Detailed description of the method for measuring film thickness in semiconductor chip manufacturing

In semiconductor manufacturing, the thickness of a thin film has a significant impact on the performance and quality of a device. The thickness of a thin film determines many important physical and chemical properties, directly affects the optical properties of refraction, reflection, and transmission, leads to important quantum size effects, and thus alters the electronic, optical,wafer test and magnetic properties of the material. Accurate measurement and control of film thickness is important for optimizing device performance, improving productivity and ensuring device reliability.

Four-Probe Method

The four-point probe method, also known as the four-point co-linear probe method, is a technique used to measure the resistivity of thin films. The four-point co-linear probe technique involves placing four equally spaced probes in contact with a material of unknown resistance. wafer level testingA probe mounted in the probe is gently placed in the center of the wafer and two external probes are used to supply current. Two internal probes are used to measure the voltage drop generated on the surface of the sample.

After obtaining the square resistivity of the raised film, a film thickness, t, can be obtained by itself by backtracking the calculation equation

Volume resistivity (ω-cm)

V = measured voltage (V)

I = measured current (I)

t = sample thickness (cm)

k = correction factor

Function: Measurement of the thickness of opaque conductive films

Ellipsometry

Ellipsometry is a non-contact,failure analysis non-destructive optical system for measuring data, which can infer the nature of the material to be measured by measuring the change of polarization information state after the reflection of different polarized light on the surface of the material to be measured.

Ellipsometry usually consists of three parts.

Light source: Provides monochromatic linearly polarized light. A laser or a monochromatic lamp can be used as the light source.

Polarizer: After the light is reflected by the sample, a polarizer is used to measure the polarization of the reflected light. It is usually a polarizer or a device that can measure the polarization state of light.

Detector:Records the light intensity coming from the analyzer structure for information.

When linearly polarized light strikes the surface of the object to be measured, the polarization state of the reflected light changes from linear to elliptical polarization due to the optical properties of the surface (e.g., refractive index, extinction coefficient, etc.). By measuring and comparing the light intensity of reflected and incident light, and analyzing the measurement results, the thickness and optical constants of the film can be deduced.

Function: Measurement of transparent and metallic films up to 50nm.

X-ray fluorescence spectrometry

X-ray fluorescence spectrometry spectroscopy (xRF) is a non-destructive technique used to analyze elements, and can measure virtually any element from boron (the fifth element in the periodic table) to uranium (the 92nd element). x-ray fluorescence spectrometry analyzers determine the chemical composition of a sample by measuring the fluorescent x-rays emitted when the sample is excited by a primary x-ray source. Each element in the sample produces a set of characteristic fluorescent X-rays that are unique to that particular element and can be used to characterize and quantify materials by comparing X-ray fluorescence spectra.

Functions: Identifies alloys, detects impurity elements, analyzes precious metals, and determines film weight and thickness.