Wilfried Vandervorst

Atomic layer deposition of hafnium oxide on germanium substrates

Germanium combined with high-κ dielectrics has recently been put forth by the semiconductor industry as potential replacement for planar silicon transistors, which are unlikely to accommodate the severe scaling requirements for sub-45‐nm generations. Therefore, we have studied the atomic layer deposition (ALD) of HfO2 high-κ dielectric layers on HF-cleaned Ge substrates. In this contribution, we describe the HfO2 growth characteristics, HfO2 bulk properties, and Ge interface. Substrate-enhanced HfO2 growth occurs: the growth per cycle is larger in the first reaction cycles than the steady growth per cycle of 0.04nm. The enhanced growth goes together with island growth, indicating that more than a monolayer coverage of HfO2 is required for a closed film. A closed HfO2 layer is achieved after depositing 4–5HfO2 monolayers, corresponding to about 25 ALD reaction cycles. Cross-sectional transmission electron microscopy images show that HfO2 layers thinner than 3nm are amorphous as deposited, while local epita...

Epitaxial staircase structure for the calibration of electrical characterization techniques

Frequently electrical characterization techniques [such as the spreading resistance probe (SRP)], rely on the availability of a set of well-calibrated, homogeneously doped Si samples to establish the calibration curves (and parameters) necessary for the conversion of resistance measurements into carrier profiles. Although ideally such a calibration should be verified daily, in practice, time considerations limit the daily verification to one (or a few) calibration samples. To remedy this situation a special multilayer Si structure has been grown consisting of a decreasing B-doped staircase containing seven flat 4–5 μm thick calibration layers doped from 1020/cm3 down to 1015/cm3 separated by slightly (factor 2–3) higher doped 1–2 μm thick interface layers. The latter are included to facilitate the SRP calibrations as the SRP correction factor within the calibration layers now becomes very close to one. Since presently, a calibration curve can be generated quickly from a single measurement, daily measureme...

A 0.314/spl mu/m/sup 2/ 6T-SRAM cell build with tall triple-gate devices for 45nm applications using 0.75NA 193nm lithography

This paper describes the fabrication process of a fully working 6T-SRAM cell of 0.314/spl mu/m/sup 2/ build with tall triple gate (TTG) devices. A high static noise margin of 172 mV is obtained at 0.6 V operation. Transistors with 40nm physical gate length, 70nm tall & 35nm wide fins, 35nm wide HDD spacer are used. Low-tilt extension/HALO implants, NiSi and Cu/low-k BEOL are some of the key features. This is an experimental demonstration of a fully working tall triple gate SRAM cell with the smallest cell size ever reported.

Oxygen induced broadening effects studied by RBS and SIMS

Abstract The redistribution of As from a shallow As-implant (5 keV) in Si following oxygen bombardment has been studied by grazing exit RBS. The oxygen bombardment was performed in an ion implanter (12.5 keV O+, room temperature and 40 K), and a reactive ion elcher (1.7 keV O+2). For 12.5 keV O+ bombardment the As redistributes very rapidly in the sample; displacements up to 50 nm are observed. Implantation at 40 K shows only a very small reduction in spreading of the As distribution indicating a very low activation energy for the defect-induced diffusion. Bombardment with 1.7 keV O+2 does not broaden the internal As distribution as much as at 12.5 keV O+ but our results indicate that the As-atoms segregate at the oxide-silicon interface. Enhanced segregation in the reactive ion etcher results in a much larger decay length than under SIMS-bombardment conditions.

Vapor phase doping with N-type dopant into silicon by atmospheric pressure chemical vapor deposition

Atomic layer doping of phosphorus (P) and arsenic (As) into Si was performed using the vapor phase doping (VPD) technique. For increasing deposition time and precursor gas flow rate, the P and As doses tend to saturate at about 0.8 and 1.0 monolayer of Si, respectively. Therefore, these processes are self-limited in both cases. When a Si cap layer is grown on the P-covered Si(001), high P concentration of 3.7 × 10 20 cm -3 at the heterointerface in the Sicap/P/Si-substrate layer stacks is achieved. Due to As desorption and segregation toward the Si surface during the temperature ramp up and during the Si-cap growth, the As concentration at the heterointerface in the Si-cap/As/Si-substrate layer stacks was lower compared to the P case. These results allowed us to evaluate the feasibility of the VPD process to fabricate precisely controlled doping profiles.

