US20010023112A1 - Shallow trench isolation on a silicon substrate using nitrogen implant into the side wall - Google Patents
Shallow trench isolation on a silicon substrate using nitrogen implant into the side wall Download PDFInfo
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- US20010023112A1 US20010023112A1 US09/837,136 US83713601A US2001023112A1 US 20010023112 A1 US20010023112 A1 US 20010023112A1 US 83713601 A US83713601 A US 83713601A US 2001023112 A1 US2001023112 A1 US 2001023112A1
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- 239000000758 substrate Substances 0.000 title claims abstract description 64
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 title claims abstract description 58
- 229910052710 silicon Inorganic materials 0.000 title claims abstract description 58
- 239000010703 silicon Substances 0.000 title claims abstract description 58
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 title claims abstract description 42
- 229910052757 nitrogen Inorganic materials 0.000 title claims abstract description 39
- 238000002955 isolation Methods 0.000 title description 7
- 239000007943 implant Substances 0.000 title 1
- -1 nitrogen ions Chemical class 0.000 claims abstract description 50
- 238000000034 method Methods 0.000 claims abstract description 39
- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 claims description 28
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 25
- 229910052814 silicon oxide Inorganic materials 0.000 claims description 19
- 229910052581 Si3N4 Inorganic materials 0.000 claims description 17
- 230000001590 oxidative effect Effects 0.000 claims description 10
- 238000005530 etching Methods 0.000 claims description 8
- 239000012212 insulator Substances 0.000 claims description 5
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 4
- 239000001301 oxygen Substances 0.000 claims description 4
- 229910052760 oxygen Inorganic materials 0.000 claims description 4
- 238000001312 dry etching Methods 0.000 claims description 3
- 238000004140 cleaning Methods 0.000 claims description 2
- 150000002500 ions Chemical class 0.000 claims 1
- 230000003647 oxidation Effects 0.000 description 8
- 238000007254 oxidation reaction Methods 0.000 description 8
- 230000008021 deposition Effects 0.000 description 5
- 230000015572 biosynthetic process Effects 0.000 description 4
- 229910021420 polycrystalline silicon Inorganic materials 0.000 description 4
- 229920005591 polysilicon Polymers 0.000 description 4
- 238000005468 ion implantation Methods 0.000 description 3
- 239000000356 contaminant Substances 0.000 description 2
- 238000001020 plasma etching Methods 0.000 description 2
- 230000007812 deficiency Effects 0.000 description 1
- 238000003795 desorption Methods 0.000 description 1
- 238000007654 immersion Methods 0.000 description 1
- 238000002513 implantation Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000003071 parasitic effect Effects 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
Images
Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/70—Manufacture or treatment of devices consisting of a plurality of solid state components formed in or on a common substrate or of parts thereof; Manufacture of integrated circuit devices or of parts thereof
- H01L21/71—Manufacture of specific parts of devices defined in group H01L21/70
- H01L21/76—Making of isolation regions between components
- H01L21/762—Dielectric regions, e.g. EPIC dielectric isolation, LOCOS; Trench refilling techniques, SOI technology, use of channel stoppers
- H01L21/76224—Dielectric regions, e.g. EPIC dielectric isolation, LOCOS; Trench refilling techniques, SOI technology, use of channel stoppers using trench refilling with dielectric materials
- H01L21/76237—Dielectric regions, e.g. EPIC dielectric isolation, LOCOS; Trench refilling techniques, SOI technology, use of channel stoppers using trench refilling with dielectric materials introducing impurities in trench side or bottom walls, e.g. for forming channel stoppers or alter isolation behavior
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/70—Manufacture or treatment of devices consisting of a plurality of solid state components formed in or on a common substrate or of parts thereof; Manufacture of integrated circuit devices or of parts thereof
- H01L21/71—Manufacture of specific parts of devices defined in group H01L21/70
- H01L21/76—Making of isolation regions between components
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/70—Manufacture or treatment of devices consisting of a plurality of solid state components formed in or on a common substrate or of parts thereof; Manufacture of integrated circuit devices or of parts thereof
- H01L21/71—Manufacture of specific parts of devices defined in group H01L21/70
- H01L21/76—Making of isolation regions between components
- H01L21/762—Dielectric regions, e.g. EPIC dielectric isolation, LOCOS; Trench refilling techniques, SOI technology, use of channel stoppers
- H01L21/76224—Dielectric regions, e.g. EPIC dielectric isolation, LOCOS; Trench refilling techniques, SOI technology, use of channel stoppers using trench refilling with dielectric materials
- H01L21/76232—Dielectric regions, e.g. EPIC dielectric isolation, LOCOS; Trench refilling techniques, SOI technology, use of channel stoppers using trench refilling with dielectric materials of trenches having a shape other than rectangular or V-shape, e.g. rounded corners, oblique or rounded trench walls
- H01L21/76235—Dielectric regions, e.g. EPIC dielectric isolation, LOCOS; Trench refilling techniques, SOI technology, use of channel stoppers using trench refilling with dielectric materials of trenches having a shape other than rectangular or V-shape, e.g. rounded corners, oblique or rounded trench walls trench shape altered by a local oxidation of silicon process step, e.g. trench corner rounding by LOCOS
Definitions
- the present invention relates to a process of fabricating a trench on a silicon substrate and, more particularly, to a process of forming a trench having tapered side walls on a silicon-on-insulator (SOI) substrate.
