Ofer Sneh

Thin film atomic layer deposition equipment for semiconductor processing

Abstract Atomic layer deposition (ALD) of ultrathin high-K dielectric films has recently penetrated research and development lines of several major memory and logic manufacturers due to the promise of unprecedented control of thickness, uniformity, quality and material properties. LYNX-ALD technology from Genus, currently at beta phase, was designed around the anticipation that future ultrathin materials are likely to be binary, ternary or quaternary alloys or nanolaminate composites. A unique chemical delivery system enables synergy between traditional, production-proven low pressure chemical vapor deposition (LPCVD) technology and atomic layer deposition (ALD) controlled by sequential surface reactions. Source chemicals from gas, liquid or solid precursors are delivered to impinge on reactive surfaces where self-limiting surface reactions yield film growth with layer-by-layer control. Surfaces are made reactive by the self-limiting reactions, by surface species manipulation, or both. The substrate is exposed to one reactant at a time to suppress possible chemical vapor deposition (CVD) contribution to the film. Precisely controlled composite materials with multiple-component dielectric and metal–nitride films can be deposited by ALD techniques. The research community has demonstrated these capabilities during the past decade. Accordingly, ALD equipment for semiconductor processing is unanimously in high demand. However, mainstream device manufacturers still criticize ALD to be non-viable for Semiconductor device processing. This article presents a broad set of data proving feasibility of ALD technology for semiconductor device processing.

Atomic layer deposition of SiO2 using catalyzed and uncatalyzed self-limiting surface reactions

SiO2 thin films were deposited with atomic layer control using self-limiting surface reactions. The SiO2 growth was achieved by separating the binary reaction SiCl4+2H2O→ SiO2+4HCl into two half-re...

Atomic layer controlled deposition of SiO2 and Al2O3 using ABAB… binary reaction sequence chemistry

Abstract Sequential ABAB… surface chemical reactions can be employed for atomic layer controlled deposition. We have examined the binary reactions SiCl 4 +2H 2 O⋌SiO 2 +4HCl for SiO 2 deposition and 2Al(CH 3 ) 3 +3H 2 O ⋌ Al 2 O 3 + 6CH 4 for Al 2 O 3 deposition. Each binary reaction (A + B ⋌ products) was performed sequentially by individual exposures to the A reactant and then the B reactant. If each surface reaction is self-limiting, repetitive ABAB… cycling may produce layer-by-layer controlled growth. For example, the individual “A” and “B” surface reactions for SiO 2 deposition can be described by (A) Si–OH + SiCl 4 ⋌ Si–O–SiCl 3 + HCl, (B) Si–Cl + H 2 O ⋌ Si-OH + HCl. We have studied ABAB… binary reaction sequences for SiO 2 and Al 2 O 3 deposition using laser-induced thermal desorption, temperature-programmed desorption and Auger electron spectroscopy techniques on single-crystal Si(100) surfaces. Fourier transform infrared spectroscopy techniques were also employed to examine these binary reaction schemes on high surface area SiO 2 and Al 2 O 3 samples. Controlled deposition of SiO 2 and Al 2 O 3 was demonstrated and optimized utilizing the above techniques. Under the appropriate conditions, each surface reaction was self-terminating and atomic layer controlled growth was a direct consequence of the binary reaction sequence chemistry.

Engineered tantalum aluminate and hafnium aluminate ALD films for ultrathin dielectric films with improved electrical and thermal properties

