referring now to the drawings , and initially fig1 - 5 , wafer polish apparatus is generally indicated at 10 . included is a conventional wafer carrier or chuck 12 having a downwardly facing recess 14 for holding captive a semiconductor wafer 80 ( see fig5 ). wafer carrier 12 is supported at one end of a reciprocating arm 16 which pivots about the central axis of a drive member 18 . in a known manner , the support arm 16 reciprocates back and forth sweeping out an arcuate path , as indicated in fig3 . extreme positions of the support arm 16 and wafer carrier 12 are shown exaggerated in fig3 for purposes of illustration . it is generally preferred that the wafer carrier 12 be driven for rotation about its central axis so as to rotate in the direction of arrow 22 shown in fig1 . in addition to imparting a reciprocating motion to the wafer carrier , support element 18 also applies a carefully controlled downward pressure on the wafer located within carrier 12 . if desired , the support element 18 and arm 16 can be replaced by the arrangement shown in commonly assigned u . s . pat . no . 5 , 329 , 732 , the disclosure of which is incorporated by reference as if fully set forth herein . in u . s . pat . no . 5 , 329 , 732 the wafer carrier 12 is supported from above by mechanism which imparts a reciprocating motion of the kind indicated in fig3 . referring again to fig1 - 5 , a polish wheel assembly is generally indicated at 30 . polish wheel assembly 30 includes an underlying , supporting , polish wheel 32 having an upper , support surface 33 ( see fig7 ) to which a layer of suitable polish pad material 34 has been affixed by conventional means , such as pressure sensitive adhesive . according to one aspect of the present invention , the upper surface of polish table 32 is divided into two parts , 32a and 32b , by an annular groove 42 . preferably , polish table 32 has a hollow center 44 and , accordingly , recess 42 forms two nested , concentric , spaced - apart annular surface portions in the polish wheel . the outer annular surface portion of the polish wheel is covered with an annular polish pad section 34a , while the inner polish wheel portion 32b has its upper surface covered with an annular polish pad section 34b . referring now to fig2 a probe assembly is generally indicated at 50 and includes a probe 52 and a controller 54 mounted to one side of the polish wheel assembly . as can be seen in fig3 - 5 , for example , controller 54 is mounted on a table 56 located adjacent the polish wheel . probe 52 has a free end 58 which is upturned away from a generally arcuate portion 60 . an upstanding portion 62 rises out of recess 42 as can be seen in fig1 allowing the probe end 64 to extend above the surface of the polish wheel , as can be seen in fig1 . probe 52 is supported in cantilever fashion from controller 54 and is mounted for rotation along the central axis of stub end portion 66 , in the direction of the arrows 68 , as shown in fig2 . preferably , arcuate portion 60 of probe 52 is made slightly larger than the radius of carrier 12 so as to allow the upright portion to clear the polishing wheel . the probe 52 preferably is constructed so as to retain its desired shape in a self - supporting manner . the outer sheaf of the probe cable can , if desired , be made sufficiently rigid for this purpose . alternatively , the probe and / or probe cable can be fitted within an outer supporting conduit . in fig1 probe 52 is rotated in a downward direction such that the arcuate portion 60 and free end 58 are received within recess 42 , as shown in fig6 . with probe 52 rotated in the opposite direction by controller 54 , the probe is raised out of recess 42 so as to allow maintenance operations to be performed on the polish wheel . the internal construction within probe 52 is of conventional design . referring to fig1 , the probe 52 includes a ferrule or lens housing 130 , preferably formed of a 316 stainless steel and having a forward or open end 132 for receiving a conventional optical lens ( such as part no . a31 , 854 ( available from edmund scientific company of barrington , n . j .). lens housing 130 includes a second end 134 which is threaded to receive a nut 138 used to secure a conventional optical cable 140 . preferably , the nut 138 includes external threads received within the threaded hollow end 136 of housing 130 . the nut 138 is preferably sealed to housing 130 with a viton o - ring 142 . as an optional feature , housing 130 includes an internal annular restriction 144 , preferably having a cross - sectional angle of approximately 90 degrees and having an internal free end terminating in a radius of 0 . 