Research For IGBT Backside Metallization Influence VCEsat

Insulated gate bipolar transistor(IGBT)is the core device of power conversion applications.Collector-Emitter saturation voltage(VCEsat)of IGBT is a key parameter.Higher VCEsat,higher power loss and higher heating during IGBT turn-on,and it will impact energy saving and device lifetime.VCEsat of IGBT is closely related to the backside metallization process,so the influence of backside metallization on VCEsat is studied in this paper.The effects of pre-clean,evaporation and magnetron sputtering,baking of backside metal on VCEsat of 1200V FS IGBT were studied.The relationship between VCEsat and the density of Al spiking was expounded.The main contents are as follows:Study on pre-cleaning process before metal deposition.The native oxide film can be removed by cleaning with 10%hydrofluoric acid before backside metal deposition.VCEsat is unchanged when DHF clean time is set from 10S to 60S which indicates that the process window is enough.When the queue time between pre-clean and metal deposition is less than4hrs,VCEsat keep stable.When the queue time is more than 8hrs VCEsat will increase because of native oxide growth.We can also use Ar~+plasma to etch the native oxide.When the etching time ranges from 10S to 30S,the VCEsat is invariable,which indicates that dry clean process window is enough.Vacuum evaporation and magnetron sputtering are used for backside metal deposition.The backside metal processed by vacuum evaporation requires high temperature baking,which makes aluminum and silicon form Al spiking.The experiment of baking temperature split shows that the higher density of Al spiking,the lower VCEsat we get.The best condition of the baking temperature is 350 degree Celsius.Under the conditions,the density of Al spiking is highest,and the VCEsat is 1.74V,the standard deviation is 0.04V.As the temperature continues to raise,the size of Al spiking increases,but the density decreases,so the VCEsat decreases.By heating the substrate during aluminum film deposition,a higher density of Al spiking can be obtained when backside metal processed by magnetron sputtering.VCEsat can decrease to 1.69V from 1.74V and the standard deviation will also decrease to 0.025V from 0.04V.The comparative analysis shows that the VCEsat of IGBT backside metal fabricated by magnetron sputtering process integrated with dry pretreatment is 3%lower than that processed by evaporation.In magnetron sputtering process,when we set the heater temperature from 350 degree Celsius to 450 degree Celsius,the VCEsat are all less than 1.72V,which is better than 1.74V(the minimum value of vacuum evaporation).The process window of sputtering is larger than evaporation.