1. IC Microanalysis LLC – January __, 2011
Introduction
A review of US patent xxxxxxx and cursory technical research was performed in order to
determine the possible current and future product market applications and adoption for the
invention.
Conclusions
The invention is primarily focused towards product areas that require high aspect ratio etching
of materials which is of great interest in a number of product areas.
Possible Product Market Applications
Product Market Product Feature
3D wafer level packaging through-silicon vias
multi-layered integrated circuit devices through-silicon vias
power semiconductors trench (power MOSFETs)
high-density DRAMs capacitor trenches
CCD or CMOS image sensors Through-silicon vias
microelectromechanical systems (MEMS) etching individual components
o actuators
o photonic devices
o piezoelectronic devices
solar cells through-silicon vias
flat panel displays through-silicon vias
Market Adoption
The primary current methodology for etching high-profile trenches and defining features is
Deep Reactive-Ion Etching (DRIE) using the Bosch methodology. This method uses Inductively
Coupled Plasma (ICP) etchers to perform multiple etch and deposition phases, producing a
nearly vertically-etched pattern or trench.
Some elements of the ‘xxx invention are likely used in current processes, such as pulsed RF
drive and pulsed biasing. However, the utilization of electro-negative gases and synchronized
timing of the RF and biasing pulses does not appear to be currently used.
Future market adoption within the remaining lifetime of the ‘xxx patent depends upon how
well the existing processes work with decreasing feature sizes and increasing utilization of the
processes across more product lines. Based upon a cursory first-generation citation analysis,
some aspects of the invention are seen as innovative. A more detailed analysis would be
required to determine which aspects hold the most promise.
2. IC Microanalysis LLC – January __, 2011
A great deal of research is on-going to develop better methods for high-aspect ratio etching.
Some of these are focused on the utilization of electro-negative gases (primarily halogen) and
minimizing the electrons to obtain ion-ion plasmas.
The primary inventive aspect of the ‘xxx is the synchronized timing of the RF and biasing pulses
to enable the most efficient ion-ion etching with the addition of an electro-negative gas. To
produce both positive and negative ions the timing of the pulses in relation to each other are
critical. No research papers were found that indicated anyone else was working on processes
that produced both types of ions, except for those of the patents author. Based upon the
limited forward citations, the apparent lack of similar research in the critical areas covered by
this patent during the first ten years of the patents’ life, and the success of current applications,
it is speculated that at this specific time the chance of market adoption of the ‘xxx invention is
low.
However, it should be understood that some of the defined product markets are still in their
early stages of development and growth, so innovative new processes are regularly being
developed. In addition, existing inventions that may have application to these markets are likely
to be incorporated as these technologies evolve. The ‘xxx invention is generally focused on an
area of technology (high aspect ratio etching) that is of growing interest and utilization in many
of these product markets. So currently unforeseen problems in any of these market areas may
require solutions that may be addressed by the ‘xxx invention, potentially increasing its value.
Discussion
Brief Patent Overview
The USPxxxxxxx invention describes a plasma etching system using ion-ion (electron-free)
plasmas, an electro-negative gas, and synchronized RF drive and substrate bias timing.
The primary inventive element is the synchronization of a substrate bias waveform to a pulsed
RF drive. A delay is included between the end of the RF drive pulse and the start of the bias
pulse to allow the electron population to drop to approximately zero. By using a source gas
mixture which has highly electro-negative components, substrate bombardment with negative
ions can be achieved. Inductively-coupled RF drive is used for plasma generation in the
preferred embodiment.
Possible Product Applications
The invention is primarily focused towards applications that require high-aspect ratio etching of
materials. These include MEMs components and through-silicon vias for 3D wafer level
packaging, multi-layered integrated circuits, solar cells, image sensor chips, and flat-panel
displays. Possible applications also include trenches in power MOSFETs and capacitor trenches
in high density DRAMs. Many of these product area applications are still in their infancy, and
3. IC Microanalysis LLC – January __, 2011
therefore enjoy extensive research and development efforts in both industry and university
environments.
Similar Current Applications and Equipment
The primary current methodology for etching high-profile trenches and defining features for
MEMs devices is the Deep Reactive-Ion Etching (DRIE). This methodology uses two primary
technologies, Bosch and Cryogenic. The Bosch method has gained favor for current product
manufacturing and is widely utilized in many of the product application areas described above.