- SOI silicon-on-insulator
- An integrated circuit or an array of discrete integrated circuit devices includes numerous semiconductor devices. Current leakages and parasitic capacitances between devices can interfere with the intended operation of the circuit. Therefore, in many circuits, it is necessary to electrically isolate devices from one another. Several isolation techniques have been developed to meet that requirement.
- a silicon-on-insulator (SOI) structure is a structure in which a buried insulating layer electrically isolates a silicon layer from a silicon substrate.
- the SOI structure does not always occupy the entire silicon substrate. Often, the SOI structure occupies only a portion of the silicon substrate.
- Shallow Trench Isolation is a process used in isolating devices formed on SOI substrates.
- STI involves etching trenches, having side walls and bottoms, in the SOI substrate. Following etching, the trenches are filled with an oxide.
- STI shallow trench isolation processing
- An object of the present invention is to provide a process for fabricating a trench using STI in which the trench side walls are spaced further apart adjacent the exposed surface than adjacent the trench bottom.
- the present invention provides a process for fabricating a trench having a tapered shape, side walls, and a bottom on a silicon substrate.
- the substrate has an exposed surface.
- the trench side walls are spaced further apart adjacent the exposed surface than adjacent the trench bottom. The process comprises the following steps:
- the nitrogen ions are implanted on the initial trench side walls at an angle of from about 10 degrees to about 60 degrees relative to the exposed surface.
- FIG. 1 shows in schematic representation a silicon substrate comprising a trench structure having side walls spaced further apart adjacent the trench bottom than adjacent the top of the silicon layer portion of the trench side wall;
- FIG. 2A shows the structure of FIG. 1 after the trench has been filled with an oxide, producing a seam in the center of the trench;
- FIG. 2B shows the structure of FIG. 2A after the seam has been filled with polysilicon, causing shorts between deposited poly gates;
- FIG. 3 shows in schematic representation a silicon substrate
- FIG. 4 shows in schematic representation a silicon substrate having a trench with substantially perpendicular side walls
- FIG. 5 shows in schematic representation a top view of FIG. 4
- FIG. 6 illustrates the angle to the exposed surface in which nitrogen ions are implanted into the trench side walls
- FIG. 7 shows in schematic representation a silicon substrate having a tapered trench structure
- FIG. 8 shows in schematic representation a tapered trench of a silicon substrate that has been filled with oxide.
- the apparatus is made by the Shallow Trench Isolation (STI) process.
- the STI process comprises the steps of etching trenches, having side walls and bottoms, in the SOI substrate, oxidizing the silicon layer portions of the trench sidewalls, and filling the trenches with an oxide.
- FIG. 1 shows a side view of a silicon substrate 1 after the steps of etching a trench 18 and oxidizing those portions 19 , 20 of the side walls 24 , 26 of the trench 18 comprising a silicon layer 14 .
- the substrate 1 comprises a silicon wafer 10 , a buried silicon oxide layer 12 formed on the silicon wafer 10 , the silicon layer 14 , a silicon nitride layer 16 , and the trench 18 .
- the next step in STI processing comprises filling the trench 18 with an oxide 32 .
- an oxide 32 As a result of the bottleneck-shape of the trench 18 , a shape in which the width of the trench 18 is greater near the bottom then at the top, it is very difficult to fill the trench 18 with an oxide 32 . This difficulty results in the formation of a seam 22 in the center of the trench 18 as illustrated in FIG. 2A.
- FIG. 2B shows the structure of FIG. 2A after the seam 22 has been filled with polysilicon 40 .
- the polysilicon 40 fills the seam 22 during deposition of poly gates 42 and may cause shorts between the poly gates 42 .
- the present invention provides a process for fabricating a trench 18 using shallow trench isolation (STI) in which the side walls 24 , 26 of the trench 18 are spaced further apart adjacent the exposed surface than adjacent the trench bottom.
- STI shallow trench isolation
- FIG. 3 shows a side view of an embodiment of a silicon substrate comprising a silicon-on-insulator (SOI) substrate 1 .
