JP6887655B2 - Electrodes and capacitors for bismuth-based dielectrics - Google Patents
Electrodes and capacitors for bismuth-based dielectrics Download PDFInfo
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- 239000003989 dielectric material Substances 0.000 title claims description 20
- 239000003990 capacitor Substances 0.000 title claims description 14
- 229910052797 bismuth Inorganic materials 0.000 title claims description 11
- JCXGWMGPZLAOME-UHFFFAOYSA-N bismuth atom Chemical compound [Bi] JCXGWMGPZLAOME-UHFFFAOYSA-N 0.000 title claims description 11
- 229910052715 tantalum Inorganic materials 0.000 claims description 7
- GUVRBAGPIYLISA-UHFFFAOYSA-N tantalum atom Chemical compound [Ta] GUVRBAGPIYLISA-UHFFFAOYSA-N 0.000 claims description 3
- 239000012528 membrane Substances 0.000 claims 1
- 150000001247 metal acetylides Chemical class 0.000 claims 1
- 238000010438 heat treatment Methods 0.000 description 25
- 229910052751 metal Inorganic materials 0.000 description 18
- 239000002184 metal Substances 0.000 description 17
- 238000009792 diffusion process Methods 0.000 description 11
- 239000010408 film Substances 0.000 description 11
- 239000000463 material Substances 0.000 description 9
- 238000005259 measurement Methods 0.000 description 8
- 239000010936 titanium Substances 0.000 description 8
- 238000004833 X-ray photoelectron spectroscopy Methods 0.000 description 7
- 238000004458 analytical method Methods 0.000 description 7
- 239000004065 semiconductor Substances 0.000 description 7
- 230000015572 biosynthetic process Effects 0.000 description 6
- 230000007547 defect Effects 0.000 description 6
- 229910052719 titanium Inorganic materials 0.000 description 6
- 239000011777 magnesium Substances 0.000 description 5
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 4
- 239000007772 electrode material Substances 0.000 description 4
- 238000011156 evaluation Methods 0.000 description 4
- 229910052749 magnesium Inorganic materials 0.000 description 4
- 238000000034 method Methods 0.000 description 4
- 229910052758 niobium Inorganic materials 0.000 description 4
- 239000010955 niobium Substances 0.000 description 4
- 229910052760 oxygen Inorganic materials 0.000 description 4
- 239000001301 oxygen Substances 0.000 description 4
- 230000000694 effects Effects 0.000 description 3
- 150000004767 nitrides Chemical class 0.000 description 3
- 229910052697 platinum Inorganic materials 0.000 description 3
- 230000005469 synchrotron radiation Effects 0.000 description 3
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 2
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 2
- 238000000137 annealing Methods 0.000 description 2
- 230000004888 barrier function Effects 0.000 description 2
- 229910052790 beryllium Inorganic materials 0.000 description 2
- ATBAMAFKBVZNFJ-UHFFFAOYSA-N beryllium atom Chemical compound [Be] ATBAMAFKBVZNFJ-UHFFFAOYSA-N 0.000 description 2
- 229910052791 calcium Inorganic materials 0.000 description 2
- 239000011575 calcium Substances 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 238000003411 electrode reaction Methods 0.000 description 2
- 238000000608 laser ablation Methods 0.000 description 2
- 238000005204 segregation Methods 0.000 description 2
- 229910052712 strontium Inorganic materials 0.000 description 2
- 239000000758 substrate Substances 0.000 description 2
- 229910015902 Bi 2 O 3 Inorganic materials 0.000 description 1
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 1
- UOACKFBJUYNSLK-XRKIENNPSA-N Estradiol Cypionate Chemical compound O([C@H]1CC[C@H]2[C@H]3[C@@H](C4=CC=C(O)C=C4CC3)CC[C@@]21C)C(=O)CCC1CCCC1 UOACKFBJUYNSLK-XRKIENNPSA-N 0.000 description 1
- GYHNNYVSQQEPJS-UHFFFAOYSA-N Gallium Chemical compound [Ga] GYHNNYVSQQEPJS-UHFFFAOYSA-N 0.000 description 1
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 1
- CBENFWSGALASAD-UHFFFAOYSA-N Ozone Chemical compound [O-][O+]=O CBENFWSGALASAD-UHFFFAOYSA-N 0.000 description 1
- 229910004121 SrRuO Inorganic materials 0.000 description 1
- 229910002367 SrTiO Inorganic materials 0.000 description 1
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 1
