U.S. patent application number 12/470971 was filed with the patent office on 2010-06-10 for process for manufacturing contact elements for probe card assembles.
This patent application is currently assigned to FORMFACTOR, INC.. Invention is credited to Li Fan, John K. Gritters.
Application Number | 20100140793 12/470971 |
Document ID | / |
Family ID | 42230173 |
Filed Date | 2010-06-10 |
United States Patent
Application |
20100140793 |
Kind Code |
A1 |
Fan; Li ; et al. |
June 10, 2010 |
Process For Manufacturing Contact Elements For Probe Card
Assembles
Abstract
A process for making contact elements for a probe card assembly
includes steps of forming a first continuous trench in a substrate
along a first direction, and forming simultaneously a plurality of
tip structures adjacent one to another in the first continuous
trench in a second direction substantially normal to the first
direction, each of the tip structures being part of, or adapted to
be part of at least one corresponding contact element capable of
forming an electrical contact with a terminal of an electronic
device.
Inventors: |
Fan; Li; (San Ramon, CA)
; Gritters; John K.; (Livermore, CA) |
Correspondence
Address: |
N. KENNETH BURRASTON;KIRTON & MCCONKIE
P.O. BOX 45120
SALT LAKE CITY
UT
84145-0120
US
|
Assignee: |
FORMFACTOR, INC.
Livermore
CA
|
Family ID: |
42230173 |
Appl. No.: |
12/470971 |
Filed: |
May 22, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61120814 |
Dec 8, 2008 |
|
|
|
Current U.S.
Class: |
257/734 ; 216/11;
216/18; 257/E23.01 |
Current CPC
Class: |
Y10T 29/49002 20150115;
G01R 3/00 20130101; H01L 2924/0002 20130101; G01R 1/06711 20130101;
H01L 2924/0002 20130101; H01L 2924/00 20130101 |
Class at
Publication: |
257/734 ; 216/18;
216/11; 257/E23.01 |
International
Class: |
H01L 23/48 20060101
H01L023/48; C23F 1/00 20060101 C23F001/00 |
Claims
1. A process for making contact elements for a probe card assembly,
comprising: forming a first continuous trench in a substrate along
a first direction; forming simultaneously a plurality of tip
structures adjacent one to another in the first continuous trench
in a second direction substantially normal to the first direction,
each of the tip structures being part of, or adapted to be part of
at least one corresponding contact element capable of forming an
electrical contact with a terminal of an electronic device; and
forming one or more second continuous trenches on a bottom surface
of the first continuous trench for increasing a height for each of
the tip structures and modifying a tip formation line of the tip
structures defined by the first continuous trench.
2. The process of claim 1 wherein the second continuous trenches
provide at least one of the tip structures with a tip configured in
pyramid, mesa, cubic, ridge, or other suitable shapes.
3. A process for making contact elements for a probe card assembly,
comprising: forming a first continuous trench in a substrate along
a first direction; and forming simultaneously a plurality of tip
structures adjacent one to another in the first continuous trench
in a second direction substantially normal to the first direction,
each of the tip structures being part of, or adapted to be part of
at least one corresponding contact element capable of forming an
electrical contact with a terminal of an electronic device, wherein
at least one of the tip structures is formed along one side of the
first continuous trench without reaching an opposite side thereof
in the second direction.
4. The process of claim 3 wherein the at least one of the tip
structures is formed by using a positive photoresist material or a
buried anti-reflective coating in a lithographic process.
5. The process of claim 3 wherein at least one of the tip
structures is arranged on one side of the first continuous trench
in alignment with another of the tip structures on an opposite side
of the first continuous trench.
6. The process of claim 3 wherein at least one of the tip
structures is arranged on one side of the first continuous trench
in alignment with a dummy structure on an opposite side of the
first continuous trench.
7. A process for making contact elements for a probe card assembly,
comprising: forming a first continuous trench in a substrate along
a first direction; and forming simultaneously a plurality of tip
structures adjacent one to another in the first continuous trench
in a second direction substantially normal to the first direction,
each of the tip structures being part of, or adapted to be part of
at least one corresponding contact element capable of forming an
electrical contact with a terminal of an electronic device, wherein
at least one of the tip structures is formed along one side of the
first continuous trench, reaching but not stretching over an
opposite side thereof, in the second direction.
8. A process for making contact elements for a probe card assembly,
comprising: forming a first continuous trench in a substrate along
a first direction; and forming simultaneously a plurality of tip
structures adjacent one to another in the first continuous trench
in a second direction substantially normal to the first direction,
each of the tip structures being part of, or adapted to be part of
at least one corresponding contact element capable of forming an
electrical contact with a terminal of an electronic device, wherein
each of the beams has a first portion immediately adjacent to its
corresponding tip structure and a second portion away from its
corresponding tip structure.
9. The process of clam 8 wherein each of the tip structures is
attached to at least two beams extending therefrom in different
directions.
10. The process of claim 9 further comprising forming at least two
posts attached to the at least two beams, respectively.
11. The process of claim 8 wherein each of the beams comprises
palladium, cobalt, nickel, cobalt, gold, rhodium and any
combination thereof.
