CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2019-162315, filed on Sep. 5, 2019; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to an electrostatic chuck.

BACKGROUND

An electrostatic chuck is used to attract and hold a processing object such as a semiconductor wafer, a glass substrate, etc., inside a plasma processing chamber that performs etching, CVD (Chemical Vapor Deposition), sputtering, ion implantation, ashing, etc. The electrostatic chuck applies electrical power for electrostatic attraction to a built-in electrode and attracts and holds a substrate such as a silicon wafer, etc., by an electrostatic force.

When performing plasma processing, for example, plasma is generated by applying a voltage from an RF (Radio Frequency) power supply (a high frequency power supply) to an upper electrode provided at an upper portion inside a chamber and to a lower electrode provided lower than the upper electrode.

In a conventional electrostatic chuck, the plasma is generated using, as the lower electrode, a base plate provided in a lower portion of the electrostatic chuck. However, the plasma controllability is limited in such a configuration because it is desirable to perform better control of the wafer in-plane distribution of the plasma density by selecting the appropriate frequency.

Therefore, in recent years, it is being attempted to increase the plasma controllability by embedding a lower electrode for plasma generation in a dielectric layer provided on a base plate. However, when merely embedding the lower electrode in the dielectric layer, there are problematic cases in which the in-plane uniformity of the plasma density cannot be sufficiently obtained. Also, there are problematic cases in which electric field concentration and dielectric breakdown occur at end portions of the lower electrode embedded in the dielectric layer.

SUMMARY

According to the embodiment, an electrostatic chuck includes a ceramic dielectric substrate, a base plate, at least one first electrode layer, and at least one second electrode layer. The ceramic dielectric substrate includes a first major surface and a second major surface. The first major surface is configured to have an object placed thereon and clamped by the electrostatic chuck. The second major surface is at a side opposite to the first major surface. The base plate supports the ceramic dielectric substrate. The first electrode layer is provided inside the ceramic dielectric substrate. The first electrode layer is connected to a high frequency power supply from a side of the second major surface. The second electrode layer is provided inside the ceramic dielectric substrate. The second electrode layer is connected to a clamping power supply. The first electrode layer is provided between the first major surface and the second major surface in a Z-axis direction. The Z-axis direction extends from the base plate toward the ceramic dielectric substrate. The second electrode layer is provided between the first electrode layer and the first major surface in the Z-axis direction. The first electrode layer includes a first portion and a second portion. The first portion is positioned more centrally of the ceramic dielectric substrate than is the second portion when projected onto a plane perpendicular to the Z-axis direction. The first portion includes a first surface at a side of the first major surface, and a second surface at a side opposite to the first surface. The second portion includes a third surface at the side of the first major surface, and a fourth surface at a side opposite to the third surface. The third surface is positioned between the first surface and the second electrode layer in the Z-axis direction. A distance along the Z-axis direction between the fourth surface and the first major surface is constant. A second thickness of the second portion in the Z-axis direction between the third surface and the fourth surface varies such that the second thickness at a circumferential end portion of the second portion is less than the second thickness at a central portion of the second portion.