- QCWXUUIWCKQGHC-UHFFFAOYSA-N Zirconium Chemical compound [Zr] QCWXUUIWCKQGHC-UHFFFAOYSA-N 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 229910052787 antimony Inorganic materials 0.000 description 1
- WATWJIUSRGPENY-UHFFFAOYSA-N antimony atom Chemical compound [Sb] WATWJIUSRGPENY-UHFFFAOYSA-N 0.000 description 1
- 229910052785 arsenic Inorganic materials 0.000 description 1
- RQNWIZPPADIBDY-UHFFFAOYSA-N arsenic atom Chemical compound [As] RQNWIZPPADIBDY-UHFFFAOYSA-N 0.000 description 1
- 229910052788 barium Inorganic materials 0.000 description 1
- DSAJWYNOEDNPEQ-UHFFFAOYSA-N barium atom Chemical compound [Ba] DSAJWYNOEDNPEQ-UHFFFAOYSA-N 0.000 description 1
- JRPBQTZRNDNNOP-UHFFFAOYSA-N barium titanate Chemical compound [Ba+2].[Ba+2].[O-][Ti]([O-])([O-])[O-] JRPBQTZRNDNNOP-UHFFFAOYSA-N 0.000 description 1
- 229910002113 barium titanate Inorganic materials 0.000 description 1
- 239000003985 ceramic capacitor Substances 0.000 description 1
- 229910052804 chromium Inorganic materials 0.000 description 1
- 239000011651 chromium Substances 0.000 description 1
- 238000002425 crystallisation Methods 0.000 description 1
- 230000008025 crystallization Effects 0.000 description 1
- 238000003795 desorption Methods 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- -1 for example Inorganic materials 0.000 description 1
- 229910052733 gallium Inorganic materials 0.000 description 1
- 229910052732 germanium Inorganic materials 0.000 description 1
- GNPVGFCGXDBREM-UHFFFAOYSA-N germanium atom Chemical compound [Ge] GNPVGFCGXDBREM-UHFFFAOYSA-N 0.000 description 1
- 229910052737 gold Inorganic materials 0.000 description 1
- 229910052735 hafnium Inorganic materials 0.000 description 1
- VBJZVLUMGGDVMO-UHFFFAOYSA-N hafnium atom Chemical compound [Hf] VBJZVLUMGGDVMO-UHFFFAOYSA-N 0.000 description 1
- 229910052738 indium Inorganic materials 0.000 description 1
- APFVFJFRJDLVQX-UHFFFAOYSA-N indium atom Chemical compound [In] APFVFJFRJDLVQX-UHFFFAOYSA-N 0.000 description 1
- 238000001659 ion-beam spectroscopy Methods 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
- 239000011733 molybdenum Substances 0.000 description 1
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- 238000005240 physical vapour deposition Methods 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 230000003405 preventing effect Effects 0.000 description 1
- 230000002265 prevention Effects 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000012827 research and development Methods 0.000 description 1
- 229910052706 scandium Inorganic materials 0.000 description 1
- SIXSYDAISGFNSX-UHFFFAOYSA-N scandium atom Chemical compound [Sc] SIXSYDAISGFNSX-UHFFFAOYSA-N 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
- CIOAGBVUUVVLOB-UHFFFAOYSA-N strontium atom Chemical compound [Sr] CIOAGBVUUVVLOB-UHFFFAOYSA-N 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 229910052717 sulfur Inorganic materials 0.000 description 1
- 239000011593 sulfur Substances 0.000 description 1
- 229910052716 thallium Inorganic materials 0.000 description 1
- BKVIYDNLLOSFOA-UHFFFAOYSA-N thallium Chemical compound [Tl] BKVIYDNLLOSFOA-UHFFFAOYSA-N 0.000 description 1
- 239000010409 thin film Substances 0.000 description 1
- 229910052718 tin Inorganic materials 0.000 description 1
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 description 1
- 229910052721 tungsten Inorganic materials 0.000 description 1
- 239000010937 tungsten Substances 0.000 description 1
- 229910052720 vanadium Inorganic materials 0.000 description 1
- LEONUFNNVUYDNQ-UHFFFAOYSA-N vanadium atom Chemical compound [V] LEONUFNNVUYDNQ-UHFFFAOYSA-N 0.000 description 1
- 229910052725 zinc Inorganic materials 0.000 description 1
- 239000011701 zinc Substances 0.000 description 1
- 229910052726 zirconium Inorganic materials 0.000 description 1
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Description
本発明はビスマス（Ｂｉ）系誘電体材料用電極に関し、特に誘電体材料中のＢｉが拡散することを抑止する電極に関する。本発明は更に、このような電極とＢｉ系誘電体材料とを用いたキャパシタに関する。 The present invention relates to an electrode for a bismuth (Bi) -based dielectric material, and more particularly to an electrode that suppresses the diffusion of Bi in the dielectric material. The present invention further relates to a capacitor using such an electrode and a Bi-based dielectric material.
