JP2005269628A - Quartz resonator and manufacturing method of electrode film thereof - Google Patents
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本発明は、水晶振動子に関し、特に蒸着前にボンバード処理を行い、電極膜の抵抗率を小さくしてＱ値を改善した水晶振動子とその電極膜の製造方法に関する。 The present invention relates to a quartz crystal resonator, and more particularly to a quartz crystal resonator in which a bombarding process is performed before vapor deposition to reduce the resistivity of the electrode film to improve the Q value and a method for manufacturing the electrode film.
圧電振動子は小型であること、経年変化が小さいこと、高精度、高安定な周波数が容易に得られること等のため、通信機器から電子機器まで広く用いられている。中でも周波数−温度特性が３次曲線を呈するＡＴカット水晶振動子と、温度補償回路を備えた発振回路とを組み合わせた温度補償水晶発振器は、携帯電話等に多量に用いられている。 Piezoelectric vibrators are widely used from communication equipment to electronic equipment because of their small size, small secular change, high accuracy, and high frequency stability. In particular, a temperature-compensated crystal oscillator in which an AT-cut crystal resonator whose frequency-temperature characteristic exhibits a cubic curve and an oscillation circuit including a temperature-compensation circuit are used in large quantities in mobile phones and the like.
最近、高速大容量通信システムに用いられる基準信号用発振器は、ＵＨＦ帯での高い発振周波数安定性、発振周波数の大きな可変量、低ジッタ、小型化等が要求されている。発振器の高周波化を図る方法としては、基本波水晶振動子の高周波化、水晶振動子の高調波振動の利用及び逓倍回路を用いる手段等がある。高調波振動の利用は、水晶振動子の共振抵抗が大きくなり、且つ誘導性領域が狭くなるため発振させるのが難しい。発振したとしても容量比が高調波次数の二乗倍で大きくなるため、十分な周波数可変範囲を得ることができない。また、逓倍回路を用いる手段では、ジッタ特性の劣化を来すだけではなく、回路が大きくなるという問題がある。これらの問題を解決すべく、最近ではＳＴカット基板上に形成したＵＨＦ帯弾性表面波共振子を用いて、基準信号用発振器を構成している（非特許文献１）。 Recently, reference signal oscillators used in high-speed and large-capacity communication systems are required to have high oscillation frequency stability in the UHF band, a large variable amount of oscillation frequency, low jitter, miniaturization, and the like. As a method of increasing the frequency of the oscillator, there are means for increasing the frequency of the fundamental crystal resonator, utilizing the harmonic vibration of the crystal resonator, and using a multiplier circuit. The use of harmonic vibration is difficult to oscillate because the resonance resistance of the crystal resonator is increased and the inductive region is narrowed. Even if it oscillates, the capacity ratio increases by the square of the harmonic order, so that a sufficient frequency variable range cannot be obtained. Further, the means using the multiplier circuit has a problem that not only the jitter characteristic is deteriorated but also the circuit becomes large. In order to solve these problems, a reference signal oscillator has recently been constructed using a UHF band surface acoustic wave resonator formed on an ST cut substrate (Non-patent Document 1).