2 millimeter , so as to form an internal diameter of approximately 7 millimeters . the lens 134 is installed within housing 130 in a fluid - type arrangement , using a suitable feeling adhesive . the cable 140 has a free end prepared in a conventional manner , which is thereafter inserted within housing 130 , preferably in a nitrogen - filled environment . nut 138 and o - ring 132 are then applied to seal the nitrogen - filled interior of housing 130 , to prevent undesirable fogging of lens 134 . in the preferred embodiment , the free end 58 of probe 52 has optical monitoring capability for direct observation of a wafer being polished . if desired , the probe may include a conventional air jet means ( not shown ) for keeping the face of free end 58 clean and free of slurry so as to allow continuous , uninterrupted monitoring . as indicated in fig3 the free end 58 of probe 52 is located adjacent the exposed surface of a wafer held in carrier 12 . as the carrier is reciprocated back and forth , and rotated about the central axis of carrier 12 , the probe 52 is made to observe the entire surface of the semiconductor wafer , on an ongoing real - time basis , without interfering with the polishing operation . referring to fig7 as mentioned above , the upper surface of annular polish wheel portions 32a , 32b are covered with respective annular portions 34a , 34b of polish pad material . in the preferred embodiment , as mentioned , the polish pad material is secured to the polish wheel with a suitable contact adhesive . preferably , installation of the polish pad material is accomplished by covering both inner and outer annular portions of the polish wheel with a single , unitary polish pad . initially , the polish pad material spans the recess 42 , and is trimmed away from the recess by a knife blade or other cutting instrument . referring again to fig7 annular polish wheel portions 32a , 32b have opposed vertical faces 60 , 62 . the relative dimensions of recess 42 are shown exaggerated in the drawings , for clarity of illustration . it is preferred that the lateral width w of recess 42 range between 2 % and 6 % of the outer radius of the polish wheel . most preferably , the lateral width w of recess 42 ranges between 2 % and 4 % of the polish wheel radius . if desired , the polish pad material could be trimmed substantially parallel to the wall faces 60 , 62 . however , in operation , the polish pad material is compressed by pressure applied to carrier 12 , pressing the semiconductor wafer against the polish pad material . depending on the type of polish pad material and the amount of pressure applied , it is possible that the polish pad material would &# 34 ; grow &# 34 ;, extending beyond wall faces 60 , 62 . in certain types of polishing operations , this may result in unwanted surface pattern formations . accordingly , it is preferred that the cuts on annular polish pad portions 34a , 34b be made upwardly diverging by an angular relief , θ ranging between 0 ° and 60 °. most preferably , the angle of relief , θ , ranges between 10 ° and 45 °. by employing the angular relief mentioned above , a beveled edge is imparted to the opposed edges 64 , 66 of annular polish pad portions 34a , 34b . as can be seen in fig5 it is generally preferred that the radially inner edge of polish pad portion 34b and the radially outer edge portion of polish pad portion 34a also be beveled to prevent unwanted surface formations on a polished surface of the semiconductor wafer . referring again to fig5 semiconductor wafer 80 is shown positioned slightly above the upper surface of the polish pad and slightly below carrier recess 14 , for clarity of illustration . in operation , the semiconductor wafer 80 is held captive in recess 14 and is pressed against the polish pad material . in certain instances , the polish pad material may be caused to undergo a certain amount of compression . as can be seen in fig5 this results in the underneath surface of semiconductor wafer 80 being closely spaced with respect to the free end 58 of probe 52 . as the wafer carrier is oscillated back and forth in the direction of arrow 82 and is spun about the central axis of wafer carrier 12 ( as indicted by arrow 84 ), portions of the wafer surface travel alternately across the polish pad material and the free end 58 of probe 52 , with the underneath surface of semiconductor wafer 80 being monitored continuously on a real - time basis . as will be appreciated , virtually the entire surface of the semiconductor wafer is directly observed with the arrangement of the present invention . although , in the preferred embodiment , probe 52 operates on an optical basis , the probe could also operate beyond the frequencies of visible light . in addition , two adjacent probes could be employed , one for transmission and one for reception , for example , if desired . the probes could , for example , resemble the probe 52 shown in fig1 , except that the 90 degree bend could be replaced by a smaller angled bend , e . g . 