F. Sarubbi

Pure boron-doped photodiodes: A solution for radiation detection in EUV lithography

A pure boron chemical vapor deposition (CVD) technology, which forms delta-doped boron surface layers during diborane B2H6 exposure at 700degC, has been successfully used to fabricate silicon-based p+n photodiodes for radiation detection in the extreme-ultra-violet (EUV) spectral range. Outstanding electrical and optical performance has been achieved in terms of extremely low dark current (< 50 pA at reverse bias of 10 V), near theoretical responsivity (0.266 A/W at 13.5 nm wavelength), and excellent stability to high radiation doses (< 1% responsivity degradation after 0.2 MJ/cm2 exposure). Therefore, the diodes are suitable candidates for photon detection functions in the next-generation EUV lithography systems.

High Effective Gummel Number of CVD Boron Layers in Ultrashallow

Deposited boron layers fabricated by exposing silicon to diborane (B2H6) gas in an atmospheric-pressure chemical vapor deposition reactor are investigated with respect to their electrical properties. At the applied temperatures from 500°C to 700°C, the deposition forms a nanometer-thick layer stack of amorphous boron (α-B) and boron-silicon compound (BxSiy), whereas the crystalline Si substrate is p-doped to depths below 10 nm, depending on the temperature and exposure time. The as-deposited layers can be used to fabricate high-quality p+n diodes with low series resistance and low saturation current values that are comparable with those of conventional deep p+ junctions. By investigating p-n-p structures with p+ B-deposited emitters, it is shown that the presence of the α-B layer increases the effective Gummel number of the diffused emitter up to about a factor of 60. The α-B layer is also demonstrated to be a stable and controllable supply of B for the formation of deep p-type regions by thermal drive-in.

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Silicon-based p+n junction photodiodes have been successfully fabricated for radiation detection in the extreme ultraviolet (EUV) spectral range. The diode technology relies on the formation of a front p+ active surface region by using pure boron chemical vapor deposition (CVD), which grows delta-like B-doped layers on Si substrates. Therefore, the technique can ensure defect-free, highly-doped, and extremely ultra shallow junctions that significantly enhance the sensitivity to UV radiation with respect to commercial state-of-the-art detectors, as confirmed by near theoretical responsivity (0.266 A/W, at 13.5 nm radiation wavelength). Outstanding performance has also been achieved in terms of extremely low dark current (< 50 pA, at a reverse bias of 10 V) and pulsed response time (< 100 ns) for 0.1 cm2 large area devices. In addition, the fabricated photodiodes exhibit negligible degradation to high-dose radiation exposure. Owing to these features, the presented photodiode technology, which profits from low cost, reduced complexity, and full compatibility with standard Si processing, offers a reliable solution for the implementation of detectors in industrial applications based on EUV radiation, such as next-generation 13.5 nm wavelength lithography.

Diode Configurations

Two linear low-loss varactor configurations for tunable RF applications are compared. The wide tone-spacing varactor stack provides the best linearity for signals with relative large tone spacing like receiver jammer situations. The narrow tone-spacing varactor stack offers the highest linearity for in-band-modulated signals, and is better suited to adaptive transmitters. Both structures make use of a varactor with an exponential C(VR) relation, and so the different requirements of transmit and receive chains can be addressed in one technology. Both configurations have been realized in a silicon-on-glass technology. The measured Q at 1.95 GHz is from ~ 40 to 200 over a capacitance tuning range of 3.5 with the maximum control voltage of 12 V. The measured OIP3 of both structures are roughly 60 dBm.

High performance silicon-based extreme ultraviolet (EUV) radiation detector for industrial application

This paper reviews special RF/microwave silicon device implementations in a process that allows two-sided contacting of the devices: the back-wafer contacted silicon-on-glass (SOG) substrate-transfer technology (STT) developed at DIMES. In this technology, metal transmission lines can be placed on the low-loss glass substrate, while the resistive/capacitive parasitics of the silicon devices can be minimized by a direct two-sided contacting. Focus is placed here on the improved device performance that can be achieved. In particular, high-quality SOG varactors have been developed and an overview is given of a number of innovative highly-linear circuit configurations that have successfully made use of the special device properties. A high flexibility in device design is achieved by two-sided contacting because it eliminates the need for buried layers. This aspect has enabled the implementation of varactors with special Ndx -2 doping profiles and a straightforward integration of complementary bipolar devices. For the latter, the integration of AlN heatspreaders has been essential for achieving effective circuit cooling. Moreover, the use of Schottky collector contacts is highlighted also with respect to the potential benefits for the speed of SiGe heterojunction bipolar transistors (HBTs).