12. A tested die produced by a probe card assembly having contact
elements made by a process comprising: forming a first continuous
trench in a substrate along a first direction; forming a
photoresist layer over the first continuous trench using a
photomask shielding at least one end of the first continuous trench
from being exposed to light during the lithographic process; and
depositing conductive materials in openings of the photoresist
layer for forming simultaneously a plurality of tip structures
adjacent one to another in the first continuous trench in a second
direction substantially normal to the first direction, each of the
tip structures being part of, or adapted to be part of at least one
corresponding contact element capable of forming an electrical
contact with a terminal of an electronic device.
13. The tested die of claim 12 wherein the forming a first
continuous trench comprises performing an etching process to
provide sidewalls of the first continuous trench with a
predetermined slope.
14. The tested die of claim 12 wherein the tip structures have a
depth to width ratio ranging approximately from 1 to 15.
15. The tested die of claim 12 further comprising forming one or
more second continuous trenches on a bottom surface of the first
continuous trench for increasing a height for each of the tip
structures and modifying a tip formation line of the tip structures
defined by the first continuous trench.
16. The tested die of claim 15 wherein the second continuous
trenches provide at least one of the tip structures with a tip
configured in pyramid, mesa, cubic, ridge, or other suitable
shapes.
17. The tested die of claim 12 wherein at least one of the tip
structures is formed along one side of the first continuous trench
without reaching an opposite side thereof in the second
direction.
18. The tested die of claim 17 wherein the at least one of the tip
structures is formed by using a positive photoresist material or a
buried anti-reflective coating in a lithographic process.
19. The tested die of claim 17 wherein at least one of the tip
structures is arranged on one side of the first continuous trench
in alignment with another of the tip structures on an opposite side
of the first continuous trench.
20. The tested die of claim 17 wherein at least one of the tip
structures is arranged on one side of the first continuous trench
in alignment with a dummy structure on an opposite side of the
first continuous trench.
21. The tested die of claim 12 wherein at least one of the tip
structures is formed along one side of the first continuous trench,
reaching but not stretching over an opposite side thereof, in the
second direction.
22. The tested die of claim 12 further comprising forming
simultaneously a plurality of beams attached to their corresponding
tip structures.
23. The tested die of claim 22 wherein each of the beams has a
first portion immediately adjacent to its corresponding tip
structure and a second portion away from its corresponding tip
structure.
24. The tested die of clam 23 wherein each of the tip structures is
attached to at least two beams extending therefrom in opposite
directions.
25. The tested die of claim 24 further comprising forming at least
two posts attached to the at least two beams, respectively.
26. The tested die of claim 20 wherein each of the beams comprises
palladium, cobalt, nickel, cobalt, gold, rhodium and any
combination thereof.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This application is a non-provisional of U.S. Provisional
Patent Application 61/120,814 filed Dec. 8, 2008 and entitled
"Process For Manufacturing Contact Elements For Probe Card
Assemblies."
BACKGROUND
[0002] A probe card assembly is an apparatus typically used in
testing an electronic device. The probe card assembly can function
as an interface between a tester and the electronic device under
test (DUT), which in some examples can be an integrated circuit
either on a wafer or in singulated form. The tester and the probe
card assembly can be electrically connected by a number of links.
The probe card assembly can be electrically connected to the DUT
via electrical contacts between contact elements, which can be
customarily referred to as probes, of the assembly and terminals of
the DUT. The tester can generate test signals to and receive test
result signals from the DUT via the electrical path therebetween,
and determine whether the DUT is defective based on the received
test result signals.
[0003] Ideally, the contact elements (or probes) of the probe card
assembly can have characteristics that are resilient such that the
contact elements (or probes) exhibit primarily elastic behavior in
response to an applied load or contact force. The contact elements
can be typically arranged in an array with their corresponding tip
structures forming a contour or plane to be matched with a contour
or plane of the DUT. Because the contour of the tip structures of
the contact elements may not perfectly match the contour of the
DUT, some of the tip structures would contact the DUT earlier than
others when the probe card assembly and DUT move toward each other
relatively. The resilient characteristic of the contact elements
enables the contour of the tip structures to match the contour of
the DUT under pressure created by moving the probe card assembly
and the DUT against each other. The contact elements can be
resilient, so that they would not be crushed when the probe card
assembly and the DUT are pushed against each other, and could
return or return substantially to their initial positions when the
DUT is moved away from the assembly. It is desired that the contact
elements be reliable so that they can form electrical contacts
repetitively in order to test a large number of DUTs.
[0004] As semiconductor processing technology advances, electronic
devices become increasingly compact. Accordingly, the contact
elements of the probe card assembly need to be made in an
increasingly small pitch. Thus, technology innovation in the probe
card industry is desired to meet design challenges in making
contact elements for those ever shrinking electronic devices.
SUMMARY
[0005] Embodiments of the invention are related to a process for
making contact elements for a probe card assembly. In some
embodiments, the process can include forming a first continuous
trench in a substrate along a first direction, and forming
simultaneously a plurality of tip structures adjacent one to
another in the first continuous trench in a second direction
substantially normal to the first direction, each of the tip
structures being part of, or adapted to be part of at least one
corresponding contact element capable of forming an electrical
contact with a terminal of an electronic device.
