Collection Methods

For example, in 2011, IBM's PELM operations worldwide processed over 37,950 metric tons of end-of-life products which was about 97.6 percent of the total amount processed recycled.^[12] Since we are only focusing on processors from Intel for this project we will use the estimate of 97.6 percent for our 46,700kg (the total silicon weight in processors for 2010) to estimate the amount of silicon recovered. This gives us a total of 45,579.2kg of estimated silicon that can be saved from these processors per year. We plan on collecting the processors by providing free recycling to consumers. In cooperation with Intel the customer would send their processor(s) in to Intel. As a third party, we would then either purchase or have Intel donate their scrap wafers and the CPU's that consumers sent in by mail to our program. By parterning with Intel we believe that we would receive around 90% of the total processors produced in a year. If there is an estimated 67,040,000 Intel CPU's made per year 60,336,000 would be returned to our company. Multiplying by the amount of silicon in an average CPU (.697g) then we would able to recycle around 42054kg of pure Si per year. We would also build our plant next to Intel's so that shipping between the plants can be ignored

Contaminants

• Typical corrosive wastes for processors include: Sulfuric Acid, Hydroflouric Acid, Phosphoric Acid, Nitric Acid, Ammonium Hydroxide, and Hydrogen Peroxide. These acids are used for etching, stripping and cleaning the wafers. Tetramethyl Ammonium Hydroxide is used as a positive photoresistant developer.^[13]
• The requirements of extreme purity for electronic device fabrication require additional purification steps in order to produce electronic-grade silicon (EGS). In order for the purity levels to be acceptable for subsequent crystal growth and device fabrication, EGS must have carbon and oxygen impurity levels less than a few parts per million (ppm), and metal impurities at the parts per billion (ppb) range or lower(see table below). Besides the purity, the production cost and the specifications must meet the industry desires.^[14] However because we are not planning on recycling our silicon wafers in electronics but in solar panels we can be a little more liberal with amount of contaminants in our silicon.

Table 1. Typical impurity concentrations found in electronic-grade silicon (EGS).^[15]

Purification Methods

• Methods for reclamation of wafers from the electronics industry already exist. Wafers that have all electronics deposited can be cleaned, polished and reused.^{[verification needed]} This process can also be used to clean existing processor chips which have the same surface properties as the uncut wafers.
• The processor chips are chemically treated to remove impurities.
  1. First they are treated in a mixture of sulfuric acid and hydrogen peroxide.
  2. Next is an etch in hydrofluoric acid followed by an alkaline etch using ammonium hydroxide or potassium hydroxide.
  3. The chips are then ground and polished to remove remaining surface features.
  4. Finally, residual particles are removed during a two stage cleaning process. The first step uses a mixture of water, hydrogen peroxide, and ammonium hydroxide and the second uses water, hydrogen peroxide, and hydrochloric acid. This process results in clean, pure silicon with a slight thickness reduction.^[16] The thickness loss is up to 10 microns or about 1.5% of silicon.^[17]
• Once the silicon is cleaned of impurities it can be melted down and cast into ingots of polycrystalline silicon and cut into square ingots for use in solar cells^[18]
• Overall, very little silicon is lost. About 1.5% is lost during the cleaning process. Even assuming triple the thickness loss during cleaning to be conservative, only 4.5% of silicon is lost. There are also likely to be significant kerf losses from sawing. One source estimates 35% kerf loss during wafer production^[19] but the dust from wafer cutting can be recycled back into melt for new ingots. It is likely that at least 95% of silicon could probably be recovered from this process.

Characterization Methods

There are a few different ways you can characterize a silicon based semi-conductor. There is the Electrical characterization, the optical characterization, and the physical/chemical characterization.

Electrical characterization helps you determine the resistivity, carrier concentration, mobility, contact resistance, barrier height, depletion width, oxide charge, interface states, carrier lifetimes, and deep level impurities. Two-Point Probe, Four-Point Probe, Differential Hall Effect, Capacitance-Voltage Profiling, DLTS, and DLCP.

Optical characterization includes microscopy microscopy, ellipsometry, photoluminescence, transmission spectroscopy, absorption spectroscopy, raman spectroscopy, reflectance modulation, cathodoluminescence. There are still alot of other methods out these are merely an example of some of the tools available.

Physical/Chemical characterization techniques utilize ion beams X-rays, and electron beams to measure the physical characteristics of the semiconductor. these include (electron Beam) SEM, TEM, AES, EMP, EELS, (Ion Beam) Sputtering, SIMS, RBS, (X-rays) XRF, XPS, XRD, X-ray topography Neutron Activation Analysis (NAA) Chemical Etching.

