Probing plate for wafer testing

A probing plate for wafer testing is provided with a plurality of probes arranged so as to correspond to a plurality of bonding pads of semiconductor devices fabricated on a semiconductor wafer. The probing plate has a base plate formed of an insulating material, such as a photosensitive glass, and has contact fingers each having a raised portion in the free end thereof, contact conductors respectively formed on the surfaces of the raised portions of the contact fingers so as to be brought into contact with the corresponding bonding pads, and wiring conductors formed in a predetermined pattern on the surface of the base plate so as to extend respectively from the contact conductors. The contact conductors and the wiring conductors are formed simultaneously by a photolithographic process. The contact fingers and the raised portions thereof are also formed by subjecting the base plate to a photolithographic process. Forming the contact conductors over the surfaces of the raised portions of the contact fingers prevents accidental contact of the contact conductors with the bonding pads of semiconductor devices other than the objective semiconductor devices.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a probing plate for wafer testing and, 
more particularly, to a probing plate for wafer testing having a plurality 
of probes arranged so as to correspond to a plurality of electrodes of a 
semiconductor device (semiconductor chip) fabricated on a semiconductor 
wafer. 
2. Description of the Background Art 
Generally, a checking equipment (hereinafter, referred to as "wafer 
prober") for measuring the electrical characteristics of a semiconductor 
device formed on a semiconductor wafer in a semiconductor integrated 
circuit (IC) manufacturing process employs a probing plate. The probing 
plate is formed by fixedly arranging probes in a pattern corresponding to 
that of the electrodes, i.e., the bonding pads or solder bumps, of the 
semiconductor device on an insulating holding plate. 
A conventional wafer tester will be described with reference to FIG. 9A 
showing a conventional probing plate for wafer testing incorporated into a 
wafer prober and FIG. 9B showing probes in contact with bonding pads 
formed on a wafer. 
A wafer 1 mounted with a plurality of semiconductor device, such as LSIs 
(large-scale integrated circuits) is fixed on a wafer chuck 8. The wafer 
chuck 8 can be moved vertically and horizontally by a moving mechanism 9. 
A large number on the order of several hundreds of bonding pads 2 are 
formed on the upper surface of the wafer 1 for each semiconductor chip. 
Slender probes 3 are arranged and held on a probe holding plate 4 so as to 
correspond to the bonding pads 2, respectively. The probe holding plate 4 
is positioned above the wafer 1. The probes 3 are formed of tungsten, 
chromium or a tungsten-chromium alloy. The probe holding plate 4 is formed 
of an insulating material, such as glass or an epoxy resin. A conductive 
pattern 5 is formed of a metal, such as copper over one surface of the 
probe holding plate 4, and the probes 3 are connected electrically to the 
conductive pattern 5 by soldering or the like. The size of the contact 
area of the electrode pads 2 with which the tip of the probe 3 is brought 
into contact is in the range of about 50 to about 100 .mu.m in diameter. 
The external diameter of the base of the probe 3 connected to the probe 
holding plate 4 is in the range of about 150 to about 200 .mu.m. A 
conductive pattern 5, which is the same as the conductive pattern 5 
connected to the proves 3, is formed on the other surface of the probe 
holding plate 4 and is connected through through holes to the former 
conductive pattern 5. The conductive pattern 5 is in electrical contact 
with contact pins (hereinafter, referred to as "pogo pins") 7 provided on 
the test head 6 of a LSI tester, not shown. The probe holding plate 4 is 
held fixedly on the plate holding member 12. 
The testing procedure using the probing plate for wafer testing for testing 
the electrical characteristics of a semiconductor devices on a wafer will 
be described hereinafter. The position of the wafer chuck 8 is adjusted by 
the moving mechanism 9 so that the bonding pads 2 of one or a plurality of 
semiconductor devices formed on the wafer 1 are brought into contact 
respectively with the corresponding probes 3 fixed on the probe holding 
plate 4. The wafer chuck 8 is moved vertically so that the undersurfaces 
of the bonding pads 2 are in appropriate contact with the corresponding 
probes 3, respectively. Consequently, the semiconductor devices formed on 
the wafer 1 are connected electrically through the conductive patterns 5 
and the pogo pins 7 of the test head 6 to the LSI tester for signal 
transmission between the semiconductor devices on the wafer 1 and the LSI 
tester for testing the electrical characteristics of the semiconductor 
devices assembled on the wafer 1. 
