USH655H - Radiation hardening of MISFET devices - Google Patents
Radiation hardening of MISFET devices Download PDFInfo
- Publication number
- USH655H USH655H US06/469,372 US46937283A USH655H US H655 H USH655 H US H655H US 46937283 A US46937283 A US 46937283A US H655 H USH655 H US H655H
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- United States
- Prior art keywords
- insulator
- silicon
- type
- semiconductor device
- zinc sulfide
- 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.)
- Abandoned
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- 238000005510 radiation hardening Methods 0.000 title description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims abstract description 48
- 239000012212 insulator Substances 0.000 claims abstract description 31
- 229910052984 zinc sulfide Inorganic materials 0.000 claims abstract description 30
- 239000005083 Zinc sulfide Substances 0.000 claims abstract description 29
- 239000000377 silicon dioxide Substances 0.000 claims abstract description 24
- DRDVZXDWVBGGMH-UHFFFAOYSA-N zinc;sulfide Chemical compound [S-2].[Zn+2] DRDVZXDWVBGGMH-UHFFFAOYSA-N 0.000 claims abstract description 23
- 235000012239 silicon dioxide Nutrition 0.000 claims abstract description 11
- 230000005855 radiation Effects 0.000 claims abstract description 10
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 24
- 229910052710 silicon Inorganic materials 0.000 claims description 24
- 239000010703 silicon Substances 0.000 claims description 24
- 239000004065 semiconductor Substances 0.000 claims description 16
- 229910021419 crystalline silicon Inorganic materials 0.000 claims description 9
- 239000007943 implant Substances 0.000 claims description 9
- 239000000758 substrate Substances 0.000 claims description 8
- 230000015556 catabolic process Effects 0.000 claims description 2
- 238000006731 degradation reaction Methods 0.000 claims description 2
- 238000002955 isolation Methods 0.000 claims 3
- 239000011810 insulating material Substances 0.000 abstract description 10
- 230000005865 ionizing radiation Effects 0.000 abstract description 4
- 230000005684 electric field Effects 0.000 description 3
- 230000005669 field effect Effects 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 238000005513 bias potential Methods 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 239000002178 crystalline material Substances 0.000 description 2
- 229910044991 metal oxide Inorganic materials 0.000 description 2
- 150000004706 metal oxides Chemical class 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 230000000717 retained effect Effects 0.000 description 2
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 229910021486 amorphous silicon dioxide Inorganic materials 0.000 description 1
- 229910052796 boron Inorganic materials 0.000 description 1
- 229910003460 diamond Inorganic materials 0.000 description 1
- 239000010432 diamond Substances 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000001465 metallisation Methods 0.000 description 1
- 230000002035 prolonged effect Effects 0.000 description 1
- 238000012827 research and development Methods 0.000 description 1
- WGPCGCOKHWGKJJ-UHFFFAOYSA-N sulfanylidenezinc Chemical compound [Zn]=S WGPCGCOKHWGKJJ-UHFFFAOYSA-N 0.000 description 1
- -1 zinc sulfide compound Chemical class 0.000 description 1
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Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/40—Electrodes ; Multistep manufacturing processes therefor
- H01L29/43—Electrodes ; Multistep manufacturing processes therefor characterised by the materials of which they are formed
- H01L29/49—Metal-insulator-semiconductor electrodes, e.g. gates of MOSFET
- H01L29/51—Insulating materials associated therewith
- H01L29/517—Insulating materials associated therewith the insulating material comprising a metallic compound, e.g. metal oxide, metal silicate
Definitions
- This invention generally relates to MIS field effect devices and in particular concerns the insulating material used between discrete transistors found in such devices.
- a MIS (metal-insulator-semiconductor) device includes a semiconductor substrate, an insulating layer on the substrate, and a gate electrode disposed on the insulating layer.
- the insulating layer in prior art devices is usually an oxide, and the devices are usually called MOSFETs (metal-oxide-insulator field-effect-transistors).
- MOSFETs metal-oxide-insulator field-effect-transistors
- additional source and drain electrodes are disposed to either side of the gate electrode and a lateral current may be caused to flow between the source and drain electrodes through application of proper bias potential to the gate electrode.
