摘要
四探针测试技术是半导体工业检测电阻率时采用最为广泛的测试手段之一。随着时代的不断进步,半导体产业飞速发展,以单晶硅片为衬底的集成电路集成度越来越高,目前正进入甚大规模集成电路(ULSI)时代,测试在整个集成电路生产过程中的地位越来越重要。许多器件的重要参数与电阻率有关,因此这对晶体电阻率的均匀性,电学特性提出了更为严格的要求,特别是微区的电特性和均匀性引起了人们的广泛关注。在这样的背景下,四探针测试技术需要有新的发展。
目前微区薄层电阻测量存在的问题是依据显微镜视力观察,用手工操作将探针定位于微区图形的阴影区。这样,完成Φ200mm(8时)圆片杂质的扩散分布需要对许多图形进行测试,需要花费很长的时间,当测试Φ300mm硅片时问题就更为突出。本文将图象与视觉测量系统引入四探针测试系统中,对采集到的原始探针图像进行预处理、边缘提取等操作,以便实现探针针尖的识别,然后由电机控制实现探针的自动定位。这样测试系统可以自动获得全片的薄层电阻分布,为超大规模集成电路检测杂质分布和扩散的均匀性提供信息。
本文还利用单片机系统设计了薄层电阻测试电路,对于程序中用到的范德堡隐函数,利用非线性反演和规范化拟合的方法推导出其多项式显函数形式。这不仅给对我们编写程序提供了方便,也为使用范德堡法和Rymaszewski法测量薄层电阻提供了便利。
Four-point probe measurement technique is one of the most extensive means for examining the resistivity in the semiconductor industry.With continuous progress, semiconductor industry develops at a very fast speed,the integration level of IC becomes higher and higher.Presently,the IC production is entering into the age of ULSI, then testings are more and more important. Many important properties of semiconductor devices are relevant with their resistivity,which brings forward strict demands to the uniformity of the resistivity.Especially micro-area's characteristics attract extensive attention.Under this background, four-point probe measurement technique requires a new development.
At present,the problem in testing sheet resistance for micro-areas is that probes must be set up at the suitable locations by handwork.In order to know the wafer's impurity distributing,we need test many times,so will waste a lot of time.If the wafer's diameter would be 300mm,this problem will be more serious.In this paper,image analysis is introduced,through pre-processing and edge picking-up,the probe tips are recognized.Then probe tips will be aligned respectively in two perpendicular directions through driving stepper motors.Thus the distribution of sheet resistance for whole wafer is got by automatic testing and it offers information for detecting the impurity distribution and the diffusion uniformity.
In this paper,the circuit used for testing sheet resistance is designed using single chip processor.Additionally,we have expressed Van der pauw function as a polynomial form through local and global reversal development by using the normalized polynomial match,being convenient not only for programming, but also for sheet resistance testing when using Van der pauw and Rymaszewski methods.
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