GB2246662A

GB2246662A - Testing photodetector devices

Info

Publication number: GB2246662A
Application number: GB9026969A
Authority: GB
Inventors: Yasuaki Yoshida
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1990-07-30
Filing date: 1990-12-12
Publication date: 1992-02-05
Anticipated expiration: 2010-12-12
Also published as: FR2665302B1; GB9026969D0; GB2246662B; JPH0485961A; FR2665302A1

Abstract

A photodetector device includes a light receiving part 1 such as a photodiode array, a signal reading-out part 2 such as a silicon charge coupled device first bumps for electrically connecting the light receiving pant and the signal reading-out part, a test element 15, 16 disposed on the light receiving part, a wiring 26 disposed on the signal reading-out part, and a second bump 3 arranged so as to electrically connect the test element and the wiring. A probe card is touched on the wiring of the signal reading out part and a characteristic of a pn junction of the light receiving part is thus measured. Therefore, the characteristic of a test element provided on the light receiving part can be measured after it is flip-chip bonded, whereby fault analysis can be easily performed. The device may be an infra red imager. <IMAGE>

Description

A Photodetector Device FIELD OF THE INVENTION The present invention relates to a photodetector device, and more particularly to a test structure of an infrared imager.

BACKGROUND OF THE INVENTION Figure 8 shows a perspective view of a prior art infrared imager and figure 9 is a schematic diagram of figure 8. In these figures, reference numeral 1 designates a two dimensional photodiode array including, for example, 128 x 128 pieces of pixels. A silicon CCD 2 for conducting signal reading-out is disposed on the two dimensional photodiode array 1. Indium bumps 3 are disposed between the silicon CCD 2 and the two dimensional photodiode array 1 thereby to connect them. Reference numeral 4 designates an incident ray. Reference numeral 5 designates an output circuit, reference numeral 6 designates a vertical CCD, and reference numeral 7 designates a horizontal CCD.

The two dimensional photodiode array 1 and silicon CCD 2 are electrically connected by indium bumps 3. The infrared ray 4 detected by a two dimensional photodiode ~ array 1 is stored for a predetermined time by the silicon CCD 2 and is converted into a time sequence signal, thereby to be output from the output circuit 5.

When Cdo 2Hgo 8Te is used as material of the two dimensional photodiode array 1 constituting the above described infrared imager, it is well known that imaging of infrared ray of 10 micron band is possible.

Figure 4 shows a plan view showing a structure of a two dimensional photodiode array using Cdo 2Hgo 8Te and figure 5 shows a cross-sectional view in lines A-A' of figure 4.

In these figures, a substrate 9 comprises CdTe. A p type semiconductor layer 8 comprising Cdo 2Hgo 8Te is disposed on the substrate 9. N type region 28 is produced at the surface region of the semiconductor layer 8, and forms a pn junction 10 with semiconductor layer 8. Reference numeral 11 designates a incident light receiving region in the photodiode array 1. A test element group (hereinafter referred to as TEG") 12 which is formed n side electrode pads 15 and a p side electrode pad 16 are disposed on the region except for the rectangular light receiving region ll.

A p side electrode 18 is provided on the surface of the semiconductor layer 8 except for the light receiving region ll. N side electrode pads 13 are disposed on the n type region 28 in the light receiving region 11, and p side electrode pad 14 is disposed on the p side electrode 18 confronting to the n side electrode pads. And an insulating film 17 is provided on the surface of the semicondúctor layer 8 and on the p side electrode 18. N+ layer 28-is produced in the semiconductor layer 8.

Figure 4 shows an example of 3 x 3 pixels in the light receiving region 11. Usually a device having such as 128 x 128 pixels is used.

In the two dimensional photodiode array of the above described structure, infrared ray 4 is incident from the side of the substrate 9 and is converted into electron whole pairs in the semiconductor layer 8, and those which have - reached the pn junction 10 by diffusion is detected as a signal.

The TEG 12 monitors the characteristics of the pn junction 10 produced on the two dimensional photodiode array 1 by touching a probe of a probe card on the n side electrode pad 15 and the p side electrode pad 16 of TEG, such as I-V characteristics of the pn junction 10 can be measured.