However, since the conventional probing plate for wafer testing employs 
probes, the diameter of the probes must be reduced according to the 
reduction in the size and pitch of the bonding pads formed on the wafer, 
which entails increase in the contact resistance between the bonding pads 
and the probes. Further more, difficulty in manufacturing the probes and 
in mounting the probes on the probe holding plate is enhanced as the 
diameter of the probes is reduced. That is, reduction in the size of 
probes makes it difficult to accurately attach a plurality of minute 
probes to the probe holding plate so that the probes can be highly 
accurately positioned relative to a plurality of bonding pads formed on 
the wafer by precision processes. 
A wafer probing unit developed to solve such problems is disclosed in 
Japanese Patent Laying-Open Gazette No. 162045/1983. This wafer probing 
unit is shown in FIGS. 10A and 10B. As shown in FIGS. 10A and 10B, in this 
wafer probing unit, probe fingers 21 are formed in a flat quartz plate 20 
by selectively removing portions of the flat quartz plate 20 by 
photolithographic techniques, and leads 22 for transmitting electric 
signals from the bonding pads of semiconductor devices to an external 
equipment are formed on the surfaces of the probe fingers 21 by 
photolithographic techniques. Metallic needles 23 are fitted in through 
holes 24 formed near the free ends of the probe fingers 21 and are fixed 
to the probe fingers 21 and connected electrically to the leads 22 by a 
conductive adhesive, respectively. 
Since the probe fingers are formed simultaneously by photolithographic 
techniques, the probe fingers 21 are formed in a high positional accuracy. 
However, processing the free ends of the probe fingers 21 to attach the 
metallic needles 23 to the probe finger 21 is very difficult. 
FIG. 11 shows another conventional wafer probing plate which is disclosed 
in Japanese Patent Laying-Open Gazette No. 144142/1984. In this wafer 
probing plate, conductive wiring patterns 32 are formed on both sides of a 
ceramic plate 30 and are interconnected through through holes. Copper or 
gold contact pads 33 serving as probes are formed on the conductive wiring 
pattern 32 for electrical contact with the bonding pads of semiconductor 
devices. Connecting pins 31 are fixed to one side edge of the ceramic 
plate 30 and are connected to the conductive wiring pattern 32. The 
contact pads 33, as well as the conductive wiring patterns 32, can be 
formed accurately at positions respectively corresponding to those of the 
bonding pads of the semiconductor devices by a vapor deposition process or 
a printing process. However, it is difficult to form the copper or gold 
contact pads 33 on the ceramic plate 30 in a high density so that the 
contact pads 33 coincide respectively with bonding pads arranged at very 
small intervals on the order of 30 .mu.m. Although the height of the 
contact pads 33 from the surface of the ceramic plate 30 is the thickness 
of the conductive films forming the contact pads 33, it is difficult to 
form the conductive films in an accurate thickness so that the contact 
pads 33 will not come into contact accidentally with the bonding pads of 
the semiconductor devices other than those to be tested. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a probing plate for 
wafer testing, capable of being positioned at a high accuracy relative to 
the plurality of bonding pads of semiconductor devices formed by minute 
processing techniques. 
It is another objective of the present invention to provide a probing plate 
for wafer testing having probes which will not accidentally come into 
contact with the bonding pads of semiconductor devices other than those to 
be tested. 
It is a further object of the present invention to provide a probing plate 
for wafer testing, capable of being readily manufactured. 
It is still a further object of the present invention to provide a probing 
plate for wafer testing, provided with contact fingers having enhanced 
elasticity. 
A probing plate for wafer testing according to the present invention has a 
plurality of probes arranged so as to correspond to the plurality of 
bonding pads of semiconductor devices formed on a semiconductor wafer. The 
probing plate comprises an electrically insulating base plate having a 
plurality of contact fingers each having a raised portion in the free end 
thereof, contact conductors formed over the surfaces of the raised 
portions of the contact fingers, and wiring conductors formed in a 
predetermined pattern so as to extend respectively from the contact 
conductors. A conductive film is formed in a predetermined pattern to form 
the wiring conductors, which are connected respectively to the contact 
conductors. 