- application of a biased potential to the gate produces a conducting layer beneath the metal oxide allowing lateral current flow between the source and drain electrodes.
- application of a bias potential to the gate electrodes produces an insulating region between the source and drain electrodes which serves to decrease current conduction.
- MOS devices when exposed to ionizing radiation such as would occur in a space environment, suffer radiation damage in the form of charge trapped in the oxide and/or at the oxidesemiconductor interface and undergo various changes in the electrical characteristics thereof.
- the circuits in which these MOS devices are found become unstable and in some instances are actually rendered inoperative.
- a MOSFET device with a substantially improved useful life when subjected to a radiation environment is sorely needed.
- Another object of the invention is to correct unstable conditions of silicon dioxide when subjected to radiation within a typical MOSFET device.
- silicon dioxide the typical MOSFET insulating material
- Zinc sulfide has the same crystalline structure of silicon but allows greater hole mobility thereby helping to reduce the degradation normally occurring under radiation conditions.
- the invention may be manufactured as one of three variations. Crystalline zinc sulfide may replace silicon dioxide as the gate insulator, the field insulator, or both the gate insulator and field insulator.
- FIG. 1 is a cross-sectional view of a conventional MOSFET device.
- FIG. 2 is a cross-sectional view of an embodiment of the present invention in which zinc sulfide has been introduced.
- FIG. 3 is a cross-sectional view of an alternate embodiment of the present invention in which zinc sulfide has been introduced.
- FIG. 4 is a cross-sectional view of another alternate embodiment of the present invention in which zinc sulfide has been introduced.
- a conventional N-channel MOSFET which utilizes silicon dioxide as an insulating material.
- a MOSFET device comprises a substrate 12 of semiconductor material such as silicon, a p-type silicon epitaxial layer 14 disposed on the semiconductor substrate into which n-type silicon 16 is implanted to form p-n transistor junctions. Drain and source regions, 18 and 20, respectively, are provided and affixed to the n-type silicon implant.
- a layer 22 of silicon dioxide (SiO 2 ) is placed over large areas of crystalline silicon between discrete transistors for use as a field insulator to insulate interconnecting metallization runs from the crystalline silicon.
- a layer 24 of silicon dioxide is also placed between a gate contact 26 for the transistor and a channel formed by the n-type silicon implants. This layer insulates the gate from the channel, yet allows the applied charge to form an electric field which enhances or depletes the channel as necessary.
- the SiO 2 gate insulator is usually much thinner than the field oxide.
- the problem with the use of SiO 2 for gate and field oxides is that SiO 2 is an insulator and forms an amorphous layer on top of the crystalline silicon. Ionizing radiation causes electron-hole pairs to form in the SiO 2 . The electrons are much more mobile than the holes and diffuse away rapidly. The holes move very slowly through the SiO 2 and appear as a layer of trapped charge.
- the trapped holes produce an electric field which alters other electric fields and changes the electrical operating characteristics of the FET. Prolonged exposure to ionizing radiation destroys the device. As the holes begin to diffuse, some of them cross the SiO 2 -Si interface and produce the little understood interface states. Interface states also cause a change in device performance and may destroy the device.
- One theory is that interface states are dangling bonds from the silicon into the SiO 2 caused by a hole passing across the interface.
- Interface states and trapped charge in field oxides eventually lead to the electrical connection of adjacent devices or transistors which may adversely affect the function of the intergrated circuit.
- trapped charge and interface states will cause shifts in the transistor threshold voltage and will eventually force it to cease normal operation.
- FIGS. 2, 3, and 4 show an N-channel MOSFET, each of which is comprised of the same basic elements as FIG. 1.
- the MOSFET comprises a substrate 12 of semiconductor material such as silicon, a p-type silicon epitaxial layer 14 disposed on the semiconductor substrate into which n-type silicon 16 is implanted to form p-n transistor junctions. Drain and source regions, 18 and 20, respectively, are provided and affixed to the n-type silicon implant.
- the zinc sulfide on silicon MISFET devices may be manufactured as one of three variations, FIG. 2, 3, or 4, respectively.
- FIG. 2 shows a layer of zinc sulfide 30 placed over the large areas of crystalline silicon for use as a field insulator.
- the conventional SiO 2 gate insulator 24 is retained according to this embodiment.
