CA1059646A - Methods of manufacturing infrared detector elements - Google Patents
Methods of manufacturing infrared detector elementsInfo
- Publication number
- CA1059646A CA1059646A CA257,013A CA257013A CA1059646A CA 1059646 A CA1059646 A CA 1059646A CA 257013 A CA257013 A CA 257013A CA 1059646 A CA1059646 A CA 1059646A
- Authority
- CA
- Canada
- Prior art keywords
- portions
- wafer
- elemental
- infra
- body portions
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 238000000034 method Methods 0.000 title claims abstract description 46
- 238000004519 manufacturing process Methods 0.000 title claims description 19
- 239000000463 material Substances 0.000 claims abstract description 54
- 230000000873 masking effect Effects 0.000 claims abstract description 20
- 238000005530 etching Methods 0.000 claims abstract description 16
- 239000004020 conductor Substances 0.000 claims abstract description 11
- 238000011282 treatment Methods 0.000 claims description 31
- 229920002120 photoresistant polymer Polymers 0.000 claims description 27
- 230000008569 process Effects 0.000 claims description 13
- 229910000661 Mercury cadmium telluride Inorganic materials 0.000 claims description 9
- MCMSPRNYOJJPIZ-UHFFFAOYSA-N cadmium;mercury;tellurium Chemical compound [Cd]=[Te]=[Hg] MCMSPRNYOJJPIZ-UHFFFAOYSA-N 0.000 claims description 9
- 238000007517 polishing process Methods 0.000 claims description 7
- 238000012956 testing procedure Methods 0.000 claims description 5
- 238000000151 deposition Methods 0.000 claims description 3
- 230000008021 deposition Effects 0.000 claims description 3
- 230000002093 peripheral effect Effects 0.000 claims description 3
- 238000009826 distribution Methods 0.000 claims description 2
- 230000001590 oxidative effect Effects 0.000 claims description 2
- 238000011946 reduction process Methods 0.000 claims description 2
- 239000000126 substance Substances 0.000 claims description 2
- 238000005498 polishing Methods 0.000 abstract description 35
- 239000010410 layer Substances 0.000 description 98
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 22
- 229910052737 gold Inorganic materials 0.000 description 22
- 239000010931 gold Substances 0.000 description 22
- 238000012545 processing Methods 0.000 description 15
- 238000000926 separation method Methods 0.000 description 8
- 229910052715 tantalum Inorganic materials 0.000 description 8
- GUVRBAGPIYLISA-UHFFFAOYSA-N tantalum atom Chemical compound [Ta] GUVRBAGPIYLISA-UHFFFAOYSA-N 0.000 description 8
- 239000002344 surface layer Substances 0.000 description 6
- 230000015572 biosynthetic process Effects 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 238000012360 testing method Methods 0.000 description 4
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 3
- 238000013459 approach Methods 0.000 description 3
- 239000002245 particle Substances 0.000 description 3
- 238000005476 soldering Methods 0.000 description 3
- 239000000758 substrate Substances 0.000 description 3
- 238000004381 surface treatment Methods 0.000 description 3
- 241000905957 Channa melasoma Species 0.000 description 2
- 206010070834 Sensitisation Diseases 0.000 description 2
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 2
- 238000003491 array Methods 0.000 description 2
- 229910052793 cadmium Inorganic materials 0.000 description 2
- BDOSMKKIYDKNTQ-UHFFFAOYSA-N cadmium atom Chemical compound [Cd] BDOSMKKIYDKNTQ-UHFFFAOYSA-N 0.000 description 2
- 239000004744 fabric Substances 0.000 description 2
- 150000002500 ions Chemical class 0.000 description 2
- 238000005304 joining Methods 0.000 description 2
- VCEXCCILEWFFBG-UHFFFAOYSA-N mercury telluride Chemical compound [Hg]=[Te] VCEXCCILEWFFBG-UHFFFAOYSA-N 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 229920000136 polysorbate Polymers 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 239000002002 slurry Substances 0.000 description 2
- WKBOTKDWSSQWDR-UHFFFAOYSA-N Bromine atom Chemical compound [Br] WKBOTKDWSSQWDR-UHFFFAOYSA-N 0.000 description 1
- 241000587161 Gomphocarpus Species 0.000 description 1
- WATWJIUSRGPENY-UHFFFAOYSA-N antimony atom Chemical compound [Sb] WATWJIUSRGPENY-UHFFFAOYSA-N 0.000 description 1
- GDTBXPJZTBHREO-UHFFFAOYSA-N bromine Substances BrBr GDTBXPJZTBHREO-UHFFFAOYSA-N 0.000 description 1
- 229910052794 bromium Inorganic materials 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 238000005137 deposition process Methods 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 239000003822 epoxy resin Substances 0.000 description 1
- WPYVAWXEWQSOGY-UHFFFAOYSA-N indium antimonide Chemical compound [Sb]#[In] WPYVAWXEWQSOGY-UHFFFAOYSA-N 0.000 description 1
- QSHDDOUJBYECFT-UHFFFAOYSA-N mercury Chemical compound [Hg] QSHDDOUJBYECFT-UHFFFAOYSA-N 0.000 description 1
- 229910052753 mercury Inorganic materials 0.000 description 1
- 229940057952 methanol Drugs 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 229920000647 polyepoxide Polymers 0.000 description 1
- 230000000750 progressive effect Effects 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
- 230000001235 sensitizing effect Effects 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 238000004544 sputter deposition Methods 0.000 description 1
- 239000007858 starting material Substances 0.000 description 1
- 230000001550 time effect Effects 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
- H01L31/1828—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof the active layers comprising only AIIBVI compounds, e.g. CdS, ZnS, CdTe
- H01L31/1832—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof the active layers comprising only AIIBVI compounds, e.g. CdS, ZnS, CdTe comprising ternary compounds, e.g. Hg Cd Te
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L25/00—Assemblies consisting of a plurality of individual semiconductor or other solid state devices ; Multistep manufacturing processes thereof
- H01L25/03—Assemblies consisting of a plurality of individual semiconductor or other solid state devices ; Multistep manufacturing processes thereof all the devices being of a type provided for in the same subgroup of groups H01L27/00 - H01L33/00, or in a single subclass of H10K, H10N, e.g. assemblies of rectifier diodes
- H01L25/04—Assemblies consisting of a plurality of individual semiconductor or other solid state devices ; Multistep manufacturing processes thereof all the devices being of a type provided for in the same subgroup of groups H01L27/00 - H01L33/00, or in a single subclass of H10K, H10N, e.g. assemblies of rectifier diodes the devices not having separate containers
- H01L25/041—Assemblies consisting of a plurality of individual semiconductor or other solid state devices ; Multistep manufacturing processes thereof all the devices being of a type provided for in the same subgroup of groups H01L27/00 - H01L33/00, or in a single subclass of H10K, H10N, e.g. assemblies of rectifier diodes the devices not having separate containers the devices being of a type provided for in group H01L31/00
- H01L25/042—Assemblies consisting of a plurality of individual semiconductor or other solid state devices ; Multistep manufacturing processes thereof all the devices being of a type provided for in the same subgroup of groups H01L27/00 - H01L33/00, or in a single subclass of H10K, H10N, e.g. assemblies of rectifier diodes the devices not having separate containers the devices being of a type provided for in group H01L31/00 the devices being arranged next to each other
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L31/08—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors
- H01L31/09—Devices sensitive to infrared, visible or ultraviolet radiation
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
- H01L2924/0001—Technical content checked by a classifier
- H01L2924/0002—Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
Landscapes
- Engineering & Computer Science (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Power Engineering (AREA)
- Physics & Mathematics (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Computer Hardware Design (AREA)
- Electromagnetism (AREA)
- Life Sciences & Earth Sciences (AREA)
- Sustainable Development (AREA)
- Manufacturing & Machinery (AREA)
- Light Receiving Elements (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE:
A method of forming in a wafer of infra-red sensitive material a large plurality of infra-red detector elements each comprising a body having a rec-tangular surface configuration with a pair of low resistance contacts extending on oppositely located curved edges of the body at opposite sides of a sensi-tive area of the body. A wafer of the infra-red sensitive material is adhered to a supporting body and by a combination of masking etching and polishing techniques a plurality of elemental body portions of reduced thickness are defined in the wafer having oppositely located curved edges. Thereafter electri-cally conductive material is deposited to form the contacts on the surface of each elemental body portion and finally the elemental body portions and applied contacts are removed from the supporting body.
A method of forming in a wafer of infra-red sensitive material a large plurality of infra-red detector elements each comprising a body having a rec-tangular surface configuration with a pair of low resistance contacts extending on oppositely located curved edges of the body at opposite sides of a sensi-tive area of the body. A wafer of the infra-red sensitive material is adhered to a supporting body and by a combination of masking etching and polishing techniques a plurality of elemental body portions of reduced thickness are defined in the wafer having oppositely located curved edges. Thereafter electri-cally conductive material is deposited to form the contacts on the surface of each elemental body portion and finally the elemental body portions and applied contacts are removed from the supporting body.
Description
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,~ P~IB 32,508 .
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This invention relates to methods of manufacturing a plurality of infra-red detector elements.
; The manufacture of infra-red detector devices comprises the formation of infra-red detector . elements, the mounting of the elements on suitable substrates, the application of electrical connections --to the elements, the testing of the elements provided with said connections and the eventual final encap-10 sulation of the elements and applied contacts in a suitable envelope. Infra-red detector devices in some forms comprise only a single infra-red detector element and in other forms comprise a plurality of infra-red detector elements, for example arranged i` 15 as a linear array. For devices in which the operation is dependant upon the intrinsic photoconductivity of the infra-red sensitive material the manufacture of the elements comprises steps such as material preparation, -element definition by a combination of etching and 20 polishing techniques, surface treatments and application . .
of contact layers. For some infra-red detector devices the infra-red sensitive material employed, for example `
cadmium mercury telluride, is difficult to prepare and costly. Therefore any steps that can be taken in 25 element manufacture which lead to economies in the use ;.
