Photothermal Activation of Shallow Dopants Implanted in Silicon

Dopant impurities were implanted at high dose and low energy (10¹⁵ cm⁻², 0.5–2.2 keV) into double-side polished 200 mm diameter silicon wafers and electrically activated to form p–n junctions by 10 s anneals at temperatures of 1,025, 1,050, and 1,075°C by optical heating with tungsten incandescent lamps. Activation was studied for P, As, B, and BF₂ species implanted on one wafer side and for P and BF₂ implanted on both sides of the wafer. Measurements included electrical sheet resistance (Rs) and oxide film thickness. A heavily boron-doped wafer, which is optically opaque, was used as a hot shield to prevent direct exposure to lamp radiation on the adjacent side of the test wafer. Two wafers with opposing orientations with respect to the shield wafer were annealed for comparison of exposure to, or shielding from, direct lamp illumination. Differences in sheet resistance for the two wafer orientations ranged from 4% to 60%. n-Type dopants implanted in p-type wafers yielded higher Rs when the implanted surface was exposed to the lamps, as though the effective temperature had been reduced. p-Type dopants implanted in n-type wafers yielded lower Rs when the implanted surface was exposed to the lamps, as though the effective temperature had been increased. Effective temperature differences larger than 5°C, which were observed for the P, B, and BF₂ implants, exceeded experimental uncertainty in temperature control.     

InSb晶片化学抛光研究

机械抛光会给InSb晶片表面造成一定程度的机械损伤,增加表面的粗糙度,从而影响器件的性能.化学抛光可以有效地去除表面划痕,改善晶片的表面形貌,降低粗糙度.用低浓度的澳一甲醇溶液对机械抛光后的InSb晶片进行了化学抛光,并对化学抛光前后的InSb晶片进行了表面形貌、总厚度偏差(TTV),粗糙度、表面组分和杂质对比分析.实验结果表明,用低浓度的溴-甲醇溶液对InSb晶片进行化学抛光,腐蚀速率平稳且容易控制,能有效去除表面划痕,从而得到光滑、平坦的表面.晶片表面的粗糙度为6.443nm,TTV为3.4μm,In/Sb原子比接近1.与传统的腐蚀液CP4-A,CP4-B相比,用低浓度的溴-甲醇溶液对InSb晶片进行化学抛光,可以获得更低的表面粗糙度和TTV,且In/Sb的原子比更接近于1.     

清洗工艺对锗外延片表面点状缺陷的影响

锗外延片表面的雾、水印及点状缺陷等会影响太阳电池的性能和成品率,其中点状缺陷出现的比例最高。研究了锗抛光片清洗工艺对外延片表面点状缺陷的影响,获得了无点状缺陷、低粗糙度及高表面质量的锗单晶片。采用厚度为175μm p型<100>锗单面抛光片进行清洗试验,研究了SC-1溶液的不同清洗时间、清洗温度和去离子水冲洗温度对锗抛光片外延后点状缺陷的影响,分析了表面SiO_2残留和锗片表面粗糙度对外延片表面点状缺陷的影响。结果表明点状缺陷主要是由于锗单晶抛光片表面沾污没有彻底清洗干净以及清洗过程中产生新的缺陷造成的。采用氢氟酸溶液浸泡、SC-1溶液低温短时间清洗结合低温去离子水冲洗后的锗抛光片进行外延,用其制备的太阳电池光电转换效率由原来的25%提高到31%。     

硫化镉晶片抛光工艺研究

研究了硫化镉(CdS)晶片Cd面的化学机械抛光(CMP)工艺。采用硅溶胶抛光液和NaClO氧化剂,分别使用聚氨脂和磨砂革抛光垫进行粗抛和精抛实验,并研究了氧化剂掺入量、抛光转速、抛光压力等工艺条件对CdS晶片表面质量的影响。结果表明,在抛光液中氧化剂体积分数为6%左右、抛光盘的转速为90～100 r/min、压强为55～60 g/cm2条件下可得到平整度较好、表面缺陷低、表面粗糙度低的高质量抛光表面。金相显微镜和微分干涉显微镜下观测抛光片表面无划痕、无桔皮产生,原子力显微镜测试得到抛光后CdS晶片Cd面的表面粗糙度值仅为0.385 nm。     

