Please enable JavaScript.

Coggle requires JavaScript to display documents.

Preparation of Semiconductor (Bulk Growth), Czochralski, Float Zone…

- - - - 1.Starting material: silicon dioxide for SI, gallium and arsenide for GaAs
        2.Single crystal grown from chemical process, distillation and reduction for SI, synthesis for GaAs
        3.Formation of wafer through etching and polished
        
        SI
        
        1.Start from pure sand(silicon dioxide), or known as quartzite.
        2.The silicon dioxide place together with different kind of carbon. overall reaction : SiC+SiO2 = Si+SiO+CO
        
        The silicon is then pulverized and react with hydrogen chloride HCI to form trichlorosilane(SiHCl3)
        Si+ 3HCI = SiHCI +H2
        
        The trichlorosilane (SiHCI3) is then undergo reduction to form EGS (electronic grade silicon)
        SiHCI3+H2=Si+3HCI
        
        EGS is then ready for preparation of single crystal silicon
        
        GaAs
        
        Starting materials are pure gallium and arsenide.
        
        Due to different vapor pressure of gallium and arsenide with GaAs, synthesis method is required for the preparation of GaAs
        
        Arsenic has much higher vapor pressure at the melting point of GaAsTherefore, an evacuated quartz tube system with two different temperatures is used for the synthesis process.
        
        High purity of arsenic is placed inside the graphite boat and heated to around 600+ ℃, high purity of gallium is placed in another graphite boat and heated to around 1200+ ℃.
        
        This will produce an overpressure of arsenic and arsenic can transport to gallium melt and hence formation of GaAs.
- - - - CZ - FZ
        
        • Both CZ and FZ methods are suitable to produce crystals with single -elements. For example, they are able to produce Si and Ge crystals but not compound-based crystals.
        
        • Both methods use vertical melting of crystal.
        
        • Both crystals that are produced by these two methods will create a cylindrical-shaped crystal that can be sawed to produce wafers.
      - CZ - LCZ
        
        • Both methods use the technique of pulling crystal ingot from the crucible rotating in opposite directions relative to the crucible.
        
        • CZ and LCZ contain the same impurity types in the crystal which are oxygen and carbon.
        
        • Each method allows the addition of dopant pellets in the molten if extrinsic semiconductors are needed.
      - CZ - BS
        
        • Each method uses a crucible to produce the crystals.
        
        • Similar to the CZ method, BS employs a crystal growth from melt.
        
        • Similar to the CZ method, BS can produce single crystals.
      - FZ - LCZ
        
        • Both methods have the ability to produce single crystals.
        
        • Both methods use vertical melting of the crystal similar to the comparison between CZ – FZ.
        
        • Again, similar to CZ – FZ comparison, both crystals that are produced by these two methods will create a cylindrical-shaped crystal that can be sawed to produce wafers.
      - FZ-BS
        
        • Both of these have a similar crystal production direction, that is the vertical direction.
        • FZ produces cylindrical-shaped crystal boules. This is also seen in the vertical direction of the BS method.
      - LCZ - BS
        
        • Both methods can be used to produce compound crystals.
        
        • Both methods employ a crucible though, in BS, it is referred to as a boat.
        
        • Similar to LCZ and CZ methods, BS employs a crystal growth from melt-through pulling.
  - - - CZ - FZ
        
        • Even though both of these methods produce single-element crystals, the FZ method produces better quality crystals as compared to the CZ method in terms of purity.
        
        • FZ does not use a crucible while CZ uses a silica-fused crucible.
        
        • The melting process differs. In CZ, the molten stays in the crucible stationary while the ingot is pulled out. On the other hand, FZ uses an RF coil to move the molten from bottom to top.
      - CZ -LCZ
        
        • Since the melting temperature for each element differs, therefore the pressure will differ as well. In the LCZ method, the net pressure will be different as compared to the CZ method.
        
        • In LCZ, there is an additional layer called the liquid encapsulate that covers the molten. This is not found in the traditional CZ method.
        
        • Even though both methods share the same name but LCZ is a modified version of CZ. LCZ is able to produce compound crystals while CZ cannot.
      - CZ - BS
        
        • In the CZ method, the method of producing a single crystal is done in a single direction, that is the vertical direction. However, in the BS method, there are two directions which are horizontal and vertical.
        
        • CZ method produces single crystals in cylindrical shape while in BS horizontal method, the crystal is D-shaped.
        
        • BS employs a moving boat through a temperature gradient. CZ has a stationary crucible with a non-existent adiabatic zone.
      - FZ - LCZ
        
        • FZ method can only produce single crystals while LCZ can produce compound crystals.
        
        • FZ does not employ a crucible but instead it uses an RF coil to move the molten. In LCZ, the molten remains stationary but rotated while the crystal ingot is pulled rotating opposite direction relative to the crucible.
      - FZ - BS
        
        • FZ can only produce single crystals while BS has the ability to produce compound crystals.
        
