METHOD AND APPARATUS FOR MEASURING ELECTRON DENSITY OF PLASMA AND PLASMA PROCESSING APPARATUS

• US 20070284044A1
• Filed: 05/01/2007
• Published: 12/13/2007
• Est. Priority Date: 04/24/2003
• Status: Active Grant

• Current Assignee: Tokyo Electron Limited
• Original Assignee: Tokyo Electron Limited
• Inventors: Koshimizu, Chishio, Yamazawa, Yohei, MATSUMOTO, Naoki, Segawa, Sumie, Matsudo, Tatsuo
• Granted Patent: US 7,582,182 B2
• Time in Patent Office: Days
• US Class Current: 156/345.290
• CPC Class Codes: G01N 21/68 using high frequency electric fields
• CPC Class Codes: H01J 37/32174 Circuits specially adapted for controlling the RF discharge
• CPC Class Codes: H01J 37/32935 Monitoring and controlling tubes by information coming from the object and/or discharge
• CPC Class Codes: H01J 37/32972 Spectral analysis
• CPC Class Codes: H01L 21/31116 by dry-etching

Abstract

An apparatus for measuring plasma electron density precisely measures electron density in plasma even under a low electron density condition or high pressure condition. This plasma electron density measuring apparatus includes a vector network analyzer in a measuring unit, which measures a complex reflection coefficient and determines a frequency characteristic of an imaginary part of the coefficient. A resonance frequency at a point where the imaginary part of the complex reflection coefficient is zero-crossed is read and the electron density is calculated based on the resonance frequency by a measurement control unit.

Claims

1. An apparatus for monitoring plasma, comprising:

an insulating pipe inserted and attached into and to a chamber in or into which plasma is created or introduced;

a coaxial cable provided with a probe portion formed by exposing a front core wire of the coaxial cable, and inserted into the insulating pipe from one end of the insulating pipe;

an actuator for moving the coaxial cable in the insulating pipe in the axial direction thereof;

a scalar reflection coefficient measuring unit for, while sweeping frequencies, transmitting electromagnetic signals of respective frequencies to the probe portion of the coaxial cable at certain power to be irradiated to a surrounding space, measuring reflection coefficients from the levels of signals reflected through the probe portion with respect to the respective frequencies, and obtaining frequency characteristics of the reflection coefficients; and

a measurement operation unit for measuring a plasma absorption frequency based on a first frequency characteristic obtained by the reflection coefficient measuring unit in a state where the plasma does not exist in the chamber and a second frequency characteristic obtained by the reflection coefficient measuring unit in a state where plasma exists in the chamber, at a measurement location determined by a location of the probe portion.

2. The apparatus of claim 1, wherein

in the state where the plasma does not exist in the chamber, the probe portion is sequentially positioned at a plurality of measurement locations by moving the coaxial cable in the axial direction thereof using the actuator, and the first frequency characteristics of the reflection coefficients is obtained at the respective measurement locations by the reflection coefficient measuring unit;

and

in the state where the plasma exists in the chamber, the probe portion is sequentially positioned at the plurality of measurement locations by moving the coaxial cable in the axial direction thereof using the actuator, and the second frequency characteristic of the reflection coefficients is obtained at the respective measurement locations by the reflection coefficient measuring unit.

3. The apparatus of claim 1, wherein the coaxial cable has an outer conductor made of stainless steel.

4. The apparatus of claim 1, wherein the insulating pipe is hung between first and second supports provided in the sidewalls of the chamber.

5. The apparatus of claim 4, wherein at least one of the first and second supports is formed of a through hole.

6. The apparatus of claim 5, further comprising an O-ring for air-tightly and fixedly attaching the insulating pipe in the through hole.

7. The apparatus of claim 1, further comprising a grounding conductor, one end of which is connected to a grounding potential portion of the chamber and the other end of which is connected to the outer conductor of the coaxial cable.

8. The apparatus of claim 7, wherein an electromagnetic wave absorber for absorbing a noise signal propagating along the outer conductor through electromagnetic induction is provided at a location of the probe portion side of the coaxial cable when viewed from a location where the grounding conductor and the outer conductor of the coaxial cable are in contact with each other.

9. The apparatus of claim 8, wherein the electromagnetic wave absorber includes one or more bead-shaped ferrite members placed around the coaxial cable along the axial direction thereof.

10. The apparatus of claim 1, further comprising a cooling mechanism connected to the other end of the insulating pipe to allow cooling gas to flow inside the insulating pipe.

11. The apparatus of claim 1, wherein the measurement operation unit has an electron density operation means for calculating electron density in the plasma based on the measured plasma absorption frequencies.