Backside Secondary Ion Mass Spectrometry Research Articles

Effect of optimal rapid thermal alloying of ohmic contacts to microwave pseudomorphic HEMTs

Gallium Arsenide (GaAs) pseudomorphic High Electron Mobility Transistors (pHEMTs) are currently used as active devices in manufacturing Monolithic Microwave Integrated Circuits (MMICs) for microwave and millimetre wave applications like Transmit-Receive (T/R) modules in Radars and communication. Low contact resistances (Rc) of pHEMT devices are necessary to obtain low access resistances to the device channel, for enhancement of transconductance and cut-off frequency. Devices formed by optimal and suboptimal conditions of rapid thermal alloying by infra-red optical radiation are investigated using cross-section transmission electron microscopy (XTEM), backside secondary ion mass spectrometry (backside SIMS) and thermal imaging techniques to understand the role of optimal alloy formation and its role in enhancement of device parameters.

Front-side and back-side secondary ion mass spectrometry analyses on advanced doping processes for ultra-large scale integrated circuit: A case study

The issues caused by the artifacts of sputtering/re-deposition and ion knock-in effects of the conventional front-side secondary ion mass spectrometry (SIMS) measurement are extensively investigated. Back-side SIMS measurement is used to confirm these hypotheses and resolve these issues. Based on back-side SIMS data, plasma immersion ion implantation (PIII) processed wafers show superior junction characteristics and less damages than beamline (BL)-based implant processed wafers, including shallower junction depth (58.9 nm vs. 64.2 nm), similar junction abruptness (9.0 nm/dec vs. 8.7 nm/dec), and less end-of-range defects. They are opposite to the misleading conclusions that front-side SIMS data provided. A better electrical performance by PIII processed device than that by BL-based implant processed device is demonstrated.

Suppression of p-type parasitic channel formation at the interface between the aluminum nitride nucleation layer and the high-resistivity silicon substrate

In this study, GaN-based epitaxial structures were grown on high-resistivity silicon (HRSi) substrates by metalorganic chemical vapor deposition. The p-type parasitic channels generated at the interfaces of the aluminum nitride (AlN) nucleation layers and HRSi substrates were characterized by surface capacity measurement, backside secondary ion mass spectrometry, and spread resistance profiling. The 2-nm thick silicon nitride (SiNx) layer formed by nitridation on the HRSi substrates was used to suppress the Al diffusion from the 50-nm AlN nucleation layer and also prevented from generation of the p-type parasitic channels. The p-type parasitic channels induced insertion losses at high frequencies. Transmission line measurement was used to determine the insertion losses. The insertion loss of the GaN-based epitaxial structure with the optimized 25-nm AlN nucleation layer on the 2-nm SiNx layer was -2.72 dB/mm. It was only 0.04 dB/mm higher than that of the annealed HRSi substrate (-2.68 dB/mm) at 10 GHz. Obviously, the diffusion of Al from the optimized 25-nm thick AlN nucleation layer into the HRSi substrate can be alleviated by the SiNx layer, thereby reduced insertion loss.

New sample preparation method using room-temperature direct bonding in backside SIMS analysis

Secondary ion mass spectrometry (SIMS) is one of the tools to investigate the dopant or impurity profiles of the semiconductor materials. In particular, the backside SIMS is a useful technique to examine the diffusion of dopant at the surface while minimizing knock-on effect. However, it is very difficult to prevent insulating samples from charging when O2+ source is used for positive secondary ion detection in magnetic sector SIMS. In order to overcome the problem, the authors have employed a new sample preparation method using a room-temperature direct bonding (RTDB). The authors investigated the depth profiling of insulating samples, which were stacked on a dielectric silicon dioxide films with silicon wafer as a magnetic sector SIMS instrument. The samples treated with and without RTDB were compared, and the results show that the depth profiles of RTDB-treated sample could be obtained no sign of charge-up in the backside SIMS analysis.