- FIG. 3 shows a layer of zinc sulfide 32 placed between the gate contact 26 and the channel formed by the n-type silicon implants 16.
- the conventional SiO 2 field insulator is retained according to this embodiment.
- FIG. 4 shows a layer of zinc sulfide 32 placed between the gate contact and the channel for use as the gate insulator and also a second layer of zinc sulfide 30 placed over the large area of crystalline silicon for use as a field insulator.
- all of the conventional SiO 2 insulating material has been replaced with zinc sulfide material.
- Zinc sulfide has a zincblende crystal structure with a lattice constant of 5.42 Angstroms.
- Crystalline silicon has a diamond structure with a lattice constant of 5.43086 Angstroms. There is only a 0.2% variation in the lattice spacing and crystalline ZnS will continue from crystalline silicon.
- Silicon has a bandgap energy of 1.12 eV.
- ZnS has a bandgap of 3.6 eV.
- the ZnS acts as a semiinsulator atop the silicon and can effectively replace SiO 2 as the insulator for a properly designed transistor.
- the advantage of crystalline ZnS atop crystalline Si is the total dose radiation survivability.
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- Engineering & Computer Science (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Power Engineering (AREA)
- Physics & Mathematics (AREA)
- Ceramic Engineering (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Computer Hardware Design (AREA)
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Abstract
A MISFET device which typically utilizes silicon dioxide as an insulating material and which becomes inoperative under ionizing radiation conditions can be made to significantly enhance its radiation survivability by introducing crystalline zinc sulfide as an insulating material. The invention may be manufactured as one of three variations. Crystalline zinc sulfide may replace silicon dioxide as the gate insulator, the field insulator, or both the gate and field insulators.
Description
The invention described herein may be manufactured and used by or for the Government of the United States for all governmental purposes without the payment of any royalty.
This invention generally relates to MIS field effect devices and in particular concerns the insulating material used between discrete transistors found in such devices.
A MIS (metal-insulator-semiconductor) device includes a semiconductor substrate, an insulating layer on the substrate, and a gate electrode disposed on the insulating layer. The insulating layer in prior art devices is usually an oxide, and the devices are usually called MOSFETs (metal-oxide-insulator field-effect-transistors). With a MOS field-effect device, additional source and drain electrodes are disposed to either side of the gate electrode and a lateral current may be caused to flow between the source and drain electrodes through application of proper bias potential to the gate electrode. Specifically, in the "enhancement" mode, application of a biased potential to the gate produces a conducting layer beneath the metal oxide allowing lateral current flow between the source and drain electrodes. In the "depletion" mode of operation, application of a bias potential to the gate electrodes produces an insulating region between the source and drain electrodes which serves to decrease current conduction.
MOS devices, when exposed to ionizing radiation such as would occur in a space environment, suffer radiation damage in the form of charge trapped in the oxide and/or at the oxidesemiconductor interface and undergo various changes in the electrical characteristics thereof. The circuits in which these MOS devices are found become unstable and in some instances are actually rendered inoperative. A MOSFET device with a substantially improved useful life when subjected to a radiation environment is sorely needed.
Prior work in this area includes U.S. Pat. No. 3,799,813 to Danchenko which discloses a technique for radiation hardening of MOS devices by the introduction of boron into the insulating oxide. While this patent is suitable for its intended purpose, it does not provide the simplicity and degree of protection that the present invention provides, nor does it involve the use of the same insulating material.
It is therefore an object of the present invention to produce a metal oxide semiconductor device which has improved survivability when exposed in a radiation environment.
Another object of the invention is to correct unstable conditions of silicon dioxide when subjected to radiation within a typical MOSFET device.
According to the invention, silicon dioxide, the typical MOSFET insulating material, is replaced, in whole or part, with a zinc sulfide compound. Zinc sulfide has the same crystalline structure of silicon but allows greater hole mobility thereby helping to reduce the degradation normally occurring under radiation conditions. The invention may be manufactured as one of three variations. Crystalline zinc sulfide may replace silicon dioxide as the gate insulator, the field insulator, or both the gate insulator and field insulator.
FIG. 1 is a cross-sectional view of a conventional MOSFET device.
FIG. 2 is a cross-sectional view of an embodiment of the present invention in which zinc sulfide has been introduced.
