Thickness Measurement

Silicon Wafer

Ocean Optics offers both modular and fully integrated systems for determining optical and non-optical thin film thickness characteristics for applications in semiconductor, industrial, medical and consumer markets. Our customers have successfully configured systems for measuring the thickness of silicon wafers, determining photoresist layers for masks and testing the hardness and wear of coatings. Components for high-volume OEM applications are also available.

Thin film measurement instrumentation has evolved from complex, difficult to use systems to today’s compact, practical tools that provide a simple but powerful and flexible interface. With coverage ranging from the vacuum ultraviolet to the infrared, these devices offer a level of accuracy and repeatability that makes spectroscopic techniques useful for a broad range of applications.

Application & Technical Notes

PDF: App Note – Thickness Measurement of ARC and Silicon Thin Films

PDF: App Note – Transmission Measurements of Polymer Thin Films

Example Setups

Example Setup: Thin Film Thickness Measurement

Overview

A thin film on a substrate can act as an etalon, creating an interference pattern superimposed on the surface reflectivity when viewed in reflection. The spacing of the pattern’s sinusoidal peaks, when combined with the refractive index of the material, can be used to calculate the thickness of the material.

Spectra observed in our operating software reveal oscillations caused by optical interference within the layers of the thin film substrate. Analysis of the wavelength position of the minima or maxima can determine either the thin film’s thickness (with the known refractive index of the film) or its refractive index (with the known film thickness). Keep in mind that the thickness of samples may not be uniform; we recommend measuring several locations on the film.

Spectrometer

The HR2000+ES enhanced-sensitivity spectrometer is one of many good options for reflectrometry of thin films. The spectrometer is preconfigured with a wide-range grating set for ~200-1050 nm, a 10 µm slit and a detector collection lens for enhanced sensitivity. Also, the optical bench has a quartz window for UV transmission and the OFLV-200-1100 variable longpass order-sorting filter to eliminate second- and third-order effects.

Sampling Optics

A QR400-7-VIS-NIR reflection probe positioned at 90° to the sample measures specular reflectance from surfaces such as thin films. We couple our HL-2000 tungsten halogen light source to the probe for illumination and add a reflection probe holder and specular reflectance standard (not shown) to complete the sampling setup.

Alternatively, we replace the probe holder and reflectance standard with a Single-point Reflection Stage and Si-SiO2 reference wafer (see illustration). STEP-WAFER reference standards are available in UV-VIS and VIS-NIR wavelengths, are 100 mm in diameter and are 5-step wafers with calibrated thickness ranges of 0-500 nm and 600-1100 nm.

Software

OceanView spectroscopy software completes the system.

Thin Film Thickness Measurement System Components

HR2000+ES	High-resolution spectrometer with enhanced sensitivity is configured with an extended-range grating (200-1050 nm), 10 µm slit and variable longpass filter and quartz window (DET2B-200-1100)
HL-2000	Tungsten halogen light source (360-2400 nm)
QP400-7-UV-VIS	Premium-grade 400 µm diameter fiber optic reflection probe; 2 m length
Reflection probe fixture options	RPH-1 holds 0.25” (6.35 mm) diameter probes at 45° and 90° to the surface	STAGE Single-point Reflection Stage holds 0.25” (6.35 mm) diameter probes and accommodates substrates up 150 mm in diameter
Reference standard options	STAN-SSH high-reflectivity specular reflectance standard	STEP-WAFER options are Si-SiO2 reference wafers for thickness measurements of thin films on silicon wafers and other substrates
OceanView	Spectroscopy operating software