Epi-Ready Substrates

university wafer substrates

What is The Differences Between Mirror Polishing and Epi Ready?

A Renewable Energy Laboratory Engineer asked the following:


Would you be able to give me some insight to the silicon wafer processing differences between mirror polishing and EPI ready.  My understanding is that mirrored is just a nitric etch and EPI is CMP processed.  Is that correct and is the CMP higher quality?  How much better?  Any info you could provide would be great. 


Epi-Ready means that the surface is in a condition such the a monocrystalline Epi layer can be successfully grown on it. This implies that surface roughness is in the order of 1nm and the surface is free of dust particles and metal contamination. Long range measure of surface uniformity, such as TTV or TIR is is is moderate, such as TTV<10µm. It is achieved by CMP polishing.

Optical polish means that it reflects light without significant distortion. This implies surface roughness less than half wavelength of visible light, so less than 150nm. A few small scratches or pits can be tolerated. This can be achieved by a Bright acid etch or low quality CMP polish or grinding or lapping with very small grain size abrasive. For Optical mirrors or lenses, the long range measure of surface uniformity, such as TTV or TIR can be very demanding, such as TTV<0.1µm.

Reference #224848 for specs and pricing.

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What Does Epi-Ready Mean?

Epitaxy is the process of depositing highly controlled silicon-based crystalline films, a critical process epi-ready silicon substratetechnology for creating advanced transistors and memory devices as well as wafer manufacturing. In semiconductor fabrication, epitaxial growth can be used to create a perfect crystalline foundation layer on which to build a semiconductor device, or to deposit a crystalline film with engineered electrical properties, or even alter mechanical attributes of an underlayer to generate compressive or tensile strain in the device’s lattice. Applied’s epi technology provides high-quality wafer substrates for these applications with processes that include optical and X-ray inspection, AFM surface characterization, triple crystal X-ray diffraction, SEM and TEM material characterisation.

In the semiconductor industry, the term "epi-ready" refers to a substrate wafer that is prepared and primed for epitaxial growth. Essentially, the wafer's surface is meticulously cleaned and made free of contaminants, oxides, and other impurities, ensuring that it's suitable for the deposition of a high-quality epitaxial layer.

Here's a bit more detail:

  1. Surface Smoothness: The surface of an epi-ready wafer is typically polished to a very smooth finish, ensuring that any epitaxial layer grown on it will be uniform and defect-free.

  2. Contamination-Free: The wafer undergoes rigorous cleaning processes to ensure the removal of any foreign particles, residues, or oxides. Any contaminants can adversely affect the quality of the epitaxial layer, leading to defects that might compromise the performance of devices manufactured from the wafer.

  3. Specific Orientations: Wafers can be cut in specific crystallographic orientations (like (100) or (111) for silicon wafers). An epi-ready wafer is often specified by its orientation, as this can influence the properties and behavior of the epitaxially grown layer.

  4. Desired Electrical Properties: An epi-ready wafer can also be doped to have certain electrical properties, serving as the starting point for creating semiconductor devices with specific characteristics.

In summary, when a wafer is described as "epi-ready" in the semiconductor industry, it indicates that the wafer is prepped and in optimal condition for epitaxial deposition, ensuring the subsequent growth process will yield the desired results.

Epi-Ready Substrates

In the semiconductor industry, epi-ready substrates are used for growth of crystalline thin films. These substrates are made of a single semiconductor material with a uniform structure that allows the deposition of various dopants on them. The result is a high-performance semiconductor device. The epitaxial process is a popular method for making photonics and radio-frequency (RF) semiconductor devices. UniversityWafer offers epi-ready silicon wafers that are ideal for forming these types of devices.

Sapphire epi-wafers are a monocrystalline, high-purity substrate that can be used for a wide range of applications. They have a flat surface, are resistant to heat, and are chemically stable. They can be used in a variety of ways, including as a substrate for LEDs and solar cells. They also provide excellent optical properties.

The 6H-SiC substrate is an ideal platform for growing GaN epitaxial layers by MBE, MOCVD, and sandwich sublimation techniques. This is due to the fact that the 6H-SiC substrate has a good lattice match with GaN. This enables the epitaxial layer to be grown with less strain on the interface, which is an important step in minimizing defects and enhancing performance.

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Epi-ready wafers

Epi-ready wafers are used for forming semiconductor devices. These wafers undergo strict electrical, chemical, and mechanical specifications before they can be used for manufacturing semiconductors. They are also subjected to epitaxial growth, a process that involves depositing a thin layer of single-crystal silicon over a base wafer through chemical vapor deposition. The result is an enlarged disintegration voltage across the wafer, which helps increase device performance.