- the substrate 1 having an exposed surface 8 , comprises a silicon wafer 10 , a buried silicon oxide layer 12 formed on the silicon wafer 10 , a silicon layer 14 , and a silicon nitride layer 16 .
- a thin oxide layer 15 of from about 0.006 ⁇ m to about 0.01 ⁇ m can optionally be deposited between the silicon layer 14 and the silicon nitride layer 16 to reduce damage to the silicon layer 14 caused by deposition of the silicon nitride layer 16 .
- the thickness of the silicon oxide layer 12 is from about 0.1 ⁇ m to about 0.4 ⁇ m, the thickness of the silicon layer 14 is from about 0.1 ⁇ m to about 0.2 ⁇ m, and the thickness of the silicon nitride layer 16 is from about 0.1 ⁇ m to about 0.15 ⁇ m. In a more preferred embodiment, the thickness of the silicon oxide layer 12 is about 0.4 ⁇ m, the thickness of the silicon layer 14 is about 0.18 ⁇ m, and the thickness of the silicon nitride layer 16 is about 0.12 ⁇ m.
- FIG. 4 shows a side view of a substrate 1 having an initial trench 18 extending into the interior of the substrate 1 .
- standard photomasking and etching of the silicon substrate 1 , through the silicon nitride layer 16 , thin oxide layer 15 (if present), and silicon layer 14 results in an initial trench 18 having a bottom 21 and four initial trench side walls 24 , 26 , 28 , and 30 .
- Side walls 24 and 26 are shown in FIG. 4.
- FIG. 5 is a top view of FIG. 4 showing all four side walls 24 , 26 , 28 , and 30 of initial trench 18 .
- Initial trench side walls 24 , 26 , 28 , and 30 are substantially perpendicular to the exposed surface 8 of the substrate 1 .
- initial trench 18 can be cleaned using methods commonly known in the art, which typically include a preliminary step of plasma oxidation stripping or immersion in an inorganic resist stripper, followed by the removal of residual organic contaminants and the desorption of remaining atomic and ionic contaminants.
- methods commonly known in the art typically include a preliminary step of plasma oxidation stripping or immersion in an inorganic resist stripper, followed by the removal of residual organic contaminants and the desorption of remaining atomic and ionic contaminants.
- S. Wolf & R. N. Tauber discuss such cleaning processes on pages 516-517 of their text, titled Silicon Processing for the VLSI Era, Volume 1 —Process Technology (1986).
- FIG. 6 shows the step of nitrogen ion implantation into the side walls 24 , 26 , 28 , and 30 of initial trench 18 .
- the nitrogen ions 50 are implanted at an angle ( ⁇ ) to the exposed surface 8 of the substrate 1 .
- Ion implantation is a process in which energetic, charged atoms or molecules are directly introduced into a substrate, such as a silicon wafer.
- nitrogen ions 50 are implanted on each side wall 24 , 26 , 28 , and 30 of initial trench 18 .
- a first position of the substrate 1 is determined so that nitrogen ions 50 are beamed at a direction parallel to side walls 28 and 30 onto side wall 24 .
- the substrate 1 is then rotated by 90 degrees about a rotation axis parallel to the top of the substrate 1 and fixed in a second position.
- Nitrogen ions 50 are then beamed at a direction parallel to side walls 24 and 26 onto side wall 28 .
- the substrate 1 is then rotated by 90 degrees about a rotation axis parallel to the top of the substrate 1 and fixed in a third position.
- Nitrogen ions 50 are then beamed at a direction parallel to side walls 28 and 30 onto side wall 26 .
- the substrate 1 is then rotated by 90 degrees about a rotation axis parallel to the top of the substrate 1 and fixed in a fourth position. Nitrogen ions 50 are then beamed at a direction parallel to side walls 24 and 26 onto side wall 30 .
- the optimal angle ( ⁇ ) of nitrogen ion implantation depends on the thickness of the silicon nitride layer 16 and the size of the trench 18 .
- the side walls 24 , 26 , 28 , and 30 of trench 18 are implanted with from about 5 keV to about 15 keV nitrogen ions 50 to a dose of from about 1 ⁇ 10 14 /cm 2 to about 1 ⁇ 10 15 /cm 2 , and the nitrogen ions 50 are implanted at an angle ( ⁇ ) of from about 10 to about 60 degrees relative to the exposed surface 8 .
- the side walls 24 , 26 , 28 , and 30 of trench 18 are implanted with about 10 keV nitrogen ions 50 to a dose of about 5 ⁇ 10 14 /cm 2 at an angle ( ⁇ ) of about 20 degrees.
- ⁇ angle
- the side walls 24 , 26 , 28 , and 30 of trench 18 are implanted with about 10 keV nitrogen ions 50 to a dose of about 5 ⁇ 10 14 /cm 2 at an angle ( ⁇ ) of about 20 degrees.
