Method and apparatus for conditioning a CMP pad

The present invention relates to a method and apparatus for conditioning a polishing pad used in chemical mechanical polishing in which a consistent pressing force can be provided between an abrasive conditioning member and the polishing pad. Specifically, a moveable weight member is provided that can be selectively moved along a length of a support arm in the conditioning apparatus. The position of the weight member relative to the position at which the abrasive conditioning member is mounted alters the resultant pressing force in view of the change in moment created. In a particular example, the positioning of the weight member can be automatically controlled using a drive mechanism controlled by a control unit, such as a computer. In a more particular example, the positioning of the weight member can be dynamically controlled if the control unit receives an external feedback upon which its control of the weight member position is based, such as a detected value of the pressing force exerted by the abrasive conditioning member. Finally, if the apparatus is appropriately arranged to permit the weight member to travel to an opposite side of the location at which the support arm is mounted from the abrasive conditioning member, then a “negative pressing force” can be generated, such that effective pressing forces less than the resting weight of the pad conditioning apparatus can be realized.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus used to condition a chemical mechanical polishing (CMP) pad used for CMP polishing of semiconductor wafers during semiconductor device fabrication.

BACKGROUND OF THE INVENTION

Chemical mechanical polishing (sometimes known in the art as chemical mechanical planarization), or CMP, is in general a well-known process used in the fabrication of semiconductor devices. CMP combines mechanical polishing (using, for example, abrasive slurries) with selective chemical reactions to increase the mechanical removal rate of material. The chemical reaction(s) particularly provide greater material removal selectivity than mechanical polishing alone.

CMP is commonly used to flatten the surface of a wafer after etch and/or deposition steps, generally to such a degree that subsequent photolithography steps have a sufficient focus margin.

In general, CMP is performed by using a polishing pad in combination with a slurry of water, abrasives, and reactive chemicals for the desired chemical reaction or reactions. The polishing pad is caused to be pressed against the wafer surface and relative motion between the wafer and the pad is imparted (that is, by moving one or both of the wafer and the pad).

The polishing pad is conventionally a porous pliable material. Polyurethane foam is particularly common for use as a polishing pad. Surface asperities of the polishing pad are critical to the polishing process because they provide the mechanical polishing action. However, as the pad is used for polishing, it tends to become smoother as the asperities are rubbed away and/or as slurry residues build up in the pores. As a result, the polishing process is degraded. It is therefore conventionally known to condition the polishing pad to roughen the surface and increase the open porosity of the foam.

FIGS. 1 and 2are a side elevational and a perspective view, respectively, of a conventional CMP pad conditioning apparatus10. As generally shown, an abrasive member, such as a member12coated with an abrasive, such as diamond, is pressed, relatively, against a surface of the polishing pad (not illustrated) with a certain force. The member12and the surface of the polishing pad are then moved relative to one another.

For example, abrasive member12is mounted on an arm14(by way of a mount or support20) in a known manner. The arm14may be in turn pivotably mounted in a known manner such that the arm14can be raised or lowered so as to press a surface of member12against a surface of a polishing pad as desired. The arc labeled R inFIGS. 1 and 2indicate this motion of arm14about an axis17.

An alternative known system (not illustrated) does not pivot but instead applies a vertical pressing force by way of support20, such as by extending and retracting support20along its axis.

As seen inFIGS. 1 and 2, arm14may be also laterally rotatable about an axis16so that the arm14(and the member12mounted thereon) can sweep out an arc of motion relative to a polishing pad surface. The lateral sweeping motion of arm14may be powered, such as by a conventional motor (not shown) connected to shaft18.

As mentioned above, arm14is preferably mounted at shaft18in a manner permitting an opposite end of arm14to translate vertically. In particular, this vertical translation permits member12to be lowered into contact with a polishing pad. The connection between arm14and shaft18is any standard arrangement permitting the required motion about axis17, for example and without limitation, a hinge pin or a bushing/shaft assembly.

Arm14may be raised and lowered by any conventional means, including without limitation, manual and mechanical means (the latter not being shown).

In addition, the member12is mounted on the arm14by way of a mount or support20so as to accommodate raising or lowering arm14relative to the horizontal while maintaining a surface of member12in contact with a surface of the polishing pad. For example, a conventional gimbal, hinge pin, ball and socket joint, etc. structure may be provided to mount member12. In general, member12is mounted so as to be pivotable about axes21and23, which motion permits all angles of orientation between abrasive member12and an opposing polishing pad surface to be accommodated.

At the outset, it will be appreciated that the simple resting weight of the arm14, member12, and member mount20will tend to cause arm14to rotate about axis17on shaft18(as indicated by the arrow R), which will correspond to a given pressing force against a polishing pad surface opposed to member12. In an alternative known arrangement, the arm14does not pivot about axis17. Instead the member mount20(with member12mounted thereon) is axially movable, and its resting weight corresponds to a given pressing force against a polishing pad opposed to member12.

However, the relative pressing force between the member12and the polishing pad is a very important factor in controlling polishing pad conditioning, such that variations in the pressing force cause variations in polishing pad conditioning.

