FR2833755A1 - Production of a hybrid photodetector array on a read circuit involves hybridization of a first substrate containing photodetectors and a second substrate containing a read circuit - Google Patents

Abstract

Production of a hybrid photodetector array on a read circuit involves: forming photodetectors on a thin semiconducting layer (13); forming the read circuit on a second substrate (20); hybridization of the first and second substrates; and removal of the remaining part (11) of the first substrate (10) and obtaining a hybrid photodetector array on a read circuit. Production of a hybrid photodetector array on a read circuit involves: (a) forming photodetectors on a thin semiconducting layer (13) used for forming a photodetector array, the semiconducting layer (13), preferably made of silicon, being separated from the remaining part (11) of the first substrate (10) by a barrier layer (12) made of SiO2 (preferred), Si3N4 or diamond and preferably comprising at least two sub-layers, for thinning down the first substrate (10), and the photodetectors having bonding pads (18) for connection to the read circuit; (b) forming the read circuit comprising CMOS transistors, bipolar transistors or Bi-CMOS transistors on a second substrate having bonding pads for connection to the photodetectors; (c) hybridization of the first (10) and second substrates by electrical connections (30) comprising fusible metallic balls between the bonding pads of the substrates; and (d) removal of the remaining part (11) of the first substrate (10) by polishing and/or etching and obtaining a hybrid photodetector array on a read circuit after removing the remaining part (11) of the first substrate (10). After producing the hybrid photodetector array on a read circuit, at least one other layer is applied on the photodetector array in order to implement optical treatment of the surface. The other layer can be an antireflection layer or an optical filter layer. The area of the thin semiconducting layer in contact with barrier layer is preferably doped in order to form a common electrode for the photodetector array. Localized electrical connections are formed with the doped area across the barrier layer. The space between the electrical connections, separating the photodetector array from the read circuit, is filled with an electrically insulating material.

Description

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METHOD FOR PRODUCING A MATRIX OF PHOTODETECTORS
HYBRIDED ON A READING CIRCUIT
DESCRIPTION Technical field
The invention relates to a method for producing a matrix of photodetectors, in particular visible light detectors, hybridized on a read circuit.

 The method can be a collective process, allowing the simultaneous production of several matrices of photodetectors. These matrices are most often intended to retranscribe images. They can also be used to exploit light signals from measuring devices.

 The photodetector arrays deliver electrical signals in relation to the light intensities received. Some deliver several signals in parallel, either to transmit the information more quickly, or to separate the signals from different color filters (and therefore wavelengths).

State of the art
Several variants are known in the techniques for producing photodetector matrices hybridized on read circuits. The common principle is to separately manufacture the read circuit and the matrix, and then associate them. Photodetectors are photodiodes that all have their cathode in common.

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 Several hybridization techniques exist. One of the most used is the technique of fusible beads.

 One of the problems encountered comes from the final thickness that the matrix of photodetectors must exhibit. This thickness must be a few tens of micrometers at most to maintain the compromise between photon absorption and charge collection.

A first known method for obtaining such a photodetector matrix consists in using a thin plate, of the desired thickness for the matrix, during the entire course of the photodetector embodiment process. This method presents a significant risk of breakage of the thin plate and presents the obligation to use non-standard equipment.

A second known method is to use a plate of standard thickness which is thinned once the hybridization has been performed and / or the chip cut is done. This thinning step makes it difficult to obtain a polished optical surface with low recombination of the electron-hole pairs. The control of the remaining small thickness is also difficult to control. Moreover, a common electrode can not easily be made on the face of the matrix which is intended to be illuminated. To overcome this problem, it has been proposed to make, opposite the face to be illuminated, a cathode ring or points around the matrix.

However, this way of doing things leads to electrical losses.

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Presentation of the invention
The present invention makes it possible to overcome the drawbacks of the prior art by using, to obtain the matrix of photodetectors, a plate of standard thickness but of non-standard and complex structure.

