GB1559473A - Manufacturing infra-red detector elements - Google Patents
Manufacturing infra-red detector elements Download PDFInfo
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- GB1559473A GB1559473A GB30800/75A GB3080075A GB1559473A GB 1559473 A GB1559473 A GB 1559473A GB 30800/75 A GB30800/75 A GB 30800/75A GB 3080075 A GB3080075 A GB 3080075A GB 1559473 A GB1559473 A GB 1559473A
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- 238000004519 manufacturing process Methods 0.000 title claims description 23
- 239000000463 material Substances 0.000 claims description 52
- 238000000034 method Methods 0.000 claims description 45
- 229920002120 photoresistant polymer Polymers 0.000 claims description 27
- 238000011282 treatment Methods 0.000 claims description 25
- 230000000873 masking effect Effects 0.000 claims description 18
- 238000005530 etching Methods 0.000 claims description 15
- 229910000661 Mercury cadmium telluride Inorganic materials 0.000 claims description 11
- MCMSPRNYOJJPIZ-UHFFFAOYSA-N cadmium;mercury;tellurium Chemical compound [Cd]=[Te]=[Hg] MCMSPRNYOJJPIZ-UHFFFAOYSA-N 0.000 claims description 11
- 239000004020 conductor Substances 0.000 claims description 11
- 238000004381 surface treatment Methods 0.000 claims description 8
- 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
- 238000009826 distribution Methods 0.000 claims description 2
- 230000002093 peripheral effect Effects 0.000 claims description 2
- 238000011946 reduction process Methods 0.000 claims description 2
- 239000000126 substance Substances 0.000 claims description 2
- 239000010410 layer Substances 0.000 description 91
- 238000005498 polishing Methods 0.000 description 34
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 20
- 229910052737 gold Inorganic materials 0.000 description 20
- 239000010931 gold Substances 0.000 description 20
- 238000012545 processing Methods 0.000 description 15
- 238000000926 separation method Methods 0.000 description 8
- 239000002344 surface layer Substances 0.000 description 8
- 229910052715 tantalum Inorganic materials 0.000 description 7
- GUVRBAGPIYLISA-UHFFFAOYSA-N tantalum atom Chemical compound [Ta] GUVRBAGPIYLISA-UHFFFAOYSA-N 0.000 description 7
- 230000000694 effects Effects 0.000 description 5
- 230000015572 biosynthetic process Effects 0.000 description 4
- 238000012360 testing method Methods 0.000 description 4
- 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
- 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
- WPYVAWXEWQSOGY-UHFFFAOYSA-N indium antimonide Chemical compound [Sb]#[In] WPYVAWXEWQSOGY-UHFFFAOYSA-N 0.000 description 2
- 238000005304 joining Methods 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 239000002002 slurry Substances 0.000 description 2
- 238000004544 sputter deposition Methods 0.000 description 2
- 241000587161 Gomphocarpus Species 0.000 description 1
- 241000976924 Inca Species 0.000 description 1
- 229910052793 cadmium Inorganic materials 0.000 description 1
- BDOSMKKIYDKNTQ-UHFFFAOYSA-N cadmium atom Chemical compound [Cd] BDOSMKKIYDKNTQ-UHFFFAOYSA-N 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
- 230000001419 dependent effect Effects 0.000 description 1
- 238000005137 deposition process Methods 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000005538 encapsulation Methods 0.000 description 1
- 239000003822 epoxy resin Substances 0.000 description 1
- 239000004744 fabric Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000002161 passivation Methods 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
- 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
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Microelectronics & Electronic Packaging (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)
Description
(54) IMPROVEMENTS IN METHODS OF
MANUFACTURING INFRA-RED
DETECTOR ELEMENTS (71) We, MULLARD LIMITED, of Abacus House, 33 Gutter Lane,
London EC2V 8AH, a British Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement :- 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 connectors to the elements, the testing of the elements provided with said connections and the eventual final encapsulation 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 as a linear array. For devices in which the operation is dependent 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 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 element manufacture which lead to enconomies in the use of such material are significant. However the problem arises that there may exist a wide variety of requirements for different element sizes and characteristics and mounting configurations depending upon the particular infra-red detector device to be manufactured, for example the size of the sensitive area of the elements may be as small as 25 micronsx25 microns and as large as 2 mmx2 mm. When forming the element or elements from a slice of the infra-red sensitive material it is thus costly if for each different configuration a fresh slice of such material has to be used as the starting body.
