Remote Plasma-assisted Oxidation Research Articles

Remote Plasma Processing of Sapphire Substrates for Deposition of TiN and TiO<SUB>2</SUB>

The paper uses remote plasma assisted deposition, oxidation and nitridation processes for depositing thin films of metallic TiN on crystalline sapphire (0001) substrates. These films on sapphire substrates are being studied as window materials for high power radio frequency (RF) power tubes. A sequence of four process steps has been performed in a reactor chamber that isolates the deposition and surface-processing chamber from the plasma generation region. The chamber is part of an ultra-high-vacuum (UHV) compatible multi-chamber cluster in which the sequence of four process steps can be interrupted after each step, and surface chemistry changes can be identified by in-line Auger electron spectroscopy (AES). The four process steps, performed after an ex-situ chemical clean and blow-dry in nitrogen gas, are (i) a remote plasma-assisted oxidation (RPAO) in which surface contaminants including adventitious carbon are removed; (ii) a remote plasma-assisted nitridation (RPAN) process which forms a superficial layer of generic AION used to increase surface adhesion of the TiN films; (iii) a remote plasma-enhanced chemical-vapor deposition (RPECVD) process for deposition of 2 to 5 nm thick TiN films, and finally (iv) a second RPAN step that increases the ratio of Ti-N bonding in the TiN films with respect to adventitious O-atom incorporation from the Ti precursor, Ti tetra-butoxide.

Influence of Si/SiO 2 interface properties on electrical performance and breakdown characteristics of ultrathin stacked oxide/nitride dielectric films

In this work, the influence of Si/SiO 2 interface properties, interface nitridation and remote-plasma-assisted oxidation (RPAO) thickness (<1 nm), on electrical performance and TDDB characteristics of sub-2 nm stacked oxide/nitride gate dielectrics has been investigated using a constant voltage stress (CVS). It is demonstrated that interfacial plasma nitridation improves the breakdown and electrical characteristics. In the case of PMOSFETs stressed in accumulation, interface nitridation suppresses the hole traps at the Si/SiO 2 interface evidenced by less negative V t shifts. Interface nitridation also retards hole tunneling between the gate and drain, resulting in reduced off-state drain leakage. In addition, the RPAO thickness of stacked gate dielectrics shows a profound effect in device performance and TDDB reliability. Also, it is demonstrated that TDDB characteristics are improved for both PMOS and NMOS devices with the 0.6 nm-RPAO layer using Weibull analysis. The maximum operating voltage is projected to be improved by 0.3 V difference for a 10-year lifetime. However, physical breakdown mechanism and effective defect radius during stress appear to be independent of RPAO thickness from the observation of the Weibull slopes. A correlation between trap generation and dielectric thickness changes based on the C– V distortion and oxide thinning model is presented to clarify the trapping behavior in the RPAO and bulk nitride layer during CVS stress.

Low-temperature preparation of GaN-SiO2 interfaces with low defect density. I. Two-step remote plasma-assisted oxidation-deposition process

In previous studies, device-quality Si-SiO2 interfaces and dielectric bulk films (SiO2) were prepared using a two-step process: (i) remote plasma-assisted oxidation (RPAO) to form a superficially interfacial oxide (∼0.6nm) and (ii) remote plasma-enhanced chemical vapor deposition (RPECVD) to deposit the oxide film. The same approach has been applied to the GaN-SiO2 system. Without an RPAO step, subcutaneous oxidation of GaN takes place during RPECVD deposition of SiO2, and on-line Auger electron spectroscopy indicates a ∼0.7-nm subcutaneous oxide. The quality of the interface and dielectric layer with/without RPAO process has been investigated by fabricated GaN metal-oxide-semiconductor capacitors. Compared to single-step SiO2 deposition, significantly reduced defect state densities are obtained at the GaN-SiO2 interface by independent control of GaN-GaOx interface formation by RPAO and SiO2 deposition by RPECVD.

