1. Field of the Invention
The invention relates to semiconductor wafer processing equipment and, more particularly, the invention relates to a method and apparatus for selectively marking a semiconductor wafer with identifiable markings.
2. Description of the Background Art
Identifying defects on the surface of a wafer, such as particulate contaminants and other surface irregularities, is extremely important to integrated circuit manufacturing processes. To eliminate defect sources, defects are identified and analyzed to determine the source of the defect. Thereafter, corrective action can be taken to reduce or eliminate the defect source.
Typically, the defect identification process is accomplished in two steps. First, a laser scanner device scans a wafer with a laser and analyses the backscatter of the laser to locate defects on the surface of the wafer. One such laser scanner device is a Tencor SurfScan 6200, manufactured by Tencor Instruments. Second, each defect located by the scanner is analyzed to identify the root cause of the defect. The most commonly employed analysis tool is a high magnification imaging system such as a scanning electron microscope (SEM). An SEM is used to identify the defect and/or the source of the defect by inspecting the defect at high magnification. Additionally, the SEM may be accompanied by instrumentation for performing chemical analysis of the defect. Such instrumentation includes an energy dispersive x-ray (EDX) detector. Other tools may include instrumentation for performing an Auger analysis, an atomic force microscope (AFM), a tunneling electron microscope (TEM), an optical spectrometer and the like.
Since the SEM as well as other analysis tools use a high magnification (on the order of 200 to 2000 times), rapidly positioning the SEM at the defect location can be time consuming. Although the laser device provides defect coordinates that are accurate to approximately 300 microns, a substantial amount of time can be spent manually searching, for example, a 300 by 300 micron region with the SEM for a defect having dimensions of a few tenths of micron.
Additionally, when using a SEM (or other optical analysis tool) to analyze a "bare" wafer, i.e., a wafer having no surface features, the SEM has difficulty focusing on the wafer surface. Without an accurate focus, finding a small defect on the surface is nearly impossible.
Furthermore, some defects are identified by laser scanning, but cannot be seen with a SEM. As such, the SEM operator may search for a defect for a long period of time until realizing the defect cannot be seen with the SEM.
Some defect analysis tools, e.g., an atomic force microscope (AFM), are not readily useful when a large search area is used. Generally, the field of view for an AFM is approximately 10 .mu.m.sup.2, and the search area is as large as 300 .mu.m.sup.2. Unfortunately, an AFM requires approximately five minutes to obtain a 10 .mu.m.sup.2 image. As such, 900 images are required to cover a 300 .mu.m.sup.2 search area, requiring 4500 minutes to complete the search.
Therefore, a need exists in the art for a method and apparatus that selectively marks a wafer proximate a defect such that the defect can be rapidly identified and examined with a SEM or other defect analysis system.