Wafer thickness, measuring

Because most, but not all, emitted X-rays come from the surface of the wafer, a wafer thickness measurement is made prior to each XRF analysis to enable a wafer thickness correction factor to be applied. The equipment for measuring wafer thickness is made up of an Fe-55 nuclear source and a Geiger tube radiation detector (Figure 5). Thickness measurements of the known standards and shipboard sediment wafers are carried out by positioning the wafer between the nuclear source and the radiation detector and recording the attenuation of the X-ray radiation as it passes through the sediment sample. A comparison of the wafer data to that of the calibrated samples enables rapid, nondestructive determination of the thickness of the sediment samples (Figure 6). 

Draw the dimensionless molar density profile of reactant A within a porous wafer catalyst for the following values of the intrapeUet Damkohler number. The reaction kinetics are zeroth-order and the characteristic length L is one-half of the wafer thickness, measured in the thinnest dimension. Put all five curves on the same set of axes and be as quantitative as possible on both axes. Dimensionless molar density I a is on the vertical axis and dimensional spatial coordinate rj is on the horizontal axis. 

This measures the curvature about an axis perpendicular to the dispersion plane, i.e. the cylindrical curvature, and it may be necessary to rotate the wafer through 90° to get the orthogonal component. This may be related to absolute stress in the wafer with knowledge of the wafer thickness, diameter and elastic modulus. The most accurate method is to measure a number of points on a wafer and use a linear regression formula for the average curvature. 

These carriers were generally capable of providing 5-7% nonuniformity at 6- to 7-mm edge exclusion. The nonuniformity is more precisely called the within-wafer nonuniformity (WIWNU) and is defined by the standard deviation of a set of film thickness measurements on a wafer divided by the mean of that set. Smaller numbers denote better process control. Better performance was limited in part by the manner in which the carrier held the wafer during polish. 

Coppeta et al. [10] made slurry film measurements during using laser-induced fluorescence. By addition of a fluorescent dye to the polishing slurry film thickness was experimentally from the fluorescence intensity of the lubrication film as measured through a transparent substrate. Film thickness measurements were in good agreement with those of Levert et al. [7,8]. This technique can also be used to study slurry transport across the wafer surface, diameter variation in lubrication film thickness, and slurry mixing effects [11]. 

In addition to a tight distribution of the thickness variation within a wafer, the average of a group of individual thicknesses must also be targeted within a certain range. Statistically, the control of the WIWNU is the control of standard deviation of individual thicknesses, and the control of final thickness post CMP is the control of the mean. The variation of the mean from wafer to wafer is called wafer-to-wafer nonuniformity (WTWNU). All the thicknesses mentioned in this section are actually the means of many individual thickness measurements in each wafer. Control is not easy, for reasons discussed in the following. 

Vandenberg et al.15 used liquid/solid ellipsometry to obtain kinetic data. The thickness of the APTS coating on oxidized silicon wafers was measured, as a function of immersion time in APTS/toluene solution. The deposition profile showed a fast initial... 

In the plasma etching experiment, the response variable is the range of thickness measurements on the wafer after etching. It is a measure of the consistency or... 

Methods. Polyamic acid in NMP was spin-coated onto a Si or Quartz wafer (diameter = 2.25 inches) coated with Cr, and then cured to polyimide at 400 °C. The purpose of the 500-750-A-thick layer of chromium is to enhance wettability and to give good reflectance to the Quartz wafer. Kapton H (PMDA-ODA) and Upilex S (BPDA-PDA) films were employed for gravimetric analysis. Around 5-um thick layers were used to measure the thickness change. The 100-1000-A-thick layers were employed to obtain XPS and ER IR spectra. The samples for contact angle measurement, XPS and ER IR were dried under vacuum at ambient temperature for 12-24 h and the samples for gravimetric analysis were dried at 85 °C for 12 h. The samples for film thickness measurement were fully re-cured to polyimide. 

In a typical procedure, a layer of [M(TRPyP)] (CF3S03)4 is inihally deposited by dipping the substrate into a 0.1 mM methanol soluhon and allowing it to dry in air. Next, it is dipped into an aqueous Na4[M (TPPS)] solution and washed with water to obtain a monolayer of ion-paired porphyrins. This process can be repeated several times to get mulhlayer hlms in a reproducible way. The thickness of such a him on silicon wafers was measured by atomic force microscopy (AFM) as 12.7 A, and increases linearly with the number of bilayers. According to this, the porphyrin molecules should be laying hat on the surface in a face-to-face arrangement of the [MXTPPS)]" - and [M(TRPyP)] + ion pairs (285). 

Unpattemed electroplated copper wafers were polished using an IPEC 472 polisher equipped with an IR temperature sensor which measures pad surface temperature. The copper rate was determined from copper thickness measurements from a Tencor RS55 resistance monitor, calibrated to cross-sectional SEM micrographs. The SEM tools are regularly calibrated to national standards. 

Since this method captures film thickness information from various areas covered by the CCD camera, the thickness distribution of an area can be measured at extremely high speed. For example. Fig. 6-a shows a three-dimensional plot of the thickness distribution around the Fig. 5-a test pattern taken with the CMP Semi-lnSitu Monitor. Please compare this with Fig. 6-b which shows a three-dimensional plot of an 8-inch wafer film measurement taken with another simultaneous film thickness measurement system with different optical specifications. 

Table 1 shows the CMP Semi-InSitu Monitor s specifications and the results of a recent performance evaluation. Compared with conventional optical spectrometric film thickness measurement systems, the reproducibility of CMP Semi-InSitu Monitor measurements is slightly lower due to the presence of water on the wafer. Nevertheless, when measuring SiO single films at 3 E over repeated trials, the reproducible accuracy is within 4 nm, which is more than sufficient to effectively control CMP processing. 

As for measurement time, the system takes about 7 seconds for pre-alignment and 4.6 seconds for the measurement sequence for each selected point (including stage movement, fine-alignment, auto focusing, and film thickness measurement). Consequently, when 5 points are measured the total measurement time for each wafer is 30 seconds. 

This system employs a simultaneous film thickness measurement method, which incorporates a two-dimensional CCD camera detector , a variable wavelength light source, and an analyzer for the captured image data. With this configuration the system can, not only measure test pattern film thickness but also be used for a variety of visual wafer checks and film data inspections for Cu and other metal films during metal CMP. Moreover, we now have evidence that the system may even be able to handle moving wafers. With such potential, this system could evolve into a true In-Situ Monitor which measures film thickness inside the CMP unit itself with the same precision and accuracy. 

The Hewlett Packard 9825-S computer with internal tape drive and printer was used for shipboard data storage and elemental analyses calculations. Data handling involves input of sample identification number, wafer thickness values, and XRF measurements. The computer is programmed to use this data for elemental analyses calculation and hard-copy printout. 

Lawing, A. Improving the results of post-CMP wafer-scale thickness measurements. Microbiology 2002, 20(1), 31-37. 

By combining this technique with capacitive coupling or ultrasound reflection, wafer thickness and wafer flatness information is also obtained. A further step is to wafer-map the data. Using optical scanning, surface defect maps are generated (2.) and insulator thickness variations are measured ellipsometrically and displayed. As discussed further on, recombination lifetime maps can also be generated by non-contacting methods. 

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