Low-temperature preparation of GaN-SiO2 interfaces with low defect density. II. Remote plasma-assisted oxidation of GaN and nitrogen incorporation

Low-temperature remote plasma-assisted oxidation and nitridation processes for interface formation and passivation have been extended from Si and SiC to GaN. The initial oxidation kinetics and chemical composition of thin interfacial oxide were determined from analysis of on-line Auger electron spectroscopy features associated with Ga, N, and O. The plasma-assisted oxidation process is self-limiting with power-law kinetics similar to those for the plasma-assisted oxidation of Si and SiC. Oxidation using O2∕He plasma forms nearly pure GaOx, and oxidation using 1% N2O in N2 forms GaOxNy with small nitrogen content, ∼4–7at.%. The interface and dielectric layer quality was investigated using fabricated GaN metal-oxide-semiconductor capacitors. The lowest density of interface states was achieved with a two-step plasma-assisted oxidation and nitridation process before SiO2 deposition.

Remote plasma-assisted oxidation of SiC: a low temperature process forSiC–SiO2 interface formation that eliminates interfacial Si oxycarbide transition regions

Remote plasma-assisted oxidation of SiC is a low temperature process,300 °C, for the formation of device quality interfaces on SiC. This paperdiscusses two aspects of the process: (i) the motivation for eliminating hightemperature oxidation processes that can generate silicon oxycarbide,Si–O–C, interfacial regions which can be a source of interfacial defects and (ii) the kinetics of theremote plasma-assisted oxidation process that effectively eliminates interfacial Sioxycarbide transition regions. The differences between interfacial relaxation atSi–SiO2 and SiC–SiO2 are based on the relative stabilities of the suboxides of Si and SiC,SiOx and (Si,C)Ox, respectively.

Device-quality GaN–dielectric interfaces by 300 °C remote plasma processing

In previous studies, device-quality Si–SiO 2 interfaces and dielectric bulk films (SiO 2) were prepared using a two-step process; (i) remote plasma-assisted oxidation (RPAO) to form a superficially interfacial oxide (∼0.6 nm) and (ii) remote plasma enhanced chemical vapor deposition (RPECVD) to deposit the oxide film. The same approach has been applied to GaN–SiO 2 system. Low-temperature (300 °C) remote N 2/He plasma cleaning of the GaN surface, and the kinetics of GaN oxidation using RPAO process and subcutaneous oxidation during the SiO 2 deposition using an RPECVD process have been investigated from analysis of on-line Auger electron spectroscopy (AES) features associated N and O. Compared to single-step SiO 2 deposition, significantly reduced defect state densities are obtained at the GaN–dielectric interfaces by independent control of GaN–GaO x ( x∼1.5) interface formation by RPAO, and SiO 2 deposition by RPECVD.

Oxide formation and passivation for micro- and nano-electronic devices

A low-temperature remote plasma-assisted oxidation process for interface formation and passivation has been extended from Si and SiC to GaN. The process, which can be applied to nano-scale structures including quantum dots and wires, provides excellent control of ultra-thin interfacial layers which passivate the GaN substrate, preventing a parasitic or subcutaneous oxidation of the substrate during plasma deposition of SiO2. The remote plasma processing for GaN–SiO2 heterostructures includes: (i) an in situ nitrogen plasma surface clean; (ii) a remote plasma-assisted oxidation for formation of an interfacial GaOx (x=1.5) transition region between the GaN and deposited dielectric; and (iii) a remote plasma-enhanced chemical vapor deposition of an SiO2 dielectric.

Low temperature semiconductor surface passivation for nanoelectronic device applications

A low temperature remote plasma assisted oxidation (RPAO) process for interface formation and passivation has been extended from Si and SiC to GaN. The process, which can be applied to nanoscale structures including quantum dots and wires, provides excellent control of ultra-thin interfacial layers which passivate the GaN substrate, preventing a parasitic or subcutaneous oxidation of the substrate during plasma deposition of SiO 2. This remote plasma processing for GaN-dielectric heterostructures includes: (i) an in situ nitrogen plasma surface clean, (ii) RPAO for formation of an interfacial GaO x transition region between the GaN and deposited dielectric, and (iii) a remote plasma enhanced chemical vapor deposition of an SiO 2 dielectric.

