U.S. patent application number 16/414642 was filed with the patent office on 2019-09-05 for precision screen printing with sub-micron uniformity of metallization materials on green sheet ceramic.
The applicant listed for this patent is Applied Materials, Inc.. Invention is credited to Steven E. Babayan, Phillip Criminale, Anthony Huang, Shih-Ying Huang, Stephen Prouty.
Application Number | 20190273008 16/414642 |
Document ID | / |
Family ID | 61069490 |
Filed Date | 2019-09-05 |
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United States Patent
Application |
20190273008 |
Kind Code |
A1 |
Huang; Shih-Ying ; et
al. |
September 5, 2019 |
PRECISION SCREEN PRINTING WITH SUB-MICRON UNIFORMITY OF
METALLIZATION MATERIALS ON GREEN SHEET CERAMIC
Abstract
Precision screen printing is described that is capable of
sub-micron uniformity of the metallization materials that are
printed on green sheet ceramic. In some examples, puck is formed
with electrical traces by screen printing a paste that contains
metal on a ceramic green sheet in a pattern of electrical traces
and processing the printed green sheet to form a puck of a
workpiece carrier. In some example, the printing includes applying
a squeegee of a screen printer to the printed green sheet in a
squeegeeing direction while the green sheet is on a printer bed of
the screen printer. The method further includes mapping the printer
bed at multiple locations along the squeegeeing direction,
identifying non-uniformities in the printer bed mapping, and
modifying a printer controller of the screen printer to compensate
for mapped non-uniformities in the printer bed.
Inventors: |
Huang; Shih-Ying; (San Jose,
CA) ; Babayan; Steven E.; (Los Altos, CA) ;
Criminale; Phillip; (Livermore, CA) ; Prouty;
Stephen; (San Jose, CA) ; Huang; Anthony; (San
Jose, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Applied Materials, Inc. |
Santa Clara |
CA |
US |
|
|
Family ID: |
61069490 |
Appl. No.: |
16/414642 |
Filed: |
May 16, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
15667281 |
Aug 2, 2017 |
|
|
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16414642 |
|
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|
62371636 |
Aug 5, 2016 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H05K 1/165 20130101;
H05K 2203/0139 20130101; H01L 21/6831 20130101; H05K 1/181
20130101; H05K 2203/162 20130101; H05K 2203/166 20130101; H05B
3/283 20130101; H05K 1/167 20130101; B41F 15/423 20130101; H05K
3/1233 20130101; H05K 1/0201 20130101; H05K 1/0306 20130101; H01L
21/67103 20130101; H05B 2203/017 20130101; H05K 3/0097 20130101;
H01L 21/68785 20130101; H05K 3/1291 20130101; H05K 1/0212 20130101;
B41P 2200/40 20130101; H05K 2203/163 20130101; H01L 21/6833
20130101 |
International
Class: |
H01L 21/683 20060101
H01L021/683; H05K 1/16 20060101 H05K001/16; H05K 3/12 20060101
H05K003/12; H05K 3/00 20060101 H05K003/00; H05K 1/02 20060101
H05K001/02; H05K 1/18 20060101 H05K001/18; H01L 21/67 20060101
H01L021/67; B41F 15/42 20060101 B41F015/42; H01L 21/687 20060101
H01L021/687; H05B 3/28 20060101 H05B003/28 |
Claims
1. A top plate of a workpiece carrier, comprising: a plurality of
ceramic green sheets; and a printed ceramic green sheet having
conductive patterns printed thereon, the printed sheet being
embedded within the plurality of ceramic green sheets, wherein the
plurality of ceramic green sheets are sintered and hardened.
2. The top plate of claim 1, wherein the conductive patterns form
resistive heaters.
3. The top plate of claim 1, wherein the printed sheet further
comprises electrical components attached to the sheet and coupled
to the patterns.
4. The top plate of claim 3, wherein the conductive patterns form a
coil.
5. The top plate of claim 1, further comprising a frame to carry
the hardened plurality of green sheets.
6. The top plate of claim 1, wherein the ceramic green sheets are
formed of ceramic powder and glass compacted with a binder.
7. The top plate of claim 1, wherein the printed conductive
patterns comprise a conductive metal in a paste form including a
suspension and a dispersant dispensed into patterns.
8. The top plate of claim 1, wherein the conductive patterns
comprise a plurality of heater traces, each heater trace having a
resistivity of at least 50.OMEGA..
9. The top plate of claim 1, wherein printed ceramic green sheet
comprises Al.sub.2O.sub.3.
10. The top plate of claim 1, wherein printed ceramic green sheet
comprises AlN.
11. The top plate of claim 1, wherein the conductive patterns
comprise a conductive material selected from the group consisting
of tungsten, molybdenum, zinc, silver and gold.
12. The top plate of claim 1, further comprising: an upper circular
platform above a lower concentric circular base, the lower
concentric circular base having a diameter greater than a diameter
of the upper circular platform.
13. The top plate of claim 12, wherein the upper platform has
internal electrodes to electrostatically attach a workpiece to the
top plate.
14. The top plate of claim 1, further comprising: internal
electrodes to electrostatically attach a workpiece to the top
plate.
15. An electrostatic chuck, comprising: a top plate, comprising: a
plurality of ceramic green sheets; and a printed ceramic green
sheet having conductive patterns printed thereon, the printed sheet
being embedded within the plurality of ceramic green sheets,
wherein the plurality of ceramic green sheets are sintered and
hardened; a cooling plate beneath the top plate; and an adhesive
attaching the top plate to the cooling plate.
16. The electrostatic chuck of claim 15, further comprising: a base
plate beneath the cooling plate.
17. The electrostatic chuck of claim 16, further comprising: an
insulating plate between the cooling plate and the base plate.
18. The electrostatic chuck of claim 15, wherein the top plate
further comprises: an upper circular platform above a lower
concentric circular base, the lower concentric circular base having
a diameter greater than a diameter of the upper circular
platform.
19. The electrostatic chuck of claim 15, further comprising:
internal electrodes to electrostatically attach a workpiece to the
top plate.
20. A plasma system, comprising: a processing chamber body having
sidewalls and a bottom wall defining a processing region; an
electrostatic chuck in the processing region, the electrostatic
chuck comprising: a top plate, comprising: a plurality of ceramic
green sheets; and a printed ceramic green sheet having conductive
patterns printed thereon, the printed sheet being embedded within
the plurality of ceramic green sheets, wherein the plurality of
ceramic green sheets are sintered and hardened; and a cooling plate
beneath the top plate; and an adhesive attaching the top plate to
the cooling plate; a lid coupled to a top portion of the chamber
body; and a showerhead between the lid and the processing region.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 15/667,281 filed on Aug. 2, 2017, which claims benefit
from U.S. Provisional Application No. 62/371,636 filed on Aug. 5,
2016, the entire contents of which are hereby incorporated by
reference herein.
FIELD
[0002] The present description relates to the field of carriers for
workpieces that are made into microelectronic and micromechanical
devices and, in particular, to forming such carriers using screen
printing on green sheet ceramic.
BACKGROUND
[0003] In the manufacture of semiconductor chips, a workpiece, such
as a silicon wafer or other substrate is exposed to a variety of
different processes in different processing chambers. The chambers
may expose the wafer to a number of different chemical and physical
processes whereby minute integrated circuits and micromechanical
structures are created on the substrate. Layers of materials which
make up the integrated circuit are created by processes including
chemical vapor deposition, physical vapor deposition, epitaxial
growth, and the like. Some of the layers of material are patterned
using photoresist masks and wet or dry etching techniques. The
substrates may be silicon, gallium arsenide, indium phosphide,
glass, or other appropriate materials.
[0004] The processing chambers used in these processes typically
include a substrate support, pedestal, or chuck to support the
substrate during processing. In some processes, the pedestal may
include an embedded heater to control the temperature of the
substrate and, in some cases, to provide elevated temperatures that
may be used in the process. An electrostatic chuck (ESC) has one or
more embedded conductive electrodes to generate an electric field
that holds the wafer on the chuck using static electricity.