Epitaxial growth is used for a wide variety of applications, including photonics and radio-frequency semiconductor components. In addition, it can be used to manufacture high-efficiency and lightweight solar cells. In order to produce these epi-ready wafers, a base wafer is first coated with silicon oxide. After the wafer is polished and cleaned, it is ready for epitaxial growth.

The deterioration of an epi-ready GaAs substrate can be slowed by storing the wafer at different temperatures. In this study, bare and GaAs epi-ready wafers were stored at 200 degrees Celsius, room temperature, and -20 degrees Celsius for up to 2 years. The surface morphology of these wafers was assessed using atomic force microscopy AFM. The results showed that the bare GaAs epi-ready wafer had a flat surface with a root mean square roughness of 0.02 nm. However, the surface of the re-grown GaAs was observed to have a much higher root mean square roughness and etch residues with dot shapes.

What Substrates Can Be Made Epi-Ready?

There are many substrates that can be made "epi-ready" or ready for epitaxial growth. Here's a list of some common ones, although the exact choice depends on the specific application:

Silicon (Si)

The most common substrate in the semiconductor industry due to its excellent semiconductor properties.

A Phd candidate requested the following quote:

Can you please provide a suitable alternate for SUMCO Epitaxial Wafer P/N V1609123. Please see specs below: Struct : P/P+ Dia 200 Orient <100> Type P+ Dopant BO Res 0.0110-0.0155 Thick 710-740 EPI1: PBO 8.8-11.2 4.9-5.1 If so, please provide a quote.

UniversityWafer, Inc. Quoted:

8" Silicon Wafer, EPI ready Prime
Thickness: 725+/-25um
Surface: SSP

Reference #255773 for specs and pricing.

Germanium (Ge)

Often used in high-speed electronics and optoelectronics.

A nanotechnology researcher requested a quote for the following:

I am interested in this product I found on your website: ID 1927, germanium wafers 100mm diameter, Orientation: <100> 6° towards <111> ± 0.5°. I have one question: are those substrate epi-ready polished?

I would like to know if you have an idea of possible contamination on the surface.

I would like to make sure of the flat orientation, is it along 100 or 110 ?. Those wafers have the orientation <100> 6° towards <111> ± 0.5°.

Reference #267112 for specs and pricing.

Gallium Arsenide (GaAs)

Used in applications that require high electron mobility, like high-frequency and fast electronics.

A technical instructor at a major university requested the following quote:

We’re looking for a wafer of epi-ready Gallium Arsenide.

We would like to receive a wafer in the next few weeks to see if it works for us and aren’t sure what is in stock and has good pricing since we don’t need high performance wafers.

50mm diameter would be plenty. We would like one side polished and the other side unpolished. We would like for it to be undoped. Whatever thickness you have in stock is probably fine. Polycrystalline would be fine, or crystalline is also fine.

We would prefer undoped but can tolerate some doping if they’re more available, we just want to be able to see the optical band gap.

Quantity of 1-5 is plenty, if you have a minimum order please let us know!

Our specs are really just that it has an optical bandgap we can see in our spectrophotometer. The mobility, resistivity, and other specs shouldn’t matter so whatever is the lowest cost is fine for us. We would prefer undoped to get cleaner results but even doped wafers should show us what we are looking for.

UniversityWafer, Inc. Quoted:

50.8mm, gaas, undoped, (100), 350um, single side polished, resistivity>1E7 ohm.cm, mobility>4000 ohm.cm

Reference #240822 for specs and pricing.

Gallium Nitride (GaN)

Commonly used in LEDs, laser diodes, and high-power electronics.

A graduate student requested the following quote:

Please provide price and lead time for 4pcs of the following. Basic description: 100mm / 4” freestanding n-type GaN substrate, qty 4 Details: 100mm / 4” diameter freestanding GaN substrate, prime/production grade c-plane, miscut between 0.3 and 0.7 degrees towards m Minimum 400um thickness Bow < 30um (0002) and (10-12) XRD rocking curve FWHM < 100 arcsec Dislocation density < 2x106 cm-2 uniformly/randomly distributed (i.e. not periodic) n-type doped, electron concentration minimum 1x1018 cm-3 Single-side polished, Ga-face epi ready – roughness < 1nm RMS No through-wafer holes/pits/micropipes

UniversityWafer, Inc. Quoted:

