Chemical mechanical polishing pad with window

1. A chemical mechanical polishing pad, comprising:

a polishing layer having a central axis, an outer perimeter, a polishing surface, a base surface and a polishing layer thickness, T P , perpendicular to a plane of the polishing surface measured from the polishing surface to the base surface;

an endpoint detection window having a polishing side, a platen side and a window thickness, T W , perpendicular to the polishing side measured from the polishing side to the platen side;

a subpad having a top surface, a bottom surface, a plurality of cross members, a plurality of apertures, an outer edge and a subpad thickness, T S , perpendicular to the top surface measured from the top surface to the bottom surface; wherein the plurality of apertures are separated by the plurality of cross members; wherein the plurality of apertures comprises at least three adjacent apertures; wherein the three adjacent apertures consist of an inner aperture, a center aperture and an outer aperture; wherein the inner aperture has an inner aperture cross sectional area, A i , parallel to the plane of the polishing surface, wherein the inner aperture cross sectional area, A i , is substantially constant across the subpad thickness, T s ; wherein the center aperture has a center aperture cross sectional area, A c , parallel to the plane of the polishing surface wherein the center aperture cross sectional area, A c , is substantially constant across the subpad thickness, T s ; wherein the outer aperture has an outer aperture cross sectional area, A o , parallel to the plane of the polishing surface wherein the outer aperture cross sectional area, A o , is substantially constant across the subpad thickness, T s ; wherein the plurality of cross members consists of an inner member and an outer member; wherein the inner member separates the inner aperture from the center aperture; and, wherein the outer member separates the center aperture from the outer aperture; and,

a stack adhesive;

wherein the endpoint detection window is incorporated into the chemical mechanical polishing pad, wherein the polishing side is disposed toward the polishing surface of the polishing layer;

wherein the stack adhesive is interposed between the base surface of the polishing layer and the top surface of the subpad;

wherein the plurality of apertures is in optical communication with the endpoint detection window; and,

wherein the polishing surface of the polishing layer is adapted for polishing of a substrate.

2. The chemical mechanical polishing pad of claim 1 , wherein the plurality of apertures extend from the bottom surface of the subpad to the top surface of the subpad.

3. A method of polishing, comprising:

providing a chemical mechanical polishing apparatus having a table, a light source and a photosensor;

providing a substrate;

providing a chemical mechanical polishing pad of claim 1 ;

installing onto the table the chemical mechanical polishing pad with the polishing surface disposed away from the table;

optionally, providing a polishing medium at an interface between the polishing surface and the substrate;

creating dynamic contact between the polishing surface and the substrate, wherein at least some material is removed from the substrate; and,

determining a polishing endpoint by transmitting light from the light source through the endpoint detection window and analyzing the light reflected off the substrate, back through the endpoint detection window and incident upon the photosensor.

4. The chemical mechanical polishing pad of claim 1 , wherein the outer aperture has an outer aperture average cross sectional area, A o-avg , parallel to the plane of the polishing surface across the subpad thickness, T s ;

wherein the inner aperture has an inner aperture average cross sectional area, A i-avg , parallel to the plane of the polishing surface across the subpad thickness, T s ;

wherein the center aperture has an center aperture average cross sectional area, A c-avg , parallel to the plane of the polishing surface across the subpad thickness, T s ; and,

wherein

0.75* A o-avg ≦A i-avg ≦1.25* A o-avg ; and,

0.5*( A i-avg +A o-avg )≦ A c ≦1.25*( A i-avg +A o-avg ).

5. The chemical mechanical polishing pad of claim 4 , wherein the endpoint detection window has a window cross sectional area, W a , parallel to the plane of the polishing surface; wherein the window cross sectional area, W a , is substantially constant across the window thickness, T W .

6. The chemical mechanical polishing pad of claim 5 ,

wherein the endpoint detection window has a window length, W L , parallel to the plane of the polishing surface measured along a window long dimension, LD W , of the endpoint detection window;

wherein the endpoint detection window has a window width, W W , parallel to the plane of the polishing surface measured along a window short dimension, SD W , of the endpoint detection window;

wherein the window long dimension, LD W , is perpendicular to the window short dimension, SD W ;

wherein the polishing layer has a polishing layer radial line, PL R , on the plane of the polishing surface that intersects the central axis and extends through the outer perimeter of the polishing layer;

wherein the endpoint detection window is incorporated into the chemical mechanical polishing pad such that the window long dimension, LD W , projects a window long dimension projection, pLD W , on the plane of the polishing surface; wherein the window long dimension projection, pLD W , substantially coincides with the polishing layer radial line, PL R ;

wherein the plurality of apertures have an aperture length, A L , parallel to the plane of the polishing surface measured along an aperture long dimension, LD A , of the plurality of apertures;

wherein the plurality of apertures have an aperture width, A W , parallel to the plane of the polishing surface measured along an aperture short dimension, SD A , of the plurality of apertures;

wherein the aperture long dimension, LD A , is perpendicular to the aperture short dimension, SD A ; and,

wherein the plurality of apertures is integrated into the subpad such that the aperture long dimension, LD A , projects an aperture long dimension projection, pLD A , on the plane of the polishing surface; wherein the aperture long dimension projection, pLD A , substantially coincides with the window long dimension projection, pLD W .

7. The chemical mechanical polishing pad of claim 6 ,

wherein the inner member has an inner member width, W IM , parallel to the plane of the polishing surface measured along the aperture long dimension, LD A , of the plurality of apertures;

wherein the outer member has an outer member width, W OM , parallel to the plane of the polishing surface measured along the aperture long dimension, LD A , of the plurality of apertures;

wherein the inner aperture has an inner aperture dimension, D i , parallel to the plane of the polishing surface measured along the aperture long dimension, LD A , of the plurality of apertures;

wherein the outer aperture has an outer aperture dimension, D o , parallel to the plane of the polishing surface measured along the aperture long dimension, LD A , of the plurality of apertures;

wherein the aperture length, A L , of the plurality of apertures is essentially constant across the subpad thickness, T S , and across the aperture width, A W , of the plurality of apertures;

wherein the plurality of apertures has an average aperture length, A L-avg , across the subpad thickness, T S , and across the aperture width, A W , of the plurality of apertures;

wherein the aperture width, A W , of the plurality of apertures is essentially constant across the subpad thickness, T S , and across the aperture length, A L , of the plurality of apertures;

wherein the plurality of apertures has an average aperture width, A W-avg , for the plurality of apertures across the subpad thickness, T S , and across the aperture length, A L , of the plurality of apertures; and,

wherein

A L-avg ≦W L-avg ; and,

A W-avg ≦W W-avg .