BPSG Films Research Articles

Deposition of borophosphosilicate glass films using the TEOS–dimethylphosphite–trimethylborate system

Modernization of horizontal low pressure deposition system has been performed. The liquid source delivery system using the bubblers has been developed. The PSG and BPSG film deposition processes and film properties using TEOS-Dimethylphosphite-TEB system have been studied. It is shown that the use of dimethylphosphite allows varying the phosphorus concentration in the wide range. It is found that the optimal range of the total boron and phosphorus concentration ensuring the acceptable topology planarity and resistance to defect formation during storage is 8.7±0.3 wt% when the phosphorus concentration is 3.0—3.8 wt%. It is found that at use of the TEOS-DMP-TEB system the depletion of the phosphorus concentration along reaction zone does not occur, and the total dopant concentration is practically constant. At the same time the deposition rate of BPSG films is 9.0—10.0 nm/min and the good film thickness uniformity are ensured. The as-deposited films have “mirror-like surface” that is proof of minimal surface roughness. The BPSG films with optimal composition are characterized by the reduced reaction capability against atmospheric moisture.

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.

Instability of Chemical Composition in PECVD BPSG film

A serious concern for borophosphosilicate (BPSG) interlayer is still about film stability in terms of dopant out-diffusion and defect formation. The thermal and compositional instabilities of the PECVD BPSG depend on dopant concentration in the film and on stoichiometry of SiOx matrix. This study addresses the diffusivity of boron and phosphorus through the BPSG and the low temperature oxide (LTO) films. Phosphorus significantly diffuses out of the BPSG film during high temperature densification. The significant boron out-gassing happens in the as-deposited film even at room temperature. This effect depends on the BPSG film composition and whether the LTO film is present or not. The effect is explained based on the change in the charge state in the silicon-oxide interface. The dopant out-diffusion is restricted from the oxygen-rich BPSG film. In addition, the effect of the undoped cap layer on the BPSG is discussed.

The Role of Borophosphosilicate Chemistry in Heterogeneous Nucleation

This study aims to solve the conflict between two important features of PECVD BPSG film: good flow ability and low defectiveness, which can ultimately alter the electrical characteristics of devices. The film flow associates with the amount of phosphorus and boron dopants, which, in their turn, are a source of boron phosphate imperfections. The films' compounds SiO2-B2O3-P2O3/P2O5 have to be thus kept appropriately to satisfy both requirements. Unstable glass structure carries an excessive amount of hydrogen related species, especially H2O, which is a catalyst for defects. Such films are also vulnerable to additional moisture from the air. The as-deposited film instability brings on defect generation and out-gassing / counterdoping problems during the relaxation process when film is being stored and heated. This work studies the film structure that is modulated by the deposition parameters in order to get optimized ratios of N2O/SiH4, P2O3/P2O5 and SiO2/P2O5. Special attention is paid to the oxygen-rich film's composition with low SiH4 precursor.

Strain partition of Si/SiGe and SiO2/SiGe on compliant substrates

Strain partitioning of crystalline Si and amorphous SiO2 deposited on crystalline SiGe on a compliant viscous borophosphorosilicate (BPSG) glass has been observed. Pseudomorphic epitaxial Si was deposited on SiGe films, which were fabricated on BPSG by wafer bonding and the Smart-cut® process. The strains in SiGe and Si films were found to change identically during a high-temperature anneal which softened the BPSG film, indicating a coherent interface between SiGe and Si films and precluding slippage or the formation of misfit dislocations along the interface. The stress balance between the layers dictated the final state, which confirmed that BPSG was a perfectly compliant substrate and did not exert any force on the layers above it. Similar results were found for amorphous SiO2 deposited on SiGe on BPSG and then annealed. This shows that the viscous BPSG is an effective compliant substrate for the strain engineering of elastic films without the introduction of dislocations.