- FIG. 7 shows a side view of a resulting tapered trench 18 a after oxidation of the side walls 24 , 26 , 28 , and 30 of initial trench 18 , resulting in tapered side walls 24 a and 26 a .
- the oxidation rate of the side walls 24 , 26 , 28 , and 30 is affected by nitrogen ion concentration which proportionally retards trench side wall oxidation.
- the high concentration of nitrogen ions in the silicon nitride layer 16 which forms the portion of the side walls 24 and 26 adjacent the exposed surface 8 , inhibits oxidation.
- the silicon layer 14 which forms the portion of the side walls 24 a and 26 a adjacent trench bottom 21 , has a lower concentration of nitrogen ions. Oxidation of the portion of the side walls 24 a and 26 a of the trench 18 a adjacent the silicon layer 14 results in oxide formation in proportion to nitrogen ion concentration.
- the nitrogen ions 50 are implanted at an angle ( ⁇ ) relative to the exposed surface 8 , more nitrogen ions 50 are implanted into the portion of the side walls 24 a and 26 a of the trench 18 a adjacent the silicon layer 14 and the bottom 21 of the trench 18 a than in the silicon nitride layer 16 portion of the side walls 24 and 26 adjacent the exposed surface 8 , thereby producing a tapered shape upon oxidation.
- a portion of silicon layer 14 adjacent the side walls 24 a and 26 a of the trench 18 a is also oxidized.
- the side walls 24 , 26 , 28 , and 30 are oxidized using dry oxygen at a temperature of about 1 , 000 ° C.
- FIG. 8 shows a side view of the tapered trench 18 a shown in FIG. 7 after tapered trench 18 a has been filled with the oxide 32 .
- steps known in the art can be used to complete an STI structure.
- the present invention can be used in bulk STI processes.
- a silicon substrate comprising an SOI substrate was formed by the following steps.
- a 0.4 ⁇ m layer of silicon oxide 12 was formed on a silicon wafer 1 and a 0.18 ⁇ m silicon layer 14 was formed on the silicon oxide layer 12 using the separation by implantation of oxygen (SIMOX) process.
- a 0.008 ⁇ m layer of silicon oxide (thin silicon oxide layer 15 ) was next formed on the silicon layer 14 followed by deposition of a 0.12 ⁇ m layer of silicon nitride 16 on the thin silicon oxide layer 15 .
- An initial trench 18 extending from the exposed surface 8 of the substrate 1 into an interior of the substrate was formed by photomasking and plasma etching.
- the plasma etching was selective to stop at the silicon oxide layer 15 , producing a trench depth of 0.308 ⁇ m.
- the initial trench side walls 24 , 26 , 28 , and 30 were implanted with 10 keV nitrogen ions 50 to a dose of 5 ⁇ 10 14 /cm 2 at an angle ( ⁇ ) of 30 degrees with respect to the exterior, exposed surface 8 of the substrate 1 .
- the trench side walls 24 , 26 , 28 , and 30 were next oxidized with dry oxygen at 1,000° C., resulting in a tapered trench 18 a in which the trench side walls 24 , 26 , 28 , and 30 were spaced further apart adjacent the exposed surface 8 of the substrate 1 than adjacent the trench bottom 21 .
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Abstract
A process for fabricating a tapered trench on a silicon substrate. The process comprises the steps of forming an initial trench in the substrate and implanting nitrogen ions on the initial trench side walls. More nitrogen ions are implanted adjacent the exposed surface of the substrate than adjacent the trench bottom. Finally, the initial trench side walls are oxidized to create the tapered shape.
Description
- The present invention relates to a process of fabricating a trench on a silicon substrate and, more particularly, to a process of forming a trench having tapered side walls on a silicon-on-insulator (SOI) substrate.
- An integrated circuit or an array of discrete integrated circuit devices includes numerous semiconductor devices. Current leakages and parasitic capacitances between devices can interfere with the intended operation of the circuit. Therefore, in many circuits, it is necessary to electrically isolate devices from one another. Several isolation techniques have been developed to meet that requirement.
- A silicon-on-insulator (SOI) structure is a structure in which a buried insulating layer electrically isolates a silicon layer from a silicon substrate. The SOI structure does not always occupy the entire silicon substrate. Often, the SOI structure occupies only a portion of the silicon substrate.
- Shallow Trench Isolation (STI) is a process used in isolating devices formed on SOI substrates. STI involves etching trenches, having side walls and bottoms, in the SOI substrate. Following etching, the trenches are filled with an oxide.
