Dr Owain Thomas, Senior Applications Engineer, Oxford Instruments Plasma Technology
Deposited films such as Silicon nitride and silicon oxide are used in HBLEDs to passivate the final devices.
Current methods include batch PECVD processing which has a typical load of up to 8 x 4” substrates or 40 x 2" substrates with a growth rate of 14-15 nm/min. Considerable amounts of interest have recently been directed towards single wafer LED processing which requires higher deposition rates to maintain throughput requirements. It is also known within the consortium, that the deposition temperature must also be kept low to achieve functional devices. These requirements restrict the ability of conventional PECVD which require high temperatures and low deposition rates in order to allow high quality material to be deposited, probably through allowing sufficient time for excess hydrogen to outgas from the growing film.
High density films can be deposited at low temperatures (<150ºC) using the ICP-CVD technique but with typical deposition rates of 10nm/min. Recent development work at OIPT has achieved much higher deposition rates of > 140nm/min at the same low temperatures, whilst maintaining good film quality, film thickness uniformity and film stress control.
Additional ICP-CVD process repeatability tests which have been conducted by depositing high deposition rate SiO2 (>140nm/min) at low temperatures (<150ºC) on 75 x 100mm wafers.
These recent advances have shown the capability of ICP-CVD in achieving high quality films at low temperatures with high throughput. Therefore due to these additional benefits of ICP-CVD several HBLED manufactures are now considering the ICP-CVD technique as an alternative to conventional PECVD.