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PHB.32508 15.6.76 . . .
of such material are significant. ~Iowever, the problem arises that there may exist a wide variety of requirements for differen-t elernent si~es and characteristics and mounting configurations depending upon the particular infra-red detector device to be manufactured, for example the si~e of the sensiti.ve area of the elements may be as small as 25 microns x 25 microns and as large as 2 mm x 2 mm. 1~hen forming the element or elements from a slice of the infra-red sensitive material it is thu.s costly if for each _ different con~iguration a fresh slice of such material ~
has to be used as the starting body. For the manu~
facture of the devices comprising an array of infra-red detector elements the further problem of yield occurs 1~hen, as is customary, the array comprises the arrangement of the detector elements in one or more groups each formed in a common body of the infra-red sensitive material. This so-called 'monolithic' approach to the fabrication of a group of detector elements gives rise to many problems. Thus where, for exarnple, a group of ten elements are formed in a single comb-shaped body the problem arises that if after mounting and application of electrical connections one of the individual elements of a group is found to be faulty on testing then the whole group has to be replaced. Other problems arise in the so-called monollthic approach, par-ticularly in connection with the spacing of the individual elements in a group " .
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PIIB.3Z508 15.6.76 ~; ~o~g64 'I
formed in a common body. Where the separation of the active surface areas of the elements in such a body is defined by an etching process there exists a limitation for the minimum separation that can be 3 5 achieved because in general when etching the body of infra-red sensitive material the width of a channel ~ill normally be considerably in excess of the thickness of the body. Even if the thickness of the body is reduced to 6 microns it is not j 10 readily possible by etching to achieve a separation of individual elements of less than 12 microns.
~ ~urthermore if the processing is such that the ¦ individual elements are defined before the final j reduction in thickness the handling and further `¦ 15 processing of bodies of such small thickness may be I extremely difficult.
¦ Another problem which arises, both in single elcment devices and in arrays, is the provision of electrical colmections to the or each individual infra-red detector elem0nt. Hitherto this has been ~, effected by joining wire leads onto metallised surface j portions of the element or elements, for example, by a thermocompression bonding process or a soldering process. Due to the deformation of the wire end that is associated with the bonding operation, for example as occurs in nail-head bonding, steps have to be taken to ensure that the area of -the part of the e:Lement to . ~ ~
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I PH~.32508 15.6.76 ~ i969!~6 ` 1 - ! which the wire is bonded is sufficient to accommodate ': ~
i the finally deformecL wire end in such manner that said ~ deformed wire end lies entirely on the element. This can ; unduly complicate the element design and place further ¦ 5 limitations on the achievable minimum separation between adjoining elements in an array. Also problems occur when joining the other ends of the wire leads, for example by soldering, to lead-out conductors.
Another problem associated with the so-~ 10 called monolithic approach to element fabrication ¦ arises when it is desired to produce multi-element detector devices in which the separation of the ¦ elements, for example in a linear array, is not uniform.
i This non-uniformity of spacing may be desired, for example, when different degrees of resulution are required at different parts of the array of detector elements. The formation of a plurality of elements in a single body with different spacing between elements at different parts of the array i 20 gives rise to many difficulties and can be extremely ~ costly in terms of the material required.
i According to the invention there is provided ¦ a method of manufacturing a plurality of infra-red ~; detector elements each comprising a body of infra-red j 25 sensitive material having a substantially rectangular surface configuration with a pair of low resistance electrical contacts spaced apart on one surface of the .~ :
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¦ body at opposite sides of a sensitive area of the . element, wherein a wafer of the infra-red sensi t ive : material i.s adhered to a supporting body, a first -~ plurality of substantially parallel extending channels are formed extending in the wafer material to define on the supporting body a plurality of substantially parallel strip portions of the infra-red sensitive , material, a treatment to obtain a reduction in the ) thickness of the strip portions is effected and to `j 10 obtain a curvature of theexposed longitudinal edges ¦ of the strip portions, a second plurality of ':~ substantially parallel extending channels are formed .~ - in the wafer material of the strip portions in a ;~ direction substantially normal to the longitudinal ~ -15 direction of the strip portions to define on ~e !' sup~orting body an array of rectangular elemental ., ,.
' body portions of the infra-red sensitive material each i having curved edges on two opposite sides, electrically ~ conductive material is deposlted to form on the surface :! 20 of each elemental body portion a pair of electrical .¦ contact layers which are spaced apart and adjoin the opposltely located curved edges, and the elemental body portions with applied contact layers are removed fronl the supporting body.
This method can provide slgnificant ~l advantages in terms o~ material savings, flexibili-ty - of providing elements of different sensitive areas, , .~ ' - .
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1~35~L6 enhanced detector performance, small separation of elements in multi-element devices, and provision of external electrical connections as will be described hereinafter. The method pnGvides the elements in ~, - 5 individual form rather than as a monolithic assembly and in such manner that their further assembly and contacting in the manufacture of an infra-red detector device is readily facilitated in a desirable manner.
In particular the provision of the elements with applied contact layers adjoining the oppositely loca~ed curved edges enables the further assembly of the elements either in single element devices or in multi-: element devioes to be effect~d with the electrical connections applied thereto by way of deposited con-ductive layers. mis obviates the necessity of using wire bonding of soldering with the previously mentioned attendant disadvantagesO In respect of this method --of asse~bly and contacting reference is invited to our , ;
oo-pending Canadian Patent Application No. 257,014.
The asse~bly of the individual elements on a substrate may be, for example by means of adhe ing the elements to an msulating substrate with an epoxy resin. Such a methcd may be used both for single element devices and multi-element devioes. In respect of the latter the considerable advantage arises that the spacing of the elements may be obtained as desired. me spacing may ,~
be considerably smaller than is obtained PHB 32,508 - .
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in monolithically formed multi-element devices and furthermore, for example in a linear array, the pitch distances between the elements may be varied as is desired. Furthermore the formation, if desired, of two-dimensional arrays with any desired spacing is readily facilitated.
The method in accordance with the invention for forming the elements enables considerable materials ` savings to be made because in any one wafer which ` 10 is processed it is readily possible to provlde elements of different sensitive areas, for example `i`
by appropriate choice of the separation of the second ~ plurality of channels. Furthermore enhanced element !,; performance may be achieved because various surface treatments can be readily accommodated in the method.
Prior to adhering the wafer of infra-red sensitive material to the supporting body the wafer may be subjected to an oxidizing treatment to form an oxide on the surface of the wafer which is to be adhered to the supporting body. In this manner the surface of the subsequently formed infra-red sensitive elements situated opposite the surface at which in ~, operation the radiation is incident will be provided with a layer which is found to enhance the performance of the detector elements.
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7 After adhering the wafer of infra-red sensitive material to the supporting body and prior to forming the first plurality of channels in the wafer material the wafer may be subjected to an initial thickness reduction process via the surface thereof remo-te from the supporting body. This thickness reduction may be effected by a mul$i-stage polishing process, with progressively less damage being - produced in successive stages, for example by varying ~, 10 the size of the abrasive particles used in successive ~ stages and also correspondingly varying the hardness `~ of a base lap used in the process until the desired 7 thickness is obtained.
i The treatment to obtain a reductlon in ~, 15 thickness of the strip portions and to obtain a curvature of the exposed longitudinal edges of the strip portions may comprise the combination of a polishing process 7 ' followed by an etching process.
Z Subsequént-to forming the second plurality ,, 20 of channels in the wafer material exposed surface .
parts of the elemental body portions may be subjected to a passivatingtreatment. The carrying outof the passivating treatment at this s-tage of the processing, that is subsequent to defining the array of sub-1 25 stantially rectangular elemental body portions 9 is advantageous because it enables exposed side ., . .
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PHB~32508 15.6.76 3LOS~6~
;, surfaces of the elemental body portions, ~hich in the finally produced elemen-t will adjoin the main sensitive area surface parts, to be subjected to thapassiva~ng treatment. This is desirable because in a device produced without the passivated side surfaces there could occur a degradation in performance when the device is s-ubjected to elevated temperatures.
, In a preferred form immediately prior to the passi-~: vating treatment the exposed surface parts of i 10 the elemental body portions are subjected to an etching ;~ ~f `~ treatment.
Thepassivating treatment may be confined to central surface areas of the elemental body portions which extend across said elemental body portions, said ar~as being defined by masking layer portions ~ present on opposite sides of said areas adjacent the `¦ cur~ed edges of the elemental body por-tions. The masking , layer portions may be of photoresist~
¦ Subsequent to the passivating treatment ~, 20 and prior to applying the contact layers the said masking layer portions may be removed and a further ., .
masking layer applied and defined so that each passi-vating surface area is covered by a masking layer ~ portion with the exception of a pair~of oppositely J '- 25 located peripheral strip parts thereof extending substan-tially parallel to the curved edges of the elemental body portions, a material removal treatment .~ .
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PHN.32.508 15.6.76 `: - ~596~;, ~ .
` J being effected at -the exposed s-trip parts of the pasci-`:~ vated surface areas in the presence of the masking ~i layer portions. In this manner the oxidized surface areas are slightly reduced in their lateral extent ¦ 5 prior to applying the contact layars in order to avoid problems of mask alignment when applying the contact , layers.
The said material removal treatment to , reduce the lateral extent of thepassivated surface j 10 areas may be effected by a polishing process, I for example with a lapping cloth and a very fine `~1 abrasive.
The further masking layer may be of photo-resist and the electrical contact layers formed by deposition of the electrically conductive material of ,:: . .
the exposed surface parts of the elemental body portions ¦ and the photoresist masking layer surface parts fol]owed by the chemical removal of the photoresist ~1 masking layer and the electrically conductive material ,, 20 deposited thereon. In this manner the deposited ., conductive material i~s removed from above the active ~-l surface areas of the elements by a so-called 'lift-off' technique. The use of such a technique is advantageous compared with one in which the conductive ma~erial is first deposi-ted o~er the entire surface and then defined photolithographically, particularly when the ` deposited conductive material is of gold, because ~, .
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~ ~596~6 ,, it may not be possible to etch the conductive material without removing the underlying passivating layer and possibly the material of the elemental body portions.