In one aspect of the present invention, portions of an electrically 
insulating base plate are removed selectively by photolithographic 
techniques to form contact fingers respectively having raised portions, 
and arranged at predetermined intervals so as to correspond to the 
plurality of bonding pads of semiconductor devices; the height of the 
surfaces of the raised portions of the contact fingers from the major 
surface of the base plate is greater than the height of the bonding pads 
of the semiconductor device. Preferably, the raised portions of the base 
plate are formed in such a height by photolithographic techniques. The 
base plate may be formed of a photosensitive glass. Terminals to be 
connected electrically to the contact pins of the wafer prober may be 
included in the wiring conductors. When the terminals are formed in such a 
manner, the wiring conductors may include wiring conductors formed on the 
other surface of the base plate and connected through through holes 
thereto. Preferably, the surface area size of each contact conductor is 
smaller than that of the corresponding bonding pad of the semiconductor 
device. 
According to the present invention, the contact conductors are formed over 
the surfaces of the raised portions of the contact fingers, respectively. 
Accordingly, only the contact conductors are able to be brought into 
contact with the corresponding bonding pads of the semiconductor devices 
to be tested, so that the accidental contact of the contact conductors 
with bonding pads other than those of the semiconductor devices to be 
tested is prevented. Since such probe consists of the contact finger 
having the raised portions of the base plate and the contact conductor, 
the probes can be formed accurately in the base plate in a high density at 
minute intervals by photolithographic techniques. Furthermore, the contact 
conductors and the wiring conductors can be readily formed in an integral 
conductive layer by photolithographic techniques. 
These objects and other objects, features, aspects and advantages of the 
present invention will become more apparent from the following detailed 
description of the present invention when taken in conjunction with the 
accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
First Embodiment 
Referring to FIGS. 1A, 1B and 1C showing a probing plate for wafer testing, 
in a first embodiment according to the present invention, a base plate 10 
formed of a photosensitive glass or ceramics, such as alumina, has 
hundreds of minute contact fingers 10a formed by selectively removing a 
portion of the central region thereof. In FIG. 1A, only several contact 
fingers 10a are shown for simplicity. Intervals between the contact 
fingers 10a are on the order of 30 .mu.m and the width of the contact 
fingers 10a is on the order of 50 .mu.m, which correspond respectively to 
the pitches and size of the bonding pads of semiconductor devices to be 
tested. Metallic wiring conductors 11, such as ITO (Indium Tin Oxide) 
wiring conductors, are formed over the surfaces of the free ends of the 
contact fingers 10a, respectively. As shown in FIG. 1B, one side of the 
free end of each contact finger 10a is raised in a step so that a contact 
conductor 11a formed over the surface of the step will be in contact only 
with a bonding pad 2a of a semiconductor device 1a to be tested and will 
not be in contact with an adjacent bonding pad 2b of other semiconductor 
device 1b which is not to be tested. That is, the height H of the step is 
greater than the height h (about 20 .mu.m) of the bonding pads and is on 
the order of 50 .mu.m or below. The thickness of the base plate 10 is in 
the range of about 0.5 to about 2.0 mm and the thickness of the metallic 
wiring conductor 11 is in the range of about 2 to 3 .mu.m. The surface 
area size of the bonding pads 2a is on the order of 50 .mu.m.times.50 
.mu.m. The surface area size of the contact conductors 11a of the metallic 
wiring conductors 11 is smaller than that of the bonding pads 2a. The 
contact fingers 10a and the metallic wiring conductors 11 may be formed by 
precision photolithographic techniques, which will be described afterward. 
Referring to FIGS. 2A and 2B showing a wafer prober employing the probing 
plate shown in FIGS. 1A and 1B, a wafer 1 carrying a plurality of LSIs 
thereon is fixedly mounted on a wafer chuck 8. The wafer chuck 8 can be 
moved vertically and horizontally by a moving mechanism 9 to position 
bonding pads 2 arranged on the wafer 1 relative to the corresponding 
contact fingers 10a of the base plate 10 disposed above the wafer chuck 8. 
