Using KOH Etching for Batch Processing

Using KOH Etching for Batch ProcessingEtching baths with varying concentrations of potassium hydroxide (KOH) and controlled temperatures are used in creating microscopic structures on silicon wafers. Modutek can supply equipment such as PFA Teflon tanks, circulation and filtering systems and cassette handling equipment that supports KOH etching. The company designs and builds individualized systems for customers who want to use KOH etching and the resulting systems deliver accurate control, high repeatability, consistent performance and superior output quality.

The KOH Etching Process
The KOH etching process is well understood and is a preferred method for creating silicon wafer nano structures for semiconductor manufacturing and in research facilities. The process delivers controlled and uniform results with high precision and it is relatively safe.

The silicon surface is masked to allow etching and cavity creation in specific areas according to the layout of the final semiconductor product. The etch rate can be controlled by varying the concentration of KOH and the bath temperature. KOH etching is also impacted by the following:

  • The lattice planes of the crystalline silicon
  • Boron doping of the silicon
  • The presence of atomic defects in the silicon crystal
  • Natural impurities

Orienting the lattice planes in a particular direction can influence and control the direction of the etching and the shape of the cavities created in the silicon. Similarly, boron doping can be used to stop etching in a particular direction. Together with the mask, these factors permit the creation of cavities of the required shapes and orientations. Defects in the silicon crystal or natural impurities may reduce the quality of the final product and can result in defective items.

Advantages of KOH Etching
KOH etching provides excellent results and is used extensively because of the following advantages:

  • Safe and easy to handle
  • Rapid etching
  • Excellent reproducibility
  • Low cost
  • High precision when process variables are tightly controlled

Modutek can supply equipment that builds on the listed advantages to deliver corresponding benefits to the customer.

Modutek’s KOH Etching Process Equipment
Modutek’s wet bench technology supports KOH processing, and Modutek examines each request in detail before building the equipment for a particular application. This includes the KOH processing tank, the recirculating system and the silicon wafer handling. Sizes, capacities and control characteristics are adjusted for the customer’s requirements.

The systems supplied by Modutek use the latest technology to provide high accuracy and excellent output quality. Etch rates can be controlled precisely and etch uniformity is guaranteed. Even long etch times, such as up to 3 days, can be handled reliably and safely.

Modutek’s KOH processing tanks are PFA Teflon with all-Teflon fluid paths. The tanks are manufactured onsite using advanced PFA sheet welding techniques designed to minimize impurities and unwanted by-products. The tanks are available as static or as recirculating baths.

The static baths can be ambient temperature baths or temperature controlled from 30 to 100 degrees centigrade. The recirculating temperature controlled baths feature heat-up rates of 2 to 3 degrees centigrade per minute and a temperature control accuracy of plus/minus 0.5 degrees centigrade. The available semi automatic cassette handling reduces costs and increases reliability.

In each case Modutek makes sure that the equipment supplied fits into the existing or a new installation and is compatible with any other wet processing systems. Modutek’s specialists work to ensure the supplied equipment satisfies the customer’s requirements and meets or exceeds performance expectations.

Wet Processing Systems for Solar Cell Manufacturing

Wet Processing Systems for Solar Cell ManufacturingSolar cell manufacturing facilities and research labs use wet processing equipment to etch and clean solar cell silicon wafers. Efficient removal of wafer saw damage, adding of texture, chemical polishing and cleaning of the wafers with reliable, safe wet processing systems is a key factor for increased facility productivity and high quality output. Modutek offers the latest wet bench and ozone cleaning technology to meet customer requirements either with standard systems or customized solutions.

Silicon Wafer Saw Damage Removal

Solar cell silicon wafers are cut from silicon bricks with wire saws, leaving a damaged surface with irregular crystal structure and a damaged crystal lattice. The wafers are placed in an etching bath that removes a thin layer of damaged crystal and leaves a smooth and uniform surface. Modutek wet processing equipment delivers high throughput with accurate controls and consistent results for this process.

Silicon Wafer Texturing

Silicon wafers used for solar cells absorb more light and convert light to electricity more efficiently when their front surface is etched with a microscopic texture. The texture reduces reflection of light from the solar cell surface and promotes internal reflection. For monocrystaline silicon, an etching bath removes small pyramid shapes from the surface of the silicon, leaving an even, consistent texture. For multi crystal silicon, the surface can be etched the same way, but the result is uneven and less effective due to the different orientations of the crystals. Alternative solutions with ion-etching and masks are available.

Chemical Polishing

After the front of the wafer is textured, the rear side remains comparatively rough. Such roughness can reduce the life span of the solar cell and impacts performance. By polishing the rear side of the cell and the edges in an etching bath, internal light reflection is improved and a higher efficiency cell can be manufactured.

Ozone Pre-Cleaning

The cutting of silicon wafers with a wire saw uses a slurry applied to the wires. The cut wafers are contaminated with the slurry and have to be cleaned before they can be etched, textured and polished. The Modutek Ozone Cleaning Process uses ozone dissolved in a mild acid bath to deliver high-performance cleaning at low cost.

The Modutek Ozone Cleaning Process reduces the use of expensive and environmentally harmful chemicals while improving throughput and producing wafer output with fewer defects. The equipment itself is less expensive than other cleaning solutions and there are lower costs due to reduced use of water and for disposal of waste.

Modutek Wet Processing Systems for the Solar Industry

Modutek has been providing wet processing equipment for semiconductor manufacturing for over 35 years and has the experience to examine customer applications and recommend the best solutions. For solar cell manufacturers, Modutek can offer the right equipment for cleaning, etching, polishing and texturing the silicon wafers and can make recommendations on the processes to be used.

In some cases it may make sense to combine saw damage removal with texturing or with polishing and different chemical baths may be appropriate for different customer needs. Modutek can advise customers which wet processing systems they need and can customize equipment if required. Modutek supplies wet processing systems and related equipment to solar cell manufacturers in the United States as well as around the world. Contact Modutek for a free quote or consultation to discuss which equipment to use for your application requirements.