[0006] Embodiments of the invention are related to a tested die
produced by a probe card assembly having contact elements made by a
process. In some embodiments of the invention, the process includes
forming a first continuous trench in a substrate along a first
direction, forming a photoresist layer over the first continuous
trench using a photomask shielding at least one end of the first
continuous trench from being exposed to light during the
lithographic process, and depositing conductive materials in
openings of the photoresist layer for forming simultaneously a
plurality of tip structures adjacent one to another in the first
continuous trench in a second direction substantially normal to the
first direction, each of the tip structures being part of, or
adapted to be part of at least one corresponding contact element
capable of forming an electrical contact with a terminal of an
electronic device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIGS. 1-9 illustrate a process for making contact elements
in accordance with some embodiments of the invention.
[0008] FIGS. 10-17 illustrate various contact elements made by
processes in accordance with some embodiments of the invention.
[0009] FIG. 18 illustrates an exemplary probe card assembly in
which the contact elements made by the processes in accordance with
some embodiments of the invention can be implemented.
[0010] FIG. 19 illustrates an exemplary system where a probe card
assembly can be implemented with the contact elements made by the
processes in accordance with some embodiments of the invention.
[0011] Where possible, identical reference numbers are used herein
to designate elements that are common to the figures. The images
used in the drawings may be simplified for illustrative purposes
and are not necessarily depicted to scale.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0012] This specification describes exemplary embodiments and
applications of the invention. The invention, however, is not
limited to these exemplary embodiments and applications or to the
manner in which the exemplary embodiments and applications operate
or are described herein. Moreover, the figures can show simplified
or partial views, and the dimensions of elements in the figures can
be exaggerated or otherwise not in proportion for clarity. In
addition, as the terms "on" and "attached to" are used herein, one
object (e.g., a material, a layer, a substrate, etc.) can be "on"
or "attached to" another object regardless of whether the one
object is directly on or attached to the other object or there are
one or more intervening objects between the one object and the
other object. Also, directions (e.g., above, below, top, bottom,
side, up, down, over, under, "x," "y," "z," etc.), if provided, are
relative and provided solely by way of example and for ease of
illustration and discussion and not by way of limitation. In
addition, where reference is made to a list of elements (e.g.,
elements a, b, c), such reference is intended to include any one of
the listed elements by itself, any combination of less than all of
the listed elements, and/or a combination of all of the listed
elements.
[0013] Embodiments of the invention can relate to processes for
making a plurality of contact elements having their tip structures
simultaneously formed in a continuous trench of a substrate. The
continuous trench can be configured to provide the contact elements
with tip structures capable of forming pressure contacts with
terminals or bond pads of an electronic device. The processes can
prevent undesired cross-link of a photoresist material during a
lithographic step when forming the contact elements, and enable
them to be made in a fine pitch, which is important for testing
electronic devices of continuously shrinking scales.
[0014] FIGS. 1-9 illustrate a process for making contact elements
for probe card assemblies in accordance with some embodiments of
the invention. FIG. 1 shows a step in the process where a
continuous trench 102 is formed in a substrate 100. The substrate
100 can comprise a semiconductor material, such as silicon, or any
other materials suitable to serve as a sacrificial layer where a
continuous trench can be formed for constructing contact elements
thereon. A first photoresist layer 104 can be formed on the
substrate 100 through a lithographic process. The first photoresist
layer 104 can have an opening 106 defining the continuous trench
102. An etching process can be performed to remove the portion of
the substrate 100 exposed by the opening 106 to from the continuous
trench 102. In some embodiments of the invention, a
crystallographic etching can be performed to provide sidewalls 108
of the continuous trench 102 with a desired slope. An etchant, such
as KOH, can be used in the crystallographic etching process. Due to
etch rate selectivity among crystal planes of the substrate 100,
the sidewalls 108 can be controlled in a desired range of angle and
profile, which, as will become clear in following paragraphs, can
be advantageous in making the contact elements. Alternatively, in
some other embodiments of the invention, milling, dry etching, wet
etching, or a combination thereof can be used to form the
continuous trench 102. Process settings and conditions of these
techniques can be controlled to provide the continuous trench 102
with the sidewalls 108 in a desired range of angle and profile.
Non-limiting examples of the settings and conditions can include
temperature, choices of etchant, flow rate of etchant, electrical
or magnetic fields applied, etc. It is noted that the etching
technique used can have characteristics of isotropic etching,
anisotropic etching, or both.
[0015] It is noted that although only one continuous trench 102 in
the substrate 100 is illustrated, the number thereof can be more
than one. Accordingly, the first photoresist layer 104 can have
more than one opening in order to define more than one continuous
trench.
[0016] After the formation of the continuous trench 102, the first
photoresist layer 104 can be removed, and a seed layer 110 can be
formed on and/or over the substrate 100, as shown in FIG. 2. In
some embodiments of the invention, the seed layer 110 can comprise
aluminum, copper, titanium, other suitable materials, and a
combination thereof.
[0017] A second photoresist layer 112 can be formed over the seed
layer 110 as shown in FIGS. 3 and 4 where FIG. 3 is a
cross-sectional view of the structure along line A-A in FIG. 4. The
second photoresist layer 112 can be disposed on the seed layer 110
through techniques such as spin coating, spray coating,
electrophoretical deposition, or other suitable techniques. A
photomask 114 having one or more predetermined openings 116 can be
placed above the second photoresist layer 112 during a lithographic
process. In some embodiments of the invention, the second
photoresist layer 112 can be made of a negative photoresist
material, which hardens when exposed to light. During the
lithographic process, portions 112a of the second photoresist layer
112 cross link and harden when they are exposed to light through
the openings 116 of the photomask 114. Once the exposed portions
112a of the second photoresist layer 112 become hardened, the
unexposed regions of the photoresist layer 112 can be removed
through developing processes. In some embodiments of the invention,
the second photoresist layer 112 can be made of positive
photoresist materials, which soften when exposed to light. The
exposed positive photoresist materials can then be developed away
leaving the unexposed regions on the seed layer 110. It is noted
that although the photomask 114 is illustrated as having only three
openings 116 over the continuous trench 102, the number thereof can
be more or less than three.