- Unfortunately, there is a problem in implementing shallow trench isolation processing (STI) in SOI substrates. Following etching, and before filling the trenches with an oxide, the silicon layer portions of the trench side walls are oxidized. This step produces a bottleneck-shaped trench in which the trench side walls are wider adjacent the trench bottom than adjacent the top of the silicon layer portion of the trench side wall. After the step of oxidizing the silicon layer portion of the trench side walls, the next step in STI processing comprises filling the trenches with an oxide. The bottleneck shape of the trench makes filling the trench with an oxide difficult. This difficulty results in the formation of a seam in the center of the trench. This seam may open up during subsequent processing steps, leading to several problems. For instance, the seam might cause shorts between subsequently deposited poly gates if filled with polysilicon during the poly gate deposition step.
- The deficiencies of the conventional processes of fabricating a trench on a silicon substrate using shallow trench isolation (STI) show that a need still exists for a process to eliminate the bottleneck-shaped trench produced after oxidizing the trench side walls. To overcome the shortcomings of the conventional processes, a new process is provided. An object of the present invention is to provide a process for fabricating a trench using STI in which the trench side walls are spaced further apart adjacent the exposed surface than adjacent the trench bottom.
- To achieve these and other objects, and in view of its purposes, the present invention provides a process for fabricating a trench having a tapered shape, side walls, and a bottom on a silicon substrate. The substrate has an exposed surface. The trench side walls are spaced further apart adjacent the exposed surface than adjacent the trench bottom. The process comprises the following steps:
- forming an initial trench having initial trench side walls and a trench bottom extending from the exposed surface into an interior of the substrate;
- implanting nitrogen ions on the initial trench side walls so that more nitrogen ions are implanted adjacent the exposed surface than adjacent the trench bottom; and
- oxidizing the trench side walls, thereby creating a trench having the tapered shape.
- In a preferred embodiment, the nitrogen ions are implanted on the initial trench side walls at an angle of from about 10 degrees to about 60 degrees relative to the exposed surface.
- It is to be understood that both the foregoing general description and the following detailed description are exemplary, but are not restrictive, of the invention.
- The invention is best understood from the following detailed description when read in connection with the accompanying drawing. It is emphasized that, according to common practice, the various features of the drawing are not to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawing are the following figures:
- FIG. 1 shows in schematic representation a silicon substrate comprising a trench structure having side walls spaced further apart adjacent the trench bottom than adjacent the top of the silicon layer portion of the trench side wall;
- FIG. 2A shows the structure of FIG. 1 after the trench has been filled with an oxide, producing a seam in the center of the trench;
- FIG. 2B shows the structure of FIG. 2A after the seam has been filled with polysilicon, causing shorts between deposited poly gates;
- FIG. 3 shows in schematic representation a silicon substrate;
- FIG. 4 shows in schematic representation a silicon substrate having a trench with substantially perpendicular side walls;
- FIG. 5 shows in schematic representation a top view of FIG. 4;
- FIG. 6 illustrates the angle to the exposed surface in which nitrogen ions are implanted into the trench side walls;
- FIG. 7 shows in schematic representation a silicon substrate having a tapered trench structure; and
- FIG. 8 shows in schematic representation a tapered trench of a silicon substrate that has been filled with oxide.
- The present invention will next be described with reference to the drawing in which similar numbers indicate the same elements in all figures. Such figures are intended to be illustrative rather than limiting and are included to facilitate the explanation of the apparatus of the present invention. The apparatus is made by the Shallow Trench Isolation (STI) process. The STI process comprises the steps of etching trenches, having side walls and bottoms, in the SOI substrate, oxidizing the silicon layer portions of the trench sidewalls, and filling the trenches with an oxide.