しかし、ＳＴカット弾性表面波共振子は、ＡＴカット水晶振動子に比べ容量比は２倍程度と大きく、また、周波数温度特性は２次の温度特性を呈するので、ＡＴカット水晶振動子に比べかなり劣る。このため、ＳＴカット弾性表面波共振子を用いた発振器は、周波数可変範囲から周波数温度特性を引いた絶対可変量が十分に確保ができないという問題がある。この問題を解決するため、ＵＨＦ帯のＡＴカット基本波水晶振動子の開発が望まれる。
ＡＴカット水晶振動子の高周波化を図るには、水晶基板の薄板化必要である。従来の研磨加工技術では、水晶基板の厚さは10マイクロメートル（μm）程度が限度であり、これを共振周波数に換算すると160MHz程度である。機械的強度を十分に維持し、ＵＨＦ帯での基本波振動を得る方法として、米国特許U.S. Patent 3694677に開示されているように、エッチング技法を用いて基板中央部のみを数マイクロメートルまで加工して振動部とする、所謂逆メサ型水晶子が開発された。この構造を用いた水晶振動子で、2 GHzの基本波振動が得られた記述されている（非特許文献２、３）。
However, the ST-cut surface acoustic wave resonator has a capacitance ratio that is about twice as large as that of an AT-cut quartz crystal, and the frequency temperature characteristic exhibits a second-order temperature characteristic. Inferior. For this reason, an oscillator using an ST cut surface acoustic wave resonator has a problem that an absolute variable amount obtained by subtracting the frequency temperature characteristic from the frequency variable range cannot be sufficiently secured. In order to solve this problem, it is desired to develop an AT-cut fundamental wave crystal resonator in the UHF band.
In order to increase the frequency of the AT-cut quartz resonator, it is necessary to make the quartz substrate thinner. In the conventional polishing technique, the thickness of the quartz substrate is limited to about 10 micrometers (μm), which is about 160 MHz when converted into a resonance frequency. As a method of obtaining a fundamental wave vibration in the UHF band while maintaining sufficient mechanical strength, as disclosed in US Pat. No. 3694677, only the central part of the substrate is processed to several micrometers using an etching technique. Thus, a so-called inverted mesa crystal was developed. It is described that a fundamental wave vibration of 2 GHz is obtained with a crystal resonator using this structure (Non-Patent Documents 2 and 3).
図２８は、実験に用いた小型水晶振動素子の斜視図である。実験に用いた水晶基板は一方の面は平坦面、他方の面の一部は凹陥状を呈し、外形寸法は2.4 mm (X) ×2.3 mm (Z') ×0.07 mm (Y')（以下、水晶基板Ａと称す）と、 0.85 mm (X) ×1.25 mm (Z') ×0.07 mm (Y') （以下、水晶基板Ｂと称す）との二種類で、中央に凹陥した振動部が形成されている。振動部はウェットエッチングにより厚さ2.2 μmに加工されており、その平面領域は水晶基板Ａでは0.95 mm (X) ×0.85 mm (Z') 、水晶基板Ｂでは0.32 mm (X) ×0.25 mm (Z') である。なお、端部には電極配線用の貫通穴が設けられている。
ここで、振動部の側面の傾斜は、エッチング速度の結晶方位依存性により生成されたものであり、文献４、５に記述されているように、その傾斜角はWulff-Jaccodineの理論に従う。ＡＴカット水晶の場合は、Z'軸方向に緩やかな傾斜ができる（非特許文献４、５）。
FIG. 28 is a perspective view of a small crystal resonator element used in the experiment. The quartz substrate used in the experiment was flat on one side and partly concave on the other side, and the outer dimensions were 2.4 mm (X) × 2.3 mm (Z ') × 0.07 mm (Y') The crystal part A) and 0.85 mm (X) x 1.25 mm (Z ') x 0.07 mm (Y') (hereinafter referred to as crystal board B). Is formed. The vibrating part is processed to a thickness of 2.2 μm by wet etching, and its planar area is 0.95 mm (X) x 0.85 mm (Z ') for quartz substrate A and 0.32 mm (X) x 0.25 mm (for quartz substrate B). Z '). A through hole for electrode wiring is provided at the end.
Here, the inclination of the side surface of the vibration part is generated due to the crystal orientation dependency of the etching rate, and the inclination angle follows Wulff-Jaccodine theory as described in References 4 and 5. In the case of an AT-cut quartz, a gentle inclination can be made in the Z′-axis direction (Non-Patent Documents 4 and 5).
