WO1992006502A1 - Dispositif d'imagerie ayant un transistor a film mince ameliore et structures de dispositif photosensible - Google Patents

Dispositif d'imagerie ayant un transistor a film mince ameliore et structures de dispositif photosensible Download PDF

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Publication number
WO1992006502A1
WO1992006502A1 PCT/US1991/007336 US9107336W WO9206502A1 WO 1992006502 A1 WO1992006502 A1 WO 1992006502A1 US 9107336 W US9107336 W US 9107336W WO 9206502 A1 WO9206502 A1 WO 9206502A1
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WO
WIPO (PCT)
Prior art keywords
semiconductor material
layer
thin film
photosensitive
film transistor
Prior art date
Application number
PCT/US1991/007336
Other languages
English (en)
Inventor
Robert Forrest Kwasnick
Original Assignee
General Electric Company
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by General Electric Company filed Critical General Electric Company
Publication of WO1992006502A1 publication Critical patent/WO1992006502A1/fr

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components 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
    • H01L27/144—Devices controlled by radiation
    • H01L27/146—Imager structures
    • H01L27/14643—Photodiode arrays; MOS imagers

Definitions

  • the present invention is related to the field of photosensitive imaging arrays, and more particularly, to such imaging arrays which incorporate thin film transistors for control of readout.
  • One type of photosensor array comprises a substrate having an array of amorphous silicon (a-Si) thin film transistors (TFT's) disposed thereon.
  • the thin film transistors in turn, have an array of amorphous silicon photodiodes disposed thereover and in contact therewith, wit-h one photodiode associated with and connected to each thin film transistor.
  • Such imagers can be fabricated with a relatively high density of relatively small photosensitive cells and can be made much larger in area as compared to such photosensor arrays fabricated in monocrystalline silicon. As a consequence, such imagers have found application in a number of products.
  • the most common form of such a photosensitive array employs inverted thin film transistors and in sequence from the substrate up, comprise a gate electrode pattern disposed on the substrate and configured to serve as a scan line for a row of thin film transistors by connecting the gates of all of the thin film transistors on a row in parallel, a gate dielectric overlying the gate electrode pattern and exposed portions of the substrate, a layer of intrinsic amorphous silicon having a thinner layer of N + doped amorphous silicon disposed thereon with that silicon layer being patterned to provide the thin film transistors of the readout system, a layer of source/drain metallization disposed over the layers of semiconductor material and patterned to provide the source and drain electrodes of the individual thin film transistors and to couple a column of thin film transistors in parallel to a data scan line integral with the drain metallization of the transistors of that column.
  • the source electrodes are individually isolated to individual cells.
  • a second layer of amorphous silicon overlies this structure and is patterned to be restricted to individual segments, each disposed in ohmic contact with the source electrode of its associated thin film transistor. That source electrode serves as the bottom or readout contact for that photodiode.
  • the upper contact for the photodiodes is typically a transparent conductor which makes contact to all of the diodes. While such photosensitive arrays are successfully fabricated at reasonably low cost, there are yield problems in the fabrication of such arrays which increase the cost of the individual arrays. One of the yield problems is that during patterning of the amorphous silicon which forms the photodiodes, the.
  • An improved structure for the thin film transistors of such a photosensitive array and of the photosensitive array itself is needed which facilitates fabrication of such arrays with greater yield and higher reliability.
  • a primary object of the present invention is to provide a thin film transistor structure for photosensitive arrays which has increased immunity to deterioration during patterning of overlying semiconductor material.
  • Another object of the present invention is to provide a photosensitive device semiconductor layer configuration which results in improved reliability and ease of fabrication of a photosensitive array employing thin film transistors.
  • Another object of the present invention is to provide an improved method for fabricating thin film transistor photosensitive arrays which results in simplified fabrication and higher yield.
  • This semiconductor layer is configured in accordance with the intended source electrode pattern so that it underlies the entire area occupied by the source electrode for that thin film transistor and the entire area occupied by the semiconductor material of the overlying photosensitive device.
  • that material is intentionally patterned to underlie the entire area occupied by the source electrode.
  • This change in semiconductor layer configuration eliminates a step in the source electrode which is typically on the order of 2,500A high where the source electrode extends beyond the edge of the thin film transistor semiconductor material in the prior art configuration. That step in the prior art structure is a location where many faults and opens occur as a result of inadequate passivation of the source metallization and the semiconductor material of the thin film transistor.
  • Figure 1 is a plan view illustration of a portion of a prior art thin film transistor photodiode photosensitive 'array
  • Figures 2 and 3 are cross-sections taken through the structure of Figure 1 along the section lines 2-2 and 3- 3;
  • Figure 4 is a plan view illustration of a similar portion of a thin film transistor photodiode photosensitive array in accordance with the present invention; and Figures 5 and 6 are " cross-sections through the structure of Figure 4 taken along the lines 5-5 and 6-6 in Figure 4.