ＳｉＣ素子等の高温で動作可能な半導体素子の研究・開発が進められているが、このような半導体素子を使用した回路中あるいは半導体素子中に組み込んで使用できる、高温環境下で使用可能なキャパシタ用材料が求められている。高温用半導体素子の一つの典型的な用途として自動車分野がある。自動車用の半導体は単に高温環境下で動作できればよいだけではなく、自動車が外気に直接触れる環境下で使用されることから、極寒地域でもエンジンが起動したら直ちに走行を開始する場合があることを考えると、そこで使用される半導体回路あるいは集積回路は−４０℃程度から正常に動作することが求められる。一方、例えばエンジン制御用高温センサの直近に設置される信号処理回路に使用される場合には高温側で４００℃までの動作が求められる。すなわち、高温用半導体を使用した回路あるいはその集積回路は用途によっては−４０℃〜４００℃の広い温度範囲で正常に動作することが求められる。あるいはハイブリッド自動車や電気自動車で使用されるスナバ回路でも高温側が２５０℃程度の温度範囲での動作が求められる。更には、民生用途を考えると、メンテナンスなしでも長期間に渡って当初の特性を維持して安定動作することも必要となる。 Research and development of semiconductor devices that can operate at high temperatures, such as SiC devices, are underway, and capacitors that can be used in high-temperature environments that can be used in circuits using such semiconductor devices or by incorporating them into semiconductor devices. Materials are required. The automobile field is one of the typical applications of high temperature semiconductor devices. Considering that semiconductors for automobiles need not only be able to operate in a high temperature environment, but also because they are used in an environment where automobiles are in direct contact with the outside air, they may start running as soon as the engine starts even in extremely cold regions. The semiconductor circuit or integrated circuit used there is required to operate normally from about -40 ° C. On the other hand, for example, when it is used in a signal processing circuit installed in the immediate vicinity of a high temperature sensor for engine control, operation up to 400 ° C. is required on the high temperature side. That is, a circuit using a high temperature semiconductor or an integrated circuit thereof is required to operate normally in a wide temperature range of −40 ° C. to 400 ° C. depending on the application. Alternatively, even a snubber circuit used in a hybrid vehicle or an electric vehicle is required to operate in a temperature range of about 250 ° C. on the high temperature side. Furthermore, considering consumer use, it is also necessary to maintain the initial characteristics and operate stably for a long period of time without maintenance.
従来市販されてきたキャパシタは低温側ではともかく、４００℃もの高温で使用可能なものはない。例えばＢａＴｉＯ３系の市販品の積層セラミックスキャパシタの使用温度範囲は−５５℃〜１５０℃程度であり、タンタルキャパシタでも市販品の使用温度範囲は−５５℃〜１７５℃程度しかない。 Aside from the low temperature side, there is no capacitor that has been commercially available that can be used at a high temperature of 400 ° C. For example, the operating temperature range of a commercially available multilayer ceramic capacitor of the BaTIO 3 system is about −55 ° C. to 150 ° C., and the operating temperature range of a commercially available tantalum capacitor is only about −55 ° C. to 175 ° C.