[0018] The photomask 114 is designed to protect the second
photoresist layer 112 from undesired photo interference due to
sidewall deflections during the lithographic process. The photomask
114 can shield one or more ends of the continuous trench 102 in the
longitudinal direction, thereby preventing light from hitting
sidewalls 108 thereof and being deflected to blur the pattern
transferred from the photomask 114 to the second photoresist layer
112. This enables the exposed portions 112a of the second
photoresist layer 114 to harden in a desired manner, thereby
creating a desired pattern of openings during the lithographic
process.
[0019] FIG. 5 illustrates a cross-sectional view of the substrate
100 and the remaining portions 112a of the second photoresist layer
112 along a line A-A as shown in FIG. 4. One or more conductive
layers can be formed on the seed layer 110 by techniques, such as
electroplating or chemical vapor deposition. In some embodiments of
the invention, a first conductive layer 118, a second conductive
layer 120, and a third conductive layer 122 can be formed on the
seed layer 110 sequentially. The first, second, and third
conductive layers 118, 120 and 122 can comprise palladium, cobalt,
nickel, gold, rhodium, other metallic materials, and/or any
combination thereof. Specifically, the first layer 118 can comprise
palladium-cobalt, and their alloys, the second layer 120
nickel-cobalt, and their alloys, and the third layer 122 gold and
its alloys. The first layer 118 can be made of a material suitable
for forming an electrical contact with a terminal or bond pad of a
DUT, as well as a material suitable for resiliency. The second
layer 120 can be made of a material having spring characteristics
to provide desired resiliency for the entire structure of the
first, second and third layers 118, 120, and 122.
[0020] It is noted that although three conductive layers are
illustrated in FIG. 5, the number thereof can be more or less than
three. It is further noted that in some embodiments of the
invention, the seed layer 100 can be optional depending on the
sacrificial substrate used. For example, a metal sacrificial
substrate with machined or etched continuous trenches can serve as
an electroplated surface without a seed layer.
[0021] Conventionally, a single contact element is usually formed
in a single trench, and therefore cannot be placed in close
proximity with other contact elements since the trenches are
aniostropically tapered with a larger opening at the top than the
bottom. Thus, the pitch of the contact elements made by
conventional methods can be quite large. Moreover, the conventional
methods do not necessarily require a photomask that shields one or
more ends of a continuous trench for purposes of preventing
undesired cross-link of a photoresist material during a
lithographic process when forming the contact elements.
[0022] FIG. 6 illustrates a cross-sectional view of the substrate
100, on which a stack of seed layer 110, first conductive layer
118, second conductive layer 120, and third conductive layer 122
are constructed, along a line B-B as shown in FIG. 4. The
cross-sectional view in FIG. 6 shows a profile of a contact element
200 in the making. The contact element 200 can comprise a tip
structure 202 constructed upon the seed layer 110, and formed by
first conductive layer 118, second conductive layer 120, and third
conductive layer 122 in the continuous trench 102, and a beam
structure 204 constructed by the same layers extending from or
attached to the tip structure 202 along the surface of the
substrate 100 outside the continuous trench region.
[0023] As shown in the drawing, the sloped sidewalls 108 of the
continuous trench 102 can configure the tip structure 202 into a V
shape with a tapered tip (as shown at the bottom of the drawing)
suitable to form a pressure contact with a terminal or bond pad of
a DUT (not shown in the figure). This tapered tip can be
advantageous in applying a large amount of pressure to break a
possible oxide layer formed on the terminal or bond pad, thereby
lowering the resistance there between. In some embodiments of the
invention, the bottom surface 206 of the continuous trench 102,
which defines the contact area between the tip and the terminal or
bond pad of the DUT, can be made wider or narrower by way of design
choice in order to create various degrees of tip pressure the
structure 102 may apply. In some embodiments of the invention, the
tip structure 202 can extend over the entire continuous trench 102
in a transverse direction. In some other embodiments, the tip
structure 202 can be made in various lengths at the continuous
trench 102 without running over it entirely. Details of those
embodiments will be discussed in following paragraphs.
[0024] FIG. 7 illustrates a perspective view of a plurality of
contact elements 200 made simultaneously in the continuous trench
102 with the remaining portions 112a of the second photoresist
layer 112 omitted in order to better demonstrate how the process
according to embodiments of the invention is able to simultaneously
fabricate a plurality of tip structures 202 of the contact elements
200 in a fine pitch. For example, the space between two neighboring
tip structures 202 can range approximately from 20 to 100 .mu.m. As
shown in the drawing, each of the tip structures 202 can have a
width W much smaller than its depth D. In some embodiments of the
invention, the depth to width ratio can range approximately from 1
to 15, and in some embodiments, the ratio can be from approximately
10 to 15. In some embodiments of the invention, the tip structures
202 can be arranged in a pitch as fine as a lithographic process
allows. This enables a probe card assembly implemented with those
tip structures to test the DUTs having terminals in a fine pitch
layout. Moreover, the alignment of the tip structures formed along
the length of the trench can be extremely precise relative to each
other in a direction transverse to the trench in which they were
formed because the tip structures were formed in the same
continuous trench.