In particular, the pressing force of a conditioning assembly passively resting on a polishing pad cannot be changed to provide different conditioning results or to conform to conditioning requirements for different polishing pad materials.

Some conventional arrangements envision fixedly mounting a weight on the arm in order to provide a different pressing force than that corresponding to the passive weight of the assembly.

Also, some conventional pad conditioning arrangements use sensors, such as load cells, as part of a calibration process to determine a given pressing force. However, this still does not address the problem of adjusting the pressing force during operation. Also, the magnitude of the pressing force still cannot be altered.

SUMMARY OF THE INVENTION

In view of the foregoing, a method and apparatus for conditioning a CMP polishing pad are provided as defined in the claims appended hereto.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 3is a side elevational view of an example of a pad conditioning apparatus100according to the present invention. Certain features are common with the conventional arrangement seen inFIGS. 1 and 2and are therefore identically numbered.

Apparatus100particularly includes a moveable weight member102arranged to be moveable and selectably positionable along a length of the arm14. In general, the pressing force applied by member12against a polishing pad (not shown) will increase as the position of weight member102approaches the position where abrasive member12is mounted on arm14and will decrease as weight member102moves away from that position.

Any mechanically suitable method may be used to mount the weight member102on arm14so as to be moveable therealong. For example,FIG. 3illustrates weight member102mounted to as to slide on a rod or bar104supported by and extending between a pair of mounts106a,106bwhich are in turn each fixed on arm14. Another arrangement (not illustrated) could comprise mounting the weight member so as to be slidably engaged in a slot formed in the arm14. Weight member102is optionally in sliding contact with a surface of the arm14.

As before, the arm14is mounted by any conventional means (such as a hinge pin) with respect to shaft18so as to be pivotable about a horizontal axis17generally perpendicular to the axis of rotation16, so as to permit the opposite end to move vertically towards and away from a surface of a polishing pad. At the other end of arm14, mount20for supporting abrasive member12is preferably freely pivotable with respect to the arm14and/or abrasive member12(by way of, for example, a ball and socket joint) so that a surface of abrasive member12can be maintained flush against a surface of a polishing pad. In particular, mount20is free to pivot at least about orthogonal axes21,23so as to be able to place a surface of abrasive member12in any needed orientation so as to remain flush against a surface of the polishing pad.

FIG. 4illustrates a particular example of the present invention in which weight member102′ is threadedly mounted on a rotatable drive screw104′. Drive screw104′ is rotatably mounted on supports106a′ and106b′. The drive screw104′ is driven to rotate as desired by a conventional controllable drive motor (not shown) housed in, for example, support106b′.

The selective rotation of drive screw104′ causes weight member102′ to be displaced along the arm14in accordance with the direction in which drive screw104′ is made to rotate. With a known thread pitch, the linear displacement of weight member102′ can be correlated to a number of turns of the drive screw104′. This can in turn be correlated to the position of the weight member102′ along the arm14, so as to arrive at a known value of the resultant pressing force between the abrasive member12and the polishing pad being conditioned. This interrelationship of process parameters may sometimes be referred to as a “recipe” for conditioning a given polishing pad. The recipe may for example take into account one or both of the abrasive material of the member12and the material constituting the polishing pad being conditioned.

The rotation of drive screw104′ may be automatically controlled by an external control unit108, such as a computer or the like, that provides the drive screw motor with control signals by a technically appropriate connection (physical or not)110.

The control unit108may receive external inputs that affect its control of the drive screw104′. In a particular example, the control unit may receive an input signal corresponding to a presently detected pressing force between the abrasive member12and the polishing pad. The pressing force could be detected, for example, by load cells, as described above with respect to conventional practice. Therefore, if a variation from a desired pressing force is detected, the control unit108can dynamically adjust the position of weight member104′ in order to regain the desired pressing force.

Other known methods could be used to displace the weight member along the arm, such as push-pull extensible rods and the like connected to the weight member.

FIG. 5illustrates a further variant of the present invention. In general, the apparatus illustrated inFIG. 5is similar to that illustrated inFIG. 4, except for the fact that weight member102′ is permitted to move along arm14′ to either side of the location at which arm14′ is mounted at18. This may correspond either to extending one end of arm14′ in comparison with arm14ofFIG. 4, or to moving the location at which arm14′ is supported inwards (i.e., away from the end of arm14′).

In general, if weight member102′ is moved to the opposite side of mount18from the location at which abrasive member12is mounted, a moment is created in the opposite sense of that created by the passive weight of the abrasive member/arm combination. More particularly, this offers the possibility of expanding the range of pressing forces that can be generated by the apparatus so as to include pressing forces less than that created by the resting weight of the pad conditioning apparatus. That is, positioning the weight member102′ on the opposite side of shaft18in effect counteracts the weight of the apparatus extending on the other side of shaft18.

In all other respects, the implementation of the present invention illustrated inFIG. 5is identical to that shown inFIG. 4.

Although the present invention has been described above with reference to certain particular preferred embodiments, it is to be understood that the invention is not limited by reference to the specific details of those preferred embodiments. More specifically, the person skilled in the art will readily appreciate that modifications and developments can be made in the preferred embodiments without departing from the scope of the invention as defined in the accompanying claims.