Pattern Dependency and Loading Effect of Pure-Boron-Layer Chemical-Vapor Deposition

Mohammadi, V.; Boer, W.B. de; Scholtes, T.L.M.; Nanver, L.K.

doi:10.1149/2.024201jss

Cited by 17 publications

(18 citation statements)

References 16 publications

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“…The layer thickness was measured in-line using ellipsometry which has an acceptable accuracy and good repeatability for smooth layers. 10 To obtain smooth layers in all cases where the boron-on-boron deposition rate is to be determined, the initial deposition is performed at 700 C, at which temperature complete (monolayer) B coverage of the Si is readily achieved. 7 Subsequently, a series of thicker layers are deposited at the temperature to be investigated.…”

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Temperature dependence of chemical-vapor deposition of pure boron layers from diborane

2012

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Surface reaction mechanisms are investigated to determine the activation energies of pure boron (PureB) layer deposition at temperatures from 350 C to 850 C when using chemical-vapor deposition from diborane in a commercial Si/SiGe epitaxial reactor with either hydrogen or nitrogen as carrier gas. Three distinguishable regions are identified to be related to the dominance of specific chemical reaction mechanisms. Activation energies in H 2 are found to be 28 kcal/mol below 400 C and 6.5 kcal/mol from 400 C to 700 C. In N 2 , the value decreases to 2.1 kcal/mol for all temperatures below 700 C. The rate of hydrogen desorption is decisive for this behavior. Pure boron (PureB) layer depositions have in recent years been applied for creating the p þ -region of extremely shallow, less than 10-nm deep, silicon p þ n junction diodes for a number of leading-edge device applications. 1 Particularly impressive performance has been achieved for the application to bulk-Si photodiodes for detecting low penetration-depth beams. [2][3][4][5] Ideal diode characteristics have been achieved for deposition temperatures in the 400 C-700 C range. The option of depositing at temperatures below $500 C, which together with the fact that the deposition is conformal and highly selective to Si, makes PureB technology highly compatible with amorphous-/polysilicon-/ crystalline-silicon thin-film device processing. Moreover, these properties also make it an attractive process for creating junctions on silicon nanowires and advanced CMOS (complementary metal-oxide-semiconductor) transistors including source/drain in p-type FinFETs. 6,7 These applications require a sub-3-nm thick layer to avoid excess series resistance through the high-resistivity PureB layer.In the present work, the deposition is performed in a commercial Si/SiGe epitaxial reactor by exposing the Si surface to diborane (B 2 H 6 ). At 700 C, in the first few seconds of exposure, the boron atoms interact with the Si surface sites to quickly build up something like an atomic layer plane, and upon further deposition, the boron coverage readily exceeds one monolayer (1 ML). After this, the boron atoms will be deposited on a full PureB surface, which is a process that has a much slower, well-controlled deposition rate. In the past, it has been shown that less than 2-nm-thick layers can be deposited with good reliability and uniformity by a suitable adjustment of deposition parameters such as deposition time, temperature, partial pressures, and flow rates. 8 In this paper, an investigation is presented of the surface reaction mechanisms and activation energies of PureB layer deposition in the temperature range of 350 C to 850 C. At the lower temperatures, the carrier gas has a large influence on the ability to create the first full boron coverage of the Si. Nevertheless, by first creating a full PureB coverage at 700 C, which is smooth and uniform, and then proceeding with the low-temperature depositions, the boron-on-boron activation energies could be determined over the whole temp...

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Temperature dependence of chemical-vapor deposition of pure boron layers from diborane

2012

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“…• C. 4 In addition, the 700 • C PureB deposition can be deposited with well-controlled uniformity and reproducibility down to a thickness of 2 nm in a conformal manner with high selectivity to silicon rather than silicon oxide, 5 making this technology attractive for advanced device architectures.…”

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Effects of Annealing on Chemical-Vapor Deposited PureB Layers

Rine

Vlooswijk

Mohammadi

et al. 2013

ECS J. Solid State Sci. Technol.