[0025] It is noted that although only two contact elements 200 with
their corresponding tip structures 202 in a continuous trench 102
are illustrated, the number thereof for a single continuous trench
can be more than two. It is also noted that although the contact
elements 200 are drawn as having an identical shape and length, in
some embodiments of the invention, their shapes and lengths can be
different. It is also noted that materials 203 deposited or plated
at two ends of the continuous trench 102 are formed as a result of
the photomask 114 that is configured to shield light from the ends
in order to prevent cross-link of the photoresist layer 112 during
a lithographic step shown in FIG. 7.
[0026] FIG. 8 illustrates a cross sectional view where a third
photoresist layer 210 having one or more predetermined openings is
formed over the beam structure 204 and the tip structure 202
through techniques such as spin coating, spray coating,
electrophoretical deposition, or other suitable techniques in
accordance with some embodiments of the invention. Conductive
materials can be deposited into the opening of the third
photoresist layer 210 to form a post 208 on the beam structure 204.
The beam structure 204 can include a first portion immediately
adjacent to its corresponding tip structure 202 and a second
portion away from its corresponding tip structure 202. The second
portion of the beam structure 204 can be wider than the first
portion, as shown in FIG. 7. The wider second portion of the beam
structure 204 allows for easy alignment between the post 208 and
the beam structure 204, thereby facilitating the formation of the
post 208 thereon. Thereafter, the remaining portion 112a of the
second photoresist layer 112 and the third photoresist layer 210,
and the substrate 100 can be removed using etch techniques to
un-mask the contact element 200 that includes the tip structure
202, the beam structure 204, and the post 208. Note that in some
embodiments, the second portion can be narrower than the first
portion.
[0027] FIG. 9 illustrates a perspective view of a plurality of
contact elements 200 made by utilizing a continuous trench in
accordance with some embodiments of the invention. Each of the
contact elements 200 can be resilient in forming an electrical
contact between its tip structure 202 and a terminal or bond pad of
a DUT (not shown in the figure). The beam structure 204 can deflect
when the tip structure 202 is pressed against the DUT, and return
or return substantially to its original position when it is moved
away from the DUT. Proper materials can be selected to improve the
reliability of the beam structure 204. For example, the beam
structure 204 can comprise materials, such as palladium, cobalt,
nickel, gold, rhodium, other metallic materials, and/or any
combination thereof. As such, the process according to embodiments
of the invention is able to make contact elements that are
resilient and/or reliable in a fine pitch. In some embodiments of
the invention, there can be more than one post 208 attached to each
tip structure 202. In some embodiments, there can be a space formed
in the beam structure 204 of each tip structure 202. A non-limiting
example of such contact elements can be found in U.S. patent
application Ser. No. 11/862172, entitled "Reduced Scrub Contact
Element" filed on Sep. 26, 2007. Furthermore, all or portions of
the tip structures 202 (for example, the "V" shaped portion)
relative to each other can be precisely aligned along a line
intersecting the tip structures 202 because they were formed in the
same continuous trench. Conventional processes for making contact
structures may differ from this because the individual trenches
into which the tips were made are not continuous (which may result,
for example, from mask position differences from one location to
another across the mask).
[0028] It is noted that although FIGS. 1-9 illustrate a process for
making the tip structures, beam structures, and posts in a sequence
of process steps, they can be made in separate processes in some
embodiments of the invention. For example, the tip structures can
be made in a continuous trench in a set of process steps, and then
separated from the continuous trench to become a "bucket" of loose
tip structures adapted to be attached to their corresponding beam
structures and/or posts in a separate set of process steps.
[0029] FIG. 10 illustrates a cross-sectional view of one of a
plurality of contact elements 301 simultaneously formed in a
continuous trench 306 in a substrate 302 by a process similar to
that described above in accordance with some embodiments of the
invention. The process can provide the contact element 301 with a
tip structure 300 extending along one side of the continuous trench
306 without reaching an opposite side thereof in a transverse
direction. Such tip structure 300 can shorten the length of the
contact element 301 in accommodation of a predetermined space
requirement.
[0030] In some embodiments of the invention, the tip structure 300
of the contact element 301 can be made by using a positive
photoresist material in a lithographic process. The lithographic
process can be controlled to select a desired photomask pattern and
exposure/development conditions to form a photoresist layer 307 on
one side of the trench 309. Since a positive photoresist material
remains if shielded away from light, the formation of the
photoresist layer 307 on one side of the trench 309 would not cause
undesired cross-linking of a photoresist material on the other side
thereof due to deflection of light from the sidewall of the trench
307.
[0031] In some embodiments of the invention, the tip structure 300
can be made by using a buried anti-reflective coating (BARC) (not
shown in the figure) on one side of the trench 307 during a
lithographic process. When exposed to light, BARC can absorb it and
reflect no or a negligible amount of light. When forming the tip
structure 300, BARC can be disposed underneath an undeveloped
photoresist material on one side of the trench 307. During a
development step, the BARC can eliminate undesired reflection of
light between the sidewalls of the trench 309, and therefore
prevent undesired cross-link of the photoresist material from
occurring. This allows for the tip structure 300 to be formed on
only one side of the trench 309. Note that BARC is often used
together with a negative photoresist material. However, in some
instances, it may be used together with a positive photoresist
material.