The base plate 10 having the contact fingers 10a is fastened with screws 
13a to a probing plate holding plate 4 formed of an insulating material, 
such as glass or an epoxy resin. The metallic wiring conductors 11 formed 
in a predetermined pattern on one surface of the base plate 10 
interconnect electrically the contact conductors 11a, which come into 
contact with the corresponding bonding pads 2, and terminal conductors 
11b, which are brought into electrical contact with pogo pins 7a, 
respectively. The pogo pins 7a are fixed by soldering or suitable means to 
metallic wiring conductors 5 formed of copper or the like in a 
predetermined pattern on the probing plate holding plate 4. Metallic 
terminal pads 5a respectively connected to the metallic wiring conductor 5 
are in electrical contact with pogo pins 7 of the test head 6 of a LSI 
tester, not shown. The probing plate holding plate 4 is fastened with 
screws 13b to a holding member 12 of the wafer prober. 
In the wafer prober thus constructed, electric signals are transmitted 
between the semiconductor devices fabricated on the wafer 1, and the LSI 
tester through the following paths. Each bonding pad 2 is in contact with 
the contact conductor 11a, which in turn is connected electrically through 
the wiring conductor 11 to the terminal conductor 11b. The terminal 
conductor 11b is connected electrically through the pogo pin 7a to the 
wiring conductor 5 and the contact pad 5a formed on the probing plate 
holding plate 4. The contact pad 5a formed on the probing plate holding 
plate 4. The contact pad 5a is connected electrically through the pogo pin 
7 of the test head 6 to the LSI tester. 
As shown in FIG. 2B, the extremities of the metallic wiring conductors 11 
formed on the base plate 10 are expanded to form the contact conductors 
11a, which are brought into contact with the bonding pads, and the 
terminal conductors 11b, which are brought into contact with the pogo pins 
7a fixed to the probing plate holding plate 4. Accordingly, the contact 
conductors 11a and terminal conductors 11b of the metallic wiring 
conductors are able to be brought into electrical contact securely with 
the corresponding bonding pads 2 and the corresponding pogo pins 7a, 
respectively. Similarly, the metallic wiring conductors 5 are connected 
securely with the pogo pins 7 of the test head 6 of the LSI tester through 
the electrical contact of the contact pads 5a formed by expanding one end 
of each metallic wiring conductor 5. In this embodiment, the wafer 1 is 6 
to 8 in. (152.4 to 203.2 mm) in diameter. The distance between the 
opposite contact fingers 10a of the probing plate, namely, the distance 
between the two bonding pads 2 of an objective circuit, is on the order of 
10 mm. 
Second Embodiment 
Referring to FIG. 3, an insulating base plate 10 formed of a photosensitive 
glass or ceramics is provided with through holes 11c, and metallic 
terminal pads 11d are formed over the through holes 11c, respectively. 
Metallic wiring conductors 11 are formed on one surface of the base plate 
10. Contact conductor 11a is formed at one end of each metallic wiring 
conductor 11. The metallic wiring conductors 11 are connected by 
conductive layers formed over the inner surfaces of the through holes 11c 
to the terminal pads 11d. Thus, the contact conductors 11a, which are 
brought into contact with bonding pads 2, are connected electrically to 
the terminal pads 11d. 
Electric signal transmission paths between the bonding pads 2 and pogo pins 
7 provided on the test head 6 of a LSI tester, not shown, will be 
described with reference to FIGS. 4A and 4B showing a wafer prober 
employing the probing plate in the second embodiment. The bonding pads 2 
arranged on a wafer 1 fixedly held on a wafer chuck 8 are brought into 
contact with the contact conductors 11a of the metallic wiring conductors 
11 formed on contact fingers 10a. The contact conductors 11a are connected 
through the metallic wiring conductors 11 and the conductive layers formed 
over the inner surfaces of the through holes 11c to the terminal pads 11d, 
respectively. The terminal pads 11d are in contact with the pogo pins 7 of 
the LSI tester. 
Shown in FIGS. 5A and 5B is another wafer prober employing the probing 
plate having the through holes 11c shown in FIG. 3. This wafer prober 
differs from that shown in FIG. 4A in that the wafer prober has a probing 
plate holding plate 4 provided with through holes 14. The base plate 10 
are placed so that the through holes 11c are aligned respectively with the 
through holes 14 of the probing plate holding plate 4, and the through 
holes 11c and 14 are filled with solder 15. Metallic wiring conductors 5 
formed on one surface of the probing plate holding plate 4 are connected 
respectively to metallic wiring conductors 5d formed on the other surface 
of the same by the solder 15 filling the through holes 14. The terminal 
pads 11d formed on the surface of the base plate 10 facing the probing 
plate holding plate 4 are joined to the metallic wiring conductors 5d, 
respectively, so that the metallic wiring conductors 11 are connected 
electrically to the metallic wiring conductors 5. 