Comparison of B2O3 and BN deposited by atomic layer deposition for forming ultrashallow dopant regions by solid state diffusion

In this study, the authors investigated atomic layer deposition (ALD) of B2O3 and BN for conformal, ultrashallow B doping applications and compared the effect of dopant-containing overlayers on sheet resistance (Rs) and B profiles for both types of films subjected to a drive-in thermal anneal. For the deposition of B2O3, tris(dimethylamido)borane and O3 were used as coreactants and for the deposition of BN, BCl3 and NH3 were used as coreactants. Due to the extreme air instability of B2O3 films, physical analysis was performed on B2O3 films, which were capped in-situ with ∼30 Å ALD grown Al2O3 layers. For the BN films, in-situ ALD grown Si3N4 capping layers (∼30 Å) were used for comparison. From spectroscopic ellipsometry, a thickness decrease was observed after 1000 °C, 30 s anneal for the B2O3 containing stack with 60 ALD cycles of B2O3, whereas the BN containing stacks showed negligible thickness decrease after the annealing step, regardless of the number of BN cycles tested. The postanneal reduction in film thickness as well as decrease in Rs for the B2O3 containing stack suggests that the solid state diffusion dopant mechanism is effective, whereas for the BN containing stacks this phenomenon seems to be suppressed. Further clarification of the effectiveness of the B2O3 containing layer compared to the film stacks with BN was evidenced in backside secondary ion mass spectrometry profiling of B atoms. Thus, B2O3 formed by an ALD process and subsequently capped in-situ followed by a drive-in anneal offers promise as a dopant source for ultrashallow doping, whereas the same method using BN seems ineffective. An integrated approach for B2O3 deposition and annealing on a clustered tool also demonstrated controllable Rs reduction without the use of a capping layer.

Switching Mode and Mechanism in Binary Oxide Resistive Random Access Memory Using Ni Electrode

Resistive-switching (RS) modes in different CMOS-compatible binary oxides have been shown to be governed by the interplay with the Ni top electrode. Unipolar RS and metallic low-resistance state in polycrystalline HfO2 and ZrO2 are distinct from the preferential bipolar RS and semiconductive low-resistance state in amorphous Al2O3 and SiO2. Backside secondary ion mass spectrometry (SIMS) has shown the formation of Ni filaments in HfO2, in contrast to the formation of oxygen-vacancy filaments in Al2O3. The differences have been explained by strong dependence of Ni migration on the oxide crystallinity. Additionally, the RS mode can be further tailored using bilayer structures. The oxide layer next to the Si bottom electrode and its tendency of forming Ni filaments play significant roles in unipolar RS in the bilayer structures, in support of the conical-shape Ni filament model where the connecting and rupture of filaments for unipolar RS occur at the smallest diameter near the bottom electrodes.

Penetration of Copper-Manganese Self-Forming Barrier into SiO2 Pore-Sealed SiCOH during Deposition

The incorporation of a self-forming Cu diffusion barrier on pore-sealed SiCOH was investigated. SiCOH films 20% porous and 230 nm thick were capped with 36 nm SiO2. Fabricated structures (Cu-Mn/SiO2/SiCOH) were subjected to a back-side Secondary Ion Mass Spectrometry (SIMS) depth profile study to assess the extent of metal migration. SIMS depth profiles revealed that Cu and Mn diffused in significant amounts across the SiO2 layer during fabrication steps. A mass transport model was used to describe the migration of metal species. The diffusion coefficient for Cu in the SiO2 pore-sealing layer is approximately D∼5.62 × 10−16 cm2/sec.