Rapid thermal processing of silicon wafers with emissivity patterns

Fabrication of devices and circuits on silicon wafers creates patterns in optical properties, particularly the thermal emissivity and absorptivity, that lead to temperature nonuniformity during rapid thermal processing (RTP) by infrared heating methods. The work reported in this paper compares the effect of emissivity test patterns on wafers heated by two RTP methods: (1) a steadystate furnace or (2) arrays of incandescent lamps. Method I was found to yield reduced temperature variability, attributable to smaller temperature differences between the wafer and heat source. The temperature was determined by monitoring test processes involving either the device side or the reverse side of the wafer. These include electrical activiation of implanted dopants after rapid thermal annealing (RTA) or growth of oxide films by rapid thermal oxidation (RTO). Temperature variation data are compared with a model of radiant heating of patterned wafers in RTP systems.     

Perspectives on emissivity measurements and modeling in silicon

A spectral emissometer operating in the wavelength range of 1–20 μm and temperature range of 30–900°C has been utilized to simultaneously measure the reflectance, transmittance and emittance of silicon. Interesting differences in the optical properties have been reported due to differences in surface morphology. Quantitative results of the effects of rough side incidence versus smooth side on the optical properties of the same silicon wafer are analyzed in this study. This analysis is based on a standard one-parameter, multiple-reflection model as extended by Vandenabeele and Maex to include effects of a roughened surface. Their modification essentially replaces the usual internal attenuation factor by an enhanced effective attenuation factor to take into account the effects of surface roughness. In the present study, it has been found that this very simple model gives a good account of the optical properties when radiation is incident on the smooth side of the wafer but fails for incidence for the roughside.     

不同抛光方式下InSb晶片表面质量的对比研究

本文分别以加双氧水的化学机械抛光和未加双氧水的纯机械抛光方式对InSb晶片进行表面处理,通过分析氧化膜的生成,以及对InSb晶片的表面划痕、表面粗糙度和表面损伤的表征,开展了两种不同抛光方式下InSb晶片的表面质量对比研究.结果表明,在化学机械抛光过程中,InSb晶片表面有氧化层生成,该氧化层能保护材料表面免受损伤;并...     

An effort in planarising microwave plasma CVD grown polycrystalline diamond (PCD) coated 4 in. Si wafers

Large area CVD grown diamond coatings should have very smooth surface in many of its applications, like microwave power transmission windows etc. Combination of mechanical and chemical forces during polishing helps to achieve desired surface roughness of the polycrystalline diamond (PCD) coatings. Authors report the variation of pressure, slurry feeding rate, addition of chemicals and the time of polishing to observe the efficiency of chemo-mechanical polishing (CMP) technique in planarising CVD diamond material grown over 100 mm diameter silicon wafers. PCD were found to be polished by bringing down the as-grown surface roughness from 1.62 µm to 46 nm at some points on large areas. One coherence scanning interferometer was used to check the roughness at different stages of CMP. Raman spectroscopy was used to evaluate the polished PCD samples in terms of their quality, internal stress at different positions on the same wafer surface after CMP process. It was found that the well polished regions were of better quality than the less polished regions on the same wafer surface. But due to coating non-uniformity of the deposited PCD grown by microwave plasma CVD over large area, CMP could not produce uniform surface roughness over the entire 100 mm diameter wafer surface. We concluded that CMP could effectively but differentially polish large area PCD surfaces, and further process improvements were needed.     

