Borophosphosilicate Glass Film Research Articles

Factors Delineating Stability of the As-Deposited PECVD BPSG Film

This study aims to define a better condition to enhance the stability of the as-deposited plasma-enhanced chemical vapor deposition borophosphosilicate glass (PECVD BPSG) film. Stability is discussed in terms of optimized film composition . Stable oxygen-rich films show better flow ability, lower dopant fluctuation through the growing oxide, reduced film stress, and lesser nitrogen and hydrogen incorporation into the growing film. Optimization of the B/P ratio, along with a lower amount of hydrogen-related species, especially , which is a catalyst for defects, makes the film less vulnerable to defect formation. The film structure can be modulated by the deposition parameters to get optimized ratios of , , and . Special attention is paid to the BPSG films with low –precursor gas flow. The limited condition for flow is also discussed.

Dependence of the Fracture of PowerTrench MOSFET Device on Its Topography in Cu Bonding Process

Dependence of the fracture-resistance of a PowerTrench MOSFET device on its topography in Cu bonding process was investigated. Two different topographies, namely dimple and round, have been tested. A significantly higher cratering rate has been clearly observed on dimple topography. The dimple topography exhibited a cratering rate of 371 k ppm levels compared to 0 ppm in round topographies. Three-dimensional nonlinear finite-element analysis has shown that the largest compressive and shear stresses and their locations were identified, respectively, in borophosphosilicate glass (BPSG)/barrier metal layers of the dimple topography. The round topography had the smallest stress in BPSG/barrier metal layers. The higher compressive stress transferred to silicon in the dimple topography during the bonding process can induce a local crack, consequently causing silicon fracturing during the shearing processes. A significant improvement in the cratering performance was observed when the Al bond pad metal layer was reinforced by adding a barrier layer sandwiched in the Al metal layers. The cratering rate decreased to 1300 ppm levels. Additionally, the change in composition of a BPSG layer caused cratering was briefly discussed and an oxygen rich BPSG film in round topography was confirmed by the energy dispersive spectroscopy (EDS) of a cross-sectional TEM sample. It has been found that the cratering rate on dimple topography significantly increased from 1 k ppm to 100 k ppm levels, when the resulting residual Al pad thickness is less than 0.65 mum for Cu bonding performed with different ultrasonic (US) power and bond forces.

Atmospheric Pressure Plasma Enhanced Chemical Vapor Deposition of Borophosphosilicate Glass Films

Borophosphosilicate glass (BPSG) films have been grown on silicon wafers by plasma enhanced chemical vapor deposition at atmospheric pressure (AP-PECVD). Tetraethoxysilane (TEOS), triethylborate (TEB), and trimethylphosphite (TMPI) were adopted as precursors, and argon and oxygen were respectively used as the carrier and reactive gases to produce stable plasma at atmospheric pressure. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and refractive index and stress measurements were employed to characterize BPSG films. The effects of input radio-frequency (RF) power and precursor (TEB and TMPI) flow rate on deposition rate were studied. Results indicated that the deposition rate of BPSG films increases with increasing input RF power and precursor flow rate. In addition, reactive gaseous species were detected by optical emission spectroscopy to reveal the possible reaction process of BPSG film deposition.

Process Window Enlargement for Borderless Contact Formation by BPSG Stack Structure

Anomalous oxynitride loss after steam borophosphosilicate glass (BPSG) flow is observed for a borderless contact structure, and such loss engenders possible bit line shorts to word line. This phenomenon becomes more severe for BPSG film with higher phosphorous concentration. Phosphoric acid generation is deduced as the major mechanism. To enlarge process windows, a BPSG/undoped silicate glass stack has been proposed to withstand etch by acid. From practical application to 256 Mb dynamic random access memory process, this stack also shows a higher bit line contact yield and comparable contact sheet resistance with conventional stacks. More important, this technique could be fully integrated into incumbent ultralarge scale integrated technologies.