Atmospheric pressure chemical vapour deposition of BPSG films from TEOS, O3, TMB, TMPi : Determination of a chemical mechanism

Atmospheric pressure chemical vapour deposition of BPSG films from TEOS, O₃, TMB, TMP_i : Determination of a chemical mechanism

Optimization of post-CMP cleaning process for elimination of CMP slurry-induced metallic contaminations

We have invetigated the slurry-induced metallic contaminations of undoped and doped silicate oxide surface during the post-chemical mechanical polishing (CMP) cleaning process. The metallic contaminations by CMP slurry were evaluated in the four different oxide films, such as plasma enhanced tetra-ethyl-ortho-silicate glass (PE-TEOS), O3-boro-phospho-silicate glass (O3-BPSG), PE-BPSG, and phospho-silicate glass (PSG). Prior to entering the post-CMP cleaner, all films were polished with KOH-based slurry. The total X-ray fluorescence (TXRF) measurements showed that all oxide surfaces are heavily contaminated by potassium and calcium during polishing, which is due to the CMP slurry. The polished O3 BPSG films presented higher potassium and calcium contaminations compared to PE-TEOS film because of a mobile ion gettering ability of phosphorus. For PSG oxides, the slurry-induced mobile ion contamination increased with an increase of phosphorus content. In addition, the polishing removal rate of PSG oxides had a linear relationship with phosphorus content.

Removal Rate, Uniformity and Defectivity Studies of Chemical Mechanical Polishing of BPSG Films

ABSTRACTWafers where deposited with BPSG films having phosphorus concentration varying from 3.65 to 6.25% and boron concentration varying from 4 to 5.7%. These wafers were polished using CMP and the rates were found to depend on dopant concentrations. A fit to the data indicated that removal rates were more than 3 times as sensitive to boron concentration compared to phosphorus concentration. For a constant phosphorus concentration of 5%, each percent increase in boron increases CMP removal rate by 340 Å/min. For a constant boron concentration of 5%, each percent increase in phosphorus increases CMP removal rate by 96 Å/min.

Difference of Si nodules precipitating from Al-X wt.% Si (X=0.5 ∼ 3.3)

Si nodules that appear in the. Al-Si electrode of integrated circuits often reduce their reliability. We have been studying methods for reducing the Si nodules precipitated on an insulated film such as a BPSG film. In our previous study, we proposed a growth mechanism for Si nodules on the insulated film, based on the detailed analysis of the interface between the Si nodule and the insulated film [6]. In this paper, the relationship between the Si contents (X) of Al-X wt.% Si film and the generation of the Si nodules is discussed in relation to the developed growth mechanism of Si nodules on the insulated film. Al-X wt.% Si films (X=0.5,0.7,1.0,3.3 ) deposited on the insulated film by sputtering method are annealed at 723 K for 30 min according to the usual IC procedure. The Si nodules are observed by TEM, SEI (scanning electron image) and SEM. In the case of X=0.7 or more, Si nodules are precipitated on the insulated film, while in the case of X=0.5, no Si nodule is precipitated. According to the EDX analysis of the Si nodule/BPSG interface, it is observed that at the central part of the interface, an Si-0 layer is formed, and at the periphery, an Al-Si-P-0 layer is formed. It is thought that in the case of X=0.5, all of the Si nodules are dissolved in the AI film during annealing because the Si solubility in Al is 0.5 wt.% at 723 K according to the Al-Si phase diagram. While in the case of X>0.5 wt.%, Si nodules exist during annealing, Si nodules are precipitated on the BPSG film after annealing. In the case of X=0.7, Si nodules are grown on the BPSG film, while in the case of X-3.3, the Si nodules are grown both on the BPSG film and within the Al film. The difference is thought to come from the Si contents.

Electron and hole trapping in doped oxides

An electron paramagnetic resonance, thermally stimulated current, and capacitance-voltage study has been carried out on phosphorus (PSG), boron (BSG), and boron and phosphorus (BPSG) co-doped oxide films on Si. The principal spin-active defects are the phosphorus-oxygen-bole-center (POHC) and the boron-oxygen-hole-center (BOHC), which are unpaired electrons on oxygen atoms with P or B in the near vicinity. The centers are activated by hole capture. We find that holes are trapped in the PSG, BSG, and BPSG dielectrics; however, hole trapping is most effective in the PSG and BPSG dielectrics. We find that electrons are trapped to differing extents in the doped films. The BPSG films are the most efficient in trapping electrons the PSG films are the least efficient. The electrical data can be explained by assuming that the precursor to the BOHC is negatively charged and the precursor to the POHC is electrically neutral. Last, the charge trapping properties of PSG, BSG, and BPSG dielectrics are compared and contrasted with those observed in thermally grown oxides.