  • FIG 1 a portion of a prior art thin film transistor photodiode photosensitive array is ili-strated in plan view.
  • the central portion of this illustration is one pixel 160 of such a photosensitive array and has adjacent thereto small segments of the adjacent pixels to more clearly illustrate the overall configuration of the device.
  • This same structure is illustrated in cross-section in Figures 2 and 3 which are taken along the lines 2-2 and 3-3 in Figure 1.
  • the structure shown in plan view in Figure 1 has a plurality of levels.
  • In the center of the pixel 160 is a relatively large, usually rectangular (and typically substantially square) segment 150 of semiconductor material in which the photosensitive device for that cell is fabricated.
  • the source metallization 138 includes a projection which extends over the semiconductor material 130-132 of the thin film transistor and overlaps slightly with the gate metallization 118 for that transistor.
  • the gate metallization 118 is disposed on the substrate 112 and is the lowest level portion of the structure identified in Figure 1.
  • the source/drain metallization of the thin film transistor also includes stripes which extend vertically in the figure which are disposed on either side of the pixel 160. These conductors are known as data lines in the thin film transistor photosensitive array art. Each data line includes a projection which extends over the gate electrode of the thin film transistor for each pixel in the column served by that data line. In this manner, any data read out of any of the photosensitive cells in that column appears on that data line.
  • the gate metallization 118 is common to all of the thin film transistors in a given row of this array and is known as a scan line.
  • the gate metallization is about 1,800A thick, the gate dielectric is about 1500A thick and the semiconductor material is about 2,500A thick.
  • the source/drain metallization is typically 4000A thick. Consequently, with the vertical step at the edge of the semiconductor material which is typically produced by many fabrication processes, the source electrode extends over a step which is about five-eighth its own thickness.
  • the source metallization is typically retains a substantially vertical edge which is difficult to adequately passivate. The problems created by this step are further exacerbated by the tendency of the source metallization to etch, during the etching of the source metallization, at a faster rate along steps, probably due to stress in the source metal going across the step.
  • the passivation layer 148 which extends over " this step in the source metallization has a significant propensity for penetration by the etchant which patterns the overlying semiconductor material.
  • the effect of such penetration varies with the degree of passivation present prior to the beginning of the etching process and can vary from slight deterioration in the operating characteristics of the device to the creation of an open circuit which renders that pixel of the device inoperative. While in many applications a few inoperative pixels can be tolerated, they are considered undesirable even in those applications and are not permitted in many other applications.
  • this • problem is overcome by changing the pattern used to pattern the semiconductor material of the thin film transistor.
  • this edge is eliminated by patterning the semiconductor material to underlie the entire source electrode of that transistor and the entire semiconductor material of the photosensitive device for that pixel of the array.
  • the semiconductor material 32 extends into the interior of the pixel from the gate electrode protrusion into that pixel and forms a substantially rectangular picture frame 32 around the source electrode 38 for that pixel.
  • the semiconductor material of the photosensitive device forms a picture frame around both the source metallization and the underlying semiconductor material, except where they extend out to the active area of the thin film transistor in the upper left portion of the pixel 60.
  • the gate electrode material for this array is preferred to fabricate the gate electrode material for this array as a two layer conductor comprised of chromium as a thin first layer and molybdenum as a thick second layer as taught in related Application Serial No. (RD-19,810), entitled, "Thin Film Transistor
  • the source/drain metallization is also preferred to fabricate the source/drain metallization as a two layer structure having a thin first layer of chromium and a relatively thick second layer of molybdenum as taught in related Application Serial No. (RD-19,511), entitled, "Thin Film Transistor Structure for Uniform Characteristics Across a Wafer and Method of Fabrication", in order to provide a sloped sidewall on the source/drain metallization which facilitates the passivation of those sidewalls by a subsequently deposited passivation layer 48.
  • RD-19,511 entitled, "Thin Film Transistor Structure for Uniform Characteristics Across a Wafer and Method of Fabrication
  • This inventive structure ⁇ iy be fabricated in substantially the same manner as the prior art structure with but with a change in the configuration of the semiconductor material of the thin film transistors.
  • the source electrode disposed entirely on the semiconductor material of the thin film transistor as has been described, many of the resulting benefits can be obtained by locating the edge of the semiconductor material of the thin film transistor far enough under the semiconductor material of the photosensitive device that the step in the source electrode is protected from exposure to the etchant used to pattern the semiconductor material of the photosensitive device by both that semiconductor material itself and the photoresist which protects those portions of that semiconductor material which are to be retained in the final device structure. This eliminates the risk of ineffective passivation of the step in the source metallization resulting in penetration by the semiconductor etchant.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Electromagnetism (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Solid State Image Pick-Up Elements (AREA)

