FR2665302A1 - PHOTODETECTOR DEVICE HAVING CONNECTION BLOCKS. - Google Patents

Abstract

A photodetector device includes a light receiving part (1), a signal reading part (2), first blocks for electrically connecting the signal receiving part and the signal reading part, a test element placed on it. the signal receiving part, an interconnection structure (26) placed on the signal reading part, and a second block (3) arranged so as to electrically connect the test element and the interconnection structure. This device makes it possible to measure the characteristic of a pn junction (10) of the light receiving part after the complete manufacture, which offers the possibility of easily analyzing a possible defect.

Description

I

  PHOTODETECTOR DEVICE COMPRISING

CONNECTION BLOCKS

  The present invention relates to a photodetector device, and it

  relates more particularly to a test structure of an infrared imager

  red. Figure 8 shows a perspective view of an infrared imager of the prior art, and Figure 9 is a circuit diagram corresponding to

  Figure 8 In these figures, reference 1 designates a photo-

  two-dimensional diodes which includes for example 128 x 128 pixels A dis-

  charge coupled positive (or CCD) to silicon 2 which is intended to ac-

  complete the signal read operation is placed on the photo network

  two-dimensional diodes 1 Indium blocks 3 are placed between the

  positive with charge coupling to silicon 2 and the bi-photodiode array

  1, to connect them together Reference 4 designates an incident ray Reference 5 designates an output circuit, reference 6

  denotes a device with vertical charge coupling and the reference 7 desi-

  gn a device with horizontal charge coupling.

  The network of photodiodes iorrs Llet the coupling device

  of charge to silicon 2 are electrically connected by blocks of in-

  dium 3 The infrared ray 4 which is detected by the array of photodiodes

  two-dimensional 1 is stored for a predetermined time by the device

  charge coupled positive to silicon 2, and it is converted into a signal

  in time sequence, so as to be transmitted by the output circuit 5.

  When using Cd 02 Hgo 8 Te for the material of the photo-

  two-dimensional diodes 1 constituting the infrared imager described above, it is well known that an image of infrared rays can be formed in

the 10 micrometer strip.

  FIG. 4 shows a plan view of a structure of a two-dimensional photodiodes network using Cd 02 Hg O 8 Te, and FIG. 5 shows a section along the line AA ′ in FIG. 4 In these figures, a substrate 9 consists of Cd Te A p 8 type semiconductor layer, consisting of Cd 02 Hg 0, 8 Te, is placed on the substrate 9 An N 28 type region is formed in the surface region of the semiconductor layer 8, and

  it forms a pn junction 10 with the semiconductor layer 8 The re-

  ference It designates a region for receiving incident light in the

  array of photodiodes 1 A group of test elements 12, which consists of

  killed by electrode pads on side n, 15, and by an electrode pad

  on the p side, 16, are formed over the entire region other than the region of re-

  rectangular light concept 11 An electrode on the p side, 18, is formed

  mée on the surface of the semiconductor layer 8, except in the region

  light receiving 11 n-side electrode pads, 13, are formed

  placed on the N-type region 28 in the light receiving region 11, and an electrode pad on the p side, 14, is formed on the electrode on the p side, 18, facing the electrode pads on the n side Finally, an insulation layer 17 is formed on the surface of the semiconductor layer 8 and on the electrode on the p side, 18 An N layer 28 is formed in the layer of

semiconductor 8.

  Figure 4 shows an example of a 3 x 3 pixel array in the light receiving region 11 Usually a device is used

having for example 128 x 128 pixels.

  In the two-dimensional photodiodes array having the structure

  above, an infrared ray 4 falls on the side of the substrate 9 and it is converted into electron-hole pairs in the semiconductor layer 8, and those of these pairs which have reached the pn junction 10 by diffusion are

  detected as a signal.

  The group of test elements 12 makes it possible to check the characteristics

  ticks of the pn junction 10 which is formed on the two-dimensional photodiodes array 1, by applying a probe from a probe card to the electrode pad on the n side, 15, and to the electrode pad on the p side, 16, of the group of test elements, thus making it possible to measure for example a

  I-V characteristic of the pn junction 10.

  Figure 6 is a plan view showing coupled devices

  of silicon charge which are connected to the array of two-way photodiodes

  Figure 4, and Figure 7 shows a section along lines B-B 'of Figure 6 In these figures, the reference 19 denotes a substrate

  made of p-type silicon, and an N region is formed in the substrate if

  p-type silicon, 19 An insulating layer 22 is formed on the surface of the p-type silicon substrate 19 and pads 21 are formed on the

  p 19 type silicon substrate or on the N 20 layer, through the

  insulation 22 The reference 23 designates a connection pad and the

  ference 24 designates an interconnection for the attack of the coupling device

  vertical load range 6 and of the horizontal load coupling device

  tal 7, and this interconnection 24 is shown diagrammatically, without

show its details.