Relationships Between Gas-Phase Film Deposition, Properties and Structures of Thin SiO2 and BPSG Films

This paper is devoted to the analysis of relationships between chemical vapor deposition (CVD) features and silicon dioxide and silicate glass film properties and structures. Deposition processes have been quantitatively characterized using an empirical parameter the effective constant of the deposition rate, The observed CVD kinetic features are explained by using a simplified multiroute and multistep kinetic scheme of the silicon-based thin-film gas-phase deposition processes, and a classification of the studied processes. The basic physical and chemical properties of thin glass films are explained in terms of the glass structural disordering, which defines the oxide film density, wet etch rate, shrinkage, and intensity of film-moisture interaction. The structure disordering depends in reverse order with respect to It is shown that the borophosphosilicate glass (BPSG) film structure and properties are affected by the quantity of boron atoms with a threefold coordination with respect to the oxygen atoms. The boron coordination in BPSG film tends to change from threefold to fourfold coordination along with the increase of phosphorus to boron ratio in the film. The best BPSG structural ordering and the best film properties correspond to the boron concentrations defined by an empirical equation The respective glass film structure is supposed to consist of and tetrahedra. © 2003 The Electrochemical Society. All rights reserved.

Effects of Borophosphosilicate Glass Dopant Concentrations on Isotropic Etch Profile

AbstractIn the process of chemically etching contact openings, film characteristics of the Borophosphosilicate glass (BPSG) film strongly effect the formation of an ideal contact profile. Ideal contact profiles represent a wine glass shape to provide better metal step coverage into the contact opening in comparison to a vertical sidewall profile. The rounded shape of the wine glass is etched chemically (isotropic) allowing for etch in the vertical and horizontal direction. As the addition of dopants to the oxide film effect the etch rate, the profile of the isotropic etch will change which in turn effects the electrical device properties, down stream processes and device reliability.BPSG film characteristics are the area of investigation. Characteristics of concern are weight percent concentrations of boron and phosphorus, film density and dopant concentration profiles in relation to depth. To evaluate the entire contact formation module, chemical etch characteristics including etch rate in relation to film depth for thermal oxide films were also investigated. Experimentation in the form of a response surface design was used to model effects of previously discussed BPSG film characteristics.To achieve the desired and predictable wet etch rate of BPSG in a buffered oxide etch (BOE), calculated control limits were placed on the boron and phosphorus dopant concentrations. Results showed that dopant effects on the isotropic etch process exceeded the control capability of dopant concentrations in the deposition process. In relating process control capabilities to 6σ techniques, a Cpk above 1.5 is considered capable. To eliminate previously discussed defects created in the isotropic etch process, reject limits for dopant concentrations in a BPSG film deposition process would need to be set well within the typical 6σ giving a Cpk below 1.5

Development of self-aligned contact technology for 0.18 μm static random access memory devices

A self-aligned contact (SAC) technology is developed for the application of electrical contacts between the local interconnect and the silicon diffusion regions for 0.18 μm static random access memory cells. The key components of this SAC technology include the deposition and gap fill of borophosphosilicate glass (BPSG) films, a selective oxide etch process, and metal-plug contact formation by Ti/TiN-liner silicidation and W filling. The BPSG film, deposited by plasma enhanced chemical vapor deposition, has exhibited an ability of filling 0.04 μm spaces with an aspect ratio (AR) of about 10:1 after reflow at 800 °C. Reduction of the reflow temperature without gap-fill deterioration by increasing the B incorporation in the BPSG film is not feasible due to an increase of BPSG defects. The oxide SAC etch performance is modulated by an oxide-to-nitride etch selectivity which has shown a strong dependence on the wafer temperature. The etch process window is improved by optimization of the process conditions including the wafer temperature uniformity. A novel SAC etch process was demonstrated for an ∼0.2 μm SAC opening. The electrical performance of a contact with an AR as high as 10:1 has met the design requirement, which has indicated sufficient liner silicidation and an excellent W plug process. Investigation of the contact resistance dependence on the contact AR has shown a reduction in contact resistance with increasing AR. All these findings are very instructive for our development projects.

