PECVD Nitride Research Articles

Strain Modification of PECVD Nitride By Plasma Immersion Ion Implantation Processes

Strain engineering was introduced in the microelectronics industry almost two decades ago to improve the carrier mobility due to the modification of the band structures in the Metal Oxide Field Effect Transistor (MOSFET) channel [1, 2]. One method to induce local strain in the transistor channel consists in using Contact Etch Stop Layer (CESL) as stress liner. In order to improve both n-MOS and p-MOS performance, the use of a dual stressed liner (DSL) integration is a solution that combines tensile and compressive films on the same wafer [3]. However, the poor mechanical stability of the compressive PECVD nitride layer when exposed to a high thermal budget, combined with the increased integration complexity, limits the interest of the DSL approach. An alternative solution to tackle these limitations consists in locally transforming the tensile CESL nitride into compressive by Plasma Immersion Ion Implantation (PIII).For this study, PIII processes were performed on 300mm silicon bare wafers capped with a 35nm tensile PECVD nitride. Various species (Hydrogen (H), Helium (He) and Nitrogen (N)) implanted at various acceleration voltages (increasing from 1 to 6 in arbitrary units) and doses (A<B<C) were studied using a Pulsion® tool manufactured by IBS. After these processes, the samples were characterized by various techniques such as ellipsometry, bow measurement, Scanning Electron Microscopy observations, Secondary Ion Mass Spectrometry or FTIR analysis.The stress of the various nitride layers was determined by the Stoney formula, using the curvature measurements and the layer thickness determined by ellipsometry, assuming the shift of the bow results only from the change in nitride stress. Results show that, for all the species studied, the PIII process provides the capability to change the nitride stress from initially tensile to neutral or even compressive when increasing the dose and the acceleration voltage (Fig.1). The largest stress modifications were achieved with nitrogen and hydrogen. For the latter however, the blistering of the nitride layer is observed for the highest doses due to an excessive hydrogen concentration, which is prohibitive for further process integration. By using helium PIII process, the stress change is less for identical process parameters (Fig.1), leading to a neutrally stressed nitride layer. Increasing the helium dose to modify the nitride stress further leads to a consumption of the layer, which limits the use of helium only to the reversal of the mechanical stress.To verify that the stress change will remain during the subsequent process steps, curvature measurements were performed after a consequent thermal budget, equivalent to PMD deposition, applied after the PIII processes. The results show no significant change of the stress level.We demonstrated the capability of PIII processes to turn a tensile CESL nitride layer into a compressive one in a reasonable processing time thanks to the high beam current achievable with PIII process, without any consumption of the layer and without the need of a post implantation thermal treatment. Complementary analysis are on-going to fully characterize the impact of each species on the CESL physicochemical properties and thereby understand its stress evolution. Thanks to these encouraging results, the most promising conditions of all the species mentioned above will be experimented on electrical structures to quantify the related static performance gain.This project (OCEAN12) has received funding from the ECSEL Joint Undertaking (JU) under grant agreement No 783127. The JU receives support from the European Union’s Horizon 2020 research and innovation programme and France, Germany, Austria, Portugal, Greece, Spain, Poland.[1] S. Ito, et al, “Mechanical Stress Effect of Etch-Stop Nitride and its Impact on Deep Submicron Transistor Design”, 2000 IEDM Tech. Dig., p. 247[2] T.K. Kang, IEEE ELECTRON DEVICE LETTERS, VOL. 33, NO. 6, JUNE 2012.[3] H. S. Yang, “Dual Stress Liner for High Performance sub-45nm Gate Length SO1 CMOS Manufacturing”, IEDM 2004 Figure 1

Strain Modification of PECVD Nitride By Plasma Immersion Ion Implantation Processes

The impact of Plasma Immersion Ion Implantation (PIII) processes with various species (hydrogen, helium and nitrogen) on the stress of a tensile PECVD nitride film was evaluated. Ellipsometry measurements indicated no consumption of the nitride but a change in the optical index, signaling a material modification. The initial stress of the nitride was modified by PIII from tensile to mechanically neutral and even compressive. Hydrogen and nitrogen appeared to be more efficient to modify the stress than helium.

