Reducing backside deposition at wafer edge

A process chamber for depositing a film on a wafer, comprising:

• a pedestal configured to receive the wafer, the pedestal having,
• a central top surface extending from a central axis of the pedestal to a top surface diameter, the central top surface having a plurality of wafer supports defined thereon, the wafer supports configured to support the wafer during deposition processing at a support level above the central top surface,
• an annular surface extending from the top surface diameter to an outer diameter of the annular surface, the annular surface being at a step down from the central top surface,
• at least three separate carrier ring supports positioned at the outer diameter of the annular surface, the carrier ring supports extending radially inward of the outer diameter of the annular surface, the carrier ring supports being secured to the pedestal at a fixed height;
• a carrier ring having an annular body with a bottom surface and a top surface, the bottom surface of the annular body of the carrier ring configured to be supported by the carrier ring supports during the deposition processing such that a substantially planar region of the bottom surface of the annular body is at a first vertical separation above the annular surface that is predetermined by the fixed height of the carrier ring supports, the carrier ring having an inner diameter and a step down surface is defined proximate to and surrounding the inner diameter, the step down surface being relative to the top surface that extends from the step down surface to an outer diameter of the annular body, the step down surface being an inner annular surface of the carrier ring;
• wherein when the carrier ring is seated on the carrier ring supports, then the carrier ring surrounds the central top surface, and the step down surface of the carrier ring is positioned at a process level that is at a second vertical separation from the support level over the top surface of the pedestal;
• wherein the first vertical separation defines a lower gap between the substantially planar region of the bottom surface of the carrier ring and the annular surface, the lower gap being less than about 0.15 mm, and the second vertical separation defines an upper gap between the step down surface of the carrier ring, when the carrier ring is seated on the carrier ring supports, and a bottom surface of the wafer when the wafer is seated on the plurality of wafer supports on the pedestal, the upper gap being maintained at less than about 0.15 mm when the wafer is seated on the wafer supports during the deposition processing;
• wherein an edge of the wafer is configured to overhang over the top surface diameter so that the edge of the wafer overhangs and resides over the step down surface of the carrier ring when the wafer is present in the process chamber and supported on the wafer supports;
• wherein the lower gap and the upper gap limit access by process gasses to a backside of the wafer during a deposition process, the lower gap and upper gap limiting deposition on the backside of the wafer at an edge region of the wafer to less than about 20% of deposition on a front side of the wafer at the edge region, the edge region being defined at approximately 3 mm from the edge of the wafer;
• wherein the carrier ring is configured to support the wafer during transport of the wafer to or from the pedestal;
• wherein the carrier ring includes a plurality of carrier ring wafer supports defined on the step down surface of the carrier ring, the step down surface being an inner annular surface of the carrier ring, the carrier ring wafer supports being configured to engage the wafer when the wafer is supported by the carrier ring during transport, the carrier ring wafer supports protruding above the step down surface of the carrier ring by a height amount that is less than the second vertical separation.

A process chamber for depositing a film on a wafer, comprising:

• a pedestal configured to receive the wafer, the pedestal having,
• a central top surface extending from a central axis of the pedestal to a top surface diameter, the central top surface having a plurality of wafer supports defined thereon, the wafer supports configured to support the wafer during deposition processing at a support level above the central top surface,
• an annular surface extending from the top surface diameter to an outer diameter of the annular surface, the annular surface being at a step down from the central top surface,
• at least three separate carrier ring supports positioned at the outer diameter of the annular surface, the carrier ring supports extending radially inward of the outer diameter of the annular surface, the carrier ring supports being secured to the pedestal at a fixed height;
• a carrier ring having an annular body with a bottom surface and a top surface, the bottom surface of the annular body of the carrier ring configured to be supported by the carrier ring supports during the deposition processing such that a substantially planar region of the bottom surface of the annular body is at a first vertical separation above the annular surface that is predetermined by the fixed height of the carrier ring supports, the carrier ring having an inner diameter and a step down surface is defined proximate to and surrounding the inner diameter, the step down surface being relative to the top surface that extends from the step down surface to an outer diameter of the annular body, the step down surface being an inner annular surface of the carrier ring;
• wherein when the carrier ring is seated on the carrier ring supports, then the carrier ring surrounds the central top surface, and the step down surface of the carrier ring is positioned at a process level that is at a second vertical separation from the support level over the top surface of the pedestal;
• wherein the first vertical separation defines a lower gap between the substantially planar region of the bottom surface of the carrier ring and the annular surface, the lower gap being about 0.1 mm or less, and the second vertical separation defines an upper gap between the step down surface of the carrier ring, when the carrier ring is seated on the carrier ring supports, and a bottom surface of the wafer when the wafer is seated on the plurality of wafer supports on the pedestal, the upper gap being maintained at about 0.1 mm or less when the wafer is seated on the wafer supports during the deposition processing;
• wherein an edge of the wafer is configured to overhang over the top surface diameter so that the edge of the wafer overhangs and resides over the step down surface of the carrier ring when the wafer is present in the process chamber and supported on the wafer supports;
• wherein the lower gap and the upper gap limit access by process gases to a backside of the wafer during a deposition process, the lower gap and upper gap limiting deposition by the deposition process on the backside of the wafer at an edge region of the wafer to less than about 20% of deposition on a front side of the wafer at the edge region, the edge region being defined at approximately 3 mm from the edge of the wafer;
• wherein the carrier ring includes a plurality of carrier ring wafer supports defined on the step down surface of the carrier ring, the step down surface being an inner annular surface of the carrier ring, the carrier ring wafer supports being configured to engage the wafer when the wafer is supported by the carrier ring during transport, the carrier ring wafer supports protruding above the step down surface of the carrier ring by a height amount that is less than the second vertical separation.