FIG. 3 is a cross-sectional view of an alternate embodiment of the present invention in which zinc sulfide has been introduced.
FIG. 4 is a cross-sectional view of another alternate embodiment of the present invention in which zinc sulfide has been introduced.
Referring to FIG. 1 of the appended drawing, a conventional N-channel MOSFET is shown which utilizes silicon dioxide as an insulating material. Typically, such a MOSFET device comprises a substrate 12 of semiconductor material such as silicon, a p-type silicon epitaxial layer 14 disposed on the semiconductor substrate into which n-type silicon 16 is implanted to form p-n transistor junctions. Drain and source regions, 18 and 20, respectively, are provided and affixed to the n-type silicon implant. A layer 22 of silicon dioxide (SiO2) is placed over large areas of crystalline silicon between discrete transistors for use as a field insulator to insulate interconnecting metallization runs from the crystalline silicon. A layer 24 of silicon dioxide is also placed between a gate contact 26 for the transistor and a channel formed by the n-type silicon implants. This layer insulates the gate from the channel, yet allows the applied charge to form an electric field which enhances or depletes the channel as necessary. The SiO2 gate insulator is usually much thinner than the field oxide. The problem with the use of SiO2 for gate and field oxides is that SiO2 is an insulator and forms an amorphous layer on top of the crystalline silicon. Ionizing radiation causes electron-hole pairs to form in the SiO2. The electrons are much more mobile than the holes and diffuse away rapidly. The holes move very slowly through the SiO2 and appear as a layer of trapped charge. The trapped holes produce an electric field which alters other electric fields and changes the electrical operating characteristics of the FET. Prolonged exposure to ionizing radiation destroys the device. As the holes begin to diffuse, some of them cross the SiO2 -Si interface and produce the little understood interface states. Interface states also cause a change in device performance and may destroy the device. One theory is that interface states are dangling bonds from the silicon into the SiO2 caused by a hole passing across the interface.
Interface states and trapped charge in field oxides eventually lead to the electrical connection of adjacent devices or transistors which may adversely affect the function of the intergrated circuit. In gate oxides, trapped charge and interface states will cause shifts in the transistor threshold voltage and will eventually force it to cease normal operation.
Replacing the amorphous SiO2 with crystalline material zinc sulfide allows greater hole mobility thereby helping to reduce the number of trapped holes, i.e., the quantity of trapped charge. Secondly, since the crystalline material has the same crystal structure as silicon, the problem with dangling bonds is eliminated thereby reducing the production of interface states. Therefore, zinc sulfide on silicon field effect transistors has greater radiation survivability than conventional MOSFETs.
Referring to FIGS. 2, 3, and 4, the embodiments of the invention are shown which are substantially similar to the conventional MOSFET of FIG. 1 but zinc sulfide has been introduced as an insulating material replacing silicon dioxide. As in FIG. 1, FIGS. 2, 3, and 4 show an N-channel MOSFET, each of which is comprised of the same basic elements as FIG. 1. Namely, the MOSFET comprises a substrate 12 of semiconductor material such as silicon, a p-type silicon epitaxial layer 14 disposed on the semiconductor substrate into which n-type silicon 16 is implanted to form p-n transistor junctions. Drain and source regions, 18 and 20, respectively, are provided and affixed to the n-type silicon implant. However, the use of SiO2 as the insulating material has been curtailed or abandoned according to the embodiments presented in FIGS. 2, 3, and 4. The zinc sulfide on silicon MISFET devices may be manufactured as one of three variations, FIG. 2, 3, or 4, respectively.
FIG. 2 shows a layer of zinc sulfide 30 placed over the large areas of crystalline silicon for use as a field insulator. The conventional SiO2 gate insulator 24 is retained according to this embodiment.
FIG. 3 shows a layer of zinc sulfide 32 placed between the gate contact 26 and the channel formed by the n-type silicon implants 16. The conventional SiO2 field insulator is retained according to this embodiment.
FIG. 4 shows a layer of zinc sulfide 32 placed between the gate contact and the channel for use as the gate insulator and also a second layer of zinc sulfide 30 placed over the large area of crystalline silicon for use as a field insulator. With this embodiment, all of the conventional SiO2 insulating material has been replaced with zinc sulfide material.