Effect of thermal and pulse laser annealing on photoluminescence of CVD silicon nitride films

The light-emitting properties of Si-rich silicon nitride films deposited on the Si (100) substrate by plasma-enhanced (PECVD) and low-pressure chemical vapor deposition (LPCVD) have been investigated. In spite of the similar stoichiometry (SiN1.1), nitride films fabricated by different techniques emit in different spectral ranges. Photoluminescence (PL) maxima lay in red (640 nm) and blue (470 nm) spectral range for the PECVD and LPCVD SiN1.1 films, respectively. It has been shown that equilibrium furnace annealing and laser annealing by ruby laser (694 nm, 70 ns) affect PL spectra of PECVD and LPCVD SiN1.1 in a different way. Furnace annealing at 600 °C results in a significant increase of the PL intensity of the PECVD film, while annealing of LPCVD films result only in PL quenching. It has been concluded that laser annealing is not appropriate for the PECVD film. The dominated red band in the PL spectrum of the PECVD film monotonically decreases with increasing an energy density of laser pulses from 0.45 to 1.4 J/cm2. Besides, the ablation of PECVD nitride films is observed after irradiation by laser pulses with an energy density of &gt; 1 J/cm2. This effect is accompanied by an increase in blue emission attributed to the formation of a polysilicon layer under the nitride film. In contrast, the LPCVD film demonstrates the high stability to pulsed laser exposure. Besides, an increase in the PL intensity for LPCVD films is observed after irradiation by a double laser pulse (1.4 + 2 J/cm2) which has not been achieved by furnace annealing.

On the Impact of Strained PECVD Nitride Layers on Oxide Precipitate Nucleation in Silicon

PECVD nitride layers with different layer stress ranging from about 315 MPa to −1735 MPa were deposited on silicon wafers with similar concentration of interstitial oxygen. After a thermal treatment consisting of nucleation at 650°C for 4 h or 8 h followed annealing 780°C 3 h + 1000°C 16 h in nitrogen, the profiles of the oxide precipitate density were investigated. The binding states of hydrogen in the layers was investigated by FTIR. There is a clear effect of the layer stress on oxide precipitate nucleation. The higher the compressive layer stress is the higher is a BMD peak below the front surface. If the nitride layer is removed after the nucleation anneal the BMD peak below the front surface becomes lower. It is possible to model the BMD peak below the surface by vacancy in-diffusion from the silicon/nitride interface. With increasing duration of the nucleation anneal the vacancy injection from the silicon/nitride interface decreases and with increasing compressive layer stress it increases.

Progress in the Development of All-Back-Contacted Silicon Solar Cells

N-type all-back-contact (ABC) silicon solar cells incorporating a simple oxide-nitride passivation scheme are presently being developed at the Australian National University. Having already achieved promising efficiencies with planar ABC cells [1], this work analyses the cell performance after integrating a surface texturing step into the process flow. Although the textured cells have significantly lower front surface reflection, the measured short-circuit current density is actually lower than that of the planar cells. Photoconductance decay data indicate the presence of high carrier recombination at the textured surface of the ABC cells, which are deposited with a stack of thermal oxide and LPCVD nitride. Further examination confirmed that high carrier recombination is due to stress induced by the LPCVD nitride on the peaks and valleys of the textured surface. Use of PECVD nitride instead of LPCVD nitride as an antireflection layer avoids the degraded carrier lifetime caused by the textured surface. Therefore, PECVD nitride should be a good substitute for constructing the oxide-nitride stacks of our future ABC cells.

AN EFFECTIVE PASSIVATION FILM STACK FOR THIN FILM BST CAPACITORS

ABSTRACT Thin film voltage tunable ferroelectric capacitors on various substrates are promising for use in high power microwave and other RF systems. Benefits of ferroelectric capacitors include miniaturization and integration with other passive devices. Commercialization of ferroelectric components requires compliance with certain industry standards for reliability. For ferroelectric capacitors the requirement to pass the THB test requires a silicon nitride layer in the back end of the process (after interconnect metalization). However the nitride layer deposition process results in a drastic increase in the leakage of the BST capacitors. This effect is attributed to the exposure of the ferroelectric material to atomic hydrogen which is a by-product of the PECVD deposition process. This paper presents results of different passivation materials for ferroelectric capacitors and for a barrier layer which preserves the performance of ferroelectric capacitors during a PECVD nitride deposition. This allows qualification of ferroelectric capacitors to industry reliability standards.

