Integration of in situ spectral ellipsometry with MMST machinecontrol

The transformation of desired physical effects to process settings has been achieved through extensive use of appropriate in situ sensors for the MMST program. In situ sensors like an ellipsometer can be used to monitor film thicknesses as well as etch or growth rate in real time, and to determine endpoint time. This capability is opposed to conventional processing, which uses pilot wafers and ex situ statistical process control. In situ sensors enable real-time wafer-to-wafer compensation for equipment and process drifts and also diagnosis of equipment status for preventive maintenance. This paper discusses the use of a spectral ellipsometer (SE) developed at Texas Instruments and the issues involved in the integration of this SE to the machine control as well as to the factory-wide computer integrated manufacturing (CIM) environment for feedforward and feedback control     

Application of spectroscopic ellipsometry for real-time control of CdTe and HgCdTe growth in an OMCVD system

A multi-wavelengthinsitu spectroscopic ellipsometer system is described. The hardware can acquire accurate ellipsometric data at 44 wavelengths in less than one second, is simple and compact, and is well suited forin-situ monitoring of chemical vapor deposition. The software used for data analysis is capable of determining the growth rate and composition of the growing layer in real time. These tools were used to study the organometallic chemical vapor deposition of CdTe, HgTe, and HgCdTe on GaAs. We could obtain the dielectric constants of these materials at the growth temperature and also the growth rate and composition of the layers in real time. Feedback control of CdTe growth was performed by connecting an analog control voltage line from the data acquisition/ analysis computer to the dimethylcadmium mass flow controller. Using dielectric constants of HgCdTe for two different compositions at the growth temperature, composition control of HgCdTe was attempted in a similar manner.     

Composition control of long wavelength MBE HgCdTe using In-situ spectroscopic ellipsometry

Improved composition control of Hg_1-xCd_xTe layers grown by molecular beam epitaxy using in-situ spectroscopic ellipsometry is described. This has increased our composition yields from <40% to approximately 70% for a specification of x to within 0.0015 of target composition. Knowledge of composition during growth also enables corrections to effusion cell temperatures so that the in-depth composition profile can be controlled. Further improvements were obtained after active composition control was implemented whereby the ellipsometer controls the Te cell temperature to maintain the desired composition.     

Improvement of the accuracy of the In-situ ellipsometric measurements of temperature and alloy composition for MBE grown HgCdTe LWIR/MWIR structures

Spectroscopic ellipsometry (SE) has proven to be a very reliable technique for the in-situ monitoring of the substrate temperature and alloy composition during the HgCdTe epitaxy. In this work, the influence of the variations in the angle of incidence and the spectral wavelength shift on the measured accuracy of the growth temperature and alloy composition are studied, and a method for precisely determining these variations independent of the modeling of the SE data has been developed. It is shown that the stability of the fittings of the optical models for in-situ applications increases and that the couplings between model parameter decreases upon either eliminating the angle of incidence as an independent model parameter or correcting for the shifts of the wavelength offset. The variations in the angle of incidence and wavelength shift, which arise in the M88 ellipsometer from reflected beam deflections, were precisely calibrated in two dimensions as a function of alignment parameters, using a thick thermally grown SiO₂/Si sample and were parameterized for our experimental geometry. A new extension of theWVASE software was developed to correct the raw SE data in real time for wavelength shift and the angle of incidence drift. A comparison of the corrected and uncorrected results of in-situ temperature measurements for HgCdTe and CdZnTe(211) B/Si(211) clearly demonstrates that the proposed method significantly enhances the accuracy of temperature and composition readings over a broad range of values in these parameters.     

