Rapid Thermal Diffusion Research Articles

Rapid Isothermal Annealing of Doped and Undoped Spin-on Glass Films

AbstractThe rapid thermal annealing of doped (SOD) and undoped (SOG) glass films spinned onto silicon from diluted or undiluted solutions has been investigated. The dilution performed by methanol has allowed to obtain oxide films as thin as 10 nm.The optical measurements of annealed SOG films have shown that good oxide films without oxygen deficiency are achievable. The electrical characteristics of Al-gate capacitors assessed by Capacitance-voltage measurements have shown a great dependence of the water content in the range of 600–850°C before reaching a typical dielectric constant value near 3.8 at higher temperatures. Low Interface state densities values obtained at temperature up to 900°C confirm the curing effect of a rapid thermal annealing.On the other hand, we have demonstrated that the efficiency of rapid thermal diffusion from boron or phosphorus SOD films deposited on Si wafers depends on the source composition and its thickness. In particular, we have shown that it is possible to control the junction depth, the surface concentration and the minority-carrier diffusion length by varying the amount of dopant concentration in the solution, the thickness of the doped oxide film and the rapid thermal processing parameters. Futhermore, the remaining doped SOG film can play the role of an efficient oxide passivation layer.

The benefits of fluorine in pnp polysilicon emitter bipolar transistors

BF/sub 2/ implantation into polysilicon and its subsequent rapid thermal diffusion into single crystal silicon is commonly used for the fabrication of pnp polysilicon emitter bipolar transistors. In this paper the effect of the fluorine, which is introduced into the polysilicon during the BF/sub 2/ implant, is investigated. Pnp polysilicon emitter bipolar transistors are fabricated in which the boron and fluorine are implanted separately, with the fluorine only going into one half of each wafer. Electrical results show that fluorine has two interrelated effects. In devices given a low thermal budget emitter drive-in, a drop in base current by a factor of approximately 3.2 is observed when the fluorine is present, together with an improvement in the ideality of the base characteristics. This is explained by the passivation of trapping states at the polysilicon/silicon interface by the fluorine. In contrast, in devices-given a higher thermal budget emitter drive-in, an increase in base current by a factor of approximately 2.5 is observed, when fluorine is present. This is explained by the action of the fluorine in accelerating the breakup of the interfacial layer. A model is proposed to explain this behavior.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Shallow n+ Junctions in Silicon by Arsenic Gas‐Phase Doping

Shallow arsenic junctions were formed in short processing times using gas‐phase rapid thermal diffusion with arsine or tertiarybutylarsine (TBA). A 60 s gas‐phase diffusion at 1100°C using 3.6% arsine in helium at 760 Torr formed 150 nm junctions with a measured sheet resistance of 100 Ω/□. Shallow junctions were also formed with a 12 min diffusion at 900°C using 10% TBA in argon at 10 Torr. These TBA‐formed junctions have arsenic concentration at the silicon surface greater than and a sheet resistance of 244 Ω/□. In addition, TEM cross sections show no process‐induced damage at the junction for gas‐phase doping.

Silicon doping from phosphorus spin-on dopant sources in proximity rapid thermal diffusion

Rapid thermal diffusion (RTD) of phosphorus has been investigated using a spin-on dopant (SOD) deposited on a silicon wafer and placed as a dopant source in proximity to a processed Si wafer. In such a process, the efficiency of doping is affected by the amount of P supplied from the SOD to the processed wafer. Doping in RTD is controlled by the thickness of the SOD and its structure, which depends on low-temperature baking. Experimental results of secondary-ion-mass spectroscopy analyses and sheet resistance indicate that diffusion coefficients of phosphorus in the SOD during RTD are considerably larger than in thermal oxides.