 The subject of the invention is therefore a method for producing a hybridized photodetector matrix on a read circuit, comprising: - producing photodetectors on the surface of a thin semiconductor layer of a first substrate to form a matrix of photodetectors, the thin layer, of determined thickness, being separated from the remaining portion of the first substrate by a so-called stop layer at the thinning of the first substrate, the photodetectors having connection pads for their connection to the reading circuit; - The realization of the read circuit on a second substrate, the second substrate having on the surface of the connection pads for the connection of the reading circuit to the photodetectors, - the hybridization of the first substrate and the second substrate by means of connection means electrical arranged between the connection pads of the photodetector matrix and the connection pads of the circuit of lec ture, - the elimination of the remaining portion of the first substrate and obtaining a photodetector matrix hybridized on a read circuit.

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 Thus, the final thickness of the photodetector matrix is determined in the manufacture of the first substrate and no longer by the thinning of a solid substrate.

 The passivation of the face of the photodetector matrix for collecting incident light may be performed during the manufacture of the first substrate, that is to say at the beginning of the process and no longer at the end. This has the advantage that fewer impurities enter the photosensitive material.

 The remaining portion of the first substrate may be chosen fragile (thus easier to eliminate) and different from the thin layer to be preserved.

substrat peut être obtenue par polissage et/ou gravure - peut--ssage et/ou gravure de cette partie restante. Elimination of the remaining part of the first

substrate can be obtained by polishing and / or etching - can - ssage and / or etching of this remaining part.

 If the barrier layer is transparent, obtaining a hybridized photodetector matrix on a read circuit can be obtained after the removal of the remaining portion of the first substrate.

 The barrier layer may be selected from SiO 2, Si 3 N 4 and diamond.

 The semiconductor thin film of the first substrate may be silicon and the SiO 2 barrier layer.

 The barrier layer may comprise at least two sublayers. One of the underlays may have a higher mechanical strength and the other may have better passivation qualities.

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 After obtaining a photodetector matrix hybridized on a read circuit, at least one other layer may be added to the photodetector matrix to perform surface optical treatment. The other added layer may be an antireflection layer for optimizing the transmission or an optical filter layer for filtering certain wavelengths.

 The region of the semiconductor thin film of the first substrate, in contact with the stop layer, may be a doped zone to form a common electrode for the photodetector matrix. In this case, the method may also comprise the localized formation of electrical connection means with the doped zone, through the stop layer.

 The realization of the reading circuit may comprise the production of CMOS, bipolar or Bi-CMOS transistors.

 The method may further comprise filling the space between the electrical connection means separating the matrix of photodetectors from the reading circuit by an electrical insulating material.

 Advantageously, the electrical connection means arranged between the connection pads of the photodetector matrix and the corresponding connection pads of the read circuit comprise fusible metal balls.

Brief description of the drawings
The invention will be better understood and other advantages and particularities will appear on reading

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 of the description which follows, given by way of non-limiting example, accompanied by the appended drawings, among which: FIGS. 1A to 1F illustrate the production of a first variant of photodetector matrix hybridized on a reading circuit, according to the invention; FIGS. 2A to 2C illustrate the production of a second hybridized photodetector matrix variant on a read circuit, according to the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
FIGS. 1A to 1F are cross-sectional views illustrating the embodiment of a first variant of the invention.

 FIG. 1A shows an SOI substrate 10 consisting of a silicon wafer 11 successively supporting a silicon oxide layer 12 and a thin layer of silicon 13. Such a substrate is commercially available, the thickness, the type and the doping of the thin layer 13 can be chosen to control.

 This SOI substrate undergoes the following conventional steps: surface passivation oxidation and protection of the thin layer of silicon to obtain a layer of silicon oxide approximately 0.5 μm thick 1 - photolithography of a layer of resin deposited on the oxidized thin layer to define active zones, etching of the surface oxide layer,

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 removal of the resin, fine pre-implantation oxidation of the zones of the thin layer of silicon defined by etching (approximately 0.02 am thick), photolithography of a resin layer to define N + zones, implantation of N + dopants in the zones defined above, removal of the resin, deposition of another resin layer and photolithography of the resin deposited to define P + zones, implantation of complementary dopants P +, removal of the resin. - partial deoxidation to allow electrical contact with the implanted zones, - diffusion annealing and dopant activation, - deposition of a metal layer, - deposition of a resin layer and photolithography of the resin deposited for define zones without metal, - etching of the metal layer, - removal of the resin.