[0005] An ESC will have a top plate, referred to as a puck, a
bottom plate or base, referred to as a pedestal, and an interface
or bond to hold the two together. The top surface of the puck has a
contact surface that holds the workpiece which can be made of
various materials, e.g. polymers, ceramic, or a combination, and
may have coatings all over or over selective locations, etc. A
variety of components are embedded into the puck including
electrical components for holding or chucking the wafer, and
thermal components for heating the wafer.
[0006] Because the circuits and structures formed on the workpiece
are very small, the thermal and electrical environment provided by
the workpiece support must be very precise. When the temperature is
not uniform or consistent across the workpiece, the circuits and
structures will have variations. If one support is different from
another support, then the circuits and structures will vary with
different supports. For extreme cases, the processes may require
adjustment for use with different supports. This directly affects
the quality and yield of the circuits and structures produced on
the workpieces. As a result, a puck with embedded, thermal and
electrical components has stringent dimensional requirements, both
in-plane and vertical, to ensure consistent performance not only
across the surface of a particular ESC but also from one ESC to
another ESC.
SUMMARY
[0007] Precision screen printing is described that is capable of
sub-micron uniformity of the metallization materials that are
printed on green sheet ceramic. In some examples, puck is formed
with electrical traces by screen printing a paste that contains
metal on a ceramic green sheet in a pattern of electrical traces
and processing the printed green sheet to form a puck of a
workpiece carrier. In some example, the printing includes applying
a squeegee of a screen printer to the printed green sheet in a
squeegeeing direction while the green sheet is on a printer bed of
the screen printer. The method further includes mapping the printer
bed at multiple locations along the squeegeeing direction,
identifying non-uniformities in the printer bed mapping, and
modifying a printer controller of the screen printer to compensate
for mapped non-uniformities in the printer bed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Embodiments of the present invention are illustrated by way
of example, and not limitation, in the figures of the accompanying
drawings in which:
[0009] FIG. 1 is a cross-sectional side view diagram of an
electrostatic chucking (ESC) apparatus structure according to an
embodiment.
[0010] FIG. 2 is a top view diagram of a printer set-up for
symmetric ink printing (SIP) according to an embodiment.
[0011] FIG. 3 is a side cross-sectional view diagram of a
traditional squeegee set up for SIP.
[0012] FIG. 4 is a side cross-sectional view diagram of an
adjustable printer according to an embodiment.
[0013] FIG. 5 is a graph of motor encoder transducer feedback
against exposure sequence according to an embodiment.
[0014] FIG. 6 is a graph of printed ink thickness against the
motorized encoder according to an embodiment.
[0015] FIG. 7 is a graph of printed ink thickness against targeted
heater trace resistivity per a design according to an
embodiment.
[0016] FIG. 8 is an isometric diagram of a printer and squeegee
rails to show adjustment points according to an embodiment.
[0017] FIG. 9 is a top view diagram of a printer set-up for
symmetric ink printing (SIP) with multiple squeegee positions
according to an embodiment.
[0018] FIG. 10 is a graph of motor encoder values against each of
eight different positions along the path of the squeegee according
to an embodiment.
[0019] FIG. 11 is a graph of printed ink thickness against lot
numbers according to an embodiment.
[0020] FIG. 12 is a graph of ink thickness against squeegee gap
according to an embodiment.
[0021] FIG. 13 is a graph of printed ink thickness against batch
size of printed green sheets according to an embodiment.
[0022] FIG. 14 is a graph of printed ink thickness or printed ink
resistivity against a mask thickness design parameter identified as
X according to an embodiment.
[0023] FIG. 15 is a table of data collected when designing a print
screen and squeegee gap configuration according to an
embodiment.
[0024] FIG. 16 is a process flow diagram of a method for highly
repeatable squeegee set up according to an embodiment.
[0025] FIG. 17 is a process flow diagram of a method for conformal
precision screen printing according to an embodiment.
[0026] FIG. 18 is a process flow diagram of a method of
compensation for ink thickness trending according to an
embodiment.
[0027] FIG. 19 is a process flow diagram of a method for screen
mask design according to an embodiment.
[0028] FIG. 20 is an isometric view of an assembled electrostatic
chuck suitable for use according to an embodiment.
[0029] FIG. 21 is a schematic of a plasma etch system including a
pedestal assembly suitable for use in according to an
embodiment.
DETAILED DESCRIPTION
[0030] In the following description, numerous details are set
forth, however, it will be apparent to one skilled in the art, that
the present invention may be practiced without these specific
details. In some instances, well-known methods and devices are
shown in block diagram form, rather than in detail, to avoid
obscuring the present invention. Reference throughout this
specification to "an embodiment" or "one embodiment" means that a
particular feature, structure, function, or characteristic
described in connection with the embodiment is included in at least
one embodiment of the invention. Thus, the appearances of the
phrase "in an embodiment" or "in one embodiment" in various places
throughout this specification are not necessarily referring to the
same embodiment of the invention. Furthermore, the particular
features, structures, functions, or characteristics may be combined
in any suitable manner in one or more embodiments. For example, a
first embodiment may be combined with a second embodiment anywhere
the particular features, structures, functions, or characteristics
associated with the two embodiments are not mutually exclusive.
[0031] As described herein, a top plate can be made for a chuck,
pedestal, or carrier that supports a workpiece, for example a
silicon or other wafer, in a carrier. The top plate may be formed
of ceramic with embedded electrical components and provide very
high accuracy in the shape and the size of the embedded components.
This provides better control over process parameters on the
workpiece. The components are also more consistent from top plate
to top plate. This provides more consistent production results as
the top plates wear out and are replaced. As a result, smaller and
more accurate features may be formed on the workpiece with higher
quality and uniformity, reducing cost, increasing production
quantities, and reducing down time for adjusting production
parameters.
[0032] A method for screen printing with sub-micron uniformity is
disclosed herein. This method is suitable for screen printing of
some materials that require precision print thickness and
uniformity over screen mask patterns. An illustrated application is
the printing of metallization material on green sheet ceramic that
is a core process for making uniform heater trace patterns used in
an electrostatic chucking (ESC) apparatus. The ESC is of special
importance to semiconductor processing for chip device performance
and wafer yield.
[0033] An ESC with very high temperature uniformity benefits from
very high uniform printing of metallization materials, on green
sheet ceramic. Materials that are printed onto a surface including
any that have metallization materials will be referred to below
simply as ink. In examples herein, an ESC puck is made of multiple
green sheets, and some of them are ink printed with heater trace
and electrostatic electrode patterns. The print uniformity may be
at a sub-micron level.
[0034] FIG. 1 is a cross-sectional side view diagram of an
electrostatic chucking (ESC) apparatus structure. The ESC 2 has a
cooling base 4 made of a thermally conductive material, such as
aluminum or an alloy. There is an input port 6 and an output port 8
coupled to an external thermal fluid pump and heat exchanger.
Within the cooling base, the ports are coupled to internal cooling
channels 20 that circulate the thermal fluid through the base to
help control the temperature of the ESC. A ceramic puck 12 is
attached to the cooling base 4 with a thermally conductive bond
layer 10. The bond layer is typically a type of adhesive but other
materials may be used instead. A workpiece 14 such as a silicon
wafer, glass sheet, gallium arsenide wafer or other workpiece is
held in place on the puck 12 by an electrostatic charge.
[0035] The electrostatic charge is generated and held by chucking
electrodes 16 within the puck. The electrodes may be charged or
discharged using contacts (not shown) on the side or bottom of the
puck. Heater traces 18 may also be formed within the puck to heat
the workpiece using resistive heating from the conductive traces,
for example. Multiple traces may be used to apply different amounts
of heat by different traces to more precisely control the
temperature of the puck and thereby the wafer.
[0036] The ceramic puck may be formed of multiple green sheets that
are ink printed, laminated, machined, sintered, polished, and have
surface features that are created in a series of complex processes.
Interconnects for both heater traces and the electrode in the puck
are not shown. The quality of the heater trace 18 patterns affects
the ESC temperature uniformity performance.
[0037] A ceramic green sheet may be formed in any of a variety of
different ways. In some embodiments, 90-96% ceramic powder, e.g. of
Al.sub.2O.sub.3 or AlN and glass, is compacted with a binder, e.g.
plasticizers, at high pressure and then briefly sintered to form a
pliable material that may be handled at room temperature and then
hardened later by sintering. The green sheets may be in any of a
variety of different thicknesses. As example, the green sheets may
be from 0.05 mm to 0.5 mm thick and carried in a stainless steel
frame for handling purposes.