Figure 6 is a plan view showing silicon CODs connecting two dimensional photodiode arrays of figure 4, figure 7 shows a cross-sectional view in lines B-Bg of figure 6. In these figures, reference numeral 19 designates a p type silicon substrate and an n+ region 20 is produced in the p type silicon substrate 19. An insulating film 22 is provided on the surface of the p type silicon substrate 19 and pads 21 are provided on the p type silicon substrate 19 or on the n+ layer 20 through the insulating film 22.

Reference numeral 23 designates a bonding pad and reference numeral 24 designates a wiring for driving vertical CCD 6 and horizontal CCD 7, and the wiring 24 is schematically shown and the detail thereof is not shown.

A vertical CCD 6 is a CCD for collecting charges in the vertical direction and a horizontal CCD 7 is a CCD for collecting charges in the horizontal direction. An output circuit 5 is provided to output the output of the horizontal CCD 7.

In the above described two dimensional photodiode array 1, when wafer process is concluded, the characteristics of pn junction 10 is evaluated by TEG 12 and make sure of the quality of the photodiode array 1 and selected, and thereafter, an indium bumps 3 is produced on the pad 13 at the side of n side electrode and on the pad 14 at the side of p side electrode. And as shown in figure 3, it is flipchip bonded at high temperature about 150 C and is thermocompression bonded to the silicon CCD 2, thereby completing an infrared imager.

As described above, while a two dimensional photodiode array 1 is flip-chip bonded on a silicon CCD 2, a process of thermocompression bonding at high temperature is required.

Therefore, the two dimensional photodiode array 1 is likely to deteriorate due to the thermal stress and mechanical stress at the bonding and further it is necessity to cool the device at about 77 K when it is really operated. Therefore, there is great possibility that there arises cracks in the two dimensional photodiode array by the thermal stress due to the difference in the thermal expansion coefficient between the silicon substrate 19 of the silicon CCD 2 and the CdTe substrate 9 of the photodiode array 1.

However, in the prior art infrared imager constituted as above, the characteristics of the two dimensional photodiode array 1 can not be directly monitored after the two dimensional photodiode array and the silicon CCD 2 are flip-chip bonded, and therefore the I-V characteristics of the two dimensional photodiode array 1 deteriorates due to the above described cause. Thus even if the sensitivity of the infrared imager is deteriorated, it can not be specified whether the cause of default resides in the two dimensional photodiode array 1 or in the silicon CCD 2.

SUMMARY OF THE INVENT ION The present invention is directed to solving the above described problems and has for its object to provide a photodetector device capable of monitoring the characteristics of the two dimensional photodiode array even after it is flip-chip bonded.

Other objects and advantages of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific embodiment are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

In accordance with the present invention, a test element disposed on a light receiving substrate and a wiring connected to the test element via a bump provided on the signal reading-out substrate are provided. In measuring a characteristics of a photodetector device, a probe of a probe card is touched on the wiring of a signal reading-out substrate and a characteristics of a pn junction of the light receiving substrate is measured. Therefore, even after the light receiving substrate and signal reading out substrate are electrically connected by flip-chip bonding on the characteristics of a test element disposed on a light receiving part substrate can be directly specified.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a plan view showing a silicon CCD of a photodetector device in accordance with a first embodiment of the present invention; Figure 2 is a cross-sectional view showing a photodetector device in accordance with the first embodiment of the present invention; Figure 3 is a cross-sectional view showing a photodetector device according to the prior art; Figure 4 is a plan view showing a two dimensional photodiode array which is common through the present invention and the prior art; Figure 5 is a cross-sectional view in line A-A' of figure 4; Figure 6 is a plan view showing a silicon CCD according to the prior art; Figure 7 is a cross-sectional view in line B-B' of figure 6; Figure 8 is a perspective view showing a photodetector device according to the prior art; and Figure 9 is a schematic diagram showing the device of figure 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described in detail with reference to the drawings.

Figure 1 shows a plan view of a silicon CCD of a photodetector device in accordance with a first embodiment of the present invention and figure 2 shows a cross-section of the photodetector device corresponding to C-C' crosssection of figure 1.

In figure 2, the two dimensional photodiode array 1 itself is the same as that of the prior art. An n side electrode pad 15 of the TEG 12 for monitoring the characteristics of the pn junction 10 is produced on the two dimensional photodiode array 1 through the insulating film 17. A p side electrode pad 16 is provided connected with the p side electrode metal 18 through the insulating film 17. A connection pad 25 of the TEG 12 is provided on the substrate 19 of the silicon CCD 2. A wiring 26 for taking out the signal of the TEG 12 is disposed on the insulating film 22 provided on the surface of the p type silicon substrate 19 of silicon CCD 2. A bonding pad 27 is provided at the end of the wiring 26 of the TEG 12.

