U.S. patent application number 13/652220 was filed with the patent office on 2014-04-17 for microchip charge patterning.
This patent application is currently assigned to PALO ALTO RESEARCH CENTER INCORPORATED. The applicant listed for this patent is PALO ALTO RESEARCH CENTER INCORPORATED. Invention is credited to Eugene M. Chow, Bing R. Hsieh, JengPing Lu, Armin R. Volkel, Gregory L. Whiting.
Application Number | 20140106512 13/652220 |
Document ID | / |
Family ID | 49328425 |
Filed Date | 2014-04-17 |
United States Patent
Application |
20140106512 |
Kind Code |
A1 |
Chow; Eugene M. ; et
al. |
April 17, 2014 |
MICROCHIP CHARGE PATTERNING
Abstract
A method of forming a charge pattern on a microchip includes
depositing a material on the surface of the microchip, and using an
external device to develop charge in the material.
Inventors: |
Chow; Eugene M.; (Fremont,
CA) ; Lu; JengPing; (Fremont, CA) ; Volkel;
Armin R.; (Mountain View, CA) ; Hsieh; Bing R.;
(Pleasanton, CA) ; Whiting; Gregory L.; (Mountain
View, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
PALO ALTO RESEARCH CENTER INCORPORATED |
Palo Alto |
CA |
US |
|
|
Assignee: |
PALO ALTO RESEARCH CENTER
INCORPORATED
Palo Alto
CA
|
Family ID: |
49328425 |
Appl. No.: |
13/652220 |
Filed: |
October 15, 2012 |
Current U.S.
Class: |
438/127 ;
257/E21.502 |
Current CPC
Class: |
H01L 2224/95145
20130101; H01L 24/95 20130101; H01L 2223/5448 20130101; H01L
2223/5442 20130101; H01L 2924/10253 20130101; H01L 23/544 20130101;
G03G 5/02 20130101; H01L 2223/54426 20130101; H01L 2924/10329
20130101; H01L 2224/95085 20130101; H01L 2223/54433 20130101 |
Class at
Publication: |
438/127 ;
257/E21.502 |
International
Class: |
H01L 21/56 20060101
H01L021/56 |
Claims
1. A method of forming a charge pattern on a microchip, comprising:
depositing a material on the surface of the microchip; using an
external device to develop charge in the material; and singulating
the wafer into microchips after charging.
2. The method of claim 1, wherein using an external device to
develop the charge comprises charging the material with one of
either a corotron or a scorotron.
3. The method of claim 1, wherein depositing the material comprises
depositing a photoconductor.
4. The method of claim 1, wherein depositing the material comprises
laminating a dry film photoresist onto a wafer and exposing the dry
film photoresist to ultraviolet light, and developing the charge
comprises charging the exposed photoresist with a scorotron.
5. The method of claim 4, wherein exposing the dry film comprises
applying a stencil mask to the dry film resist to expose a portion
of a low conductivity region and applying a first charge with a
scorotron.
6. The method of claim 4, further comprising re-exposing the dry
film resist with a second charge with a scorotron.
7. (canceled)
8. The method of claim 1, wherein the depositing of the material
comprises depositing one of a polymer, an inorganic material or a
mixture of an inorganic and a polymer.
9. The method of claim 8, wherein developing the charge comprises
tribo-charging.
Description
BACKGROUND
[0001] Systems exist that assemble microchips automatically based
upon some sort of encoding such as electrostatic or magnetic
coding. The system uses the encoding to identify and position the
microchips as part of the assembly process.
[0002] Examples of these systems can be found in U.S. Pat. No.
7,861,405, and its related cases, US Patent Publications
20100192365, 20100186221, and 20100186222, owned by the assignee of
this application. Another example is shown in U.S. Pat. No.
7,332,361, that teaches charge-encoded elements having basic or
acidic surfaces capable of carrying charge in non-polar liquids
with charge control agents. Examples include two-particle
electrophoretic ink, liquid toner, inorganic oxides and polymers.
Standard photolithography or ink-jet technology can be used to
pattern these materials to form charge-encoded elements. All of
these references are incorporated by reference here. The system
uses a charge or magnetic polarity on the chip to sort and position
the microchips.