4'' epi-ready freestanding n-type GaN substrate wafer
Basic description: 100mm / 4” freestanding n-type GaN substrate, qty 4
100mm / 4” diameter freestanding GaN substrate, prime/production grade
c-plane, miscut between 0.5 degrees towards m
Minimum 400um thickness
Bow < 30um
(0002) and (10-12) XRD rocking curve FWHM < 100 arcsec
Dislocation density < 2x106 cm-2 uniformly/randomly distributed (i.e. not periodic)
n-type doped, electron concentration minimum 1x1018 cm-3
Single-side polished, Ga-face epi ready – roughness < 1nm RMS
No through-wafer holes/pits/micropipes

Reference #265567 for specs and pricing.

Gallium Phopshide (GaP): Gallium Phosphide is a semiconductor material used in optoelectronic devices such as LED light bulbs, where it's often used to produce green light. It's also used in the creation of semiconductor wafers. As with the other materials listed previously, making a GaP substrate "epi-ready" involves polishing and cleaning the substrate surface to ensure it is ready for the epitaxial growth of another layer of material. The resulting "epi-ready" GaP substrates can then be used in various applications such as microelectronics, optoelectronics, and photovoltaics.

A Postdoctoral Associate requested the following quote:

I was wondering if you have GaP wafers in stock. Below is the spec that I need. GaP (100), on-axis (<2deg offcut also works), 2-inch, SSP, epi-ready, thickness 300-700um, qty of 2-3. Doping doesn't matter. 

UniversityWafer, Inc. Quoted:

Item# H228 : n-type GaP:S [100] 2" 460 P/E ITME >0.115(4.8-5.7)E17 >115 <5E4 US Flats; Epi

Reference #260186 for specs and pricing.

Indium Phosphide (InP)

Often used in high-speed electronics and optoelectronics.

A university researcher requested a quote for the following:

I'd like to ask for quotation for epi-ready undoped Indium Phosphide wafers. The specs are shown below. 1. Specs : undoped InP / [100] / 2" / 350um / SSP Qty : 1 2. Specs : undoped InP / [111] / 2" / 350um / SSP Qty : 1 Also, if it is possible to get 4" wafers for both specs, please include it in the quotation.

Reference #256599 for specs and pricing

Silicon Carbide (SiC)

Used in high-power, high-temperature, and high-frequency applications.

A postdoc requeted the followng quote:

I am writing to know whether you can provide epi-ready SiC wafers with specifications in the attachment. Quantity will be 10~15 pieces each.

UniversityWafer, Inc. Quoted:

4H-SIC, n typem Research grade
Diameter 100.0mm, MPD: N/A
Orientation: On-axis
Resistivity: 0.013-2.000 ohm-cm
Double side polish, Si face CMP, epi ready

4H-SIC, n type Research grade
Diameter 100.0mm, MPD: <1/cm2
Orientation: 4 off-axis
Resistivity: 0.015-0.028 ohm-cm
Double side polish, Si face CMP, epi ready

Reference #221033 for specs and pricing.

Sapphire (Al2O3)

Typically used as a substrate for the growth of materials for blue LEDs, laser diodes, and other optical devices.

A Postdoc requested the following:

Hello, I am interested in buying Epi-ready c-cut and r-cut sapphire 50.8mm DSP any thickness. Can you help me out? 

UniversityWafer, Inc. Quoted:

Sapphire Wafer
2", 430um, DSP, C cut

Sapphire Wafer
2", 430um, DSP, C cut

Reference #270426 for more specs and pricing.

Indium Antimonide (InSb)

Commonly used in infrared detectors and other optoelectronic devices.

Cadmium Telluride (CdTe)

Used in photovoltaic applications and infrared optical windows.

A senior Epitaxy Engineer requested a quote for the following:

I'm looking for CdTe(100) epi-ready substrates: 1) 10 pieces of CdTe(100), undoped, 5x5x1.0mm single side polished 2) 5 pieces of CdTe(100), undoped, 10x10x1.0mm single side polished Could you please specify what are the structural properties of the substrates and the quality (roughness) of the surface. Could you please send me a quote for the expected pieces.

Reference #259336 for specs and pricing.

Zinc Oxide (ZnO)

Used in transparent conducting oxides and piezoelectric devices.

Remember that the epi-ready preparation process varies depending on the substrate material. The substrate must be carefully cleaned and treated to remove any dust, oils, and other contaminants that could interfere with the epitaxial growth process. This often involves a combination of chemical and physical treatments.