Subsequent to the a~plication of the contact layers the elemen-tal body portions may be re~oved from the supporting body individually by mechanical means, for example by lifting with a fine tool.
When using mechanical means for the removal, the elemental body portions may be removed from selected positions of -the array and subjected to testing procedures, for example to measure the resistivity, responsitivity, cut-off wavelength, 1 15 time constant and D , in order to evaluate the characteristics of the eIemental body portions and their distribution in the array. In this manner a form of map of the characteristics of the elemental body portions can be obtained and thereafter the elemental body portions can be selected for removal in accordance with the desired characteristics of the detector devices to be manufactured. Such a form of testing is advantageously employod when the properties of the original starting wa~er are not constant over all parts of the wafer.
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PHB.32. So8 15.6.76 ~i9~6 I For the manufacture of a multi~element infra-red detector device a group of adjacently situated elemental body portions in the array on the supporting body may be selected for removal in accordance with the evaluated characteristics of the elemental body portions removed for the testing purposes.
At least the first plurality of substantially parallel extending channels may be formed in the ¦ 10 wafer with a uniform spacing. In this manner all the ~j elemental body portions subsequently produced will have the same cross-dimension in a direction betwe~n the curved edges at two opposite sides. By varying the spacing of the said second plurality of the ¦ 15 channels which are formed in the previously defined strips of the infra-red sensitivq material the width of the elemental body portions, that is the cross-dimension in the direction parallel to the curved I edges at two opposite sides,may be varied. In this -~ 20 manner in any one starting wa~er -there may be formed ~, a plurality of elemental body por-tions of at least ¦ two different si'2ies of the active surface areas.
The method in accordance with the invention may be employed in the production of infra-red de-tector elements of various materials, particularly high cost materials. One such material is cadmium mercury telluride l -13-~, :
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where the material preparation of desired characteristics is time consuming and calls for economies whereever possible in elemen-t formation. Nevertheless the method t may also be advantageously employed in the production 1 5 oP infra-red detector elements in other materials where the cost savings on materials are not quite so relevant, for example in indiuln antimonide.
An embodiment of the invention will now be described, by way of example, with reference to ! 10 the accompanying diagrammatic drawings~ in which:
Figure 1 is a cross-sectional view of a ~¦ wafer of cadmium mercury telluride moun-ted on a polishing block and at a stage in the manu~acture after effecting a surface treatment;
~¦ 15 Figure 2 shows in cross-section the wafer a~ter mounting on a further polishing block;
. Figure 3 shows in cross-section the residual , .
wafer on the further polishing block after a thickness ~' reduction step;
Figures 4 and 5 show in plan view and cross-. section respectively the wafer on the further polishing block a~ter a further step in the processing, ~igure 5 being a section on the line V-V in Figure 4;
. Figure ~ shows in cross-section the wafer ~ .
~3 ' 25 on the further polishing block after a further thickness reduction step;
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PHB.3Z.508 15.6.76 10596~
Figure 7 shows in plan view a portion of the wafer after a further step in the processing, . and ~ Figures 8 and 9 are cross-sectional views 1 5 taken along the line VIII-VIII and IX-IX respectively of Figure 7;
Figures 10 to l2 show in cross-section ~ part of the wafer at further s-tages of the processing;
1 . Figures 13 and 14 show in cross-section and plan view respectively the same part of the waf`er at a further stage in the processing after effecting a ¦ passivàtion treatment, Figure 14 being a cross-il s~ction along the line XIV-XIV in Figure 13;
Figures 15 and 16-show in cross-section ~ 15 the same part of the wafer at further stages in the processing;
Figures 17 and 18 show in cross-section and plan view respectively the same part of the i wafer at a stage in the processing after individual elemental body portions of thewafer have been provided 3 with contact layers, Figure 17 being a cross-section ¦ along the line XVII-XVII in Figure 18;
Figure 19 is an enlarged plan view of one elemental body portion with applied contact layers I . 25 . as present on the polishing block, and Figures 20 and 2l are cross-sectional views taken on the line XX-XX and XXI-XXI resp. of Figure 19.
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~05~646 ; The Figures in the accompanying drawings are not to scale and consequently the relative dimensional proportions are totally distorted, particularly in a practical embodiment the thickness of the various layers in relation to their lateral extend will be much smaller than may otherwise be apparent from the drawings.
~, The embodiment now to be described `, comprises the manufacture of a large plurality of, i 10 in the range of two thousand, infra-red detector l elements of cadmium mercury telluride. In this -¦ embodiment the material composition, that is the ¦ atomic ratio of cadmlum to mercury, is such as to I produce a cut-off ~ravelength in-~eregion of 12 microns.
:! 15 The starting material is a disc-shaped ¦ ~wafer of the cadmium mercury telluride of approximately 10 mm diameter and 0.5 mm thickness.
~; The wafer 1 is mounted on a ceramic polishing block 2 with a layer of wax 3. The polishing , block has raised shoulders of 200 microns height.
Polishing of the surface of the wafer projecting .
byond the shoulders is effected by a rotary machine usinga-base lap and an abrasive slurry. The polishing is a multi-stage process ~ith progressively less ! 25 damage being produced in the crystal structure as the thickness is reduced to the desired value O:r , 200 microns. This progressive reduction in damage , .
~; .
.j PHB.32.508 15.6.76 ,,1 is achieved by the use of progressively finer abrasive particles and base laps. This polishing is continued until the surface of the wafer lies flush with the surfaces of the shoulders of the polishing block 2. To remove the remainder of the surface ' damage and etching treatment is effected with an `I etchant comprising bromine in met-hanol.
A paasivating treatment is then effected ~ith the wafer 1 still remaining adhered to the polishing block 2 so that treatment is effected on the exposed upper and side surfaces.
~igure 1 shows the wafer 1 of 200 microns thickness having an oxide surface layer 4.
¦ The wafer 1 is now removed from the polishing ¦ 1$ block 2 and is adhered via the oxidised major surface to a further polishing block 5 of high density alumina.
3 The supporting body forr~ed by the polishing block 5 has outer shoulders of 25 microns in height and within the shoulders the surface has a layer 6 of tantalum thereon. The wafer 1 is adhered to the tantalum layer 6 with a layer of wax 7~
Although the previously formed oxide surface i layer 4 is shown in Figure 2 in the following Figures it is omitted for the sake of convenience of illus-tration.
A multi-stage polishing operation is effected with a rotary lapping machine using an alumina slurry, the particle size and base laps being chosen such that .. .
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~ ~--P~.32.508 15.6.76 ~oS9i64~;
the damage produced is progressively reduced in successive stages. This polishing is effected until the polished surface of the wafer 1 is substantially co-planar with the raised shoulders of the polishing block 5. Figure 3 shows the wafer 1 after thie thickness reduction step, the wafer 1 now having a thickness of approximately 25 microns.
With the wafer 1 of reduced thickness still adhered via the wax layer 7 to the tantal-um layer 6 on the polishing block 5 a layer of photo-resist is applied on the upper surface of th~ wafer 1.
A photomasking and developing process is then effected to define a plurality of substantially parallel strip-.1 .
i shaped openings in the photoresist layer. An etching 'I 15 treatment is then effected using a suitable etchant for cadmium mercury telluride to form in the wafer ¦ a first plurality of substantially parallel extending channels 8 which define on the polishing block a plurality of substarltially parallel extending strip 1 20 portions 9 of cadmium mercury telluride.~Figures 4 t and 5 show the channels 8 and the strips 9. In this example the channels 8 are of approximately 50 microns in width and the strips are all o~ approximately 200 microns in width.
The next stage in the processing is the ' removal of the parts of the photoresist layer remaining , .' ' .
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P~B.32.508 ' 15.6.7G
,;
on the 5 trip portions 9. Thereafter a thickness reduction is effected in order to reduce the thickness of the strip portions 9 to approximately 8 microns andat the same time effect a curvature of the exposed upper longitudinal edges of the strip portions 9. This is effected by first polishing -~ wi-th a lapping machine using a fine grade pad and a ` fine abrasi~e until the resldual thicl~ness of` the strip portions 9 is approximately 12 microns and thereafter etching the strip portions 9 to remove i material of a thickness in the region of L~ to 5 microns.
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,~¦ In this manner the upper longitudinal edges of the strip portions are rounded and this effect is utilised l 15 in order to enable the external contacting of the ¦ elements when finally produced. Furthermore the etching is found to have a sensitising effect which yields an enhanced detector performance. Figure 6 shows in cross-section the strip portions 9 after the etching process. ~ue to the distortion of the relative dimensions in the drawing the rounding of the longitudinal edges does not appear to be s~gnificant ¦ but in practice it is found that the curva-ture extends ~ in the cross-section over a clistance of at least -:! 25 15 microns from the bottom surface at each longitudinal edge. It is also noted that during the polishing to effect the sald reduction in thickness from 12 microns ;
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i ' l - PIIB.32.508 : 15.6.76 ~L05964G
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to 7 to 8 microns the exposed wax layer par-ts in the channels 8 are removed. Thus in the section O:r Figure 6 the wax layer 7 is now present only below each strip portion 9.
~' 5 The next stage in the processing is the application of a layer of photoresist on the upper surfaces of the strip portions. Using a conventional photomasking and developing process a plurality of i substantially parallel extending strips situated .~ 10 normal to the strip portions 9 are removed from the photoresist layer and etching of the exposed materia].
3 of the strip portions 9 is effected using a suitable I etchant for cadmium mercury telluride to obtain a plurality of substantially parallel extending channels 10 in the wafer material of the s-trip portions to ~ define on the polishing block an array of substantially `I rectangular elemental body portions 11 of cadmium ' mercury telluride. Figure 7 i5 a plan view of part of the wafer after forming the channels 10 and thus defining the elemental body portions 11, the remaining parts of the photoresist layerused for the masking , having b.een removed. Figures 8 and 9 are cross-sections `j along the lines VIII-VIII and IX-IX respectively of ~¦ Figure 7. Figure 8 shows the rounding o-f the edges of the elemental body portions 11 on two opposite sides in contrast to the near vertical edges (Figure ~) on the other two sides of the elemental body portions.
In this exa.mple the width of the channels 10 as ,, --ZO--!