Temperature measurement of metal-coated silicon wafers bydouble-pass infrared transmission

We report the measurement of the temperature of metal-coated silicon wafers by a double-pass infrared transmission technique. Infrared light incident on the backside of the wafer passes through the wafer, and is re-emitted out the backside after reflecting off the metal surface on the front side of the wafer. The temperature is inferred by the change in the re-emitted signal due to absorption in the wafer. The work has been demonstrated on double-polished wafers from 100°C to 550°C using wavelengths from 1.1 to 1.55 μm. A method for overcoming limitations of the present arrangement for wafers with a rough backside is proposed     

Modeling of three-dimensional effects on temperature uniformity inrapid thermal processing of eight inch wafers

A three-dimensional steady-state model of the industry-standard AG Associates 4108 Heatpulse Rapid Thermal Processing system has been developed for the study of thermal uniformity across 8 inch wafers. The model combines radiation energy transfer among all solid surfaces in the chamber with energy transfer among the chamber materials and to the process ambient. Surfaces included are those of the tungsten filaments of the lamps, the silicon wafer, the polysilicon annular thermal guard ring, the quartz process tube, and the gold reflectors which surround the lamps and process tube. These surfaces are divided into approximately 4800 individual surface elements for the radiation transfer allowing very accurate thermal analysis. The model has previously been shown to provide very good agreement with experiment for temperature distributions across an 8 inch wafer. The model is presently used to make quantitative examinations of asymmetric effects occurring in a RTP chamber which cannot be examined by 2-dimensional models. Situations examined include the effect of nonuniform lamp power distributions. Also examined is tilting of the wafer with respect to the flow tube and reflective chamber     

An In Situ Approach to Real-Time Spatial Control of Steady-State Wafer Temperature During Thermal Processing in Microlithography

We proposed an in situ method to control the steady-state wafer temperature uniformity during thermal processing in microlithography. Thermal processing of wafer in the microlithography sequence is conducted by the placement of the wafer on the bake-plate for a given period of time. A physical model of the thermal system is first developed by considering energy balances on the system. Next, by monitoring the bake-plate temperature and fitting the data into the model, the temperature of the wafer can be estimated and controlled in real-time. This is useful as production wafers usually do not have temperature sensors embedded on it, these bake-plates are usually calibrated based on test wafers with embedded sensors. However, as processes are subjected to process drifts, disturbances, and wafer warpages, real-time correction of the bake-plate temperatures to achieve uniform wafer temperature at steady state is not possible in current baking systems. Any correction is done based on run-to-run control techniques which depends on the sampling frequency of the wafers. Our approach is real-time and can correct for any variations in the desired steady-state wafer temperature. Experimental results demonstrate the feasibility of the approach     

Silicon p-i-n photodetector using internal reflection method

A semiconductor photodetector is proposed which makes use of an internal reflection method to enhance the photoresponse. This method is to let the incident light be multiply-reflected in the detector so that a long distance is traveled and most of the photon energy is absorbed by the detector. Theoretical analysis of the steady-state and time-dependent photoresponses for a p-i-n photodetector is presented. The photodetector is found to be particularly useful in detection of light with wavelengths near the intrinsic absorption edge. The photodetectors are fabricated from 4000 Ω.cm n-type, oriented silicon wafers. Both sides of the wafer are polished with one side inclined one-half degree with respect to the other. The p+n junction and the ohmic contact are formed by alloy method. The measured photoresponses for wavelengths of 1.0 and 1.1 µm are in reasonable agreement with the theoretical predictions.     

125mm低阻硅抛光片清洗技术研究

在125 mm(5英寸)硅抛光片清洗过程中,发现硅片边缘容易出现"色斑"现象。对这一现象进行了分析,通过工艺试验,消除了这种现象。     

The effect of surface roughness on the radiative properties ofpatterned silicon wafers

The radiative properties of patterned silicon wafers have a major impact on the two critical issues in rapid thermal processing (RTP), namely wafer temperature uniformity and wafer temperature measurement. The surface topography variation of the die area caused by patterning and the roughness of the wafer backside can have a significant effect on the radiative properties, but these effects are not well characterized. We report measurements of room temperature reflectance of a memory die, logic die, and various multilayered wafer backsides. The surface roughness of the die areas and wafer backsides is characterized using atomic force microscopy (AFM). These data are subsequently used to assess the effectiveness of thin film optics in providing approximations for the radiative properties of patterned wafers for RTP applications     

