Silicon Drift Detectors with the Drift Field Induced by PureB-Coated Trenches

Abstract

Junction formation in deep trenches is proposed as a new means of creating a built-in drift field in silicon drift detectors (SDDs). The potential performance of this trenched drift detector (TDD) was investigated analytically and through simulations, and compared to simulations of conventional bulk-silicon drift detector (BSDD) configurations. Although the device was not experimentally realized, the manufacturability of the TDDs is estimated to be good on the basis of previously demonstrated photodiodes and detectors fabricated in PureB technology. The pure boron deposition of this technology allows good trench coverage and is known to provide nm-shallow low-noise p + n diodes that can be used as radiation-hard light-entrance windows. With this type of diode, the TDDs would be suitable for X-ray radiation detection down to 100 eV and up to tens of keV energy levels. In the TDD, the drift region is formed by varying the geometry and position of the trenches while the reverse biasing of all diodes is kept at the same constant voltage. For a given wafer doping, the drift field is lower for the TDD than for a BSDD and it demands a much higher voltage between the anode and cathode, but also has several advantages: it eliminates the possibility of punch-through and no current flows from the inner to outer perimeter of the cathode because a voltage divider is not needed to set the drift field. In addition, the loss of sensitive area at the outer perimeter of the cathode is much smaller. For example, the simulations predict that an optimized TDD geometry with an active-region radius of 3100 µm could have a drift field of 370 V/cm and a photo-sensitive radius that is 500-µm larger than that of a comparable BSDD structure. The PureB diodes on the front and back of the TDD are continuous, which means low dark currents and high stability with respect to leakage currents that otherwise could be caused by radiation damage. The dark current of the 3100-µm TDD will increase by only 34% if an interface trap concentration of 10 12 cm −2 is introduced to approximate the oxide interface degradation that could be caused during irradiation. The TDD structure is particularly well-suited for implementation in multi-cell drift detector arrays where it is shown to significantly decrease the cross-talk between segments. The trenches will, however, also present a narrow dead area that can split the energy deposited by high-energy photons traversing this dead area. The count rate within a cell of a radius = 300 µm in a multi-cell TDD array is found to be as high as 10 Mcps.

Characterization and modeling of thermally-induced doping contaminants in high-purity germanium

“…On the other hand, in the case of high purity silicon, used e.g. in silicon drift detectors, a contaminant threshold limit of 10 12 cm −3 is requested to guarantee the optimal performance of the device [17]. The 10 10 cm −3 limit makes quite difficult a direct measure of the contaminants (e.g.…”

Boron-Silicon Film Chemical Vapor Deposition Using Boron Trichloride, Dichlorosilane and Monomethylsilane Gases

“…In contrast, boron trichloride (BCl 3 ) gas has the safe nature, such as nonflammable and less toxic properties. 2 Accounting for that the boron trichloride has been widely known and used as an etching process gas, [6][7][8][9][10][11][12][13][14][15][16][17][18] the boron trichloride gas is further expected to be a safe and reactive boron dopant gas. 19 Thus, the boron production process should be studied in detail using the boron trichloride gas.…”

Low temperature pure boron layer deposition for Si diode and micromachining applications

“…Situations where the latter could have been useful were in the past encountered in connection with the fabrication of photodetectors and silicon-on-glass varactors [18,[115][116][117]. Both involved microstructuring of the Si using conventional dielectric masking layers, to either reduce resistance/capacitance parasitics [118][119][120] or to fabricate through wafer apertures [115]. In the course of this past research the robustness of the B-layers used for diode fabrication with respect to etching in TMAH or KOH became apparent and it had to be taken into account when designing process flows.…”