For the manufacture of the devices comprising an array of infrared detector elements the further problem of yield occurs when, 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 example, 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 monolithic approach, particularly in connection with the spacing of the individual elements in a group 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 achieved because in general when etching the body of infra-red sensitive material the width of a channel will 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
readily possible by etching to achieve a separation of individual elements of less than 12 microns. Furthermore if the processing is such that the individual elements are defined before the final reduction in thickness the handling and further processing of bodies of such small thickness may be extremely difficult.
Another problem which arises, both in single element devices and in arrays, is the provision of electrical connections to the or each individual infra-red detector element.
Hitherto this has been effected by joining wire leads onto metallised surface 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 element to which the wire is bonded is sufficient to accommodate the finally deformed 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 limitations on the achievable minimum separation between adjoining elements in an array.
Aiso problems occur when joining the other ends of the wire leads, for example by soldering, to lad-out conductors.
Another problem associated with the socalled 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.
This non-uniformity of spacing may be desired, for example, when different degrees of resolution 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 gives rise to many difficulties and can be extremely costly in terms of the material required.
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 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, wherein 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 is effected to obtain a reduction in the thickness of the strip portions and to obtain a rounding 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 rectangular element body portions of the infra-red sensitive material each having rounded 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 ad join the opposite
located rounded edges, and the elemental
body portions with applied contact layers
are removed from the supporting body.
This method can provide significant
avantages in terms of material savings,
flexibility of providing elements of different
sensitive areas, enhanced detector
performance, small separation of elements
in mutli-element devices, and provision of
external electrical connections as will be
described hereinafter.
The method provides the elements in
individual from 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 particurar the provision of
the elements with applied contact layers
adjoining the opposite located rounded
edges enables the further assembly of the
elements either in single element devices or
in mutli-element devices to be effected with
the electrical connections applied thereto
by way of deposited conductive layers. This
obviates the necessity of using wire bonding
or soldering with the previously mentioned
attendant disadvantages. In respect of this
method of assembly and contacting
reference is invited to our co-pending
Patent Application No. 3086/76 (PHB
32509), Serial No. 1559474. The assembly of
the individual elements on a substrate may be, for example, by means of adhering the
elements to an insulating substrate with an
epoxy resin. Such a method may be used
both for single element devices and multielement devices. In respect to the latter the
considerable advantage arises that the
spacing of the elements may be obtained as
desired. The spacing may be considerably
smaller than is obtained 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 is
processed it is readily possible to provide
elements of different sensitive areas, for
example by appropriate choice of the
separation of the second plurality of
channels. Furthermore enhanced element
performance may be achieved because
various surface treatments as will be
described hereinafter can be readily accommodated in the method with enhanced effect.
Prior to adhering the wafer of infra-red sensitive material to the supporting body the wafer may be subjected to a surface treatment to form a passivating layer at least at 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.
After the 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 remote from the supporting body. This thickness reduction may be effected by a multi-stage polishing process, with progressively less damage being produced in successive stages, for example by varying the size of the abrasive particles used in successive stages and also corresponding varying the hardness of a base lap used in the process until the desired thickness is obtained.
The treatment to obtain a reduction in thickness of the strip portions and to obtain a rounding of the exposed longitudinal edges of the strip portions may comprise the combination of a polishing process followed by an etching process.
Subsequent to forming the second plurality of channels in the wafer material exposed surface parts of the elemental body portions may be subjected to a passivating treatment. The carrying out of the
passivating treatment at this stage of the processing, that is subsequent to defining the array of substantially rectangular elemental body portions, is advantageous because it enables exposed side surfaces of the elemental body portions, which in the finally produced element will adjoin the main sensitive area surface parts, to be subjected to the surface 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 subjected to elevated temperatures. In a preferred form immediately prior to the passivating treatment the exposed surface parts of the elemental body portions are subjected to an etching treatment.
The passivating treatment may be confined to central surface areas of the elemental body portions which extend across said elemental body portions, said areas being defined by masking layer portions present on opposite sides of said areas adjacent the rounded edges of the elemental body portions. The masking layer portions may be of photoresist.
Subsequent to the passivating treatment 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 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 rounded 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 masking layer portions. In this manner the passivated surface areas are slightly reduced in their lateral extent prior to applying the contact layers in order to avoid problems of mask alignment when applying the contact layers.
