Specialized Wafer Etching for Critical Wet Processing Applications

The success of the wet process application depends on selecting wet bench processes designed for the tasks at hand. Specialized equipment can support different etching and cleaning processes and can be used to make sure that the process selected can fulfill specific application requirements.

Depending on the etching or the cleaning task to be performed, specific wafer etching processes are needed. For example, the fabrication of solar cells has different requirements compared to the requirements for the creation of microscopic structures for a processor. Here are the following major process characteristics which can impact wafer manufacturing:

1)     Low particle count – these characteristics are especially critical for the smallest structures. A high particle count can cause defects in micro structures, which result in higher failure rates during final testing.

2)     Etching speed – If the goal is to remove substance as fast as possible, high-speed etching can be used, but with this process, precision can be compromised.

3)     Selectivity – for highly selective processes, the substrate material is not affected by the etchant while the material to be removed is etched rapidly.

4)     Precise control – this characteristic becomes more critical as the dimensions of the micro-structures decrease and the packing of components becomes denser.

5)     Undercutting – It compromises control precision but can be minimized or eliminated with anisotropic etching by selecting the proper process and the orientation of the silicon crystal planes.

Choosing the right process to deliver the etching characteristics required will have a high impact on wafer etching process line performance. Key performance indicators that include product rejection rates, throughput, downtimes and operating costs can vary greatly, depending on the best match of the process to application.

Modutek's wet process stations are specialized for different processes and also guarantee safe and reliable operations. The company offers a complete line of wet process stations and can deliver solutions for general etching and cleaning, as well as for specialized applications. Modutek's equipment supports several processes, including:

• Piranha etch – removes organic material from substrates and is often used to remove photoresist from silicon wafers. Modutek can determine whether piranha etch is a good fit for a specific application.
• KOH etching process – the etch rate is controlled by changing the temperature of the KOH etching (potassium hydroxide). Modutek supports this process with baths that provide tight temperature control.
• Buffered Oxide Etch (BOE) – is used primarily to etch silicon dioxide and silicon nitride. Modutek supports this process with its sub-ambient filtered baths.
• Ozone resist strip – it cleans organic residue while reducing particle count. Modutek supports this with the ozone strip process which does not use chemicals

For more details about this topic, read the complete article “Specialized Wafer Etching for Critical Wet Processing Applications”. If you would like to set up a free consultation to discuss any questions you may have, contact Modutek at 866-803-1533 or email to Modutek@modutek.com.

How Quartz Tanks Improve Wafer Manufacturing

Chemicals used in wet process wafer manufacturing need to be contained in process tanks that can resist etching, corrosion and remain inert. In some applications, a process may require heating, filtration or the regular addition of chemicals. Quartz tanks are made from semiconductor grade flame-polished quartz and are impervious to the acids and bases used in wafer processing. They minimize contamination of wafers from particles and can be supplied in heated and re-circulating models.

Wet bench processing of silicon wafers consists of fabrication steps such as etching and diffusion with cleaning required in between the steps. The wafers are “masked” to etch specific parts of the wafer to confine diffusion to certain target areas. Once each process step is done, the masking material must be cleaned off.

Cleaning the wafers completely without contamination is crucial. When the wafer is not clean and still has contaminants, even a single particle can result in a badly formed structure or conductor. When such malformations are incorporated into the final product, it can result in defective or lower-quality semiconductor components.

Modutek offers specialized quartz tanks that are made from semiconductor grade flame-polished quartz and are impervious to the acids and bases used in wafer processing. Quartz tank controls allow operators to program reproducible process environments and make sure temperatures and chemical concentrations are consistent. Heating, chemical spiking, and filtration are the three important areas for which specialized control systems are useful.

Heating – Modutek's high-temperature re-circulating baths and constant temperature tanks heat up rapidly with a temperature rise of up to two degrees centigrade per minute. Quick heating helps improve throughput and accurate temperature control helps ensure high-quality results.

Chemical spiking – Periodic spiking restores the chemical concentration of the chemicals to the desired effect. Modutek has developed an innovative “bleed and feed” spiking method for the sulfuric acid and hydrogen peroxide process.

Filtration – Modutek's quartz tanks can also reduce particle counts and wafer contamination. The quartz re-circulating tank can filter out particles down to 0.2 microns, improving output quality and reducing component failure rates.

The complete article, “How Quartz Tanks Improve Wafer Manufacturing” explains more details. If you have questions and would like to set up a free consultation, contact Modutek at modutek@modutek.com or call 866-803-1533.