[0003] These references make general mention of possible methods of
how chips have the charge or polarity, but give no details. For
example, issues can arise with the deposition of the charge or
polarity. Currently, no current technique exists to deposit a
charge pattern on isolated microchips. One approach has charged one
end of a nanowire, another has charged up one side of a symmetric
microchip, but no work appears to be done on isolated microchips or
charge patterning.
[0004] The fabrication process should be compatible with existing
devices on the chips. In addition, the process should not increase
the manufacturing costs, but still allow the patterning on a
scalable level between larger areas and small features. In order to
provide a flexible system, the system should allow for varying
magnitudes of charge density, and ideally but not necessarily, both
positive and negative polarity, for multiple levels of chip control
and identification. The charge patterns should have good stability
to allow long shelf life of the patterned devices.
[0005] Another issue with patterning may arise with the chips being
attracted to each other. They may gather together or conglomerate
based upon their respective charges. The density of the chips needs
to remain low enough the chips do not exchange charge by contact
with each other.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 show an embodiment of an overall method of forming
charge patterns on microchips.
[0007] FIG. 2 shows an embodiment of a method of forming charge
patterns on a microchip.
[0008] FIG. 3 shows an embodiment of a method of printing charge
patterns on a microchip.
[0009] FIGS. 4-7 show an embodiment of a method of
photolithographically forming charge patterns on a microchip.
[0010] FIGS. 8-10 show an embodiment of a method of forming a
charge pattern using a scorotron.
[0011] FIGS. 11-13 show an embodiment of a method of forming a
bipolar charge template.
[0012] FIGS. 12-16 show an alternative embodiment of a method of
forming a bipolar charge template.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0013] FIG. 1 shows an overall embodiment of a method of forming
charge patterns on a microchip. At 11, the microchips are
fabricated on a substrate, such as silicon, gallium arsenide,
complementary metal oxide semiconductor (CMOS) etc. The process
then deposits materials on the microchips to enable charging at 13.
In one approach, shown in more detail in FIGS. 2-7, the microchips
are then submersed in a fluid that causes charge to develop on the
materials deposited. In another approach, shown in more detail in
FIGS. 8-16, the materials on the microchips are charged using an
external device. The end result is microchips with charge patterns
on their surfaces in 19.
[0014] FIG. 2 shows an embodiment of a method of forming charge
patterns on a microchip. The process will more than likely begin at
the wafer level at 10, after manufacture of the individual
microchips on the wafer. This allows the process of charge
patterning to occur in a more mass-produced manner, using
techniques compatible with chip fabrication processes. However, no
limitation is intended by this discussion and none should be
implied. The individual chips can be patterned using the same
techniques after singulation from the wafer.
[0015] Using manufacturing techniques compatible with chip
processing, the manufactured microchip 12 has a shield 14 to
protect the circuitry on the chip. The shield has an insulator 16.
The insulator allows charge or material patterns deposited on the
surface to avoid interaction with the circuitry on the microchip.
The pattern ABBAB may represent different charges, such as +--+-,
or a pattern of materials into which charge will be developed.
Through the techniques discussed in more detail further, the charge
pattern may consist of alternating regions of differing charge
magnitude and/or polarity. The embodiment in this portion of the
discussion has the patterns being charge.
[0016] Once singulated, the microchips can be placed into a fluid
to create an `ink` bottle 22 or other dispenser. The fluid may
contain other additives such as a charge control agent. The charge
control agent may either allow the charge to remain stable on the
surface of the chips 12, or may cause the charge to develop on the
surface of the wafer. The charge generation may take the form of
depositing a material, and developing a charge in the material
thorough the interaction of the charge patterning material with the
fluid component of the ink.
[0017] One approach uses deposition of a thin-film of the charge
patterning material using solution processing techniques such as
spin-coating, printing, dip-coating or self-assembly, or vapor
deposition techniques such as plasma enhanced chemical vapor
deposition (PECVD) or atomic layer deposition (ALD), followed by
immersion in solution after deposition of the film. Examples of
materials that could be deposited by solution or vapor techniques
include polymers such as polyethylene, polystyrene,
polymethylmethacrylate, and parylene and polyvinylalcohol, as well
as cationic and anionic polyelectrolytes such as
polystyrenesulfonic acid, polyallylamine, polyacrylic acid, and
poly(diallyldimethylammonium chloride). Other examples include
organometallic salts such as zinc stearate or aluminum stearate as
well as oxides, such as silica, alumina or titania. In addition
materials which foam self-assembled monolayers such as
octadecyltrichlorosilane, phenethyltrichlorosilane,
hexamethyldisilazane, allyltrimethoxysilane or
perfluorooctyltrichlorosilane may also be used.