Nitrogen incorporation in ultrathin gate dielectrics: A comparison of He/N2O and He/N2 remote plasma processes

Ultrathin Si oxynitride films grown by low-temperature remote plasma processing were examined by on-line Auger electron spectroscopy and angle-resolved x-ray photoelectron spectroscopy to determine the concentration, spatial distribution, and chemical bonding of nitrogen. The films were grown at 300 °C on Si(100) substrates using two radio-frequency remote plasma processes: (i) He/N2O remote plasma-assisted oxidation (RPAO) and (ii) two-step remote plasma oxidation/nitridation. A 5 min He/N2O RPAO process produces a 2.5 nm oxynitride film incorporating approximately 1 monolayer of nitrogen at the Si–SiO2 interface. The interfacial nitrogen is bonded in a N–Si3 configuration, as in silicon nitride (Si3N4). By comparison, a 90 s He/N2 remote plasma exposure of a 1 nm oxide (grown by 10 s He/O2 RPAO) consumes substrate Si atoms creating a 1 nm subcutaneous Si3N4 layer. The nitrogen areal density obtained via the two-step process depends on the initial oxide thickness and the He/N2 remote plasma exposure time. Moreover, as the oxide thickness is increased (by increasing the He/O2 remote plasma exposure), the nitrogen distribution shifts away from the Si–SiO2 interface and into the oxide. More nitrogen with a tighter distribution is incorporated using He versus Ar dilution. Insight into the remote plasma chemistry was provided by optical emission spectroscopy. Strong N2 first positive and second positive emission bands were observed for He/N2O and He/N2 remote plasmas indicating the presence of N2 metastables and ground-state N atoms.

Ar/N 2 O remote plasma-assisted oxidation of Si(100): Plasma chemistry, growth kinetics, and interfacial reactions

The kinetics of Ar/N2O remote plasma-assisted oxidation of Si(100) and the mechanism of nitrogen incorporation at the Si–SiO2 interface were investigated using mass spectrometry, optical emission spectroscopy, and on-line Auger electron spectroscopy. N2, O2, and NO are the stable products of N2O dissociation in the plasma. The maximum NO partial pressure occurs at 10 W applied rf power; N2 and O2 are the predominant products for applied powers greater than 50 W. Ar/N2O remote plasmas are prolific sources of atomic O; in contrast, atomic N is not produced in significant concentrations. Ar/N2O remote plasma-assisted oxidation was investigated at 300 °C for applied rf powers of 5, 20, and 50 W. The oxide growth kinetics are slower than expected for a purely diffusionally controlled process. A diffusion-reaction model that incorporates first-order loss of the oxidizing species as it diffuses through the growing oxide layer fits the data very well. The initial oxidation rate increases linearly with plasma density, suggesting that the near-surface concentration of oxidizing species scales with the surface flux of plasma electrons. Nitrogen is incorporated at the Si–SiO2 interface in direct proportion to the N2 partial pressure in the Ar/N2O remote plasma. Molecular NO does not react at the Si–SiO2 interface at 300 °C, its role in Si thermal oxynitridation notwithstanding. Nitrogen incorporation at the Si–SiO2 interface was also achieved by exposure of ultrathin Ar/O2 plasma oxides to a remote 20 W Ar/N2 plasma.

Monolayer-level controlled incorporation of nitrogen in ultrathin gate dielectrics using remote plasma processing: Formation of stacked “N–O–N” gate dielectrics