[0038] Alternatively a green body or any other pliable ceramic
material may be used. A green body in some examples is a monolithic
compacted block of ceramic power and binder with other fillers.
After forming as described below it may be sintered in a furnace
under heat and pressure. Such a process may also be applied to the
green sheets as mentioned below.
[0039] As described herein heater trace patterns and other
structures may be formed by printing a paste onto a green sheet.
The green sheet may be stacked with other green sheets so that the
paste is embedded between green sheets. Different pastes may be
dispensed into different patterns to form different types of
electrical components. The paste is used to form embedded or
surface conductive components. The paste contains a suitable
conductive material such as a metal like tungsten, molybdenum,
zinc, silver, gold, or a suitable refractory material in a powder,
for example, and carried in a suitable suspension and dispersant.
The paste is dried, sintered, or cured with the stacked green
sheets to form a finished puck.
[0040] The stacked green sheets are pressed together with
sufficient pressure to form a single, stable structure. The paste
is dried to be hard enough to undergo the stacking and the
compaction without too much deformation. The lamination of
individual ceramic green sheets with the desired thermal and
electrical components is then sintered to consolidate the separate
sheets into a single solid entity. This is later converted to the
final top plate or puck using additional finishing processes such
as machining, grinding, polishing, grit blasting, cleaning, etc.
Because metal or refractory materials may be dispensed on to
intermediate sheets, these features can be embedded within the
resulting structure after the sheets are pressed together.
[0041] For repeatable and consistent quality of ESCs in a
production lot, or from various lots, the described method first
identifies some hidden printer hardware's skews for eliminating or
minimizing later hard-to-identify root causes for systematic print
skew.
[0042] FIG. 2 is a diagram of a printer set-up for symmetric ink
printing (SIP) to show the direction of different possible skews.
The printer 22 includes a printing table 24 that carries the green
sheet 26 that is to be printed. The printer swipes the workpiece
with a squeegee 28 that runs across the workpiece.
[0043] Major set up skews are first recognized and minimized. The
centers of both screen mask and squeegee may be aligned with the
center of the heater trace patterns. In particular, a symmetric
alignment between a heater trace pattern center, screen mask center
and squeegee center are mandated with a tight tolerance. The
centers of heater trace patterns are typically located on the
center 30 of the screen mask. On the printer, the screen mask is
positioned over the workpiece 26. Ink is pushed through the screen
by the squeegee to form an ink pattern on the workpiece as the
squeegee is drawn across the screen. This is shown as starting at a
start position and ending at the end position at which the squeegee
is shown as resting in the diagram. The printed pattern squeezed
through the screen mask is the pattern of heater and other
electrical traces on the workpiece.
[0044] The center of a mounted squeegee 32 may also be aligned with
the center of the screen's heater trace patterns 30. Any hidden or
ignored hardware skews can cause a printing skew. Such a skew could
make a heater trace design ineffective. This printer hardware
alignment tenet is then used for a method referred to herein as
Symmetric Ink Printing (SIP) of metallization materials.
[0045] Traditional printing methods use some shimming devices for
setting up the squeegee for each production order. FIG. 3 is a
diagram of a traditional squeegee set up. A setup method has been
used to add different types of shimming devices. The printer 302
has a printing bed 304 and a sample, test, or trial workpiece 306
is placed on the bed. A mask 308 is placed over the workpiece. The
squeegee 310 is mounted on brackets or rails 312 and then trials
are conducted. Shimming devices 314 are added to the rails to
compensate for any lack of parallelism. After this process, the
squeegee is in a new more accurate position 316.
[0046] Unfortunately, the actual printed ink thickness and its
uniformity cannot be known at the time of set up. Operators repeat
the complete set up process if trial printing outcomes are not
satisfactory. The desired squeegee gap should enable conformal
printing that leads to high uniform ink thickness over all of the
heater trace patterns.
[0047] Both the squeegee gap and parallelism to the printer bed are
only approximated with the use of shimming devices, but the printed
ink thickness and its uniformity are actually not known at that
time. The printer setup conditions may also drift away after the
queue time for measuring printed ink for a trial. Therefore, the
traditional printing method is not capable of producing print
uniformity at a sub-micron level.
[0048] Therefore, the repeatability of squeegee mounting on its
holder may be important. Dedicated brackets or alignment fixtures
for squeegee mounting may be used for ensuring high mounting
repeatability from lot to lot production as shown in FIG. 4.
[0049] FIG. 4 is a side cross-sectional diagram of an adjustable
printer. The printer 402 has a printer bed 404 that carries a
workpiece 406. A print screen 408 is fastened to the printer bed
over the workpiece 406. The print screen may or may not be fitted
with shims 414 on one or both sides as in FIG. 3, depending on the
implementation. Squeegee brackets 422, 424 are mounted one on each
side of the squeegee 410 to hold it in position as it swipes over
the print screen 408 from its initial start position 410 to its
finished position 416.
[0050] The right side bracket 422 is the same as in FIG. 3, but the
left side bracket 424 has been adjusted with a shim 426 at the
squeegee mount. This shim allows the system to compensate for any
misalignment between the two brackets. As shown there is a larger
gap 430 on the left side than on the right. The bracket shim can
compensate for this while the screen shims 414 may compensate for
any misalignment with the screen and the workpiece. Optionally
either or both types of shims may be removed as unnecessary.
[0051] The encoder from a motorized actuator may be used to
precisely control the squeegee gap at the resolution of the
encoder. The squeegee mounting brackets may be very useful with
this approach. The squeegee slant may be compensated with the
printer's `auto-zero" feature or with an alternative means.
[0052] Precision Screen Printing with Motorized Actuator
[0053] Some embodiments use a method with a motorized actuator
(linear or rotary) with an encoder, one on each end of the squeegee
mount, that is typically integral, or can be added, to the printer
system. A motor encoder may be available from the printer
controller. The motorized actuator precisely controls the squeegee
gap and compensates for its un-parallelism at resolutions of a
single motor encoder (e.g. a step count). Further, some printers
have a built-in auto-zero feature with some sorts of transducer
feedback, as shown in FIG. 5, so that the required encoder
compensation can be easily obtained. With the use of dedicated
squeegee mounting brackets, the printer squeegee set up can achieve
high repeatability from lot to lot.
[0054] FIG. 5 is a diagram of motor encoder transducer feedback on
the vertical axis against exposure sequence on the horizontal axis.
The data has points only for each exposure numbered 2 through 10 in
this example, and a straight line is drawn through the data points
to show whether this is an overall increasing or decreasing trend.
In this example data, there is no significant trend through the
sequence of exposures.
[0055] The squeegee set up is highly repeatable with the use of
brackets. In this example, the squeegee set up is much more
repeatable than with the traditional shimming method.
Un-parallelism, due to any of a variety of different reasons, can
be compensated by the printer's auto-zero feature, which in this
example is estimated to be close to 1 mm.
[0056] With the above described SIP printer set up method that uses
a motor encoder as a control, the printed heater traces have high
repeatability of the printed ink on green sheet ceramic. After
sintering, a metallization process of printed ink, the resultant
heater trace patterns are able to produce an ESC puck of high
temperature uniformity with lot-to-lot repeatability.
[0057] Precision printing of a desired ink thickness, on the other
hand, may be achieved with a knowledge-based model that is
established with a lean DOE (Design of Experiment) plan to cover
regions of interest. For a given screen mask design, a high
resolution one-on-one relationship between heater trace resistivity
to printed ink thickness can be thus derived in a DOE plan.
[0058] FIG. 6 is a diagram of a graph of printed ink thickness on
the vertical axis against the motorized encoder in steps on the
horizontal axis. The ink thickness 520 amount and the motor encoder
value or steps value 522 meet at a point 524 on the graph. A
correlation curve 526 may then be drawn through the points to
determine the correlation based on the DOE. A high resolution
one-on-one relationship between printed ink thicknesses to squeegee
motor encoder steps can thereby be derived in the same DOE
experiment. Once a knowledge-based model is developed, an operator
may set up the printer squeegee and print by referencing the
model.