[0032] FIG. 11A illustrates a cross-sectional view of one of many
contact elements 404 simultaneously formed in a continuous trench
406 in a substrate 402 by a process similar to that described above
in accordance with some embodiments of the invention. The process
can provide the contact element 404 with a tip structure 400
extending along one side of the continuous trench 406, reaching but
not stretching over an opposite side thereof. Such tip structure
400 can be used to adjust the length of the contact element 404 in
accommodation of a predetermined space requirement. In some
embodiments of the invention, surfaces 402a and 402b at both sides
of the continuous trench 406 can be made at the same height as
shown in the figure. In some embodiments of the invention, the
surface 402b at one side of the continuous trench 406 can be made
lower or higher than the surface 402a at the other side.
[0033] FIG. 11B illustrates a top view of a plurality of contact
elements 410 simultaneously formed in a continuous trench 412
having a corner 414 in accordance with some embodiments of the
invention. The contact elements 410a placed at the corner 414 can
have their tip structures shorter than the width D1 of the
continuous trench 412. For example, the contact elements 410a can
be similar to that shown in FIG. 11A. Thus, the corner 414 of the
continuous trench 412 can be utilized to build the contact elements
410, thereby providing flexibility in laying out the contact
elements, and increasing the spacing density of the contact
elements 410. In some embodiments of the invention, an outer part
of the corner 414 can be protected by a shield (not shown) to avoid
undesired cross-link of a photoresist material during a
lithographic process. As such, a material 416 can be incidentally
formed at part of the corner 414 simultaneously with the contact
elements 410 during a plating or depositing process as a result of
the shield being used in a preceding lithographic process. An end
of the contact element 410a can be configured to approximate the
profile of the continuous trench 412 at the inner part of the
corner 414. This can be advantageous in reducing undesired
cross-link of a photoresist material at the inner part 418 of the
corner 414 during a lithographic process. In some embodiments of
the invention, the end of the contact element 410a at the inner
part 418 of the corner 414 can have a square end or other
configurations. These configurations can be formed generally by a
process described above. Because the inner ends of the contact
elements 410a can be placed closely together, the risk of
cross-linking can be reduced to a manageable degree for the various
configurations.
[0034] FIG. 12 illustrates a top view of a plurality of tip
structures 500 simultaneously formed in a continuous trench 502 in
a direction substantially normal to a longitudinal direction of the
continuous trench 502 by a process similar to those described above
in accordance with some embodiments of the invention. Each of the
tip structures 500 can be arranged on one side of the continuous
trench in alignment with another of the tip structures 500 on an
opposite side of the continuous trench. In such arrangement, a tip
structure 500 on one side can function as a shield to prevent
another tip structure 500 on the other side from photo interference
during a lithographic process. As a result, undesired cross-link of
a photoresist material during the lithographic process can be
avoided. It is noted that materials at the ends of the continuous
trench 502 can be formed as a result of an anti-deflection shield
used in a lithographic process when constructing the contact
elements 500.
[0035] FIG. 13 illustrates a top view of a plurality of tip
structures 600 simultaneously formed in a continuous trench 602 in
a direction substantially normal to a longitudinal direction of the
continuous trench 602 by a process similar to those described above
in accordance with some embodiments of the invention. Each of the
tip structures 600 can be arranged on one side of the continuous
trench 602 in alignment with another of the tip structures 600 or a
"dummy" structure 604 on an opposite side of the continuous trench
602. A "dummy" structure refers to any structure formed in the
continuous trench 602 without any active functions, e.g., forming
an electrical contact with a terminal or bond pad of an electronic
device, other than matching a normally functioning contact element
600 on an opposite side of the continuous trench 602 in order to
prevent undesired cross-link during a lithographic process. In such
arrangement, a tip structure 600 or dummy structure 604 on one side
can function as a shield to prevent another tip structure 600 on
the other side from photo interference during a lithographic
process. It is noted that materials at the ends of the continuous
trench 602 can be formed as a result of an anti-deflection shield
used in a lithographic process when constructing the contact
elements 600.
[0036] FIG. 14A illustrates a top view of a plurality of tip
structures 700 simultaneously formed in a first continuous trench
702 in a direction substantially normal to a longitudinal direction
of the continuous trench 702 by a process in accordance with some
embodiments of the invention. One or more second trenches 704
depicted by dotted lines can be formed on the bottom surface of the
continuous trench 702. In some embodiments of the invention, the
second trenches 704 can be formed in alignment with each other by
lithographic and etching processes.
[0037] FIG. 14B illustrates a perspective view of one of the tip
structures 700 removed from the continuous trench 702. The tip
structure 700 can comprise a tip 706 protruding from a surface
thereof. The tip 706 can be formed by conductive materials
deposited into the second trench 704. The tip 706 can take various
configurations depending on the shape of the second trenches 704.
For example, the tip 706 can have a pyramid or mesa shape where the
peak of the tip 706 is smaller than the base. In some other
embodiments of the invention, the tip can have a cubic shape such
as the tip 708 shown in FIG. 14C.
