Shallow Doped Layer Research Articles

Modulation of Schottky barrier at metal/Ge contacts by phosphoric acid coating and excimer laser annealing

Germanium is an attractive material for advanced devices such as high speed transistors and high efficiency optical devices. To realize the high performance operation, low resistive contacts to Ge are required. However, the Fermi level in Ge at metal/Ge contacts is often pinned near the valance band edge. This Fermi level pinning generates high Schottky barrier heights at metal/Ge contacts regardless the work function of the metals, which results in low resistive contacts to p-type Ge but high resistive contacts to n-type Ge. Thus, a technique for modulating the Schottky barrier heights at metal/Ge contacts is desired. For this purpose, effects of surface treatments of Ge using phosphoric acid coating and excimer laser annealing (LA) were investigated. After LA without phosphoric acid coating, the reverse current of the Al/n-type Ge contacts is increased by an order of magnitude. On the other hand, the reverse current is significantly increased by three orders of magnitude after LA with phosphoric acid coating. Here, the Schottky barrier heights are decreased from 0.56 to 0.50 eV and from 0.59 to 0.49 eV after LA for samples without and with phosphoric acid coating, respectively. These phenomena are attributed to formation of very thin GeOx surface layers and very shallow doped layers having very high P concentrations, respectively. This technique is useful for modulation of the Fermi level pinning for metal/Ge contacts with the low thermal budget.

Ultrashallow Junction Electrodes in Low-Loss Silicon Microring Resonators

Electrodes in close proximity to an active area of a device are required for sufficient electrical control. The integration of such electrodes into optical devices can be challenging since low optical losses must be retained to realise high quality operation. Here, we demonstrate that it is possible to place a metallic shallow phosphorus doped layer in a silicon micro-ring cavity that can function at cryogenic temperatures. We verify that the shallow doping layer affects the local refractive index while inducing minimal losses with quality factors up to 10$^5$. This demonstration opens up a pathway to the integration of an electronic device, such as a single-electron transistor, into an optical circuit on the same material platform.

Sheet Resistance Increase of Shallow Doped Silicon during Native Oxidation in Air

An increase in sheet resistance of shallow doped silicon during air exposure was investigated. Shallow phosphorus doping of silicon wafers was carried out by an atomic-layer doping process forming a pn-junction close to its surface. The sheet resistance Rs of the n+-doped layer was found not to be constant during its contact to air after the process, but showed a remarkable step-like increase with time. After the removal of native oxide by an HF-treatment a similar behavior could be observed during re-oxidation. This behavior may be associated with a layer-by-layer growth of native oxide in conjunction with a silicon consumption and deactivation of dopants in the shallow doped subsurface layer. The observation suggests studying appropriate time-dependent surface related processes by means of the simple four-point probe setup by measuring surface affected sheet resistance changes of shallow doped layers.

N and p-type doping of PECVD a-SiC:H obtained under “silane starving plasma” condition with and without hydrogen dilution

N and p-type doping of highly structural and chemically ordered a-Si 0.5C 0.5:H films are studied. Ion implantation is utilized as doping technique and the films are obtained by rf plasma chemical vapor deposition (PECVD) in the so-called “silane starving plasma” condition, which plays an important role to improve the structural properties of a-SiC:H films. Since hydrogen plasma improves even more the structural properties of the material, the doping efficiency is studied in two types of a-Si 0.5C 0.5:H samples grown with and without hydrogen dilution of the precursor gaseous mixture. For n-type doping, phosphorus was implanted in concentrations varying between 10 18 and 10 21 cm −3, according to previous theoretical simulations. For p-type doping boron and, for the first time in a-SiC:H technology, boron difluoride (BF 2) were implanted, both with a fixed concentration of 10 20 cm −3. The electrical characterization for phosphorus doping shows that the conductivity of the films increases with increasing impurity concentration and, in the best case a room temperature dark conductivity of ∼10 −4 (Ω cm) −1 and an dark conductivity activation energy of 0.1 eV were obtained. For p-type doping the results indicate that BF 2 + is much more efficient than boron, which is related to the production of a shallow doped layer, in accordance to observations in c-Si. In this way a p-type dark conductivity of ∼10 −1 (Ω cm) −1 and energy of 20 meV were obtained.

New method of Plasma doping with in-situ Helium pre-amorphization

A new method of plasma doping process was developed to achieve the ultra shallow junction with low sheet resistance (Rs) and very steep abruptness. In-situ Helium pre-amorphization (He-PA) was employed in conjunction with plasma doping (PD) of dopant species. The optical absorption rate of the amorphous Si layer and the junction depth (Xj) were predominantly controlled by the He-PA conditions. The increase in the optical absorption of the shallow doped layer enabled the high activation of the dopant species. The feasibility of this new technique to form ultra-shallow p+−n junction was studied by using spike rapid thermal annealing (RTA) and flash lamp annealing (FLA). Excellent results on Rs, Xj, abruptness of profiles and reverse-biased leakage current of p+−n diode were obtained. The thickness control and the uniformity of the amorphous Si layer in the He-PA process were discussed.