Shallow-Junction Formation by Rapid Thermal Diffusion into Silicon from Doped Spin-on Glass Films

ABSTRACTHere we investigate the possibility to use rapid thermal annealed spin-on doped glass (SOG) films as a doping source as well as a surface passivation layer. The dilution of the SOG liquid source with methanol allows to control the oxide film thickness and the dopant concentration. The results show that the combination of spin-on film (after dilution) and RTP can produce shallow lightly doped emitters. Junction depths less than 0.2 µm and surface concentrations in the range 1−20 × 1019 cm−3 are obtained. Sheet resistances lower than 150 Ω/□ are easily reached. Moreover, the minority-carrier diffusion length is improved due to the gettering effect induced by phosphorus diffusion. The use of the remaining SOG oxide film as a passivation layer makes this technique favourable for some application.

Fabrication of submicron junctions-proximity rapid thermal diffusion of phosphorus, boron, and arsenic

Various techniques used in fabrication of deep submicron junctions are reviewed with respect to their advantages and disadvantages in silicon very large scale integration (VLSI) circuits technology. Proximity rapid thermal diffusion is then presented as an alternative process which results in very shallow junctions with high dopant concentrations at the surface. The feasibility of Si doping with B, P, and As for both planar and 3-D structures such as trench capacitors used in high density DRAM memories is shown based on sheet resistance measurements, secondary ion mass spectroscopy and scanning electron micrographs. Retardation effect of arsenic diffusion similar to the well known inhibition of silicon or SiO/sub 2/ deposition in chemical vapor deposition (CVD) processes is identified and discussed. >

Boron Doping using Proximity Rapid Thermal Diffusion from Spin-on-Dopants

ABSTRACTProximity rapid thermal diffusion (RTD) has been investigated as a doping technique for p-type boron doped junctions. The efficiency of RTD has been studied as a function of process variables (temperature, time, and ambient) and evaluated based on sheet resistance measurements, secondary ion mass spectroscopy (SIMS), spreading resistance (SR), and Fourier transmission infrared absorption (FTIR) in a spin-on-dopant source (SOD). The doping efficiency in source wafers is controlled by different mechanism than in processed wafers. Strong influence of dopant incorporation in the processed wafers on oxygen content in the diffusion ambient is observed especially at low diffusion temperatures.

Rutherford backscattering analysis of phosphorus gettering of gold and copper

The extrinsic gettering of Au and Cu by phosphorus diffusion in a classical or rapid thermal furnace has been analyzed by Rutherford backscattering (RBS) measurements. Accumulation of Au and Cu in the phosphorus-doped region has been clearly evidenced after classical or rapid thermal diffusion of phosphorus from a spin-on deposited silicon glass source in the temperature range 950–1050 °C for typical durations of 15 min and 25 s, respectively, confirming the existence of classical as well as a rapid thermal gettering effect.

Investigation of Proximity Rtd for Submicron Junctions in Vlsi Si Devices

ABSTRACTProximity rapid thermal diffusion is presented as a doping process for fabrication of very shallow junctions. The kinetics of Si doping with B, P and As is investigated using sheet resistance measurements, secondary ion mass spectroscopy and FTIR analyses. The efficiency of doping is affected by the dopant transport in the SOD which depends on the structure and composition of the SOD.

Epitaxial regrowth of n+ and p+ polycrystalline silicon layers given single and double diffusions