近年、ＢａＴｉＯ３−Ｂｉ（Ｍｇ，Ｎｂ）Ｏ３（以下、ＢＴ−ＢＭＮと略称することがある）（特許文献１）等の高温でも高誘電率を維持する材料が開発された。また、類似組成の誘電体ＢａＴｉＯ３−Ｂｉ（Ｍｇ０．５Ｔｉ０．５）Ｏ３が非特許文献１及び２で報告されている。このようなＢｉを成分元素として含有する誘電体材料（Ｂｉ系誘電体材料と称する）は高温環境下で使用可能なキャパシタ用の誘電体材料として有望視されているが、解決すべき問題点も残されている。
In recent years, materials that maintain a high dielectric constant even at high temperatures, such as BaTiO 3- Bi (Mg, Nb) O 3 (hereinafter, may be abbreviated as BT-BMN) (Patent Document 1), have been developed. Further, a dielectric material BaTiO 3- Bi (Mg 0.5 Ti 0.5 ) O 3 having a similar composition has been reported in
これまでのＢｉ系酸化物材料は室温、低温が主な応用ターゲットであったため、電極はこれまで良好な電極となることが経験的にわかっているＰｔ、Ａｕ等をそのまま使用しても問題はなかった。しかし、本願発明者の研究により、高温環境で使用するＢｉを含む高誘電体薄膜材料では、試料作成時における加熱状態、及び素子使用時の高温環境でのＢｉの拡散、脱離によって生じる誘電率の減少に加えて、Ｂｉが電極材料中にまで拡散することによる電極と誘電体との界面の熱的不安定性が高温下で使用されるＢｉ系誘電体を使用するキャパシタの特性を劣化させるとの知見を得た。 Since the main application targets of Bi-based oxide materials so far are room temperature and low temperature, there is no problem even if Pt, Au, etc., which have been empirically known to be good electrodes, are used as they are. There wasn't. However, according to the research of the inventor of the present application, in the high dielectric thin film material containing Bi used in a high temperature environment, the dielectric constant generated by the heating state at the time of sample preparation and the diffusion and desorption of Bi in the high temperature environment when the element is used. In addition to the decrease, the thermal instability of the interface between the electrode and the dielectric due to the diffusion of Bi into the electrode material deteriorates the characteristics of capacitors using Bi-based dielectrics used at high temperatures. I got the knowledge of.
本発明の課題は、上述した従来技術の問題点を解消し、製造プロセスや使用中での高温下でＢｉ系誘電体材料中のＢｉが電極中に拡散しないようにすることにある。 An object of the present invention is to solve the above-mentioned problems of the prior art and prevent Bi in the Bi-based dielectric material from diffusing into the electrode under high temperature during the manufacturing process or use.
本発明の一側面によれば、ベリリウム、マグネシウム、カルシウム、ストロンチウム、バリウム、スカンジウム、イットリウム、ランタン、チタン、ジルコニウム、ハフニウム、バナジウム、ニオブ、タンタル、クロム、モリブデン、タングステン、亜鉛、アルミニウム、ガリウム、インジウム、タリウム、硫黄、ゲルマニウム、スズ、砒素及びアンチモンからなる群から選択される少なくとも一の元素を含む、ビスマス系誘電体材料用電極が提供される。
ここで、前記元素を少なくとも前記ビスマス系誘電体材料との界面側に含んでよい。
また、前記ビスマスを拡散しくい元素を金属、並びに前記元素の炭化物及び窒化物からなる群から選択される少なくとも一つの形態で含んでよい。
本発明の他の側面によれば、ビスマス系誘電体材料の膜と、前記膜に隣接した上記何れかの電極とを設けたキャパシタが与えられる。
According to one aspect of the invention, beryllium, magnesium, calcium, strontium, barium, scandium, ittium, lantern, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, zinc, aluminum, gallium, indium. , A bismuth-based dielectric material electrode comprising at least one element selected from the group consisting of thallium, sulfur, germanium, tin, arsenic and antimony.
Here, the element may be contained at least on the interface side with the bismuth-based dielectric material.
Further, the bismuth may be contained in at least one form selected from the group consisting of a metal and a carbide and a nitride of the element.
According to another aspect of the present invention, a capacitor provided with a film of a bismuth-based dielectric material and any of the above electrodes adjacent to the film is provided.
本発明によれば、高温環境下でもＢｉ系誘電体材料中のＢｉが電極中に拡散せず、これにより高温に曝されることによるキャパシタ特性の劣化を防止することができる。 According to the present invention, Bi in the Bi-based dielectric material does not diffuse into the electrode even in a high temperature environment, and thereby it is possible to prevent deterioration of the capacitor characteristics due to exposure to a high temperature.
本発明の実施の態様によれば、熱拡散の理論からＢｉ拡散の抑制に効果がある金属を含む電極材料（単金属、炭化金属、窒化金属）をＢｉ系誘電体材料用電極として提供する。この金属としては例えばＴａ、Ｔｉを使用することができる。 According to the embodiment of the present invention, an electrode material (single metal, carbide metal, metal nitride) containing a metal effective in suppressing Bi diffusion is provided as an electrode for a Bi-based dielectric material from the theory of thermal diffusion. As this metal, for example, Ta and Ti can be used.