PHB.32.508 `: 15.6.76 ~0~ 646 ! finally etched is approxinlately 30 microns and the final surface area of the elemen-tal body portions 11 as shown in Figure 7 is 200 microns x 50 microns.
¦ The next step in the processing is the applica-tion of a further layer 12 of pho-toresist to the surface of the elemental body portions 11 and the ~-; exposed surface portions of the wax layer 7 and the tantalum layer 6 on the polishing block 5.
By a photomasking and developing step the photoresist layer 12 is defined so that openings 13 (Figure 10) ¦ are formed therein, said openings being in the form of strips of approximately 50 microns width extending parallel to the channels 8 and exposing the elemental body portions 11 at one end thereof at which a rounded ¦ 15 edge is present and also exposing the adjoining part ~¦ of the tantalum layer 6 on the polishing block 5 from which part the wax layer 7 was previously removed in the thickness reduction polishing step. ~igure 10 ~ is a cross-section, corresponding to the section of ¦ 20 Figure 8, showing the photoresist layer 12 and the openings 13 therein.
A layer of gold of 0.5 micron thickness :
~ is now applied by sputtering. The gold is thus ¦ deposi-ted on the photoresist layer 12 and in the ¦i 25 openings 13. The photoresist layer 12 is then dissolved in a suitable solvent and the deposi-ted gold thereon ,' ~ .
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PHB.32.508 15.6.'j6 1J ~059~;~6 . i is thereby removed by a lift-off technique.
Figure 11 shows a section, corresponding to the section of Figure 10, with gold layer strips 14 -~' of approximately 50~microns width forming contact .
between the upper surfaces of the elemental body ~; portions 11 and the tantalum layer 6 on the polishing - - block 5. The gold layer portions 14 are required to establish this electrical connection for a subsequently effected process because due to the combination of the oxide layer previously provided and located at the lower surfaces of the elemen*al body ~ i .
portions and the separation of the said body portlons 1 from the tantalum layer 6 by the wax layer 7 the ¦ elembntal body portions 11 would otherwise all be ,~ .
¦ 15 effectively isolated.
¦ A further layer 15 of photoresist is applied ¦ on the upper surface of the assembly and by a photo-~ masking and developing step apertures 16 in the form ,, .
,, of rectangular strips of approximately 80 microns - 20 width are formed in the photoresist layer 15.
Figure 12 is a cross-section, corresponding to the ~ section of ~igure 11, showing the strip apertures 16 " which arc located centrally on the surfaces of the elemental body portions 11. These strip aperturesl6 Z5 have a wid-th in the direction of the larger cross dimensions of the elemental body port:ions, that is '~
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PHB.32.508 1~.6.76 ~5~
in the direction of the section of Figure 119 which is slightly larger than the desired final dimension of the active surface areas of the ¦ elemental body portions.
I 5 In the presence of the defined photoresist j layer 15 is exposed surface portions are subjected ! to a sensitisation treatment by etching ~ to remove material over at most 1 1 micron thickness. There is then effected a passivatin~
treatment. Figure 12 diagrammatically shows in broken ¦ outlineapassivat~g layer 17 produced at the exposed surfaces of the elemental body portions 11.
The residual parts of the photoresist ~¦ layer 15 are now dissolved and Figures 13 and 14 ¦ 15 respectively show in plan view and section the ¦ assembly thus formed with the gold layer strips 14 still present and the elemental body portions 11 having surface parts provlded withap~qivat~ layer 17.
~i The gold strips 14 are shown shaded in the plan view of Figure 13 for clarity of illustra-tion. It is to be ~, noted that as the photoresist layer was removed from ! parts of the channels 10 be-tween the~ elemental body g- portions 11 along the strip apertures 16 parts of ¦ the longitudinal side surfaces of the elemental body por-tions 11 are also exposed to the passivati~g treatment and the carrying out of this process at Z
' 3 PHB.32.508 15.6.76 s~64l6 ., i this stage, that is after the element definition, can be advantageous :in this respect:.
The next step is -the application of a further layer of photoresist 18 followed by a photomasking and developing step for definition of apertures therein. The apertures are formed so that the passivated surface area on each elemental body .
portion 11 remains covered with the photoresist layer 18 with the exception of a pair of oppositely located peripheral strip parts 19 thereof extending substantially parallel tothe curved edges of the . elemental body portions 11. The photoresist layer 18 is left remaining in the channels 10 between the :~ elemental body portions and in parts of the channels 8 as shGwn in ~igure 15 be-tween the elemental body ~¦ portions it covers the exposed tantalum layer parts ,' and also partly overlaps the gold contact strips 14 where they are present on the tantalum layer 6.
' . A material removal treatment is now.~j 20 effected at -the exposed strip parts 19 of the passi-~-~ ` vated surface areas in the presence of the defined photoresist layer 18. This is obtained by a polishi.ng I process using a lapping cloth and a fine abrasive.
`~ It is possible toeffect the material removal in this manner because in general the photoresist layer has a ~reater abrasive resistance -than the passivated surface
,~ P~IB 32,508 .
` ~OS9G46 `
This invention relates to methods of manufacturing a plurality of infra-red detector elements.
; The manufacture of infra-red detector devices comprises the formation of infra-red detector . elements, the mounting of the elements on suitable substrates, the application of electrical connections --to the elements, the testing of the elements provided with said connections and the eventual final encap-10 sulation of the elements and applied contacts in a suitable envelope. Infra-red detector devices in some forms comprise only a single infra-red detector element and in other forms comprise a plurality of infra-red detector elements, for example arranged i` 15 as a linear array. For devices in which the operation is dependant upon the intrinsic photoconductivity of the infra-red sensitive material the manufacture of the elements comprises steps such as material preparation, -element definition by a combination of etching and 20 polishing techniques, surface treatments and application . .
of contact layers. For some infra-red detector devices the infra-red sensitive material employed, for example `
cadmium mercury telluride, is difficult to prepare and costly. Therefore any steps that can be taken in 25 element manufacture which lead to economies in the use ;.
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PHB.32508 15.6.76 . . .
of such material are significant. ~Iowever, the problem arises that there may exist a wide variety of requirements for differen-t elernent si~es and characteristics and mounting configurations depending upon the particular infra-red detector device to be manufactured, for example the si~e of the sensiti.ve area of the elements may be as small as 25 microns x 25 microns and as large as 2 mm x 2 mm. 1~hen forming the element or elements from a slice of the infra-red sensitive material it is thu.s costly if for each _ different con~iguration a fresh slice of such material ~
has to be used as the starting body. For the manu~
facture of the devices comprising an array of infra-red detector elements the further problem of yield occurs 1~hen, as is customary, the array comprises the arrangement of the detector elements in one or more groups each formed in a common body of the infra-red sensitive material. This so-called 'monolithic' approach to the fabrication of a group of detector elements gives rise to many problems. Thus where, for exarnple, a group of ten elements are formed in a single comb-shaped body the problem arises that if after mounting and application of electrical connections one of the individual elements of a group is found to be faulty on testing then the whole group has to be replaced. Other problems arise in the so-called monollthic approach, par-ticularly in connection with the spacing of the individual elements in a group " .
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PIIB.3Z508 15.6.76 ~; ~o~g64 'I
formed in a common body. Where the separation of the active surface areas of the elements in such a body is defined by an etching process there exists a limitation for the minimum separation that can be 3 5 achieved because in general when etching the body of infra-red sensitive material the width of a channel ~ill normally be considerably in excess of the thickness of the body. Even if the thickness of the body is reduced to 6 microns it is not j 10 readily possible by etching to achieve a separation of individual elements of less than 12 microns.
~ ~urthermore if the processing is such that the ¦ individual elements are defined before the final j reduction in thickness the handling and further `¦ 15 processing of bodies of such small thickness may be I extremely difficult.
¦ Another problem which arises, both in single elcment devices and in arrays, is the provision of electrical colmections to the or each individual infra-red detector elem0nt. Hitherto this has been ~, effected by joining wire leads onto metallised surface j portions of the element or elements, for example, by a thermocompression bonding process or a soldering process. Due to the deformation of the wire end that is associated with the bonding operation, for example as occurs in nail-head bonding, steps have to be taken to ensure that the area of -the part of the e:Lement to . ~ ~
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I PH~.32508 15.6.76 ~ i969!~6 ` 1 - ! which the wire is bonded is sufficient to accommodate ': ~
i the finally deformecL wire end in such manner that said ~ deformed wire end lies entirely on the element. This can ; unduly complicate the element design and place further ¦ 5 limitations on the achievable minimum separation between adjoining elements in an array. Also problems occur when joining the other ends of the wire leads, for example by soldering, to lead-out conductors.
Another problem associated with the so-~ 10 called monolithic approach to element fabrication ¦ arises when it is desired to produce multi-element detector devices in which the separation of the ¦ elements, for example in a linear array, is not uniform.
i This non-uniformity of spacing may be desired, for example, when different degrees of resulution are required at different parts of the array of detector elements. The formation of a plurality of elements in a single body with different spacing between elements at different parts of the array i 20 gives rise to many difficulties and can be extremely ~ costly in terms of the material required.
i According to the invention there is provided ¦ a method of manufacturing a plurality of infra-red ~; detector elements each comprising a body of infra-red j 25 sensitive material having a substantially rectangular surface configuration with a pair of low resistance electrical contacts spaced apart on one surface of the .~ :
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: PHB.32508 : 15.6.~j6 ~ s~ a6 .,.,1 .
¦ body at opposite sides of a sensitive area of the . element, wherein a wafer of the infra-red sensi t ive : material i.s adhered to a supporting body, a first -~ plurality of substantially parallel extending channels are formed extending in the wafer material to define on the supporting body a plurality of substantially parallel strip portions of the infra-red sensitive , material, a treatment to obtain a reduction in the ) thickness of the strip portions is effected and to `j 10 obtain a curvature of theexposed longitudinal edges ¦ of the strip portions, a second plurality of ':~ substantially parallel extending channels are formed .~ - in the wafer material of the strip portions in a ;~ direction substantially normal to the longitudinal ~ -15 direction of the strip portions to define on ~e !' sup~orting body an array of rectangular elemental ., ,.