Depth profiling in secondary ion mass spectrometry for ultra‐thin layer with nanometer order thickness by mesa‐structure fabrication

We attempted to make an accurate depth profiling in secondary ion mass spectrometry (SIMS) including backside SIMS for ultra‐thin nanometer order layer. The depth profiles for HfO2 layers that were 3 and 5 nm thick in a‐Si/HfO2/Si were measured using quadrupole and magnetic sector type SIMS instruments. The depth profiling for an ultra‐thin layer with a high depth resolution strongly depends on how the crater‐edge and knock‐on effects can be properly reduced. Therefore, it is important to control the analyzing conditions, such as the primary ion energy, the beam focusing size, the incidence angle, the rastered area, and detected area to reduce these effects. The crater‐edge effect was significantly reduced by fabricating the sample into a mesa‐shaped structure using a photolithography technique. The knock‐on effect will be serious when the depth of the layer of interest from the surface is located within the depth of the ion mixing region due to the penetration of the primary ions. Finally, we were able to separately assign the origin of the distortion to the crater‐edge effect and knock‐on effect. Copyright © 2012 John Wiley & Sons, Ltd.

Ohmic contacts to pseudomorphic HEMTs with low contact resistance due to enhanced Ge penetration through AlGaAs layers

AuGe/Ni ohmic contacts are used as source and drain electrodes of pseudomorphic HEMTs (pHEMTs). High alloying temperatures are generally believed to be necessary to enhance penetration of the alloy materials through the AlGaAs layers in order to establish a very low resistance path for the source–drain currents to access the two-dimensional electron gas (2DEG) layer. Here we have performed alloying experiments in the temperature range of 390–450 °C, and the contact resistance was determined using transfer length method measurements. Germanium diffusion was studied using backside secondary ion mass spectrometry. During our study, we have observed that doping of the channel by germanium is possible even at lower temperatures. But alloying at lower temperatures does not appreciably enhance the concentration throughout the different device layers below the contact pads. Hence, unlike MESFET alloying, higher alloying temperatures are essential for increasing the doping concentration so as to reduce the contact resistance and overcome the resistance of the AlGaAs layers.

Evaluation of Hydrogen in Tantalum Thin Films Using Secondary Ion Mass Spectrometry

The hydrogen distribution in tantalum and tantalum oxide thin films has been examined by secondary ion mass spectrometry (SIMS). Tantalum and tantalum oxide thin films implanted with deuterium were analyzed by conventional SIMS. Metal–insulator–metal (MIM) devices were analyzed by backside SIMS. The results of these measurements show that the hydrogen distribution is concentrated on the front side in tantalum films, while the hydrogen distribution in tantalum oxide films is not affected by SIMS measurement. A model has been proposed to explain the cause of an anomalous hydrogen peak forming at the interface between the tantalum oxide and tantalum films in the MIM devices. In the model, when the tantalum oxide film covering the tantalum film is removed by primary ion beam sputtering, hydrogen atoms in the tantalum film are quickly discharged to a vacuum in a sample chamber and the anomalous hydrogen peak is detected.

Effect of composition on the thermal stability of sputter deposited hafnium aluminate and nitrided hafnium aluminate dielectrics on Si (100)

Hafnium aluminate (HfAlO) and nitrided hafnium aluminate (HfAlON) dielectrics were sputter deposited on Si (100) substrate. The N2∕(N2+Ar) flow ratio was varied between 0 and 66.6% in order to vary the nitrogen concentration. The Hf/Al ratio was varied from 0.5 to 1. In situ x-ray photoelectron spectroscopy and electrical measurements were utilized to characterize the as-deposited HfAlO and HfAlON films. The thermal stability studies of the HfAlO and HfAlON thin films after a 1000 °C, 10 s argon rapid thermal anneal were performed using grazing incidence x-ray diffraction and backside secondary ion mass spectrometry. Suppression of crystallization and no detectible outdiffusion of hafnium and aluminum into the silicon substrate were seen for HfAlO and HfAlON thin films with a Hf/Al ratio of 0.5.