電極は片面ニッケル7 nm（１０−９ｍ）を下地とした金30 nm（Ａｕ／Ｎｉ；30 nm／7 nm）とした。ここで、水晶基板Ｂの外形寸法を小型化したのは、電極膜厚が薄い分、励振電極から引き出すリード電極の短縮や電極パターンの面積縮小により導通損失を抑制できると推測したからである。
振動部平坦面の電極形状は二次元的エネルギ閉じ込めを考慮し、ＡＴカット水晶基板の面内異方性に即した楕円形にした（非特許文献６、７）。楕円形電極の寸法は容量比、励振電流二乗特性、及び非調和振動等を考慮して、水晶基板１では長軸253μm (X)、短軸200μm (Z')とし、水晶基板２では長軸200μm (X)、短軸158μm (Z')とした。また、凹面の電極形状は平坦面の励振電極とのマスクアライメント不良がないよう、振動部を被う矩形にした。
The electrode was gold 30 nm (Au / Ni; 30 nm / 7 nm) with a single-sided nickel 7 nm (10 −9 m) as a base. Here, the reason why the external dimensions of the quartz substrate B are reduced is that it is estimated that the conduction loss can be suppressed by shortening the lead electrode drawn out from the excitation electrode and reducing the area of the electrode pattern because the electrode film thickness is thin.
In consideration of two-dimensional energy confinement, the shape of the electrode on the flat surface of the vibration part is an ellipse that conforms to the in-plane anisotropy of the AT-cut quartz substrate (Non-Patent Documents 6 and 7). Considering the capacitance ratio, excitation current square characteristics, anharmonic vibration, etc., the ellipsoidal electrode has a major axis of 253 μm (X) and a minor axis of 200 μm (Z ′), and the major axis of the quartz substrate 2. 200 μm (X) and short axis 158 μm (Z ′). In addition, the concave electrode shape is a rectangle that covers the vibrating portion so that there is no mask alignment failure with the flat excitation electrode.
振動部の厚さが2.2 μmである水晶基板Ａ、Ｂに楕円形電極を付けて、水晶振動子を試作し、その諸特性をインピーダンスアナライザを用いて測定した。図２９は水晶基板Ｂを用いた水晶振動子（以下、水晶振動子Ｂと称す）の周波数−インピーダンス特性を示す図であり、主振動S０の基本波周波数は622 MHzで、主振動の高周波側に非調和振動が多数励起された。特に主振動に近接して１次の非調和振動S１（623 MHz）が強制に励起されている。この非調和振動S１は、主振動S０との共振周波数差が1.2 MHzである。なお、S１の共振抵抗は、S０のそれの1.9倍であるが、発振器を構成しての評価では１次の非調和振動S１での異常発振は認められなかった。 Quartz crystals were fabricated by attaching elliptical electrodes to quartz substrates A and B with a vibrating portion thickness of 2.2 μm, and their characteristics were measured using an impedance analyzer. FIG. 29 is a diagram showing frequency-impedance characteristics of a crystal resonator (hereinafter referred to as crystal resonator B) using a crystal substrate B. The fundamental frequency of the main vibration S 0 is 622 MHz, and the high frequency of the main vibration is shown. Many anharmonic vibrations were excited on the side. In particular, the primary anharmonic vibration S 1 (623 MHz) is forcibly excited in the vicinity of the main vibration. This anharmonic vibration S 1 has a resonance frequency difference of 1.2 MHz with respect to the main vibration S 0 . The resonance resistance of S 1 is 1.9 times that of S 0 , but no abnormal oscillation was observed in the first-order anharmonic vibration S 1 in the evaluation of the oscillator.
