A high-density plasma processing system featuring a radial line slot antenna has been developed for high-quality thin film formation at low temperature. This system is characterized by a high plasma density (above 1012 cm−3), a low electron temperature (below 1 eV) and a low plasma potential (less than 9 V). High-integrity silicon oxide films grown by direct oxidation of silicon surface at 400°C have been developed by introducing oxygen radical oxidation where oxygen radicals are obtained by a high-density plasma in He/O2 ambient. It is confirmed that the breakdown field intensity of oxide film is more than 15 MV/cm and the charge-to-breakdown is larger than 10 C/cm2under a constant stress current density of 0.1 A/cm2. The same high-density plasma system has also been applied for the direct nitridation of silicon surface using Ar/N2 or Ar/N,/H, gas ambient. The electrical properties of the silicon nitride are excellent enough to extend scaling limit of thermally grown silicon oxide. An advanced gas distribution system consisting of a newly-developed vaporizer, a flow control system, an electrically controlled valve and an advanced gas pumping system can control various source gas concentrations in the process chamber very accurately from the first atomic layer deposition. The newly-developed plasma and advanced gas distribution systems are suitable for the formation of high dielectric constant and ferroelectric films for ULSI in the 21st Century.

Wafers prepared with HF and RCA cleaning were oxidized at atmospheric pressure O2 with an incandescent-lamp processor using temperature ramping at rates up to 150°C/s for heating and 80°C/s for cooling. The minimum oxidation time obtained by the “spike” method of turning off lamp power prior to reaching a desired peak temperature is effectively 2s. Film thickness for spike oxidation ranges from about 1.6 nm for peak temperature of 1000°C to about 2.2 nm for peak temperature of 1100°C. Activation energies of 2.5 eV are determined for 1.5 – 4 nm films. Films grown for varied times and temperatures to produce equal oxide thickness, as measured by ellipsometry, show nearly equivalent physical properties in measurements by corona-charge and Kelvin probe surface photovoltage techniques.

We prepared an atomically flat silicon substrate which had a step-terrace structure and observed the topography of the ozone-oxidized surface to clarify whether homogeneous oxidation occurs with ozone. The oxide was formed with high-concentration ozone gas with a thickness of 2.5nm at a temperature of 350°C. The oxide surface still maintained the same step-terrace structure as observed before oxidation, which revealed that ozone-oxidation occurs layer-by-layer and produces an atomically flat oxide. XPS and MEIS analyses show that the stoichiometry of ozone oxide grown at 350°C is the same as that of an oxide grown thermally at 750°C.

Radical oxidation at thickness of under 2.0 nm in an ultrahigh vacuum (UHV) system with an electron cyclotron resonance (ECR) plasma has been studied. The interface roughness and oxide density were evaluated by atomic force microscopy (AFM) and grazing incidence xray reflectrometry, respectively. We found the oxide thickness could be easily controlled at Tsub = 750°C when using radical oxygen at 5.0×10−3Torr. The interface roughness at a thickness of 1.8 nm, measured by the root mean square (RMS), was 0.11 nm. The density of the radical oxide fell as the oxide thickness decreased, especially at less than 2.0 nm. However, the density of the radical oxide annealed in molecular oxygen at 5×10−3Torr and Tsub = 750°C increased, without the oxide thickness increasing. We think that the first insertion of an oxygen atom into the first Si layer has a much higher energy barrier than that into a SiOx layer. The radical oxygen can pass through this higher energy barrier, and thus oxygen molecules fill the oxide layers. This mechanism means that we can control the oxide thickness and density separately at thickness of less than 2.0 nm through the radical oxidation time and the annealing time in molecular oxygen. We expect low-pressure radical oxidation to be the most suitable process for future ultrathin gate oxidation.

We incorporated significant density of nitrogen only near the top surfaces of the thermally grown oxides by the fluorination at room temperature followed by atomic nitrogen treatment around 550°C. Average nitrogen concentration of more than 6 percent was obtained in the nitrided layer with thickness below 1 nm. We fabricated MOS devices using the nitrided oxide films without hydrogenation, and measured capacitance-voltage characteristics. The density of nitridation-induced interface defects in the MOS device was estimated to be below 2×1010 cm−2. The proposed technique identifies a unique process for obtaining high quality ultrathin dielectrics.

Plasma immersion ion implantation (PIII) has been employed to controllably place nitrogen ions from an inductively coupled plasma into a thin furnace grown gate oxide 2.0nm thick with implant voltages from 25 to 500V. Control of the implant energy enables shallow implantation confining the nitrogen mainly within the oxide. Rapid thermal annealing is essential in repairing any damage to the implanted silicon dioxide and silicon while consolidating the bonding of nitrogen into the oxide film prior to gate polysilicon deposition. High frequency capacitance-voltage measurements of capacitors made with BF2+ implanted gates throughout a series of furnace anneals demonstrates the efficiency for blocking boron compared to non-nitrided oxides of similar thickness. Tddb measurements verify excellent reliability compared to a non-implanted oxide for both stress polarities.