[0038] FIG. 15A illustrates a top view of a plurality of tip
structures 800 simultaneously formed in a first continuous trench
802 in a direction substantially normal to a longitudinal direction
of the first continuous trench 802 by a process in accordance with
some embodiments of the invention. At least one second continuous
trench 804 can be formed on the bottom surface of the first
continuous trench 802. Each of the tip structures 800 can be
disposed across the second continuous trench 804. In some
embodiments of the invention, there can be two or more second
continuous trenches 804 formed in the first continuous trench 802,
where each of the second continuous trenches 804 can be used to
form tips for one or more tip structures. FIG. 15B illustrates a
perspective view of one of the tip structures 800 removed from the
first and second continuous trenches 802 and 804 where the tip 806
has a ridge configured on an elevated surface of the tip structure
800. It is noted that although the second continuous trenches are
illustrated as having only one level in FIG. 4, multiple levels can
be employed to fabricate tip structures in a multi-staged
manner.
[0039] The tip, which may take various shapes as described above,
can apply a high pressure when forming an electrical contact with a
terminal or bond pad of a DUT. As discussed above, such pressure
contact can be advantageous, because it helps the tip structure to
break a possible oxide layer often formed on a terminal or bond pad
of a DUT, thereby lowering the resistance there between. The second
continuous trench formed in the first continuous trench can
increase the height of the tip structure. This in turn increases
the allowable travel distance of the tip structure when the contact
element is pressed again a DUT, thereby increasing the pressure
exerted by the tip structure of the contact element to the DUT.
Moreover, the second continuous trench can modify a tip formation
line of the tip structures defined by the first continuous trench,
thereby ensuring proper contacts to be formed between the tip
structures and their corresponding terminals or bond pads of the
DUT.
[0040] FIG. 16 illustrates a top view of a plurality of tip
structures 810 simultaneously formed in a first continuous trench
812 by a process in accordance with some embodiments of the
invention. One or more second trenches 814 depicted by dotted lines
can be formed on the bottom surface of the first continuous trench
812. In some embodiments of the invention, the second trenches 814
can be arranged in two or more rows. A number of dummy structures
816 can be employed to prevent cross-link during a lithographic
process. In some embodiments of the invention, ones of the second
trenches 814 can have an elongated shape extending across two or
more neighboring tip structures 810.
[0041] FIG. 17 illustrates a cross-sectional view of a contact
element 900 fabricated by a process in accordance with some
embodiments of the invention. The contact element 900 can include a
tip structure 902 to which two beams 904a and 904b are attached at
two sides thereof. Posts 906a and 906b are attached to the beams
904a and 904b, respectively. The beams 904a and 904b and the posts
906a and 906b can provide the tip structure 902 with double
suspensions that decrease the probe scrub ratio, stabilize the
spring during over travel to prevent buckling at fine pitch probing
requirements such as 20 um pitch probing layouts, thereby providing
reliable contacts with a DUT. For example, a conventional double
suspended contact element disclosed in U.S. Pat. No. 6,426,638,
entitled "Compliant Probe Apparatus," would have a larger probe
scrub ratio than the contact elements 900, as the conventional tip
structure is on the side of the double suspension beams, whereas
the tip structure 902 is directly underneath the beams 904a and
904b.
[0042] It is noted that the contact element 900 illustrated in the
drawing can be fabricated in a process where a plurality of tip
structures are made simultaneously in a continuous trench. Although
the tip structure 902 is shown to be supported by two beams, the
number thereof can be more than two in some embodiments of the
invention.
[0043] FIG. 18 shows a cross sectional view of an exemplary probe
card assembly 18, in which contact elements made by a process in
accordance with some embodiments of the invention can be
implemented. The probe card assembly 18 can be configured to
provide both electrical pathways and mechanical support for contact
elements 16 that will directly contact a DUT. The probe card
electrical pathways can be provided through a printed circuit board
(PCB) 30, an interposer 32, and a space transformer 34. Test data
can be provided through flexible cable connectors 24 typically
connected around the periphery of the PCB 30. Channel transmission
lines 40 can distribute signals from the connectors 24 horizontally
in the PCB 30 to contact pads on the PCB 30 to match the routing
pitch of pads on the space transformer 34. The interposer 32 can
include a substrate 42 with spring probe electrical contacts 44
disposed on both sides. The interposer 32 can electrically connect
individual pads 31 on the PCB 30 to pads forming a land grid array
(LGA) on the space transformer 34. Traces 46 in a substrate 45 of
the space transformer 34 can distribute or transform pitches of
connections from the LGA to spring contact elements 16 configured
in an array. The space transformer substrate 45 can be constructed
from either multi-layered ceramic or organic based laminates. The
space transformer substrate 45 with embedded circuitry, contact
elements and LGA can be referred to as a probe head.
[0044] Mechanical support for the electrical components can be
provided by a back plate 50, bracket (Probe Head Bracket) 52, frame
(Probe Head Stiffener Frame) 54, leaf springs 56, and leveling pins
62. The back plate 50 can be provided on one side of the PCB 30,
while the bracket 52 can be provided on the other side and attached
by screws 59. The leaf springs 56 can be attached by screws 58 to
the bracket 52. The leaf springs 56 can extend to movably hold the
frame 54 within the interior walls of the bracket 52. The frame 54
then includes horizontal extensions 60 for supporting the space
transformer 34 within its interior walls. The frame 54 can surround
the probe head and maintain a close tolerance to the bracket 52
such that lateral motion can be limited.
