Deep Level Transient Spectroscopy study of 3D silicon Mahfuza Ahmed

Outline Introduction DLTS Measurement of Non Irradiated 3D silicon Detector CV measurement using Agilent B1500A Semiconductor Device Analyzer Conclusion

Introduction: The 3D p-type silicon detector, 3DCA2-W7(1) which is measured is fabricated in a double –sided configuration with columns of one type of doping etched from the front side of the device and the other type etched from the back side. Neither set of column passes through the full thickness of the substrate. This is a semi-3D type detector. The sample has: 2.4mm µm pitch These were measured using smart microscope

3DCA2-W7(1) sample under smart microscope

DLTS Measurement:  CV Measurement  Temperature scan : Majority and minority carrier trap measurement  Arrhenius plot

Fig.(a) The diode at reverse bias,(b) at zero bias during the filling phase, © at reverse bias immediately after the filling phase. DLTS Principle

Capacitance –Voltage measurement : DLTS machine Depletion voltage 5V From 1/C 2 vs Voltage plot Neff = 1.49*10 13 cm -3 Resistivity = Ωcm

DLTS temperature scan of a hole trap. A peak is observed at 252K Reverse bias : -5V Filling Voltage :0V Frequency : 1Hz Filling pulse: 50ms The concentration Of the Hole trap at 252K is: 5*10 10 cm -3 N t = 2 N eff dC max /C

DLTS temperature scan of electron trap: no non-irradiated defect is observed Reverse Bias:-5V Filling Voltage:3V Frequency: 1 Hz Filling pulse : 50ms

From the Arrhenius plot the energy level and the cross- section of the trap were calculated. This involved measurement using the frequency scan mode at six temperature around the hole trap peak temperature(252K). Several sets of temperature versus peak frequency were obtained. The frequency was then converted to an emission rate, e n, by the relation en=2.17*f into the following equation: A plot of ln(e n /T 2 ) vs 1/T gives a slope of and an intercept. Therefore the energy level of a defect can be calculated from the slope and the cross-section from he intercept.

From the Arrhenius plot of the 252K peak the energy level of the hole trap is obtained and it is Ev+0.75 eV the hole capture cross-section is 4.97* cm -3 These two values are far from that we were expected. The capture cross-section is too big. The capture cross section will be measured using filling pulse method which gives more correct value and ten times smaller then that obtained from the Arrhenius plot. It should note that DLTS theory is based on planar pn junction where the charges move vertically and capacitance calculated assuming a parallel plate capacitors, in 3D silicon technology the charges move horizontally and depletion region is cylindrical around the cylindrical electrodes.

CV Measurement by Agilent B1500A Semiconductor Device Analyzer CV measurements were performed at various frequencies at room temperature using the Agilent B1500A Semiconductor Analyzer. The capacitance – voltage measurement at 1kHz looks different than the others. The measured capacitance values are frequency dependent. The capacitance at 0V are plotted against frequency. The capacitance at zero voltage decreases linearly with frequency. The frequency dependence of the CV measurements have been observed before in the case of irradiated detector [1]. In Ref[2] it is also reported that this dependency is due to the defects introduced by the dry etching process. The principle mechanism that causes deep defect within dry etched material is ion channeling [3]. This occurs when an atom is scattered into the crystal along a low index direction. When the ion loss energy, it creates point defect sand localized defect complexes, depending on the energy.

CV measurement at 1 kHz and 500kHz There is a bump at -4V in the 1 kHz, but it disappear in the 500kHz.This will be investigated.

Conclusion: The first DLTS measurement of the Non -irradiated 3D p-type Si diode has been performed and a non- irradiated deep hole trap is observed. Capacitance at 0V is observed to be decreased linearly with frequency. Further work: DLTS measurement of Irradiated 3DCA2-W7(2) sample. CV Measurement of the same irradiated sample using Agilent B1500A Semiconductor Device Analyzer

References: [1] Z.Li and H.W. karner, ‘Studies of frequency dependent C-V characteristics of neutron irradiated p + n silicon detectors.’ IEEE Trans. Nucl.Sci. NS-38 2(1991), p.244 [2] Giulio, P. Roy et.al, ‘ Technology development of 3D detectors for high –energy physics and imaging’ – Nuclear Instruments and Methods in Physics Research Section A, Vol.487 (2002), [3] M. Rahman, ‘ Channeling and diffusion in dry –etching damage’ J.Appl. Phys. 82 5(1997), p