Chemical mechanical polishing of PSG and BPSG dielectric films: the effect of phosphorus and boron concentration

Chemical-mechanical polishing of blanket and patterned oxide films doped with phosphorus and boron has been studied. FTIR was used to characterize the film microstructure. Experimental results show that an increase of phosphorus level promoted the polish rate of PSG film. We also found that increasing the boron content enhanced the polish rate of BPSG films although phosphorus contents is decreased. This implies that boron is more effective than phosphorus in enhancing the polishing rate of BPSG films. However, the hardness of these doped films is slightly affected by doping level. Excellent planarity achieved by CMP is demonstrated for patterned wafers. Here, we also identify inversion patterns for the composite dielectric formed by a thin hard film on the top of a thick soft film. Such inversion phenomenon can be used for monitoring CMP process as a means of end point detection.

Interfacial Reactions in Al-Alloy/Ti/Silicon-Dioxide-Based Substrate Structures for Multilayered Interconnects

Interfacial reactions in Al-alloy/Ti/borophosphosilicate glass (BPSG)/Si-substrate structures have been investigated up to the annealing temperature of 550° C. The interfacial reaction changes according to the annealing temperature. Below 500° C, a reaction between Al alloy and Ti occurs, and the main reaction product is Al3Ti. The underlying BPSG film remains almost inert. At 550° C, the substrate BPSG film is no longer inert and a reaction between Al alloy, Ti and underlying BPSG film takes place. The reaction never occurs without the Ti layer. Reactions in the Al-Ti-Si-O four-component system must be considered in this temperature range. The main reaction product is Ti7Al5Si12. After the Ti layer is consumed for Al3Ti formation, Al3Ti and BPSG react to form Ti7Al5Si12, and a lot of Al moves into BPSG film through the Ti7Al5Si12. Reaction retardation by alloying Al with Si also occurs in this temperature range.

A 0.6 micron triple level metal process for high performance application specific integrated circuits

This paper describes a 0.6 micron triple level interconnect scheme for ASIC application. This interconnect scheme has been used with 0.6 micron twin well CMOS technology having polycide gates. Excellent planarization of BPSG films was achieved at a low reflow temperature by using TEOS/0 3-based APCVD BPSG. Sandwich layers of TiW/Al-1%Cu/TiW were used for interconnects. A void-free Inter-Metal-Oxide (IMO) planarization with good device reliability was achieved using a combination of silicon-rich silane-based PECVD oxide, TEOS-based PECVD oxide and SOG etchback process. In order to achieve the maximum packing density, metal 3 is used as a routing layer and has the same pitch as metal 1 and metal 2 layers. It has been demonstrated that the device and the interconnect reliabilities for this metallization scheme are excellent.

Process investigations for a 30-GHz f/sub T/ submicrometer double poly-Si bipolar technology

Major process issues are investigated to establish a manufacturable process for a 30-GHz f/sub T/ deep-trench isolated submicrometer double polysilicon bipolar technology. A thinner deep-trench surface oxide minimizes crystal defects generated by thermal stresses during the subsequent processes, and significantly improves collector-to-emitter leakage currents in npn transistors. The effects of reactive-ion-etch (RIE) process used for the base surface oxide etch are evaluated in terms of current gain, emitter resistance, and cutoff frequency of the npn transistors. Silicon surface roughness created by an RIE process produces a nonuniform interface oxide film between the emitter polysilicon and the silicon surface, which results in a lower current gain due to a retardation of arsenic diffusion from the emitter polysilicon through the unbroken thicker portion of the interface oxide film. Lateral pnp transistors and Schottky diodes using a vanadium silicide are characterized as a function of epitaxial layer thickness. Schottky diodes are integrated with high performance npn transistors without using extra photo-masking process steps. The reverse leakage currents of Schottky diodes fabricated by using an RIE process are acceptable for practical use in circuits. A planarization process is investigated by employing an RTA reflow of BPSG films deposited in an LPCVD furnace. The maximum RTA reflow temperature is limited to 1000/spl deg/C in order to maintain an acceptable integrity of TiSi/sub 2/ layer formed on top of the n+ polysilicon layer. The planarity achieved by an RTA reflow at a temperature between 975/spl deg/C and 1000/spl deg/C is acceptable for double polysilicon bipolar integrated circuits using metal interconnects produced by an electroplated gold process.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Fluoride Interference in the Determination of Boron by Inductively Coupled Plasma Emission Spectroscopy

Boron determination in borophosphosilicate glass films by the ICP-AES or ICP-MS technique can be performed after dissolution of the sample in HF solution. However, addition of HF to boric acid standard solution can cause a drift in the slope of the calibration curve. The signal change was correlated with the kinetics of the borontetrafluoride complex formation reaction. The mechanism was explained by the selectively increased boron transport into the plasma, which was caused by the more efficient diffusion of borontrifluoride gas through the aerosol particles into the nebulizer gas. With the kinetics of borontetrafluoride complex formation taken into consideration, an accurate and precise method was developed for the determination of boron in BPSG films.