A low thermal budget approach to monolayer-level controlled incorporation of nitrogen in ultrathin gate dielectrics using 300 °C, remote plasma processing is discussed. Incorporation of approximately 1 ML of nitrogen at the Si–SiO2 interface in an “N–O” structure has been achieved by remote plasma-assisted oxidation of the Si surface followed by N2/He remote plasma nitridation, each at a process pressure of 0.3 Torr. The interface nitridation reduces direct and Fowler–Nordheim tunneling by at least one order of magnitude, independent of film thickness. Incorporation of nitrogen at the top surface of the oxide in a concentration equivalent to about 1–2 molecular layers of silicon nitride in an “O–N” structure has been accomplished by N2/He remote plasma nitridation at 300 °C, but at a reduced process pressure of 0.1 Torr. Top surface nitridation has been shown to prevent boron diffusion out of p+ poly-Si gate electrodes during high-temperature activation anneals, e.g., at 1000 °C. Combining interfacial and top surface nitridation processes resulted in a “N–O–N” structure that was effective in reducing tunneling leakage currents and suppressing boron out-diffusion from p+ poly-Si gate electrodes.

Differences between Interfacial Bonding Chemistry at SiC-SiO&lt;sub&gt;2&lt;/sub&gt; Interfaces Prepared by Low-Temperature Remote Plasma-Assisted Oxidation and High Temperature Conventional Thermal Oxidation

Differences between Interfacial Bonding Chemistry at SiC-SiO&lt;sub&gt;2&lt;/sub&gt; Interfaces Prepared by Low-Temperature Remote Plasma-Assisted Oxidation and High Temperature Conventional Thermal Oxidation

Ultrathin oxide gate dielectrics prepared by low temperature remote plasma-assisted oxidation

Monolayer N-atom incorporation at Si−SiO 2 interfaces in device-quality SiO 2 gate oxides has been accomplished by a three-step low-thermal budget process: (i) 300°C remote plasma-assisted oxidation in N 2O to form the nitrided Si−SiO 2 interface, (ii) 300°C remote plasma-assisted chemical vapor deposition from SiH 4 and O 2 or N 2O to form the oxide layer, and (iii) a 30 s 900°C post-deposition rapid thermal anneal for chemical and structural relaxation. This paper reports on an extension of lowtemperature plasma processing to ultra-thin gate dielectrics (<3 nm) that is based on the first of the three steps identified above: the 300°C remote plasma-assisted oxidation in O 2 or N 2O. This paper: (i) highlights interrupted processing Auger electron spectroscopy measurements to monitor (a) growth rate and (b) interfacial nitrogen; (ii) discusses the reactions pathways for the plasma-assisted oxide growth process; (iii) contrasts (a) plasma-assisted and (b) furnace and rapid thermal oxidation processes.

Differences between silicon oxycarbide regions at SiC[sbnd]SiO2 prepared by plasma-assisted oxidation and thermal oxidations

The initial stages of SiCSiO2 interface formation by low temperature (300°C) remote plasma assisted oxidation (RPAO) have been studied by on-line Auger electron spectroscopy (AES) for flat and vicinal 6H SiC(0001) wafers with Si(0001) and C faces (0001), focusing on (i) interfacial bonding and (ii) oxidation rates for thickness up to about 2 nm.

Plasma-engineered Si−SiO 2 interfaces: monolayer nitrogen atom incorporation by low-temperature remote plasma-assisted oxidation in N 2O

This paper presents experimental studies in which N-atoms have been incorporated at Si−SiO 2 interfaces by forming the interface and oxide film by a 300 °C remote plasma-assisted nitridation/oxidation process using N 2O. Process dynamics have been studied by interrupted plasma processing using on-line Auger electron spectroscopy (AES). Based on the on-line AES, and complementary ex situ secondary ion mass spectroscopy and optical second harmonic generation results, monolayer nitrogen atom interface coverage has been confirmed. The factors that contribute to preferential nitrogen atom attachment at the Si−SiO 2 interface have been identified.

