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Fourier Transform Infra-Red Spectroscopy for Measuring Thinly Planarized Wafers in Stacked Three-Dimensional Structure Processing

IP.com Disclosure Number: IPCOM000084986D
Publication Date: 2005-Mar-02
Document File: 4 page(s) / 70K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method that uses a Fourier transform infra-red (FTIR) spectrometer to measure and compute the physical thickness of a wafer that has been bonded to a substrate wafer. Benefits include a solution that improves accuracy, precision, and measurement speeds.

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Fourier Transform Infra-Red Spectroscopy for Measuring Thinly Planarized Wafers in Stacked Three-Dimensional Structure Processing

Disclosed is a method that uses a Fourier transform infra-red (FTIR) spectrometer to measure and compute the physical thickness of a wafer that has been bonded to a substrate wafer. Benefits include a solution that improves accuracy, precision, and measurement speeds.

Background

Investigations are underway for manufacturing processes in which multi-layer stacks of devices and interconnects are built in 3D fashion. One approach is to bond two processed wafers together, grinding or polishing one of the two wafers thin, then repeating the process. The key to success in the stacked 3D manufacturing approach is accurately measuring the thickness of the bonded wafer after the thinning process. Lacking a metrology to determine the thickness post grind hinders development and defeats the manufacturability of the process.

The current state of the art is less than satisfactory; it uses a micron-level caliper to measure the post-bonded/pre-thinning total stack thickness, followed by a second measurement of the post-bonded/post-thinned total stack thickness. The resulting bonded wafer thickness is then inferred through the known wafer thickness and the difference of the two measurements.

General Description

The basis of the FTIR is a modulated light source; the emerging, modulated beam is directed through an aperture to the sample with an incident angle of 30 degrees from normal. The reflected beam is then directed back to the infra-red detector and measured as a function of the time and frequency (see Figure 1). The resulting signal from the "un-phase shifted" light is called the center burst. The center burst is where all light emerging from the interferometer satisfies the total constructive interference condition. For example, two photons emerging from the source, through the interferometer, are reflected from the top-most surface and have the same path length. 

If the sample is a bi-layer stack with a well-defined interface between two materials of different refractive index, then another constructive interference recombination occurs. This results in a phase shift between two coincident p...