Growth Kinetics and Deposition‐Related Properties of Subatmospheric Pressure Chemical Vapor Deposited Borophosphosilicate Glass Film

Growth kinetics of borophosphosilicate glass (BPSG) films prepared by the chemical reaction of tetraethylorthosilicate (TEOS), triethylborate, and triethylphosphate, with ozone‐oxygen mixture has been studied using a single‐wafer deposition chamber at 373–458°C under reduced pressure or subatmospheric pressure condition (SABPSG). Based on the comparison of the effective reaction rate constants and other kinetic features, the similarity of BPSG deposition kinetic for different types of precursors and deposition conditions are shown. Fourier transform infrared spectroscopy, X‐ray fluorescence analysis, secondary ion mass spectrometry, stress measurement, optical microscopy, scanning electron microscopy, atomic force microscopy, surface laser scanning, capacitance‐voltage, current voltage, and surface charge analysis techniques have been used for the characterization of SABPSG film properties. Moisture absorption and surface defect formation phenomena have been studied for both as‐deposited and furnace annealed films with boron and phosphorus ranging from 3 to 6 wt %. The liquid state, solid state, and crystalline BPSG surface defects have been characterized and their relationships have been shown. A multipath and multistep reaction mechanism scheme of TEOS‐ozone BPSG deposition process with the formation of active intermediate products, a scheme of porous TEOS‐ozone BPSG film with embedded dopant‐rich clusters, and a scheme of defect formation and growth on BPSG films are discussed. Empirical equations of quantitatively optimized BPSG dopant concentration range are presented by taking into account flow properties, defect formation, and moisture absorption processes in the film. © 1999 The Electrochemical Society. All rights reserved.

Two Step Rapid Heating Reflow of Borophosphosilicate Glass and Estimation for a Coefficient of Heating Delay by Thermal Analyses

The reflow of borophosphosilicate glass (BPSG) was studied by the rapid heating technique in two step irradiations using a halogen lamp. Pre-annealing (800° C, 30 s) during the first step irradiation, which aims to reduce the heating delay for the BPSG film, was carried out prior to high temperature heating (1050–1200° C, 20 s). The reflow angle with pre-annealing is consistently smaller than that without pre-annealing. Moreover, the reflow difference between with pre-annealing and without pre annealing decreases with increasing temperature because the heating delay for the BPSG film increases. The heating delay is primarily caused by thermal resistance between the film and the silicon wafer because, as the result obtained from the finite element method indicated, the heat conduction delay between the film surfaces was negligibly small. The equation for heat resistance can be solved analytically and the thermal resistance coefficient can be estimated by this solution, using the physical parameters of the film and the experimental results.

Electrical and Physical Characterization of Tetraethylorlthosilicate‐ O 3 Borophosphosilicate Glass

The reflow properties of tetraethylorthosilicate‐ (TEOS‐) borophosphosilicate glass (BPSG) under furnace and rapid thermal processing conditions that we have studied show good void‐free, subquarter micron gapfill, and planarization. Thick BPSG films on reflow exhibit positive charge buildup at the oxide/Si interface that cause a shift in the flatband voltage. The amount of phosphorous in the BPSG film, the BPSG film thickness, and the BPSG deposition temperature determine the extent of this flatband shift. We observed a linear correlation of the flatband shift and the amount of carbon migration and pileup at the oxide/Si interface during reflow. Using current‐voltage, triangular voltage sweep, and secondary ion mass spectroscopy and field threshold voltage measurements, we demonstrate that under appropriate deposition conditions the flatband shift can be brought to negligible levels.

Gap Fill and Film Reflow Capability of Subatmospheric Chemical Vapor Deposited Borophosphosilicate Glass

This work presents a systematic process characterization of subatmospheric chemical vapor deposited (SACVD) borophosphosilicate glass (BPSG). The effects of deposition pressure, ozone concentration, ozone flow, and dopant concentration on the film reflow profile and film properties are presented. Our results indicate that a decrease in the deposition pressure from atmospheric conditions to 200 Torr provides more than a 200% increase in SACVD BPSG deposition rate without affecting film quality. Phosphorous is incorporated in the stable form of at all deposition pressures. Higher ozone concentrations improve SACVD BPSG film reflow and film properties. Moreover, at higher dopant concentrations, both film shrinkage and stress‐temperature hysteresis decrease.

