Ultrathin strained-SOI by stress balance on compliant substrates and FET performance

Ultrathin, strained-silicon-on-insulator (s-SOI) structures without a residual silicon-germanium (SiGe) underlayer have been fabricated using stress balance of bi-layer structures on compliant borophosphorosilicate glass (BPSG). The bi-layer structure consisted of SiGe and silicon films, which were initially pseudomorphically grown on a silicon substrate and then transferred onto BPSG by a wafer bonding and SmartCut process. The viscous flow of the BPSG during a high-temperature anneal then allowed the SiGe/Si bi-layer to laterally coherently expand to reach stress balance, creating tensile strain in the silicon film. No dislocations are required for the process, making it a promising approach for achieving high-quality strained-silicon for device applications. To prevent the diffusion of boron and phosphorus into the silicon from the BPSG, a thin nitride film was inserted between the bi-layer and BPSG to act as a diffusion barrier, so that a lightly doped, sub-10-nm s-SOI layer (0.73% strain) was demonstrated. N-channel MOSFETs fabricated in a 25-nm silicon layer with 0.6% strain showed a mobility enhancement of 50%.     

Silicon Nitride Films Deposited by RF Sputtering for Microstructure Fabrication in MEMS

In the present work, we report silicon nitride films deposited by a radio- frequency (RF) sputtering process at relatively low temperatures (<260°C) for microelectromechanical system (MEMS) applications. The films were prepared by RF diode sputtering using a 3-inch-diameter Si₃N₄ target in an argon ambient at 5 mTorr to 20 mTorr pressure and an RF power of 100 W to 300 W. The influence of the film deposition parameters, such as RF power and sputtering pressure, on deposition rate, Si-N bonding, surface roughness, etch rate, and stress in the films was investigated. The films were deposited on single/double-side polished silicon wafers and transparent fused-quartz substrates. To explore the RF-sputtered silicon nitride film as a structural material in MEMS, microcantilever beams of silicon nitride were fabricated by bulk, surface, and surface-bulk micromachining technology. An RF-sputtered phosphosilicate glass film was used as a sacrificial layer with RF-sputtered silicon nitride. Other applications of sputtered silicon nitride films, such as in the local oxidation of silicon (LOCOS) process, were also investigated.     

An improvement of hot-carrier reliability in the stackednitride-oxide gate n- and p-MISFET's

Thin LPCVD stacked nitride-oxide gate MISFET's offer the potential for high current drive as a consequence of the high permittivity of the nitride. However, thin nitride-oxide films have yet to be used in actual MISFET's for LSI products because thin nitride films have poor masking ability during re-oxidation and low reliability under hot-carrier stress. We have investigated improvements to thin LPCVD stacked nitride-oxide films as regards masking ability during re-oxidation and hot-carrier reliability. The method proposed to improve film quality is densification through high-temperature rapid thermal processes and its effectiveness has been tested. Simple rapid thermal annealing (RTA) did not improve the film quality at all. On the other hand, rapid thermal nitridation (RTN) on the deposited nitride film improved it considerably. The reason for the improvement by RTN was investigated     

变温LPCVD沉积氮化硅薄膜的均匀性优化

以低压化学气相沉积(LPCVD)热壁立式炉为实验平台,由二氯硅烷和氨通过LPCVD工艺合成氮化硅薄膜,利用降温成膜提高氮化硅薄膜的膜厚均匀度.基于气体碰撞理论建立了氮化硅薄膜沉积速率与反应气体浓度的关系式.分析比较了LPCVD炉内不同升温速率沉积氮化硅薄膜的表面性能.发现在变温沉积阶段,选择合适的降温速率是实现薄膜沉积...     