Continued scaling of device dimensions requires deposition of high-quality thin films with a thickness of 50 angstroms or less. Nucleation effects in typical CVD processes make it difficult to achieve continuous films in this thickness regime. Atomic layer deposition (ALD), a technique developed over 25 years ago but applied to IC processing only recently, enables deposition of ultra-thin films with atomic-scale precision. This technique offers 100 percent step coverage of high aspect ratio features, as-deposited films which are amorphous and free of pinholes, excellent within-wafer uniformity and wafer-to-wafer uniformity, and favorable electrical properties. Moreover, ALD offers the opportunity to engineer material properties by creating layered structures (nanolaminates) and mixtures (alloys) which combine advantageous properties of different materials. These last features may be critical in efforts to replace silicon dioxide as the industrys dielectric workhorse if no single material emerges as a suitable direct replacement. The nanolaminate capability of ALD will be discussed with physical and electrical data on nanolaminates of aluminum oxide with tantalum pentoxide and aluminum oxide with hafnium oxide. Individual nanolaminate layers can be varied from tens of angstroms to as little as 1-2 atomic layers. Data for Al 2 O 3 /Ta 2 O 5 and Al 2 O 3 /HfO 2 alloys will also be presented demonstrating the ability to create materials with controlled, variable composition. The alloy and nanolaminate capabilities enable the creation of graded interfaces and atomically smooth transitions between different materials. Prospects for application of these materials to gate stacks and capacitors will be assessed.

Atomic layer growth of SiO2 on Si(100) using SiCl4 and H2O in a binary reaction sequence

Abstract The atomic layer control of SiO2 growth can be accomplished using binary reaction sequence chemistry. To achieve this atomic layer growth, the binary reaction SiCl4 + 2H2O → SiO2 + 4 HCl can be divided into separate half-reactions: (A) SiOH ∗ +SiCl 4 →SiOSiCl ∗ 3 +HCl , SiCl ∗ +H 2 O→SiOH ∗ +HCl , where the asterisks designate the surface species. Under the appropriate conditions, each half-reaction is complete and self-limiting and repetitive ABAB... cycles should produce layer-by-layer-controlled SiO2 deposition. The atomic layer growth of SiO2 thin films on Si(100) was achieved at temperatures from 600–680 K with reactant pressures from 1–50 Torr. These experiments were performed in a small high pressure chamber situated in an ultrahigh vacuum (UHV) apparatus. This design couples high pressure conditions for film growth with an UHV environment for surface analysis using laser-induced thermal desorption (LITD), temperature-programmed desorption (TPD) and Auger electron spectroscopy (AES). The controlled growth of a stoichiometric and chlorine-free SiO2 film on Si(100) was demonstrated using these techniques. SiO2 growth rates of approximately 0.73 ML of oxygen (1.1 A of SiO2) per AB cycle were obtained at 600–680 K. Additional vibrational spectroscopic studies performed in a second vacuum chamber utilized transmission Fourier transform infrared (FTIR) experiments on high surface area, oxidized porous silicon to monitor the surface species during the binary reaction sequence chemistry. These FTIR measurements observed the SiCl stretching vibration at 625 cm−1 and the SioH vibration at 3740 cm−1 and confirmed that each half-reaction was complete and self-limiting. These studies illustrate the feasibility of atomic-layer-controlled SiO2 growth and have determined the reactant pressures and substrate temperatures required for the SiO2 binary reaction sequence chemistry.

Adsorption and desorption kinetics of H2O on a fully hydroxylated SiO2 surface

Abstract The adsorption and desorption kinetics of H2O were studied on a well-defined, fully hydroxylated SiO2 surface. The measurements were performed on a planar, thin SiO2 film grown on Si(100) using chemical vapor deposition techniques. The experiments were conducted under ultra-high vacuum conditions and utilized laser-induced thermal desorption (LITD) techniques. The initial adsorption was characterized by a temperature-independent H2O sticking coefficient. At later times, the sticking coefficient approached zero as constant H2O coverages were obtained that decreased versus surface temperature. The desorption rate increased at higher H2O coverages and this coverage dependence was attributed to repulsive dipole-dipole interactions between partial SiO−…H3O+ surface species. Novel experiments using H2O16 and H2O18 were employed to measure the isothermal desorption rates at constant H2O coverage. Arrhenius plots of these isosteric rates revealed that the desorption activation energy decreased with H2O coverage and could be modeled by E d (θ)=21.3−15.4θ 1 2 kcal mol −1 . The larger desorption rate at higher H2O coverage participates in defining a constant coverage where the desorption and adsorption fluxes are equal during the adsorption experiments. The temperature dependence of the H2O desorption rate explains the decrease of this constant H2O coverage versus surface temperature. At coverages higher than θ≈0.3 ML, the desorption activation energy decreased below the H2O condensation energy. Consequently, H2O multilayer formation occurred at low temperatures at θ ≥ 0.3 ML. The adsorption and desorption kinetics were used to determine the steady-state H2O coverage on hydroxylated SiO2 surfaces. H2O coverages of θ ≥ 0.3 ML were predicted under typical ambient and stratospheric conditions.