[0018] The charge patterning material may not be a pure material
but rather a blend of one or more materials, possibly to enhance
charge generating properties, improve processing performance, or
impart new functionality to the film such as making it light
sensitive. For materials deposited from solution, they would likely
be first dissolved in a solvent such as toluene, hexane, water,
isopropanol, or tetrahydrofuran to enable solution processing. An
example process may involve spin coating the material onto the
surface of the microchip, patterning the material either using
light directly if a light-sensitive formulation of the
charge-patterning material is used, or in a separate step through
photolithographic/etching cycles, and immersing the chip into
solution where free charges are formed through interaction between
the fluid and the material.
[0019] In FIG. 4, a first polymer is spun onto the insulator 16 and
photolithographically defined in FIG. 5, exposing a portion of the
insulator 16. A second polymer 42 is then spun on or otherwise
deposited on the first polymer and the exposed insulator in FIG. 6.
The second polymer is then patterned to define a region separate
from the first region, typically with a region of the insulator.
The two different polymers then retain different charges, or
magnitudes of charge to form a charge pattern. In addition to the
use of two solution processed polymers, other embodiments may use a
combination of a solution processed material to generate one
polarity/magnitude of charge and a vapor deposited material to
generate another polarity/magnitude of charge, other embodiments
could use two different vapor deposited materials.
[0020] If immersed in a polar liquid, such as water, most surfaces
become charged, as some of the surface molecules dissociate, Charge
tends to be more negative or positive depending on the chemical
composition of the surface. Typical functional groups that develop
a negative surface change include sulfonic acids, phosphonic acids,
and carboxylic acids amongst others. Typical functional groups that
develop positive surface charges include amines and imidazoles,
amongst others. The range of Coulomb interaction of the charged
microchips is controlled by the ionic strength of the solution, but
is typically rather short, in the range of 1 to 10 micrometers due
to the high ion content.
[0021] In this embodiment the use of non-polar fluids is desired
however, since such Coulomb interactions between charged entities
are felt over much larger length scales, in the range of 10-100
micrometers. Examples of non-polar fluids include isoparaffinic
liquids such as the isopar series of fluids, and other hydrocarbon
liquids such as dodecane. In non-polar liquids charge control
agents, typically amphiphilic surfactant materials (both ionic and
non-ionic), such as phosphatidylcholine (lecithin), sorbitan
monooeleate (span-80), aluminum-di-tert-butyl salicylate (ALOHOS),
polyisobutylene succinimide (OLOA), or sodium dioctylsulfosuccinate
(AOT) amongst others may need to be added to the liquid to assist
in developing charge.
[0022] If the surrounding liquid is air, charging of the surface
can be done through tribo-actions. For example; in Xerography, the
toner particles are charged by contacting specifically designed
developer particles. The charge patterning material has to be
selected such that it charges in specific ways when contacted with
the developer material. The density of the chips should stay low
enough to control charge exchange between microchips accidentally
hitting each other.
[0023] In another approach, shown in FIG. 3, an ink-jet head 30 can
deposit the charge-patterning material. Candidate material may
include waxes, polymers, such as polyelectrolytes, or blends of
materials amongst others. After deposition of the charge patterning
material, as in previous descriptions the chips would be singulated
and immersed in a fluid where free charges would be generated.
[0024] In another approach, a self-assembled monolayer can be used
along with another material, such as an oxide, to create charged
regions on the chip. This could be accomplished, for example, by
first depositing the oxide, then depositing the self-assembled
monolayer having the desired functionality over the oxide. Using
photolithography and etching this self-assembled monolayer could
then be patterned revealing the oxide underneath. In another
approach, the oxide could be deposited followed be patterning of a
sacrificial blocking material (such as photoresist), deposition of
the self-assembled monolayer could then take place, followed by
removal of the sacrificial material, again revealing the underlying
oxide surface, creating an oxide, self-assembled monolayer pattern.