Low Temperature Silicon Nitride Deposition by Inductively Coupled Plasma CVD for GaAs Applications

In order to take advantage of silicon nitride films as an ILD layer on GaAs devices, the ICP CVD silicon nitride films were investigated by parametric study of effects of deposition parameters on the physical properties of silicon nitride film deposited in the range of 50 ~ 200oC temperature. Good quality of films could be achieved, including low moisture absorption, low H content (<15 at.%), good resistance to BOE etching (<50 Aå/min), smooth film surface (2.0 nm roughness), and reasonable film stress, as compared to the conventional PECVD nitride film, while the process temperature is much lower than the conventional PECVD process. This silicon nitride film was applied to the GaAs HBT device structure and showed very promising results of the gap-filling capability and planarization for next level of metallization. These results indicate the possibility of using the ICP CVD silicon nitride films as an ILD layer in the GaAs devices instead of polymer type dielectrics, which typically require a long cure time at high temperature of 300oC or higher.

Indentation Characterization of Fracture Toughness and Interfacial Strength of PECVD Nitrides after Rapid Thermal Annealing

AbstractThis work presents the result of mechanical characterization of the fracture toughness and interfacial strength of PECVD silicon nitride films deposited on silicon subjected to rapid thermal annealing (RTA) processing between 200 and 800 °C. Both micro- and nano-indentation techniques are employed to perform the experiments. In conjunction with the model proposed by Marshall and Lawn for data reduction, the fracture toughness of un-heat treated nitride is obtained as 2.2 MPa√m based on a series of Vickers micro-indentation tests and this value is essentially unchanged if the RTA temperatures are below 400°C. Further increase in RTA temperature would significantly enhance the fracture toughness. On the other hand, using nanoindentation testing in conjunction with the model proposed by Marshall and Evans, the interfacial strength between the nitride and silicon is determined as 17.2 J/m2 for un-heat treatment nitrides and it could also be significantly enhanced by RTA processes with temperatures exceeding 400°C. These results should be useful for related MEMS or IC structure fabrication for the concerns of maintaining the structural integrity and improve fabrication performance in related applications.

OS3-2-6 Full-field wafer level thin film stress measurement by fringe reflection method with LCD

Wafer topography measurement by using the phase-shifting shadow Moire method has been reported recently. However shadow Moire method is not capable to measure the wafer with a specular surface. In this paper, a wafer topography measurement system with LCD (liquid crystal display) is designed and demonstrated based on four-step phase stepping fringe reflection method using LCD. Wafer bows can be achieved by analyzing the fringe patterns reflected from the specular surface, and film stress can be obtained subsequently by transforming this wafer curvature using a conversion equation such as Stoney's formula. Surface profile of PECVD nitride and oxide coated wafers are measured by a shadow Moire system from the substrate side, and by a fringe reflection system from the coated specular side. A very good agreement between the results obtained from the two methods. Comparing to the result from a commercial profiler, the difference is less than 2μm. This system is especially suitable for stressed films with specular surface. Wafer bow obtained by fringe reflection method is based on full-field information and it would have a better accuracy and better thin film stress characterization

Mechanical stress in thin film microstructures on silicon substrate

Analysis of residual stress in thin films and its influence on silicon microstructures was performed. Deflection behaviour of silicon membranes due to built-in stress in deposited thin films was investigated in the scope of different bilayer structures which are commonly met in microstructures such as piezoresistive pressure sensors. Silicon membranes are usually covered by thin films such as thermal oxide, LPCVD or PECVD nitride, as required by the actual fabrication process. In our case, high compressive stress was determined for stoichiometric LPCVD nitride (1.2 GPa) and PECVD nitride (706 MPa) while for thermal oxide tensile stress of 298 MPa was determined. Furthermore, thin film cantilever and bridge microstructures were designed, fabricated and investigated, showing that by a proper combination of thin films in the stacked layer, residual stress can be reduced to a reasonable amount without compromising the dielectric properties of thin films.

Optimization of low temperature silicon nitride processes for improvement of device performance

This paper gives some insights in the applications where PECVD nitrides can be introduced to replace the LPCVD layers and how the process parameters need to be varied to obtain the desired properties. Film properties like stress, hydrogen content, wet etch rate and deposition rate are reported. The nitrides are optimized for specific applications and examples on the influence of nitride properties on device performance are given. It is important to investigate that the advantage of the high film integrity of nitride layers used in the past is not lost due to the strong demand for developing new process schemes with low thermal budget layers. We show that PECVD films are a valid alternative for LPCVD and that the majority of the film properties satisfy the criteria to use PECVD films as contact-etch-stop layers, silicidation blocking films and spacer materials.