Since we are trying to utilize the silicon from these processors for use in photovoltaic cells it makes clear sense to utilize the electrical characterization of the materials involved. The other characterization methods were included merely to illustrate how many different ways there is to show how a semiconductor can be tested to determine exactly what it's exact composition is. This will basically be used to confirm the information that would be obtained from Intel as far as the type of silicon used in their processors. Sadly this information is proprietary so we don't know anything other than the average purity of silicon for processor use. thankfully the purity for this application is significantly higher than that needed for use in a photo voltaic cell.

Energy Needed for Recycling

To keep the energy needed to transport a wafer to our facility we will be locating it next to an Intel plant that receives waste processors. Those would then be obtained put through the entire process of recycling them. Information regarding the actual energy used by individual machines that actually handle these processor dies is very hard to come by and not made publicly available. However there is a wealth of information about the energy savings involved in wafer reclamation processes. IBM claims that depending on the process, it can save between 30% and 90% of the energy used to produce wafers from scratch.^[20] It takes 2130 kWh to produce one kilogram of single crystal silicon from scratch.^[21] With a conservative estimate of 50% energy saving, this could result in 1065 kWh per kilogram for the reclamation portion of the process. Using a ZT-90D directional solidification furnace we a 90 kg crucible capacity, the energy required would be 73 kWh per kilogram.^[22] This results in a total energy of 1138 kWh per kilogram of silicon for all of the processing steps combined.

Alternatives to Straight Recycling

• Instead of straight recycling, which is the process of removing impurities and utilizing the raw silicon. You could also retool the processors to obtain continued work, however you will not be able to get this device to work as well as a new one. The rough process for working a die (individual processor) could possibly be done a couple of different ways. One if the processor still works it can be just used in new application. Say you have a calculator that needs a main processing unit you could utilize a computer processor that still works to run the calculator. This processor was originally meant to run a lot more than just the components of a calculator, but instead of being thrown out and/or destroyed it has found new life.

Now say you have a processor that is having hardware issues and cannot function anymore. You could grind off the old transistors and any circuitry to then redeposit new circuitry onto the dies. Even though this is possible it doesn't mean that it is really feasible, since you would have to retool each individual die by itself. We believe the best process would be to merely remove the impurities from the dies and utilize the silicon for the creation of photo-voltaic cells. Since the silicon already exceeds the purity level needed for solar cells, further purification will not be required. The following statement alludes to the use of full scrap wafers already being utilized for the creation of solar cells.

• The wafer reclamation process produces monitor wafers from scrap product wafers - generating an overall energy savings of up to 90%. When monitors wafers reach end of life they are sold to the solar industry. Depending on how a specific solar cell manufacturer chooses to process a batch of reclaimed wafers - they could save between 30 - 90% of the energy that they would have needed if they'd used a new silicon material source.^[23]

Semiconductor Recycling Facility

Equipment and Processing

1. Chemical Stripping Orca^TM Automated Wet Process System will chemically strip the processors of contaminants.
2. Surface Grinder Waida Super Precicion Surface Grinder will grind all remaining electronics on the processor off.
3. Cleaning Process Orca^TM Automated Wet Process System will then wash away all excess contaminates that remain from griding.
4. Melting in Furnace Polycrystalline Silicon Casting Furnace will then melt all the pure silicon into ingots which will then be trimmed to form blocks.

Safety Plan

The Occupational Safety and Health Administration (OSHA) is an organization with the United States Department of Labor. The recycling facility described above will follow all OSHA requirements. More information on OSHA regulations can be found on their website at http://www.osha.gov/.

Material Safety Data Sheets (MSDS)

Material Safety Data Sheets are required for all chemicals that enter the plant and will be placed in easily accessible to all employees. A list of the primary materials used in this recycling process, along with links to their MSDS, can be found below.

• Sulfuric Acid[H₂SO₄ MSDS]^[24]
• Hydrofluoric AcidHF MSDS^[25]
• Phosphoric Acid H₃PO₄ MSDS^[25]
• Nitric Acid HNO₃ MSDS^[25]
• Ammonium HydroxideNH₄OH MSDS^[25]
• Hydrogen Peroxide[2(HO) MSDS]^[26]
• Hydrochloric AcidHCl MSDS^[26]
• WaterH₂O MSDS^[26]

Safety Training

The recycling facility will have a Safety Training Program. The purpose of this program will be to train new employees on current and long-term safety issues as well as continue to provide continuing safety training to all employees. The Safety Training Program will focus on, but not limited to the topics below:

• How to read a MSDS
• Emergency Response: Hazardous Chemicals
• Review of Hazardous Chemicals
• How to prevent/clean-up spills
• How to properly label containers
• Procedures for handling chemicals
• Procedures for fire or large scale chemical spills

Semiconductor Material Flow Diagram

The following Flow Diagram outlines the workflow in the recycling plant. While the file is not a Dia file as requested, we were not able to download the Dia program onto the school computers and decided that Visio was the best alternative.