Substrates Used In Semiconductors

university wafer substrates

Flat Silicon Substates

A PhD candidate requested a quote for the following.

I am interested in purchasing some silicon wafers. My needs are relatively basic. I need cheap 4" wafers with 100 orientation and a good quality one-side polish primarily as a flat substrate. I do not want reclaimed wafers but am unfamiliar with the grades of silicon wafers. I have been using Prime grade wafers, but would like more information about Test grade and the other grades. I would prefer low dopant levels and higher resistivity but do not want to pay extra for high purity silicon. Please let me know what you have in stock that matches my needs.

Reference #99494 for specs and pricing.

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InN Layers on a Substrate

A Chemical Engineering professor requested a quote for the following.

Question:

Do you, by any chance, have any InN wafers or InN layers on a substrate?  We also might be able to use particulate inN if it is high enough quality.

Answer:

We can buy polycrystalline InN, of moderate purity, perhaps 99.99%, in powder form. I think that I quoted you prices.

I expect that it is possible to deposit a thin layer (about 1um) of InN by Electron Beam evaporation or a thicker layer, by sputtering, on a Sapphire substrate. The result would be a polycrystalline layer.
Presumably we can deposit InN as a compound, or we can try to synthesize during deposition from Ammonia and Indium Chloride, which might give a purer layer.
However, we have never done either of above processes. Perhaps we can undertake this as a project, on best effort basis, but you would have to budget at least $8,000.00 for the project. If this is within the scope of your inquiry, then we can try to work out details.

We do deposit, by MOCVD, GaN on Sapphire[C] substrates. The resultant film is monocrystalline albeit with EPD in the order of 1E7/cm2.
We can undertake to deposit InN on Sapphire[C], but chances are that the thickest that we could make the film is perhaps 20nm before the lattice mismatch would cause the film to crack. Such a trial would cost about $2,500.00.

InN like GaN, AlN and Sapphire form Wurtzite crystals, with a/c lattice distances as follows:
InN 3.545/5.703; GaN 3.189/5.185A; AlN 3.084/?; Sapphire 4.758/12.941.
I do not know exactly how GaN atoms arrange their lattice to grow on Sapphire with such an apparent mismatch.
However, I know that it is easier to grow AlN on Sapphire[C] than to grow GaN on Sapphire[C]. Looking at the lattice a parameter progression from AlN to GaN to InN, it is probable that it will be more difficult to grow InN than GaN. Still, if you are in a position to fund it, we can try to grow it.

Reference RFQ#109936  for specs and pricing.

 

What is a Substrate?

A substrate is the surface or material on which a process occurs or on which another material is deposited. In different scientific and industrial contexts, the term "substrate" can have specific meanings:

  1. In Biology: A substrate is the surface or medium on which an organism lives, grows, or obtains its Substrates used by the research communitynourishment. For example, the substrate could be soil for plants or agar in a petri dish for bacteria.

  2. In Chemistry: A substrate is the substance on which an enzyme acts. For example, in a chemical reaction, the substrate is the molecule that is modified by the enzyme.

  3. In Electronics: A substrate is the base material on which devices or circuits are built. For example, in semiconductor manufacturing, silicon wafers serve as the substrate on which integrated circuits are fabricated.

  4. In Materials Science: A substrate is the material onto which another material is applied. For instance, when growing thin films or nanomaterials like carbon nanotubes, the substrate is the material on which these films or structures are deposited.

In the context of carbon nanotube growth that you've been considering, the substrate is typically a solid material, like fused quartz, on which the nanotubes grow during the chemical vapor deposition (CVD) process.

Substrates Used in Biology

Glass or Plastic Coverslips (for Microscopy)
  • Type: Glass or plastic coverslips are often used in cell biology for imaging cells under a microscope.
  • Purpose: They serve as substrates for cells to adhere to and be observed under various microscopy techniques.
  • Common Forms: Circular or rectangular, typically ranging in size from 12 mm to 24 mm in diameter (for round coverslips).
  • Specs: Glass coverslips are usually pre-cleaned and may be coated with substances to enhance cell attachment (e.g., poly-L-lysine).

