XXI DAE-BRNS High Energy Physics Symposium 2014, IIT Guwahati Development of Silicon Pad and Strip Detector in High Energy Physics Manoj Jadhav Department of Physics I.I.T. Bombay
2 Manoj Jadhav, IIT Bombay. DAE-BRNS HEP Symp. 2014, IIT Guwahati Outline! Introduction! Silicon Pad Detector! Oxidation! Photolithography! P and N type Doping! Metallization! Silicon Strip Detector! Summary
Silicon Semiconductor Detector Mean energy loss by MIP in Silicon, (de/dx) mean = 388 ev/µm, For t sensor = 250 µm, E pair = 3.63 ev e - h + pairs created = 27000 e - h + pairs, Intrinsic charge carrier, 1.45 X 10 10 A sensor = 0.25 cm 2 n i.t sensor.a sensor = 9 X 10 7 Which is 4 orders bigger. Operate at low temp Reverse bias Landau Distribution 3 Energy loss: Bethe Bloch Function
Silicon Pad Detector The most simple detector is a large surface diode with guard rings.! No position resolution! Good for basic tests (IV, CV, Pulse) 4
Silicon Pad Detector n-type Si detector:! n-type bulk (111) : ρ = 3-5 kωcm! Thickness 250 ± 10 µm! Integration of coupling capacitances in standard planar process! SiO 2 with a thickness of 100 200 nm between p + and aluminum strip AC coupled! n + layer on backplane to avoid Schottky contact and improve ohmic contact! Operating voltage < 200 V! Aluminum metallization AC coupling blocks leakage current from the amplifier. 5
Silicon Pad Detector Step 1: Oxidation! RCA cleaned! Wet Oxidation at 1050 o C (H 2 + O 2 )! A thin layer of SiO 2 630 ± 10 nm (ellipsometer Meas.)! 56% of the oxide above original surface and 44% below 6 Thermal Oxidation Silicon Bulk Original Si surface SiO 2 Additional layer Consumed layer 1.27 1.00
Silicon Pad Detector Step 2: Photolithographic Mask! CleWin (16 devices/2 wafer)! Printing Mask! Print on transparency + glass! Laser Writer LW405 + Iron oxide on glass! 8 mm X 8 mm sensor! 5 mm X 5 mm pad + guard rings 7
Silicon Pad Detector Step 3: Photolithography (PLG - Level 1)! Double sided mask aligner! Transfer photomask to wafer/patterning of SiO 2! Photoresist ~ 2 µm spinner! Exposure 70 mj/cm 2! Sample developing! SiO 2 etching (BHF 5:1) (Buffered Hydrofluoric Acid) 8
Silicon Pad Detector Step 4: Doping! Plasma Immersion Ion Implantation! Boron for p type; Phosphorus for n type! Energy 2 kev; Dose: 5 X 10 15 atoms/cm 2! Anneal at 950 o C + N 2 and O 2 to activate ions and provide AC coupling 9
Silicon Pad Detector Step 4A: Time of Flight - Secondary Ion Mass Spectroscopy (ToF-SIMS)! Doping profile from Plasma Immersion Ion Implantation.! Concentration of activated charge carriers and junction depth after annealing. Boron Doping Profile Phosphorus Doping Profile 10
11 Silicon Pad Detector Step 5: Metallization! Equipment: 4-Target e-beam Evaporator Aluminized wafer! Al deposition! 500 nm on P + doping side! 250 nm on back contact i.e. N + side! To avoid absorption and deterioration of energy resolution due to energy straggling! Aluminum spikes are much less likely observed in crystal with orientation <111> than on <100> surfaces
Silicon Pad Detector Step 6: Photolithography (PLG Level 2)! Double sided mask aligner; Patterning of Al! Exposure 70 mj/cm 2! Sample developing Al etchant (Acetic acid + Nitric Acid + Phosphoric Acid) 12 Silicon Pad Detector
Silicon Strip Detector Single sided strip detector! n-si wafer, 250 ±10 µm, Resistivity (ρ) = 3-5 kωcm! 2 cm X 2 cm sensor, 1.92 X 1.92 cm 2 active area! 50 µm pitch, 384 strips! Biasing methods,! polysilicon biasing (radiation hard, extra PLG)! punch through biasing (chipper) 13
14 Summary #" The fabrication of two wafers (32 sensors) have been completed for Silicon Pad Detector. #" Plasma Immersion Ion Implantation process gives doping concentration of ~10 15 atoms/cm 3 for boron and phosphorus. " Preliminary characterization and development of electronic readout system is in run. " The fabrication of Silicon Strip Detector is in process. # Thank You
15 Backup Slides
16 Landau Distribution! Energy deposition is non-deterministic and statistical fluctuation are very asymmetric
17 Characterization! Keithley 2410 source meter for IV measurement and Keithley 4200 SMU for capacitance measurement
Silicon Strip Detector Poly-Silicon Biasing! Deposition of poly-crystalline silicon between p+ implants and a common bias line.! Typical sheet resistance of up to R s 4 kω/sq. Depending on width and length a resistor of up to R 20 MΩ is achieved (R = R s length/width).! Drawback: Additional production steps and photo lithographic masks required. 18
Silicon Strip Detector Punch Through Biasing! Punch through effect: the increase of the depletion zone with increasing bias voltage (V pt = punch through voltage).! Advantage: No additional production steps required. 19 1.) 2.) 3.)