Radiation-induced charge effects in buried oxides with different processing treatments

Abstract

We characterize the radiation-induced charge trapping and transport propehes of the buried-oxide (BOX) layer using the photocurrent response technique and capacitance-voltage shift measurements for a variety of silicon-on-insulator (SOI) materials. We observe dramatic differences as a result of different BOX processing conditions. The radiation response of the SO1 as a whole is shown to be consistent with the basic properties of the material(s) contained in the BOX layer. In comparison to standard separation by implantation of oxygen (SIMOX) material, SIMOX receiving a supplemental oxygen implant and lowtemperature anneal produces large normalized photocurrent values indicating that both radiation-generated charge carriers move through the BOX. Of the materials examined, the bond-andetch-back silicon-on-insulator (BESOI) material containing a silicon nitride layer produced the lowest normalized photocurrents, heavy trapping of both carriers. By comparison BESOI with thermal oxide layers traps neither carrier in the oxide bulk.The results of this study should be considered in the design of radiation-hardened components and when considering processing variations.In our previous work [2], we examined bond-and-etch-back silicon-on-insulator (BESOI) material from several different vendors. We recorded a range of values for the normalized currents, depending on the vendor, with Zc,,,/lco typically in the range 0.7 to 1.1. Using standard pre-and post-irradiation capacitancevoltage (C-V) measurements, laTge mid-gap voltage shifts, AVw, were also measured. These results led us to conclude that most of the radiation-generated charge carriers move through the BOX layer, but that a substantial fraction become trapped at one of the interfaces.Separation by implantation of oxygen (SIMOX) is the leading SO1 material for future radiation-hardened microelectronics. Much research has been performed on standard SIMOX material and we, along with many others, have shown that this material traps holes in the bulk oxide layer very heavily and that the electrons move large distances in the BOX]. Through the use of the photocurrent technique, measurements obtained on all SIMOX material examined to date yield values of Ic,,,/Zco = 0.55 k 0.05, consistent with this interpretation of the transport properties. Additionally, large AVq relative to dose are measured in this material, indicating a large fraction of hole trapping. INTRODUC~ION EXPERIMENTAL DETAILSThe photoconduction current technique is an important tool in the analysis of the charge-trapping and transport properties in the buried-oxide (BOX) layer of silicon-on-insulator (SOI) material. This method, developed in our earlier work [l], provides a way to determine the amount of radiation-generated charge moving through the BOX layer. The experiment measures the photocurrent,fcm, resulting from the motion of the x-raygenerated electrons and holes in the BOX. In our analysis,Icm is normalized U, a theoretic maximum value, Ice, yielding a fraction lc,JIco. Values of the fractional cur...

Electrical properties and radiation hardness of SOI systems with multilayer buried dielectric

“…An electron trapping was assumed to explain the positive midgap voltage shifts at the top interface observed at low doses [ rad(SiO )] and high applied electric fields (1 mV/cm) for similar three-layer bond-and-etch structures containing the Si N [11], [12]. The low dose response of the SiO -Si N -SiO layers observed in the present study may also be attributed to the electron trapping in the Si N or at the Si N -SiO interfaces.…”

“…Fabrication of SOI structures with a nitride interlayer in the buried insulator by the wafer bonding method has been reported in [11] and [12], but fabrication of thin silicon films (below 1 m in thickness) with good homogeneity and thickness uniformity using wafer bonding is rather costly.…”

Structural inhomogeneity and silicon enrichment of buried SiO2 layers formed by oxygen ion implantation in silicon

“…[39][40][41][42] Even in the low-dose (D ϭ4ϫ10 17 O ϩ cm Ϫ2 ) SIMOX BOX where silicon inclusions are absent, the hole trapping probability remains at nearly 100% indicating that hole traps are related to oxide network imperfections. 14 The high-temperature annealing of thermally grown SiO 2 sandwiched between two silicon layers, such as in the BOX of bonded structures, 43,44 causes the hole trapping properties to be similar to those of the SIMOX BOX. It thus follows that it is the PIA in confined circumstances that generates a large density of hole traps in the oxide layer.…”