Dependence of electrical properties of HfSiON gate dielectrics on TaSiN metal electrode thickness

We have studied the effect of tantalum–silicon–nitride (TaSiN) metal electrode thickness on the electrical properties of ultrathin HfSiON gate dielectrics formed by atomic layer deposition (ALD) technology using Hf(N(CH3)(C2H5))4 and SiH(N(CH3)2)3 precursors. The TaSiN/HfSiON gate stacks were intended for use in conventional metal gate transistors with a high temperature thermal budget of 950 °C. Leakage current, effective mobility and the drain current in 30 nm thick TaSiN gate electrodes were improved with respect to the values for 10 nm thick TaSiN gate electrodes. From back-side secondary ion mass spectrometry (SIMS) analyses, it was concluded that thick TaSiN gate electrodes suppressed the nitrogen diffusion from the SiN hard mask into HfSiON/SiON gate stacks during activation annealing.

Dopant effects on the thermal stability of FUSI NiSi

The thermal stability of fully silicided (FUSI) NiSi with arsenic or boron doping on silicon on insulator (SOI) was investigated. After the stacks were subjected to a typical back-end of line (BEOL) thermal annealing in a N 2 ambient, abnormal oxidation of As doped FUSI NiSi stacks is observed by X-ray photoelectron spectroscopy (XPS), and confirmed by high-resolution transmission electron microscopy (HRTEM). X-ray diffraction (XRD) results show Ni-rich phases like Ni 3Si are formed due to abnormal oxidation of FUSI NiSi. In contrast to As doped stacks, no phase transformation nor abnormal oxidation are observed for B doped stacks under similar annealing. However, backside secondary ion mass spectrometry (SIMS) results indicate B penetration through a 3 nm SiON layer into the Si channel after N 2 annealing for 4 h at 400 °C. There is no evidence for Ni diffusion into the Si channel for B doped stacks. However, Ni penetration into the Si channel is observed for As doped stacks due to the enhancement of abnormal oxidation of FUSI NiSi.

Thermal stability of lanthanum scandate dielectrics on Si(100)

The authors have examined the thermal stability of amorphous, molecular beam deposited lanthanum scandate dielectric thin films on top of Si (100) after a 1000°C, 10s rapid thermal anneal. After the anneal, crystallization of LaScO3 is observed. Excellent suppression of lanthanum and scandium diffusion into the substrate silicon is indicated by the back-side secondary ion mass spectrometry (SIMS) analyses. In contrast, front-side SIMS and high-resolution electron energy loss analyses of the amorphous Si∕LaScO3∕Si (100) stack indicated the outdiffusion of lanthanum and scandium into the silicon capping layer during the anneal.

Ni Diffusion Studies from Fully-Silicided NiSi into Si

The interdiffusion of Ni from fully silicided NiSi metal gates through gate dielectrics into the Si substrate after N 2 annealing or forming gas annealing consistent with back-end-of-line thermal budgets is presented by using back-side secondary ion mass spectrometry profiling. Ni penetration is observed through 1.3 nm thick SiON into the Si channel region after annealing for 60 min at temperatures of 350-400°C. However, Ni penetration through 1.5 nm HfSiON/0.8 nm SiO 2 film into the Si channel is close to the limit of detection after annealing under similar conditions. The results suggest that Ni penetration can be suppressed by a dielectric film with sufficient thickness.

Interfacial Diffusion Studies of Cu ∕ ( 5 nm Ru ) ∕ Si Structures: Physical Vapor Deposited vs Electrochemically Deposited Cu

In contrast to physical vapor deposition (PVD), the electrochemical deposition (ECD) process is dependent upon substrate resistivity. ECD of Cu on ultrathin Ru diffusion barriers remains a technological challenge due to large resistivity increase over a wide plating area. Results are presented from the comparative investigation of interfacial stability and Cu diffusion processes in PVD and ECD structures. Cu can be conformally electroplated onto surfaces (ca. ) with over 94% efficiency. However, lesser uniformity and conformality of ECD Cu are observed on samples with larger surface areas. The transmission electron microscopy (TEM) reveals that ECD Cu film is less densely packed (ca. ) than PVD Cu. HRTEM studies in conjunction with surface analyses using optical microscopy and four-point probe resistivity measurements show that Ru can successfully impede Cu diffusion up to for , but fails at . Interfacial profiling data obtained from back side secondary-ion mass spectrometry (SIMS) analysis agree with TEM results. X-ray photoelectron spectroscopy (XPS) investigation on nitric acid-etched PVD and ECD samples shows the presence of residual ECD Cu after annealing, suggesting that ECD Cu diffuses further into Ru than PVD Cu.

