In situ monitoring technique and apparatus for chemical/mechanical planarization endpoint detection

A process for in situ monitoring the thickness of a dielectric material on a lateral surface of an electrically conductive substrate having less than about one megohm-cm resistivity, which comprises

• placing the substrate so that a surface of an electrode structure faces the dielectric material, said electrode structure comprises a measuring electrode, an insulator surrounding the measuring electrode, a guard electrode surrounding said insulator and another insulator surrounding the guard electrode,
• interposing between the substrate and the surface of the electrode structure a film of a conductive liquid with resistivity of less than about 100,000 ohm-cm, said film being in contact with the dielectric material and with the surface of the electrode structure,
• measuring the capacitance between the substrate and the electrode structure by applying a measuring (drive) voltage with an operating frequency of up to 5000 Hz to the surface of the measuring electrode and bootstrapping the guard electrode with a guard voltage, and by maintaining constant displacement current resulting from said voltage application, the amplitude of the drive voltage being proportional to the thickness of the dielectric layer, and
• in which two equal electrode structures are arranged side by side, and said measuring voltage is applied to one electrode structure at 180.degree. out of phase to the measuring voltage being applied to the other electrode structure.

An apparatus for monitoring the thickness of a dielectric layer remaining on a surface of a workpiece during polishing in a lapping machine with a polishing slurry, said workpiece comprising a conductive portion with resistivity of less than about one megohm-cm and dielectric material on a lateral face of the conductive portion, which apparatus comprises

• at least one electrode structure having a flat surface for facing the lateral face of the workpiece being polished, said electrode structure comprising a conductive measuring electrode, an insulator surrounding the measuring electrode, a conductive guard electrode surrounding the insulator and being separated by the insulator from the measuring electrode and another insulator surrounding the guard electrode,
• means for providing a conductive liquid medium (the polishing slurry) such that the said face of the workpiece and said flat surface of the electrode structure interface through the liquid medium (aqueous slurry), and
• means for measuring the capacitance between the conductive portion of the workpiece and the electrode structure, the measuring means comprises means for supplying drive voltage with an operating frequency of up to 5000 Hz to the measuring electrode and in a bootstrap arrangement to the guard electrode while maintaining constant displacement current resulting from the voltage application, the amplitude of the drive voltage being proportional to the thickness of the dielectric layer thereby measuring the capacitance of the dielectric layer undergoing polishing.

An apparatus for monitoring the thickness of a dielectric layer remaining on a surface of a workpiece during polishing in a lapping machine with a polishing slurry, said workpiece comprising a conductive portion with resistivity of less than about one megohm-cm and dielectric material on a lateral face of the conductive portion, which apparatus comprises

• at least one electrode structure having a flat surface for facing the lateral face of the workpiece being polished, said electrode structure comprising a conductive measuring electrode, an insulator surrounding the measuring electrode, a conductive guard electrode surrounding the insulator and being separated by the insulator from the measuring electrode and another insulator surrounding the guard electrode,
• means for providing a conductive liquid medium (the polishing slurry) such that the said face of the workpiece and said flat surface of the electrode structure interface through the liquid medium (aqueous slurry),
• means for measuring the capacitance between the conductive portion of the workpiece and the electrode structure, the measuring means comprises means for supplying drive voltage to the measuring electrode and in a bootstrap arrangement to the guard electrode while maintaining constant displacement current resulting from the voltage application, the amplitude of the drive voltage being proportional the to the thickness of the dielectric layer thereby measuring the capacitance of the dielectric layer undergoing polishing, and
• in which two equal electrode structures are arranged side by side, said measuring voltage is applied to one electrode structure at 180.degree. out of phase to the measuring voltage being applied to the other electrode structure.

A process of fabricating a device, which comprises

• fabricating a device structure on a substrate so as to yield a non-planar surface, said substrate having resistivity of less than about one megohm-cm,
• forming a layer of dielectric material over the non-planar surface,
• reducing the thickness of said dielectric layer progressively,
• monitoring the remaining thickness so as to determine a desired end-point of the reduction, and
• continue fabrication of said device,
• wherein said desired end-point is determined by measuring the capacitance between the substrate and an electrode structure facing the substrate while the face of the substrate and the surface of the electrode structure facing the substrate are interfaced by a continuous conductive film of a liquid with resistivity of less than about 100,000 ohm-cm, said electrode structure comprising a measuring electrode, an insulator surrounding the measuring electrode, a guard electrode surrounding said insulator and another insulator surrounding the guard electrode,
• wherein said capacitive measuring includes measuring the capacitance and simultaneously removing effects of leakage resistance on the measuring result by applying a measuring voltage with an operating frequency of up to 5000 Hz to the measuring electrode and in a bootstrap manner to the guard electrode, and by maintaining constant displacement current resulting from said voltage application, the amplitude of the drive voltage being proportional to the thickness of the dielectric layer.

A process of fabricating a device, which comprises

• fabricating a device structure on a substrate so as to yield a non-planar surface, said substrate having resistivity of less than about one megohm-cm,
• forming a layer of dielectric material over the non-planar surface,
• reducing the thickness of said dielectric layer progressively,
• monitoring the remaining thickness so as to determine a desired end-point of the reduction, and
• continue fabrication of said device,
• wherein said desired end-point is determined by measuring the capacitance between the substrate and an electrode structure facing the substrate while the face of the substrate and the surface of the electrode structure facing the substrate are interfaced by a continuous conductive film of a liquid with resistivity of less than about 100,000 ohm-cm, said electrode structure comprising a measuring electrode, an insulator surrounding the measuring electrode, a guard electrode surrounding said insulator and another insulator surrounding the guard electrode,
• wherein said capacitive measuring includes measuring the capacitance and simultaneously removing effects of leakage resistance on the measuring result by applying a measuring voltage with an operating frequency of up to 5000 Hz to the measuring electrode and in a bootstrap manner to the guard electrode, and by maintaining constant displacement current resulting from said voltage application, the amplitude of the drive voltage being proportional to the thickness of the dielectric layer, and
• in which two equal electrode structures are arranged side by side, and said measuring voltage is applied to one electrode structure a 180.degree. out of phase to the measuring voltage being applied to the other electrode structure.

An apparatus for measuring the thickness of a dielectric region on a lateral face of article having a conductive portion with resistivity of less than about one megohm-cm and dielectric material on a lateral face of the conductive portion, which comprises

• an electrode structure having a flat surface, the dielectric layer on said article facing the said flat surface, said electrode structure comprises a measuring electrode, an insulator surrounding the measuring electrode, a guard electrode surrounding the insulator and another insulator surrounding the guard electrode,
• conductive liquid means for interfacing the conductive article and the flat surface of the electrode structure and for establishing an electrical connection between the conductive article and said flat surface of the electrode structure,
• means for measuring the capacitance between the conductive article and the measuring electrode structure, the measuring means comprises means for supplying drive voltage to the measuring electrode and in a bootstrap arrangement to the guard electrode thereby measuring the capacitance of the dielectric layer thickness without interfering leakage resistance;
• and
• in which two equal electrode structures are arranged side by side, and said measuring voltage is applied to one electrode structure at 180.degree. out of phase to the measuring voltage being applied to the other electrode structure.