Determining Pad-Wafer Contact using Dual Emission Laser Induced Fluorescence

Abstract

It is becoming increasingly clear that understanding the small scale polishing mechanisms operating during CMP requires knowledge of the nature of the pad-wafer contact. Dual Emission Laser Induced Fluorescence (DELIF) can be used to study the fluid layer profile between the polishing pad and the wafer during CMP. Interactions between the polishing pad surface and the wafer can then be deduced from the fluid layer profile. We present a technique and some preliminary data for instantaneous measurement of in-situ pad-wafer contact, defined as the point at which the fluid film thickness goes to zero, using DELIF. The imaging area is 1.30mmx1.74 mm with a resolution of 2.

Editors' Choice—Efficiency of a CMP Pad at Removing Protective Material from Copper during CMP

“…Both can be experimentally characterized using confocal reflectance interference contrast microscopy (C-RICM) 6 or dual emission laser induced fluorescence (DELIF). 8 Once the experimentally observed average oxidation rate of copper is known, t 0 and t as-as can be determined from a plot of the oxidation rate of copper as a function of time elapsed since a bare surface of copper was raised to an anodic potential as illustrated in Figure 9. Since the measured oxidation rate, i measured , is the average of the current densities from the entire surface of the copper where some [5] When a spot on the surface is abraded by an asperity, the oxidation rate at the point will increase immediately because the fraction of sites occupied by protective materials, θ t 0 is lowered.…”

Simulated Effects of Measurement Noise on Contact Measurements Between Rough and Smooth Surfaces

“…2a. This secondary peak is the only feature of the histogram that correlates to changes in applied pressure [13], which in turn implies that information about pad-wafer contact is contained in this region, since contact area must increase with increased pressure.…”

“…While contact has been measured between opaque surfaces using ultrasonic measurements [10], the spatial resolution of such techniques is limited to just less than 1 mm. In order to observe micronscale effects, such as single asperity contact, other optical methods, such as interferometry [11], confocal reflectance interference contrast microscopy (C-RICM) [12], and Dual Emission Laser-Induced Fluorescence (DELIF) [13] must be employed. These methods often require modifying one of the opaque surfaces with an optical window.…”

“…The DELIF method provides a way of measuring contact information in situ [13]. DELIF is used to measure the fluid, i.e.…”

“…2b only shows a smoothed secondary peak and an inflection point between the secondary and primary peak. The contact threshold for the images in [13] is chosen based upon the location of the infection point that separates the secondary from the primary peak. The sum of the area under the secondary peak, shaded in gray, is the contact percentage for the imaged region in Fig.…”