Substrates Used In Surface Chemistry Research

Flat Silicon Wafers for MEMS Surface Chemistry Development

A PhD candidate requested a quote for the following.

I've got a MEMS device that needs some surface chemistry development. Since the device surface is low-stress silicon nitride, and since it's pretty expensive, I'd like to do most of the chemistry experiments on other substrates. 

Therefore, my requirements are very simple -- I need a substrate that is flat, big enough to handle with a gloved hand (so, not too much smaller than the 1" diameter range), relatively smooth, and as inexpensive as possible.  The only stringent requirement is that the SiN layer be low stress grade, the kind that is used to make micromechanical devices. 

That will ensure that the stoichiometry and surface morphology are at least similar to the actual device to which I'll be applying what I develop.  Other than that, I'm pretty flexible, and can even use an array of different substrates that might be left over from previous runs.

Reference #97779 for specs and pricing.

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Cleavable Silicon Wafers For Surface Chemistry Application

A corporate scientist requested a quote for the following.

Looking for thick wafer 100mm or 150mm (100) SSP 500-1000um, cleavable into square pieces or surface chemistry application. Do you offer with amino or epoxy silane?

 I am looking for the cheapest 1000μm thick silicon wafer w/ native oxide that can be deiced into 1"x 3" pieces (Approximately 10 pieces) , so possibly 2 6" wafers diced with 7 pieces each. If you can think of or have a cheaper way to provide 1" x 3" pieces, that would work as well.

Reference #115246 for specs and pricing.

(111) Silicon for Surface Chemistry Testing

A graduate student requested a quote for the following.

Any diameter, (111) full range spanning 4 orders of magnitude, one at each magnitude 0.01, 1, 10, 100 500um SSP  minimum possible ca 10cm2 of each type. We want to test some surface chemistry on n and p type 111 wafers over a range of resistivities. We need 8 wafers (4 of each type) that have a difference in magnitude of resistivity between each wafer. If you have any broken wafers etc of these types they would be fine for us to do our tests before ordering the type that works best. 

Reference #120934 for specs and pricing.

Germanium Subtrates for Surface Chemistry Studies

A postdoctoral fellow requested a quote for the following.

I'm looking for (111) test grade 4 silicon wafers, one wafer each of p-type and n-type Germanium and Si.  I'm planning a purchase, but I'm not sure what's going to work for my surface chemistry, so I'd like to try out a couple before I purchase a bunch of wafers.  I'd just like a native oxide layer but the wafer themselves need to be probably as thick as possible (5mm or more) and at least 3" if not 4 or 5.

Reference #124156 for specs and pricing.

Thermal Oxide on Silicon Wafers for Surface Chemistry Experiments

A corporate scientist requested a quote for the following.

I am basically looking for a silicon wafer with an 100-200nm thermal oxide layer grown on it. I am planning on doing surface chemistry and ellipsometry. I am not doing any electronic measurements or anything, I am just looking for a controlled substrate that mimics the properties of glass.

Reference #147411 for specs and pricing.

Gallium Phosphide Substrates for Surface Experiments

A Ph.D. in Control Science and Engineering, requested the following quote.

I am looking for GaP wafer(approx. 600-1000nm thick) but I require it to be as smooth as possible (whatever that value is) since I am going to use it for some surface chemistry experiments. 

I want the thickness to be approximately 1 microns and resistivity to be
as low as possible. Furthermore, I wanted to know a couple of things:

1. What is the substrate on which the GaP is grown?
2. What is the roughness of the final substrate?

Reference #168863 for specs and pricing.

Surface Chemistry That Mimics Silicon Nitride AFM Tips

A Research Scientist studying soft matter materials requested the follwoing quote.

I'm looking for silicon nitride wafers whose surface chemistry would mimic that of silicon nitride AFM tips.  It looks like most offerings are silicon nitride coatings on top of silicon (or other wafer).  Is that the only option for a bulk silicon nitride surface?  Is it even possible to just make a wafer of silicon nitride?  Any info. You can provide is greatly appreciated.  

Reference #169284 for specs and pricing.

N-Type Silicon Wafers for Surface Chemistry

A graduate student requested the following quote.

I am a graduate and would like to request a quote for the following:
n-type Silicon wafer, single side polished, no doping. Also, I want to request quote for two different size:

1. Your smallest available and
2. 3 inch

I need Si wafer N-type, prefer no doping or Boron doping if you do not have undoped ones. 3 inch diameter and single side polished. I have not orientation preferences but want my wafers to be perfect, no scratches or broken ends. The end application is surface chemistry and hence I have no orientation or resistivity preferences.

Could you pls put together a quote for me and I can immediately call you to place the order.

I will appreciate your prompt response int his regard

Reference #170321 for specs and pricing.

Silicon Carbide Substrates for Surface Chemisry Experiments

A postdoc requested a qutoe for the following.

Looking for SiC wafers.  I am using these as test substrates for surface chemistry experiments, and I don't much care about doping, resistivity, etc.  (Or even if the wafers are whole.)  I suppose I'd prefer the beta (3C) if there is a choice, but it's really not that important.