In-situ monitoring of the growth of Bi2 Te2 and Sb2 Te3 films and Bi2 Te3-Sb2 Te3 superlattice using spectroscopic ellipsometry

In this work, we present in-situ monitoring of the growth of bismuth telluride (Bi₂Te₃) and antimony telluride (Sb₂Te₃) thin films as well as Bi₂ Te₃-Sb₂Te₃ superlattice using a spectroscopic ellipsometer (SE). Bi₂Te₃ and Sb₂ Te₃ films were grown by metalorganic chemical vapor deposition (MOCVD) at 350 C. A44-wavelength ellipsometer with spectral range from 404 nm to 740 nm was used in this work. The optical constants of Bi₂ Te₃ and Sb₂Te₃ at growth temperature were determined by fitting a model to the extracted in-situ SE data of optically thick Bi₂ Te₃ and Sb₂ Te₃ films. Compared to the optical constants of Bi₂ Te₃ and Sb₂ Te₃ at room temperature, significant temperature dependence was observed. Using their optical constants at growth temperature, the in-situ growth of Bi₂ Te₃ and Sb₂ Te₃ thin films were modeled and excellent fit between the experimental data and data generated from the best-fit model was obtained. In-situ growth of different Bi₂ Te₃-Sb₂ Te₃ superlattices was also monitored and modeled. The growth of Bi₂ Te₃ and Sb₂ Te₃ layers can be seen clearly in in-situ SE data. Modeling of in-situ superlattice growth shows perfect superlattice growth with an abrupt interface between the two constituent films.     

Model Predictive Control of Si1−xGex Thin Film Chemical–Vapor Deposition

This paper integrates in situ robust and efficient fundamental models and noninvasive optical sensors with state-of-the-art estimation and model predictive control techniques in order to grow unusual and aggressive Si_1-xGe_x alloy films. A model predictive controller is presented that utilizes a dynamic process model and feedback from a spectral ellipsometer to reconstruct the current state of a Si_1-xGe_x growing film in real time. Si _1-xGe_x films grown utilizing feedback from a spectral ellipsometer are compared to films grown using open-loop recipes, which is the current industrial practice. These films are compared quantitatively utilizing the offline characterization techniques, auger spectrometry, and secondary-ion-mass-spectrometry analysis. The model predictive controller presented in this paper detects and rejects unmeasured disturbances allowing for precise control over film qualities. In this paper, films grown utilizing feedback from an optical sensor are shown to be up to 51% truer to desired profiles, when compared with similar films grown using open-loop recipes. The experimental results presented in this paper provide the first demonstration of feedback control using online optical film measurements to grow aggressive alloy composition profiles in which flow rates of several component gases and reactor temperatures must be varied simultaneously in order to achieve the profile of interest     

Real-Time monitoring of III-V molecular beam epitaxial growth using spectroscopic ellipsometry

We report the real-time monitoring of monolayer thickness changes in AlAs and GaAs layer growth on rotating GaAs substrates using spectroscopic ellipsometry (SE). A phase-modulated spectroscopic ellipsometer was integrated with a III-V MBE system by triggering spectral acquisition synchronously with substrate rotation. Absolute thickness accuracy was verified using ex situ SE measurement. Reasonable agreement was also obtained between in situ growth rate measurements by SE and reflection high energy electron diffraction. The precision and speed of this method appears suitable for real-time control of quantum devices, such as resonant-tunneling diodes.     

Real-time control of HgCdTe growth by organometallic vapor phase epitaxy using spectroscopic ellipsometry

The use of spectroscopic ellipsometry for monitoring the vapor phase epitaxial growth of mercury cadmium telluride (Hg_1−xCd_xTe) in real-time is demonstrated. The ellipsometer is used to perform system identification of the chemical vapor deposition reactor used for the growth of CdTe and to measure the response of the reactor to different growth conditions. The dynamic behavior of the reactor is also studied by evaluating the gas transport delay. The optical constants of Hg_1−xCd_xTe are determined at the growth temperature for different compositions.In-situ real-time composition control is performed during the growth of Hg_1−xCd_xTe. The required target compositions are attained by the ellipsometer and appropriate corrections are also made by the controller when a noise input in the form of a temperature variation is introduced.     