' body portions of the infra-red sensitive material each i having curved edges on two opposite sides, electrically ~ conductive material is deposlted to form on the surface :! 20 of each elemental body portion a pair of electrical .¦ contact layers which are spaced apart and adjoin the opposltely located curved edges, and the elemental body portions with applied contact layers are removed fronl the supporting body.
This method can provide slgnificant ~l advantages in terms o~ material savings, flexibili-ty - of providing elements of different sensitive areas, , .~ ' - .
i' P~. 32,508.
1~35~L6 enhanced detector performance, small separation of elements in multi-element devices, and provision of external electrical connections as will be described hereinafter. The method pnGvides the elements in ~, - 5 individual form rather than as a monolithic assembly and in such manner that their further assembly and contacting in the manufacture of an infra-red detector device is readily facilitated in a desirable manner.
In particular the provision of the elements with applied contact layers adjoining the oppositely loca~ed curved edges enables the further assembly of the elements either in single element devices or in multi-: element devioes to be effect~d with the electrical connections applied thereto by way of deposited con-ductive layers. mis obviates the necessity of using wire bonding of soldering with the previously mentioned attendant disadvantagesO In respect of this method --of asse~bly and contacting reference is invited to our , ;
oo-pending Canadian Patent Application No. 257,014.
The asse~bly of the individual elements on a substrate may be, for example by means of adhe ing the elements to an msulating substrate with an epoxy resin. Such a methcd may be used both for single element devices and multi-element devioes. In respect of the latter the considerable advantage arises that the spacing of the elements may be obtained as desired. me spacing may ,~
be considerably smaller than is obtained PHB 32,508 - .
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` 105964i~i ~
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in monolithically formed multi-element devices and furthermore, for example in a linear array, the pitch distances between the elements may be varied as is desired. Furthermore the formation, if desired, of two-dimensional arrays with any desired spacing is readily facilitated.
The method in accordance with the invention for forming the elements enables considerable materials ` savings to be made because in any one wafer which ` 10 is processed it is readily possible to provlde elements of different sensitive areas, for example `i`
by appropriate choice of the separation of the second ~ plurality of channels. Furthermore enhanced element !,; performance may be achieved because various surface treatments can be readily accommodated in the method.
Prior to adhering the wafer of infra-red sensitive material to the supporting body the wafer may be subjected to an oxidizing treatment to form an oxide on the surface of the wafer which is to be adhered to the supporting body. In this manner the surface of the subsequently formed infra-red sensitive elements situated opposite the surface at which in ~, operation the radiation is incident will be provided with a layer which is found to enhance the performance of the detector elements.
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~ PIIB.32508 ! 15.6.76 ~05964G
7 After adhering the wafer of infra-red sensitive material to the supporting body and prior to forming the first plurality of channels in the wafer material the wafer may be subjected to an initial thickness reduction process via the surface thereof remo-te from the supporting body. This thickness reduction may be effected by a mul$i-stage polishing process, with progressively less damage being - produced in successive stages, for example by varying ~, 10 the size of the abrasive particles used in successive ~ stages and also correspondingly varying the hardness `~ of a base lap used in the process until the desired 7 thickness is obtained.
i The treatment to obtain a reductlon in ~, 15 thickness of the strip portions and to obtain a curvature of the exposed longitudinal edges of the strip portions may comprise the combination of a polishing process 7 ' followed by an etching process.
Z Subsequént-to forming the second plurality ,, 20 of channels in the wafer material exposed surface .
parts of the elemental body portions may be subjected to a passivatingtreatment. The carrying outof the passivating treatment at this s-tage of the processing, that is subsequent to defining the array of sub-1 25 stantially rectangular elemental body portions 9 is advantageous because it enables exposed side ., . .
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PHB~32508 15.6.76 3LOS~6~
;, surfaces of the elemental body portions, ~hich in the finally produced elemen-t will adjoin the main sensitive area surface parts, to be subjected to thapassiva~ng treatment. This is desirable because in a device produced without the passivated side surfaces there could occur a degradation in performance when the device is s-ubjected to elevated temperatures.
, In a preferred form immediately prior to the passi-~: vating treatment the exposed surface parts of i 10 the elemental body portions are subjected to an etching ;~ ~f `~ treatment.
Thepassivating treatment may be confined to central surface areas of the elemental body portions which extend across said elemental body portions, said ar~as being defined by masking layer portions ~ present on opposite sides of said areas adjacent the `¦ cur~ed edges of the elemental body por-tions. The masking , layer portions may be of photoresist~
¦ Subsequent to the passivating treatment ~, 20 and prior to applying the contact layers the said masking layer portions may be removed and a further ., .
masking layer applied and defined so that each passi-vating surface area is covered by a masking layer ~ portion with the exception of a pair~of oppositely J '- 25 located peripheral strip parts thereof extending substan-tially parallel to the curved edges of the elemental body portions, a material removal treatment .~ .
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PHN.32.508 15.6.76 `: - ~596~;, ~ .
` J being effected at -the exposed s-trip parts of the pasci-`:~ vated surface areas in the presence of the masking ~i layer portions. In this manner the oxidized surface areas are slightly reduced in their lateral extent ¦ 5 prior to applying the contact layars in order to avoid problems of mask alignment when applying the contact , layers.
The said material removal treatment to , reduce the lateral extent of thepassivated surface j 10 areas may be effected by a polishing process, I for example with a lapping cloth and a very fine `~1 abrasive.
The further masking layer may be of photo-resist and the electrical contact layers formed by deposition of the electrically conductive material of ,:: . .
the exposed surface parts of the elemental body portions ¦ and the photoresist masking layer surface parts fol]owed by the chemical removal of the photoresist ~1 masking layer and the electrically conductive material ,, 20 deposited thereon. In this manner the deposited ., conductive material i~s removed from above the active ~-l surface areas of the elements by a so-called 'lift-off' technique. The use of such a technique is advantageous compared with one in which the conductive ma~erial is first deposi-ted o~er the entire surface and then defined photolithographically, particularly when the ` deposited conductive material is of gold, because ~, .
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i 1 ¦ PIIB.32.508 15.6.7G
~ ~596~6 ,, it may not be possible to etch the conductive material without removing the underlying passivating layer and possibly the material of the elemental body portions.
Subsequent to the a~plication of the contact layers the elemen-tal body portions may be re~oved from the supporting body individually by mechanical means, for example by lifting with a fine tool.
When using mechanical means for the removal, the elemental body portions may be removed from selected positions of -the array and subjected to testing procedures, for example to measure the resistivity, responsitivity, cut-off wavelength, 1 15 time constant and D , in order to evaluate the characteristics of the eIemental body portions and their distribution in the array. In this manner a form of map of the characteristics of the elemental body portions can be obtained and thereafter the elemental body portions can be selected for removal in accordance with the desired characteristics of the detector devices to be manufactured. Such a form of testing is advantageously employod when the properties of the original starting wa~er are not constant over all parts of the wafer.
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PHB.32. So8 15.6.76 ~i9~6 I For the manufacture of a multi~element infra-red detector device a group of adjacently situated elemental body portions in the array on the supporting body may be selected for removal in accordance with the evaluated characteristics of the elemental body portions removed for the testing purposes.
At least the first plurality of substantially parallel extending channels may be formed in the ¦ 10 wafer with a uniform spacing. In this manner all the ~j elemental body portions subsequently produced will have the same cross-dimension in a direction betwe~n the curved edges at two opposite sides. By varying the spacing of the said second plurality of the ¦ 15 channels which are formed in the previously defined strips of the infra-red sensitivq material the width of the elemental body portions, that is the cross-dimension in the direction parallel to the curved I edges at two opposite sides,may be varied. In this -~ 20 manner in any one starting wa~er -there may be formed ~, a plurality of elemental body por-tions of at least ¦ two different si'2ies of the active surface areas.
The method in accordance with the invention may be employed in the production of infra-red de-tector elements of various materials, particularly high cost materials. One such material is cadmium mercury telluride l -13-~, :
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'1 . Pl-I~.32.508 15.6.76 . ~ 59~41l~
where the material preparation of desired characteristics is time consuming and calls for economies whereever possible in elemen-t formation. Nevertheless the method t may also be advantageously employed in the production 1 5 oP infra-red detector elements in other materials where the cost savings on materials are not quite so relevant, for example in indiuln antimonide.
An embodiment of the invention will now be described, by way of example, with reference to ! 10 the accompanying diagrammatic drawings~ in which:
Figure 1 is a cross-sectional view of a ~¦ wafer of cadmium mercury telluride moun-ted on a polishing block and at a stage in the manu~acture after effecting a surface treatment;
~¦ 15 Figure 2 shows in cross-section the wafer a~ter mounting on a further polishing block;
. Figure 3 shows in cross-section the residual , .
wafer on the further polishing block after a thickness ~' reduction step;
Figures 4 and 5 show in plan view and cross-. section respectively the wafer on the further polishing block a~ter a further step in the processing, ~igure 5 being a section on the line V-V in Figure 4;
. Figure ~ shows in cross-section the wafer ~ .
~3 ' 25 on the further polishing block after a further thickness reduction step;
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PHB.3Z.508 15.6.76 10596~
Figure 7 shows in plan view a portion of the wafer after a further step in the processing, . and ~ Figures 8 and 9 are cross-sectional views 1 5 taken along the line VIII-VIII and IX-IX respectively of Figure 7;
Figures 10 to l2 show in cross-section ~ part of the wafer at further s-tages of the processing;
1 . Figures 13 and 14 show in cross-section and plan view respectively the same part of the waf`er at a further stage in the processing after effecting a ¦ passivàtion treatment, Figure 14 being a cross-il s~ction along the line XIV-XIV in Figure 13;
Figures 15 and 16-show in cross-section ~ 15 the same part of the wafer at further stages in the processing;
Figures 17 and 18 show in cross-section and plan view respectively the same part of the i wafer at a stage in the processing after individual elemental body portions of thewafer have been provided 3 with contact layers, Figure 17 being a cross-section ¦ along the line XVII-XVII in Figure 18;
Figure 19 is an enlarged plan view of one elemental body portion with applied contact layers I . 25 . as present on the polishing block, and Figures 20 and 2l are cross-sectional views taken on the line XX-XX and XXI-XXI resp. of Figure 19.