This article investigates the epitaxial regrowth of n-type and p-type polycrystalline silicon (polysilicon) layers deposited on silicon, which are subjected to either a single emitter diffusion or consecutive base and emitter diffusions. A wide range of diffusion conditions is considered, covering both rapid thermal and furnace diffusion in the temperature range 950–1200 °C. The sheet resistances of single-diffused n-type polysilicon layers are significantly higher than those of double diffused layers for rapid-thermal emitter diffusions in the temperature range 1025–1125 °C. This is explained by the epitaxial regrowth of the polysilicon during the emitter diffusion, caused by the partial break-up of the interfacial oxide during the base diffusion. In contrast the sheet resistances of single- and double-diffused p-type polysilicon layers are found to be similar. Rutherford backscattering spectra are presented which show that the structures of the single- and double-diffused polysilicon layers are similar. This is explained by the effect which fluorine, incorporated into the polysilicon during the BF2 emitter implant, has in accelerating the break-up of the interfacial oxide during the early part of the emitter diffusion. Estimates are made of the time to break up the interfacial oxide layer and the time to vertically epitaxially align the polysilicon at different temperatures, and activation energies of 4.9 and 4.7 eV, respectively obtained. In n-type polysilicon, the epitaxial regrowth is dominated by the time to break up the interfacial oxide layer, whereas in BF2 implanted p-type polysilicon it is dominated by the time to vertically epitaxially align the polysilicon. A vertical epitaxial alignment rate of 1000 Å/s is obtained for n-type polysilicon at 1050 °C, compared with 240 Å/s for p-type polysilicon at 1100 °C.

Light Induced Rapid Thermal Diffusion of Boron Atom in Silicon

We have studied the light induced rapid thermal diffusion of boron atom in silicon. The samples were heated by the rapid thermal processor. We have carried out spreading resistance and deep level transient spectroscopy (DLTS) measurements. The impurity distribution profile is much shallower and steeper than that of conventional thermal diffusion and the diffusion depth can be controlled to 0.1 μm. Several peaks in the deep level transient spectra were detected and the density of these defects ranges from 0.5×1012 to 5.6×1012 /cm3. The passivation and annihilation of these defects have been studied. We have also made the planar diode whose diameter is 500 μm. The reverse current and the back breakdown voltage of the planar diode are 10-9 A and 80 V respectively.

Rapid thermal diffusion of boron implanted as boron difluoride in preamorphized silicon

The diffusion of boron, implanted into crystal and preamorphized silicon in the form of boron difluoride, has been studied using secondary-ion mass spectroscopy and cross-sectional transmission electron microscopy. A 90-keV silicon implant creates an amorphous layer extending from the silicon surface to a depth of 186 nm as measured by Rutherford backscattering spectroscopy. The as-implanted boron profiles are contained completely within the amorphous layer. Results indicate that boron diffusion in the amorphous layer is suppressed during rapid thermal annealing between 1000 and 1150 °C. Discussion of this is based on the effect of fluorine on the boron diffusion.

Shallow-junction formation on silicon by rapid thermal diffusion of impurities from a spin-on source

Rapid thermal diffusion (RTD) of P and/or B into silicon wafer from spin-on sources using tungsten halogen lamps was successfully used to fabricate very shallow n/sup +/-p and/or p/sup +/-n junctions. RTD was performed in the temperature range of 600-1080 degrees C for 5-60 s, and the heating rates were varied in the range 10-83 degrees C/s. Effects of the two-step RTD, high temperature for several seconds, and subsequent low temperature for 60 s, were also examined. The RTD of P was carried out from P-doped oxide films and that of B was carried out from polymeric boron-doped films. Using RTD one can obtain a very shallow junction, thinner than 20 nm in depth. The impurity diffusion by RTD is similar to conventional furnace processing. However, the RTD of P and/for B was enhanced with the heating rate, especially at 83 degrees C/s. This was assumed to be caused by the stress field induced in the heating stage. The junction depth, I-V characteristics, spectral response, and cell parameters of fabricated photodiodes are presented. >

Spectral responses of GaAs photodiodes fabricated by rapid thermal diffusion

The spectral responses of GaAs photodiodes fabricated by rapid thermal diffusion (RTD) of Zn are presented. The authors tried controlling the p/sup +/-n junction depth by the heating rate of RTD, without extending the diffusion time. It is found that Zn diffuses from the surface to a deeper position as the heating rate increases. Consequently, the spectral response of photodiodes formed by RTD is strongly dependent on the heating rate of RTD. A large improvement in the short-wavelength response between 400 and 800 nm is observed as the heating rate decreases.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Estimation of effective diffusion time in a rapid thermal diffusion using a solid diffusion source

