Plasma Processing Apparatus

What is this patent about?

’808 is related to the field of plasma processing, specifically addressing the challenge of maintaining a vacuum seal around pins that move vertically through a mounting table within a plasma processing apparatus. These pins are used to lift and separate wafers from the mounting table during transfer. The background highlights that temperature variations can cause the mounting table to expand or contract, leading to misalignment between the pins and their insertion holes, which compromises the seal and degrades the vacuum within the processing chamber.

The underlying idea behind ’808 is to introduce a movable member within a recess in the pin insertion hole, positioned between the pin and the wall of the hole. This movable member is sealed both to the pin and to the recess wall using two separate sealing elements. The key inventive insight is that this arrangement allows the movable member to shift slightly in response to forces caused by pin misalignment, thereby relieving localized compression on the primary seal and maintaining a more consistent and reliable vacuum seal.

The claims of ’808 focus on a plasma processing apparatus that includes a wafer stage with through-holes for pins. Each through-hole assembly features an annular recess, a pin, an annular member within the recess, a first annular sealing member between the pin and the annular member, and a second annular sealing member between the annular member and the recess. The apparatus also includes actuators to vertically move the pins.

In practice, the mounting table, which supports the wafer, experiences temperature fluctuations during plasma processing. These fluctuations cause the table to expand or contract, leading to a deviation between the axis of the pin and the axis of the pin insertion hole. Without compensation, this deviation would compress the primary seal unevenly, creating a leak path. However, the movable member, sealed with two O-rings (or similar seals), can shift slightly within its recess, accommodating the misalignment. This ensures that the primary seal remains relatively uniformly compressed against the pin, preventing vacuum leaks.

This design differs from prior approaches that rely on a single, fixed seal around the pin. The conventional approach is vulnerable to leaks when misalignment occurs due to thermal expansion. By introducing the movable member and the secondary sealing element, ’808 provides a more robust and reliable sealing solution that maintains the vacuum integrity of the plasma processing chamber, even under varying temperature conditions and mechanical stresses. This is particularly important for achieving consistent and high-quality plasma processing results.