The n side electrode pad 15 of the TEG 12 of the two dimensional photodiode array 1 is electrically connected with the pad 25 which is newly provided on the insulating film 22 of the silicon CCD 2 via indium bump 3, and the pad 25 is connected with a bonding pad 27 by the wiring 26 on the surface of the insulating film 22 for taking out the detecting signal of the TEG 12.

In the structure of this embodiment, in producing step of silicon CCD 2, the pad 25 for connecting the TEG 12 provided on the photodiode array 1, the wiring 26, and the bonding pad 27 are produced on the insulating film 22 of the silicon CCD at the same step of producing the pad 21 and while flip-chip bonding the silicon CCD 2 and the two dimensional photodiode array 1, the n side electrode pad 15 of the TEG 12 on the two dimensional photodiode array 1 and the TEG connection pad 25 on the CCD 2 are connected by indium bump 3, and thus the structure is easily obtained.

In such structure of the embodiment, even after the photodiode array 1 and the CCD 2 are flip-chip bonded, the characteristics of the pn junction 10 of the photodiode array 1 such as I-V characteristics, can be measured easily by touching a probe of a probe card on the bonding pad part 27, thereby even if the sensitivity of the infrared imager is deteriorated, it is possible to accurately specify whether the cause of default of the photodetector device resides in the light receiving part or the reading-out part after the flip chip bonding, thereby enabling to perform a faulty analysis easily.

While in the above illustrated embodiment a silicon CCD is used in the signal reading-out part, the present invention can be also applied to the other signal readingout method comprising such as MOS system.

While in the above illustrated embodiment an infrared imager element is described, other sensor such as visible imager can be employed by replacing the light receiving section.

As is evident from the foregoing description, according to the present invention, a test element is disposed on the light receiving part substrate, a wiring is arranged on the signal reading-out substrate insulated from the other parts, and the test element and the wiring are connected via bumps.

Therefore, the characteristics of the test element provided on the light receiving part substrate can be measured even after it is flip-chip bonded, thereby enabling to perform faulty analysis easily,

Claims

WHAT IS CLAIMED IS:

1. A photodetector device, comprising: a light receiving part including a pn junction; a signal reading-out part; first bumps for electrically connecting said light receiving part and said signal reading-out part; a test element disposed on said light receiving part; a wiring disposed on said signal reading-out part; and second bump arranged so as to electrically connect said test element and said wiring.

2. A photodetector device of claim 1 wherein said light receiving part comprises a two dimensional photodiode array.

3. A photodetector device of claim 1 wherein said signal reading-out part comprises silicon CCDs or is of MOS type signal reading-out system.

4. A photodetector device of claim 1 wherein said wiring disposed on the signal reading-out part is insulated from other elements.

5. A photodetector device of claim 1 wherein said wiring has a second bump bounding portion and a probe card touching portion.

6. A photodetector device of claim 1 wherein said light receiving part detects infrared ray.

7. A method for measuring a characteristic of a photodetector device, comprising a light receiving part including a pn junction, a signal reading-out part, first bumps for electrically connecting said light receiving part and said signal reading-out part, a test element disposed on said light receiving part, a wiring disposed on said signal reading-out part, and second bump arranged so as to electrically connect said test element and said wiring, which method comprises: touching a probe of a probe card on said wiring of said signal reading-out part; and a characteristics of said pn junction of said light receiving part being measured.

8. A method for measuring a characteristic of a photodetector device of claim 7 wherein said wiring has a second bump bounding portion and a probe card touching portion, and said probe of probe card is touched on said probe card touching portion of said wiring.

9. A photodetector device when constructed, adapted and arranged to perform substantially as described hereinbefore with reference to and as shown in figures 1 and 2 of the drawings.

9. A photodetector device including an array of photodetective elements for light detection together with a plurality of additional photodetective elements, separately wired from the elements of said array, by which means testing can be performed during operational use of the device.

10. A photodetector device when constructed adapted and arranged to perform substantially as described hereinbefore with reference to and as shown in figures 1 and 2 of the drawings.