This second approach has the benefit in that the self-assembled
monolayer deposition and blocking material removal steps can be
carried out either at the wafer scale, or at the chiplet scale
after wafer singulation.
[0025] FIGS. 4-7 show processes of an embodiment in which
photolithographic patterned polymers, inorganic materials or a
mixture of the two are used. These materials can either be
tribo-charged or chemically charged using a charge control agent,
in a dielectric fluid to carry different polarities of charge.
Photolithographic defined charging of a dielectric with a corona
device is another approach, using dry film resist. Commercially
available dry film resists express substantial conductivity
difference between exposed ultraviolet and unexposed regions. FIGS.
4-7 show a process for photolithographic materials.
[0026] In a photoconductor coating embodiment, one may use
inorganic photoconductor materials such as amorphous silicon and
selenium, or single layer or multilayer organic photoconductors. If
such a photoconductor coating is used, it receives charge from a
corotron or scorotron to give the desired charge signs and
patterns. As the terms are used here, a corotron is a corona
charging device typically used in electrophotography/Xerography
that has a wire connected to a high voltage power source. In a
typical application, the wire generates an electric field that
charges up a photoreceptor in preparation for receiving charged
toner particles. A scorotron is a screen corotron.
[0027] Another embodiment uses photolithographic define charging of
a dielectric with a corona device. Commercially available dry film
resist expresses substantially conductivity difference between
ultraviolet exposed and unexposed regions. FIGS. 8-10 show one
embodiment of such a process. In FIG. 8, a dry film resist is
laminated onto the insulator layer 16 over the microchip or
microchip wafer 12. In FIG. 9, ultraviolet light exposes a portion
52 of the dry resist, creating high and low conductivity regions.
In FIG. 10, the wafer or microchip 12 is grounded by connection 54
and charged with a scorotron or corotron 56, to form charge
patterns based upon the previously exposed regions 50 and 52 of the
dry film resist. This forms a single charge template, where the
surface has one polarity of charge. One may verify the charge
patterns by spreading beads of known charge and imaging with a
camera, or measuring the field directly in air with a non-contact
electrostatic volt meter.
[0028] FIGS. 11-13 show an embodiment of a method of forming a dual
charge template. Ultraviolet light exposes a portion of the dry
film resist 50 to form a low conductivity region 52. Using a
stencil mask 62 on top of the dry film resist allows exposure of
only a portion of the low conductivity region formed by the UV
exposure. The scorotron 64 applies charge of a first polarity to a
portion of the low conductivity region not protected by the mask
62. The process shifts the mask 62 to cover the charged portion of
the low conductivity region. The scorotron then charges the
uncharged portion of the low conductivity region with a lower dose
of the opposite sign ions to create the other sign charge pattern.
In order to differentiate between the two scorotron processes, the
opposite sign charge pass of the scorotron is referred to as
66.
[0029] In an alternative embodiment, a bipolar or a dual charge
template can result from a dual exposure, shown in FIGS. 14-16.
FIG. 14 shows a first exposure forming a first low conductivity
region 52 on the dry film resist 50. This first region then
receives a first polarity charge from a scorotron 62. The dry film
resist then receives a second exposure of UV light to form a second
low conductivity region 70. This second region then receives a
charge of the opposite polarity from the scorotron 64.
[0030] In this manner, charge patterns can be generated on the
surface of microchips, either before or after singulation from a
wafer. The techniques used are compatible with semiconductor
fabrication processes, either using scorotron or corotron charging,
tribo-charging, or by application of charged materials. Free
charges may then be generated directly or through the interaction
of these materials with the surrounding fluid in the chip "ink."
The charge patterns contain information usable in automated systems
to sort, organize and arrange microchips into larger circuits.
[0031] It will be appreciated that several of the above-disclosed
and other features and functions, or alternatives thereof, may be
desirably combined into many other different systems or
applications. Also that various presently unforeseen or
unanticipated alternatives, modifications, variations, or
improvements therein may be subsequently made by those skilled in
the art which are also intended to be encompassed by the following
claims.
* * * * *