  The vertical charge coupling device 6 is a device with

  load range for collecting loads in the vertical direction,

  and the horizontal charge coupled device 7 is a device

  load range which is intended to collect charges in the horizontal direction An output circuit 5 is incorporated to transmit the signal

  output of the horizontal charge coupled device 7.

  In the two-dimensional photodiode array 1 which is described below

  above, when the manufacturing process of the wafer is finished, we

  assesses the characteristics of the pn 10 junction using the group of elements

  test elements 12, to check the quality of the array of photodiodes 1, and to make a selection, after which blocks of indium are formed on the pads 13 corresponding to the electrode on the n side, and on the pads 14 corresponding to the electrode on the p side As shown in FIG. 3, the network is then welded by inversion ("flip-chip" technique) at a high temperature of around 150 C, and it is welded by thermocompression to the charge coupled device with silicon 2, to complete the

  manufacture of an infrared imager.

  zo As described above, when an array of two-dimensional photodiodes-

  nel 1 is welded by the turning technique on a seaming device

  charge range with silicon 2, it is necessary to carry out a treatment

  high temperature thermocompression welding The photo-

  two-dimensional diodes 1 is therefore liable to be damaged by the con-

  thermal stress and mechanical stress at the time of welding, and it is also necessary to cool the device to approximately 77 K during its actual operation. There is therefore a considerable risk of the appearance of cracks in the two-dimensional photodiodes network under the effect of the thermal stress which is due to the difference in coefficient of thermal expansion between the silicon substrate 19 of the device with

  charge range with silicon 2 and the Cd Te 9 substrate of the pho-

todiodes 1.

  However, in the infrared imager of the prior art having the

  structure above, you cannot directly control the characteristics

  of the two-dimensional photodiode array 1 after the latter and the silicon charge-coupled device 2 have been soldered by tecdniqoe

  of iutourneent, and the cause pircitee causes a degradation of the

  I-V characteristics of the two-dimensional photodiode array 1 Therefore, even if the sensitivity of the infrared imager deteriorates, we cannot

  determine if the cause of the fault lies in the bi-photodiode array

  dimensional 1 or in the silicon charge coupled device 2.

  The invention aims to solve the problems described above, and its object is to provide a photodetector device capable of controlling the characteristics of the two-dimensional photodiodes network, even after

  that the latter was welded by the technique of turning or "flipchip".

  The present invention provides a test element disposed on a light receiving substrate, and an interconnection structure connected to the test element by means of a block placed on the signal reading substrate for measuring a characteristic of a photodetector device, a probe of a probe card is placed on the interconnection structure of the signal reading substrate, and the characteristic of a pn junction of the light receiving substrate is measured Consequently, even after the light receiving substrate and the signal reading substrate have been electrically connected by reverse welding, one can directly specify the characteristics of a test element which is

  found on the light receiving substrate.

  Other characteristics and advantages of the invention will be better

  understood on reading the description which follows of an embodiment

  tion, given by way of nonlimiting example The rest of the description

  refers to the accompanying drawings in which: Figure 1 is a plan view showing a silicon charge coupled device of a photodetector device according to a first embodiment of the invention;

  FIG. 2 is a section showing a photodetector device

  form in the first embodiment of the invention;

  FIG. 3 is a section showing a photodetector device

  form to the prior art; FIG. 4 is a plan view showing an array of two-dimensional photodiodes which is common to the present invention and to the prior art. FIG. 5 is a section along line A-A 'in FIG. 4; Figure 6 is a plan view showing a silicon charge coupled device according to the prior art; Figure 7 is a section along line B-B 'of Figure 6

  FIG. 8 is a perspective view showing a photo-

  detector according to the prior art; and

  FIG. 9 is a diagram showing the device of FIG. 8.

  FIG. 1 shows a plan view of a device with silicon charge coupling of a photodetector device in accordance with a mode of

  embodiment of the invention, while FIG. 2 shows a section of the device

  positive photodetector, corresponding to a section line C-C 'of the fi

gure 1.

  In FIG. 2, the two-dimensional photodiodes array 1 itself is identical to that of the prior art. An electrode pad on the n side,

  , from the group of test elements 12, intended to check the characteristics

  ques of the pn junction 10, is formed on the two-dimensional array of photodiodes

  1, with interposition of the insulation layer 17 An electrical pad

  p-side trode, 16, is connected to the p-side electrode metal, 18, at

  through the insulation layer 17 A connection pad 25 of the group of elements

  test elements 12 is placed on the substrate 19 of the silicon charge coupled device 2 An interconnection structure 26 for directing towards

  the signal from the group of test elements 12 is placed on the outside

  insulation 22 which is formed on the surface of the p-type silicon substrate, 19, of the charge-coupled silicon device 2 A welding pad 27 is placed at the end of the interconnection structure 26 of the

group of test items 12.

