WO2006100457A1 - A method of forming a bragg reflector stack - Google Patents
A method of forming a bragg reflector stack Download PDFInfo
- Publication number
- WO2006100457A1 WO2006100457A1 PCT/GB2006/001005 GB2006001005W WO2006100457A1 WO 2006100457 A1 WO2006100457 A1 WO 2006100457A1 GB 2006001005 W GB2006001005 W GB 2006001005W WO 2006100457 A1 WO2006100457 A1 WO 2006100457A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- tungsten
- silicon dioxide
- tungsten nitride
- layer
- nitride layer
- Prior art date
Links
- 238000000034 method Methods 0.000 title claims abstract description 15
- 229910052721 tungsten Inorganic materials 0.000 claims abstract description 45
- 239000010937 tungsten Substances 0.000 claims abstract description 45
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims abstract description 32
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 claims abstract description 24
- -1 Tungsten Nitride Chemical class 0.000 claims abstract description 21
- 235000012239 silicon dioxide Nutrition 0.000 claims abstract description 16
- 239000000377 silicon dioxide Substances 0.000 claims abstract description 16
- 238000000151 deposition Methods 0.000 claims abstract description 9
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 18
- 229910052757 nitrogen Inorganic materials 0.000 claims description 9
- 230000008021 deposition Effects 0.000 claims description 4
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 5
- 229910052710 silicon Inorganic materials 0.000 description 5
- 239000010703 silicon Substances 0.000 description 5
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 4
- 238000012360 testing method Methods 0.000 description 4
- 238000005334 plasma enhanced chemical vapour deposition Methods 0.000 description 3
- 238000000623 plasma-assisted chemical vapour deposition Methods 0.000 description 3
- 239000000758 substrate Substances 0.000 description 3
- 229910052786 argon Inorganic materials 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- NRTOMJZYCJJWKI-UHFFFAOYSA-N Titanium nitride Chemical compound [Ti]#N NRTOMJZYCJJWKI-UHFFFAOYSA-N 0.000 description 1
- 230000003466 anti-cipated effect Effects 0.000 description 1
- 230000032798 delamination Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000013101 initial test Methods 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 238000007655 standard test method Methods 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H3/00—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators
- H03H3/007—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks
- H03H3/02—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of piezoelectric or electrostrictive resonators or networks
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H3/00—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators
- H03H3/007—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks
- H03H3/02—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of piezoelectric or electrostrictive resonators or networks
- H03H2003/025—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of piezoelectric or electrostrictive resonators or networks the resonators or networks comprising an acoustic mirror
Definitions
- Bragg reflector stacks have many applications, but they are commonly used in bulk acoustic wave devices and in that application at least, it is known to form them by depositing alternate Silicon Dioxide and Tungsten layers upon a silicon wafer. Such a stack is illustrated in Figure 1.
- a thin titanium nitride layer can act to improve the adhesion of Tungsten to Silicon Dioxide, but this requires additional time, complexity and expense, when forming a multi layered stack, because the substrate would have to be removed to a separate chamber after each Silicon
- Dioxide deposition or the target would have to be changed. This is particularly the case where high quality stacks are required over the surface of a large substrate eg. 200mm or larger. This requires large targets that cannot readily be moved and virtually dictates a single wafer/single target type system. Therefore each metal requires its own target and each target requires its own process chamber.
- Tungsten Nitride layers are deposited at every Silicon Dioxide/Tungsten interface e.g. above and below the Tungsten.
- the Tungsten Nitride layer and the Tungsten layer are sputter deposited and the same target is used for each layer.
- nitrogen will be flowed in together with the sputter gas (typically argon) and it is particularly preferred that the flow of nitrogen is varied to produce a graded adhesion layer. It is anticipated that it will be desirable to have a higher level of nitrogen at the interface with the silicon dioxide to enhance adhesion and a reduce amount of nitrogen adjacent the upper surface on which the Tungsten will be deposited so that one is closer to depositing Tungsten on Tungsten.
- the Tungsten Nitride layer may have a thickness in the range of about
- At least one of the Silicon Dioxide layers may be a tensile layer.
- the stress in the stack may be tuned to compensate for the Tungsten Nitride thickness by changing the Tungsten deposition pressure, bias power if used, target power and possibly nitrogen concentration. In the last case the difference between stochiometric and non stochiometric Tungsten Nitride may provide sufficient stress change.
- Figure 1 is a schematic view of a known Bragg reflector stack
- Figure 2 is a schematic representation of the applicant's embodiment of a
- test adhesion or seed layer of Tungsten Nitride was deposited in a standard sputter apparatus which the following process details: power: 1kW to a
- Tungsten Nitride layer deposited was about 100A.
- references to Tungsten Nitride are not limited to Stochiometric WN but any Tungsten film in which nitrogen has been added to effect an improvement in adhesion between a Tungsten layer and another layer of an acoustic reflector structure.