[0059] In a similar way, a DOE plan may be carried out to obtain
highly repeatable correlation covering a design specification
window of heater trace resistivity. For a targeted heater trace
resistivity, the operator looks in the DOE model for the
corresponding motor encoders and then prints the green sheets.
[0060] FIG. 7 is a diagram of a graph of printed ink thickness on
the vertical axis against the targeted heater trace resistivity per
the design. A particular ink thickness 530 intersects with a
particular heater trace resistivity 532 based on empirical values
at an intersection 534 on the graph. Multiple experimental data
points may then be used to build a correlation curve 536. This
curve like the thickness/encoder correlation curve may be used to
set the parameters for a particular trace printing task.
[0061] The described method may be implemented in many different
ways in ESC ceramic puck manufacturing. Metallization materials
referred to in this method may be of any refractory-based metal
that is formulated in liquid form or ink. The green sheet ceramic
referred to in this method may be of alumina based or aluminum
nitride based ceramic, regardless of their purity level or additive
formulation materials. This method can be used for printing of
non-metallization material where precise and high uniform thickness
of materials is desired. The motorized actuator may be linear or
rotary. Any encoder information from the motorized actuator may be
used to represent the control limit of squeeze set up.
[0062] Traditional metallization materials printing on green sheet
ceramic may have the following disadvantages:
[0063] 1) Inaccurate and non-repeatable print thickness: Current
traditional printer squeegee set up methods employ some types of
shimming devices. This type of set up process relies on the
operator's experience, and results are not repeatable for ESC
applications. The thickness of printed metallization materials is
only known by guessing at the time of trial printing. Lot-to-lot
set up suffers low repeatability.
[0064] 2) Time-consuming: Trial printing of metallization materials
is necessary for the shimming method. Printed ink takes a lengthy
queue time to ink stabilization before a thickness measurement can
take place.
[0065] 3) Drifting of squeegee set up after trial printing:
residual ink materials left on the screen mask will dry up during
measurement queue time. Screen mask cleaning has impacts on
subsequent printing. Print results often drift when production sets
in.
[0066] 4) Cumbersome production scheduling: Operators need to re-do
squeegee set up if the trial run results are way off from the
manufacturing specification. Such re-do uncertainty impacts
manufacturing scheduling in a complicated manufacturing
environment.
[0067] 5) Compromised quality: Manufacturing engineering tends to
accept sub-par quality because of the cumbersome squeegee set-up
process.
[0068] Implementation of SIP Printing Method
[0069] SIP printing methods with metallization materials on green
sheet ceramics may be directly applied to an Electrostatic Chucking
(ESC) Apparatus. The printing methods may be applied to an ESC that
has single or multiple main heaters in the ESC puck for
semiconductor wafer processing applications. The printing methods
may be applied to an ESC that has a symmetric or un-symmetric
layout of mini heaters in the ESC puck. These mini heaters are used
for versatile thermal control. The printing methods may be applied
to metallization materials on green sheet ceramics for non-ESC
applications where high printing uniformity on green sheet ceramic
is desired.
[0070] FIG. 8 is an isometric diagram of a printer and squeegee
rails to show adjustment points. The printer bed 404 has a right
422 and left 424 squeegee rail mounted to it. The squeegee runs
from a start position 410 to a finish position 416 across a print
screen. Both printer bed flatness and the lack of precise
parallelism of the squeegee rails impact the consistency of the ink
printing. Squeegee gaps (h1, h2, h3, h4) are indicated on the right
and left sides of the squeegee at each rail and at the two
positions 410, 416. The gaps are not the same if the printer bed is
not perfectly flat. In addition, the gaps will not be the same for
each measurement if the squeegee mounting is not consistent.
[0071] A method may be applied to aid with precision screen
printing that is capable of sub-micron uniformity of the
metallization materials on the green sheet ceramic. First the
screen mask and the squeegee are set up to be aligned with the
heater trace center. Then the squeegee gap and parallelism to the
printer bed are optimized using the printer's auto-zero feature.
The auto-zero feature results are recorded with motor encoders. As
an example at a center location the motor encoder might be set at
Left=25000, Right=25850.
[0072] FIG. 9 is a top view diagram of the same printer bed 404 and
squeegee 416. In this example, the heater traces center 430 may be
aligned with the print screen's center line 432 and the squeegee's
center 4345 but only at one point. Any misalignment will result in
lines from the aligned center diverging. FIG. 9 also shows examples
of 7 different positions (L1, . . . L7) along the path of the
squeegee from start to end.
[0073] The printer squeegee's auto-zero feature may be used at each
of these multiple locations along the squeegeeing direction to map
out a conformal parallelism. The mapped data may then be programmed
into a squeegee control software parameter set for conformal
printing. The auto-zero at multiple locations (L1, . . . L7) may be
mapped to the printer bed's un-flatness.
[0074] FIG. 10 is a graph showing measurements that might be used
with the motor encoder. FIG. 10 is a graph of motor encoder values
or steps on the vertical axis against each of eight different
positions along the path of the squeegee. The printer squeegee's
auto-zero feature is used at each of the eight multiple locations
along the squeegeeing direction to obtain conformal parallelism
over the heater trace pattern. There is a different value on the
right rail from the left rail and so there are two set of data
point for each squeegee position (L1 . . . L8).
[0075] A Compensation Method for Print Thickness Trending Based on
SIP Printing Method
[0076] Using the principles discussed herein a method may be
described that compensates for print thickness in SIP printing.
Such a method uses:
[0077] 1) a symmetric ink printing method which first identifies
hidden printer hardware's skews for eliminating or minimizing those
later hard-to-identify root causes for systematic print skew,
and
[0078] 2) a motorized actuator encoder to precisely control
squeegee set up, namely gap and parallelism to the printer bed.
[0079] 3) with this SIP printing method a knowledge-based model is
then established with a lean DOE plan. Operators can use this
simple and repeatable method for setting up squeegee easily without
trial printing.
[0080] Printer bed un-flatness and squeezing rail un-parallelism
along the squeezing direction are another major root cause of an
inconsistent temperature contour in an ESC that is formed using
printed green sheets or green bodies. An inconsistent temperature
contour may affect chamber matching and CD (critical dimension)
tuning as shown in FIG. 9. In this figure, seven locations along
the squeezing direction are mapped on the printer bed, among which
five locations cover heater traces of the screen mask pattern. The
obtained set of motor encoder values is equivalent to a fingerprint
of the conformal planar relationship during squeezing and that
relationship can be programmed into a printer control system for
conformal printing.
[0081] After the parameters or motor encoder steps are determined
for a particular printer bed, screen, and ink are set, the ink
thickness may still vary over time and with use. Printed ink
thickness may be uniform across the print screen but the thickness
can trend upward or downward over a large production lot.
[0082] FIG. 11 is a graph of printed ink thickness on the vertical
axis for lot numbers on the horizontal axis. There is an average
ink thickness value for each lot and a line is drawn through the
values to show the increasing trend. In this example, the ink
thickness increases 1.5 .mu.m through the printing of 60 ceramic
green sheets from the first sheet to the last. This much change can
be critical to some applications and, therefore, limits the lot
size. Root causes for trending could be multiply complex and
confounded. They may include: changing of ink viscosity during
printing, changing of screen tension screen mask cleaning, screen
mask lifting, etc. Regardless of these complex trending mechanisms,
the trend may be compensated to flatten the trend.
[0083] It may be observed for many systems that there is a linear
relationship between the squeegee gap or motor encoder position and
the ink thickness. FIG. 12 is a graph of ink thickness on the
vertical axis against the squeegee gap on the horizontal axis.
There are two data points at two different gaps that produce two
different thicknesses. If there were additional points then the
same straight line could be drawn through all of them.
[0084] For any given screen mask design, a flattening method may be
used that relies on the linear relationship between the squeegee
gap/encoder and the ink thickness. In the example data shown in
FIG. 11, the trending is estimated at a 1.5 .mu.m thickness change
over a printing of 60 green sheets. To improve the printing
precision, this linear relationship may be measured with a simple
DOE plan. A DOE as shown in FIG. 12 may set the squeegee at two
gaps of (x1, x2) .mu.m or equivalent motor encoder steps and then
generates the corresponding paired ink thickness of (y1, y2) .mu.m.
