconductor manufacturing?
- To increase the size of silicon wafers
- To improve the thermal properties of the substrate
- To enhance the electrical conductivity of silicon
- To remove or deactivate undesired impurities (correct)
Which step in silicon purification involves treating metallurgical grade silicon with HCl?
Which step in silicon purification involves treating metallurgical grade silicon with HCl?
- Formation of chlorosilanes (correct)
- Melt above 1600 °C
- Grinding metallurgical grade silicon
- Silicon deposition on filament
What type of environment is critical for minimizing contaminations during semiconductor processing?
What type of environment is critical for minimizing contaminations during semiconductor processing?
- A cold environment to prevent oxidation
- A clean room with controlled temperature and humidity (correct)
- A vacuum environment with no air circulation
- An open environment with high humidity
What is the native oxide thickness in the RCA cleaning process?
What is the native oxide thickness in the RCA cleaning process?
What is a critical temperature threshold for the melting of silicon in its purification process?
What is a critical temperature threshold for the melting of silicon in its purification process?
What is the primary function of HEPA filters in a clean room?
What is the primary function of HEPA filters in a clean room?
In the purification process, what follows the production of chlorosilanes?
In the purification process, what follows the production of chlorosilanes?
Which component is an essential part of the Czochralsky technique in crystal development?
Which component is an essential part of the Czochralsky technique in crystal development?
What is the significance of a glossy floor in a clean room?
What is the significance of a glossy floor in a clean room?
What is the final purity level of silicon achieved through the purification process described?
What is the final purity level of silicon achieved through the purification process described?
Flashcards
Siemens Technique
Siemens Technique
A technique used to purify silicon for semiconductor manufacturing. It involves converting metallurgical grade silicon to chlorosilanes (SiClxHy) which are volatile, then depositing purified silicon on a heated filament. After weeks a high purity silicon (99.9999%) is obtained.
Czochralski Method
Czochralski Method
A method for growing single crystals of silicon. A seed crystal is dipped into molten silicon and slowly pulled up, while rotating, to control the crystal's growth.
Vacancy
Vacancy
A type of point defect in a crystal lattice where an atom is missing from its usual position.
Interstitial
Interstitial
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Clean Room
Clean Room
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RCA Cleaning
RCA Cleaning
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Gettering
Gettering
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Wafer Cleaning
Wafer Cleaning
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Silicon Wafer
Silicon Wafer
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Native Oxide
Native Oxide
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Study Notes
Introduction to Integrated Circuit Fabrication
- Integrated circuits (ICs) are complex electronic circuits fabricated on a single semiconductor substrate (typically silicon).
- Fabrication involves multiple steps including wafer production, purification, crystal growth, and device processing.
Silicon Crystal Structure
- Silicon crystals are characterized by a repeating unit cell in the x, y, and z directions.
- Silicon's basic structure is a diamond crystal structure
- Crystal planes and directions are defined using a coordinate system.
- Planes are identified by Miller indices.
Silicon Purification
- Silicon is purified from raw materials (like sand) using methods like the Siemens technique.
- Chlorosilanes (volatile compounds) are generated and subsequently treated to achieve high purity.
- Purification yields very high purity silicon (99.9999%).
Crystal Growth Techniques: Czochralski
- This technique is used to grow single-crystal silicon ingots.
- A seed crystal is dipped into a molten silicon pool and slowly withdrawn.
- Important control parameters include pull rate, melt temperature, and rotation rate.
Crystal Growth Techniques: Float Zone
- An alternative method for refining or growing single crystals.
- The process involves heating a rod of polysilicon in a high-frequency electromagnetic field, causing it to melt and reform.
Properties of Silicon Wafers
- Wafers are sliced from the ingot.
- Wafers are typically polished on one side.
- The initial wafers contain trace amounts of impurities and dopants (O, C, and others)
Dopant Incorporation and Crystal Defects
- Dopants are incorporated during crystal growth, but spatial variation can arise.
- Defects (point, line, and volume) exist in the crystal and usually reduce device performance.
Contamination Control
- Contamination control is critical for integrated circuit fabrication.
- This involves using 'clean rooms' with high air quality and other measures.
- RCA cleaning, a standard process, is used to remove organic, metal and alkali ions from wafers.
- Ultrasonication is used to mechanically remove contaminants.
Gettering
- Gettering is used to remove metal and alkali ions from device active regions (important for device performance).
- Gettering utilizes 'trap' sites in the wafer.
- There are intrinsic and extrinsic gettering methods.
- Heavy metals diffuse rapidly within silicon.
Moore's Law
- Moore's Law describes the observation that the number of transistors on integrated circuits doubles approximately every two years.
- This trend has driven significant advancements in computing technology.
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