45 degrees . in this manner , a pair of oppositely directed mirror - image probes could be mounted for simultaneous operation within channel 42 . as mentioned above , it is preferred that a slurry or some form of fluid material be present between the upper surface of the polish pad material and the bottom surface of semiconductor wafer 80 . as the semiconductor wafer 80 passes over the probe 52 , it is possible that slurry may become deposited on the probe free end 58 . as mentioned above , the probe of the preferred embodiment includes cleaning means which passes a jet of air over the face of the probe , keeping the probe face clean . also , substantial quantities of slurry may accumulate in recess 32 . accordingly , as shown in fig5 a vent passageway 88 is formed in polish wheel 32 to direct slurry out of recess 42 . if desired , a vacuum may be applied adjacent the bottom floor of recess 42 to draw slurry material away . for example , a passageway may be formed between recess 42 and the central portion 44 of polish wheel 32 for convenient conventional coupling to a vacuum source . as mentioned , it is generally preferred that the radially inner and outer annular portions of the polishing wheel be covered with a single unitary polishing pad which is thereafter divided by cutting in accordance with the above description . accordingly , it is desired that the probe be removed from recess 42 to facilitate replacement of the polishing pad . as mentioned above , probe 52 is preferably mounted for rotation by controller 54 . however , other types of mounting arrangements are also possible . for example , probe 52 could be mounted with the same type of mechanism as a conventional phonograph tone arm in which the free end of the probe is first raised above recess 42 and then swung in a horizontal direction over the top of the polishing wheel . further , the rotational drive of the controller 54 could be mounted on a conventional elevator or lifting mechanism to raise the probe out of recess 42 , before rotation is initiated . using any of the above arrangements , the probe is rotated out of recess 42 in preparation for the polishing pad replacement . one advantage of the above described arrangements is that the probe remains connected to control circuitry throughout various phases of operation of the polishing wheel . referring now to fig8 an alternative arrangement is shown with a probe 90 having a free end 92 for direct observation of the semiconductor wafer being polished . free end 42 is carried at one end of a relatively short arcuate portion 94 , generally resembling the arcuate portion 60 shown above . probe 90 includes a second free end 96 comprising a plug portion for slip fit connection to a socket member 110 . probe 90 is mounted on a pair of arms 102 , which are removably connected to a hanger 104 suspended from an overlying support member 106 . the support member 106 extends upwardly from the table 56 or is otherwise supported from the floor on which the polishing machine is positioned . when service of the polishing wheel is required , separable connector 110 is removed from the free end of probe 96 and arms 102 are removed from hanger 104 , allowing the probe 90 to be lifted out of recess 42 . referring now to fig9 an alternative arrangement is shown with probe 120 mounted in polish wheel 132 and having an upper free end positioned within recess 42 . the lower end of probe 120 is received within a communications module 122 which converts the probe data into a form which can be carried along conductors 124 , which in turn are terminated with a conventional rotational coupling ( not shown ) adjacent the center of polish wheel 32 . if desired , the communications module could take the form of a radio transmitter , so as to eliminate the need for electrical connectors 124 and an associated rotational coupling . thus , it can be seen that arrangements are provided for the continuous monitoring of a wafer surface during polishing or other surface operation . existing commercial probe components can be readily employed with the present invention , with a minimum of modification . the probe arrangement of the present invention has found immediate use in end point determination for polishing operations . however , continuous monitoring of wafer surfaces according to principles of the present invention can also be employed for other purposes , such as the surfacing of computer data storage hard disk substrates , coated hard disks and magnetic read / write heads . if desired , other conventional constructions of optical probes and probes operating in regimes other than those which are optically sensible may be used . the drawings and the foregoing descriptions are not intended to represent the only forms of the invention in regard to the details of its construction and manner of operation . changes in form and in the proportion of parts , as well as the substitution of equivalents , are contemplated as circumstances may suggest or render expedient ; and although specific terms have been employed , they are intended in a generic and descriptive sense only and not for the purposes of limitation , the scope of the invention being delineated by the following claims .