Ion Beam Analysis of Amorphous and Nanocrystalline Group III-V Nitride and ZnO Thin Films

The ion beam analysis (IBA) techniques of Rutherford backscattering spectrometry (RBS), elastic recoil detection analysis (ERDA), nuclear reaction analysis (NRA), and particle-induced x-ray emission (PIXE) have been used to quantitatively determine composition, uniformity, impurity, and elemental depth profiles of major, minor, and trace elements of group III-V nitride and zinc oxide (ZnO) thin films prepared by various growth techniques. The IBA revealed that an amorphous GaN film prepared by ion beam assisted deposition (IBAD) has large variations in film thickness and composition coupled with typically 10–20% oxygen that was found to be essential to stabilize their amorphous structure. The IBA characterization of plasma-assisted molecular beam epitaxy (PAMBE) grown GaN, InN, and InCrN films revealed composition, impurity, and uniformity information of the films. The IBA of ZnO films prepared by radio frequency (RF) sputtering showed that the Zn/O ratio often varied significantly over the film thickness. Hydrogen was found to be a major impurity in the films with around one present in the as-deposited ZnO films. It is clearly shown that the nondestructive, quantitative, and rapid IBA measurements are very useful to develop and optimize growth protocols in respect to film thickness, stoichiometry, and especially in regard to hydrogen and oxygen impurities for group III-V nitride and ZnO thin films prepared by various growth techniques.     

应用高频激励源制备低应力氮化硅薄膜研究

研究了在等离子体增强化学气相沉积(PECVD)法制备氮化硅薄膜时,射频功率和腔室压力对氮化硅薄膜应力的影响以及应力与沉积速率的关系。通常认为高频下制备得到的氮化硅膜呈现张应力,但是通过实验,表明即使应用高频(13.56MH z)作为激励源同样可以沉积出呈现压应力的氮化硅薄膜。并使用角度可变光谱型椭偏仪观察了薄膜的厚度和低应力氮化硅膜的m app ing图,利用傅立叶变换红外光谱仪(FT IR)对不同应力状态下的氮化硅膜的化学键结构进行了分析。     

淀积参数对PECVD氮化硅薄膜力学特性的影响

等离子增强化学气相淀积(PECVD)法制备的氮化硅薄膜具有沉积温度低、生长速率高和残余应力可调节等特点,研究其力学特性对研制MEMS器件和系统具有重要意义。采用HQ-2型PECVD淀积台,在沉积温度为350℃,NH3流量为30cm3/min的条件下,通过改变氩气稀释至5%的SiH4流量和射频功率大小,制备了具有压应力、微应力和张应力的多种氮化硅薄膜样品。采用纳米压痕仪Nanoidenter-G200对淀积薄膜的杨氏模量和硬度进行测试,结果表明,在较小的SiH4流量和较高的射频功率条件下,淀积的氮化硅薄膜具有更高的杨氏模量和硬度。     

纳米硅镶嵌氮化硅薄膜的制备与光致发光特性

为研究氮化硅薄膜发光材料的制备工艺及其光致发光机制,实验采用射频磁控反应溅射技术与热退火处理制备了纳米硅镶嵌氮化硅薄膜材料.利用红外光谱(IR)、X射线衍射谱(XRD)、能谱(EDS)和光致发光谱(PL),对不同工艺条件下薄膜样品的成分、结构和发光特性进行研究,发现在制备的富硅氮化硅薄膜材料中形成了纳米硅颗粒,并计算出其平均尺寸.在510 nm光激发下,观察到纳米硅发光峰,对样品发光机制进行了讨论,认为其较强的发光起因于缺陷态和纳米硅发光.     

X波段FBAR用AlN薄膜制备研究

采用中频磁控溅射法,在硅基上制备了X波段薄膜体声波谐振器(FBAR)滤波器用AlN压电薄膜。对AlN薄膜进行了分析表征,结果表明,AlN压电薄膜具有良好的(002)面择优取向,摇摆曲线半峰宽为2.21°,膜厚均匀性优于0.5%,薄膜应力为-5.02 MPa,应力可在张应力和压应力间进行调节。将该AlN薄膜制备工艺应用于FBAR器件的制作,研制出X波段FBAR器件,谐振频率为9.09 GHz,插入损耗为-0.38 dB。     

Filament-activated chemical vapour deposition of nitride thin films

We have applied the novel method of hot filament-activated chemical vapour deposition (HFCVD) for low-temperature deposition of a variety of nitride thin films. In this paper the results from our recent work on aluminium, silicon and titanium nitride have been reviewed. In the HFCVD method a hot tungsten filament (1500–1850°C) was utilised to decompose ammonia in order to deposit nitride films at low substrate temperatures and high rates. The substrate temperatures ranged from 245 to 600°C. The film properties were characterised by a number of analytical and optical methods. The effect of various deposition conditions on film properties was studied. All the films obtained were of high chemical purity and had very low or no detectable tungsten contamination from the filament metal.     