        • FZ has only one direction of crystal fabrication while BS has two.
        
        • FZ method produces better quality crystal as compared to the BS method in terms of purity.
        
        • BS has a temperature gradient to influence the molten state while FZ has an RF coil.
      - LCZ - BS
        
        • LCZ has only one distinct shape of crystal growth while BS has two which are D-shaped if a horizontal direction is used and cylindrical shaped in the vertical direction.
        
        • The wastage of crystals in BS is more prominent (40% of the crystal is lost due to sawing and cutting process).
- - - - Liquid Encapsulated Czochralski
        
        Crystal growth process used to produce high-quality Compound Crystal semiconductor materials.
        
        The process involves growing a crystal from a melt using the Czochralski process, but with the added step of encapsulating the melt in a layer of liquid that serves as a thermal and chemical barrier.
        
        Preparation of the starting material: This typically involves melting a high-purity semiconductor compound material such as gallium
        arsenide (GaAs) in a crucible.
        
        Encapsulation of the melt: The melt is then encapsulated in a layer of liquid, which serves as a thermal and chemical barrier. This can be done using a variety of techniques, such as dipping a rod into the melt or using a slurry of particles suspended in a liquid.
        
        The liquid encapsulant is a molten boron trioxide (B2O3) layer about 1 cm thick.
        
        The molten B2O3 is inert to the GaAs surface and serves as a cap to cover the melt.
        
        Prevent vaporization of GaAs, since the pressure on its surface is higher than 1 atm (760 Torr)
        
        Coupled with inert gas over pressure.
        
        Silica crucible is replaced with a graphite crucible, because the B2O3 dissolves in silicon dioxide.
        
        Crystal growth: A seed crystal is then introduced into the melt and pulled out slowly while being rotated. As the crystal is pulled, it grows in a compound-crystal form. The rate at which the crystal is pulled and the temperature of the melt can be carefully controlled to achieve the desired properties in the resulting crystal.
      - Bridgman-Stockbarger
        
        Preparation of a seed crystal: A small piece of single crystal, called the seed crystal, is cut from a larger crystal of the same material. The seed crystal is usually polished to a mirror finish to ensure good contact with the melt.
        
        Preparation of the melt: The material to be grown into a single crystal is melted in a high-temperature furnace or induction heater. The melt is then cast into a cylindrical shape, called the boule.
        
        Crystal growth: The seed crystal is placed in contact with the surface of the melt in a "boat", and the boule is cooled slowly from the top down. As the melt solidifies, the atoms in the seed crystal will arrange themselves in a crystalline pattern, and the resulting crystal will be a single crystal with the same crystalline structure as the seed crystal.
        
        Bridgman technique
        
        Relatively uncontrolled gradient produced at the exit of the furnace
        
        Boat is kept stationary when furnace temperature is temporally varied
        
        Stockbarger technique
        
        Better in control over the temperature gradient
        
        By utilize baffle, or shelf, separating two coupled furnaces with temperatures above and below the freezing point.
        
        Pulling the boat through a temperature gradient to grow the crystal.
        
        Annealing: Once the crystal has been grown, it is usually annealed, or heated to a high temperature and then cooled slowly via passing the melted crystal through the temperature gradient, to reduce defects and improve its mechanical and electrical properties.
        
        Cutting and polishing: The crystal is then cut and polished into the desired shape and size for the intended application.
        
        Widely used to produce compound crystals such as GaAs
        
        The Bridgman-Stockbarger technique was developed in the early 20th century by Percy Williams Bridgman, an American physicist who was awarded the Nobel Prize in Physics in 1946, and his student, Charles Stockbarger. Bridgman and Stockbarger published their work on the technique in 1922, and it has since been widely used in the production of single crystals of various materials.
        
        Geometry
        
        Horizontal
        
        Form D-shaped crystal
        
        Easiest approach
        
        High crystalline quality
        
        Crystal experiences free to expand during the entire growth process due to lower stress due to the free surface on the top of the melt.
        
        Vertical
        
        Crystals form in circular shape
        
        Crystal experiences strees due to gravity
- - - - The size and quality of crystals grown are limited by the effects of gravity on earth
      - The low gravity environment opens possibilities in containerlesw processing
        
        Due to the reduction of gravity effect and natural convection
      - The important properties
        
        Radiation heat transfer between heater and sample surface is important
        
        If material is transparent, the internal radiation is important
        
        Materials grown by FZ method have high melting temperature
        
        Conduction is always present
        
        Convection in melt induced by driving forces
        
        surface tension gradient
        
        due to temperature difference along free surface induced by heating
        
        due to concentration differences along free surface if dopants are added to the sample
        
        centrifugal force if zone is rotated
        
        buoyancy due to the gravutationa; force
  - - - Disadvantages
        
        Using vessel to hold the molten materials, so the contamination will be introduced by dissolving materials from a vessel wall
      - Finite element is developed to get a converged curved solid - liquid interface between a feed rod/melt /single crystal