Optics: measuring and testing – Inspection of flaws or impurities – Surface condition
Reexamination Certificate
2000-04-05
2003-07-29
Font, Frank G. (Department: 2877)
Optics: measuring and testing
Inspection of flaws or impurities
Surface condition
C356S237100, C156S922000, C438S016000
Reexamination Certificate
active
06600557
ABSTRACT:
BACKGROUND OF THE INVENTION
The method of the present invention generally relates to the detection of defects in a semiconductor wafer. More particularly, the present invention relates to an inspection method for detecting defects in a silicon wafer resulting from the mechanical and mechanochemical steps the silicon wafer is subjected to in a common manufacturing process.
Semiconductor wafers, such as silicon wafers, are obtained from a single crystal silicon ingot by first slicing the ingot in a direction normal to its axis, typically by means of a wire saw or internal diameter saw. This process damages the surface of the wafer, often to a depth of about 80 microns or more. In addition, sawing or slicing the ingot in way this create ridges on the wafer surface, particularly when a wire saw is employed, resulting in there being a “waviness” to the surface. Through stringent process control waviness can be minimized, but it cannot be eliminated.
In order to remove the surface damage caused by sawing or slicing, the wafers are subjected to a grinding operation to smooth or flatten the surfaces of the wafers. However, grinding does not reduce waviness. This is due to the fact that the wafers are secured to the grinding chuck by a vacuum which temporarily flattens the aspect of the wafer during grinding, when the operation is finished and the vacuum is released, the waviness of the wafers returns. Furthermore, if the grinding conditions are not closely monitored or if the grinding mechanism is not properly cleaned prior to surface grinding, additional damage, such as bumps or “dimples” may be introduced to the surface of the wafers.
The removal of these and other surface defects created by the mechanical processing of the wafer is necessary in order to obtain a wafer which meets standard requirements for smoothness and uniform thickness (or Global Backside-referenced Indicated Range). The detection and mapping of these defects are typically achieved by means of an optical instrument or tool which measures light reflected from the wafer surface; that is, the instrument inspects the wafer surface and generates an image thereof by measuring light reflected from the wafer surface as a result of variations in surface height or slope. However, in order for such measurements to be made, the surface of the wafer must be “mirror-like.”
Generally speaking, a mirror-like surface means that the wafer surface has a gloss value of at least about 250 gloss units, as determined by means common in the art (such as by a BYK Gardner Glossmeter). For purposes of comparison, it is to be noted that a wafer typically only has a gloss value of about 10 gloss units after slicing and lapping, and about 150 gloss units after grinding. As a result, in a common wafer manufacturing process, the wafer must be subjected to a time consuming and expensive mechanical or mechanochemical polishing step in order for the wafer to have a gloss value which is sufficiently high, such that it may be inspected for the presence of waviness or dimples by a instrument capable of measuring reflected light. Such instruments are generally referred to as “magic mirror”-type instruments (see, e.g., a Hologenix instrument, commercially available from Hologenix Corp.). Once a wafer has been inspected, if dimples or waviness are detected that particular wafer must be rejected. Furthermore, due to the fact that in a manufacturing environment wafers are typically processed in lots of 25 or more and that only a few representative wafers from each lot are inspected, the entire lot from which that particular wafer was selected will also be rejected.
In view of the foregoing, a need continues to exist for a process which may be utilized to yield a wafer having a gloss sufficient for optical inspection at any stage in the wafer manufacturing processing. Such a process would save time and reduce manufacturing costs because the wafer would not have to be subjected to a standard mechanical or mechanochemical polishing process prior to inspection. Such a process would also increase the gloss of a wafer without removing an excessive amount of silicon from the wafer surface. In addition, defects such as dimples and waviness could be detected much sooner in the manufacturing process, thus affording the means for early detection and correction of the source of the problem. Finally, such a process would allow wafers to be rejected in the early stages of the manufacturing, preventing defective wafers from be subjected to costly polishing and cleaning steps.
SUMMARY OF THE INVENTION
Among the objects of the present invention may be noted the provision of process for optically inspecting the surface of a silicon wafer for mechanically and mechanochemically induced defects; the provision of such a process wherein standard surface polishing processes are not required; the provision of such a process which limits the amount of silicon removed from the wafer surface; the provision of such a process which limits changes in Global Backside-referenced Indicated Range; the provision of such a process which enables inspection to be performed at any stage in the wafer manufacturing process; and, the provision of such a process which decreases overall inspection time and manufacturing costs.
Briefly, therefore, the present invention is directed to a process for inspecting a surface or edge of a silicon wafer at any stage of silicon wafer manufacturing, in order to detect mechanical and mechanochemical related defects. The process comprises treating the silicon wafer with an aqueous etch solution comprising hydrofluoric acid and an oxidizing agent, and then optically inspecting the treated wafer surface prior to said wafer being subjected to mechanical or mechanochemical polishing.
The present invention is further directed to a process for inspecting a surface of an unpolished silicon wafer at any stage of silicon wafer manufacturing, in order to detect mechanical and mechanochemical related defects. The process comprises treating the unpolished silicon wafer surface with an aqueous etch solution comprising hydrofluoric acid and an oxidizing agent, and then optically inspecting the treated surface of the unpolished wafer using an instrument capable of measuring light reflected by the treated surface.
The present invention is still further directed to a process for manufacturing a silicon wafer from a single crystal silicon ingot, wherein mechanical or mechanochemical damage resulting from the manufacturing process is detected prior the wafer being polished. The process comprises slicing the single crystal silicon ingot to obtain a silicon wafer and then treating a surface of the sliced silicon wafer with an aqueous etch solution comprising hydrofluoric acid and an oxidizing agent. The treated wafer surface is optically inspected, and then the inspected wafer is subjected to mechanical or mechanochemical polishing.
Other objects and features will be in part apparent and in part pointed out hereinafter.
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“Chemical Etching of Silicon, III. A Temperatu
Doane Tom
Erk Henry F.
Pei Zhijian
Stefanescu Anca
Font Frank G.
MEMC Electronic Materials , Inc.
Nguyen Sang H.
Senniger Powers Leavitt & Roedel
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