Ｂｉ拡散・析出を阻止するために誘電体中に添加すべき材料を探索するため、本願発明者は、本願出願人が公開している金属偏析予測システム（ＳｕｒｆＳｅｇ）を使用して解析を行った。なお、ＳｕｒｆＳｅｇはインターネット上においてhttp://surfseg.nims.go.jp/SurfSeg/menu.htmlでアクセス可能である。また、ＳｕｒｆＳｅｇが行う解析の原理等は本願発明とは直接関係しないのでここでは説明しないが、必要に応じて非特許文献３、４を参照されたい。
In order to search for a material to be added to the dielectric in order to prevent Bi diffusion / precipitation, the inventor of the present application conducted an analysis using the metal segregation prediction system (SurfSeg) published by the applicant of the present application. .. SurfSeg can be accessed on the Internet at http://surfseg.nims.go.jp/SurfSeg/menu.html. Further, the principle of analysis performed by SurfSeg is not directly related to the present invention and will not be described here, but refer to
この解析は、金属Ｂｉの表面を他の金属層で覆ったものを酸素雰囲気で熱処理を行うという単純化されたモデルに基づいて行った。また、金属Ｂｉの表面を覆う金属を、Ｐｔ、Ｒｕ、Ｔａ、Ｔｉ、Ｓｒとして解析した。その結果、表面を覆う金属層としてＰｔを使用した場合にはＢｉは容易に金属層中を拡散して表面に析出するが、Ｒｕの場合にはＰｔに比べて拡散が少なく、Ｔａ、ＴｉまたはＳｒで表面を覆った場合には拡散を充分に抑止できることが判った。ＳｕｒｆＳｅｇを使用して更に解析を進めた結果、上に挙げた金属元素だけではなく、図１に示す周期律表中で太枠線で囲まれた領域内の元素、すなわちベリリウム、マグネシウム、カルシウム、ストロンチウム、バリウム、スカンジウム、イットリウム、ランタン、チタン、ジルコニウム、ハフニウム、バナジウム、ニオブ、タンタル、クロム、モリブデン、タングステン、亜鉛、アルミニウム、ガリウム、インジウム、タリウム、硫黄、ゲルマニウム、スズ、砒素及びアンチモン、がＢｉに対して拡散防止作用を有することがわかった。 This analysis was performed based on a simplified model in which the surface of the metal Bi covered with another metal layer was heat-treated in an oxygen atmosphere. Further, the metal covering the surface of the metal Bi was analyzed as Pt, Ru, Ta, Ti, and Sr. As a result, when Pt is used as the metal layer covering the surface, Bi easily diffuses in the metal layer and precipitates on the surface, but in the case of Ru, the diffusion is less than that of Pt, and Ta, Ti or It was found that diffusion can be sufficiently suppressed when the surface is covered with Sr. As a result of further analysis using SurfSeg, not only the metal elements listed above, but also the elements in the region surrounded by the thick frame in the periodic table shown in FIG. 1, that is, beryllium, magnesium, calcium, Bi It was found that it has an anti-diffusion effect on.
なお、上述したモデルは単純化のために電極に相当する層を金属で構成される場合だけを取り扱っているが、電極材料としては金属だけではなく、Ｂｉ拡散防止作用を有する金属元素の炭化物または窒化物を使用しても同じ効果が得られる。 The model described above deals only with the case where the layer corresponding to the electrode is composed of metal for simplification, but the electrode material is not limited to metal, but is a carbide of a metal element having a Bi diffusion preventing action or a carbide. The same effect can be obtained by using a nitride.
次に、Ｂｉ系誘電体（ここではＢＴ−ＢＭＮを使用）上に電極を設けた試料を作成して、誘電体と電極との間の界面構造及び電子状態の比較を行った。この試料の概略の構造を図２に示す。電極の材料としてはＢｉが拡散しやすい材料としてＰｔを、またＢｉが拡散しにくい材料としてＴａＣとＴｉＣの一方を使用した二種類の試料を作製した。誘電体層をレーザーアブレーションで作製した（後述）後、電極をＡｒイオンビームスパッタ法により１０ｎｍ堆積した。このようにして作製した試料を評価し、その後、高速熱処理装置（ＲＴＡ）を用いてＡｒ雰囲気で５００℃において１０分間熱処理したものについて同じ評価を行った。以降の図中ではこの熱処理前の試料及びその評価結果を”as grown”、"as deposited"あるいは"as depo."、熱処理後の試料及びその評価結果を”annealed”と表記して区別する。 Next, a sample in which an electrode was provided on a Bi-based dielectric (here, BT-BMN was used) was prepared, and the interface structure and electronic state between the dielectric and the electrode were compared. The schematic structure of this sample is shown in FIG. Two types of samples were prepared using Pt as a material for the electrode to easily diffuse Bi and one of TaC and TiC as a material for which Bi is difficult to diffuse. After the dielectric layer was prepared by laser ablation (described later), the electrodes were deposited at 10 nm by the Ar ion beam sputtering method. The sample thus prepared was evaluated, and then the same evaluation was performed on the sample heat-treated at 500 ° C. for 10 minutes in an Ar atmosphere using a high-speed heat treatment apparatus (RTA). In the following figures, the sample before the heat treatment and its evaluation result are referred to as "as grown", "as deposited" or "as depo.", And the sample after the heat treatment and its evaluation result are referred to as "annealed".