Low hydrogen content silicon nitride films grown by chemical vapor deposition using microwave excited hydrogen radicals

A chemical vapor deposition method using hydrogen radicals excited by microwave plasma has been applied to obtain silicon nitride films of low hydrogen content. In this method, silane and monomethylamine were used as source gases. For a appropriate experimental condition, residual carbon and oxygen contents could be reduced to a small value and residual hydrogen content was smaller than ∼1 × 10²² cm^-3. Also, the structure of hydrogen bonding and the structural change with time of the films were measured.     

原子层沉积超薄氮化铝薄膜的椭圆偏振光谱法表征

采用原子层沉积(ALD)工艺在硅衬底上生长了35 nm以下不同厚度的超薄氮化铝(AlN)晶态薄膜。利用椭圆偏振光谱法在波长275~900 nm内测量并拟合薄膜的厚度及折射率和消光系数等光学参数。利用原子力显微镜(AFM)表征AlN晶粒尺寸随生长循环次数的变化,计算得到薄膜表面粗糙度并用于辅助椭偏模型拟合。针对ALD工艺特点建立合适的椭偏模型,可获得AlN超薄膜的生长速率为0.0535 nm/cycle,AlN超薄膜的折射率随着生长循环次数的增加而增大,并逐渐趋于稳定,薄膜厚度为6.88 nm时,其折射率为1.6535,薄膜厚度为33.01 nm时,其折射率为1.8731。该模型为超薄介质薄膜提供了稳定、可靠的椭圆偏振光谱法表征。     

p-Si TFT栅绝缘层用SiN薄膜的研究

以NH3和SiH4为反应源气体,采用射频等离子体增强化学气相沉积(RF-PECVD)法在多晶硅(p-Si)衬底上沉积了一系列SiN薄膜,并利用椭圆偏振测厚仪、超高电阻-微电流计、C-V测试仪对所沉积的薄膜作了相关性能测试.系统分析了沉积温度和射频功率对SiN薄膜的相对介电常数、电学性能及界面特性的影响.分析表明,沉积温度和射频功率主要是通过影响SiN薄膜中的Si/N比影响薄膜的性能,在制备高质量的p-Si TFT栅绝缘层用SiN薄膜方面具有重要的参考价值.     

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.     

The formation of epitaxial hexagonal boron nitride on nickel substrates

The various crystallographic forms of boron nitride (BN) are of great technological interest because of their demonstrated tribological, high-temperature, thermally conducting, electrically insulating, and wide-bandgap semiconductor properties. Unfortunately, the synthesis of crystalline BN films is still in the early stages of development. Furthermore, although polycrystalline BN films have been prepared by a variety of physical and chemical vapor deposition techniques, the capability does not currently exist for depositing large area single-crystal or oriented films of BN. Such single-crystal films are required for many applications of interest, especially in electronics. The present paper reports on a new approach to the oriented growth of boron nitride using a novel molten layer epitaxy technique. Well-oriented hexagonal boron nitride (h-BN) crystals were obtained with highly faceted crystal shapes. The h-BN was formed via precipitation from a molten, hydrogen-saturated Ni surface layer. Solid cubic BN was utilized as the source material and was dissolved into the substrate surface during a brief high-temperature anneal. It was found that surface melting occurred during this process and the B diffused into the Ni substrate, whereas the N was expelled into the growth chamber. Oriented BN was then precipitated as the surface layer was allowed to resolidify.     