The decay of triplet pyrazine in supersonic jets

The decay rates of optically excited triplet states of pyrazine in supersonic expansion were measured by using three different methods. The excess energy dependence of the radiationless rate constants in the energy range between the T1 and the S1 electronic origins of the isolated molecule was explored. Decay rates between 7×102 –2.5×104 s−1 were found in the 1500 cm−1 range of excess vibrational energy from the origin of the T1 state. The decay rates are free of mode specificity and rotational effects. The pure radiative lifetime in the measured range is rovibronic independent. The results support a model which suggests that certain vibrational modes, those which undergo large frequency changes in the excited state, control the strong vibrational energy dependence of the T1 →S0 intersystem crossing of pyrazine.

High-resolution infrared overtone spectroscopy of ArHF via Nd:YAG/dye laser difference frequency generation

The first high‐resolution spectra of ArHF excited to the vHF=2←0 manifold near 7800 cm−1 are recorded via direct infrared absorption in a slit supersonic expansion. The tunable difference frequency light is generated via nonlinear subtraction of a cw Nd:YAG laser from a tunable cw ring dye laser in temperature phase matched LiNbO3, and permits continuous single‐mode access to the 1–2 μm near‐IR region. Rotationally resolved spectra are presented for the pure HF stretching overtone (2000)←(0000), as well as for combination band excitation into the Σ bend (2100)←(0000) and Π bend (2110)←(0000) internal rotor levels built on the vHF=2 overtone stretch. Local perturbations in the Π bend spectrum are observed which arise from a resonant crossing of rotational levels with the (2002) van der Waals stretch and allow spectroscopic analysis of this state. Nonresonant coupling between the Σ and Π bend vibrational levels is evidenced by anomalous P branch/R branch transition intensities and is analyzed as Coriolis in...

Sample manipulator employing a gas‐thermal switch designed for high pressure experiments in an ultrahigh vacuum apparatus

A sample manipulator with a gas‐thermal switch was designed for high pressure surface science experiments in an ultrahigh vacuum (UHV) apparatus. The gas‐thermal switch coupled the sample mount to the cryostat using helium gas. When helium gas was present and the thermal switch was on, the cooling time constant was τ∼2.6 min. When the helium gas was evacuated, the sample mount was isolated and could be easily warmed to room temperature in ∼5 min using a small ceramic heater. The sample manipulator was built to be part of an internal high pressure chamber. The internal high pressure chamber could obtain pressures as high as 100 Torr with only small pressure excursions of ΔP≊1–2×10−10 Torr in the UHV chamber. Recovery back to UHV conditions occurred only minutes after high pressure experiments with gases or condensable materials such as H2O. This note details the rationale and mechanical design of this sample manipulator with a gas‐thermal switch for high pressure experiments in an UHV apparatus.

The decay of triplet pyrazine and methylpyrazine in supersonic jets. Substitution effects

We have measured the decay rates of optically excited triplet states of pyrazine and methylpyrazine in a supersonic jet. The excess vibrational energy dependence of the radiationless rate constants in the energy range between the T1 and the S1 electronic origins of the isolated molecules was explored. Decay rates between 5×102 and 105 s−1 were found in the 1800 cm−1 range of excess vibrational energy above the origin of the T1 state in pyrazine. In methylpyrazine the decay rates increase from 8×102 to 3.3×104 in the first 600 cm−1 excess energy range above the T1 origin. The decay rates are free of mode specificity and rotational effects. The wide dynamic range of the T1→S0 radiationless rates of pyrazine is substantially enhanced by methyl substitution. The results support a model which suggests that certain vibrational modes, those which undergo large frequency decreases in the excited state, control the strong vibrational energy dependence of the T1→S0 intersystem crossing of pyrazine. These large freq...