Segmented focus ring assembly

Embodiments of the present invention include a focus ring segment and a focus ring assembly. In one embodiment, the focus ring segment includes an arc-shaped body having a lower ring segment, a middle ring segment, a top ring segment and a lip. The lower ring segment has a bottom surface, and the middle ring segment has a bottom surface, wherein the middle ring segment is connected to the lower ring segment at the middle ring segment bottom surface. The top ring segment has a bottom surface, wherein the top ring segment is connected to the middle ring segment at the top ring segment bottom surface. The lip extends horizontally above the middle ring segment, wherein the lip is sloped radially inwards towards a centerline of the focus ring segment. In another embodiment, the focus ring assembly includes at least a first ring segment and a second ring segment.

BACKGROUND OF THE INVENTION

Field of the Invention

Embodiments of the invention generally relate to a segmented focus ring assembly for use in a plasma processing chamber.

Description of the Related Art

Continued evolution of the semiconductor requires smaller and smaller features to be patterned on substrates. As feature size shrinks, manufacturers are challenged to maintain control of device properties and performance. Maintaining control of critical dimensions of features on a semiconductor substrate is a fundamental requirement of etching processes used to form those features. During a plasma etch process, for example, the critical dimension (CD) could be the width of a gate structure, trench or via and the like.

As technology nodes advance and critical dimensions shrink, increasing emphasis is placed on reducing the amount of edge-exclusion on a substrate. Edge-exclusion refers to the area near the edge of a substrate in which no features or devices are formed. Reducing edge-exclusion provides space for forming additional devices nearer the edge of a substrate. As structures are formed closer to the edge, maintaining CD uniformity across the substrate during etching processes becomes more difficult. A common form of CD non-uniformity is known as “edge roll-off,” which features a dramatic reduction in CD control close to the edge of the substrate. Additionally, CD bias, the change in CD as successive layers are etched, declines near the edge.

Current plasma etch processes attempt to address this problem by providing a “focus ring” near the edge of the substrate that has similar composition to the substrate. It is thought that the focus ring behaves as an “extension” of the film being etched and promotes a uniform concentration of etch by-product species across the substrate. This, in turn, promotes a more uniform etch rate. However, in certain chamber designs, there is not enough room to accommodate a conventional focus ring.

Thus, there is a need for an alternative for conventional focus ring.

SUMMARY

Embodiments of the invention include a focus ring segment and a segmented focus ring assembly. In one embodiment, the focus ring segment includes an arc-shaped body having a lower ring segment, a middle ring segment, a top ring segment and a lip. The lower ring segment has a bottom surface, and the middle ring segment has a bottom surface, wherein the middle ring segment is connected to the lower ring segment at the middle ring segment bottom surface and extends horizontally above the lower ring segment. The top ring segment has a bottom surface, wherein the top ring segment is connected to the middle ring segment at the top ring segment bottom surface. The lip extends horizontally above the middle ring segment, wherein the lip is sloped radially inwards towards a centerline of the focus ring segment.

In another embodiment, a segmented focus ring assembly includes at least a first ring segment and a second ring segment. Each of the ring segments includes an arc-shaped body having a lower ring segment, a middle ring segment, a top ring segment and a lip. The lower ring segment has a bottom surface, and the middle ring segment has a bottom surface, wherein the middle ring segment is connected to the lower ring segment at the middle ring segment bottom surface and extends horizontally above the lower ring segment. The top ring segment has a bottom surface, wherein the top ring segment is connected to the middle ring segment at the top ring segment bottom surface. The lip extends horizontally above the middle ring segment, wherein the lip is sloped radially inwards towards a centerline of the focus ring segment.

DETAILED DESCRIPTION

FIG. 1is a schematic cross-sectional view of a processing chamber100having a segmented focus ring assembly102according to one embodiment of the invention. The processing chamber100has a chamber body140comprising sidewalls104and a bottom106. A lid142is disposed on the chamber body140and encloses a processing volume108. The processing chamber100is coupled to a gas source110, a vacuum pump112and a power source114.

A substrate support assembly116is disposed approximately within the processing volume108of the processing chamber100. The substrate support assembly116includes a substrate support118disposed on a substrate support pedestal138. The substrate support pedestal138is disposed on the chamber bottom106. The substrate support118supports a substrate120during processing.