Abstract

Une structure améliorée pour un réseau photosensible de photodiodes à transistor à film mince retient le matériau semi-conducteur de la couche du transistor à film mince sous la zone entière occupée par le dispositif photosensible pour chaque pixel du réseau. Ceci permet d'éliminer un gradin dans la couche sur lequel la métallisation de source du transistor à film mince est disposée et se traduit par une passivation plus fiable de cette couche, une augmentation du rendement et une réduction des coûts. Plusieurs procédés améliorés peuvent être utilisés pour la fabrication d'un tel réseau photosensible de photodiodes à transistor à film mince.
PCT/US1991/007336 1990-10-05 1991-10-02 Dispositif d'imagerie ayant un transistor a film mince ameliore et structures de dispositif photosensible WO1992006502A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US59342290A 1990-10-05 1990-10-05
US593,422 1990-10-05

Publications (1)

Publication Number Publication Date
WO1992006502A1 true WO1992006502A1 (fr) 1992-04-16

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Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/US1991/007336 WO1992006502A1 (fr) 1990-10-05 1991-10-02 Dispositif d'imagerie ayant un transistor a film mince ameliore et structures de dispositif photosensible

Country Status (3)

Country Link
EP (1) EP0504396A1 (fr)
CA (1) CA2048785A1 (fr)
WO (1) WO1992006502A1 (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0652596A1 (fr) * 1993-11-10 1995-05-10 General Electric Company Imageur et fabrication associée
US5525813A (en) * 1991-04-19 1996-06-11 Fuji Xerox Co., Ltd. Image sensor having TFT gate electrode surrounding the photoelectric conversion element
KR100364331B1 (ko) * 1994-06-16 2003-02-05 코닌클리케 필립스 일렉트로닉스 엔.브이. 텔레텍스트페이지전송방법,전송국,텔레텍스트수신기및텔레텍스트페이지를전송하기위한텔레텍스트신호

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4746989A (en) * 1984-05-04 1988-05-24 Energy Conversion Devices, Inc. Contact-type imager for scanning moving image-bearing members
US4889983A (en) * 1987-11-24 1989-12-26 Mitsubishi Denki Kabushiki Kaisha Image sensor and production method thereof
US4979007A (en) * 1986-06-17 1990-12-18 Tokyo Electric Company, Ltd. Photoelectric conversion device

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4746989A (en) * 1984-05-04 1988-05-24 Energy Conversion Devices, Inc. Contact-type imager for scanning moving image-bearing members
US4979007A (en) * 1986-06-17 1990-12-18 Tokyo Electric Company, Ltd. Photoelectric conversion device
US4889983A (en) * 1987-11-24 1989-12-26 Mitsubishi Denki Kabushiki Kaisha Image sensor and production method thereof

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
Patent Abstracts of Japan, Vol 10, No 283, E440, abstract of JP 61-100960, publ 1986-05-19 *

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5525813A (en) * 1991-04-19 1996-06-11 Fuji Xerox Co., Ltd. Image sensor having TFT gate electrode surrounding the photoelectric conversion element
EP0652596A1 (fr) * 1993-11-10 1995-05-10 General Electric Company Imageur et fabrication associée
US5516712A (en) * 1993-11-10 1996-05-14 General Electric Company Method of fabricating radiation imager with single passivation dielectric for transistor and diode
KR100364331B1 (ko) * 1994-06-16 2003-02-05 코닌클리케 필립스 일렉트로닉스 엔.브이. 텔레텍스트페이지전송방법,전송국,텔레텍스트수신기및텔레텍스트페이지를전송하기위한텔레텍스트신호

Also Published As

Publication number Publication date
CA2048785A1 (fr) 1992-04-06
EP0504396A1 (fr) 1992-09-23

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