The said material removal treatment to reduce the lateral extent of the passivated surface areas may be effected by a polishing process, for example with a lapping cloth and a very fine abrasive.
The further masking layer may be of photoresist and the electrical contact layers formed by deposition of the electrically conductive material on the exposed surface
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 electric
ally conductive material deposited thereon.
In this manner the deposited conductive material is removed from above the active 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 material is first deposited over the entire surface and then defined photolithographically, particularly when the deposited conductive material is of gold, because 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 application of the contact layers the elemental body portions may be removed 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, responsivity, cut-off wavelength, time constant and Dx (D-star), in order to evaluate the characteristics of the elemental 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 employed when the properties of the original starting wafer are not constant over all parts of the wafer.
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 m the wafer with a uniform spacing. In this manner all the elemental body portions subsequently produced will have the same cross-dimension in a direction between the rounded edges at two opposite sides. By varying the spacing of the said second plurality of the channels which are formed in the previously defined strips of the infrared sensitive material the width of the elemental body portions, that is the crossdimension in the direction parallel to the rounded edges at two opposite sides, may be varied. In this manner in any one starting wafer there may be formed a plurality of elemental body portions of at least two different sizes of the active surface areas.
The method in accordance with the invention may be employed in the production of infra-red detector elements of various materials, particularly high cost materials. One such material is cadmium mercury telluride where the material preparation of desired characteristics is time consuming and calls for economics wherever possible in element formation.
Nevertheless the method may also be advantageously employed in the production of infra-red detector elements in other materials where the cost savings on materials are not quite so relevant, for example in indium antimonide.
An embodiment of the invention will now be described, by way of example, with reference to the diagrammatic drawings accompanying the Provisional
Specification, in which :- Figure I is a cross-sectional view of a wafer of cadmium mercury telluride mounted on a polishing block and at a stage in the manufacture after effecting a surface treatment ;
Figure 2 shows in cross-section the wafer after mounting on a further polishing block ;
Figure 3 shows in cross-section the residual wafer on the further polishing block after a thickness reduction ;
Figures 4 and 5 in plan view and crosssection respectively the wafer on the further polishing block after a further step in the processing, Figure 5 being a section on the line V-V in Figure ;
Figure 6 shows in cross-section the wafer on the further polishing block after a further thickness reduction step :
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 taken along the line VIII-VIII and IX-IX respectively of Figure 7;
Figures 10 to 12 show in cross-section part of the wafer at further stages of the processing;
Figure 13 and 14 show in cross-section and plan view respectively the same part of the wafer at a further stage in the processing after effecting a passivation treatment, Figure 14 being a cross-section along the line XIV-XIV in Figure 13 ; Figures 15 and 16 show in cross-section 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 wafer at a stage in the processing after individual elemental body portions of the wafer have been provided 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 as present on the polishing block, and
Figures 20 and 21 are cross-sectional views taken along the line XX-XX and
XXI-XXI respectively of Figure 19.
The Figures in the drawings accompanying the Provisional Specification 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 extent 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, in the region of two thousand, infra-red detector elements of cadmium mercury telluride. In this embodiment the material composition, that is the atomic ratio of cadmium to mercry, is such as to produce a cut-off wavelength in the region of 12 microns.
The starting material is 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 beyond the shoulders is effected by a rotary machine using a base lap and an abrasive slurry. The polishing is a multi-stage process with progressively less damage being produced in the crystal structure as the thickness is reduced to the desired value of 200 microns. This progressive reduction in damage 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 an etching treatment is effected.
A surface treatment is then effected with the wafer I still remaining adhered to the polishing block 2 so that treatment is effected on the exposed upper and side surfaces. In this respect reference is invited to co-pending Application No. 30799/755 (PHB 32507). Figure t shows the wafer 1 of 200 microns thickness having a passivating surface layer 4.
The wafter I is now removed from the polishing block 2 and is adhered via the treated major surface to a further polishing block 5 of high density alumina. The supporting body formed 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 passivating surface layer 4 is shown in
Figure 2 in the following Figures it is omitted for the sake of convenience of illustration. 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 the damage produced is progressively reduced in successive stages.
This polishing is effected until the polished surface of the wafer I is substantially co planar with the raised shoulders of the polishing block 5. Figure 3 shows the wafer
I after this thickness reduction step, the wafer I now having a thickness of approximately 25 microns.
