The present disclosure relates to an abrasive article used for polishing or otherwise conditioning wafers, such as silicon wafers.  In particular, the disclosure relates to abrasive articles having a window system for monitoring the polishing process. 
In the course of integrated circuit manufacture, a semiconductor wafer typically undergoes numerous processing steps, including deposition, patterning, and etching steps.  Additional details on how semiconductor wafers are manufactured can be found in the article xe2x80x9cAbrasive Machining of Siliconxe2x80x9d by Tonshoff, H. K.; Scheiden, W. V.; Inasaki, I.; Koning.  W.; Spur, G. published in the Annals of the International Institution for Production Engineering Research Volume 39/2/1990, pages 621 to 635.  At each step in the process, it is often desirable to achieve a pre-determined level of surface xe2x80x9cplanarity,xe2x80x9d xe2x80x9cuniformity,xe2x80x9d and/or xe2x80x9croughness.xe2x80x9d It is also desirable to minimize surface defects such as pits and scratches.  Such surface irregularities may affect the performance of the final semiconductor device and/or create problems during subsequent processing steps. 
One accepted method of reducing surface irregularities is to treat the wafer surface with a slurry containing a plurality of loose abrasive particles, dispersed in a liquid, and a polishing pad; this is commonly referred to as xe2x80x9cplanarizingxe2x80x9d or xe2x80x9cplanarizationxe2x80x9d.  The planarization process is typically a chemical-mechanical polishing (CMP) process.  One problem with CMP slurries, however, is that the process must be carefully monitored in order to achieve the desired amount of planarization.  It is important that the planarization process be stopped when the correct thickness of layer material has been removed; that is, when the proper endpoint has been reached.  Removing too much of the layer results in loss of wafer yield, which could require redepositing of the circuitry, and not removing a sufficient amount of the layer may require continued planarization.  Various methods have been used to attempt to detect the endpoint for stopping the CMP process.  These methods include: straight timing, friction, optical results, acoustical results, and conductive characteristics.  There have been references related to endpoint detection by chemical analysis; see for example, U.S. Pat.  Nos.  6,021,679 and 6,066,564, and PCT Published application WO 99/56972.  These references disclose detecting the endpoint by monitoring a chemical reaction product caused by the reaction of a component from the abrasive slurry and the wafer. 
Additionally, there have been references that disclose using visual or optical techniques for in-situ monitoring of the CMP process; see for example, U.S. Pat.  No.  6,068,538 which discloses using a polishing device having a moveable window positioned below the wafer being processed to view the wafer surface.  During polishing, the window is removed from the wafer surface, but is moved to be adjacent the wafer during the visual inspection. 
Improvements in real-time endpoint detection methods and processes for determining when the desired level of planarization of the wafers has been obtained, are desired. 
The present disclosure is directed to fixed abrasive articles used for polishing or planarization of semiconductor wafers, and methods of using those abrasive articles for detection of the endpoint of the CMP process. 
The abrasive article is a fixed abrasive article having an element or feature therein that allows monitoring of a wafer surface therethrough.  By the term xe2x80x9cfixed abrasive articlexe2x80x9d, it is meant that the abrasive article has an abrasive coating adhered to a backing or other carrier layer.  The monitoring element allows monitoring of the wafer surface through a portion of the abrasive article; this monitoring element can be referred to as a xe2x80x9cwindowxe2x80x9d.  This window may be an area free of abrasive coating, an area having a decreased amount of abrasive coating, or any other area that allows monitoring of the wafer surface through the abrasive article.  The benefits of using a fixed abrasive article include the lack of freely moving abrasive particles, such as is encountered when using an abrasive slurry, which can interfere with the endpoint measurements through the monitoring element. 
In one embodiment, the window allows transmission of radiation therethrough, the radiation having a decrease of no greater than about 50% as it passes through the window.  The term xe2x80x9cradiationxe2x80x9d is intended to all types of radiation, including electromagnetic radiation, gamma rays, radio frequencies, microwaves, x-rays, infrared radiation, ultraviolet radiation, visible light, and the like.  The radiation may be reflected by the wafer surface or may be emitted by the surface.  In one embodiment, the window allows transmission of visible light therethrough, the transmission having a decrease no greater than about a 50% as it passes through the window. 
In another embodiment, the window allows transmission of radiation therethrough, with the amount of radiation passing therethrough sufficient to allow for quantitative evaluation of changes of the wafer surface.  That is, the amount of radiation lost during passing through the window of the abrasive article is irrelevant, as long as the level is sufficient to monitor changes in the wafer surface. 
The surface of the wafer can be monitored for changes such as temperature, visible light spectrum patterns, radiation scattering effects, and the like. 
The window, through which the wafer surface is monitored, can be continuous along an extended length of abrasive article; for example, the window can extend along the length of a roll of abrasive article.  The window can be positioned in essentially the same position along the length of the abrasive article, or the position of the window can vary.  In another embodiment, the window is a discrete window bounded by abrasive coating on all sides.  Alternately, the abrasive article can have a specific shape and size, such as an abrasive disc; the window can extend from one edge of the abrasive disc to an opposite edge, or the window can be a discrete window bounded by abrasive coating on all sides. 
The fixed abrasive article of the present disclosure can be, and preferably is, a textured or three-dimensional abrasive article.  By the terms xe2x80x9ctexturedxe2x80x9d and xe2x80x9cthree-dimensionalxe2x80x9d, it is meant that the abrasive coating has a discernible surface pattern.  The pattern or texture may be random or precisely placed on the backing.  In some embodiments, the abrasive coating is a plurality of abrasive composites on the backing; the abrasive composites may be precisely or irregularly shaped.  Preferably, the abrasive composites are precisely shaped.  The abrasive composites, whether precisely or irregularly shaped, can be of any geometrical shape defined by a substantially distinct and discernible boundary; such shapes include pyramidal, truncated pyramidal, and the like. 
The abrasive coating is a plurality of abrasive particles held to the backing by a binder.  The binder can be any material, such as a metal or ceramic binder, but is generally and preferably an organic binder.  In most embodiments, the binder is formed from a binder precursor.  In the embodiments where the binder is an organic binder, the binder is formed by the curing or polymerization of the binder precursor. 
In one preferred embodiment, the binder is formed by an addition polymerization, that is, a free-radical or cationic polymerization, of a binder precursor.  Additionally, the binder precursor can be polymerized by exposure to radiation or radiant energy, along, if necessary, with an appropriate curing agent.  Preferably, the binder precursor includes multi-functional acrylate resin(s), mono-functional acrylate resin(s), or mixtures thereof. 
Methods of making an abrasive article having a window are disclosed.  Generally, the abrasive article can be made by any method known for making abrasive articles, except that the present disclosure includes the addition of a window within the abrasive coating.  The window can be formed by various methods, including: leaving a portion of the backing without the abrasive coating, eliminating the abrasive coating on a portion of the backing after the abrasive coating has been applied, modifying the abrasive coating to provide the desired transmission properties, or removing portions of the abrasive article and applying onto a carrier backing. 
Methods of using the abrasive article to planarize the wafer and monitor the endpoint of the planarization process without removal of the abrasive article are also disclosed.  The abrasive article is brought into contact with the wafer surface at a desired pressure, preferably in the presence of a coolant or lubricant, such as water or any aqueous or non-aqueous chemistry, and the abrasive article and wafer are moved in relation to each other.  After a prescribed period of planarization, the surface of the wafer is optically examined through the window in the abrasive article.  In another embodiment, the surface of the wafer can be continuous monitored through the window in the abrasive article.