硼磷硅玻璃缺陷分析与研究

在晶圆制造中广泛运用掺杂有硼和磷的二氧化硅即硼磷硅玻璃作为绝缘介质,一般用于金属布线前的绝缘层。掺杂硼磷的作用是降低回流温度,减少热预算。但在实际运用中,由于硼磷硅玻璃性质不够稳定,常常受到环境的影响,其中的三氧化二硼和五氧化二磷容易和空气中的水汽反应生成硼酸和磷酸继而形成缺陷,造成电路短路,最终导致产品低良率,给公司造成损失。文章就硼磷硅玻璃受环境影响的异常现象进行分析研究,找到缺陷形成的根本原因及预防方法。     

六方氮化硼薄膜制备及其压电响应的研究

采用射频(RF)磁控溅射的方法,通过改变工艺参数在n型Si(100)片上制备六方氮化硼(h-BN)薄膜。通过傅立叶红外(FTIR)光谱仪,X射线衍射(XRD)仪进行结构表征,原子力显微镜(AFM)进行表面形貌和压电性能表征。测试结果表明,在射频功率为300 W、衬底温度为500℃、工作压强在0.8Pa、N2与Ar流量比为4∶20和衬底偏压在-200V时制备的六方BN薄膜具有高纯度、高c-轴择优取向,颗粒均匀致密,粗糙度为2.26nm,具有压电性并且压电响应均匀,符合高频声表面波器件基片高声速、优压电性要求。薄膜压电性测试研究表明,AFM的PFM测试方法适用于纳米结构半导体薄膜的压电性及其压电响应分布特性的表征。     

Integration of GaN thin films with dissimilar substrate materials by Pd-In metal bonding and laser lift-off

Gallium nitride (GaN) thin films grown on sapphire substrates were successfully bonded and transferred onto GaAs, Si, and polymer “receptor” substrates using a low-temperature Pd-In bond followed by a laser lift-off (LLO) process to remove the sapphire growth substrate. The GaN/sapphire structures were joined to the receptor substrate by pressure bonding a Pd-In bilayer coated GaN surface onto a Pd coated receptor substrate at a temperature of 200°C. X-ray diffraction showed that the intermetallic compound PdIn₃ had formed during the bonding process. LLO, using a single 600 mJ/cm², 38 ns KrF (248 nm) excimer laser pulse directed through the transparent sapphire substrate, followed by a low-temperature heat treatment, completed the transfer of the GaN onto the “receptor” substrate. Cross-sectional scanning electron microscopy and x-ray rocking curves showed that the film quality did not degrade significantly during the bonding and LLO process.     

Ozone/organic-source APCVD for conformai doped oxide films

Borophosphosilicate glass (BPSG) films were deposited with a new chemical vapor deposition method using ozone and organic sources under atmospheric pressure condition at 400° C called ozone/TEOS APCVD. Trimethylborate (TMB:B(OCH₃)₃) and trimethylphosphate (TMP:PO(OCH₃)₃) were utilized to dope phosphorus and boron into deposited films. Boron and phosphorus concentration in the films are easily controlled at up to 15 mole%. Conformality and reflow characteristics for the BPSG film are superior to those for BPSG film deposited by the SiH₄ + PH₃ + B₂H₆ + O₂ CVD method. Planarization of underlying patterns, which have half-micron spaces with high aspect ratio, was successfully accomplished.     

Compliant substrates: A comparative study of the relaxation mechanisms of strained films bonded to high and low viscosity oxides

Relaxation of compressively strained heteroepitaxial Si_0.7Ge_0.3 films bonded to high and low viscosity glass compliant layers was investigated. These structures were formed by transferring Si_0.7Ge_0.3 films to Si substrates covered with thermal SiO₂ and borophosphorosilicate glass (BPSG) films. Relaxation was studied through thermal annealing experiments. For the low viscosity BPSG, relaxation was observed near 800°C and was accompanied by buckling of the Si_0.7Ge_0.3 film. At this temperature, no change in the Si_0.7Ge_0.3 film bonded to thermal SiO₂ was observed, and through this comparison relaxation on BPSG is interpreted as the result of viscous flow of the glass. Finally, film buckling was successfully avoided by patterning the strained films into small areas prior to annealing, and is an indication that film expansion must be considered for elastic strain relaxation on compliant media.