 The structure obtained at the end of these steps is shown in FIG. 1B. It is a matrix of photodetectors. The surface passivation oxide layer 14 is etched for the formation of P + doped areas and N + doped areas 16. The etched metal layer provides connection pads 17 providing electrical contact with the doped areas

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 P +. It also provides connection pads 18 providing electrical contact with the N + doped areas 16.

 FIG. 1C illustrates, by way of example, a reading circuit made on a substrate 20 made of silicon and intended to be associated with the photodetector matrix produced on the SOI substrate. In known manner, amplifiers and CMOS processing circuits 21 have been made on one side of the substrate 20. P or N doping zones 22 and 23 are recognized, the polysilicon gates 24, drain and source contacts 25 and 26 and an etched silicon oxide layer 27.

 Fusible metal balls are then formed on one or the other substrate. In this exemplary embodiment, the balls 30 were formed on the connection pads 17 and 18 of the SOI substrate 10 (see FIG. 1D).

 The hybridization of the two substrates is then carried out. This is shown in Figure lE. The substrates are arranged face to face as shown in Figure 1E. The connection pads 17 and 18 are connected, via the balls 30, only with the contacts 26 of some transistors.

 The silicon wafer 11 of the substrate 10 is then removed by polishing and / or etching with selective stop on the barrier layer 12. This is shown in FIG. 1F. The fabrication accuracy of the SOI substrate determines the thickness accuracy of the photodetector array. The hard layer of silica 12 being passivating and transparent, no other layer is a priori necessary.

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 For application to other semiconductors or to improve performance, the barrier layer (or hard layer) could be associated with other layers during SOI substrate fabrication. However, the realization of hybridization and thinning would be conducted in the same manner as above.

 If the die cut has not already been made, this step may be performed at the end of the process to separate the photodetector matrices.

 Figures 2A to 2C are cross-sectional views illustrating the embodiment of a second variant of the invention.

 FIG. 2A shows an SOI substrate 100 consisting of a silicon wafer 101 successively supporting a layer 102 of silicon oxide, a very thin layer doped with silicon 109 and a thin layer of silicon 103. The layer 109 is sufficiently doped so that it can be considered as an electrode.

 Other intermediate layers could be used, for example an antireflection layer.

 The matrix of photodetectors is then made on the same principle as before to obtain the structure shown in Figure 2B which is to be compared to the structure shown in Figure 1D. Thus, FIG. 2B shows an oxide layer 104, N + doped areas 106 in electrical contact with connection pads 108. Fusible metal balls 30 have also been shown.

 It can be seen by comparing FIGS. 2B and 1D that one of the doping implantations is no longer

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 necessary because it is replaced by the doped layer 109.

 The hybridization and polishing operations are similar to those carried out for the first variant embodiment.

 Figure 2C shows the structure obtained after the hybridization, polishing operations and some additional steps.

 The reference 200 denotes a silicon substrate on which a reading circuit of the type shown in FIG. 1C has been made.

 Electrical connection elements between the doped layer 109 and the read circuit have been added. They include vias 111 passing through the oxide layer 102 to establish localized contacts with the doped layer 109. These vias are connected to a conductive pad 112, itself electrically connected to the reading circuit by an electrical connection 113.

 The additional steps may be as follows: resin deposition on the oxide layer 102 and photolithography of the resin to expose the locations of the vias, etching of the oxide layer 102 at the exposed locations until reaching the doped layer 109, - removal of the resin, - deposition of a metal layer on the oxide layer 102,

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 resin deposition on the previously deposited metal layer and photolithography of the resin to expose the areas of metal to be etched, etching of the metal layer, removal of the resin, cutting to obtain a stepped structure and setting place of the electrical connection with the reading circuit.