A trending sensitivity may be calculated as a ratio of the ink
thickness change of (y2-y1)=4 .mu.m to the squeegee gap change of
(x2-x1)=28 .mu.m.
[0085] The printer squeegee gap setting is in a range of (x1,
x2)um, and the corresponding printed ink thickness is in a range of
(y1, y2).mu.m. This relationship is important for calculating
compensation for the printed ink thickness trending. The greater
the spacing between x1 and x2 in the DOE planning the greater the
precision and the robustness of the model, but the spacing should
be narrow enough to remain in the linear region.
[0086] Motor encoder settings may be compensated by combining two
pieces of the information above. The compensation may be derived as
(28/4).times.(1.5/60)=0.175 .mu.m/sheet. An equivalent expression
with the encoder is straightforward. For example, if an encoder
unit is equivalent to 1 .mu.m then a compensation scheme would be
to change the encoder units for that one encoder for every 6th
(i.e. 1/0.175) green sheet that is printed. The printed thickness
variation after the compensation had been applied is then reduced
to 0.15 .mu.m, or 1/10 of the original trending range.
[0087] Encoder compensation may be integrated with a conformal map
(from a printer auto-zero feature). FIG. 13 illustrates calculated
results with motor encoder compensation. FIG. 13 is a graph of
printed ink thickness in the vertical against the batch size of
printed green sheets on the horizontal. The upper linear increasing
line 450 shows the increase in ink thickness if the ink thickness
is not compensated. The lower line 452 shows the ink thickness and
its variation 454 when the trend is compensated by adjusting the
motor encoding.
[0088] In this example, the squeegee setting is in a range of (x1,
x2).mu.m, and the corresponding ink thickness range is (y1,
y2).mu.m. The approach to flattening this increasing trend is based
on the relationship between ink thickness and the squeegee gap as
described above. As a result, the reduction in screen printing
performance is compensated by reducing the squeegee gap.
[0089] Once the ESC manufacturing has a repeatable temperature
contour pattern, a comparison of a wafer temperature map allows
information for improving the heater trace design or the cooling
base design or both. Highly repeatable and uniform printing of
metallization materials enables ESC design effectiveness and
efficiency for an advanced electrostatic chucking apparatus.
[0090] Implementation of SIP Printing Method
[0091] The conformal relationship data between the squeegee and the
printer bed may be programmed in the printer control software that
coordinates the motor encoder's compensation of each squeegee end
during squeezing. Optimization with motor encoder steps can be
further attempted if temperature skew is consistent and persistent
from ESC to ESC. A DOE may be planned to obtain the core data for
determining compensation parameters. FIGS. 11 and 12 show some of
the data that may be used to obtain results like those of FIG.
13.
[0092] The setup of both the screen mask and the squeegee is
aligned with the heater trace center. The squeegee gap and its
parallelism to the printer bed are optimized with the printer's
auto-zero feature and recorded with motor encoders.
[0093] The printer bed flatness and un-parallelism of the squeegee
rails both impact the consistency of the ink printing. Squeegee
gaps (h1, h2, h3, h4) of FIG. 8 are not the same because the
printer bed is not perfectly flat. Their measurement is not
repeatable if squeegee mounting is not consistent.
[0094] The printer squeegee's auto-zero feature is used at multiple
locations along squeezing direction to map out a conformal
parallelism. The mapped data can be programmed into squeegee
control software conformal printing.
[0095] Method of Screen Mask Design for a Precision Application
Based on Symmetric Ink Printing Method
[0096] A highly repeatable squeegee set up procedure for a
symmetric ink printing (SIP) method with sub-micron uniformity of
metallization materials on green sheet ceramic is described. How to
use motor encoders of squeegee motorized actuators, linear or
rotary, to map out a non-flat printer bed for a conformal
parallelism at precision of a motor encoder is also described. How
to flatten a uniform ink printing but with a linear trending of
print thickness is also described. Implementation of all these
methods with printer control software is also discussed.
[0097] An application of an SIP printing method for an optimal
screen mask design for a precision ink printing is described here.
Printing with precision thickness does require some design
iteration. An iteration can be effective if print skew is minimized
with the SIP printing method. It is useful to shorten the product
development cycle that involves a series of lengthy and complicated
ceramic sintering processes and post sintering processes.
[0098] Screen mask design involves screen wire selection and a
screen "height" parameter X. The value of X is correlated to the
realized ink thickness. Wire selection is empirically
straightforward, but design parameter X needs numerous iterations
for critical applications. A lean process for optimizing design
parameter X for a given wire diameter is described.
[0099] A new screen mask design starts with an empirical equation
developed by a mask designer. Empirical models have only first
order accuracy. The screen mask design activity may be divided into
two processes: The first process focuses on establishing a robust
model between squeegee gap and printed ink thickness, and the
second process focuses on establishing a correlation between
printed ink thickness and heater resistivity. This approach intends
to minimize the need for frequent sintering. All trial printing
green sheet ceramics are sintering in the same lot.
[0100] Process 1:
[0101] A purpose of this process is to establish a quality
correlation with a least error between the squeegee gap and the
printed ink thickness with the SIP printing method. This is
achieved by a wide spacing between x-, xo and x+. The spacing is as
wide as possible but remains in the linear region.
[0102] FIG. 14 is a graph of printed ink thickness or printed ink
resistivity in the vertical against a mask thickness design
parameter identified as X in the horizontal. Since ink thickness
and resistivity have a linear relationship for any one ink type and
processing method, these may be plotted on the same vertical
axis.
[0103] To use the FIG. 14 chart, the designer sets X=x0 as shown on
the horizontal axis and inputs it into a design equation that is
only of first order accuracy. t0 is the output ink thickness with
the design equation. The design may be validated after completing a
sintering process.
[0104] To speed up mask design, and also to obtain a quality model,
two additional screen masks with input design parameter x- and x+,
respectively, shown also on the horizontal axis, are made such that
the predicted t- and t+ are about 20%-25% less than t0 and 20%-25%
higher than t0, respectively. It is simply a DOE plan for a
correlation with better signal-to-noise ratio.
[0105] Following an SIP printing method, that is intended to print
highly uniform and repeatable ink thickness on green sheet ceramic,
a few trial green sheet ceramic with masks A, B and C are printed.
Note that manufacturing lead time for three masks is much shorter
than the lead time for sintering and other processes. With these
output data, a quality correlation model can be established between
mask design parameter X and printed ink T or resistivity, and the
results are plotted in FIG. 14.
[0106] In FIG. 14, it is assumed that X.OMEGA.=50 is the desired
value for the screen mask design parameter X that would allow the
printer to print T.OMEGA.=50, and that leads to a target heater
trace resistivity .OMEGA.=50 per ESC design. In the example there
is a gap on the horizontal axis between X.OMEGA.=50 and X0. An
encoder DOE may be implemented to close this gap using the squeegee
gap adjustment or another parameter.
[0107] Three mask designs, referenced as A, B, C in FIG. 15,
represent three levels of parameter X at the level of X+, X0, and
X-, respectively. The associated printed ink thickness is denoted
as t+, t0, t-, respectively, and resistivity after sintering as
.OMEGA.+, .OMEGA.0, .OMEGA.-, respectively. In this example, Mask B
represents the intended design, and both Mask A and C are used to
develop a robust correlation between mask design parameters to
printed ink thickness and heater trace resistivity.
[0108] FIG. 15 is a table to show an example of the types of data
that may be collected when designing a screen for a particular
printer configuration. A multi-level encoder DOE based on a
squeegee gap g0 is planned, as indicated by the squeegee gap
column. An encoder DOE for mask design B is used in this example to
develop a compensation method for mask design B.
[0109] A five level squeegee gap (g0 . . . g4) is set up to
determine a correlation between the squeegee encoder and the
printed ink thickness. Trial prints at each encoder setting may be
a minimum of 2 to estimate the error term. Trial printing with
masks A, B, and C may be of a minimum of 3.
[0110] Squeegee set up g0 is a prior set up that mask engineers
would use or a DOE would be needed for determining it. The squeegee
gap g0 may be based on prior experience from mask design engineers
or printer manufacturers can recommend as a value by experience. In
this example, a five level encoder DOE, as indicated in the encoder
DOE column, may be used if the sintering batch is big enough to
accommodate all trial green sheets in the same sintering process.