図３０は水晶振動子Ａ（パッケージサイズ3.8mm×3.8mm×0.9mm）と水晶振動子Ｂ（パッケージサイズ2.5mm×2.0mm×0.5mm）のアドミッタンス円をそれぞれ示す図である。これらの特性は無誘導共振周波数fr±0.5 MHzの範囲でアドミッタンスをプロットしたものである。図３１は水晶振動子Ａ、Ｂの諸定数を示した図である。ここで、並列容量Cpは周波数依存性を有するため、共振周波数の近傍でかつ共振の影響を受けないように、無誘導共振周波数fr×0.9 = 559.8 MHzにおける容量値を用いた。また、Q値は、最大アドミッタンスの周波数を最大アドミッタンスの２−（１／２）倍になる２つの周波数の差で除して求めた。図３０、３１から、基板を小型化し、引き出し電極等を短縮することにより、薄い電極の導通損失を抑制し共振抵抗が低減できたことが分かる。 FIG. 30 is a diagram showing admittance circles of the crystal unit A (package size 3.8 mm × 3.8 mm × 0.9 mm) and the crystal unit B (package size 2.5 mm × 2.0 mm × 0.5 mm). These characteristics are obtained by plotting admittance in the range of non-inductive resonance frequency fr ± 0.5 MHz. FIG. 31 is a diagram showing various constants of the crystal units A and B. Here, since the parallel capacitance Cp has frequency dependence, the capacitance value at the non-inductive resonance frequency fr × 0.9 = 559.8 MHz was used in the vicinity of the resonance frequency and not affected by resonance. In addition, the Q value was obtained by dividing the frequency of the maximum admittance by the difference between two frequencies that are 2− (½) times the maximum admittance. 30 and 31, it can be seen that by reducing the size of the substrate and shortening the extraction electrode, the conduction loss of the thin electrode can be suppressed and the resonance resistance can be reduced.
水晶振動子Ａ、Ｂを比較すると後者の方が、共振抵抗Rsが9.6Ω、並列容量Cpが0.98 pFと低減したことで、Figure of Merit M(= (CpRs)−1)は2.6倍と大きくなった。これにより、アドミッタンス円が大きく且つ上昇していないため、広い誘導性領域が確保できている。また、Q値は3.9倍になっている。
水晶振動子のQ値は発振器の位相雑音特性、ジッタ特性に影響を及ぼすので、Ｑ値は高い方が望ましい。人工水晶の内部損失のみで決まるQ値の固有限界値Qmは次式でほぼ表される。
Ｑｍ・ｆ＝９×１０６ （１）
ここで、周波数ｆの単位はMHzである（天然水晶で最高級の品質のものの定数は１５×１０６）。式１に周波数６２２ＭＨｚを代入するとQmは約14500と算出される。
しかしながら、実験で得られた水晶振動子ＢのQ値は約4000であり、理論値のQm の１／３にも満たない。
Comparing crystal resonators A and B, the latter has a resonance resistance Rs of 9.6Ω and parallel capacitance Cp of 0.98 pF, so Figure of Merit M (= (CpRs) −1 ) is 2.6 times larger. became. Thereby, since the admittance circle is large and does not rise, a wide inductive region can be secured. The Q value is 3.9 times.
Since the Q value of the crystal resonator affects the phase noise characteristics and jitter characteristics of the oscillator, a higher Q value is desirable. The intrinsic limit value Qm of the Q value determined only by the internal loss of the artificial quartz is approximately expressed by the following equation.
Qm · f = 9 × 10 6 (1)
Here, the unit of the frequency f is MHz (the constant of the highest quality natural quartz is 15 × 10 6 ). If a frequency of 622 MHz is substituted into Equation 1, Qm is calculated to be about 14500.
However, the Q value of the crystal resonator B obtained in the experiment is about 4000, which is less than 1/3 of the theoretical value Qm.
そこで、電極膜の抵抗率、配向性等について検討することにした。
Viancoらは、ＡＴカット水晶板上にクロムやモリブデンを下地とし、その上に金電極膜を蒸着した後、これをアニール処理して電極膜の抵抗率の変化を評価している（非特許文献８）。Viancoらは、薄膜の抵抗率増加の要因が下地電極と金電極膜との相互拡散にあることを示している。図３２（ａ）は、ＡＴカット水晶板上にニッケル下地7 nm（１０−９ｍ）、その上に金電極膜30 nm（Ａｕ／Ｎｉ；30 nm／7 nmと記す）を蒸着して形成した薄膜のX線反射率曲線を示した図であり、同図（ｂ）はこれを基に薄膜の密度とその膜厚を示す断面図である。
Therefore, it was decided to examine the resistivity, orientation, etc. of the electrode film.