- Referring now to the drawing, FIG. 1 shows a side view of a
silicon substrate 1 after the steps of etching atrench 18 and oxidizing thoseportions side walls trench 18 comprising asilicon layer 14. Thesubstrate 1 comprises asilicon wafer 10, a buriedsilicon oxide layer 12 formed on thesilicon wafer 10, thesilicon layer 14, asilicon nitride layer 16, and thetrench 18. - After oxidizing the
side walls trench 18, the next step in STI processing comprises filling thetrench 18 with anoxide 32. As a result of the bottleneck-shape of thetrench 18, a shape in which the width of thetrench 18 is greater near the bottom then at the top, it is very difficult to fill thetrench 18 with anoxide 32. This difficulty results in the formation of aseam 22 in the center of thetrench 18 as illustrated in FIG. 2A. - The
seam 22 may open up during subsequent processing steps, leading to several problems. For instance, FIG. 2B shows the structure of FIG. 2A after theseam 22 has been filled withpolysilicon 40. Thepolysilicon 40 fills theseam 22 during deposition ofpoly gates 42 and may cause shorts between thepoly gates 42. - The present invention provides a process for fabricating a
trench 18 using shallow trench isolation (STI) in which theside walls trench 18 are spaced further apart adjacent the exposed surface than adjacent the trench bottom. Forming atrench 18 having this structure eliminates the formation of aseam 22 in the center of thetrench 18 when thetrench 18 is filled with anoxide 32. - FIG. 3 shows a side view of an embodiment of a silicon substrate comprising a silicon-on-insulator (SOI)
substrate 1. In this embodiment, thesubstrate 1, having an exposedsurface 8, comprises asilicon wafer 10, a buriedsilicon oxide layer 12 formed on thesilicon wafer 10, asilicon layer 14, and asilicon nitride layer 16. Athin oxide layer 15 of from about 0.006 μm to about 0.01 μm can optionally be deposited between thesilicon layer 14 and thesilicon nitride layer 16 to reduce damage to thesilicon layer 14 caused by deposition of thesilicon nitride layer 16. - In a preferred embodiment, the thickness of the
silicon oxide layer 12 is from about 0.1 μm to about 0.4 μm, the thickness of thesilicon layer 14 is from about 0.1 μm to about 0.2 μm, and the thickness of thesilicon nitride layer 16 is from about 0.1 μm to about 0.15 μm. In a more preferred embodiment, the thickness of thesilicon oxide layer 12 is about 0.4 μm, the thickness of thesilicon layer 14 is about 0.18 μm, and the thickness of thesilicon nitride layer 16 is about 0.12 μm. - FIG. 4 shows a side view of a
substrate 1 having aninitial trench 18 extending into the interior of thesubstrate 1. In FIG. 4, standard photomasking and etching of thesilicon substrate 1, through thesilicon nitride layer 16, thin oxide layer 15 (if present), andsilicon layer 14, results in aninitial trench 18 having a bottom 21 and four initialtrench side walls Side walls side walls initial trench 18. Initialtrench side walls surface 8 of thesubstrate 1. - To form the
side walls initial trench 18 substantially perpendicular to the exposedsurface 8, dry etching techniques, which are well known in the art, are preferred. Theinitial trench 18 can be cleaned using methods commonly known in the art, which typically include a preliminary step of plasma oxidation stripping or immersion in an inorganic resist stripper, followed by the removal of residual organic contaminants and the desorption of remaining atomic and ionic contaminants. S. Wolf & R. N. Tauber discuss such cleaning processes on pages 516-517 of their text, titled Silicon Processing for the VLSI Era,Volume 1—Process Technology (1986). - FIG. 6 shows the step of nitrogen ion implantation into the
side walls initial trench 18. Thenitrogen ions 50 are implanted at an angle (α) to the exposedsurface 8 of thesubstrate 1. Ion implantation is a process in which energetic, charged atoms or molecules are directly introduced into a substrate, such as a silicon wafer. At varying orientations,nitrogen ions 50 are implanted on eachside wall initial trench 18. - In one embodiment, a first position of the
substrate 1 is determined so thatnitrogen ions 50 are beamed at a direction parallel toside walls side wall 24. Thesubstrate 1 is then rotated by 90 degrees about a rotation axis parallel to the top of thesubstrate 1 and fixed in a second position.Nitrogen ions 50 are then beamed at a direction parallel toside walls side wall 28. Thesubstrate 1 is then rotated by 90 degrees about a rotation axis parallel to the top of thesubstrate 1 and fixed in a third position.Nitrogen ions 50 are then beamed at a direction parallel toside walls side wall 26. Thesubstrate 1 is then rotated by 90 degrees about a rotation axis parallel to the top of thesubstrate 1 and fixed in a fourth position.Nitrogen ions 50 are then beamed at a direction parallel toside walls side wall 30. - The optimal angle (α) of nitrogen ion implantation depends on the thickness of the
silicon nitride layer 16 and the size of thetrench 18. In a preferred embodiment, theside walls trench 18 are implanted with from about 5 keV to about 15keV nitrogen ions 50 to a dose of from about 1×1014/cm2 to about 1×1015/cm2, and thenitrogen ions 50 are implanted at an angle (α) of from about 10 to about 60 degrees relative to the exposedsurface 8. In a more preferred embodiment, theside walls trench 18 are implanted with about 10keV nitrogen ions 50 to a dose of about 5×1014/cm2 at an angle (α) of about 20 degrees. By implantingnitrogen ions 50 at an angle (α) relative to the exposedsurface 8,more nitrogen ions 50 are implanted adjacent the exposedsurface 8 than adjacent the bottom 21 of thetrench 18. - FIG. 7 shows a side view of a resulting tapered