With the wafer I of reduced thickness still adhered via the wax layer 7 to the tantalum layer 6 on the polishing block 5 a layer of photoresist is applied on the upper surface of the wafer 1. A photomasking and developing process is then effected to define a plurality of substantially parallel stripshaped openings in the photoresist layer.
An etching 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 substantially parallel extending strip portions 9 of cadmium mercury telluride. Figures 4 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 of approximately 200 microns in width.
The next stage in the processing is the removal of the parts of the photoresist layer remaining on the strip portions 9.
Thereafter a thickness reduction is effected in order to reduce the thickness of the strip portions 9 to approximately 8 microns and at the same time effect a rounding of the exposed upper longitudinal edges of the strip portions 9. This is effected by first polishing with a lapping machine using a fine grade pad and a fine abrasive until the the residual thickness of the strip portions 9
is approximately 12 microns and thereafter etching the strip portions 9 to remove
material of a thickness in the region of 4 to 5
microns. In this manner the upper
longitudinal edges of the strip portions are
rounded and this effect is utilise in order to
enable the external contacting of the
elements when finally produced.
Furthermore the etching may be effected to
produce a sensitising effect which yields an
enhanced detector performance. Figure 6
shows in cross-section the strip portions 9
after the etching process. Due to the distortion of the relative dimensions in the
drawing the rounding of the longitudinal
edges does not appear to be significant but
in practice it is found that the rounding
extends in the cross-section over a distance
of at least 15 microns from the bottom
surface at each longitudinal edge. It is also
noted that during the polishing to effect the
said reduction in thickness from 12 microns
to 7 to 8 microns the exposed wax layer
parts in the channels 8 are removed. Thus in the section of Figure 6 the wax layer 7 is now present only below each strip portion 9.
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 substantialy parallel extending strips situated normal to the strip portions 9 are removed from the photoresist layer and etching of the exposed material of the strip portions 9 is effected using a suitable etchant for cadmium mercury telluride to obtain a plurality of substantially parallel extending channels 10 in the wafer material of the strip portions to define on the polishing block an array of substantially rectangular elemental body portions I1 of cadmium mercury telluride. Figure 7 is 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 layer used for the masking having been removed. Figures 8 and 9 are cross-sections along the lines
Vill-Vill and IX-IX respectively of
Figure 7. Figure 8 shows the rounding of the edges of the elemental body portions 11 on two opposite sides in contrast to the near vertical edges (Figure 9) on the other two sides of the elemental body portions. In this example the width of the channels 10 as finally etched is approximately 30 microns and the final surface area of the elemental body portions 1 I as shown in Figure 7 is 200 microns x50 microns.
The next step in the processing is the application of a further layer 12 of photoresist 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 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. Figure 10 is a cross-section, corresponding to the section of 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 deposited on the photoresist layer 12 and in the openings 13. The photoresist layer 12 is then dissolved in a suitable solvent and the deposited gold thereon is thereby removed by a lift-off technique. Figure I I shows a section, corresponding to the section of
Figure 10, with gold layer strips 14 of approximately 50 microns width forming contacts 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 subsequent process because due to the combination of the passivating layer previously provided and located at the lower surfaces of the elemental body portions and the separation of the said body portions from the tantalum layer 6 by the wax layer 7 the elemental body portions 11 would otherwise all be effectively isolated.
A further layer 15 of photoresist is applied on the upper surface of the assembly and by a photomasking and developing step apertures 16 in the form of rectangular strips of approximately 80 microns width are formed in the photoresist layer 15. Figure 12 is a cross-section, corresponding to the section of Figure 11, showing the strip apertures 16 which are located centrally on the surfaces of the elemental body portions I I. These strip apertures 16 have a width in the direction of the larger cross dimensions of the elemental body portions, that is in the direction of the section of Figure 11, which is slightly larger than the desired final dimension of the active surface areas of the elemental body portions.
In the presence of the defined photoresist layer 15 the exposed surface portions are subjected to a sensitisation treatment by etching to remove material over at most I micron thickness. There is then effected another passivating treatment. Figure 12 diagrammatically shows in broken out) inca passivating layer 17 produced at''the exposed surfaces of the elemental body portions li. The residual parts of the photoresist layer 15 are now dissolve and
Figures 1 possible to effect the material removal in this manner because in general the photoresist layer has a greater abrasive resistance than the passivating surface layer and furthermore has a considerably greater thickness. In this manner the passivating surface layer is removed at the exposed strip parts 19 and enables the later application of contact layers to the elemental body portions to be effected without problems of alignment occurring.