We present a novel gate oxidation process using D2O (deuterium oxide) as an oxidizing gas. The electrical and reliability characteristics of ultrathin gate oxide grown in D2O ambient have been investigated. Compared with a control oxide grown in H2O, a oxide grown in D2O exhibits a significant reduction of charge trapping and interface state generation. Based on a secondary ion mass spectroscopy (SIMS) analysis; we found a deuterium rich-layer at the Si/SiO2 interface. The improvement of electrical and reliability characteristics can be explained by the deuterium incorporation at the Si/SiO2 interface.

We tried direct oxynitridation of silicon surfaces by remote-plasma-exited nitrogen and oxygen gaseous mixtures at 700°C in a high vacuum. The oxynitrided surfaces were investigated with in-situ X-ray photoelectron spectroscopy. With increase of the oxynitridation time, the surface density of nitrogen gradually increases, but that of oxygen shows nearly saturation behavior after the rapid increase in the initial stage. We also annealed the grown oxynitride and oxide films to investigate the role of the contained nitrogen. The desorption rate of oxygen from the oxynitride films is much less than that from oxide films. We confirmed that nitrogen stabilizes the thermal stability of these oxynitride films.

The necessity to decrease silicon wafer-processing temperatures substantially has stimulated research into new and innovative techniques for the formation of thin dielectric films. A photo-decomposition technique using Nitric Oxide (NO) is one such promising method. Thermally NO-grown and NO-annealed dielectric films have already shown very encouraging physical and electrical results. This study compares thermally NO-grown oxides with thermally NO grown and assisted by ultraviolet (UV) irradiation. Methods using UV and vacuum UV light generated from low-pressure mercury or deuterium lamps to stimulate the growth of ultrathin dielectric films are described. The oxynitridation of silicon is carried out by irradiating an ultraviolet beam on the heated silicon substrate covered by a thin layer of nitric oxide gas. Typical resultant film thickness were in the range 10 –40 A after oxynitridation for various times at 500°C. MIS devices were fabricated using these films as gate insulators and were electrically characterized. Electrical characterization revealed good film qualities, rendering this new UV-NO oxynitridation technique promising for low temperature (<600°C) semiconductor processing. Films grown in NO ambient under deuterium lamp irradiation followed by NO annealing were also investigated. These results will also be presented.

In this paper, we report a novel low thermal budget process (<800°C) for engineered ultra thin oxynitride dielectrics with high nitrogen concentration (>5% a.c.) using vertical high pressure (VHP) process. VHP grown oxynitride films show >1 OX lower leakage current, higher drive current and superior hot-carrier reliability compared to control SiO2 of identical thickness (Tox,eq) grown by RTP in O2.

The principle and practice of the Jet-Vapor Deposition (JVD) technique for thin-film deposition will be introduced, followed by a presentation of the properties of ultra-thin JVD silicon nitride (designated SiN in this paper) as advanced MOS gate dielectric. Recent results on the JVD TiO2/SiN gate stack will also be presented

In this paper, we report performance and reliability of CMOS devices with ultra thin (<20Å) Si3N4gate dielectric fabricated by in-situ rapid thermal CVD (RTCVD) process, and compare with control SiO2devices of identical equivalent oxide thickness (Tox,eq). Ultra thin CVD Si3N4 devices show significantly lower gate leakage current, complete suppression of boron penetration, improved MOSFET performance, and enhanced reliability against electrical stress.

This paper presents results on the interfacial properties of Si3N4on NMOSFETs and PMOSFETs. Silicon nitride, formed by remote plasma enhanced chemical vapor deposition, was found to display severely degraded interfacial properties, in which the PMOS interfaces were significantly more degraded than NMOS interfaces. This is believed to be indicative of a relatively high density of interface traps located below the Si mid-gap that inhibit hole channel formation. These traps are believed to originate from the intrinsic nature of Si- Si3N4interface. Bonding constraint theory was applied to conclude that the Si-Si3N4interface is over-constrained compared to the Si-SiO2interface and consequently results in a higher intrinsic defectivity. A systematic study of the oxygen and hydrogen content in the silicon nitride film and its effect on electrical properties is also presented. Based on the electrical results it is concluded that the presence of oxygen either as a) a monolayer at the interface or b) within the silicon nitride film can produce high quality interfaces suitable for aggressively scaled CMOS devices.

