New Anode Short Circuit Ring GTO Thyristor

1, In this paper, we have firstly analyzed a fundamental principles of GTOthyrisrors in detail, and given the turn-off waveform for 300A/1200VGTO simulated by commercial simulator TMA-MEDICI.2, Through process experiments, the effect of P-base impurity profile,lateral uniformity of diffused concentfation and carrier lifetime, as wellas recessed gate grooving on high current turm-off ability was given, too.The results demonstrated that if the P-base concentration in the front ofcathode-gate junction is about l-3×l0¹⁷/cm^-3 then lateral resistance atP-base could meet with requirement of 2-D turn-off gain for GTOhaving superior thyristor charactCristics such as low on-state voltagedrop and high surge current. The abnormal non-uniformity of diffosedparameter and carrier lifetime profile across the large diameter of waferproduced by vacuum-sealed tube Gallium diffusion results in longer falltime during turn-off transient at small anode current. This phenomenonis so called a "limp" at turn-off waveform, induced current freezing atseveral fingers making GTO towarding to destruction. An newly Ge-Gasource sealed-tube diffusion with fillied Argon atmosphere replaced ofabove old diffusion was firstly developed in China by the author. Andconsiderable improvements have been obtained for good homogeneousof lateral parameter i.e. carrier lifetime and acceptor surface dopingconceniration (typical surface sheet resistance R_sâ–¡ l6-l7Ω/â–¡ wasneeded for GTO doping). The high current turn-off ability was realizedby means of all these improvements.3, The novel technology for wet-etching grooving of GTO recessed gatewas firstly developed in China, too. The recessed bottom at gate is so; flat that can comparable to that of dry etching of Reactive Ion Etch (RIE)and suPerior to that of GTOs made in JaPan and UK. This in tumcontriblltes to homogeneous of large diameter GTO wafeL4, It was indicated frOm analysis of tri-off losses Eoff that tail currentlosses is main part of total Eoff due tail time is l0 to 30 fold of fall timeat tum-off The anode shorts adopting in GTO design can not onlyreduce al via reducing anode emitter injection ratio but also extractstored minority carrier charges to anode in condition of optimized anodeshort pattem. This results in considerable reduction of tail currellt.5, We have firstly designed the importam structural parameters withdetailed calculations for novel ring anode shorts 1000A/2500V GTO in' China. In particulap the drastic impact of different ring shortsdistYibulion on tail current i.e. tum-off losses Eoff and on-stateperformance was considered. The novel ring anode shorts structuresimPlify the double-side alignment for the photolithgraPh, and therefOrereduce the cost of manufactWing process. The results indicated thatcombination of multiple ring-shorts having a short ratio of 50% withl2Mev electYon irradiation can result in lowest tail current/tail time.And the tum-off ability at elevated temperature is high.6, We have listed the GTO's manufacturing process and parameters moredetail. In order to obtain very long carrier lifetime wth good uniformityin pre-irradiation, the high carrier lifetime about 20Us was obtained byfirst step Ge-Ga diffosion. The high temPerature Chlorethene-oxidationwas adopted with several percent of Tri-chloroethylene (TCE) intooxidized atmosphere for total four-time oxidation in afterwards step,preventing a reduction of lifetime from ordinaIy oxidation arising frOmheavy metals condensed with oxidation-stack-fault (OSF). The last stepdiffosion is P+ Boron diffosion on anode-side as a getter tO have highvalue lifetime 60ps again. This makes cross-diffosion of P+ from anodeof one wafer onto a recessed gate region of opposite wafer, reducingdrastically gate lateral resistance and increasing extracted tam-offability via negative gate curreni. And therefore, the final optionalteclmique is that combinatio...