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l PHB.32.508 ;¦ 15.6.76 ,. I
~05~646 ; The Figures in the accompanying drawings are not to scale and consequently the relative dimensional proportions are totally distorted, particularly in a practical embodiment the thickness of the various layers in relation to their lateral extend will be much smaller than may otherwise be apparent from the drawings.
~, The embodiment now to be described `, comprises the manufacture of a large plurality of, i 10 in the range of two thousand, infra-red detector l elements of cadmium mercury telluride. In this -¦ embodiment the material composition, that is the ¦ atomic ratio of cadmlum to mercury, is such as to I produce a cut-off ~ravelength in-~eregion of 12 microns.
:! 15 The starting material is a disc-shaped ¦ ~wafer of the cadmium mercury telluride of approximately 10 mm diameter and 0.5 mm thickness.
~; The wafer 1 is mounted on a ceramic polishing block 2 with a layer of wax 3. The polishing , block has raised shoulders of 200 microns height.
Polishing of the surface of the wafer projecting .
byond the shoulders is effected by a rotary machine usinga-base lap and an abrasive slurry. The polishing is a multi-stage process ~ith progressively less ! 25 damage being produced in the crystal structure as the thickness is reduced to the desired value O:r , 200 microns. This progressive reduction in damage , .
~; .
.j PHB.32.508 15.6.76 ,,1 is achieved by the use of progressively finer abrasive particles and base laps. This polishing is continued until the surface of the wafer lies flush with the surfaces of the shoulders of the polishing block 2. To remove the remainder of the surface ' damage and etching treatment is effected with an `I etchant comprising bromine in met-hanol.
A paasivating treatment is then effected ~ith the wafer 1 still remaining adhered to the polishing block 2 so that treatment is effected on the exposed upper and side surfaces.
~igure 1 shows the wafer 1 of 200 microns thickness having an oxide surface layer 4.
¦ The wafer 1 is now removed from the polishing ¦ 1$ block 2 and is adhered via the oxidised major surface to a further polishing block 5 of high density alumina.
3 The supporting body forr~ed by the polishing block 5 has outer shoulders of 25 microns in height and within the shoulders the surface has a layer 6 of tantalum thereon. The wafer 1 is adhered to the tantalum layer 6 with a layer of wax 7~
Although the previously formed oxide surface i layer 4 is shown in Figure 2 in the following Figures it is omitted for the sake of convenience of illus-tration.
A multi-stage polishing operation is effected with a rotary lapping machine using an alumina slurry, the particle size and base laps being chosen such that .. .
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the damage produced is progressively reduced in successive stages. This polishing is effected until the polished surface of the wafer 1 is substantially co-planar with the raised shoulders of the polishing block 5. Figure 3 shows the wafer 1 after thie thickness reduction step, the wafer 1 now having a thickness of approximately 25 microns.
With the wafer 1 of reduced thickness still adhered via the wax layer 7 to the tantal-um layer 6 on the polishing block 5 a layer of photo-resist is applied on the upper surface of th~ wafer 1.
A photomasking and developing process is then effected to define a plurality of substantially parallel strip-.1 .
i shaped openings in the photoresist layer. An etching 'I 15 treatment is then effected using a suitable etchant for cadmium mercury telluride to form in the wafer ¦ a first plurality of substantially parallel extending channels 8 which define on the polishing block a plurality of substarltially parallel extending strip 1 20 portions 9 of cadmium mercury telluride.~Figures 4 t and 5 show the channels 8 and the strips 9. In this example the channels 8 are of approximately 50 microns in width and the strips are all o~ approximately 200 microns in width.
The next stage in the processing is the ' removal of the parts of the photoresist layer remaining , .' ' .
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P~B.32.508 ' 15.6.7G
,;
on the 5 trip portions 9. Thereafter a thickness reduction is effected in order to reduce the thickness of the strip portions 9 to approximately 8 microns andat the same time effect a curvature of the exposed upper longitudinal edges of the strip portions 9. This is effected by first polishing -~ wi-th a lapping machine using a fine grade pad and a ` fine abrasi~e until the resldual thicl~ness of` the strip portions 9 is approximately 12 microns and thereafter etching the strip portions 9 to remove i material of a thickness in the region of L~ to 5 microns.
~', ' .
,~¦ In this manner the upper longitudinal edges of the strip portions are rounded and this effect is utilised l 15 in order to enable the external contacting of the ¦ elements when finally produced. Furthermore the etching is found to have a sensitising effect which yields an enhanced detector performance. Figure 6 shows in cross-section the strip portions 9 after the etching process. ~ue to the distortion of the relative dimensions in the drawing the rounding of the longitudinal edges does not appear to be s~gnificant ¦ but in practice it is found that the curva-ture extends ~ in the cross-section over a clistance of at least -:! 25 15 microns from the bottom surface at each longitudinal edge. It is also noted that during the polishing to effect the sald reduction in thickness from 12 microns ;
: :1 :~ .
i ' l - PIIB.32.508 : 15.6.76 ~L05964G
.'-1. .
to 7 to 8 microns the exposed wax layer par-ts in the channels 8 are removed. Thus in the section O:r Figure 6 the wax layer 7 is now present only below each strip portion 9.
~' 5 The next stage in the processing is the application of a layer of photoresist on the upper surfaces of the strip portions. Using a conventional photomasking and developing process a plurality of i substantially parallel extending strips situated .~ 10 normal to the strip portions 9 are removed from the photoresist layer and etching of the exposed materia].
3 of the strip portions 9 is effected using a suitable I etchant for cadmium mercury telluride to obtain a plurality of substantially parallel extending channels 10 in the wafer material of the s-trip portions to ~ define on the polishing block an array of substantially `I rectangular elemental body portions 11 of cadmium ' mercury telluride. Figure 7 i5 a plan view of part of the wafer after forming the channels 10 and thus defining the elemental body portions 11, the remaining parts of the photoresist layerused for the masking , having b.een removed. Figures 8 and 9 are cross-sections `j along the lines VIII-VIII and IX-IX respectively of ~¦ Figure 7. Figure 8 shows the rounding o-f the edges of the elemental body portions 11 on two opposite sides in contrast to the near vertical edges (Figure ~) on the other two sides of the elemental body portions.
In this exa.mple the width of the channels 10 as ,, --ZO--!
PHB.32.508 `: 15.6.76 ~0~ 646 ! finally etched is approxinlately 30 microns and the final surface area of the elemen-tal body portions 11 as shown in Figure 7 is 200 microns x 50 microns.
¦ The next step in the processing is the applica-tion of a further layer 12 of pho-toresist to the surface of the elemental body portions 11 and the ~-; exposed surface portions of the wax layer 7 and the tantalum layer 6 on the polishing block 5.
By a photomasking and developing step the photoresist layer 12 is defined so that openings 13 (Figure 10) ¦ are formed therein, said openings being in the form of strips of approximately 50 microns width extending parallel to the channels 8 and exposing the elemental body portions 11 at one end thereof at which a rounded ¦ 15 edge is present and also exposing the adjoining part ~¦ of the tantalum layer 6 on the polishing block 5 from which part the wax layer 7 was previously removed in the thickness reduction polishing step. ~igure 10 ~ is a cross-section, corresponding to the section of ¦ 20 Figure 8, showing the photoresist layer 12 and the openings 13 therein.
A layer of gold of 0.5 micron thickness :
~ is now applied by sputtering. The gold is thus ¦ deposi-ted on the photoresist layer 12 and in the ¦i 25 openings 13. The photoresist layer 12 is then dissolved in a suitable solvent and the deposi-ted gold thereon ,' ~ .
; -2,~_ .
I' .
.~
PHB.32.508 15.6.'j6 1J ~059~;~6 . i is thereby removed by a lift-off technique.
Figure 11 shows a section, corresponding to the section of Figure 10, with gold layer strips 14 -~' of approximately 50~microns width forming contact .
between the upper surfaces of the elemental body ~; portions 11 and the tantalum layer 6 on the polishing - - block 5. The gold layer portions 14 are required to establish this electrical connection for a subsequently effected process because due to the combination of the oxide layer previously provided and located at the lower surfaces of the elemen*al body ~ i .
portions and the separation of the said body portlons 1 from the tantalum layer 6 by the wax layer 7 the ¦ elembntal body portions 11 would otherwise all be ,~ .
¦ 15 effectively isolated.
¦ A further layer 15 of photoresist is applied ¦ on the upper surface of the assembly and by a photo-~ masking and developing step apertures 16 in the form ,, .
,, of rectangular strips of approximately 80 microns - 20 width are formed in the photoresist layer 15.
Figure 12 is a cross-section, corresponding to the ~ section of ~igure 11, showing the strip apertures 16 " which arc located centrally on the surfaces of the elemental body portions 11. These strip aperturesl6 Z5 have a wid-th in the direction of the larger cross dimensions of the elemental body port:ions, that is '~
., .
PHB.32.508 1~.6.76 ~5~
in the direction of the section of Figure 119 which is slightly larger than the desired final dimension of the active surface areas of the ¦ elemental body portions.
I 5 In the presence of the defined photoresist j layer 15 is exposed surface portions are subjected ! to a sensitisation treatment by etching ~ to remove material over at most 1 1 micron thickness. There is then effected a passivatin~
treatment. Figure 12 diagrammatically shows in broken ¦ outlineapassivat~g layer 17 produced at the exposed surfaces of the elemental body portions 11.
The residual parts of the photoresist ~¦ layer 15 are now dissolved and Figures 13 and 14 ¦ 15 respectively show in plan view and section the ¦ assembly thus formed with the gold layer strips 14 still present and the elemental body portions 11 having surface parts provlded withap~qivat~ layer 17.