Ultrathin (tox,eq < 2.0 nm) Si3N4/SiO2(hereafter N/O) gate dielectrics with improved interface characteristics compared to devices with thermal oxides have been formed by remote plasma enhanced CVD of Si3N4onto oxides. If the Si-Si02 interface is intentionally nitrided prior to the Si3N4deposition, the increased physical thickness of the N/O stack combined with the interfacial nitridation reduces the direct tunneling current by more than two orders of magnitude. The ensuing device structure can then be characterized as N/O/N. The top nitride layer is also an effective boron diffusion barrier improving short channel characteristics in p+-poly PMOSFETs. In addition, nitrogen can also be transported to the silicon/dielectric interface during post-deposition RTAs, and this reduces degradation of transconductance during hot carrier stressing.

The oxidation kinetics of ultra thin thermally NH3-nitrided Si3N4 films in N2O ambient has been extensively studied using angle resolved x-ray photoelectron spectroscopy (ARXPS). Ultra thin (7Å) Si3N4 films formed by RTP nitridation of Si in NH3 were annealed in N2O at various temperatures (700 °C - 1000 °C) for 30 sec. ARXPS showed that Si substrate at the Si-Si3N4 interface was oxidized when annealed at 1000 °C for 30 sec, and was accompanied by the oxidation of the top Si3N4 surface. The total film thickness increases 4–5 times of that of the original Si3N4 layer. However, the oxide formed on the top Si3N4 surface is twice as thick as that formed at the Si3N4/Si interface. No interfacial oxide was found when annealing below 900°C, although the formation of the silicon oxide and oxynitride above the Si3N4 layer was still observed.

This paper reports a procedure for low-temperature formation of silicon dioxide (SiO2) using a catalytic chemical vapor deposition (Cat-CVD) system. The surface of Si(100) is oxidized at temperatures as low as 200°C and a few nm SiO2 films are formed. Electrical and structural properties of the layers are investigated. It is found that breakdown electric field, leakage current and the density of intermediate oxidation states is comparable with thermally oxidized sample.

A high-concentration ozone generator operating at atmospheric pressure has been developed for fabrication of ultra thin silicon oxide films. The generator can supply atmospheric pressure of ozone jet with ozone concentration up to 80 vol%. The ozone jet is generated by desorbing ozone at nearbyn room temperature, which has been condensed on silica-gel by passing ozone/oxygen mixture gas from a commercial ozonizer at a low temperature (<-50°C); at the temperature ozone is more selectively adsorbed on silica-gel than oxygen. The high purity ozone jet with a concentration of 25 vol% at a pressure of 1 × 105 Pa had so large oxidation power that SiO2 film as thick as 3.3 nm grew on a Si surface after 60 min exposure at 375°C. The density of the film was equivalent to that of the film formed by a conventional thermal oxidation process, judging from etching rate with dilute HF solution.

The performance of CMOS devices improves due to the addition of Ge in their poly-Si gate material. The presence of Ge in the gate increases the current drive due to the reduction of the flatband voltage. The change in the flatband voltage is due to a shift in the valence-band energy level in the gate. This shift results in a change in the barrier height for electrons tunneling from the gate. Thus, the presence of Ge in the gate increases the tunneling current in the gate. This increase may result in a limitation in the use of SiGe gates in future generations of MOSFETs with ultrathin gate dielectrics. The purpose of this work is to investigate the effect of Ge content on the tunneling current in CMOS devices with ultrathin gate dielectrics.

X-ray photoelectron spectroscopy (XPS) and photocurrent measurements for the determination of surface recombination velocity provide complementary information on the structure of the Si-SiO2 interface, being sensitive to the chemical nature of foreign species at the interface the former, and to intrinsic defects the latter. The comparison of the XPS N(1s) peaks determined for the Si-Si0 2 interfaces nitrided in NO or N2O ambients is useful to identify the species responsible for the broadening of the peak. In fact, nitridation by NO is mainly responsible for the formation of Si3N moieties at the silicon surface in which silicon atoms are partially oxidized; while nitridation by N2O proceeds with the oxidation of Si – Si backbonds to Si – N bonds, thus resulting in the formation of N(Si(O-)3)3 groups embedded in the oxide. Surface recombination velocity by photocurrent measurements gives evidence that nitridation in N2O is associated with an appreciable co-oxidation, while nitridation in NO is mainly associated with the passivation of interface states. Furthermore N2O and NO nitridation are responsible for different morphologies of the nitrided layers.

Electronic structure of two-fold coordinated nitrogen atom ≡Si2N• in Si3N4 and SiOxNy is studied in different charged states by the semiempirical quantum-chemical method MINDO/3 taking into account an atomic relaxation. It is shown theoretically that the neutral paramagnetic defect ≡Si2N• captures an electron, therefore it is an electron trap in Si3N4 and SiOxNy. The calculations show that the capturing of hole by the ≡Si2N• defect can be energetically favorable only for large oxygen concentration in oxynitride. It is predicted that the electron localization by the ≡Si2N• defect will result in the ESR signal disappearance.