Microcrystal Growth on Borophosphosilicate Glass Film during High‐Temperature Annealing

Borophosphosilicate glass (BPSG) film with a high boron and phosphorus concentration that exceeds a certain limit shows the growth of crystalline particles on the surface after annealing above 900°C in a nitrogen atmosphere. We studied the crystalline particle growth mechanism on BPSG, and found that the particles are crystal that grows during the cooling step at the end of annealing. Hence, rapid cooling of the BPSG after annealing suppresses particle growth. We also found that particle growth is affected by the annealing atmosphere; being more suppressed in an oxygen atmosphere than in a nitrogen atmosphere. In an oxygen‐steam atmosphere, particle growth is completely suppressed. From the measurements of boron and phosphorus out‐diffusion in different annealing atmospheres, we concluded that particle growth is caused by the gas‐phase reaction of the out‐diffused phosphorus and boron from the BPSG film.

Growth mechanism of Si nodules on BPSG

Si nodules that appear in the metal electrodes of integrated circuits often reduce their reliability. The growth process of Si nodules generated on boro-phospho silicate glass (BPSG) in the Al-1 wt.% Si film electrode has been investigated. The Al-1 wt.% Si films sputter deposited on BPSG films were annealed at 723 K for 30 min according to the usual integrated circuit procedure. Scanning electron microscopy and atomic force microscopy observations revealed that the Si nodules seemed to precipitate along Al grain boundaries particularly on the BPSG film and their shape appeared pyramidal. To make clear the mechanism of the growth of the Si nodule on the BPSG film, the interface between the Si nodule and the BPSG film was investigated in detail by transmission electron microscopy, electron diffraction and energy dispersive X-ray spectroscopy. As the result, it was found that there existed an amorphous silicon oxide region in the central part of the interface under the Si nodule. The amorphous silicon oxide is considered to be formed by diffusion of oxygen from the BPSG film to the Si nodule during the annealing. The amorphous silicon oxide may act as an embryo for the formation of the Si nodule and the migration of Si atoms dissolved in Al towards the embryo seems to enhance the growth of the Si nodule.

Experimental and simulation studies of thermal flow of borophosphosilicate and phosphosilicate glasses

We use EVOLVE−FLOW, a thin film thermal flow process simulator, to simulate the thermal flow of borophosphosilicate glass (BPSG) and phosphosilicate glass (PSG) thin films in trenches on patterned wafers, where two-dimensional surface evolution is appropriate. For a fixed anneal time, two parameters control the thin film flow processes: surface tension and viscosity. We demonstrate our simulator by reproducing flowed BPSG film profiles after a 15 min furnace annealing cycle. Digitized as-deposited BPSG film and substrate profiles from experimental scanning electron micrographs are used as initial profiles in the simulations. We then predict flowed phosphosilicate film profiles, and combine experiments and simulations to estimate the surface tension of PSG films in a rapid thermal annealing process. The viscosity of the PSG films is modeled as a function of temperature and phosphorus pentoxide concentration using an Arrhenius type equation. The estimated values of the viscosity and surface tension are used to simulate the PSG film profiles at different annealing times. The simulation results are in good agreement with experimental observations.

Selective Etching of Phosphosilicate Glass with Low Pressure Vapor HF

A reliable low pressure vapor etch process was developed for the selective removal of phosphorus‐doped silicon oxides. With this process, a high etch rate ratio of phosphosilicate glass (PSG) and borophosphosilicate glass (BPSG) over undoped oxide is obtained. The high etch selectivity is accomplished by controlling the total vapor pressure and/or the partial pressure. Under the low vapor pressure conditions, adsorption on the oxide surface is suppressed, resulting in a low etch rate of the undoped oxide. The etching of (B)PSG is not suppressed even at low vapor pressure, since an layer is formed on the surface and fluorine species dissolve in this layer. Because of this difference in etch mechanisms, high etch rate ratios of (B)PSG to thermal oxide of over 2000 were obtained over a wide range of conditions. Further, the low pressure vapor etch technique was successfully applied for selective damage‐free removal of the core BPSG film from cylindrical capacitor structures in DRAMs. By applying this new process, the number of process steps involved in the formation of a cylindrical capacitor can be reduced.