In Situ Phosphorus Doping of Germanium by APCVD

Germanium is increasingly being studied for application in advanced nanoelectronic devices, due to its high intrinsic carrier mobility. While broad knowledge and understanding of in-situ doping of Si is available, very little is known on in-situ doping of Ge. Phosphorus has been identified as one of the most promising n-type dopants for Ge, because of its high electrical activity. However, studies of the quality of ion-implanted P-doped Ge layers showed unsatisfactory behavior. A considerable difference between the levels of the electrical solubility and equilibrium solid solubility of P in Ge has been reported. The highest electrically active level of ionimplanted P in Ge reported to date is of 5-6×10 cm. The interest in in-situ doping of Ge was triggered by the possibility of increasing the electrically active levels obtained for n-type dopants at the same time as having better control over the shape of the dopant profile and its location. We present the first results on in-situ P doping of Ge by APCVD.

Very low temperature (250 °C) epitaxial growth of silicon by glow discharge of silane

Epitaxial growth of phosphorus‐doped silicon deposited at 250 °C from a radio‐frequency glow discharge from SiH4 is demonstrated by high‐resolution electron microscopy (HREM) and spreading resistance profile measurements. Thin epitaxial films are present at the interface between (100) Si substrates and hydrogenated amorphous silicon. After recrystallization at 700 °C, single‐crystal layers are obtained, in which HREM reveals extensive twinning. The fact that epitaxial growth can take place at 250 °C in a system with a background pressure of only 5×10−6 mbar can be attributed to the presence of species in the SiH4 plasma that reduce the native oxide and the use of HF in the cleaning procedure.

3D-carrier profiling in FinFETs using scanning spreading resistance microscopy

In this work, we demonstrate for the first time 3D-carrier profiling in FinFETs with nm-spatial resolution using SSRM. The results provide information on gate underlap, dopant conformality, source/drain doping profiles. The 3D-carrier profiles as extracted for two different device approaches (extensions vs. extension-less) are conclusive in demonstrating the differences in device performance and are consistent with first order 3D-simulations.

Structural and optical properties of Ge islands grown in an industrial chemical vapor deposition reactor

The use of Si based materials for optoelectronic applications is hampered by the indirect nature of the band gap. One possible solution by which to improve the radiative light emission is three-dimensional Stranski–Krastanow growth of Si1−xGex or pure Ge on top of Si. In this article we give a detailed overview about the growth kinetics observed for Ge growth in a standard production oriented chemical vapor deposition system. With increasing deposition time, we observed the usual changeover from monomodal to bimodal island distribution. The island morphology and density can be controlled by varying the growth conditions or by applying a thermal anneal after island growth. Island densities up to 2.3×1010 cm−2 have been obtained for depositions at 650 °C. A Si cap layer is needed for photoluminescence measurements as well as for some device structures. However, Si capping at 700 °C leads to nearly total dissolution of small islands and truncation of bigger dome-shaped islands. This can be prevented by reduc...

Assessment of profile broadening during sputtering

Abstract Some results of a computer model for the simulation of ion beam induced displacements are proposed. This model is based on the traditional linear cascade theory. It comprises a simplified approach to the description of collisional mixing in multi-element targets with varying density. Furthermore, the effects of point-defect driven motion, such as radiation enhanced diffusion and segregation, are tentatively accounted for. The model has been able to quantitatively estimate the initial swelling of the target and the width of the transient region which is observed when sputter profiling silicon with O 2 ions of various energies and for different angles of incidence. We also report on the simulation of the dramatic effect of radiation enhanced diffusion on shallow As implants, sputter profiled with oxygen, as established recently by Vandervorst et al.