Plasma-assisted formation of low defect density SiC–SiO2 interfaces

The initial stages of SiC–SiO2 interface formation by low temperature (300 °C) remote plasma assisted oxidation (RPAO) on flat and vicinal 6H SiC(0001) wafers with Si faces have been studied by on-line Auger electron spectroscopy (AES). Changes in AES spectral features associated with Si–C and Si–O bonds are readily evident as oxidation progresses; however, there are no detectable AES features that can be attributed to C–O bonds. Initial oxidation rates as determined from AES data are greater for vicinal wafers than for flat wafers paralleling results for RPAO oxidation of Si. Devices fabricated on vicinal SiC wafers require an 1150 °C anneal in an H2 containing ambient to reduce defect densities from the 1013 to 1011 cm−2 range, consistent with termination of C atom step edge dangling bonds by H atoms. Devices prepared by thermal oxidation also require a 1150 °C anneal in H2 even though silicon oxycarbide regions with C–O bonds are formed in a transition region at the SiC–SiO2 interfaces.

Plasma-assisted formation of low defect density silicon carbide-silicon dioxide, SiCSiO 2, interfaces

The initial stages of SiCSiO 2 interface formation by low temperature (300°C) remote plasma assisted oxidation (RPAO) of flat and viscinal 6H SiC(0001) surfaces have been studied by online Auger electron spectroscopy (AES). Differences in post-deposition/oxidation annealing for devices fabricated using plasma-assisted and conventional thermal processing, respectively, have been correlated with differences in interfacial bonding chemistries.

Ultra-thin gate dielectrics prepared by low-temperature remote plasma-assisted oxidation

This paper discusses the formation of ultra-thin nitrided gate oxides by a low temperature plasma assisted oxidation process using remotely excited N 2O as the source gas for both oxygen and nitrogen atoms. Three aspects of this process are addressed: (i) the differences in oxide growth rates for O 2 or N 2O plasma oxidation processes; (ii) the reaction pathways for the incorporation of nitrogen at the SiSiO 2 interface for the N 2O plasma process; and (iii) possible nitrogen atom depletion during processing steps that follow the plasma assisted oxidation/nitridation process.

Reliability of nitrided Si–SiO2 interfaces formed by a new, low-temperature, remote-plasma process

Controlled amounts of nitrogen atoms have been incorporated at Si–SiO2 interfaces by a new, low-temperature (300 °C), remote-plasma process, and corresponding improvements in device reliability are reported. Interfacial nitrogen-atom concentrations, up to 1×1015 cm−2, were obtained by a predeposition, remote plasma-assisted oxidation using mixtures of N2O and O2. Auger electron spectroscopy and secondary ion mass spectrometry studies to analyze N-atom concentrations at Si–SiO2 interfaces are discussed. Also, the results of electrical testing of submicron, n-channel metal–oxide–silicon field-effect transistors fabricated with this new process technology are reported. We found that the incorporation of N atoms at the Si–SiO2 interface increased current drive capability at high gate voltages but did not affect the threshold voltage of devices or the peak channel transconductance, gm. Device reliability, as measured by resistance to peak gm degradation after hot-carrier stressing, was found to increase with increasing N-atom concentrations at the Si–SiO2 interface.

Nitrogen-atom incorporation at Si–SiO2 interfaces by a low-temperature (300 °C), pre-deposition, remote-plasma oxidation using N2O

Nitrogen-atom incorporation at Si–SiO2 interfaces has been achieved using a N2O remote-plasma-assisted oxidation at 300 °C prior to remote plasma enhanced chemical vapor deposition of thin SiO2 gate dielectric films. The N2O remote plasma pre-deposition treatment removed residual hydrocarbon contamination, oxidized the Si surface, and incorporated nitrogen atoms at the Si–SiO2 interface. The amount of N incorporated at the Si–SiO2 interface was similar to amounts reported in the literature for oxides nitrided at much higher temperatures (800–1200 °C), where improved diffusion barrier properties and improved resistance to hot-carrier degradation were attributed to the presence of this N. The N2O remote plasma pre-deposition treatment was compared to previously developed, in situ H2 and O2 remote plasma surface treatments by Auger electron spectroscopy and secondary ion mass spectrometry measurements. Metal–oxide–semiconductor (MOS) capacitors were also fabricated to compare the electrical properties of interfaces formed with these different techniques. MOS C–V tests revealed that the interface formed by the N2O remote plasma-assisted oxidation had a low density of interface trapping states, midgap Dit=1×1010 cm−2 eV−1.