Ultra Linear Low-Loss Varactor Diode Configurations for Adaptive RF Systems

This paper places focus on the special properties of pure boron chemical-vapor deposition (CVD) thin-film layers that, in several device applications, have recently been shown to augment the potentials of silicon device integration. Besides forming a reliable an efficient dopant source for both ultrashallow and deep p+n junctions, the deposited amorphous boron (α-B) layer itself, even for sub-nm thicknesses, is instrumental in suppressing minority electron injection from the n-region into the p+ contact. Therefore, even for nm-shallow junctions where the current levels mainly will approach high Schottky-like values, the diodes exhibit saturation current levels that can become as low as that of conventional deep junctions. Moreover, the α-B layer has chemical etch properties that make it particularly suitable for integration as the front-entrance window in photodiodes for detecting nm-low-penetration-depth radiation and charged particles.

Improved RF Devices for Future Adaptive Wireless Systems Using Two-Sided Contacting and AlN Cooling

In this paper, we present an atmospheric-/reduced-pressure CVD technique based on pure boron deposition that, to our knowledge, enables the fabrication of the hitherto most shallow junctions, far less than 10 nm deep, that function with the same ideality and low current levels as conventional deep p+-n diodes.

Pure-boron chemical-vapor-deposited layers: A new material for silicon device processing

This paper reviews special RF/microwave silicon device implementations in the back-wafer contacted Silicon-On-Glass (SOG) Substrate-Transfer Technology (STT) developed at DIMES. In this technology, metal transmission lines can be placed on the low-loss glass substrate, while the resistive/capacitive parasitics of the silicon devices can be minimized by a direct two-sided contacting. Focus is placed here on the device level aspects of the SOG process. In particular, complementary bipolar device integration and high-quality varactors for high-linearity adaptive circuits are treated in relationship to developments in back-wafer contacting and the integration of AlN heatspreaders.

Extremely Ultra -Shallow p + -n Boron-Deposited Silicon Diodes Applied to DUV Photodiodes

This paper reviews the applications and potentials of back-wafer contacted silicon-on-glass (SOG) substrate-transfer technology (STT) particularly for RF and microwave silicon-device-design enhancement. This type of SOG process gives direct access to the part of the device that is usually connected via the bulk Si, by allowing advanced patterning and contacting of the backside of the wafer (back-wafer) with respect to the front of the wafer (front-wafer). In this manner the resistive and capacitive parasitics of the device itself, which in silicon often inhibit high-frequency (HF) performance, can be reduced to a minimum. At the same time new device concepts are made possible. Examples of fabricated devices (varactor diodes, vertical double-diffused MOSFETs (VDMOSFETs) and complementary bipolar transistors) are given and described in relationship to issues such as the very limited thermal budget permitted in the back-wafer processing and the inherently high thermal resistance of the SOG devices

Special RF/microwave devices in Silicon-on-Glass Technology

This paper presents a new method of supplying the high doses of boron needed for creating several micron deep p+n junctions. Chemical vapor deposition (CVD), in a Si/SiGe epitaxial reactor, of nanometer-thick pure boron layers is used to fabricate 5 μm deep p+n junctions. The 10 min B deposition is combined with a 195 min drive-in at 1100°C to give a resulting sheet resistance of 3.1 Ω/sq. For as-deposited B-layers in windows through an silicon dioxide isolation to the Si substrate, reactions of the Si with oxide at the perimeter of the deposited windows will be enhanced by the presence of the B-layer during the high-temperature drive-in. Detrimental effects such as lateral contact window widening, small surface defects and/or large spikes formation, are avoided by capping the surface of the windows with either thermal oxide in a selective process or a low-pressure CVD (LPCVD) oxide during the drive-in. A good electrical quality of the oxide capping layer was achieved. The surface morphology was investigated by atomic force and scanning electron microscopy (AFM/SEM) analysis and found to depend on the overall method of fabrication.