Two-step rapid thermal diffusion (RTD) of phosphorus and boron using a solid diffusion source is described. From the application of the Boltzmann-Matano method to SIMS profiles of phosphorus and boron after RTD, it has been found that some additional correction terms to the effective diffusion time must be introduced. In the phosphorus diffusion case, the increment of the effective diffusion time due to the supersaturation of point defects during the cooling cycle is about 3 s. In the case of boron diffusion, the additional effective diffusion time is a strong function of diffusion temperature. This has been explained as the effect of initial growth of the boron-rich layer during the glass-transfer process. The introduction of additional correction terms to the effective diffusion time makes it possible to treat the RTD process in a similar manner to normal diffusion.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

GaAs doping by rapid thermal diffusion of a laser-deposited elemental Zn source film: Shallow and laterally graded diffusions

We present an excimer-laser-based doping process useful for shallow uniform and laterally graded p-type doping of GaAs substrates. Specifically, low power 248-nm pulses from a KrF excimer laser are used to nonthermally photodeposit thin Zn layers (∼3–300 Å) from a dimethylzinc (DMZn) ambient onto selected GaAs surface regions. Uniform exposure of a sample to the laser pulses produces a source film which is laterally uniform in thickness, whereas variations in exposure time across a sample deposit a source film which is laterally graded in thickness. The surface is subsequently capped, and the Zn source is diffused into the GaAs using rapid thermal annealing. Secondary ion mass spectroscopy and spreading resistance measurements indicate that uniformly thick source depositions result in uniform diffusions with shallow junction depths and high surface concentrations. Alternatively, our measurements show that gradations in the dopant source profile translate into laterally graded doping profiles for appropriately chosen source thicknesses and diffusion parameters.

Phosphorus Gettering by Rapid Thermal Processing

ABSTRACTWe have investigated the rapid thermal diffusion of phosphorus into p-type silicon from a spin-on coated film as a function of the process temperature and time duration. The electron diffusion length LD measurements performed by the Surface PhotoVoltage (SPV) method present evidence for a get-tering phenomena since the LD values of the diffused samples are significantly improved. This result is important for the future of RTP in the area of silicon devices where carrier transport is controlled by the bulk lifetime.

Bulk diffusion length improvement by rapid thermal gettering

Rapid thermal diffusion of phosphorus into p-type silicon from a spin-coated film containing the dopant has been studied as a function of process temperature and time duration. The electron diffusion length measurements performed by the surface photovoltage method present evidence for a gettering phenomena since the diffusion length values of the diffused silicon samples are found to exceed the initial value reported for the virgin material.

Compositional disordering of strained InGaAs/GaAs quantum wells by Au implantation: Channeling effects

Compositional disordering of strained InGaAs quantum wells by the implantation of Au ions has been examined as a function of the incident implantation angle. Together, photoluminescence and secondary ion-mass spectrometry demonstrate that mixing at depths significantly greater than the mean-implantation range is due to the creation of point defects by ions which have channeled into the crystal. Compositional disordering effects due to the rapid thermal diffusion of Au ions was negligible.

Doping of trench capacitors by rapid thermal diffusion

A new rapid thermal diffusion process for shallow, heavily doped trench junctions in high density dynamic RAMs is described. Planar dopant sources are formed by spin-coating rigid substrates, such as silicon wafers or solid dopant sources, with liquid dopants. Diffusion takes place at high temperatures when the source, placed in proximity to the silicon wafer, releases dopant via evaporation followed by diffusion to the silicon surface. Well-controlled, heavily doped shallow junctions are readily obtained for B, P, and As. The doping process is shown to provide uniform doping of high-aspect-ratio trenches. Process control is achieved by controlling the wafer temperature and duration of the process. Junction depths near 0.1 mu m have been demonstrated over the entire surface of trenches 0.7 mu m in diameter and 6 mu m in depth. >