Third Embodiment 
Referring to FIGS. 6A and 6B, an elastic thin plate 16, such as a thin 
aluminum plate, is placed on one surface of a base plate 10 formed of a 
photosensitive glass or ceramics, and the elastic thin plate 16 and the 
base plate 10 are bonded together to reinforce the base plate 10 and to 
enhance the elasticity of the probing plate. An opening is formed in the 
central region of the elastic thin plate 16 so at to coincide 
substantially with an opening formed in the base plate 10. 
A process of manufacturing the probing plate for wafer testing shown in 
FIG. 3 will be described hereinafter with reference to FIGS. 7A to 7J and 
8A to 8J on an assumption that the base plate 10 is formed of a 
photosensitive glass, in which only to contact fingers are shown for 
simplicity. 
First, as shown in FIGS. 7A and 8A, a mask 17 is formed over one of the 
polished surfaces of a photosensitive glass plate 100 sensitive to 
ultraviolet (hereinafter abbreviated to "UV") radiation. The mask 17 has 
UV permeable regions 171. The surface of the photosensitive glass plate 
100 coated with the mask 17 is exposed to UV radiation traveling in the 
direction of arrows. 
Secondly, as shown in FIGS. 7B and 8B, the photosensitive glass plate 100 
is subjected to a heat treatment. Then, only portions of the 
photosensitive glass plate 100 exposed to UV radiation, namely, portions 
in which latent images are formed, are crystallized by the heat treatment. 
When heated in the heat treatment, a metallic colloid is produced in the 
exposed portions, and the crystallization is induced by the metallic 
colloid. Crystalline portions 101 thus crystallized are formed in the 
portions exposed to UV radiation. The crystalline portions 101 have very 
fine structure and are soluble in an acid solution. 
Then, as shown in FIGS. 7C and 8C, the crystalline portions 101 are 
dissolved and removed by an acid solution (an etching solution) to form 
the contact fingers and the through holes 11c. 
Then, as shown in FIGS. 7D and 8D, a mask 18 having a UV permeable portion 
181 is formed over the surface of the photosensitive glass plate 100, and 
then the photosensitive glass plate 100 is exposed to UV radiation. 
Then, as shown in FIGS. 7E and 8E, only a portion exposed to UV radiation, 
namely, a portion in which a latent image is formed, is crystallized in a 
crystalline portion 101 by a predetermined heat treatment. 
Then, as shown in FIGS. 7F and 8F, the crystalline portion 101 is etched by 
an etching acid solution for an appropriate time to remove the crystalline 
portion 101 partially by a predetermined depth to form raised portions on 
the contact fingers 10a. 
Then, as shown in FIGS. 7G and 8G, the surface of the base plate 10 is 
coated with a metallic film 110, such as an ITO (Indium Tin Oxide) film, 
by electroless plating. 
Then, as shown in FIGS. 7H and 8H, a resist film 19 is formed in a 
predetermined pattern over the metallic film 110. 
Then, as shown in FIGS. 7I and 8I, portions of the metallic film 110 are 
removed selectively by a photolithographic process using the resist film 
19 as a mask to form the contact conductors 11a to be brought into contact 
respectively with bonding pads, the metallic wiring conductors 11 
respectively extending from the contact conductors 11a, and the terminal 
conductors 11b to be brought into contact with the pogo pins. 
Then, as shown in FIGS. 7J and 8J, the resist film 19 is removed. The 
metallic wiring conductors on the other surface of the base plate 10 
opposite the surface on which the metallic wiring conductors 11 are formed 
in a process similar to that described hereinbefore with reference to 
FIGS. 7G to 7J and 8G to 8J. 
As is apparent from the foregoing description, according to the present 
invention, contact conductors of a probing plate for wafer testing to be 
brought into contact with bonding pads of objective semiconductor devices 
are formed in raised portions of contact fingers formed in an insulating 
base plate. Accordingly, accidental contact of the contact conductors with 
bonding pads other than the objective bonding pads can be prevented. 
Although the present invention has been described and illustrated in 
detail, it is clearly understood that the same is by way of illustration 
and example only and is not to be taken by way of limitation, the spirit 
and scope of the present invention being limited only by the terms of the 
appended claims.