trench 18 a after oxidation of theside walls initial trench 18, resulting in taperedside walls side walls silicon nitride layer 16, which forms the portion of theside walls surface 8, inhibits oxidation. In contrast, thesilicon layer 14, which forms the portion of theside walls side walls trench 18 a adjacent thesilicon layer 14 results in oxide formation in proportion to nitrogen ion concentration. - Because the
nitrogen ions 50 are implanted at an angle (α) relative to the exposedsurface 8,more nitrogen ions 50 are implanted into the portion of theside walls trench 18 a adjacent thesilicon layer 14 and the bottom 21 of thetrench 18 a than in thesilicon nitride layer 16 portion of theside walls surface 8, thereby producing a tapered shape upon oxidation. A portion ofsilicon layer 14 adjacent theside walls trench 18 a is also oxidized. In a preferred embodiment, theside walls - Following oxidation of the trench sidewalls24, 26, 28, and 30, the trench is then filled with an
oxide 32. FIG. 8 shows a side view of the taperedtrench 18 a shown in FIG. 7 after taperedtrench 18 a has been filled with theoxide 32. Following oxide deposition to fill thetrench 18 a, steps known in the art can be used to complete an STI structure. In addition, the present invention can be used in bulk STI processes. - In one embodiment, a silicon substrate comprising an SOI substrate was formed by the following steps. A 0.4 μm layer of
silicon oxide 12 was formed on asilicon wafer 1 and a 0.18μm silicon layer 14 was formed on thesilicon oxide layer 12 using the separation by implantation of oxygen (SIMOX) process. A 0.008 μm layer of silicon oxide (thin silicon oxide layer 15) was next formed on thesilicon layer 14 followed by deposition of a 0.12 μm layer ofsilicon nitride 16 on the thinsilicon oxide layer 15. Aninitial trench 18 extending from the exposedsurface 8 of thesubstrate 1 into an interior of the substrate was formed by photomasking and plasma etching. The plasma etching was selective to stop at thesilicon oxide layer 15, producing a trench depth of 0.308 μm. The initialtrench side walls keV nitrogen ions 50 to a dose of 5×1014/cm2 at an angle (α) of 30 degrees with respect to the exterior, exposedsurface 8 of thesubstrate 1. Thetrench side walls trench 18 a in which thetrench side walls surface 8 of thesubstrate 1 than adjacent thetrench bottom 21. - Although illustrated and described above with reference to certain specific embodiments, the present invention is nevertheless not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the spirit of the invention.
Claims (17)
1. A process for fabricating a trench, having a bottom and side walls defining a tapered shape, on a silicon substrate, the substrate having an exposed surface, wherein the trench side walls are spaced further apart adjacent the exposed surface than adjacent the trench bottom, the process comprising:
forming an initial trench having initial trench side walls and the trench bottom extending from the exposed surface into an interior of the substrate;
implanting nitrogen ions on the initial trench side walls wherein more nitrogen ions are implanted adjacent the exposed surface than adjacent the trench bottom; and
oxidizing the trench side walls, thereby creating a trench having the tapered shape.
2. The process of wherein the initial trench side walls extend into the substrate in a direction substantially perpendicular to the exposed surface and are substantially perpendicular to each other.
claim 1
3. The process according to wherein the step of implanting the nitrogen ions on the initial trench side walls comprises implanting the ions at an angle from about 10 degrees to about 60 degrees relative to the exposed surface.
claim 2
4. The process according to wherein the nitrogen ions are implanted on the initial trench side walls at an angle of about 30 degrees relative to the exposed surface.
claim 3
5. The process according to wherein the step of implanting the nitrogen ions comprises implanting from about 5 kev to about 10 keV nitrogen ions on the initial trench side walls to a dose of from about 1×1014/cm2 to about 1×1015/cm2.
claim 1
6. The process according to wherein the step of implanting the nitrogen ions comprises implanting about 10 keV nitrogen ions on the initial trench side walls to a dose of about 5×1014/cm2.
claim 5
7. The process according to wherein the step of forming the initial trench comprises photomasking and etching the substrate.
claim 1
8. The process according to wherein the etching is dry etching.
claim 7
9. The process according to wherein the substrate is a silicon-on-insulator substrate comprising a silicon oxide layer having a thickness of from about 0.1 μm to about 0.4 μm on a silicon wafer, a silicon layer having a thickness of from about 0.1 μm to about 0.2 μm on the silicon oxide layer, and a silicon nitride layer having a thickness of from about 0.1 μm to about 0.2 μm on the silicon layer.
claim 1
10. The process according to wherein the silicon oxide layer has a thickness of about 0.4 μm, the silicon layer has a thickness of about 0.18 μm, and the silicon nitride layer has a thickness of about 0.12 μm.
claim 9
11. The process according to wherein the substrate further comprises a thin silicon oxide layer having a thickness of from about 0.006 μm to about 0.01 μm between the silicon layer and the silicon nitride layer.
claim 9
12. The process according to further comprising the step of cleaning the initial trench before the step of oxidizing the trench side walls.