Zinc sulfide (ZnS) has a zincblende crystal structure with a lattice constant of 5.42 Angstroms. Crystalline silicon has a diamond structure with a lattice constant of 5.43086 Angstroms. There is only a 0.2% variation in the lattice spacing and crystalline ZnS will continue from crystalline silicon.
Silicon has a bandgap energy of 1.12 eV. ZnS has a bandgap of 3.6 eV. The ZnS acts as a semiinsulator atop the silicon and can effectively replace SiO2 as the insulator for a properly designed transistor. The advantage of crystalline ZnS atop crystalline Si is the total dose radiation survivability.
The use of zinc sulfide for gate and field insulating materials should also greatly reduce the need for costly research and development of radiation hardened field oxide processes.
Thus, while preferred constructional features are embodied in the structure illustrated herein, it is to be understood that changes and variations may be made by the skilled in the art without departing from the spirit and scope of the invention.
Claims (9)
1. A semiconductor device comprising a plurality of transistors on a chip, each transistor comprising:
a silicon substrate;
a silicon epitaxial layer of a first type disposed on said substrate;
at least two silicon implants of a second type implanted in said layer and separated by a distance;
at least one drain region affixed to a first of said silicon implants;
at least one source region affixed to a second silicon implant;
a first or gate insulator located on said epitaxial layer between said source and drain regions and overlapping a portion of said at least two silicon implants;
a second or field insulator located on said epitaxial layer adjacent to each source and drain regions but not between said regions, and said field insulator overlapping a portion of said silicon implants, said field insulator being means for providing the principal electrical isolation from other transistors on said chip;
a gate contact affixed above said gate insulator;
wherein at least one of said first and second insulators is crystalline zinc sulfide, formed with a continuous crystalline structure from the adjacent crystalline silicon epitaxial layer into the crystalline zinc sulfide, to thereby reduce the degradation occurring under radiation conditions.
2. The semiconductor device according to claim 1, wherein said first insulator is crystalline zinc sulfide, being means for providing d.c. electrical isolation between said epitaxial layer and the gate contact and being the only layer between them.
3. The semiconductor device according to claim 2, wherein said second insulator is silicon dioxide.
4. The semiconductor device according to claim 1, wherein said second insulator is crystalline zinc sulfide.
5. The semiconductor device according to claim 4, wherein said first insulator is silicon dioxide.
6. The semiconductor device according to claim 4, wherein said first and second insulators are both crystalline zinc sulfide, the first insulator being means for providing d.c. electrical isolation between said epitaxial layer and the gate contact and being the only layer between them.
7. The semiconductor device according to claim 6, wherein said first type is p-type and said second type is n-type.
8. The semiconductor device according to claim 6, wherein said first type is n-type and said second type is p-type.
9. The semiconductor device according to claim 7, wherein said gate insulator is thinner than said field insulator.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US06/469,372 USH655H (en) | 1983-02-24 | 1983-02-24 | Radiation hardening of MISFET devices |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US06/469,372 USH655H (en) | 1983-02-24 | 1983-02-24 | Radiation hardening of MISFET devices |
Publications (1)
Publication Number | Publication Date |
---|---|
USH655H true USH655H (en) | 1989-07-04 |
Family
ID=23863536
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US06/469,372 Abandoned USH655H (en) | 1983-02-24 | 1983-02-24 | Radiation hardening of MISFET devices |
Country Status (1)
Country | Link |
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US (1) | USH655H (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20050211976A1 (en) * | 2004-03-24 | 2005-09-29 | Michael Redecker | Organic field-effect transistor, flat panel display device including the same, and a method of manufacturing the organic field-effect transistor |
-
1983
- 1983-02-24 US US06/469,372 patent/USH655H/en not_active Abandoned
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20050211976A1 (en) * | 2004-03-24 | 2005-09-29 | Michael Redecker | Organic field-effect transistor, flat panel display device including the same, and a method of manufacturing the organic field-effect transistor |
US7838871B2 (en) * | 2004-03-24 | 2010-11-23 | Samsung Mobile Display Co., Ltd. | Organic field-effect transistor, flat panel display device including the same, and a method of manufacturing the organic field-effect transistor |
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