Transient thermal analysis of sapphire wafers subjected to thermal shocks

Rapid heating and cooling are commonly encountered events in integrated circuit processing, which produce thermal shocks and consequent thermal stresses in wafers. The present paper studies the heat transfer in sapphire wafers during a thermal shock as well as the dependence of the wafer temperature on various process parameters. A three-dimensional finite-element model of a single sapphire wafer was developed to analyze the transient heat conduction in conjunction with the heat radiation and heat convection on the wafer surfaces. A silicon wafer was also investigated, for comparison. It was found that the rapid thermal loading leads to a parabolic radial temperature distribution, which induces thermal stresses even if the wafer is not mechanically restrained. The study predicted that for sapphire wafers the maximum furnace temperature of 800 /spl deg/C should be held for two hours in order to get a uniform temperature throughout the wafer.     

InSb晶片清洗研究

随着红外探测器件制备工艺的不断发展,人们对InSb晶片表面质量的要求也越来越高,但是晶片在生产过程中不可避免地会引进各种杂质。研究了一种利用兆声超声并结合药液去离子水清洗InSb晶片的方法,并对清洗后的InSb晶片进行了表面颗粒度、表面有机物和表面粗糙度等方面的测量。实验结果表明,该方法能够有效去除InSb晶片表面的颗粒、有机物和金属离子杂质,但是也会略微增大晶片表面的粗糙度。     

Uniform pyramid formation on alkaline-etched polished monocrystalline (100) silicon wafers

Pyramidal texturing of monocrystalline silicon using alkaline etchants depends strongly upon the initial condition of the wafer surface and upon etching parameters. Texturization of polished wafers is often incomplete, with non-textured areas arising to yield high values of reflectance. A new technique is introduced for uniform pyramid formation on polished wafers. Nitrogen is used to expel dissolved oxygen in the etch solution, since it has been observed that oxidizing agents act to encourage polished etch surfaces.     

硅片背面软损伤工艺技术研究

硅中的金属离子杂质会明显降低少子寿命,并进一步影响硅器件的性能。因此对硅片背面喷砂工艺进行了系统的研究。通过喷砂工艺,在硅片背面形成软损伤层,使硅片具有了吸杂能力,并从吸杂机理出发,解决了吸杂工艺带来的硅抛光片表面颗粒效应,并对硅抛光片的吸杂效果及表面颗粒度进行了表征,为具有吸杂性能的“开盒即用”硅抛光片的批量化生产提供了有力的技术保证。     

磨削工艺对Ge单晶抛光片的影响

因磨削工艺不同导致Ge单晶片表面粗糙度出现很大差异,并最终影响抛光速率、抛光片的表面质量及抛光片时间依赖性雾的形成。粗糙度大的磨削片,初始抛光速率快,但抛光片达到镜面所需时间却延长。在抛光后的去蜡工序中,粗糙度大的Ge片其表面更容易粘附蜡液而导致表面质量下降。检验合格的抛光片在存储过程中表面出现时间依赖性雾,分析了时间依赖性雾的形成原因是由于粗糙的背表面更容易存储水份和有机溶剂。要提高抛光片的质量必须控制磨削片的粗糙度。     

Electromagnetic fast firing for ultrashallow junction formation

The creation of low resistivity, ultrashallow source/drain regions in MOS device structures requires rapid thermal processing (RTP) techniques that restrict diffusion and activate a significant percentage of the implanted dopant species. While current heating techniques depend upon illumination based heating, a new technology, electromagnetic induction heating (EMIH), achieves a rapid heating of the silicon by coupling electromagnetic radiation directly into the silicon wafer. Heating rates of 125/spl deg/C/s to temperatures in excess of 1050/spl deg/C have been achieved for 75- and 100-mm-diameter wafers at input powers of 1000 and 1300 W, respectively. These ramp rates are suitable for ultrashallow junction formation, and junctions shallower than 30 nm with sheet resistances lower than 600 /spl Omega//square have been achieved. This paper details the application of electromagnetic heating using radiation in the microwave, 2450 MHz, frequency regime. Experimental results, comparing microwave annealed implants to the well documented SEMATECH requirements, and simulations, utilizing a coupled electromagnetic-thermal computer model, of the heating process are discussed.