If not, some levels, e.g. levels g1 and g3, may be skipped.
Information for g2 and g4 may be sufficient to set the
constructive. In this example, the encoder levels or values are set
as follows (however any other levels may be used):
[0111] g1 encoder is set 10% more than g0
[0112] g2 encoder is set 20% more than g0
[0113] g3 encoder is set 10% less than g0
[0114] g4 encoder is set 20% less than g0
[0115] In this example there are three trial printings, as indicate
in the minimum trial printings column, with each mask design and
two trial printings with mask B at each encode level. Therefore, a
total of 17 green sheets are printed in Process A for five level
encoder DOE or 13 green sheets are printed for 3 level encoder DOE
in case of a limited sintering capacity. The same may be repeated
for Mask A and Mask B.
[0116] Process 2:
[0117] Review printing and sintering result.
[0118] If the results produced with mask design B with encoder DOE
can meet the ESC design spec then the screen mask design is
completed with one sintering process.
[0119] If the results produced with mask design B in Process A does
not meet the design requirement or there are desires to further
optimize the mask design, the quality correlation from 3 mask
designs may be used to point out the desired mask design parameter
resistivity to provide e.g. X.OMEGA.=50 is and output resistivity
to be .OMEGA.=50 with reasonable error. In a second design
iteration, an encoder DOE can be planned or ignored since the
encoder steps compensation power is already estimated in Process
A.
[0120] Among the challenges of traditional approaches of screen
mask design for critical applications is the numerous design
iterations used to achieve a design target. Ink printing quality
and consistency are inadequate due to the lack of optimization of
the printing technology. SIP precision and uniform printing
capability break up tail-chasing patterns and allow an efficient
design process with sufficient knowledge to be developed in a cost
effective manner.
[0121] The techniques described above may be represented as a
sequence of operations. Four different and related processes have
been described indicated below as Methods A, B, C, and D.
[0122] Method A: FIG. 16 is a process flow diagram of a method for
highly repeatable squeegee set up using the precision of a
motorized encoder.
[0123] 1) Start at 502 with a screen mask that is manufactured
based on a screen mask design for a target print ink thickness for
an ESC application. Measure the alignment gap between the heater
trace pattern center to the screen mask center. Compare the gap to
some tolerance. If the screen mask gap meets the tolerance then go
to the next operation.
[0124] 2) Design at 504 a set of two squeegee mounting brackets to
tightly mount a squeegee to a printer squeegee holder. The squeegee
mounting brackets are designed such that the center of a mounted
squeegee is aligned with the center of the screen mask with some
tolerance. Modify the squeegee holder for using squeegee brackets
if a hardware change is necessary.
[0125] 3) Check the printer control system for its auto-zero
capability. Auto-zero is a feature that a printer control system
uses for equalizing some transducer signals, such as pressure or
other signals, when both squeegee ends, left or right, reach a
conformal contact to a printer bed. During squeegee wipes of paste
over the screen at 506, the printer control system can record the
motor encoder values at 508 in its memory when the auto-zero
function is executed and display the encoder steps on control
interface. If auto-zero capability is not available, equip the
printer with this capability.
[0126] 4) Validate at 510 the repeatability of the squeegee
mounting at the location of the heater trace pattern center with
the printer auto-zero feature. The encoder readings from the
control interface are analyzed for repeatability. Perform
statistical analysis on the encoder data including the average and
variance. These statistic attributes in terms of the encoder depend
on the transducer resolution or sensitivity. Select an appropriate
transducer per application requirement. The encoder values may be
compared to the resulting pucks. The repeated printed green sheets
may be formed into carrier pucks at 512 and the printed electrical
traces may be tested for resistivity at 514.
[0127] 5) The difference between the encoder values averaged
between squeegee left and right ends represents the un-parallelism
of the squeegee to the printer bed, or slant skew. This difference
is characteristic for the squeegee being used and the associated
mounting brackets. The encoder information and the shims may be
used to configure the screen printer for the next batch at 516. The
encoder information with use of the auto-zero feature represents
the printer hardware capability limit for the highest possible
repeatable squeegee set-up.
[0128] Traditional squeegee set-up methods use shimming devices to
set up a squeegee gap in a time-consuming way. This method is
operated using subjective judgment without knowing the squeegee
gap, the degree of parallelism, and so on. Repeatability is poor
and difficult to apply to adjustments for sub-micron uniformity
applications. Beside the poor repeatability, trial printing with
green sheet ceramic is done for every production lot. This
traditional method is fundamentally inefficient and
ineffective.
[0129] The SIP printing method, using a repeatable squeegee set up
and encoder information in the printer control system, lays down an
architecture for a conformal and precise printing with sub-micron
uniformity for critical applications. Once a printing recipe is
established, any trained operator can repeat the same encoder
setting for a new production job. No shimming method or trial
printing is needed.
[0130] Method B: FIG. 17 is a process flow diagram of a method for
conformal precision screen printing with sub-micron uniformity over
screen mask with Symmetric Ink Printing (SIP).
[0131] A printer bed for screen printing is not perfectly made. Any
printer bed has its own unique flatness variations measured in Ra
and any one printer bed differs from other printer beds. In the
same way, any motorized squeegee motion is unique and differs for
each printer. These variations combined can cause print skew that
is hard to recognize for screen printing. There is no known method
or technology currently available in screen printing industries to
address these variations.
[0132] Conformal screen printing technology is defined as a
printing method that exerts a uniform squeegeeing pressure along
the full squeegee length of the printer bed during printing. A type
of conformal screen printing technology for large green sheet
ceramic is described below. This conformal printing is further
developed based on the SIP method described Method A above.
[0133] 6) Map at 520 the printer bed at multiple locations along
the squeegeeing direction. Equal spacing is used. The obtained
encoder data is a characteristic for a given printer system and the
squeegee being used including the squeegee mounting brackets. The
number of mapping locations are selected to allow an adequate
spline curve-fitting.
[0134] 7) Perform statistical spline curve fitting at 522 with the
above mapped data, one spline curve for each squeegee end, so two
splines are obtained. These spline curves are expressed in terms of
the encoder and represent smoothed squeegee gap compensation by the
motorized actuator that controls the squeegee gaps.
[0135] 8) Store spline data in the control system memory. The
printer control system uses these profiles in its algorithm to
actively drive squeegee gaps at 524 in the printing direction with
smoothed conformal squeegee pressure.
[0136] 9) Review the ESC temperature performance and decide if
another design iteration for the heater trace pattern is necessary
at 526. At this stage in the process, the resulting ESC will
present repeatable temperature maps with little manufacturing
variation. Temperature non-uniformity may exist but at this stage
further improvement is obtainable by design compensation for the
design cycle efficiency. The settings may be used to configure the
printer for the next set of green sheets at 516
[0137] Method C: FIG. 18 is a process flow diagram of a method of
compensation for ink thickness trending over a large print batch
suitable for use with Symmetric Ink Printing (SIP).
[0138] Printing with sub-micron uniformity may be achieved with the
SIP method in a methodical approach. However, print trending often
occurs when printing a large lot. Print trending is a combined
effect of multiple complex and interactive mechanisms between ink
viscosity, screen wire tension, screen mesh cleanliness and so on.
This may be addressed as described below.
[0139] 10) Screen print at 530 a large lot, e.g. 60 green sheets,
with the SIP method described above.
[0140] 11) Measure the print ink thickness trending rate at 532.
This rate may be measured as a ratio of thickness change to the
total number of green sheets. For example, a print thickness change
of 1.5 .mu.m is found associated with a printing lot of 60 ceramic
green sheets.
[0141] 12) Plan a two-level DOE with a wide spacing of the squeegee
gap in terms of the encoder at 534. This spacing is wide enough to
robustly determine the print thickness rate at two levels. As a
guideline, the thickness difference for this DOE is about
.+-.20%-30% of the target thickness. This DOE establishes a
translation that is useful for trending compensation by performing
multiple printings of green sheets with two or more additional
squeegee gaps.
[0142] 13) Combine results from both 11 and 12 to determine the
trending rate per sheet printing at 536. Ink thickness trending
rate is an indication of the ink thickness at different squeegee
gaps. This relationship may be translated from .mu.m/sheet to the
equivalent encoder count or value/sheet.