Investigation of PECVD dielectrics for nondispersive metal-insulator-metal capacitors

Metal-insulator-metal (MIM) capacitors with PECVD nitride exhibit trap-induced dispersive behavior, which leads to degradation in capacitor linearity at low frequencies, limiting the accuracy in precision analog circuits. While LPCVD oxide results in nondispersive behavior, the high deposition temperature excludes the use of LPCVD dielectrics for MIM capacitors using the standard back-end metal layers as capacitor bottom plates. The latter is preferred in view of the low substrate coupling needed for RF applications. In this work, alternative PECVD dielectrics have been investigated with respect to frequency dependence of voltage linearity, hysteresis, matching, and leakage characteristics. It will be shown that ONO stacks offer a combination of good voltage linearity, absence of dispersive behavior and hysteresis, excellent matching, and low leakage.

PECVD Silicon Nitride for Damascene Applications

AbstractA Pecvd silicon nitride film, Damascene Nitride™, is deposited in a PECVD chamber with a hollow cathode faceplate using silane and ammonia as precursor gases. Various techniques (FTIR, RBS-HFS, SIMS, TDS and BTS) were used to characterize the structure, composition, density and wet etch rate of the film. FTIR analysis indicates that Damascene Nitride is very similar to a high density plasma (HDP) nitride film. HFS analysis shows the film's hydrogen content to be 13%,∼6% less than other PECVD nitride films, leading to a 20% improvement in etch selectivity to FSG. The film wet etch rate is 2 times slower than that of other PECVD nitrides, and the dielectric constant k was measured to be 6.8, which is lower compared to other PECVD nitrides and HDP CVD nitrides where k∼ 7.0 and 7.5, respectively. SIMS analysis shows that Cu diffusion is &lt;250Å in the nitride, and low leakage current (10-10 A) is confirmed through BTS testing. The higher density of Damascene Nitride leads to higher etch selectivity and better Cu barrier properties, allowing a thinner nitride film to be used. Thinner nitride layers, in addition to the lower k of Damascene Nitride, leads to a 5-6% reduction in RC delay when Damascene Nitride is used with low k dielectric materials.

Feasibility of an isolation by local oxidation of silicon without field implant

Field inversion in local oxidation of silicon regions of a CMOS integrated circuit is generally avoided thanks to a field implant. In this paper the feasibility of an implant-free isolation is studied. The parasitic charge in the interlayer dielectrics is attributed to the diffusion during nitride deposition of hydrogen which react with carbon in the underlying plasma oxide. Using a PECVD nitride as the upper layer of the inter-layer dielectrics allows to maintain the leakage current at an acceptable level.

Analog characteristics of metal-insulator-metal capacitors using PECVD nitride dielectrics

The frequency dependence of PECVD nitride and LPCVD oxide metal-insulator-metal (MIM) capacitors is investigated with special attention for precision analog applications. At measurement frequencies of 1.0 MHz, nitride MIM capacitors show capacitance linearity close to that of oxide MIM capacitors, indicating potential for precision analog circuit applications. Due to dispersion effects, however, nitride MIM capacitors show significant degradation in capacitor linearity as the frequency is reduced, which leads to accuracy limitations for precision analog circuits. Oxide MIM capacitors are essentially independent of frequency.

Hydrogen Concentration Analysis in Pecvd and Rtcvd Silicon Nitride Thin Films and It's Impact on Device Performance

ABSTRACTIn this paper the impact of the ESL (Etch Stop layer) nitride on the device performance especially the threshold voltage (Vt) has been studied. From SIMS analysis, it is found that different nitride gives different H concentration, [H] in the Gate oxide area, the higher [H] in the nitride film, the higher H in the Gate Oxide area and the lower the threshold voltage. It is also found that using TiSi instead of CoSi can help to stop the H from diffusing into Gate Oxide/channel area, resulting in a smaller threshold voltage drift for the device employed TiSi. Study to control the [H] in the nitride film is also carried out. In this paper, RBS, HFS and FTIR are used to analyze the composition changes of the SiN films prepared using Plasma enhanced Chemical Vapor deposition (PECVD), Rapid Thermal Chemical Vapor Deposition (RTCVD) with different process parameters. Gas flow ratio, RF power and temperature are found to be the key factors that affect the composition and the H concentration in the film. It is found that the nearer the SiN composition to stoichiometric Si3N4, the lower the [H] in SiN film because there is no excess silicon or nitrogen to be bonded with H. However the lowest [H] in the SiN film is limited by temperature. The higher the process temperature the lower the [H] can be obtained in the SiN film and the nearer the composition to stoichiometric Si3N4.

PECVD Amorphous Silicon Nitride at 120°C for a-Si:H TFTs.