試料中の誘電体層作製の詳細は以下のとおりである。 The details of preparing the dielectric layer in the sample are as follows.
（１）先ず、レーザーアブレーション法（物理蒸着（ＰＬＤ）法）により、５ｗｔ％Ｎｂ：ＳｒＴｉＯ３基板上にＢＴ−ＢＭＮを堆積させた。
成膜条件は以下の通りであった。
・レーザー：ＫｒＦエキシマレーザー（２４８ｎｍ）を使用した。パルス幅を１０ｎｓ、強度を約３Ｊ／ｃｍ２、繰り返し周波数を５Ｈｚとした。
・ターゲット：ＳｒＲｕＯ３及び［ＢＴＯ］０．６−［Ｂｉ（Ｍｇ，Ｎｂ）Ｏ］０．４（Ｂｉ２Ｏ３−８ｗｔ％過剰）
・基板温度：５１０℃
・雰囲気：酸素／オゾン
・集光レンズ−ターゲットア間距離：３６．０ｃｍ
・ターゲット−基板間距離：３ｃｍ
(1) First, BT-BMN was deposited on a 5 wt% Nb: SrTiO 3 substrate by a laser ablation method (physical vapor deposition (PLD) method).
The film forming conditions were as follows.
-Laser: A KrF excimer laser (248 nm) was used. The pulse width was 10 ns, the intensity was about 3 J / cm 2 , and the repetition frequency was 5 Hz.
Target: SrRuO 3 and [BTO] 0.6 - [Bi ( Mg, Nb) O] 0.4 (Bi 2 O 3 -8wt% excess)
-Substrate temperature: 510 ° C
・ Atmosphere: Oxygen / Ozone ・ Distance between condenser lens and target: 36.0 cm
・ Distance between target and board: 3 cm
（２）成膜後にポストアニールにより結晶化を行った。
この処理は１気圧の酸素雰囲気中で行った。また、その温度プロファイルを図３に示す。
(2) Crystallization was performed by post-annealing after the film formation.
This treatment was performed in an oxygen atmosphere of 1 atm. The temperature profile is shown in FIG.
このようにして作製された試料に対して、Ａｌ−Ｘ線（１．５ＫｅＶ）を使用した通常のＸＰＳ及びＳｐｒｉｎｇ−８の高輝度放射光（６ＫｅＶ）を使用した硬Ｘ線光電子分光法（ＨＸ−ＰＥＳ）の測定を組み合わせることで、図４に示すように異なる深さ領域の結合状態を非破壊で評価した。なお、ＨＸ−ＰＥＳは当業者には周知の事項であるためこれ自体については詳細に説明しないが、必要であれば非特許文献５等を参照されたい。
For the sample prepared in this way, normal XPS using Al-X-rays (1.5 KeV) and hard X-ray photoelectron spectroscopy (HX) using high-intensity synchrotron radiation (6 KeV) of Spring-8. By combining the measurements of −PES), the binding states of different depth regions were evaluated non-destructively as shown in FIG. Since HX-PES is a matter well known to those skilled in the art, it will not be described in detail, but if necessary, refer to
価電子帯近傍の電子構造をＨＸ−ＰＥＳにより評価した。その結果を図５に示す。ここで、全ての試料で電極が熱処理後（annealed）もフェルミ準位Ｅｆに電子状態が存在し、電極として機能していることがわかった。図５の最上部に示したグラフはＢＴ−ＢＭＮの誘電体層を上述のようにして作製した後、電極のための層をその上に形成していない状態の試料を示す。以降の図中においてはこの試料についての評価結果を"Film"と表記する場合がある。なお、ＨＸ−ＰＥＳでは光イオン化断面積の違いから酸素２ｐが弱く出るため、価電子帯頂上の厳密な解析には通常のＸＰＳの対実験が必要であるが、ここでは仮のフェルミ位置を図６下図に示すようにした。ここでバンドギャップはチタン酸バリウム（ＢＴＯ）をベースとして仮定した。 The electronic structure near the valence band was evaluated by HX-PES. The result is shown in FIG. Here, it was found that in all the samples, even after the electrode was annealed, an electronic state existed at the Fermi level Ef and the electrode functioned as an electrode. The graph shown at the top of FIG. 5 shows a sample in a state where the dielectric layer of BT-BMN is prepared as described above and then the layer for the electrode is not formed on the dielectric layer. In the following figures, the evaluation result for this sample may be referred to as "Film". In HX-PES, oxygen 2p is weakly emitted due to the difference in photoionization cross section, so a normal XPS pair experiment is required for rigorous analysis of the valence band peak. 6 As shown in the figure below. Here, the bandgap is assumed to be based on barium titanate (BTO).