[0143] 14) Method for trend flattening is based on equivalent
encoder trending rate per consecutive sheet. The encoder value is
adjusted at 538 as the sheets are printed to compensate for the
increase in thickness of the ink as subsequent sheets are printed.
If this rate is greater than 1.0 encoder step then encode
adjustment for compensation is at the resolution of a single
encoder step. For example, if this rate is 2.5 encoder steps per
sheet then a first adjustment of 2 encoder steps for one sheet and
a next adjustment of 3 encoder steps for next sheet printing may be
done. If the rate is a fraction of the encoder steps then the
reciprocal of the fraction is the desired adjustment. For example,
if an equivalent trending rate is determined to be 0.25 encoder
steps/sheet then an adjustment of one encoder steps for every four
(1/0.25) consecutive printing may be made. The trending
compensation method may be implemented in software. A manual
adjustment is also possible. A software algorithm can be developed
to integrate all of the features herein.
[0144] Method D: FIG. 19 is a process flow diagram of a method for
screen mask design suitable for precision application with SIP
printing.
[0145] Screen mask design typically involves two design parameters,
one parameter is the wire diameter and the other is a thickness
related design parameter, called X here.
[0146] 1) Generate at 540 multiple screen printing masks with
different print thickness parameters. These may then be used to
perform tests to optimize the X value and the squeegee gap. In one
example, three screen masks are made with three different X values.
These masks are designated as Mask A, Mask B and Mask C. Note that
the same mesh wire and the same heater trace pattern are used in
these masks, only the X parameter has different values. These
values are estimated using a formula that may be theoretically or
empirically derived. The formula provides first order accuracy. In
a particular example, Mask B has X at X0, i.e. X=X0. Mask A has
X=X-, and Mask C has X=X+. Take a ratio as follows:
X-/X0=.about.80% and X0/X=.about.80%. Make all the masks available
at the same printing job described in Step 3. Mask B is a candidate
mask for the target design.
[0147] 2) Plan at 542 a DOE for squeegee set up. Squeegee set up
may be based on a parameter g0 that is empirically determined or
used as a starting estimate. A typical range may be from 50 .mu.m
to 200 .mu.m for precision screen printing. A five level DOE for
determining encoder compensation is created. This DOE is called
Encode DOE. An example is shown in FIG. 15.
[0148] 3) A total of 17 green sheets for example are printed at 544
with the SIP method described above. In the described example,
there are 3 trial prints with the use of Mask A, 3 trial prints
with the use of Mask C, and 3 trial prints with the use of B, and
all these trial print have the same squeegee setting at g0. The
encoder DOE only uses Mask B and in this DOE prints 2 trial prints
with squeegee levels at the other gap levels as shown in FIG. 15. 8
trial prints are printed in the same print job. Any other number of
levels or numbers of duplicate prints may be made depending on the
printer and its parameters.
[0149] 4) Measure at 546 the printed ink thickness with a reliable
method, either contact or non-contact methods.
[0150] 5) Convert at 548 the 17 green sheets into 17 green ESC
pucks, one puck for each printed sheet.
[0151] 6) All 17 pucks are sintered in the same sintering job. If
the sintering furnace capacity is less than 17 green pucks then the
g1 and g3 in the Encode DOE can be skipped. The same furnace and
the same job are used to eliminate variations in sintering that may
affect the measurements.
[0152] 7) Measure at 550 the individual resistivity of each puck
after sintering and any other fabrication processes required to
complete each puck, such as brazing.
[0153] 8) Construct at 552 a plot as shown in FIG. 14. All
correlation between the design parameter X, the ink thickness T,
and the resistivity .OMEGA. are all plotted. These plots are called
a knowledge-base for the screen mask design with SIP method. The
results may be used to determine parameters for a production print
screen at 554 and then an appropriate production screen is used
with the determined printer parameters and configuration at
516.
[0154] 9) If the design error is excessive, then design iteration
may be used. The choice for the X value for the next iteration may
be selected decided with the model or in another way. If the design
error is minor then the built-in encoder DOE can bridge the design
error with the encoder compensation. With this approach, screen
mask design can be completed with one sintering job or at most with
two. Screen mask development time and cost for precision
applications are greatly reduced.
[0155] FIG. 20 is an isometric view of an assembled electrostatic
chuck. A support shaft 212 supports a base plate 210 through an
isolator 216. A middle isolator plate 208 and an upper cooling
plate 206 are carried by the base plate. The top cooling plate 206
carries a dielectric puck 205 on the top surface of the upper
cooling plate. The puck has an upper circular platform 205 to
support a workpiece 204 and a lower concentric circular base 207 to
attach to the cooling plate 206. The upper platform has internal
electrodes to electrostatically attach the workpiece. The workpiece
may alternately be clamped, vacuumed or attached in another way.
There is an adhesive bond 218 between the puck 215 and the top
cooling plate 206 to hold the ceramic of the top plate to the metal
of the cooling plate. As described herein, heaters, electrodes, or
both may be formed in the puck using a printing process on green
sheets. The middle plate may perform cooling, gas flow, and other
functions, depending on the particular implementation.
[0156] The ESC is able to control the temperature of the workpiece
using resistive heaters in the puck, coolant fluid in the cooling
plate, or both. Electrical power, coolant, gases, etc. are supplied
to the coolant plate 206 and the puck 205 through the support
shaft. The ESC may also be manipulated and held in place using the
support shaft.
[0157] FIG. 21 is a partial cross sectional view of a plasma system
100 having a pedestal 128 according to embodiments described
herein. While a pedestal is shown here, the principles described
herein may be used on any of a variety of different workpiece
carriers including different types of chuck, carriers, and
pedestals. While a chamber pedestal is shown, the described
principles may also be applied to workpiece carriers that are used
outside of processing chambers. The pedestal 128 has an active
cooling system which allows for active control of the temperature
of a substrate positioned on the pedestal over a wide temperature
range while the substrate is subjected to numerous process and
chamber conditions. The plasma system 100 includes a processing
chamber body 102 having sidewalls 112 and a bottom wall 116
defining a processing region 120.
[0158] A pedestal, carrier, chuck or ESC 128 is disposed in the
processing region 120 through a passage 122 formed in the bottom
wall 116 in the system 100. The pedestal 128 is adapted to support
a substrate (not shown) on its upper surface. The substrate may be
any of a variety of different workpieces for the processing applied
by the chamber 100 made of any of a variety of different materials.
The pedestal 128 may optionally include heating elements (not
shown), for example resistive elements, to heat and control the
substrate temperature at a desired process temperature.
Alternatively, the pedestal 128 may be heated by a remote heating
element, such as a lamp assembly.
[0159] The pedestal 128 is coupled by a shaft 126 to a power outlet
or power box 103, which may include a drive system that controls
the elevation and movement of the pedestal 128 within the
processing region 120. The shaft 126 also contains electrical power
interfaces to provide electrical power to the pedestal 128. The
power box 103 also includes interfaces for electrical power and
temperature indicators, such as a thermocouple interface. The shaft
126 also includes a base assembly 129 adapted to detachably couple
to the power box 103. A circumferential ring 135 is shown above the
power box 103. In one embodiment, the circumferential ring 135 is a
shoulder adapted as a mechanical stop or land configured to provide
a mechanical interface between the base assembly 129 and the upper
surface of the power box 103.
[0160] A rod 130 is disposed through a passage 124 formed in the
bottom wall 116 and is used to activate substrate lift pins 161
disposed through the pedestal 128. The substrate lift pins 161 lift
the workpiece off the pedestal top surface to allow the workpiece
to be removed and taken in and out of the chamber, typically using
a robot (not shown) through a substrate transfer port 160.
[0161] A chamber lid 104 is coupled to a top portion of the chamber
body 102. The lid 104 accommodates one or more gas distribution
systems 108 coupled thereto. The gas distribution system 108
includes a gas inlet passage 140 which delivers reactant and
cleaning gases through a showerhead assembly 142 into the
processing region 120. The showerhead assembly 142 includes an
annular base plate 148 having a blocker plate 144 disposed
intermediate to a faceplate 146.
