半导体材料与器件的载流子输运参数成像

As modern semiconductor materials science and technology is rapidly developing, suitable advanced characterization methods are in great demand. Thorough understanding of the relationship between structure, processing, physical properties, and how they are linked to device performance is the key to innovation in materials science and engineering. Since reliable and precise measurements are needed at all stages of R&D and production, it is crucial to develop real-time, detailed non-destructive and quantitative characterization methods for quality control and property evaluation through all phases of material processing, from raw wafer fabrication to final device integration..Carrier transport properties are among the most important parameters of semiconductor materials and devices. They determine the transport behavior of electrons in semiconductors across device structures, thus having direct impact on device performance. Although there are many techniques capable of determining carrier transport parameters, to-date none of them can simultaneously meet the following four requirements: 1) measurement precision and accuracy; 2) non-contact character; 3) lateral resolution (imaging); and 4) depth-selection or axial resolution (tomographic subsurface depth-profilometry)..Based on the well-established principle of Photocarrier Radiometry (PCR), the proposal aims to develop a technique, named lock-in carrierography, for mapping (imaging) carrier transport parameters in semiconductor materials and devices. To overcome the frame rate and exposure time limitations of near-infrared cameras, a heterodyne method is introduced for high frequency carrierographic imaging which results in high-resolution near-subsurface information. The feasibility of the method is guaranteed by the natural superlinearity behavior of photoluminescence, which allows one to construct a slow enough beat frequency component from nonlinear mixing of two high frequencies..The proposed technology will help investigate comprehensively distributions, and generate maps of, lifetime compromising defects, dopant densities, carrier diffusion lengths, and interface properties. It will be further used to elucidate energy conversion mechanisms and conversion efficiencies, thereby identifying practical problems, such as furnace contamination with lifetime killer impurities or imperfectly annealed ion implantation damage, thus having excellent industrial application prospects for in-line and off-line quality control during device processing.

载流子输运参数（体复合寿命、表面复合速率、迁移率、扩散系数等）是表征半导体材料和器件性能的核心参数。从原材料制备到最终器件研制的每一道工序中，对材料内载流子输运参数的分布进行实时、精确、无损的空间表征，有助于分析掺杂浓度、杂质分布、界面状态、缺陷密度等关键因素，可实现对新结构、新工艺、器件效率的全面评估和优化，具有重要科学意义。锁相载流子辐射成像技术于2010年提出，是半导体检测领域的前沿热点技术，但由于近红外CCD的帧率和曝光时间的限制，无法实现高频成像，因而目前无法得到载流子输运参数分布的图像。本项目提出外差锁相成像原理，利用载流子辐射复合的非线性效应，实现非线性混频，构造出携带高频信息的拍频信号分量，可以突破技术瓶颈，使得动态成像频率不受限制，有望实现半导体材料和器件的载流子输运参数成像。本技术不仅能为微电子、光电子、传感器、光伏能源等领域的创新研究服务，而且具有广阔的工业应用前景。

载流子输运参数是表征半导体材料和器件性能的核心参数。光载流子辐射（PCR）技术已被证明是载流子输运参数单点测量的有力手段。基于近红外相机的锁相载流子辐射成像（LIC）技术作为PCR技术的成像延展，于2010年提出，但由于近红外CCD的帧率和曝光时间的限制，无法实现400 Hz以上的高频成像，因而无法分辨载流子输运参数分布的图像。本项目基于外差锁相成像原理，利用载流子辐射复合的非线性效应，通过非线性混频构造出携带高频信息的拍频信号分量，可以突破技术瓶颈，使得帧率只有几十赫兹的近红外相机可以表征微秒量级的载流子复合动力学参数。在原有PCR线性理论模型的基础上，考虑了光载流子复合的非线性效应，通过开展两组强度扫描的重要实验，基于实验数据分析，建立了零差和外差模式下的非线性光载流子辐射测量理论模型，该模型是深入开展载流子输运参数测量和成像的基础；基于锁相成像原理以及外差非线性混频机制，得到了单晶硅片和多晶硅太阳能电池从100 Hz到100 kHz的外差幅度图像，随着频率升高，载流子的交流扩散长度变短，成像深度变浅，后表面特征对信号的影响减小，证实了外差高频LIC成像技术可实现深度选择性成像，这同其它光学无损检测相比是一个独特优势；同时，根据外差图像的幅频数据特征，结合外差理论模型，定量反演了等效载流子寿命，并同Microwave Photoconductive Decay的测量结果对比，一致性很好。下一步的研究重点将是深入研究信号的非线性物理机制（可能是多个），以及如何从等效载流子寿命进一步分辨载流子输运参数以及多个载流子寿命。本无损检测与成像技术有望从原材料制备到最终器件研制的每一道工序中，对材料内载流子输运参数的分布进行实时、精确、无损的空间表征，有助于分析掺杂浓度、杂质分布、界面状态、缺陷密度等关键因素，可实现对新结构、新工艺、器件效率的全面评估和优化，不仅能为微电子、光电子、传感器、光伏能源等领域的创新研究服务，而且具有广阔的工业在线检测应用前景。