化学結合状態が変わらなければ価電子帯と結合スペクトル間のエネルギーは一定となる。ここでは、最も形状変化の少ないＢａ３ｄに基づいて図７に示すようにして界面のバンドアライメントを概算した。熱処理前後の各試料のＨＸ−ＰＥＳによるＢａ３ｄの測定結果を図８に示す。 If the chemical bond state does not change, the energy between the valence band and the bond spectrum is constant. Here, the band alignment of the interface is estimated as shown in FIG. 7 based on Ba3d having the least shape change. FIG. 8 shows the measurement results of Ba3d by HX-PES of each sample before and after the heat treatment.
この解析の結果、熱処理前後の各試料の界面電荷バリアが図９のように求められた。図９からわかるように、Ｐｔでは熱処理後にバンドオフセットに変化がみられる。また、電極を形成していないＢＴ−ＢＭＮ（Film）で見られる変化は、熱処理によるＢｉ偏析・離脱に起因するものと考えられる。 As a result of this analysis, the interfacial charge barrier of each sample before and after the heat treatment was obtained as shown in FIG. As can be seen from FIG. 9, in Pt, a change in the band offset is observed after the heat treatment. Further, it is considered that the change observed in BT-BMN (Film) on which no electrode is formed is caused by Bi segregation / separation due to heat treatment.
次に、電極とＢＴ−ＢＭＮとの界面において、電極の成膜時点及び成膜後の加熱時にＢｉ−電極間反応層やＢｉ欠陥層がどの程度形成されるかを、ＢＸ−ＰＥＳを用いて加熱前後の各試料のＢｉ４ｆを測定することで調べた。この測定結果を図１０に示す。図１０中の上部にある２つの下向き太矢印及び夫々の太矢印から直下へ伸びる破線は、Ｂｉ−電極間反応層及びＢｉ欠陥層に対応するピークが現れる結合エネルギー位置を示す。 Next, using BX-PES, the extent to which a Bi-electrode reaction layer or a Bi defect layer is formed at the interface between the electrode and the BT-BMN at the time of film formation of the electrode and during heating after the film formation is used. It was examined by measuring Bi4f of each sample before and after heating. The measurement result is shown in FIG. The two downward thick arrows at the top of FIG. 10 and the broken lines extending directly below each thick arrow indicate the binding energy positions where the peaks corresponding to the Bi-electrode reaction layer and the Bi defect layer appear.
図１０から、電極材料としてＰｔを使用した場合には成膜時に欠陥が形成され（as grown）、熱処理により欠陥に起因するピークの強度が大きく増大する（annealed）ことから、加熱により反応層が増加することがわかる。これに対して電極にＴａを含む材料（ＴａＣ）を使用した場合には、成膜時に欠陥が形成されるが、熱処理後もその強度変化が小さく、反応層はほとんど増加しないことがわかった。電極にＴｉを含む材料（ＴｉＣ）を使用した場合にはこの傾向はさらに顕著になった。 From FIG. 10, when Pt is used as the electrode material, defects are formed during film formation (as grown), and the intensity of peaks caused by the defects is greatly increased by heat treatment (annealed). Therefore, the reaction layer is formed by heating. It can be seen that it increases. On the other hand, when a material containing Ta (TaC) was used for the electrode, defects were formed during film formation, but the change in strength was small even after the heat treatment, and it was found that the reaction layer hardly increased. This tendency became even more pronounced when a Ti-containing material (TiC) was used for the electrodes.