Please let me know if you have anything, and if I can order small quantities.  You had some SiC advertised on sale in one of your recent emails.

Reference #91203 for specs and pricing.

Surface Chemistry Lab Setting

1 Micron Silicon Nitride to Perform Surface Chemistry

A postdoctoral scholar researchign integrated circuits requested a quote for the follwoing.

We would like to order 3 pieces of 6" p-type Silicon wafer with 1um SiN deposited on the top. The wafer thickness is not really important to us.  We only want a silicon wafer sufficiently thick that it can be handled and manipulated to perform surface chemistry.  So long as the wafer won't be excessively fragile, we can get a thinner wafer if it helps the price out.  

Reference #100082 for specs and pricing.

Single Crytal Quartz Wafers for Surface Chemistry Experiments

A bioengineering postdoc requested a quote for the following:

We are looking for the quartz with specific classification:

Single crystal quartz Defined surface plane (e.g., 100 surface) Data for surface chemistry (any surface chemistry data for the products we purchased?) Charge density information under aqueous solution conditions (e.g., DI-water or PBS buffer at PH=7.4) Please let us know if you have any products that can satisfy our requirements and quotation about this!

Reference #111162 for specs and pricing.

Undoped Silicon for Surface Chemistry

A Ph.D. postdoctoral fellow requested a quote for the following.

I would like to request a price quote for a cassette of Si wafers. We're looking for Si 100 with single- or double-side polish, any dopant, 4" silicon wafers of the cheapest grade you have. We're using these as basic substrates for surface chemistry. If you have undoped, that would also be desirable.

Reference #102304 for specs and pricing.

Sapphire Substrates for Surface Chemistry Research

A M.Sc requested a quote for the following.

I need the 150mm Sapphire wafers for surface chemistry study. We are cutting the wafers to pieces and doing surface modifications on them. Therefore, please let me know the best area/$ ratio option you can offer.

Reference #109356 for specs and pricing.

Hydrophilic vs Hydrophobic Substrates for Surface Chemistry Studies

A graduate student requested a quote for the following.

Question:

We want to study the difference in collection efficiency of hydrophilic versus hydrophobic polished 4-inch silicon wafers for airborne fall-out in cleanrooms. Do you have offerings? 

Answers:

The surface of polished monocrystalline silicon wafers, after they are washed in RCA1 solution {1 part NH4OH, 1 part H2O2, 5 parts DI H2O} then in RCA2 solution  {1 part HCl, 1 part H2O2, 5 parts DI H2O} and then rinsed in DI water and dried in Nitrogen, is Hydrophilic - water forms a thin film on the wafer and dries without a visible residue. Subsequently, if wafers are dipped in 1% HF solution, for 2-5 minutes, then dried in Nitrogen {without a DI water rinse}, the surface is Hydrophobic - water forms beads on the surface. In both cases, after exposure to air at room temperature, there forms on the surface a layer of "native oxide" perhaps 0.5nm thick, but its surface chemistry is different.

Since all wafers sold are after RCA1, RCA2, DI water rinse, their surface is hydrophilic.

We can arrange for wafer surface to be treated as described above, to make it hydrophobic however we cannot guarantee that it will remain hydrophobic while in transport and in storage until the wafer cassette is opened. However, it is normal practice to make the surface hydrophobic as described above, just before one measures the surface properties.

We recommend that for your experiments, you create a hydrophobic surface just before measurements and you are advised to repeat the RCA1, RCA2, DI water rinse to assure a hydrophilic surface just before your measurements.

A s standard (hydrophilic) wafers, for your experiments, we recommend:

Reference #114875 for specs and pricing.

How To Passivate a Silicon Wafer's Surface?

A PhD candiate studying materials science requested help with the following question.

Question:

I am new to Si surface chemistry and have a question about passivating Si surfaces. I'm looking to passivate the surface of Si with an alkyl group to make the surface hydrophobic, but I want to maintain good electrical properties of the Si. There seem to be three bond initiating platforms, the Si-H, Si-Cl, and Si-OH. I was thinking that the Si-H and Si-Cl surfaces would be better because I don't have to oxidize my Si wafer before I passivate. Also, don't oxides create defects in the bandgap of Si? I've scanned the literature a bit and it seems that for electronic applications, people typically build off of the Si-H and Si-Cl platforms. Is there a good reason for this?

Answer:

You're on the right track with your understanding of Si surface chemistry and the considerations for passivating Si surfaces with alkyl groups.

Si-H and Si-Cl Terminated Surfaces

1. Si-H Terminated Surfaces:

   • The Si-H surface is commonly used as a starting point for passivation because it’s relatively easy to generate via a hydrofluoric acid (HF) treatment.
   • Alkylation can be achieved through hydrosilylation, where an alkene or alkyne reacts with the Si-H bond, forming a Si-C bond that is covalently attached to the surface. This process effectively passivates the surface while maintaining good electrical properties because it doesn’t involve introducing oxygen, which can lead to oxide-related defects.

