Compound Semiconductors

Automation and compound semiconductors

The phenomenal diversity of compound semiconductor properties gives these materials a huge range of applications. They can:

• work at higher frequencies than silicon
• generate light more efficiently with a much wider bandgap range
• have lower noise and power figures

These advantages are moving increasing volumes of compound semiconductors into high-speed communications, and optical storage and communications devices.

The major disadvantage of compound semiconductors is cost. Batches are relatively small, and handling is still largely manual in an R&D environment. This reduces throughputs and yields. However, costs can be greatly reduced with automated handling, particularly since all the necessary equipment has been developed on the back of silicon production. 

PANalytical automated solutions

Building on expert R&D analysis instruments, PANalytical has developed efficient and repeatable automated control systems for XRD and XRF analysis. 

These systems combine R&D analysis software modules, automated handling, and SPC software in order to deal flexibly with small batches of different wafers. 

Three process development stages

The silicon industry is remarkably mature for its age. The phenomenal rate of development and miniaturization means that manufacturers need to get each new circuit into production before its window of opportunity shuts. For mobile phone and other circuits, this can be a matter of months. 

For silicon devices, process development consists of three stages: R&D, pilot production, and full-scale production. R&D develops new materials, and needs versatile processing and metrology equipment to experiment with the material properties. Once initial processing problems have been solved, R&D produces working samples. If these are successful, pilot production integrates the new materials and improves processing yields. Equipment does not need R&D's versatility, but does need semi-automation to switch quickly between different circuits. For silicon, manufacture now moves to volume production lines, which use the new materials in earnest in automated production lines. 

The compounds approach

Some advanced compound manufacturers are already adopting the approach, aiming to integrate the whole research-to-production process. Metrology is central to the approach, since it is how manufacturers gather materials and process data. Using one of the R&D metrology techniques as a 'backbone' means that essential analysis equation libraries, parametric maps and databases can accompany materials as they pass from one stage to the next. 

This eliminates much work that is normally duplicated when devices are transferred from R&D to pilot production, and again from pilot to full production. Time to market is faster, costs are lower, and throughputs and yields are higher. Always assuming, of course, that the metrology technique is suitable, and that the instrument manufacturer has built in the necessary conversion and transfer software. 

'Backbone' metrology techniques

Optical techniques gather little useful information during research and development (wavelengths are too long to view structures, and optical techniques hence only deal with averaged properties). Specialized R&D techniques gather excellent information but are either destructive, or analysis virtually needs to be run overnight. Two techniques, however, gather the relevant information in times that keep up with production lines. 

PANalytical has developed X-ray diffraction and X-ray fluorescence into 'backbone' metrology techniques, taking materials from R&D through to volume semiconductor production. XRF gives thickness and composition information for a wide range of thin films, with contamination and dopant levels and surface uniformity. XRD provides absolute, calibration-free and accurate information on crystal growth, giving material composition, film thickness, grading profile, and phase and crystal quality. 

Software and handling equipment has already been developed for the silicon industry. Manual handling for R&D is easily upgraded to single load ports for semi-automatic handling, and even dual load ports for fully automatic volume manufacture. SECS/GEM interfaces help automate communications, and a range of software modules gives in-depth analysis needed for R&D, slimming down to SPC (Statistical Process Control) software for production control. All this helps turn the 'art' of compound semiconductor manufacture into a science.