The focus ring assembly102is supported on the substrate support assembly116and engages with an edge144of the substrate support118. The focus ring assembly102is sized to closely circumscribe the substrate120to confine a predefined area in which the substrate120is disposed on the substrate support118so that the substrate does not slide or move significantly during processing.

In one embodiment the processing chamber100includes a lift hoop132with a plurality of lifting fingers134. The lift hoop132is coupled to an actuator136, such as a linear actuator or motor operable to control the vertical elevation of the lift hoop132within the processing volume108. The lifting fingers134are configured to transfer substrates between the substrate support assembly116and substrate transfer devices, such as robots, when the lift hoop132is in transfer position (not shown). The lifting fingers134are aligned with cut outs146formed in the substrate support assembly116to move the substrate120between a transfer position above the substrate support assembly116and a processing position disposed on the substrate support118.

A gas inlet such as a nozzle or gas distribution plate (shown inFIG. 1as a gas distribution plate122) is utilized to provide process and other gases into the processing volume108. The gas distribution plate122is disposed in the chamber100above the substrate support assembly116. The gas distribution plate122may include a plurality of gas passages124.

In the embodiment depicted inFIG. 1, the gas source110provides processing gas that enter the processing volume108through the gas distribution plate122. Processing gas flows through the gas distribution plate122toward the substrate support assembly116, and is evacuated via the vacuum pump112through an exhaust port126located in the bottom106of the processing chamber100. A throttle valve128is disposed in the exhaust port126and is used in conjunction with the vacuum pump112to control the pressure in the processing volume108.

In the embodiment depicted inFIG. 1, the gas distribution plate122is connected to the power source114through a match circuit130. Power is proved through the match circuit130to the gas distribution plate122to energize the process and other gases provided in the processing chamber100to form and/or sustain plasma therein.

FIG. 2is a top view of the substrate support118having the focus ring assembly102shown in phantom. In one embodiment, the focus ring assembly102has a plurality of ring segments, shown as two large ring segments200and one small ring segment202. The ring segments200,202are spaced to advantageously allow the lifting fingers134of the lift hoop132to pass through the focus ring assembly102, thereby allowing the lifting fingers134to move the substrate120between a processing position (as shown inFIG. 1) and a transfer position spaced above the substrate support118.

Each ring segment200,202of the focus ring assembly102includes an arc-shaped body220. Each arc-shaped body220may be fabricated from aluminum, quartz, or any other suitable material. In the embodiment shown inFIG. 2, the focus ring assembly102has two large ring segments200and one small ring segment202.

The ring segments200,202of the focus ring assembly102are arranged in a polar array concentric with the centerline of the substrate support118. The ring segments200,202are arranged to form a ring, wherein adjacent ring segments200,202are spaced to expose a sufficient portion of the cut outs146to allow the lifting fingers134to pass between the ring segments200,202as the substrate120is lifted from and set down upon the substrate support118.

FIGS. 3 and 4are bottom views of the large ring segment200and the small ring segment202according to one embodiment of the invention. In one embodiment, the large ring segment200has an arc angle “A” that is between about 153 degrees and about 163 degrees, for example 158 degrees. The small ring segment202has an arc “B” that is between about 39 degrees and about 49 degrees, for example 44 degrees. Both the large ring segment200and the small ring segment202include an aperture206and an arc-shaped slot208formed in a bottom surface of the body220, as discussed below with reference toFIG. 5. The aperture206and the slot208are configured to receive substrate support pins (not shown) extending from the substrate support118to align the ring segments200,202of focus ring assembly102with the substrate support assembly116. The slot208has a width C that is about double a length of an arc segment D defining the length of the slot208. In one embodiment, width C is between about 0.26 inches and about 0.28 inches, for example 0.27 inches, and length D is between about 0.13 inches and about 0.15 inches, for example 0.14 inches. The arc of the slot208allows the ring segments200,202to expand substantially without loss of concentricity with the substrate support118or significant change in an inside diameter.