The method uses multiple etch and deposit phases to produce a nearly isotropic etched pattern
or trench. DRIE etchers are currently available from a number of manufacturers and are used
extensively in the MEMs industry and are becoming the favored methodology for through-
silicon vias.
Inductively-coupled RF drive with pulsing of the drive voltage and substrate bias is currently
used for plasma generation in DRIE equipment. Tegal has an extensive line of DRIE equipment
(http://www.tegal.com/default.aspx). Cursory technical research did not find any evidence that
these systems utilized an electro-negative gas or synchronization of the RF drive pulses with the
substrate bias pulses as required by some of the invention claims. However, application notes
did show pulsing of the bias supply to help prevent notching at the silicon dioxide interface –
(http://www.tegal.com/applicationdetail.aspx?applicationID=13).
Yield Engineering Systems currently produces plasma cleaning systems that have “electron-
free” operating modes, but detailed inspection of the systems drive and biasing systems was
beyond the scope of this analysis. An associated Application Note is shown at this link:
http://www.bita.lu/datasheets/GT-AN-125-LU.pdf
A more detailed investigation into current processes and equipment should be considered to
establish which elements of the ‘xxx may already be utilized.
4. IC Microanalysis LLC – January __, 2011
Cursory Patent Innovation and Citation Analysis
With a filing date of xxxxx, the ‘xxx invention still has a good lifetime value. A number of
application areas are heavily researched so development of new methodologies is ongoing.
Examinations of the ‘xxx first generation forward citations using the USPTO online database
shows only these three citing patents:
USPxxxxxxx – Assignee: US Navy
USPxxxxxxx – Assignee: Hitachi
USPxxxxxxx – Assignee: Silicon Genesis
Comparing these citations to USPxxxxxxx referenced by the inventor in the ‘xxx Background and
Summary, we find that the ‘xxx patent currently has thirty-six first generation forward citations.
The original file date of the ‘xxx is October 1996, so it is approaching the end of its useful life.
However, a cursory search shows the inventor has a number of more recent patents with better
lifetime value and somewhat similar inventive features, including:
USPxxxxxxx
USPxxxxxxx
USPxxxxxxx
The number of forward citations is sometimes indicative of the innovative nature of the
invention. In this case, the significantly higher citation rate for the ‘xxx may mean the inventive
methodology described may be more innovative and more likely to see in current and/or near
future utilization in products than the ‘xxx.
However, the ‘xxx incorporates many of the elements of the ‘xxx, and synchronization of the
supply and bias signals may be relatively easy to implement. Therefore, the improved etching
said to be produced by the inventive features in the ‘xxx may be recognized as having a higher
value in the future as feature sizes decrease.
5. IC Microanalysis LLC – January __, 2011
Independent Claims - Element Similarity Table
Claim 1 (least limiting) Claim 14 Claim 19 Claim 27
A method for plasma A method for surface A method for plasma A method for plasma
processing, comprising the modification by negative processing, comprising the processing, comprising the
steps of: ion bombardment, steps of: actions of:
comprising the steps of:
applying power pulses
defining an intensity
modulation waveform to a
chamber
generating a substantially generating approximately generating an electron-
electron-free ion-ion equal populations of free ion-ion plasma
plasma positive and negative ions
in proximity to at least one in proximity to a in proximity to at least first
substrate substrate and second substrates
applying a bias signal having applying a bias signal applying a bias signal having applying different
signal components of having signal components alternating positive and respective bias signals to
alternating positive and of alternating positive negative polarities to a said substrates
negative polarities to said and negative polarities substrate, said bias signal
substrate defining an envelope
and imposing a delay between
at least some trailing edges of
said modulation waveform
and the respective next
leading edges of said bias
signal envelope
at times when said ion-ion during time periods when at times when said ion-ion
plasma is present the number of free plasma is present
electrons proximate to
said substrate is less than
a specified fraction of the
number of ions in one of
said populations
to induce bombardment of to induce bombardment to induce bombardment of
said substrate by both of said substrate by ions said first substrate by ions
negative and positive ions of both said populations of desired chemistry and
energy, with substantially
no electron bombardment
said delay being sufficient to
cause the free electron
density to become less than a
specified fraction of the
positive ion density inside said
chamber
to regulate the voltage
and/or composition of said
plasma by ion
bombardment of said
second substrate