Substrates Used in Chemistry

In Material Science (Surface Chemistry and Thin Film Deposition):

a. Silicon Wafers:

b. Glass Substrates:

  • Type: Glass, especially borosilicate glass, is widely used in chemical reactions and as a substrate for coatings.
  • Purpose: Glass serves as a substrate in experiments involving optical coatings, surface reactions, and thin film studies.
  • Specs:
    • Thickness: Commonly ranges from 0.5 mm to 2 mm.
    • Surface Finish: Polished or unpolished depending on the application.
    • Coating: May be pre-coated with materials like indium tin oxide (ITO) for specific applications.

c. Metal Substrates (e.g., Gold, Platinum):

  • Type: Thin films or foils of metals such as gold (Au) and platinum (Pt).
  • Purpose: Used in surface chemistry for studies involving adsorption, catalysis, and electrochemistry.
  • Specs:
    • Thickness: Typically in the range of 100 nm to several micrometers for thin films.
    • Purity: High purity (99.99% or higher) to ensure consistent results in experiments.

These substrates are chosen based on the specific chemical processes or reactions being studied, and their specifications are critical to the success and reproducibility of experiments in chemistry.

Substrates Used in Electronics

In electronics, the most commonly used substrate is silicon, particularly in the manufacturing of semiconductors and integrated circuits. Here are the key details and specifications:

1. Silicon Wafers

Silicon wafers are the primary substrate used in the electronics industry, especially for fabricating microchips, transistors, and other semiconductor devices.

  • Material:

    • Type: Monocrystalline silicon.
    • Purity: Ultra-high purity silicon, typically 99.9999999% (9N) or higher, to minimize defects in semiconductor devices.

  • Size:

    • Common diameters:
      • 100 mm (4 inches)
      • 150 mm (6 inches)
      • 200 mm (8 inches)
      • 300 mm (12 inches)
    • Thickness: Varies by wafer diameter, typically between 525 µm and 775 µm.

  • Crystal Orientation:

    • Silicon wafers are cut along specific crystallographic planes, which are denoted by Miller indices. The most common orientations are:
      • (100): Preferred for most semiconductor applications due to its favorable electronic properties.
      • (111): Used in specific applications where different etching or growth properties are needed.

  • Doping Type:

    • N-type (doped with phosphorus, arsenic, or antimony): Adds electrons as charge carriers.
    • P-type (doped with boron or gallium): Adds holes (positive charge carriers).
    • Resistivity: Controlled by the level of doping, typically ranging from a few ohm-centimeters to thousands of ohm-centimeters depending on the application.

  • Surface Finish:

    • Polished: To achieve a mirror-like surface, which is crucial for photolithography in semiconductor manufacturing.
    • Unpolished (or as-cut): Used in less sensitive processes.
    • Epitaxial Layer: Some wafers have an additional epitaxial layer grown on the surface to create a nearly perfect silicon layer with fewer defects.

  • Flatness and Warp:

    • Specifications for flatness (total thickness variation or TTV) and warp are critical to ensure the wafer can be accurately processed in subsequent steps.
    • TTV: Typically within a few micrometers (e.g., <5 µm for advanced processes).

2. Alternative Substrates (for Specialized Applications)

  • Sapphire (Al2O3):

    • Used in applications like LEDs and RF (radio frequency) devices where silicon is not suitable.
    • Size: Typically smaller than silicon wafers, often in the range of 2 inches (50.8 mm) to 6 inches (150 mm).
    • Thickness: Generally around 430 µm to 500 µm for a 2-inch wafer.
    • Crystal Orientation: Often (0001) or c-plane orientation.

  • Silicon Carbide (SiC):

    • Used for high-power and high-temperature electronics.
    • Size: Typically 4 inches (100 mm) and 6 inches (150 mm) in diameter.
    • Thickness: Similar to silicon wafers, but can vary based on specific application requirements.
    • Crystal Orientation: (0001) orientation is common, similar to sapphire.

  • Gallium Nitride (GaN) on Silicon or Sapphire:

    • Used in high-frequency and high-power electronics.
    • Size: Often grown on silicon or sapphire substrates; sizes and specifications follow those of the base material.

3. Specialty Substrates

  • Glass Substrates:
    • Used in applications like LCD displays, sensors, and microelectromechanical systems (MEMS).
    • Size: Varies widely depending on the application, from small chips to large panels.
    • Thickness: Can range from a few hundred micrometers to several millimeters.

4. Packaging Substrates

  • Printed Circuit Boards (PCBs):
    • Material: Typically made from FR4, a composite material made of woven fiberglass cloth with an epoxy resin binder.
    • Thickness: Ranges from 0.8 mm to 3.2 mm for standard boards, with multi-layer boards being thicker.

Silicon wafers remain the most critical and widely used substrate in the electronics industry, especially in semiconductor manufacturing, due to their excellent electrical properties, well-established manufacturing processes, and compatibility with advanced microfabrication techniques.