Subsequent to this polishing process a layer 20 of gold of 0.5 micron thickness is deposited on the upper surface of the assembly, including the photoresist layer parts 18 and the exposed surface parts of the elemental body portions 11. The gold is deposited by sputtering and Figure 16 is a section, corresponding to the section of
Figure 15, showing the gold layer 20 covering the surface of the photoresist layer part 18 and the exposed surface parts of the elemental body portions 11. It is noted that due to the removal of the passivating surface layer along the strip portions 19 (Figure 15) by a polishing process the gold layer 20 contacts the surfaces of the elemental body portions I I at no location where there is present any such passivating layer part, that is to say the edges of the gold contact layer 20 are in true registration with the edges of the residual part of the passivating surface layer.
Following the deposition of the gold layer 20 the remaining portions of the photoresist layer 18 are dissolve and the portions of the gold layer 20 thereon are thus removed by a lift-off effect. This leaves on each elemental body portion 11 a pair of gold contact layers 21 and 22 defining therebetween an active surface area of 50 micronsx50 microns. The contact layers 21 extend over the rounded edge at one side of the elements 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. Thus a certain asymmetry occurs in so far as the contact layers 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 assembly after dissolving the photoresist layer portions 18. The previously effected rounding of the opposite edges of the elemental body portions over which the contact layers 21 and 22 are provided enables the elemental body portions 1 I with said applied contact layers to be employed in the further manufacture of an infra-red detector device in such manner that external electrical contact to the elemental body portions is readily facilitated by a film deposition process. In this respect reference is invited to our co-pending Patent
Application No. 30806/75 Serial No.
1559474 (PHB 32509).
At the stage of the processing as shown by
Figures 17 and 18 there is present a large plurality, in the region of approximately two thousand cadmium mercury telluride elemental body portions 11 with 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 may 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 I I from selected 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 whole array can be obtained and this used when selecting one or more of the elemental body portions 11 for removal in the further manufacture of an infra-red detector device. In particular in the manufacture of a multi-element device then a group of adjacently situated elemental body portions in the array on the polishing block will be selected for removal in accordance with the evaluated characteristics of the individual element body portions previously removed for the testing procedures.
In the present embodiment the elemental body portions 11 are individually removed from 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 I1 when still adhered to the polishing block 5 via the wax layer 7 and Figures 20 and 21 are crosssections taken along the line X-X and
XXI-XXI respectively of Figure 19. In
Figures 20 and 21 the surface layer produced before mounting the wafer on the polishing block 5 is indicated by the broken line 4. The passivating layer produced after the sensitisation of the active surface area after the element definition is indicated by the broken line 17 and from
Figure 21 it is seen that this very thin 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 the passivating 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 I1 on one side thereof. On the rounded edge at the opposite side of the elemental body portion I I the residual portion of the gold strip 14 of 0.5 micron thickness is present. On this portion of the strip 14 the gold contact layer 22 of 0.5 micron thickness is present, the contact layer 22 further extending in contact with the upper surface of the elemental body portion 11. Thus on one side of the elemental body portion the composite gold contact layer 14, 22 has a thickness of I micron whereas on the other side the gold contact layer has a substantially uniform thickness of 0.5 micron.
It will be appreciated than many modifications are possible within the scope of the invention, for example the method may be applied in the manufacture of infrared detector elements of other materials, such as indium antimonide. Instead of providing an array as shown in Figure 17 where all the elemental body portions I 1 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. Although in the embodiment described the method comprises the application of ohmic contact layers 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 are formed each having a p-n junction located in the sensitive area and the contact layers extending over the rounded edges at the two opposite sides of the sensitive area of an elemental body portion respectively form contact to the p and n-type regions in the elemental body portion.
Claims (17)
- WHAT WE CLAIM IS : 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, wherein 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 is effected to obtain a reduction in the thickness of the strip portions and to obtain a rounding 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 rounded 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 opposite located rounded edges, and the elemental body portions with applied contact layers are removed from the supporting body.
