Probe for direct wafer potential measurements

Details Probe for direct wafer potential measurements Probe for direct wafer potential measurements

2001-10-31

2004-03-30

Karlsen, Ernest (Department: 2829)

Electricity: measuring and testing

Fault detecting in electric circuits and of electric components

Of individual circuit component or element

C324S754090, C324S1540PB

Reexamination Certificate

active

06714033

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to plasma etching chambers. More particularly, the present invention relates to an apparatus for measuring the dc bias voltage of a wafer during plasma processing.
BACKGROUND OF THE INVENTION
Integrated circuits are typically fabricated on a wafer of semiconductor material such as silicon or gallium arsenide. During the fabrication process, the wafer is subjected to an ordered series of steps, which may include photomasking, material deposition, oxidation, nitridization, ion implantation, diffusion and etching, in order to achieve a final product.
There are two basic types of etches: ion-assisted etches (also called reactive-ion, plasma or dry etches) and solution etches (also called wet etches). Solution etches are invariably isotropic (omnidirectional) in nature, with the etch rate for a single material being relatively constant in all directions. Reactive-ion etches, on the other hand, are largely anisotropic (unidirectional) in nature. Reactive-ion etches are commonly used to create spacers on substantially vertical sidewalls of other layers, to transfer a mask pattern to an underlying layer with little or no undercutting beneath mask segment edges, and to create contact via insulative layers.
A plasma etch system (often referred to as a reactor) is primarily a vacuum chamber in which a glow discharge is utilized to produce a plasma consisting of chemically reactive species (atoms, radicals, and ions) from a relatively inert molecular gas. The gas is selected so as to generate species which react either kinetically or chemically with the material to be etched. Because dielectric layers cannot be etched using a direct-current-induced glow discharge due to charge accumulation on the surface of the dielectric which quickly neutralizes the dc-voltage potential, most reactors are designed as radio-frequency diode systems and typically operate at a frequency of 13.56 MHz, a frequency reserved for industrial, scientific and medical, non-communication use by international agreement. However, plasma etch processes operating between 100 KHz-80 MHz have been used successfully.
FIG. 1
illustrates a conventional method for measuring the dc bias voltage of a wafer in a capacitively coupled plasma etching chamber. A wafer
102
is disposed on an electrostatic chuck
106
inside a vacuum chamber
104
. The electrostatic chuck
106
is electrically coupled to an RF generator
110
. A grounded upper electrode
108
is disposed inside the vacuum chamber
104
above the wafer
102
. During processing, plasma
112
is generated between the upper electrode
108
and the wafer
102
. The plasma
112
generates a dc bias voltage above the surface of the wafer
102
. The dc bias voltage is conventionally measured outside the vacuum chamber
104
with a measuring device
114
, such as a voltage meter, coupled to the electrostatic chuck
106
.
The problem with the above approach is that the Radio Frequency (RF) energy is transferred outside the vacuum chamber
104
. So the plasma
112
inside the vacuum chamber
104
is disturbed resulting in less accurate measurements of the dc bias voltage. Another disadvantage is that such a system measures the dc bias voltage on the electrostatic chuck
106
, and not the wafer
102
itself. There could be a substantial potential difference between the wafer
102
and the electrostatic chuck
106
due to a number of factors including wafer material or coating, process chemistry, RF power level.
A definite need exists for an apparatus for measuring the dc bias voltage in a vacuum chamber. Specifically, a need exists for an apparatus for measuring the dc bias voltage in a capacitively coupled plasma etching chamber. A primary purpose of the present invention is to solve these needs and provide further, related advantages.
BRIEF DESCRIPTION OF THE INVENTION
An apparatus for measuring the DC bias voltage of a wafer in a chamber comprises an electrical coupling, a fist filter, a second filter. The electrical coupling receives a probe for measuring the DC bias voltage in the chamber. The probe is disposed within the chamber. A first filter, coupled to the electrical coupling, is disposed within the chamber. A second filter, coupled to the first filter, is disposed outside the chamber.


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