The anomalous threshold voltage shift of N- and P-MOSFET under flow and reflow of BPSG film with RTA and/or furnace

Different post oxide annealing technologies, i.e. furnace and/or RTA were done in borophosphosilicate glass (BPSG) films under flow and reflow. It is found that the threshold voltage shift is apparent in P-MOSFET but small in N-MOSFET for a device with RTA reflow. Base on the charge pumping measurement, the donor-type interface states generated by RTA reflow process are supposed to play a major role in this shift. The authors explain the mechanism of RTA induced donor-like interface states in detail.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Borophosphosilicate Glass(BPSG) Fusion Using Rapid Thermal Annealing and Steam Reflow: Physical Properties and Device Implications

ABSTRACTWith decreasing device geometry to below sub micron dimensions, there is a greater emphasis on reducing the thermal budget by shortening and/or eliminating high temperature processing steps. The use of RTP for borophosphosilicate glass (BPSG) fusion/reflow process, which is conventionally performed in diffusion furnaces in temperature range of 850-900 °C, has gained some acceptance in recent years. BPSG films were prepared by an atmosphericpressure chemical vapor deposition(APCVD) process. BPSG film properties such as stress, shrinkage, dopant uniformity and surface stability, step coverage, and flow angle, have been examined as a function of densification/reflow cycle. We used RTP-only, furnace-only, and RTP/furnace reflow annealing cycles. The impact of various BPSG fusion scenarios on underlying Ti salicide and P-channel and N-channel devices is discussed.

Nitride-Masked Polishing (NMP) Technique for Surface Planarization of Interlayer-Dielectric Films

A reflowed borophosphosilicate glass (BPSG) film having surface ridges is polished with a colloidal silica slurry, and the ridge width effect on the planarization rate or the efficiency is investigated. The planarization rate decreases drastically with increasing ridge width; thereby it is impossible to effectively remove the wide ridges corresponding to the stacked-type memory cell array areas in a dynamic random access memory (DRAM) device. Then, a nitride-masked polishing (NMP) technique is developed in which the BPSG surface except for the ridge areas, is covered with a Si3N4 film and the ridges are selectively polished away. A BPSG film on a DRAM with stacked-type capacitors is planarized by NMP to insure a tight focus margin for photolithography below deep submicron processes.

Identification of segregation from borophosphosilicate glass films during annealing

The structure and crystallinity of a segregation on a borophosphosilicate glass (BPSG) film have been clarified by scanning electron microscopy (SEM), transmission electron microscopy (TEM), transmission electron diffraction (TED), and electron energy loss spectroscopy (EELS). The segregation arises on the BPSG film surface after annealing in nitrogen ambient. Its size is below 0.5 μm. The segregation is identified as crystalline BPO4 from the results of TED and EELS. In this letter, TED pattern of crystalline BPO4 is indicated in detail. The growth mechanism of crystalline BPO4 is proposed on the basis of a series of the results.

Borophosphosilicate glass crystal induction and suppression

Grapelike crystalline cluster defects with no specific shapes were induced in borophosphosilicate glass (BPSG) deposited in a low-pressure chemical vapor deposition tube following cooling of the film to room temperature. The crystal defects were induced by exposing the film for about 3 min to high, controlled humidity (80%–90%) and a temperature of 30±2 °C. The film was then fused for 15 min in a 900 °C furnace at four different atmospheres: N2, O2, 1:1 O2/N2, or steam (3 min)/N2 (12 min). The steam/N2 treatment was the only effective ambient to eliminate BPSG crystal defects. A chemical mechanism is proposed to explain the crystal appearance in BPSG film.