- 2. A method as claimed in Claim 1, wherein prior to adhering the wafer of infrared sensitive material to the supporting body the wafer is subjected to a surface treatment to form a passivating layer at least at the surface of the wafer which is to be adhered to the supporting body.
- 3. A method as claimed in Claim I or Claim 2, wherein 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 is subjected to an initial thickness reduction process via the surface thereof remote from the supporting body.
- 4. A method as claimed in any of Claims I to 3, wherein the treatment effected to obtain a reduction in thickness of the strip portions and to obtain a rounding 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 any of Claims I to 4, wherein subsequent to forming the second plurality of channels in the wafer material exposed surface parts of the electrical body portions are subjected to a passivating treatment.
- 6. A method as claimed in Claim 5, wherein immediately prior to the passivating treatment the exposed surface parts of the elemental body portions are subjected to an etching treatment.
- 7. A method as claimed in Claim 5 or Claim 6, wherein 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 rounded edges of the elemental body portions.
- 8. A method as claimed in Claim 7, wherein subsequent to the surface 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 rounded 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 masking layer portions.
- 9. A method as claimed in Claim 8, wherein said material removal treatment is effected by a polishing process.
- 10. A method as claimed in Claim 9, wherein the further masking layer is of photoresist and the electrical contact layers are formed by deposition of the electrically conductive material on the exposed surface 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 conductive material deposited thereon.
- I I. A method as claimed in any of Claims I to 10, wherein 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, wherein elemental body portions are removed from selected positions 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, wherein for the manufacture of a multielement 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 elemental body portions removed for the testing procedures.
- 14. A method as claimed in any of Claims 1 to 13, wherein at least the first plurality of substantially parallel extending channels are formed in the wafer with a substantially uniform spacing.
- 15. A method as claimed in any of Claims I to 14, wherein the infra-red sensitive material is cadmium mercury telluride.
- 16. A method of manufacturing a plurality of infra-red detector elements substantially as herein described with reference to the drawings accompanying the Provisional Specification.
- 17. An infra-red detector element when manufactured by a method as claimed in any of the preceding Claims.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB30800/75A GB1559473A (en) | 1975-07-23 | 1975-07-23 | Manufacturing infra-red detector elements |
| CA257,013A CA1059646A (en) | 1975-07-23 | 1976-07-15 | Methods of manufacturing infrared detector elements |
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 |
|---|---|
| GB1559473A true GB1559473A (en) | 1980-01-16 |
Family
ID=10313325
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB30800/75A Expired GB1559473A (en) | 1975-07-23 | 1975-07-23 | Manufacturing infra-red detector elements |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA1059646A (en) |
| GB (1) | GB1559473A (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2548443A2 (en) * | 1983-06-30 | 1985-01-04 | Telemecanique Electrique | Enhancement to electric switches using an insulating screen which shears the arc appearing between the contacts |
| EP0228281A1 (en) * | 1985-12-27 | 1987-07-08 | Kabushiki Kaisha Toshiba | Image sensors and methods of manufacturing same |
| US4808833A (en) * | 1985-12-27 | 1989-02-28 | Kabushiki Kaisha Toshiba | Image sensors using a photo-sensing element array and matrix wires methods of manufacturing same |
| US5647954A (en) * | 1992-02-26 | 1997-07-15 | Gec Marconi Limited | Manufacture of etched substrates such as infrared detectors |
-
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
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2548443A2 (en) * | 1983-06-30 | 1985-01-04 | Telemecanique Electrique | Enhancement to electric switches using an insulating screen which shears the arc appearing between the contacts |
| EP0228281A1 (en) * | 1985-12-27 | 1987-07-08 | Kabushiki Kaisha Toshiba | Image sensors and methods of manufacturing same |
| 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 |
| US4808833A (en) * | 1985-12-27 | 1989-02-28 | Kabushiki Kaisha Toshiba | Image sensors using a photo-sensing element array and matrix wires methods of manufacturing same |
| US5647954A (en) * | 1992-02-26 | 1997-07-15 | Gec Marconi Limited | Manufacture of etched substrates such as infrared detectors |
Also Published As
| Publication number | Publication date |
|---|---|
| CA1059646A (en) | 1979-07-31 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PS | Patent sealed | ||
| 732 | Registration of transactions, instruments or events in the register (sect. 32/1977) | ||
| 732 | Registration of transactions, instruments or events in the register (sect. 32/1977) | ||
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19920723 |