- the invention is particularly useful where the reflector structures are formed across large Silicon substrates of 200mm diameter larger and particularly where they form an underlayer to an acoustic filter.
Abstract
A method of forming a Bragg reflector stack including depositing alternate Silicon Dioxide and Tungsten layers characterised in that a Tungsten Nitride layer is deposited at at least one Silicon Dioxide/Tungsten interface.
Description
A Method of Forming a Bragg Reflector Stack
. This invention relates to Bragg reflector stacks. Bragg reflector stacks have many applications, but they are commonly used in bulk acoustic wave devices and in that application at least, it is known to form them by depositing alternate Silicon Dioxide and Tungsten layers upon a silicon wafer. Such a stack is illustrated in Figure 1.
However these stacks have been shown to experience significant delamination (blistering) problems even when total stack stress is tuned to a low level. The applicant's unpublished investigations have shown that there is very poor adhesion between the Tungsten layer and the PECVD silicon dioxide layer, as will be discussed in more detail below.
The Applicants are aware that a thin titanium nitride layer can act to improve the adhesion of Tungsten to Silicon Dioxide, but this requires additional time, complexity and expense, when forming a multi layered stack, because the substrate would have to be removed to a separate chamber after each Silicon
Dioxide deposition or the target would have to be changed. This is particularly the case where high quality stacks are required over the surface of a large substrate eg. 200mm or larger. This requires large targets that cannot readily be moved and virtually dictates a single wafer/single target type system. Therefore each metal requires its own target and each target requires its own process chamber.
The present invention consists in a method or forming a Bragg reflector stack including depositing alternate Silicon Dioxide and Tungsten layers characterised in that a Tungsten Nitride layer is deposited at at least one Silicon
Dioxide/Tungsten interface.
Preferably Tungsten Nitride layers are deposited at every Silicon Dioxide/Tungsten interface e.g. above and below the Tungsten.
It is preferred that the Tungsten Nitride layer and the Tungsten layer are sputter deposited and the same target is used for each layer. In that case nitrogen will be flowed in together with the sputter gas (typically argon) and it is particularly preferred that the flow of nitrogen is varied to produce a graded
adhesion layer. It is anticipated that it will be desirable to have a higher level of nitrogen at the interface with the silicon dioxide to enhance adhesion and a reduce amount of nitrogen adjacent the upper surface on which the Tungsten will be deposited so that one is closer to depositing Tungsten on Tungsten. The Tungsten Nitride layer may have a thickness in the range of about
20A to about 200A.
At least one of the Silicon Dioxide layers may be a tensile layer. The stress in the stack may be tuned to compensate for the Tungsten Nitride thickness by changing the Tungsten deposition pressure, bias power if used, target power and possibly nitrogen concentration. In the last case the difference between stochiometric and non stochiometric Tungsten Nitride may provide sufficient stress change.
Although the invention has been defined above it is to be understood that it includes any inventive combination of the features set out above or in the following description.
The invention may be performed in various ways and specific embodiments will now be described with reference to the accompanying drawings, in which:
Figure 1 is a schematic view of a known Bragg reflector stack; Figure 2 is a schematic representation of the applicant's embodiment of a
Bragg reflector stack.
As has been indicated above, the applicants have tested the adhesion of Tungsten to PECVD (Plasma Enhanced Chemical Vapour Deposition) Silicon Dioxide and Flowfill® and Thermal Silicon Dioxide using the Standard Test Method for Measuring Adhesion by Tape Test ASTM D 3359-97(-Test Method
B). It was found that the adhesion was classification 0B->65% removed as compared with the good adhesion to silicon, which is classification 5B-0% removed.
A test adhesion or seed layer of Tungsten Nitride was deposited in a standard sputter apparatus which the following process details: power: 1kW to a
Tungsten target of approximately 350mm diameter Gas flow: 60 seem Argon, 70sccm Nitrogen
Platen Temperature: 2000C
Chamber pressure during deposition; about 4 mTorr The Tungsten Nitride layer deposited was about 100A. A standard tape pulling test on Tungsten deposited on the Tungsten nitride layer, which was in turn deposited on Silicon Dioxide, resulted in classification 2B - 15 to 35% removed.
In the light of this a Bragg reflector with a structure as shown in Figure 2 was deposited. It will be noted that a Tungsten Nitride layer was deposited below and beneath each Tungsten layer forming an effective sandwich. The structure was functionally similar to that illustrated in Figure 1 but had greater structural integrity due to the improved adhesion between the layers.
Initial tests have shown good results with tape pulling tests (0% removed), no blistering/peeling and also no interfacial separation when the sample is cleaved and scanned by an electron microscope. This is contrary to the observations of the same stack deposited in the same apparatus with the same process when no Tungsten Nitride adhesion layer is used.