2. Si-Cl Terminated Surfaces:

   • Si-Cl surfaces can be prepared by chlorinating a Si-H surface using chlorine or HCl. The Si-Cl bond is reactive and can be used as an intermediate for further chemical modification, such as forming Si-C bonds with alkyl groups.
   • This method is also favored for electronic applications because it avoids introducing oxygen, which could potentially create mid-gap states and affect the semiconductor's electrical properties.

Si-OH Terminated Surfaces

• Si-OH Terminated Surfaces:
  • This involves oxidizing the Si surface to create a thin oxide layer (SiO2) with hydroxyl groups. While Si-OH surfaces are hydrophilic, they can be modified with alkyl groups using silanization reactions.
  • However, as you mentioned, oxidation can introduce defects (e.g., dangling bonds) within the oxide layer or at the Si/SiO2 interface, which can create electronic states in the bandgap and degrade the electrical properties of the Si. This is why Si-OH terminated surfaces are less commonly used in applications where maintaining the intrinsic electrical properties of Si is critical.

Why Si-H and Si-Cl Are Preferred

• Electrical Properties: Both Si-H and Si-Cl terminations avoid the introduction of oxygen, which can create interface states and traps that adversely affect carrier mobility and other electrical properties.
• Versatility and Stability: These terminations provide a versatile platform for further functionalization. The resulting Si-C bonds from alkylation are strong and stable, offering long-term passivation with minimal impact on the electrical characteristics of the silicon.

In summary, Si-H and Si-Cl surfaces are preferred because they provide a more controlled and defect-free approach to passivation, which is crucial for applications requiring high-quality electrical properties.

Reference #126906 for specs and pricing.

What is Surface Chemistry?

Surface chemistry in relation to semiconductor research focuses on the study and manipulation of the chemical properties and reactions that occur at the surface of semiconductor materials. This field is crucial because the surface properties of semiconductors often differ significantly from their bulk properties and can dramatically influence the performance of semiconductor devices.

Key Aspects of Surface Chemistry in Semiconductor Research

1. Surface Passivation:

   • Definition: Surface passivation involves modifying the surface of a semiconductor to reduce the density of surface states, which are electronic states at the surface that can trap charge carriers and degrade the material's electrical properties.
   • Importance: Passivation is critical for improving the performance and reliability of semiconductor devices, such as transistors and solar cells. Effective passivation can lead to enhanced carrier lifetimes, reduced surface recombination, and overall better device efficiency.

2. Interface Chemistry:

   • Definition: Interface chemistry studies the interactions at the boundary between different materials, such as a semiconductor and a dielectric layer (e.g., Si/SiO2 interface).
   • Importance: The quality of these interfaces is crucial for device operation. For example, in a metal-oxide-semiconductor (MOS) transistor, the Si/SiO2 interface must be of high quality to ensure efficient carrier mobility and low leakage currents.

3. Surface Functionalization:

   • Definition: Surface functionalization involves attaching specific chemical groups or molecules to the surface of a semiconductor to modify its chemical, physical, or electronic properties.
   • Importance: This is used in applications such as sensors, where the surface of the semiconductor can be modified to selectively bind certain molecules or ions, allowing the device to detect specific chemical species.

4. Oxidation and Etching:

   • Oxidation: The controlled growth of an oxide layer on a semiconductor surface (e.g., SiO2 on Si). This oxide layer can serve as an insulating layer, a mask for etching, or a passivation layer.
   • Etching: The selective removal of material from the semiconductor surface, which is essential in patterning and shaping semiconductor devices. Both wet (chemical) and dry (plasma) etching processes are used, each with specific implications for surface chemistry.

5. Defects and Surface States:

   • Definition: Surface states are electronic states located at the surface of a semiconductor, often resulting from defects, dangling bonds, or impurities.
   • Importance: These states can trap charge carriers, leading to recombination or scattering, which can reduce the efficiency of devices. Controlling or passivating these surface states is a major focus in semiconductor surface chemistry.

6. Surface Adsorption and Desorption:

   • Adsorption: The process by which atoms, ions, or molecules adhere to the semiconductor surface. This can be physical (physisorption) or chemical (chemisorption).
   • Desorption: The reverse process, where adsorbed species are removed from the surface.
   • Importance: Understanding and controlling adsorption and desorption processes is key for applications such as catalysis, sensor technology, and the fabrication of thin films and coatings.

Relevance to Semiconductor Devices

• Device Performance: The chemical nature of the semiconductor surface can directly impact key device parameters such as threshold voltage, on/off ratio, leakage current, and carrier mobility.
• Fabrication: Surface chemistry plays a vital role in various stages of semiconductor device fabrication, including doping, lithography, deposition, and cleaning processes.
• Nanotechnology: In nanoscale devices, surface effects become even more pronounced, making surface chemistry a critical factor in the design and optimization of nanostructured materials and devices.

In summary, surface chemistry in semiconductor research is a fundamental area that influences everything from the fabrication processes to the ultimate performance of semiconductor devices. Understanding and controlling surface reactions and properties are essential for advancing semiconductor technology.