claim 1
13. A process for fabricating a trench having a bottom and side walls defining a tapered shape on a silicon-on-insulator substrate, the substrate having an exposed surface, wherein the trench side walls are spaced further apart adjacent the exposed surface than adjacent the trench bottom, the process comprising:
forming an initial trench having initial trench side walls and the trench bottom extending from the exposed surface into an interior of the substrate by photomasking and dry etching the substrate;
implanting about 10 keV nitrogen ions to a dose of about 5×1014 cm/cm2 on the initial trench side walls at an angle from about 10 degrees to about 60 degrees wherein more nitrogen ions are implanted adjacent the exposed surface than adjacent the trench bottom; and
oxidizing the trench side walls with dry oxygen at about 1,000° C., thereby creating the tapered shape.
14. The process of wherein the substrate comprises a silicon oxide layer having a thickness of about 0.4 μm on a silicon wafer, a silicon layer having a thickness of about 0.18 μm on the silicon oxide layer, and a silicon nitride layer having a thickness of about 0.12 μm on the silicon layer.
claim 13
15. A silicon substrate having an exposed surface and a trench having a bottom and side walls defining a tapered shape extending through the exposed surface into the substrate, wherein the trench side walls are spaced further apart adjacent the exposed surface than adjacent the trench bottom, and wherein the trench is fabricated by:
forming an initial trench having initial trench side walls and the trench bottom extending from the exposed surface into the substrate;
implanting nitrogen ions on the initial trench side walls wherein more nitrogen ions are implanted adjacent the exposed surface than adjacent the trench bottom; and
oxidizing the trench side walls, thereby creating a trench having the tapered shape.
16. The substrate according to further comprising a silicon oxide layer on a silicon wafer, a silicon layer on the silicon oxide layer, and a silicon nitride layer on the silicon layer.
claim 15
17. The substrate according to further comprising a thin silicon oxide layer having a thickness of from about 0.006 μm to about 0.01 μm between the silicon layer and the silicon nitride layer.
claim 16
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US09/837,136 US6437400B2 (en) | 1998-11-20 | 2001-04-18 | Shallow trench isolation on a silicon substrate using nitrogen implant into the side wall |
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US09/197,168 US6238998B1 (en) | 1998-11-20 | 1998-11-20 | Shallow trench isolation on a silicon substrate using nitrogen implant into the side wall |
US09/837,136 US6437400B2 (en) | 1998-11-20 | 2001-04-18 | Shallow trench isolation on a silicon substrate using nitrogen implant into the side wall |
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US09/837,136 Expired - Fee Related US6437400B2 (en) | 1998-11-20 | 2001-04-18 | Shallow trench isolation on a silicon substrate using nitrogen implant into the side wall |
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Cited By (4)
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US20090227086A1 (en) * | 2008-03-06 | 2009-09-10 | Roland Hampp | Threshold Voltage Consistency and Effective Width in Same-Substrate Device Groups |
US20100244183A1 (en) * | 2009-03-31 | 2010-09-30 | Sanken Electric Co., Ltd. | Integrated semiconductor device and method of manufacturing the same |
EP2573807A1 (en) * | 2011-09-23 | 2013-03-27 | Soitec | Semiconductor structure and process for bird's beak reduction |
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US6238998B1 (en) * | 1998-11-20 | 2001-05-29 | International Business Machines Corporation | Shallow trench isolation on a silicon substrate using nitrogen implant into the side wall |
EP1049155A1 (en) * | 1999-04-29 | 2000-11-02 | STMicroelectronics S.r.l. | Process for manufacturing a SOI wafer with buried oxide regions without cusps |
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US6238998B1 (en) * | 1998-11-20 | 2001-05-29 | International Business Machines Corporation | Shallow trench isolation on a silicon substrate using nitrogen implant into the side wall |
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1998
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2001
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US20090227086A1 (en) * | 2008-03-06 | 2009-09-10 | Roland Hampp | Threshold Voltage Consistency and Effective Width in Same-Substrate Device Groups |
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US20100244183A1 (en) * | 2009-03-31 | 2010-09-30 | Sanken Electric Co., Ltd. | Integrated semiconductor device and method of manufacturing the same |
US8349698B2 (en) * | 2009-03-31 | 2013-01-08 | Sanken Electric Co., Ltd. | Integrated semiconductor device and method of manufacturing the same |
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CN103633008A (en) * | 2012-08-20 | 2014-03-12 | 中国科学院微电子研究所 | Shallow trench isolation manufacturing method |
Also Published As
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US6437400B2 (en) | 2002-08-20 |
US6238998B1 (en) | 2001-05-29 |
KR100348932B1 (en) | 2002-08-14 |
KR20000035091A (en) | 2000-06-26 |
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