Evaluation of back-side secondary ion mass spectrometry for boron diffusion in silicon and silicon-on-insulator substrates

We present a study on the redistribution of boron in (100) crystalline silicon and silicon-on-insulator (SOI) substrates after rapid thermal processing (RTP). The use of SOI back-side secondary ion mass spectrometry (SIMS) technique in obtaining an accurate diffusion profile is also investigated. Our results show that the boron diffusion profiles (using conventional frontside SIMS) do not deviate in any of the two types of substrates after RTP with a soak time of 30sec, indicating that the insulating effect of SOI substrate does not enhance the diffusion of boron. Since the profile obtained by the back-side SIMS technique is always shallower than that of front-side SIMS, it is deduced that the back-side SIMS technique gives a better representation of the real profile.

Ultra-shallow depth profiling with secondary ion mass spectrometry

Estimation methods for ultra-shallow profiling with secondary ion mass spectrometry (SIMS) were investigated. The depth and concentration of ultra-shallow profiles were calibrated using multi-delta-doped samples and bulk-doped samples. Boron profiles, whose implantation energy is 200 eV or less, were measured by backside SIMS analysis in order to minimize the atomic mixing effect. This analysis enabled accurate junction depth measurements for even 200 eV boron implanted samples when the primary oxygen ion energy was 500 eV or less, but the sample preparation time was relatively long. SIMS depth resolution functions were then extracted from surface-side and backside (true) profiles in order to deconvolute degraded surface-side profiles. This deconvolution analysis of SIMS (surface-side) profiles, using the depth resolution functions, provided profiles of similar quality to those obtained by backside SIMS analysis and was a relatively quick process.

Depth profiling for ultrashallow implants using backside secondary ion mass spectrometry

We studied accurate depth profiling for ultrashallow implants using backside secondary ion mass spectrometry (SIMS). For measuring ultrashallow dopant profiles such as 200 eV B implantation profiles, the effects of surface transient and atomic mixing are not negligible. We applied backside SIMS to analyze ultrashallow doping in order to exclude these effects. Comparing the SIMS profiles of surface side and those of backside, backside SIMS profiles showed a shallower ion implantation tail than surface-side SIMS profiles. Furthermore, backside SIMS profiles showed almost no dependence on primary ion energy. This indicates that backside SIMS provides sharp B profiles suitable for analyzing ultrashallow implants, even in the case where higher primary ion energy is used in comparison with implantation energy. The backside SIMS technique has a good potential to be used for the development of next-generation devices.

Investigation of boron penetration through decoupled plasma nitrided gate oxide using backside secondary ion mass spectrometry depth profiling

High drive-in temperature during dopant activation of p+-poly metal-oxide-semiconductor field effect transistors causes boron penetration through the thin gate oxide, which degrades the device performance. Conventional secondary ion mass spectrometry (SIMS) depth profiling is unable to accurately analyze boron penetration under rapid thermal annealing conditions due to ion knock-on and mixing effects. With the development of backside SIMS depth profiling technique using SOI wafers [Yeo et al., Surf. Interface Anal. 33, 373 (2002); Runsheim et al., J. Vac. Sci. Technol. B 20, 448 (2002)], quantification of the amount of boron penetration becomes possible. In this article, boron penetration through decoupled plasma nitridation silicon dioxide was studied by performing both front and backside depth profiling using 0.5 keV O2+ with oxygen flooding and 2 keV Cs+ primary ions at oblique incidence in a Cameca IMS-6f SIMS instrument.