P[sup +]/n Ultrashallow Junctions in Si[sub 1−x]Ge[sub x] Formed by Molecular Beam Epitaxy

The use of low temperature Si molecular beam epitaxy (MBE) has been investigated for the formation of 10 nm ultrashallow doped layers. Uniformly B-doped Si 1 - x Ge x (x = 0, 0.2, or 0.4) layers have been studied. The sheet resistance of the optimally doped, as-grown samples were substantially less than the best reported, ion-implanted shallow layers. The MBE-grown shallow-doped layers were not affected by 10 min of thermal processing up to 700°C.

Non Destructive Profile Measurements of Annealed Shallow Implants

ABSTRACTControlling the profile of shallow doped layers is critical for obtaining desired performance from deep sub-micron devices. An especially difficult challenge is measuring depth uniformity of the activated implant over the full area of a wafer.This paper demonstrates the capabilities of a new rapid, non-contact optical technique for measuring active doping depth of shallow implants. Employing a 2 Pim spot size, it provides a measurement of fine-scale spatial uniformity in dimensions approaching those of individual devices. By measuring multiple sites, it can rapidly characterize uniformity over large areas and edge-to-edge, without an edge exclusion zone.Data will be presented showing performance on layers varying in depth from 200 to 1200 Å. Edge-to-edge diameter scans on 8” wafers with le15, B11 implants at energies in the range of 200 to 2,000 eV and various RTA temperatures show radially symmetric uniformity patterns of depth and edge effects in the outermost centimeter. Measurements are validated based on correlation to spreading resistance profiles for a number of samples.

Phosphorus Direct Doping from Vapor Phase into Silicon for Shallow Junctions

Characteristics of shallow n‐type layers formed by direct doping of phosphorus from the vapor phase are presented. Shallow doped layers can be formed with depths less than 100 nm using as a source gas and hydrogen as a carrier gas. It is found that the phosphorus concentration on the surface is constant with the doping time and is determined by the flow rate of , not by the solid solubility. By varying the flow rate of , the surface phosphorus concentration is controlled in the range of 1018 to 1019 cm−3. These results show that impurities with low sticking coefficients to silicon and high vapor pressure, such as phosphorus, can be incorporated using this process, although the doping efficiency of phosphorus is low.

Strategies for shallow junction and profile formation

The main strategies for shallow doped layer formation in semiconductors are outlined and the physicochemical characteristics of two of these, direct implantation and diffusion from overlayers, are described. The changing implementation of these techniques is discussed in the context of bipolar and metal–oxide semiconductor silicon integrated circuit fabrication technologies as these have progressed to submicron geometries and ultra-large-scale integration densities. The crucial shallow one and two dimensional doped regions thus fabricated are presented as important and difficult challenges for state-of-the-art compositional analysis techniques.

A study of molecular arsenic ion implantation in silicon

The radiation damage and annealing behavior of 〈100〉 Si implanted at room temperature by As + 2 and As + at equivalent energies are compared. It is found that the radiation damage created by As + 2 implantation is greater than that created by As + implantation. Shallow doped layers in silicon have been formed by As + 2 implantation with low energies from 10 to 30 keV and doses from 5 × 10 13 to 5 × 10 15/cm 2. Rapid thermal annealing is used to control the redistribution of implanted dopant. The results indicate that abrupt n + -p junctions are shallow as 700–1500 Å can be obtained by using As + 2 implantation in combination with rapid thermal annealing.

Amorphisation of silicon by bombardment with group IV ions

An empirical recipe for the amorphisation of single crystal silicon by bombardment with the group IV ions: Si + , Ge + , Sn + and Pb + , has been developed. Samples amorphised using 29 Si + ions were implanted with boron (25 keV, 10 15 ions cm −2 ) and annealed using conventional furnace techniques. Ion channelling and sheet resistivity measurements indicate that good regrowth and complete activation of the shallow doped layers can be obtained provided amorphisation is complete. Similar results were also obtained using 70 Ge + and 118 Sn + implants.

Measurements on depletion-mode field effect transistors and buried channel MOS capacitors for the characterization of bulk transfer charge-coupled devices

The properties of bulk transfer charge-coupled devices (BCCD's) may be characterized from measurements obtained using MOS capacitors and field effect transistors. Models are presented for the MOS capacitor and field effect transistor for the case where a shallow doped layer of polarity opposite to that of the substrate is incorporated between the oxide and the substrate. These models explain the observed frequency dependence of the capacitance-voltage ( C- V) characteristics of these devices. Techniques are presented for determining the impurity profile of the buried layer from the low frequency C- V measurements made on MOS transistors. The majority carrier mobilities in the buried layer and at the surface are measured for the BCCD's and compared to the surface minority carrier mobility measured for the surface channel CCD's. Generation lifetimes at the surface, in the buried layer and in the underlying substrate are determined from capacitance-time (pulse bias C- t) measurements and leakage current measurements of the MOS capacitors and transistors. Methods are demonstrated whereby the depth from the oxide interface of the potential minimum (depth of the buried channel) and its potential can be determined as a function of the various applied biases.