Improving the performance of critical wet process applications 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. Modutek’s wet process stations are specialized for the different processes but also guarantee safe and reliable operation.
Specific Tasks Require Specialized Processes
Depending on the etching or cleaning task to be carried out, specific wafer etching process characteristics are needed. The fabrication of solar cells has different requirements than the creation of microscopic structures for a processor. The major process characteristics that can impact wafer manufacturing include the following:
- Low particle count
- Etching speed
- Selectivity
- Precise control
- Undercutting
Low particle counts are always desirable but can be critical for the smallest structures. A high particle count can result in high rates of rejection during final testing because the particles cause defects in tiny structures.
Etching speed is related to throughput. If the goal is to remove a substance as quickly as possible, high etching speed can be prioritized at the expense of other characteristics such as precision. Ideally the process speed is optimized so the process step doesn’t become a bottleneck.
For highly selective processes, the substrate material is not affected by the etchant while the material to be removed is etched rapidly. While selectivity is a basic characteristic of wet bench processing and is always important, some applications require especially high selectivity and the process has to be chosen accordingly.
Precise control becomes more and more critical as the dimensions of the micro-structures decrease and the packing of components becomes more dense. Since this tendency is a current trend in wafer manufacturing, control precision is becoming more important.
Undercutting compromises control precision but can be limited or eliminated with anisotropic etching by choosing the appropriate process and the orientation of the silicon crystal planes. When undercutting under the mask is not acceptable, anisotropic etching results in clean and sharp corners.
Choosing the right process to deliver the etching characteristics needed can have a high impact on wafer etching process line performance. Key performance indicators such as product rejection rates, throughput, down times and operating costs can vary greatly depending on the best match of process to application. An experienced equipment manufacturer can help customers choose the best solutions.
Modutek Provides Wet Process Solutions for Different Application Requirements
Modutek offers a complete line of wet process stations and can deliver solutions for general etching and cleaning as well as for specialized applications. Among the processes supported by Modutek equipment are the following:
- Piranha etch
- KOH process
- Buffered Oxide Etch (BOE)
- Ozone resist strip
Piranha etch cleans organic material from substrates and is often used to remove photoresist from silicon wafers. It cleans rapidly and does not etch the underlying silicon. Modutek can evaluate whether piranha etch is a good fit for an application.
KOH etching is characterized by good control and the possibility of use for anisotropic etching. The etch rate is controlled by changing the temperature of the KOH solution and Modutek offers baths with tight temperature control.
BOE is used primarily to etch silicon dioxide and silicon nitride. It features good control and does not undercut masks. Modutek supports BOE with its sub ambient filtered baths.
Ozone resist strip cleans organic residue while reducing the particle count. The powerful oxidizing action of the ozone combines with carbon in the organic compounds to leave wafers clean and free of particles. Modutek offers the ozone strip process as a chemical-free alternative to traditional strip methods.
With extensive experience in all areas of wet process wafer fabrication, Modutek can help choose the specialized process required for an application and deliver equipment of the highest quality. In supporting special applications as well as general etching and cleaning, Modutek ensures that it can meet all the wet process needs of its customers.
The aggressive chemicals used in wet process wafer manufacturing have to be contained in process tanks that can resist etching and corrosion while remaining inert. Depending on the application, a process may require heating, filtration or the regular addition of chemicals.