 The additional steps can also be carried out as follows: resin deposition on the oxide layer 102 and photolithography of the resin to expose the vias locations, etching of the oxide layer 102 at exposed locations up to to reach the doped layer 109, - removal of the resin, - deposition of resin on the oxide layer 102 and photolithography of the resin to expose the areas to receive the electrical connection elements, - deposition of a metal layer, - removal of the resin and unwanted metal by the so-called "lift-off" technique, - cutting to obtain a staircase structure and implementation of the electrical connection with the read circuit.

 The dimensions of the structure obtained are a function of the dimensions of the substrates used and the nature of the semiconductor used. The thickness of the photosensitive layer is from a few m to a few

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 tens of Mm. The thickness of the barrier layer is from a fraction of Mm to a few Mm. The thickness of the support plate of the SOI substrate is from a few hundred of Mm to a few mm. The thickness of the metal layers is from a fraction of Mm to a few Mm. The pitch of the connection pads is from a few Mm to a few tens of Mm.

Claims (13)

A method of producing a photodetector array hybridized on a read circuit, comprising: - producing photodetectors on the surface of a thin semiconductor layer (13, 103) of a first substrate (10, 100) to form a photodetector matrix, the thin layer, of determined thickness, being separated from the remaining portion (11, 101) of the first substrate by a layer (12, 102) known as a thinning stop layer of the first substrate, the photodetectors having connecting pads (18, 108) for their connection to the reading circuit; - producing the reading circuit on a second substrate (20, 200), the second substrate having on its surface connection pads (26) for connecting the read circuit to the photodetectors, - the hybridization of the first substrate and the second substrate by means of electrical connection means (30) arranged between the connection pads (18, 108) of the photodetector matrix s and the corresponding connection pads (26) of the reading circuit, - the elimination of the remaining part (11, 101) of the first substrate (10, 100) and the obtaining of a matrix of photodetectors hybridized on a read circuit .  2. Method according to claim 1, characterized in that said elimination of the remaining portion (11, 101) of the first substrate (10,100) is obtained by polishing and / or etching this remaining portion. <Desc / Clms Page number 14>  3. Method according to one of claims 1 or 2, characterized in that the barrier layer (12,102) being transparent, obtaining a hybridized photodetector matrix on a read circuit is obtained after the elimination of the remaining portion (11, 101) of the first substrate.  4. Method according to any one of claims 1 to 3, characterized in that the barrier layer (12,102) is selected from SiO2, Si3N4 or diamond.  5. Method according to any one of claims 1 to 3, characterized in that the thin semiconductor layer (13,103) of the first substrate (10,100) is silicon and the barrier layer (12, 102) is Si02.  6. Method according to one of claims 1 or 2, characterized in that the barrier layer comprises at least two sublayers.  7. Method according to any one of claims 1 to 6, characterized in that it further comprises, after obtaining a hybridized photodetector matrix on a read circuit, the addition of at least one other layer on the photodetector matrix to perform optical surface treatment. <Desc / Clms Page number 15>  8. Method according to claim 7, characterized in that the other layer added to the photodetector matrix is chosen from an antireflection layer and an optical filter layer.  9. Process according to any one of claims 1 to 8, characterized in that the zone (109) of the semiconductor thin layer (103) of the first substrate (100), in contact with the barrier layer (102), is a doped zone to constitute a common electrode for the matrix of photodetectors.  10. The method of claim 9, characterized in that it also comprises the localized formation of electrical connection means (111, 112) with said doped zone (109), through the barrier layer (102).  11. Method according to any one of claims 1 to 10, characterized in that the realization of the read circuit comprises the production of CMOS transistors, bipolar or Bi-CMOS.  12. Method according to any one of claims 1 to 11, characterized in that it further comprises the filling of the space between the electrical connection means separating the matrix of photodetectors from the reading circuit by an electrical insulating material. <Desc / Clms Page number 16>  13. Method according to any one of claims 1 to 12, characterized in that the electrical connection means arranged between the connection pads (18,108) of the photodetector matrix and the corresponding connection pads (26) of the read circuit. include fusible metal balls (30).