In-situ ellipsometry studies of adsorption of Hg on CdTe(211)B/Si(211) and molecular beam epitaxy growth of HgCdTe(211)B

We study the adsorption of Hg on CdTe(211)B using an 88-wavelength spectroscopic ellipsometer mounted on a commercial, molecular beam epitaxy (MBE) chamber. A detailed analysis of the pseudo-dielectric function shows that Hg is present at the surface both in chemisorbed and physisorbed form. Effective medium models for a mixture of chemisorbed and physisorbed Hg on the microscopically rough CdTe surface could not fit our data. However, a proposed model in which a partial layer of physisorbed Hg sits on top of a partial layer of chemisorbed Hg fits the measured pseudo-dielectric function well and yields precise values for the thicknesses of the chemisorbed and the physisorbed Hg layers. These values change in the expected manner as a function of Hg flux, temperature, and Te coverage. An analysis of the uncertainty in the measured thicknesses is carried out in detail, and a study of the limitations of the ellipsometer used for this study is presented. The effects of these limitations on the precision and accuracy of in-situ data are enumerated.     

椭偏仪的研究进展

主要介绍了椭偏仪的测量原理,比较了不同结构的椭偏仪,并根据具体应用需求介绍了椭偏光谱仪、红外椭偏光谱仪、成像椭偏仪和广义椭偏仪,分析了椭偏仪的数据处理过程,最后展望了椭偏仪的发展趋势.     

MOCVD原位监测垂直腔面发射激光器材料生长

利用MOCVD的原位监测控制生长垂直腔面发射激光器材料。通过GaAs／AlGaAs DBR结构生长表明系统的原位监测结果与实际结果间存在2％的偏差。修正原位监测的参数,可实现利用原位监测进行实时控制生长,从而有效地减少系统漂移对材料生长的影响,提高系统的控制精度。用于垂直腔面发射激光器(VCSEL)的外延生长中,可以有效减少生长次数并得到高质量的外延材料,制作的VCSEL器件在室温下得到10．1mw的脉冲功率和7．1mw的直流功率。     

Noncontacting measurement of thickness of thin titanium silicidefilms using spectroscopic ellipsometer

Spectroscopic ellipsometry has gained increasing attention in semiconductor process control because the technique is nondestructive and noncontacting. This paper demonstrates the capability of spectroscopic ellipsometer to measure the thickness of conducting thin films of titanium silicide. Unlike cross section TEM measurement, this technique does not involve elaborate process of sample preparation. This technique does not require calibration and is used to determine thickness of silicide films from few tens of angstrom up to tens of nanometer. The thickness of titanium silicide film measured at a single point, using spectroscopic ellipsometer and TEM analysis differs by only 4%     

PECVD法氮化硅薄膜生长工艺的研究

采用等离子体增强化学气相沉积法(PECVD),在单晶硅衬底(100)上成功制备了不同生长工艺条件下的氮化硅薄膜。分别采用XP-2台阶仪、椭圆偏振仪等手段测试了薄膜的厚度、折射率、生长速率等参数。并采用原子力显微镜(AFM)研究了薄膜的表面形貌。结果表明,温度和射频功率是影响薄膜生长速率的主要因素,生长速率变化幅度可以达到230nm/min甚至更高。对于薄膜折射率和成分影响最大的是NH3流量,折射率变化范围可以达到2.7～1.86。分析得出受工艺参数调控的薄膜生长速率对薄膜的性质有重要影响。     

AlGaN/GaN HEMT材料外延技术研究

采用低压MOCVD技术在蓝宝石和SiC衬底上生长了本征GaN和AlGaN/GaN HEMT结构材料。生长过程中采用了EpiTUNEⅡ在位监测技术,对材料生长工艺进行了模型分析以及优化控制。在获得具有良好表面形貌、晶体质量以及光荧光谱的GaN本征材料基础上,生长了AlGaN/GaN HEMT结构材料,获得了良好的2DEG性能。     

Reliability of composite solder bumps produced by an in-situ process

In an attempt to develop a thermally stable solder system, an in-situ Pb-Sn solder composite reinforced with Cu₆Sn₅ dispersoids was investigated for its thermal stability. The stability was evaluated mainly by measuring the growth rate of intermetallics at in-situ composite solder/BLM interface as a function of the number of reflow soldering cycles and aging time. The rates were compared with those of the eutectic Pb-Sn and Sn-Ag solders. After the thermal treatments, the solder joints were tested for their shear strengths. The results indicated that the in-situ composite solder has a higher shear strength and better thermal stability than the eutectic Pb-Sn solder. Jointly appointed by CAAM at POSTECH     