Substrates Used In Materials Science

In materials science, the choice of substrate depends on the specific application, such as thin-film deposition, nanomaterial growth, or surface modification studies. The most commonly used substrates and their specifications in this field are:

1. Silicon Wafers

Silicon wafers are extensively used in materials science for a wide range of applications, from thin-film growth to nanostructure fabrication.

  • Material:

    • Type: Monocrystalline silicon.
    • Purity: High purity, often 99.9999999% (9N) or higher.

  • Size:

    • Diameter: Common sizes are 100 mm (4 inches), 150 mm (6 inches), 200 mm (8 inches), and 300 mm (12 inches).
    • Thickness: Typically 525 µm to 775 µm, depending on the wafer size.

  • Crystal Orientation:

    • (100) Orientation: Most common due to its favorable surface properties for many deposition techniques.
    • (111) Orientation: Used for specific applications like MEMS and certain types of epitaxial growth.

  • Doping Type:

    • Undoped (Intrinsic): Used when electrical conductivity is not desired.
    • Doped (N-type or P-type): Selected based on the intended application, with resistivity tailored by doping levels.

  • Surface Finish:

    • Polished: Essential for high-quality thin-film deposition.
    • Unpolished (As-cut): Used in applications where surface smoothness is less critical.

2. Glass Substrates

Glass is commonly used as a substrate in materials science, especially in applications involving optical coatings, sensors, and dielectric materials.

  • Material:

    • Type: Typically borosilicate glass or fused silica.

  • Size:

    • Dimensions: Available in a variety of sizes, often in square or rectangular shapes like 25 mm x 25 mm or 50 mm x 50 mm.
    • Thickness: Ranges from 0.5 mm to 2 mm.

  • Surface Finish:

    • Polished: Used for applications requiring optical clarity and smoothness.
    • Unpolished: Used where surface roughness is not a concern.

3. Metal Substrates

Metal substrates are used for various applications, including catalysis, surface studies, and as electrodes.

  • Common Materials:

    • Gold (Au): Used for its excellent conductivity and chemical inertness.
    • Platinum (Pt): Preferred for catalytic studies and electrochemical applications.
    • Copper (Cu): Commonly used in catalysis and as a growth substrate for graphene.

  • Size:

    • Thickness: Typically in the range of 100 nm to several micrometers for thin films. Foils are often available in thicknesses ranging from 25 µm to 250 µm.
    • Dimensions: Available in various shapes, often cut into small squares or discs (e.g., 10 mm x 10 mm or 25 mm diameter).

  • Surface Finish:

    • Polished: Ensures a smooth surface for high-quality thin films.
    • Roughened: Used in applications where surface area is more critical than smoothness.

4. Sapphire (Al2O3) Substrates

Sapphire is a popular substrate for epitaxial growth of materials like gallium nitride (GaN) for LEDs and other optoelectronic devices.

  • Material:

    • Type: Single-crystal sapphire.

  • Size:

    • Diameter: Typically 2 inches (50.8 mm) to 6 inches (150 mm).
    • Thickness: Typically around 430 µm to 500 µm for a 2-inch wafer.

  • Crystal Orientation:

    • C-plane (0001): Common orientation for epitaxial growth.
    • A-plane (11-20) and R-plane (1-102): Used for specific applications where different growth properties are desired.

5. Quartz (Fused Silica) Substrates

Quartz substrates are used in optical applications, thin-film deposition, and as a substrate for high-temperature processes.

  • Material:

  • Size:

    • Dimensions: Available in various sizes, commonly 25 mm x 25 mm or 50 mm x 50 mm.
    • Thickness: Typically between 0.5 mm and 1 mm.

  • Surface Finish:

    • Polished: Used for optical applications and thin-film growth.
    • Unpolished: Suitable for high-temperature applications where surface finish is less critical.

6. Polymer Substrates

Polymers are used as flexible substrates in applications like organic electronics, flexible displays, and wearable sensors.

  • Common Materials:

    • Polyethylene Terephthalate (PET): Widely used for flexible electronics.
    • Polyimide (PI): Known for its thermal stability, used in high-temperature applications.

  • Size:

    • Thickness: Typically between 50 µm and 200 µm.
    • Dimensions: Often provided in rolls or sheets, with varying widths.

  • Surface Treatment:

    • Coated: With materials like ITO (indium tin oxide) to provide conductive properties.
    • Surface Modified: To enhance adhesion of subsequent layers or to alter surface energy.

These substrates are selected based on the specific requirements of the materials science application, including thermal stability, surface smoothness, electrical properties, and compatibility with the materials being deposited or studied.