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Chemical-vapor-deposited pure boron (PureB) layers can be used as a source of p-type boron dopants for thermal diffusion into silicon during a drive-in anneal. In this work, the effect of thermally annealing PureB layers is investigated in terms of surface morphology and electrical properties. The presence of a few nanometer-thick PureB layer on the Si surface was found to increase the silicon oxide growth rate by several factors during annealing in an oxygen-containing atmosphere. The oxide thickness was dependent on the initial PureB layer thickness and oxygen concentration during anneal. In an oxygen-limited atmosphere, the final thickness is insensitive to the anneal temperature as the reaction is diffusion-limited and, after oxide removal, a hydrophilic boron rich layer remains on the Si surface. With a high oxygen concentration, the boron is depleted by an oxidation of the boron-doped silicon resulting in a lower surface concentration and higher sheet resistance. A reaction mechanism involving the oxidation of Si-B compounds to form B 2 O 3 is proposed to explain the experimental observations. With solar cell and other photodiode applications in mind, the sheet resistance and carrier lifetime measurements were performed and show that a one-step oxidation process can simultaneously drive-in the dopants and form an oxide passivation layer. The chemical vapor deposition (CVD) of pure boron (PureB) layers has in recent years been successfully applied for fabricating extremely shallow, less than 10-nm deep, silicon p + n junction diodes. 1This has provided impressive performance of bulk-Si photodiodes for detecting low penetration-depth beams. 2,3 Ideal low-leakage diode characteristics are achieved for deposition temperatures from 400 to 700• C. 4 In addition, the 700 • C PureB deposition can be deposited with well-controlled uniformity and reproducibility down to a thickness of 2 nm in a conformal manner with high selectivity to silicon rather than silicon oxide, 5 making this technology attractive for advanced device architectures.From studies of the quantum efficiency of VUV photodiodes 3 fabricated with PureB anode regions subjected to various drive-in procedures it has been found that high efficiencies are maintained despite the increase in junction depth from a few nanometers to the hundred-nanometer range. This is accorded to the defect-free nature of the doping process and the lack of roll-off at the surface of the resulting doping profiles. These features are also attractive for the manufacture of p + emitter layers for solar cells and for the passivation of depleted interfaces in other types of photodiode structures. A batch furnace system for the CVD of PureB is currently being developed for high-throughput industrial applications. 6 For application in standard n-type crystalline silicon solar cells, substantial drive-in is required to achieve the dopant profiles and sheet resistance necessary for a low series resistance through the p-type surface layers and associated contacts. More critically, a w...

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“…Secondly, the global and local oxide coverage ratios can be optimised in the layout of the oxide mask to reduce the unnecessary boron atom accumulation over the oxide areas. Likewise, the deposition and process parameters, such as diborane partial pressure, gas flow and total deposition pressure, can be optimised to minimise the loading effects [15,24]. These will otherwise also increase the accumulation of boron atoms over certain oxide areas, thus increasing the probability of parasitic boron deposition there.…”

Section: Precautions To Minimise the Parasitic Boron Deposition At Lomentioning

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Low‐Temperature PureB CVD Technology for CMOS Compatible Photodetectors

Mohammadi¹

2016

Chemical Vapor Deposition - Recent Advances and Applications in Optical, Solar Cells and Solid State Devices

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In this chapter, a new technology for low-temperature (LT, 400°C) boron deposition is developed, which provides a smooth, uniform, closed LT boron layer. This technology is successfully employed to create near-ideal LT PureB (pure boron) diodes with low, deep junction-like saturation currents, allowing full integration of LT PureB photodiodes with electronic interface circuits and other sensors on a single chip. In this way, smart-sensor systems or even charge-coupled device (CCD) or complementary metal oxide semiconductor (CMOS) ultraviolet (UV) imagers can be realised.

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Pattern Dependency and Loading Effect of Pure-Boron-Layer Chemical-Vapor Deposition

Cited by 17 publications

References 16 publications

Temperature dependence of chemical-vapor deposition of pure boron layers from diborane

Temperature dependence of chemical-vapor deposition of pure boron layers from diborane

Effects of Annealing on Chemical-Vapor Deposited PureB Layers

Low‐Temperature PureB CVD Technology for CMOS Compatible Photodetectors

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