SiH_4-NH_3-N_2体系LPCVD氮化硅薄膜的生长动力学

以硅烷和氨气分别作为低压化学气相沉积(LPCVD)氮化硅(SiNx)薄膜的硅源和氮源,以高纯氮气为载气,在热壁型管式反应炉中,借助椭圆偏振仪和原子力显微镜,系统考察了工作压力、反应温度、气体原料组成等因素对SiNx薄膜沉积速率和表面形貌的影响。结果表明:SiNx薄膜的生长速率随着工作压力的增大单调增加,随着原料气中氨气与硅烷的流量之比的增大单调减小。随着反应温度的升高,沉积速率逐渐增加,在840℃附近达到最大,随后迅速降低。在适当的工艺条件下,制备的SiNx薄膜均匀、平整。较低的薄膜沉积速率有助于提高薄膜的均匀性,降低薄膜的表面粗糙度。     

In-situ monitoring of epitaxial film thickness by IEMI

In-situ measurement of epitaxial film thickness by infrared emission Michelson interferometer (IEMI) is presented. During in-situ experiments, epi wafers were heated inside an ultrahigh vacuum (UHV) single-wafer chemical vapor deposition (CVD) reactor or a furnace and the IR emission from the wafers was analyzed by the MI. In-situ thickness measurements have been made at temperatures ranging from 150 to 900°C for a lightly doped epi layer (0.5 Ω-cm) on top of a heavily doped substrate (0.001-0.002 Ω-cm). The accuracy of in-situ measurements is 2% of the actual epi layer thickness, compared with 0.3% for ex-situ measurements. This technique can be applied to real-time in-situ measurements of epi film growth and to real-time control of epi film thickness     

Supervisory run-to-run control of polysilicon gate etch using insitu ellipsometry

Polysilicon gate etch is a critical manufacturing step in the manufacturing of MOS devices because it determines the tolerance limits on MOS circuit performance. The etch used in the current study suffers from machine aging, which causes processing results to drift with time. Performing the etch for the same time with fixed process setpoints (recipe) for all wafers would produce unsatisfactory results. Thus, an in situ ellipsometer was employed with a new run-to-run supervisory controller, termed predictor corrector control (PCC), to eliminate the impact of machine and process drift. A novel modeling technique was used to predict uniformity from the ellipsometry data collected at a single site on the wafer. Predictive models are employed by the PCC supervisory controller to generate optimal settings (recipe) for every wafer which will achieve a target mean etch rate, while maintaining a spatially uniform etch. A 200 wafer experiment was conducted to demonstrate the benefits of process control. Implementation of PCC resulted in a 36% decrease in standard deviation from target for the mean etch rate. In addition, the data indicates that controlling etch rate may improve the control and uniformity of the line width change     

In-situ epitaxial silicon—oxide-doped polysilicon structures for MOS field-effect transistors

Limited reaction processing (LRP) has been used to achieve the in-situ growth of epitaxial silicon-oxide-doped polysilicon layers. The in-situ growth of these multiple layers was combined with the selective epitaxial growth technique to create structures for MOSFET fabrication. The results of n- and p-channel transistor fabrication utilizing these structures are presented.     

Neural-Network-Based Sensor Fusion of Optical Emission and Mass Spectroscopy Data for Real-Time Fault Detection in Reactive Ion Etching

To achieve timely and accurate fault detection in reactive ion etching, neural networks (NNs) have been applied for the fusion of data generated by two in-situ sensors: optical emission spectroscopy (OES) and residual gas analysis (RGA). While etching is performed, OES and RGA data are simultaneously collected in real time. Several pre-determined, statistically significant wavelengths (for OES data) and atomic masses (for RGA signals) are monitored. These data are subsequently used for training NN-based time series models of process behavior. Such models, referred to herein as time series NNs (TSNNs), are realized using multilayered perceptron NNs. Results indicate that the TSNNs not only predict process parameters of interest, but also efficiently perform as sensor fusion of the in-situ sensor data.