[0045] Leveling pins 62 provide the mechanical support for the
electrical elements and provide for leveling of the space
transformer 34. The leveling pins 62 can be adjusted so that brass
spheres 66 provide a point contact with the space transformer 34.
The spheres 66 contact outside the periphery of the LGA of the
space transformer 34 to maintain isolation from electrical
components. Leveling of the substrate can be accomplished by
precise adjustment of these spheres through the use of advancing
screws, or leveling pins 62. The leveling pins 62 can be screwed
through supports 65 in the back plate 50 and PCB 30. Motion of the
leveling pin screws 62 can be opposed by leaf springs 56 so that
spheres 66 are kept in contact with the space transformer 34.
Examples of such probe card assembly 18 can be found and described
in greater detail in, for example, U.S. Patent Application
Publication No. 2007/0261009.
[0046] It is noted that the probe card assembly 18 is merely an
example providing a context in which the contact elements according
to embodiments of the invention can be applied. The designs of the
probe card assembly can vary. For example, the probe card assembly
can have multiple separate substrates to which the contract
elements are attached. These various probe cards designs can all
use the proposed contact elements to form electrical contacts of a
DUT.
[0047] FIG. 19 illustrates an exemplary test system 1000, in which
a probe card assembly implemented the proposed contact structure
can be employed, in accordance with some embodiments of the
invention. As shown in FIG. 19, the test system 1000 can include a
tester 1002. Test system 1000 can also include a probe card
assembly 1018 comprising probes 1024 disposed to contact a
substrate 1026. Communications channels can be provided between the
tester 1002 and the probe card assembly 1018 by communications
connection 1004, test head 1006, and electrical connections 1016.
That is, communications connection 1004 (e.g., coaxial cables,
fiber optics, wireless transmitters/receivers) can provide
electrical signal paths between the tester 1002 and the test head
1006, which can include driver/receiver circuits 1010 and an
interface board 1012. The driver/receiver circuits 1010 can be
configured to receive signals sent by the tester 1002 through the
communications connection 1004 to the test head 1006, and the
driver/receiver circuits 1010 can also be configured to drive
signals from the test head 1006 through the communications
connection 1004 to the tester 1002. The driver/receiver circuits
1010 can be electrically connected through the interface board 1012
to electrical connection 1016, which can electrically connect the
test head 1006 to the probe card assembly 1018.
[0048] As shown in FIG. 19, the probe card assembly 1018 can be
attached to and detached from a head plate 1020 of a prober 1034,
which can comprise a housing or enclosure in which can be disposed,
among other things, a movable chuck 1028 on which the substrate
1026 can be disposed. Chuck 1028 can thus constitute a holder for
holding the substrate 1026 during testing of the substrate. (FIG.
19 includes cut away 1030, which provides a partial view into an
interior of the prober 1034.)
[0049] Once the probe card assembly 1018 is attached to the head
plate 1020 (which can comprise a top portion of the prober 1034)
and electrically connected through electrical connections 1016 to
the test head 1006 (e.g., to circuitry on the interface board
1012), chuck 1028 can move the substrate 1026 into contact with
contact elements 1024 of the probe card assembly 1018 and thereby
establishing temporary electrical connections between the contact
elements 1024 and the substrate 1026. The chuck 1028 can be capable
of moving in various directions and can be further capable of
rotating and tilting. While the contact elements 1024 are in
contact with the substrate 1026, the tester 1002 can provide test
signals, power, and ground to the substrate 1026, and the tester
1002 can analyze response signal generated by the substrate 1026 in
response to the test signals.
[0050] As mentioned, the probe card assembly 1018 can be attached
to and detached from the head plate 1020 of the prober 1034. For
example, the probe card assembly 1018 can be bolted, clamped, etc.
to the head plate 1020, and thereafter the probe card assembly 1018
can be unbolted, unclamped, etc. The probe card assembly 1018 can
also be electrically connected to and electrically disconnected
from the electrical connections 1016. Thus, a probe card assembly
1018 can be attached to the head plate 1020, electrically connected
to electrical connections 1016, and then used to test one or more
substrates 1026. Thereafter, the probe card assembly 1018 can be
detached from the head plate 1020, disconnected from the electrical
connections 1016, and removed. A different probe card assembly (not
shown) can then be attached to the head plate 1020 and electrically
connected to the electrical connections 1016 and then used to test
other substrates. The tester 1002 and test head 1006 (including any
electronics in the test head 1006, such as the driver/receiver
circuits 1010 and the interface board 1012) can thus remain in
place and be used with different probe card assemblies (e.g., like
1018).
[0051] Although specific embodiments and applications of the
invention have been described in this specification, there is no
intention that the invention be limited these exemplary embodiments
and applications or to the manner in which the exemplary
embodiments and applications operate or are described herein. For
example, particular exemplary test systems have been disclosed, but
it will be apparent that the inventive concepts described above can
apply equally to alternate arrangements of a test system. Moreover,
while specific exemplary processes for testing an electronic device
have been disclosed, variations in the order of the processing
steps, substitution of alternate processing steps, elimination of
some processing steps, or combinations of multiple processing steps
that do not depart from the inventive concepts are contemplated.
Accordingly, it is not intended that the invention be limited
except as by the claims set forth below.
* * * * *