~i The gold strips 14 are shown shaded in the plan view of Figure 13 for clarity of illustra-tion. It is to be ~, noted that as the photoresist layer was removed from ! parts of the channels 10 be-tween the~ elemental body g- portions 11 along the strip apertures 16 parts of ¦ the longitudinal side surfaces of the elemental body por-tions 11 are also exposed to the passivati~g treatment and the carrying out of this process at Z
' 3 PHB.32.508 15.6.76 s~64l6 ., i this stage, that is after the element definition, can be advantageous :in this respect:.
The next step is -the application of a further layer of photoresist 18 followed by a photomasking and developing step for definition of apertures therein. The apertures are formed so that the passivated surface area on each elemental body .
portion 11 remains covered with the photoresist layer 18 with the exception of a pair of oppositely located peripheral strip parts 19 thereof extending substantially parallel tothe curved edges of the . elemental body portions 11. The photoresist layer 18 is left remaining in the channels 10 between the :~ elemental body portions and in parts of the channels 8 as shGwn in ~igure 15 be-tween the elemental body ~¦ portions it covers the exposed tantalum layer parts ,' and also partly overlaps the gold contact strips 14 where they are present on the tantalum layer 6.
' . A material removal treatment is now.~j 20 effected at -the exposed strip parts 19 of the passi-~-~ ` vated surface areas in the presence of the defined photoresist layer 18. This is obtained by a polishi.ng I process using a lapping cloth and a fine abrasive.
`~ It is possible toeffect the material removal in this manner because in general the photoresist layer has a ~reater abrasive resistance -than the passivated surface
-2~-., :
., .
.
... .
P~IB.32.508 15.6.76 .,-~LOS9~
layer and furthermore has a considerably greater thickness. In this manner the passivated surface layer is removed a-t the exposed strip parts 19 ¦ and enables the later applica-tion of contact layers ¦ 5 to the elemental body portions to be effected without j problems of alignment oocurring.
: ~, ~ Subsequent to this polishing process a :l layer 20 of gold of 0.5 micron thi.ckness is deposited ;~ on the upper surface of the assembly, including the ¦ 10 photoresist layer parts 18 and th0 exposed surface ¦ parts of the elemental body portions 11. The gold is I deposited by sputterin~ and ~igure 16 is a section, l corresponding to the section of Figure t5, showing ¦ the gold layer 20 covering the surface of the photo-:1 15 resist layer part 18 and the exposed surface parts ¦ of the elemental body portions 11. It is noted that 7 due to the removal of thepassivated surface layer . along the strip portions 19 (Figure 15) b~ a ~ polishing process the gold layer 20 contacts the ¦ 20 surfaces of the elementa.l body portions 11 at no -¦ . location where there is presen-t any suchpassivati.on layer part, that is to say the edges of the gold con-tact layer 20 are in true registration with the edges of the residual part of the passivated surface layer.
¦ 25 Following the deposition of the gol.d layer 20 the remaining portions of the photoresist i f r~ _~
P~IB. 32, 508.
~oS96~6 layer 18 æe dissolved and the portions of the gold layer 20 thereon are thus re~oved by a lift-off effect. This leaves on each ele~ental body portion 11 a pair of gold contac-t layers 21 and 22 defining therebetween an active surface area of 50 microns x 50 microns. me contact layers 21 extend o~er the rounded edge at one side of ~he ele~ents and the contact layers 22 extend in part on the residual portions of the gold strips 14 covering the rounded edge at the other side of the elements. mus a certain asymmetry occurs in so far as the contact layer 22 are in part thicker on one side than the contact layers 21 on the other side.
Figures 17 and 18 show in cross-section and plan view respectively part of the asse~bly after dissolving the`photoresist layer portions 18.
The previously effected rounding of the opp~site ``
edges of the elemental bcdy portions over which the contact layers 21 and 22 are provided enables the elemental body portions 11 wiffh said applied contact layers to be employed in the furth~r manufacture of an infra-red detector device in such manner that ~, .. .
external electrical contact to the elemental body portions is readily facilitated by a fi~m deposition process. Xn this respect reference is invited to our co-pendi~g Canadian Patent Application No. 257,014.
.
`::
. ~
',.
i ; PHB.32.508 :l 15.6.76 596~6 .1 A-t the stzLg0 of the processing as shown ~ by ~igures 17 and 18 there is present a large plurality, ., .
`. in the region of approximately two thousand cadmium l mercury telluride elemental body portions 11 with l 5 applied contact layers all remaining adhered to the . polishing block 5 via the wax layer 7. It will be ' appreciated that due to the manner of processing, :, that is starting from a slice cut from an ingot, there rnay exist some degree of variation in the characteristics of the elemental body portions 11 throughout the whole array as formed. In order to be able to use the elemental ¦ body portions 11 effectively without appreciable wastage the next step in the processing is to remove individual elemental body portions 11 from selected . 15 positions of the array and subject the elements thus . . removed to various testing procedures as previously . described. In this way a form of 'map' of the elemental characteristics over the who]e array can be obtained ;, and this used when selecting one or more of the elemental body po:rtions 11 for removal in the further :J manufacture of an infra-red detector device.
'!I In particular in the manufacture of a multi-element `¦ device then a group of adjacently situated elemental .`l body portions in the array on the polishing block will be selected for removal in accordance with the eva:Luated characteristics of -the individual el.emental ':
~27-, ~, ,~ .
1 .
PllB.32.508 15.6.76 ~59~4~
body portions previously removed for the testing procedures.
In the present embodiment the elemental . body portions 11 are individually removed ~rom the polishing block mechanically by lifting from the wax with the aid of` a fine tool.
Figure 19 shows in an enlarged plan view one elemental body portion. 11 when s-till adhered to the I polishing block S via the wax layer 7 and Figures 20 ! 10 and 21 are cross-sections taken along the line XX-XX
and XXI-XXI respectively of Figure 19. In Figures 20 I and 21 thepassivati~ la~ produced before mounting the wafer on the polishing block 5 is indicated by the broken line 4.Thepassiva-~nlayer produced after the sensitisation of`.. the active surface layer after the element definition is indicated by the broken line 17 and from Figure 21 it is seen that this very thin i surface layer is also formed along the adjoining '~ parts of the longitudinal side faces of` the elemental body portion 11. The lateral boundaries of` the area of the upper surface over which thep~vating treatment was carried out are shown by the chain lines 24 in Figure 19. :
From Figure 20 it is seen that the gold .
contact layer of 0.5 micron thickness extends over the rounded edge of' the elemental body portion 11 .
.
.~ .
PHB 32,508 ;
~0596~6 '. ,':
on one side thereof. On the rounded edge at the opposite side of the elemental body portion ll the residual portion of the gold strip 14 of 0.5 micron thickness is present. On this portion of the strip 14 : 5 the gold contact layer Z2 of 0.5 micron thickness `
is present, the contact layer 22 further extending in contact with the upper surface of the elemental body portion ll. Thus on one side of the elemental body portion the composite gold contact layer 14, ~.
22 has a thickness of l micron whereas on the other s1de the gold contact layer has a substantially uniform thickness of O.fi micron. -It will be appreciated that many modifications are possible within the scope of the invention. For example ~i the method may be applied in the manufacture of infra-red detector elements of other materials, such as indium antimonide. Instead of providing an array as shown in . i~;,.
~` Figure 17 where all the elemental body portions ll are of the same size having equal active surface areas -the method may be employed to provide from a single starting wafer an array where there are at least two different sizes of the elemental body portions~
This can readily be effected at the first photomasking stage when defining the width of the strip portions 9.
` 25 Although in the embodiment described the method comprises the application of ohmic contact layers .. . .
- 29 - `
'',', '~
PH~.32.508 . 15.6.76 ~s9~
to elemental body portions having a uniform material composition and for use in detectors of which the operation is based on the intrinsic photoconductivity, . ' within the scope of the invention there is also a method in which the elemental body portions ar0 formed each havlng a ~ Junction located in the sensi-tive area and the contact layers extending over the curved ..
.~ edges at the two opposite sides of the sensitive area .'~ of an elemental body portion respectively form contact - 10 to -the p and n-type re~ions in the elemental body portion.
' i ' ' , !
. ~ .
~; I
. .
,~ .
., ~
.... .
.
:; , .. -30-,~ !
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' !
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., .
.
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P~IB.32.508 15.6.76 .,-~LOS9~
layer and furthermore has a considerably greater thickness. In this manner the passivated surface layer is removed a-t the exposed strip parts 19 ¦ and enables the later applica-tion of contact layers ¦ 5 to the elemental body portions to be effected without j problems of alignment oocurring.
: ~, ~ Subsequent to this polishing process a :l layer 20 of gold of 0.5 micron thi.ckness is deposited ;~ on the upper surface of the assembly, including the ¦ 10 photoresist layer parts 18 and th0 exposed surface ¦ parts of the elemental body portions 11. The gold is I deposited by sputterin~ and ~igure 16 is a section, l corresponding to the section of Figure t5, showing ¦ the gold layer 20 covering the surface of the photo-:1 15 resist layer part 18 and the exposed surface parts ¦ of the elemental body portions 11. It is noted that 7 due to the removal of thepassivated surface layer . along the strip portions 19 (Figure 15) b~ a ~ polishing process the gold layer 20 contacts the ¦ 20 surfaces of the elementa.l body portions 11 at no -¦ . location where there is presen-t any suchpassivati.on layer part, that is to say the edges of the gold con-tact layer 20 are in true registration with the edges of the residual part of the passivated surface layer.
¦ 25 Following the deposition of the gol.d layer 20 the remaining portions of the photoresist i f r~ _~
P~IB. 32, 508.
~oS96~6 layer 18 æe dissolved and the portions of the gold layer 20 thereon are thus re~oved by a lift-off effect. This leaves on each ele~ental body portion 11 a pair of gold contac-t layers 21 and 22 defining therebetween an active surface area of 50 microns x 50 microns. me contact layers 21 extend o~er the rounded edge at one side of ~he ele~ents and the contact layers 22 extend in part on the residual portions of the gold strips 14 covering the rounded edge at the other side of the elements. mus a certain asymmetry occurs in so far as the contact layer 22 are in part thicker on one side than the contact layers 21 on the other side.
Figures 17 and 18 show in cross-section and plan view respectively part of the asse~bly after dissolving the`photoresist layer portions 18.
