Created by

Advanced Energy Industries, Inc.

Abstract

Semiconductor manufacturers face ever-increasing pressure

to maximize yield. Ignition failures of remote plasma sources

undermine that goal, causing tool shutdown and process

disruption.

This paper describes the advantages of Advanced Energy’s

Xstream®, which utilizes pulsed power for ignition and a

transformer induced power delivery system during chamber

cleaning operations. Advanced Energy has designed

Xstream’s pulsed power with multiple igniters (as opposed

to a single-igniter design) to optimize error-free ignition,

even during cold starts. We also employ a dual-transformer

induced power delivery system to the main power system

that enables stable transition from ignition mode to operation

mode. Finally, Xstream’s multiple segments of electrodes

extend chamber life by distributing voltage load across the

plasma chamber.

As a result, Xstream can help semiconductor manufacturers

improve yield by decreasing unwanted sputtering and

eliminating ignition failure during the production process.

Advanced Energy has demonstrated these advantages

through testing and provides the details of this test below.

Table of Contents

Xstream Plasma System 2

Conclusions 10

References 10

Advanced Ignition of Remote Plasma Sources

Using Pulsed Ignition and Power Load

Distribution with Multiple Igniters

2 advanced-energy.com

ADVANCED IGNITION OF REMOTE PLASMA SOURCES

Xstream Plasma System

1. Plasma in Xstream

1.1 Gas breakdown and plasma sustaining

Plasmas can be classified into two main categories:

1. Fully ionized plasmas where the ions and electrons are close to thermal equilibrium, which are

referred to as “hot plasmas” and

2. Weakly ionized plasmas operating in non-equilibrium, which are referred to as “cold plasmas”

Weakly charged plasma is primarily used in the semiconductor manufacturing process. One of

the characteristics of cold plasma is its quasi-neutrality, which means that the bulk of the plasma

contains a roughly equal amount of positive and negative charges. In other words, the average

flux of positive charges and negative charges leaving the plasma are identical. On the other hand,

electrons are much more easily energized and more mobile than ions, and therefore escape the

plasma faster than the ions. To equalize the flux of ions and electrons, the plasma is charged to

a positive potential compared to its boundaries. As a result, a space charge region, called the

sheath, builds up between the plasma and all the surfaces. Positive charges are accelerated in

the sheath outwards from the plasma while the negative charges (especially the electrons) are

repelled into the plasma.

After ignition, external electron excitation is required to sustain plasma. This excitation is generally

performed using an external radio frequency (RF) electromagnetic field that excites and accelerates

the electrons. The frequency is generally too high for the low-mobility ions to follow the electromag-

netic field variations, while the light and mobile electrons follow the variations of the electromagnetic

field. Therefore, most of the energy is delivered to the electrons.

There are several modes of RF excitation: capacitive coupling, inductive coupling/ transformer

coupling, and microwave coupling. Xstream uses transformer coupling (TCP) and, to ensure

proper injection of power, an active matching network to align the output impedance of the power

supply with the impedance of the plasma.

1.2 Downstream Plasmas

Remote plasma sourcing is the process methodology in which the plasma chamber is separate

from the wafer process chambers. Among the various RF couplings, TCP has been widely used

for many years for remote plasma generation. One of the main advantages of TCP is that the