The manufacture of many types of work pieces requires the substantial planarization of at least one surface of the work piece. Examples of such work pieces that require a planar surface include semiconductor wafers, optical blanks, memory disks, and the like. Without loss of generality, but for ease of description and understanding, the following description of the invention will focus on applications to only one specific type of work piece, namely a semiconductor wafer. The invention, however, is not to be interpreted as being applicable only to semiconductor wafers.
One commonly used technique for planarizing the surface of a work piece is the chemical mechanical planarization (CMP) process. In the CMP process a work piece, held by a work piece carrier, is pressed against a polishing surface in the presence of a polishing slurry, and relative motion (rotational, orbital, linear, or a combination of these) between the work piece and the polishing surface is initiated. The mechanical abrasion of the work piece surface combined with the chemical interaction of the slurry with the material on the work piece surface ideally produces a planar surface.
The construction of the carrier and the relative motion between the polishing pad and the carrier head have been extensively engineered in an attempt to achieve a uniform removal of material across the surface of the work piece and hence to achieve the desired planar surface. For example, the carrier may include a flexible membrane or membranes that contacts the back or unpolished surface of the work piece and accommodates variations in that surface. One or more pressure zones or chambers (separated by pressure barriers) may be provided behind the membrane(s) so that different pressures can be applied to various locations on the back surface of the work piece to cause uniform polishing across the front surface of the work piece.
However, the pressure distribution across the back surface of the wafer for conventional carriers often is not sufficiently controllable during the CMP process. Thus, as illustrated in FIG. 1, a work piece with an initial non-planar profile, such as a profile 10, that is planarized by a conventional carrier will have a non-planar surface profile similar to a profile 12 after the CMP process, although a substantially planar surface is desired. Further, conventional carriers do not provide sufficient control of the pressure zones to permit a desired non-planar profile to be achieved. In addition, to the extent the planarization process can be adjusted during CMP, such as, for example, by increasing or decreasing pressures in the adjustable pressure zones, the adjustment(s) typically takes place toward the end of the CMP process, thus resulting in over-correction.
Accordingly, it is desirable to provide a method for controlling the pressures of adjustable pressure zones of a work piece carrier during CMP to achieve substantially planar, or desired non-planar, profiles. In addition, it is desirable to provide a method for controlling the CMP process sufficiently early in the process to prevent over-correction. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.