[0162] A radio frequency (RF) source 165 is coupled to the
showerhead assembly 142. The RF source 165 powers the showerhead
assembly 142 to facilitate generation of plasma between the
faceplate 146 of the showerhead assembly 142 and the heated
pedestal 128. In one embodiment, the RF source 165 may be a high
frequency radio frequency (HFRF) power source, such as a 13.56 MHz
RF generator. In another embodiment, RF source 165 may include a
HFRF power source and a low frequency radio frequency (LFRF) power
source, such as a 300 kHz RF generator. Alternatively, the RF
source may be coupled to other portions of the processing chamber
body 102, such as the pedestal 128, to facilitate plasma
generation. A dielectric isolator 158 is disposed between the lid
104 and showerhead assembly 142 to prevent conducting RF power to
the lid 104. A shadow ring 106 may be disposed on the periphery of
the pedestal 128 that engages the substrate at a desired elevation
of the pedestal 128.
[0163] Optionally, a cooling channel 147 is formed in the annular
base plate 148 of the gas distribution system 108 to cool the
annular base plate 148 during operation. A heat transfer fluid,
such as water, ethylene glycol, a gas, or the like, may be
circulated through the cooling channel 147 such that the base plate
148 is maintained at a predefined temperature.
[0164] A chamber liner assembly 127 is disposed within the
processing region 120 in very close proximity to the sidewalls 112
of the chamber body 102 to prevent exposure of the sidewalls 112 to
the processing environment within the processing region 120. The
liner assembly 127 includes a circumferential pumping cavity 125
that is coupled to a pumping system 164 configured to exhaust gases
and byproducts from the processing region 120 and control the
pressure within the processing region 120. A plurality of exhaust
ports 131 may be formed on the chamber liner assembly 127. The
exhaust ports 131 are configured to allow the flow of gases from
the processing region 120 to the circumferential pumping cavity 125
in a manner that promotes processing within the system 100.
[0165] A system controller 170 is coupled to a variety of different
systems to control a fabrication process in the chamber. The
controller 170 may include a temperature controller 175 to execute
temperature control algorithms (e.g., temperature feedback control)
and may be either software or hardware or a combination of both
software and hardware. The system controller 170 also includes a
central processing unit 172, memory 173 and input/output interface
174. The temperature controller receives a temperature reading 143
from a sensor (not shown) on the pedestal. The temperature sensor
may be proximate a coolant channel, proximate the wafer, or placed
in the dielectric material of the pedestal. The temperature
controller 175 uses the sensed temperature or temperatures to
output control signals affecting the rate of heat transfer between
the pedestal assembly 142 and a heat source and/or heat sink
external to the plasma chamber 105, such as a heat exchanger
177.
[0166] The system may also include a controlled heat transfer fluid
loop 141 with flow controlled based on the temperature feedback
loop. In the example embodiment, the temperature controller 175 is
coupled to a heat exchanger (HTX)/chiller 177. Heat transfer fluid
flows through a valve (not shown) at a rate controlled by the valve
through the heat transfer fluid loop 141. The valve may be
incorporate into the heat exchanger or into a pump inside or
outside of the heat exchanger to control the flow rate of the
thermal fluid. The heat transfer fluid flows through conduits in
the pedestal assembly 142 and then returns to the HTX 177. The
temperature of the heat transfer fluid is increased or decreased by
the HTX and then the fluid is returned through the loop back to the
pedestal assembly.
[0167] The HTX includes a heater 186 to heat the heat transfer
fluid and thereby heat the substrate. The heater may be formed
using resistive coils around a pipe within the heat exchanger or
with a heat exchanger in which a heated fluid conducts heat through
an exchanger to a conduit containing the thermal fluid. The HTX
also includes a cooler 188 which draws heat from the thermal fluid.
This may be done using a radiator to dump heat into the ambient air
or into a coolant fluid or in any of a variety of other ways. The
heater and the cooler may be combined so that a temperature
controlled fluid is first heated or cooled and then the heat of the
control fluid is exchanged with that of the thermal fluid in the
heat transfer fluid loop.
[0168] The valve (or other flow control devices) between the HTX
177 and fluid conduits in the pedestal assembly 142 may be
controlled by the temperature controller 175 to control a rate of
flow of the heat transfer fluid to the fluid loop. The temperature
controller 175, the temperature sensor, and the valve may be
combined in order to simplify construction and operation. In
embodiments, the heat exchanger senses the temperature of the heat
transfer fluid after it returns from the fluid conduit and either
heats or cools the heat transfer fluid based on the temperature of
the fluid and the desired temperature for the operational state of
the chamber 102.
[0169] Electric heaters (not shown) may also be used in the ESC to
apply heat to the workpiece assembly. The electric heaters,
typically in the form of resistive elements are coupled to a power
supply 179 that is controlled by the temperature control system 175
to energize the heater elements to obtain a desired
temperature.
[0170] The heat transfer fluid may be a liquid, such as, but not
limited to deionized water/ethylene glycol, a fluorinated coolant
such as Fluorinert.RTM. from 3M or Galden.RTM. from Solvay Solexis,
Inc. or any other suitable dielectric fluid such as those
containing perfluorinated inert polyethers. While the present
description describes the pedestal in the context of a PECVD
processing chamber, the pedestal described herein may be used in a
variety of different chambers and for a variety of different
processes.
[0171] A backside gas source 178 such as a pressurized gas supply
or a pump and gas reservoir are coupled to the pedestal assembly
142 through a mass flow meter 185 or other type of valve. The
backside gas may be helium, argon, or any gas that provides heat
convection between the wafer and the puck without affecting the
processes of the chamber. The gas source pumps gas through a gas
outlet of the pedestal assembly described in more detail below to
the back side of the wafer under the control of the system
controller 170 to which the system is connected.
[0172] The processing system 100 may also include other systems,
not specifically shown in FIG. 21, such as plasma sources, vacuum
pump systems, access doors, micromachining, laser systems, and
automated handling systems, inter alia. The illustrated chamber is
provided as an example and any of a variety of other chambers may
be used with the present invention, depending on the nature of the
workpiece and desired processes. The described pedestal and thermal
fluid control system may be adapted for use with different physical
chambers and processes.
[0173] As used in the description of the invention and the appended
claims, the singular forms "a", "an" and "the" are intended to
include the plural forms as well, unless the context clearly
indicates otherwise. It will also be understood that the term
"and/or" as used herein refers to and encompasses any and all
possible combinations of one or more of the associated listed
items.
[0174] The terms "coupled" and "connected," along with their
derivatives, may be used herein to describe functional or
structural relationships between components. It should be
understood that these terms are not intended as synonyms for each
other. Rather, in particular embodiments, "connected" may be used
to indicate that two or more elements are in direct physical,
optical, or electrical contact with each other. "Coupled" my be
used to indicate that two or more elements are in either direct or
indirect (with other intervening elements between them) physical,
optical, or electrical contact with each other, and/or that the two
or more elements co-operate or interact with each other (e.g., as
in a cause an effect relationship).
[0175] The terms "over," "under," "between," and "on" as used
herein refer to a relative position of one component or material
layer with respect to other components or layers where such
physical relationships are noteworthy. For example in the context
of material layers, one layer disposed over or under another layer
may be directly in contact with the other layer or may have one or
more intervening layers. Moreover, one layer disposed between two
layers may be directly in contact with the two layers or may have
one or more intervening layers. In contrast, a first layer "on" a
second layer is in direct contact with that second layer. Similar
distinctions are to be made in the context of component
assemblies.
[0176] It is to be understood that the above description is
intended to be illustrative, and not restrictive. For example,
while flow diagrams in the figures show a particular order of
operations performed by certain embodiments of the invention, it
should be understood that such order is not required (e.g.,
alternative embodiments may perform the operations in a different
order, combine certain operations, overlap certain operations,
etc.). Furthermore, many other embodiments will be apparent to
those of skill in the art upon reading and understanding the above
description. Although the present invention has been described with
reference to specific exemplary embodiments, it will be recognized
that the invention is not limited to the embodiments described, but
can be practiced with modification and alteration within the spirit
and scope of the appended claims. The scope of the invention
should, therefore, be determined with reference to the appended
claims, along with the full scope of equivalents to which such
claims are entitled.
* * * * *