  The N-side electrode pad 15 of the group of test elements 12 of the two-dimensional photodiodes array 1, is electrically connected via the indium block 3 to pad 25 which is now on the insulation layer. 22 of the silicon charge coupled device 2, and the pad 25 is connected to a welding pad 27 by the structure

  interconnection 26 on the surface of the insulating layer 22, to direct

  manage the detection signal of the group of test elements 12 outwards.

  In the structure of this embodiment, during the step of manufacturing the silicon charge-coupled device 2, the pad 25

  for connecting the group of test elements 12 located on the

  bucket of photodiodes 1, the interconnection structure 26 and the support stud

  27 are formed on the insulating layer 22 of the coupling device

  of silicon charge simultaneously with the formation of pad 21, and at the

  ment of the flip-chip welding of the device to

  charge coupling to silicon 2 and the two-dimensional array of photodiodes-

  nel 1, the electrode pad on side n, 15, of the group of test elements 12 on the two-dimensional photodiodes array 1, and the connection pad of group of test elements 25 on the charge-coupled device 2 are connected by blocks of indium 3, which makes it easy to obtain the

desired structure.

  In the structure of this embodiment, even after reverse welding of the array of photodiodes 1 and of the charge coupled device 2, the characteristics of the pn junction can be easily measured

  of the photodiodes network 1, such as the I-V characteristics, in ap-

  pleating a probe of a probe card on the welding pad 27, whereby even if the sensitivity of the infrared imager is degraded, it is

  possible to specify precisely whether the cause of the fault in the pho-

  the detector detects in the light receiving part or in the reading part, after reverse welding, thus making it possible to carry out

easily a fault analysis.

  Although in the embodiment which is described above, a silicon charge coupled device is used in the part of

  signal reading, it is also possible to apply the invention to the

  be a signal reading method, using for example a MOS system.

  Although the above embodiment relates to an infrared imager

  red, it is possible to use another sensor, such as a functional imager

  operating in the visible range, replacing the light receiving section.

  As is evident from the foregoing description,

  and according to the invention, a test element is placed on the substrate

  from the light receiving part, an intercon-

  nexion on the signal reading substrate, so that this structure

  be isolated from the other elements, and we connect the interconnection structure

  nexion and the test element by means of conductive blocks We can therefore measure the characteristics by means of the test element which is formed on the substrate of the light receiving part, even after it has

  been welded by turning, which makes it easy to perform an analysis

default.

  It goes without saying that numerous modifications can be made to the device and to the process described and represented, without going beyond the ambit

of the invention.

Claims (8)

  1 Photodetector device, characterized in that it comprises a light receiving part (1), comprising a pn junction (10); a signal reading part (2); of the first blocks intended   to electrically connect the light receiving part (1) and the part   signal reading tie (2); a test element (12) placed on the light receiving part (1); an interconnection structure (26) on the signal reading part (2); and a second block (3) placed so as to   electrically connect the test element (12) and the interconnection structure nexion (26).   2 Photodetector device according to claim 1, characterized   in that the light receiving part consists of a photo- two-dimensional diodes (1).   3 Photodetector device according to claim 1, characterized   in that the signal reading part includes switching devices   silicon charging range (2) or consists of a reading system MOS type signal.   4 Photodetector device according to claim 1, characterized in that the interconnection structure (26) which is located on the part   signal reading (2) is isolated from other elements.   5 Photodetector device according to claim 1, characterized   in that the interconnection structure (26) comprises a support part   second blockage (25) and a contact part with a probe card (27).   6 A photodetector device according to claim 1, character-   rised in that the light receiving part (1) detects infrared rays.   7 Method for measuring a characteristic of a photo-   detector comprising a light receiving part (1) which comprises a pn junction (10), a signal reading part (2), first blocks for electrically connecting the light receiving part (1) and the reading part signal (2), a test element (12) placed on the light receiving part (1), an interconnection structure (26)   placed on the signal reading part (2), and a second block (3) available   installed so as to electrically connect the test element (12) and the   interconnection structure (26), this process being characterized by the operations   following rations: apply a probe from a probe card to the structure   interconnection structure (26) of the signal reading part (2); and we   measures a characteristic of the pn junction (10) of the receiving part tion of light (1).   8 Method for measuring a characteristic of a photo-   detector according to claim 7, characterized in that the information structure   terconnexion (26) has a second block welding part (25) and   a contact part with a probe card (27), and the probe of the car-   te probe is applied on the contact part with a probe card   (27) of the interconnection structure (26).