High resolution particle-detectors produced by ion-implantation

NUCLEAR

INSTRUMENTS

AND METHODS

I77-I78,

56 (1967)

© NORTH-HOLLAND

PUBLISHING

CO

HIGH RESOLUTION PARTICLE-DETECTORS PRODUCED BY ION-IMPLANTATION O MEYER and G HAUSHAHN Instltut fur Angewandte Kernphystk und Zyklotron Laboratortum, Kernforschungszentrum

Karlsruhe

Received 26 June 1967 and m revised form 9 August 1967 High resolution parUcle detectors are produced by lonqmplantah o n technique It is shown that the improved performance Is due

to the fact that well-channeled ions at relatwe low energy and low ion-concentrations mm~mlze bulk damage effects

Forming thin n- or p-contacts on p- or n-type semiconducting materials by ion-implantation technique should have some advantages compared with diffusionor surface-barrier techniques a First of all ion-implantation can be performed at low temperature (anneahng temperatures up to 300°C often are sufficient) Therefore minority-carrier hfetlme is not reduced by defects produced at high temperature b The incident ion-beam has a high chemical purity due to analysis by mass-separator techniques c Ion-doped junctions are more stable to changes of ambient atmospheres and of vacuum than surface barrier-counters d One can easily get different concentration profiles of the impurity atoms by changing energy and intensity of the ion beam and can thus look at the influence on diode performance 2) So far, however, no influence on the diode properties has been observed On the other hand a serious disadvantage is that the incident ions produce highly damaged regions forming a lot of traps and recombination centers. Indeed the first workers 1'2) who produced particle detectors by ion-implantation techniques obtained no promising results The detectors had high reverse currents and bad resolution compared with counters fabricated by diffusion or surface-barrier techniques First good results in producing particle detectors by ion-implantation were reported by Kalbltzer et al 3) We were able to confirm his results and we pointed out 4) that the improved performance may be due to the fact that wellchanneled ions and relative low ran-concentrations minimize bulk damage effects This conclusion could be proved now in comparing measured hfetlmes and concentration profiles of particle-detectors produced with well aligned and non-aligned ion beams. Boron and phosphorus ions were produced by means of an reverted magnetron Ion-source s) and after acceleration analysed in a semicircular magnetic field similar to that described by Browne and Buechner6). Well etched and cleaned n-type slhcon slices (10000135000 g2-cm, 22 mm dla, 0 3-4 mm thick) cut normal

to the 111-dlrechon within 0 5° were clamped in masks with 10-15 mm dla opening Ion energies up to 10 keV were used, moving the Sl-shces with constant velocity behind a slit-diaphragm normal to the incident beam we got an uniform implantation with ion concentrations up to 1013 lons/cm / for B and 101S/cm 2 for P The diodes were usually annealed for 10 rain at 300°C and mounted on special holders for tests No surface protection was used so far

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currents of 2-3 #A at r o o m - t e m p e r a t u r e and 1 3 n A at liquid nitrogen temperature The n - n + - b a c k contact proved to be a good non-reJecting contact, even when the space charge reaches the back-contact O n the other h a n d diodes, produced with n o n - a l i g n e d ion beams from the same shces, show life-times of 50-150 #sec a n d reverse currents of 10-50 /tA at 500 V and 300 K c o m p a r a b l e with results in 2) The implanted m n c o n c e n t r a t i o n profiles on annealed diodes were examined by sheet resistivity measurements together with slow etching a n d weighing techniques It could be shown that the c o n c e n t r a t i o n profiles of diodes produced by well aligned beams have a tall of channeled ions, wlth a range at least two u m e s that of n o n - c h a n n e l e d ions of the same energy The space charge-region m the p + - c o n t a c t extends into th~s " t a d " region where bulk damage is well reduced and hfe-Ume conserved Figs 1 and 2 show the resolution for q-particles measured at r o o m temperature and conversion electrons detected at hqmd m t r o g e n temperature The m e a s u r e m e n t c o n d m o n s are given in the figures We greatly acknowledge the assistance of M r M B a u m g a r t n e r and Mr L Wlss d u r i n g performance of the measurements

,

l References

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Fig 2 The response of a 2 mm thick ion-doped counter, of area 100 mm 2, to 2°7Bt internal conversion electrons C o u n t e r s produced by well ahgned 1on beams parallel with the l l l - d l r e c h o n showed as good l - V characteristics a n d hfetlmes of minority-carriers as has been measured for surface-bamer-detectors v) For example fully depleted 3 m m thick devices (135000 Q cm, 500 V, ~ = 1-2 msec) typically show reverse

~)T Alvager and N J Hansen, Rev Scl Instr 33 (1962) -') F W Martin, W J Kmgand S Harrison, IEEE Trans Nucl Scl NS-11, no 3 (1964) 280, NS-13, no 1 (1966) 22 3) S KalbJtzer, R Bader, H Herzerand K Bethge, Z PhysJk 203 11967) 117 4) O Me~yer, Conf Semiconductor nuclear particle-detectors (Gathnburg, May, 1967) 5) G Haushahn, Eur Coll on A V F cyclotrons (Emdhoven, Aprd, 1965) ~') E B Browne and W W Buechner, Rev Scl [nstr 27 (1956) 899 T) H J kangmann and O Meyer, Nucl Instr and Meth 44 (1966) 55