It should be understood that references to Tungsten Nitride are not limited to Stochiometric WN but any Tungsten film in which nitrogen has been added to effect an improvement in adhesion between a Tungsten layer and another layer of an acoustic reflector structure. The invention is particularly useful where the reflector structures are formed across large Silicon substrates of 200mm diameter larger and particularly where they form an underlayer to an acoustic filter.
Claims
1. A method of forming a Bragg reflector stack including depositing alternate Silicon Dioxide and Tungsten iayers characterised in that a Tungsten Nitride layer is deposited at at least one Silicon Dioxide/Tungsten interface.
2. A method as claimed in claim 1 wherein a Tungsten Nitride layer is deposited at every Silicon Dioxide/Tungsten interface.
3. A method as claimed in claim 1 wherein the Tungsten Nitride and the Tungsten layer are sputter deposited and the same target is used for each layer.
4. A method as claimed in claim 2 wherein during the deposition of the
Tungsten Nitride layer to flow of nitrogen introduced into the sputter process is varied to produce a graded Tungsten Nitride layer.
5. A method as claimed in claim 3 or claim 3 wherein the flow of nitrogen is varied from Tungsten Nitride layer to Tungsten Nitride layer.
6. A method as claimed in any one of the preceding claims wherein the
Tungsten Nitride layer has a thickness in range of about 20A to about 200A.
7. A method as claimed in any one of the preceding claims wherein at least one of the Silicon Dioxide layers is a tensile layer.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US66379005P | 2005-03-22 | 2005-03-22 | |
| US60/663,790 | 2005-03-22 | ||
| GB0505792.2 | 2005-03-22 | ||
| GB0505792A GB0505792D0 (en) | 2005-03-22 | 2005-03-22 | A method of forming a bragg reflector stack |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| WO2006100457A1 true WO2006100457A1 (en) | 2006-09-28 |
Family
ID=36295359
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| PCT/GB2006/001005 WO2006100457A1 (en) | 2005-03-22 | 2006-03-21 | A method of forming a bragg reflector stack |
Country Status (1)
| Country | Link |
|---|---|
| WO (1) | WO2006100457A1 (en) |
Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3414832A (en) * | 1964-12-04 | 1968-12-03 | Westinghouse Electric Corp | Acoustically resonant device |
| US4166967A (en) * | 1976-10-19 | 1979-09-04 | Hans List | Piezoelectric resonator with acoustic reflectors |
| US5341016A (en) * | 1993-06-16 | 1994-08-23 | Micron Semiconductor, Inc. | Low resistance device element and interconnection structure |
| WO2000004574A1 (en) * | 1998-07-14 | 2000-01-27 | Applied Materials, Inc. | Improved gate electrode connection structure by in situ chemical vapor deposition of tungsten and tungsten nitride |
| US20030199105A1 (en) * | 2002-04-22 | 2003-10-23 | Kub Francis J. | Method for making piezoelectric resonator and surface acoustic wave device using hydrogen implant layer splitting |
| WO2004061154A1 (en) * | 2002-12-27 | 2004-07-22 | Ulvac Inc. | Method for forming tungsten nitride film |
-
2006
- 2006-03-21 WO PCT/GB2006/001005 patent/WO2006100457A1/en not_active Application Discontinuation
Patent Citations (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3414832A (en) * | 1964-12-04 | 1968-12-03 | Westinghouse Electric Corp | Acoustically resonant device |
| US4166967A (en) * | 1976-10-19 | 1979-09-04 | Hans List | Piezoelectric resonator with acoustic reflectors |
| US5341016A (en) * | 1993-06-16 | 1994-08-23 | Micron Semiconductor, Inc. | Low resistance device element and interconnection structure |
| WO2000004574A1 (en) * | 1998-07-14 | 2000-01-27 | Applied Materials, Inc. | Improved gate electrode connection structure by in situ chemical vapor deposition of tungsten and tungsten nitride |
| US20030199105A1 (en) * | 2002-04-22 | 2003-10-23 | Kub Francis J. | Method for making piezoelectric resonator and surface acoustic wave device using hydrogen implant layer splitting |
| WO2004061154A1 (en) * | 2002-12-27 | 2004-07-22 | Ulvac Inc. | Method for forming tungsten nitride film |
| US20050221625A1 (en) * | 2002-12-27 | 2005-10-06 | Ulvac, Inc. | Method for forming tungsten nitride film |
Non-Patent Citations (1)
| Title |
|---|
| YONG TAE KIM ET AL: "NEW METHOD TO IMPROVE THE ADHESION STRENGTH OF TUNGSTEN THIN FILM ON SILICON BY W2N GLUE LAYER", APPLIED PHYSICS LETTERS, AIP, AMERICAN INSTITUTE OF PHYSICS, MELVILLE, NY, US, vol. 61, no. 5, 3 August 1992 (1992-08-03), pages 537 - 539, XP000289379, ISSN: 0003-6951 * |
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