Systems and Methods for In-Situ Wafer Edge and Backside Plasma Cleaning

A method for plasma cleaning a peripheral region and a bottom surface of a workpiece, comprising:

• positioning the bottom surface of the workpiece on a dielectric support defined to support the workpiece in an electrically isolated manner within a region between an upper surface of a lower electrode plate and a lower surface of a dielectric upper plate, with an upper electrode plate positioned next to an upper surface of the dielectric upper plate, the lower electrode plate connected to receive radiofrequency power, the upper electrode plate electrically connected to a reference ground potential;
• positioning the dielectric support such that a top surface of the workpiece is separated from the lower surface of the dielectric upper plate by a narrow gap, and such that an open region exists between the bottom surface of the workpiece and the upper surface of the lower electrode plate;
• flowing a purge gas to a central location within the narrow gap between the top surface of the workpiece and the lower surface of the dielectric upper plate such that the purge gas flows through the narrow gap in a direction away from the central location toward a periphery of the workpiece;
• flowing a process gas to a peripheral region of the workpiece located outside the narrow gap, whereby the process gas flows into the region between the bottom surface of the workpiece and the upper surface of the lower electrode plate;
• and
• supplying radiofrequency power to the lower electrode plate so as to transform the process gas into a plasma around the peripheral region of the workpiece and within the region between the bottom surface of the workpiece and the upper surface of the lower electrode plate.

A semiconductor processing system, comprising:

• a lower showerhead electrode plate having an interior region for transforming a process gas into a plasma, the lower showerhead electrode plate having a number of vents extending from an upper surface of the lower showerhead plate to the interior region;
• a process gas supply channel formed to supply the process gas to the interior region of the lower showerhead electrode plate;
• a radiofrequency power supply connected to supply radiofrequency power to the lower showerhead electrode plate so as to transform the process gas into the plasma within the interior region of the lower showerhead electrode plate;
• a first upper plate positioned parallel to and spaced apart from the lower showerhead electrode plate;
• a second upper plate positioned next to the first upper plate such that the first upper plate is located between the lower showerhead electrode plate and the second upper plate, the second upper plate electrically connected to a reference ground potential;
• a dielectric edge ring having an annular shape with an upper surface defined to contact and support a peripheral region of a bottom surface of a workpiece and support the workpiece in an electrically isolated manner within a region between the upper surface of the lower showerhead electrode plate and a lower surface of the first upper plate;
• and
• a purge gas supply channel formed to supply a purge gas to the region between the upper surface of the lower showerhead electrode plate and the lower surface of the first upper plate at a central location of the first upper plate,
• wherein the dielectric edge ring is defined to position the workpiece proximate to and substantially parallel to the first upper plate such that the purge gas is made to flow from the purge gas supply channel over a top surface of the workpiece between the lower surface of the first upper plate and the top surface of the workpiece so as to prevent reactive constituents of the plasma from reaching the top surface of the workpiece, when the workpiece is present on the dielectric edge ring.

A method for plasma cleaning a bottom surface of a workpiece, comprising:

• positioning the workpiece on a dielectric edge ring having an annular shape with an upper surface defined to contact and support a peripheral region of the bottom surface of the workpiece, the dielectric edge ring defined to support the workpiece in an electrically isolated manner within a region between an upper surface of a lower showerhead electrode plate and a lower surface of a first upper plate, with a second upper plate positioned next to an upper surface of the first upper plate, the lower showerhead electrode plate connected to receive radiofrequency power, the second upper plate electrically connected to a reference ground potential;
• positioning the dielectric edge ring such that a top surface of the workpiece is separated from the lower surface of the first upper plate by a narrow gap, and such that an open region exists between the bottom surface of the workpiece located inside the dielectric edge ring and the upper surface of the lower showerhead electrode plate;
• flowing a purge gas to a central location within the narrow gap such that the purge gas flows through the narrow gap in a direction away from the central location toward a periphery of the workpiece;
• flowing a process gas to an interior region of the lower showerhead electrode plate;
• and
• supplying radiofrequency power to the lower showerhead electrode plate so as to transform the process gas into a plasma within the interior region of the lower showerhead electrode plate, whereby reactive constituents of the plasma flow through vents from the interior region of the lower showerhead electrode plate into the open region between the bottom surface of the workpiece located inside the dielectric edge ring and the upper surface of the lower showerhead electrode plate.