Reliability Issues of a Crack-Resistant Passivation Layer Process for Sub-Micron Non-Volatile Memory Technology

AbstractChemically vapor deposited phosphosilicate glass (PSG) has been used extensively for final passivation on EPROM and other Non Volatile Memory (NVM) technologies. The maximum amount of phosphorous that can be added to the passivation oxide (post metallization) is constrained by the stability of the as-deposited, undensified film. Atmosphericpressure chemically vapor deposited films of various dopant levels ranging from pure PSG to various boron and phosphorous wt%BPSG films were studied with respect to their passivation properties. The film performance with respect to passivation crack resistance, step coverage, and impacts on metal cracks/voids was evaluated. It was found that the crack resistance was by far more sensitive to boron concentration than that of phosphorous in the undensified film. The crack resistance is shown to be dependent on the as-deposited film densities, moisture levels and amount of shrinkage after a 400° C alloy/anneal. Other important parameters such as stress levels, UV transparency and sodium gettering capabilities were investigated. Reliability data on packaged-device level testing (both ceramic and plastic units) are also presented.

Determination of boron and phosphorus in borophosphosilicate thin films on silicon substrates by capillary electrophoresis

The application of the new technique of electrophoretic capillary ion analysis (CIA) to the analysis of borophosphosilicate thin films (BPSG) is described. CIA and ion chromatography (IC) were shown to produce equivalent analytical results for boron, but the inductively coupled plasma spectroscopic procedure using optical detection (ICP-AES) yielded results which were 4.5 wt % higher. The +5 phosphorus contents for BPSG films measured by CIA, IC, and ICP-AES are in agreement

Surface Stability and Flow Characteristics of BPSG Film by N2O Plasma Treatment

ABSTRACTBPSG films show good flow characteristics with the increase of boron and phosphorus concentration. As–deposited BPSG films with high boron and phosphorus concentration, however, have a dopant instability which results in film bursts, cracks, and precipitates, due to water absorption. Elimination of dopant instabilities of BPSG films by N2O plasma treatment is investigated. Film structure, composition and flow properties are evaluated by FT-IR, SIMS, and SEM, respectively. Dopant stability is examined after H2SO4 boiling. After H2SO4 boiling without N2O plasma treatment, BPSG films with high boron and phosphorus concentration show poor flow characteristics. Boron and phosphorus are leached out of the BPSG films by reaction with absorbed water during the H2SO4 boil. N2O plasma treatment results in a thin surface layer composed of Si-O-B bonds. These bonds do not dissolve in water. It is proposed that the thin layer consisting of Si-O-B bonds prevents the penetration of water into BPSG film during H2SO4 boiling.

Defect Reduction in Semiconductor Manufacturing a Case Study of BPO4 Elimination in BPSG Films

ABSTRACTThis paper explains the analysis and elimination of BPO4 crystal formation in an Atmospheric Pressure Chemical Vapor Deposition BPSG film. Film deposition and furnace anneal/flow parameters were studied using full factorial techniques, with anneal/flow parameters having the most significant effect. It was learned that BPO4 crystals could be readily induced by performing the anneal/flow process in a POCl3/O2 ambient. Most testing was done in a POCl3/O2 ambient and inferences made concerning the standard anneal ambient.BPO4 formation is primarily dependent on thermal processing during anneal toprovide the activation energy necessary to initiate crystal growth. Other factors include 02:Hydride ratio during film deposition, phosphorous concentration in the deposited film, deposition temperature, and anneal/flow ambient. No tested level of these secondary factors completely eliminated crystal formation.The growth of BPO4 crystals can be eliminated by controlling the thermal environment ofthe anneal/flow step. The primary means employed was to increase the rate of heat dissipation by doubling the spacing between wafers. An alternative method involves utilization of reduced anneal/flow furnace temperatures.

In-Line Monitoring of Some Planarization Processes

The processes used for the surface planarization of the interlevel dielectrics which is one of the major problems of the multilevel interconnection CMOS technology, are becoming increasingly sophisticated. As a consequence, the reproducibility of the total process requires an accurate control of these technics in order to increase die yields. The DOPED method, developed for a non-contact on-line monitoring of flow annealing of BPSG films has been applied to the “cold” planarization techniques implemented in the CNET 0.7 µm technology. Results are obtained for TEOS deposition and etchback techniques and SOG total etchback.