Wafer topography

Performs high-resolution high-accuracy wafer topography measurement using Raytex s proprietary optical measurement system... 

Based on experimental observation, Stine et al. (1997) proposed a PD CMP model for oxide polishing. Figure 6.6 shows the wafer topography and the key variables defined in the model. This model takes a straightforward consideration of local PD in a single die to reformulate Preston s equation as... 

Modeling of the CMP process. To calculate the wafer topography evolution during the CMP process, PD p(x, y) needs to he extracted from the chip layout. With initial values of up area thickness and step height, the die-level pressure distrihution p x, y) can he obtained hy solving Eqn (6.27). Once p x, y) is solved, pu(x, y) and pi x, y) can he calculated hy Eqn (6.26). Then we utilize Preston s equation with local pressures pu(x, y) and pd(x, y) to calculate the instantaneous MRR of up area and down area as... 

Figure 10. The microprobing of polymer molecular layer chemically tethered to a silicon wafer. Topography (left top), adhesion (right top), and elastic modulus (left bottom) images of the film (3x3 pm) with the worn area along with the example of force-distance curves (right bottom). Data shows low adhesion in the debris area and within the worn area and lower elastic modulus for polymer debris.

A typical LIMS instrument accepts specimens up to 19 mm (0.75 in) in diameter and up to 6 mm in thickness. Custom designed instruments exist, with sample manipulation systems that accept much larger samples, up to a 6-in wafer. Although a flat sample is preferable and is easier to observe with the instrument s optical system, irregular samples are often analyzed. This is possible because ions are produced and extracted from pm-sized regions of the sample, without much influence from nearby topography. However, excessive sample relief is likely to result in reduced ion signal intensity. 

In this chapter we discuss double-crystal topography, in which we obtain a map of the diffracting power of a crystal compared to that of a reference. We first treat the principles and geometries, the mechanisms of image contrast and resolution and the ttse of laboratory and synchrotron radiation. We then discuss applicatiorrs wafer inspection, strain contour mapping, topography of curved crystals. 

An important featnre to note in double-axis topography experiments is that when the beam area is large, the measnred rocking curve widths are not necessarily intrinsic. For example, mismatched epitaxial layers curve substrate wafers by an amonnt which depends on the degree of mismatch and layer thickness. Topographs of snch curved wafers show bands of diffracted intensity. 

An additional complication associated with the standing wave effect occurs for the exposure of resist over topography. When a resist is spin-coated onto a substrate containing steps, the resist thickness varies from one area to another on the wafer. Since the standing wave effect is a strong function of resist thickness, exposure variations resulting from variation in resist thickness in the vicinity of the step result in changes in linewidth. 

Rothman (52) investigated the planarization of polyimide films over features tens of micrometers in size and separation. Bassous and Pepper (55) studied planarization of PMMA and AZ1350J over features pertinent to Si wafer processing. A mechanical stylus was used to determine the topography of the wafer and the corresponding surface variation of the resist thickness as shown in Figure 29 where a 1.7 - pm thick AZ1350J layer was spun on steps of different space and width combinations. 

Fig. 8, Schematic diagram of (top) asperity contact during CMP, (middle) die-scale asperity contact for patterned wafer with topography height x and (bottom) die-scale asperity contact for patterned wafer with topography height x/3.

Stylus profilometry is a very simple and powerful tool in CMP. Profilometry can be used to determine the surface planarity change before and after CMP. Basically, in this technique, a stylus scans across a pattern feature in contact with a wafer, while the Z motion (height) of the stylus is monitored. This Z motion signal reflects the surface topography scanned. 

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