AbstractThe effect of a-SiNx films stoichiometry and their physical properties on the electrical integrity and masking ability is studied. The films are deposited at 120° C by 13.56 MHz PECVD from SiH4+NH3 + N2 gas mixture. They have the N/Si ratio of 1.4 to 1.7 and hydrogen concentration of 25 to 40 at.%. The electrical characterization was carried out by I-V measurements. An electrical resistivity of ∼1016 Ohm-cm and breakdown voltage of 5.5 MV/cm have been achieved for our PECVD nitride films. The performance of a-Si:H TFTs with these silicon nitride as the gate dielectric and passivation layer has been also evaluated.

Characteristics of low-temperature silicon nitride (SiN x:H) using electron cyclotron resonance plasma

Silicon nitride (SiN x :H) thin film deposited at 50°C using an electron cyclotron resonance plasma-enhanced chemical deposition (ECR PECVD) system has been explored. This 50°C silicon nitride deposited on a 150 mm diameter Si wafer shows an acceptable uniformity; ±0.9% of average index of refraction and ±6.5% of average thickness are maintained across 150 mm diameter of the Si wafer. As-deposited 50°C silicon nitrides have a leakage current density value of 2–3×10 −9 A/cm 2 at electric fields of 2 MV/cm and a breakdown electric field (i.e., field at a current density of 1×10 −6 A/cm 2) greater than 6 MV/cm. X-ray photoelectron spectroscopy (XPS) analysis displays that chemical bonding structure of this low-temperature ECR silicon nitride is very comparable to that of 250°C PECVD nitride. However, IR absorption data indicate that the low-temperature ECR nitride has more Si–H bonds and fewer N–H bonds than the high-temperature PECVD nitride. These ECR films manifest resistance to buffered oxide etchant (BOE) attack with the etch rates that are slower than 50% of a 250°C PECVD nitride. The lower concentration of N–H bonds may enable these low-temperature nitrides to resist BOE attack.

Sealing of micromachined cavities using chemical vapor deposition methods: characterization and optimization

This paper presents results of a systematic investigation to characterize the sealing of micromachined cavities using chemical vapor deposition (CVD) methods. We have designed and fabricated a large number and variety of surface-micromachined test structures with different etch-channel dimensions. Each cavity is then subjected to a number of sequential CVD deposition steps with incremental thickness until the cavity is successfully sealed. At etch deposition interval, the sealing status of every test structure is experimentally obtained and the percentage of structures that are sealed is recorded. Four CVD sealing materials have been incorporated in our studies: LPCVD silicon nitride, LPCVD polycrystalline silicon (polysilicon), LPCVD phosphosilicate glass (PSG), and PECVD silicon nitride. The minimum CVD deposition thickness that is required to successfully seal a microstructure is obtained for the first time. For a typical Type-1 test structure that has eight etch channels-each 10 /spl mu/m long, 4 /spl mu/m wide, and 0.42 /spl mu/m tall-the minimum required thickness (normalized with respect to the height of etch channels) is 0.67 for LPCVD silicon nitride, 0.62 for LPCVD polysilicon, 4.5 for LPCVD PSG, and 5.2 for PECVD nitride. LPCVD silicon nitride and polysilicon are the most efficient sealing materials. Sealing results with respect to etch-channel dimensions (length and width) are evaluated (within the range of current design). When LPCVD silicon nitride is used as the sealing material, test structures with the longest (38 /spl mu/m) and widest (16 /spl mu/m) etch channels exhibit the highest probability of sealing. Cavities with a reduced number of etch channels seal more easily. For LPCVD PSG sealing, on the other hand, the sealing performance improves with decreasing width but is not affected by length of etch channels.

Reactively sputtered aluminum nitride in GaAs processing

Reactively sputtered aluminum nitride (AlN) has been investigated as a manufacturable method of preventing surface etching and damage while minimizing surface state density on GaAs based electronic devices. Deposition conditions to obtain a film with high selectivity to fluorine etch chemistries were broad, however other preferred characteristics such as low film stress required optimization of the process conditions related to the deposition equipment. Using AlN as an etch stop during critical PECVD oxide or nitride reactive ion etches resulted in measurable device performance improvements. Most notable were a reduction in transient behavior and a reduction in across wafer variation of many device and process control monitor parameters. The AlN module process capability was further enhanced by the development of a robust wet etch removal. A high flow diluted NH 4OH was found to completely remove all AlN despite possible film changes. These compositional changes and reactions with oxide dielectrics were found to occur depending upon the type of applications.