更に、電極の成膜過程や熱処理時に誘電体層のＢＴ−ＢＭＮが電極層を通して拡散するか否かを、電極表面の組成を測定できる従来のＸＰＳを使用することで調べた（図４参照）。図１１の上半分の３つの測定結果からわかるように、全ての試料で熱処理前後とも電極表面にはＢＴ−ＢＭＮ由来のＢａは検出されなかった。これに対して、同図左下の測定結果に示すように、同じくＢＴ−ＢＭＮ由来のＢｉは熱処理後のＰｔ電極表面で大量のＢｉが検出されており、熱処理によりＰｔ電極中でＢｉの劇的な拡散が起こっており、Ｐｔ電極では界面安定性に問題があることが確認された。 Furthermore, whether or not the BT-BMN of the dielectric layer diffuses through the electrode layer during the electrode film formation process and heat treatment was investigated by using a conventional XPS capable of measuring the composition of the electrode surface (see FIG. 4). .. As can be seen from the three measurement results in the upper half of FIG. 11, Ba derived from BT-BMN was not detected on the electrode surface before and after the heat treatment in all the samples. On the other hand, as shown in the measurement result at the lower left of the figure, a large amount of Bi was also detected on the surface of the Pt electrode after the heat treatment for Bi derived from BT-BMN, and the Bi was dramatically increased in the Pt electrode by the heat treatment. It was confirmed that there was a problem with the interfacial stability of the Pt electrode.
これに対して、ＴａＣは熱処理前後ともＢｉは全く検出されなかった。また、ＴｉＣでは熱処理前の試料から僅かなＢｉが検出されたが、熱処理前後の差は誤差の範囲であった。これはＴｉＣの一部が欠陥を生じたことでＢｉが拡散した可能性があるが、熱処理に対する安定性はＴａＣと同等であった。従って、Ｔａ、Ｔｉを含む電極の界面安定性が高いことが確認された。 On the other hand, in TaC, Bi was not detected at all before and after the heat treatment. In TiC, a small amount of Bi was detected in the sample before the heat treatment, but the difference before and after the heat treatment was within the margin of error. This is because Bi may have diffused due to a defect in a part of TiC, but the stability against heat treatment was equivalent to that of TaC. Therefore, it was confirmed that the interfacial stability of the electrode containing Ta and Ti was high.
もちろん、Ｂｉ系誘電体上に形成する電極層は一様な組成の層とする必要はなく、例えば、誘電体に隣接する部分のみにＴａ、Ｔｉ等のＢｉを拡散しにくい元素を含むようにしてもよい。あるいは複数の層を積層する場合にはＢｉ系誘電体側にある一つ或いは一部の層だけにＢｉを拡散しにくい元素を含むようにすることもできる。また、本発明に基づくキャパシタでは、Ｂｉ系誘電体を挟む両側の電極が共にＢｉを拡散しにくい元素を含んでもよいし、あるいは状況によっては片方だけの電極がＢｉを拡散しにくい元素を含んでもよい。 Of course, the electrode layer formed on the Bi-based dielectric does not have to be a layer having a uniform composition. For example, even if only the portion adjacent to the dielectric contains an element such as Ta or Ti that does not easily diffuse Bi. Good. Alternatively, when a plurality of layers are laminated, it is possible to include an element that does not easily diffuse Bi in only one or a part of the layers on the Bi-based dielectric side. Further, in the capacitor based on the present invention, the electrodes on both sides of the Bi-based dielectric may both contain an element that does not easily diffuse Bi, or depending on the situation, only one electrode may contain an element that does not easily diffuse Bi. Good.
以上説明したように、本発明によれば、Ｂｉ系誘電体を使用して高温下でも電極と誘電体との界面安定性に優れたキャパシタを提供することができるので、自動車等、高温に曝されるキャパシタを使用する産業分野に大いに貢献することが期待される。 As described above, according to the present invention, it is possible to provide a capacitor having excellent interfacial stability between the electrode and the dielectric even at a high temperature by using a Bi-based dielectric, so that the capacitor is exposed to a high temperature such as an automobile. It is expected to make a great contribution to the industrial field where capacitors are used.
Claims (2)
タンタルの炭化物を含む、ビスマス系誘電体材料用電極。 An electrode for a bismuth-based dielectric material used adjacent to a bismuth-based dielectric material.
Containing carbides of tantalum, bismuth-based dielectric material for the electrode.
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