The previously effected rounding of the opp~site ``
edges of the elemental bcdy portions over which the contact layers 21 and 22 are provided enables the elemental body portions 11 wiffh said applied contact layers to be employed in the furth~r manufacture of an infra-red detector device in such manner that ~, .. .
external electrical contact to the elemental body portions is readily facilitated by a fi~m deposition process. Xn this respect reference is invited to our co-pendi~g Canadian Patent Application No. 257,014.
.
`::
. ~
',.
i ; PHB.32.508 :l 15.6.76 596~6 .1 A-t the stzLg0 of the processing as shown ~ by ~igures 17 and 18 there is present a large plurality, ., .
`. in the region of approximately two thousand cadmium l mercury telluride elemental body portions 11 with l 5 applied contact layers all remaining adhered to the . polishing block 5 via the wax layer 7. It will be ' appreciated that due to the manner of processing, :, that is starting from a slice cut from an ingot, there rnay exist some degree of variation in the characteristics of the elemental body portions 11 throughout the whole array as formed. In order to be able to use the elemental ¦ body portions 11 effectively without appreciable wastage the next step in the processing is to remove individual elemental body portions 11 from selected . 15 positions of the array and subject the elements thus . . removed to various testing procedures as previously . described. In this way a form of 'map' of the elemental characteristics over the who]e array can be obtained ;, and this used when selecting one or more of the elemental body po:rtions 11 for removal in the further :J manufacture of an infra-red detector device.
'!I In particular in the manufacture of a multi-element `¦ device then a group of adjacently situated elemental .`l body portions in the array on the polishing block will be selected for removal in accordance with the eva:Luated characteristics of -the individual el.emental ':
~27-, ~, ,~ .
1 .
PllB.32.508 15.6.76 ~59~4~
body portions previously removed for the testing procedures.
In the present embodiment the elemental . body portions 11 are individually removed ~rom the polishing block mechanically by lifting from the wax with the aid of` a fine tool.
Figure 19 shows in an enlarged plan view one elemental body portion. 11 when s-till adhered to the I polishing block S via the wax layer 7 and Figures 20 ! 10 and 21 are cross-sections taken along the line XX-XX
and XXI-XXI respectively of Figure 19. In Figures 20 I and 21 thepassivati~ la~ produced before mounting the wafer on the polishing block 5 is indicated by the broken line 4.Thepassiva-~nlayer produced after the sensitisation of`.. the active surface layer after the element definition is indicated by the broken line 17 and from Figure 21 it is seen that this very thin i surface layer is also formed along the adjoining '~ parts of the longitudinal side faces of` the elemental body portion 11. The lateral boundaries of` the area of the upper surface over which thep~vating treatment was carried out are shown by the chain lines 24 in Figure 19. :
From Figure 20 it is seen that the gold .
contact layer of 0.5 micron thickness extends over the rounded edge of' the elemental body portion 11 .
.
.~ .
PHB 32,508 ;
~0596~6 '. ,':
on one side thereof. On the rounded edge at the opposite side of the elemental body portion ll the residual portion of the gold strip 14 of 0.5 micron thickness is present. On this portion of the strip 14 : 5 the gold contact layer Z2 of 0.5 micron thickness `
is present, the contact layer 22 further extending in contact with the upper surface of the elemental body portion ll. Thus on one side of the elemental body portion the composite gold contact layer 14, ~.
22 has a thickness of l micron whereas on the other s1de the gold contact layer has a substantially uniform thickness of O.fi micron. -It will be appreciated that many modifications are possible within the scope of the invention. For example ~i the method may be applied in the manufacture of infra-red detector elements of other materials, such as indium antimonide. Instead of providing an array as shown in . i~;,.
~` Figure 17 where all the elemental body portions ll are of the same size having equal active surface areas -the method may be employed to provide from a single starting wafer an array where there are at least two different sizes of the elemental body portions~
This can readily be effected at the first photomasking stage when defining the width of the strip portions 9.
` 25 Although in the embodiment described the method comprises the application of ohmic contact layers .. . .
- 29 - `
'',', '~
PH~.32.508 . 15.6.76 ~s9~
to elemental body portions having a uniform material composition and for use in detectors of which the operation is based on the intrinsic photoconductivity, . ' within the scope of the invention there is also a method in which the elemental body portions ar0 formed each havlng a ~ Junction located in the sensi-tive area and the contact layers extending over the curved ..
.~ edges at the two opposite sides of the sensitive area .'~ of an elemental body portion respectively form contact - 10 to -the p and n-type re~ions in the elemental body portion.
' i ' ' , !
. ~ .
~; I
. .
,~ .
., ~
.... .
.
:; , .. -30-,~ !
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' !
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Claims (15)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS
1. A method of manufacturing a plurality of infra-red detector elements each comprising a body of infra-red sensitive material having a substantially rectangular surface configuration with a pair of low resistance electrical contacts spaced apart on one surface of the body at opposite sides of a sensitive area of the element, characterized in that a wafer of the infra-red sensitive material is adhered to a supporting body, a first plurality of substantially parallel extending channels are formed extending in the wafer material to define on the supporting body a plurality of substantially parallel strip portions of the infra-red sensitive material, a treatment to obtain a reduction in the thickness of the strip portions is effected and to obtain a curvature of the exposed longitudinal edges of the strip portions, a second plurality of substantially parallel extending channels are formed in the wafer material of the strip portions in a direction substantially normal to the longitudinal direction of the strip portions to define on the supporting body an array of substantially rectangular elemental body portions of the infra-red sensitive material each having curved edges on two opposite sides, electrically conductive material is deposited to form on the surface of each elemental body portion a pair of electrical contact layers which are spaced apart and adjoin the oppositely located curved edges, and the elemental body portions with applied contact layers are removed from the supporting body.
2. A method as claimed in Claim 1, characterized in that prior to adhering the wafer of infra-red sensi-tive material to the supporting body the wafer is sub-jected to an oxidizing treatment to form an oxide at least on the surface of the wafer which is to be adhered to the supporting body.
3. A method as claimed in Claim 1, characterized in that after adhering the wafer of infra-red sensitive material by the supporting body and prior to forming the first plurality of channels in the wafer material the wafer is subjected to an initial thickness reduction pro-cess via the surface thereof remote from the supporting body.
4. A method as claimed in Claim 1, characterized in that the treatment effected to obtain a reduction in thickness of the strip portions and to obtain a curva-ture of the exposed longitudinal edges of the strip portions comprises the combination of a polishing process followed by an etching process.
5. A method as claimed in Claim 1, characterized in that subsequent to forming the second plurality of channels in the wafer material exposed surface parts of the elemental body portions are subjected to a passivating treatment.
6. A method as claimed in Claim 5, characterized in that immediately prior to the passivating treatment the exposed surface parts of the elemental body portions are sub-jected to an etching treatment.
7. A method as claimed in Claim 5, characterized in that the passivating treatment is confined to a central surface of the elemental body portions which areas extend across said elemental body portions, said areas being defined by masking layer portions present on opposite sides of said areas adjacent the curved edges of the elemental body portions.
8. A method as claimed in Claim 7, characterized in that subsequent to the passivating treatment and prior to applying the contact layers the said masking layer portions are removed and a further masking layer is applied and defined so that each passivated surface area is covered by a masking layer portion with the exception of a pair of oppositely located peripheral strip parts thereof extending substantially parallel to the curved edges of the elemental body portions, a material removal treatment being effected at the exposed strip parts of the passivated surface areas in the presence of the mask-ing layer portions.
9. A method as claimed in Claim 8, characterized in that said material removal treatment is effected by a polishing process.
10. A method as claimed in Claim 9, characterized in that the further masking layer is of photoresist and the electrical contact layers are formed by deposition of the electrically conductive material on the exposed sur-face parts of the elemental body portions and the photoresist masking layer surface parts followed by the chemical removal of the photoresist masking layer and the electrically conduc-tive material deposited thereon.
11. A method as claimed in Claim 1, characterized in that subsequent to the application of the contact layers the elemental body portions are removed from the supporting body individually by mechanical means.
12. A method as claimed in Claim 11, characterized in that elemental body portions are removed from selected posi-tions of the array and subjected to testing procedures in order to evaluate the characteristics of the elemental body portions and their distribution in the array.
13. A method as claimed in Claim 12, characterized in that for the manufacture of a multi-element infra-red detector device a group of adjacently situated elemental body portions in the array on the supporting body are selected for removal in accordance with the evaluated characteristics of the ele-mental body portions removed for the testing procedures.
14. A method as claimed in Claim 1, characterized in that at least the first plurality of substantially parallel extending channels are formed in the wafer with a substan-tially uniform spacing.
15. A method as claimed in Claim 1, characterized in that the infra-red sensitive material is cadmium mercury telluride.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB30800/75A GB1559473A (en) | 1975-07-23 | 1975-07-23 | Manufacturing infra-red detector elements |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1059646A true CA1059646A (en) | 1979-07-31 |
Family
ID=10313325
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA257,013A Expired CA1059646A (en) | 1975-07-23 | 1976-07-15 | Methods of manufacturing infrared detector elements |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA1059646A (en) |
| GB (1) | GB1559473A (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2548443B2 (en) * | 1983-06-30 | 1987-05-07 | Telemecanique Electrique | IMPROVEMENT TO ELECTRICAL SWITCHES USING AN INSULATING SCREEN WHICH SHEARS THE ARC APPEARING BETWEEN THE CONTACTS |
| JPS62154780A (en) * | 1985-12-27 | 1987-07-09 | Toshiba Corp | Image sensor |
| US4803375A (en) * | 1985-12-27 | 1989-02-07 | Kabushiki Kaisha Toshiba | Image sensors and methods of manufacturing same including semiconductor layer over entire substrate surface |
| GB9204078D0 (en) * | 1992-02-26 | 1992-04-08 | Philips Electronics Uk Ltd | Infrared detector manufacture |
-
1975
- 1975-07-23 GB GB30800/75A patent/GB1559473A/en not_active Expired
-
1976
- 1976-07-15 CA CA257,013A patent/CA1059646A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| GB1559473A (en) | 1980-01-16 |
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