FIG. 5is a cross-sectional view of the of the focus ring assembly102taken along the section line passing through the aperture206of eitherFIG. 3orFIG. 4. For ease of explanation, reference numeral500refers to both the large ring segment200and the small ring segment202, hereinafter segment500. The body220of each segment500includes an outer wall502, a lower ring segment504, a middle ring segment506, and a top ring segment508. The lower ring segment504, the middle ring segment506, and the top ring segment508are generally stacked in a plane perpendicular to the centerline (CL) of the segment500, defining the arc of the segment500as a single, unitary structure comprising the body220. The outer wall502has a height E between about 0.60 inches and 0.70 inches, for example 0.65 inches. The lower ring segment504has a bottom surface512and a lower ring segment inner wall524, wherein the bottom surface512also defines the bottom surface of the segment500. The outer wall502meets the bottom surface512at a rounded corner having a radius between about 0.01 inches to about 0.11 inches, for example 0.06 inches. The bottom surface512meets the lower ring segment inner wall524at a rounded corner having a radius between about 0.01 inches and about 0.07 inches, for example 0.02 inches. The lower ring segment504has a height F defined between a bottom surface510of the middle ring segment506and the bottom surface512of the lower ring segment504of between about 0.21 inches and about 0.31 inches, for example 0.26 inches. The lower ring segment504has an outer diameter G of between about 13.70 inches and about 13.80 inches, for example 13.75 inches. In one embodiment, the outer diameter G is also the outer diameter of the segment500. The lower ring segment504has an inner diameter H between about 12.58 inches and about 12.68 inches, for example 12.63 inches.

The middle ring segment506has a height I defined between a bottom surface514of the top ring segment508a bottom surface510of the middle ring segment506of between about 0.18 inches and about 0.28 inches, for example 0.23 inches. The bottom surface510meets the lower ring segment inner wall524at a rounded corner having a radius between about 0.01 inches and about 0.07 inches, for example 0.02 inches. The middle ring segment506has an inner diameter J of between about 11.91 inches and about 12.01 inches, for example 11.96 inches. The inner diameter J is advantageously smaller than the inner diameter H to allow the bottom surface510to be supported by the substrate support assembly116, while begin relatively close to the substrate120to protect the substrate support assembly116from the processing environment.

In one embodiment, as shown inFIG. 5, the bottom surface510of the middle ring segment506has the aperture206formed therein. The aperture206has a diameter K that has the same dimensions as the diameter D of the slot208. The aperture206has an internal height L of between about 0.15 inches and about 0.25 inches, for example 0.20 inches. Although not shown inFIG. 5, the slot208is also formed in the bottom surface510of the middle ring segment506.

The top ring segment508has a top surface518and a lip520. The top surface518of the top ring segment508also defines the top surface of the segment500. The top ring segment508has an inner diameter M of between about 11.79 inches and about 11.89 inches, for example 11.84 inches. The lip520extends horizontally inward of the middle ring segment506towards the center line of the segment500. The lip520has a sloped inner surface522that extends radially inwards and downward away from the top surface518towards the center line of the segment500, and intersects the bottom surface514of the top ring segment508.

The sloped inner surface522meets the top surface518at a rounded corner having a radius between about 0.01 inches and about 0.11 inches, for example 0.06 inches. The outer wall502meets the top surface518at a rounded corner having a radius between about 0.01 inches and about 0.11 inches, for example 0.06 inches. The sloped inner surface522has an angle N defined with the top surface518of about 70 degrees and about 80 degrees, for example 75 degrees. The sloped inner surface522allows substrates that may be slightly misaligned with substrate support118to be guided to a position advantageously more concentric with the substrate support118. An area inward of the lip520corresponding with the inner diameter M beneficially forms a substrate receiving pocket that closely fits around the substrate120. In one embodiment, the substrate receiving pocket is configured to enhance temperature uniformity by preventing the substrate120from becoming substantially misaligned with the center of the substrate support assembly116. Additionally, the inner diameter M is advantageously selected to provide a substantially tight fit with the substrate120, thereby improving processing uniformity results while minimizing the area of the substrate support118exposed to the processing environment.

Since the uniformity of the dimensions between each of the segments200,202(i.e., the diameters of each segment) is important to enhance both the uniform positioning of the substrate120on the surface of substrate support118and plasma uniformity above the substrate120, the segments200,202may be fabricated from a single ring which is cut into appropriately sized segments. This ensures segment to segment dimension uniformity which is not achievable if each segment200,202were individually fabricated.

While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention thus may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.