Vianco et al. Evaluated the change in resistivity of the electrode film by depositing a gold electrode film on an AT-cut quartz plate and depositing a gold electrode film on the AT-cut crystal plate (Non-patent Document). 8). Vianco et al. Show that the cause of the increase in resistivity of the thin film is the interdiffusion between the base electrode and the gold electrode film. FIG. 32 (a) is formed by depositing a nickel base 7 nm (10 −9 m) on an AT-cut quartz plate and a gold electrode film 30 nm (Au / Ni; indicated as 30 nm / 7 nm) thereon. It is the figure which showed the X-ray-reflectance curve of the thin film, and the same figure (b) is sectional drawing which shows the density of a thin film and its film thickness based on this.
図３２（ｂ）から明らかなように、蒸着時にＡｕ／Ｎｉ；30 nm／7 nmの条件で形成した薄膜は、密度の異なる４層構造となり、上から２番目の層は膜厚全体の１／２を占め、その密度は金の密度より小さく、ニッケルと金との拡散層であると考えられる。図３２の試料は基板温度を１４０℃とし、ニッケル、金を蒸着した後、アニール処理は行っていないので、蒸着中に拡散が進行したものと思われる。ちなみに、ニッケルと金とのバルク密度は、それぞれ、9.04 ×103 kg/m3、 19.4×103 kg/m3、バルク抵抗率はそれぞれ6.9×10−8 Ωｍ、2.2×10−8 Ωｍであり、ニッケルのバルク抵抗率は金の３．１倍である。
一般に下地電極は基板と金電極膜との密着性を強固にするために用いられるが、下地電極の抵抗率は金のそれよりも大きく、下地電極と金との拡散層の抵抗率は金のそれよりも大きくなる。
As is clear from FIG. 32 (b), the thin film formed under the conditions of Au / Ni; 30 nm / 7 nm at the time of vapor deposition has a four-layer structure with different densities, and the second layer from the top is 1 of the entire film thickness. The density is less than the density of gold and is considered to be a diffusion layer of nickel and gold. The sample in FIG. 32 has a substrate temperature of 140 ° C., and after nickel and gold are vapor-deposited, annealing is not performed. Therefore, it is considered that diffusion progressed during vapor deposition. By the way, the bulk densities of nickel and gold are 9.04 × 10 3 kg / m 3 and 19.4 × 10 3 kg / m 3 , respectively, and the bulk resistivity is 6.9 × 10 −8 Ωm and 2.2 × 10 −8 Ωm, respectively. Yes, the bulk resistivity of nickel is 3.1 times that of gold.
Generally, the base electrode is used to strengthen the adhesion between the substrate and the gold electrode film, but the resistivity of the base electrode is larger than that of gold, and the resistivity of the diffusion layer between the base electrode and gold is that of gold. It will be bigger than that.
Chopraらは、マイカやガラス上に金電極膜を蒸着及びスパッタを用いて形成して、金電極膜の抵抗率の膜厚依存性を評価し、その結果、単結晶膜は多結晶膜に比べ抵抗率が低いことを示した（非特許文献９）。また、家木らは、ＳＡＷ共振子のストレスマイグレーション対策として、ＳＴカット（33.5°回転Ｙカット）水晶板上に単結晶アルミニウム電極を形成した。成膜は基板温度が150℃、蒸着速度が4 nm/sの条件で、単結晶アルミニウム電極膜が得られたと記している（非特許文献３）。格子定数からみると、ＡＴカット水晶板と金電極膜との関係はこの組合せに類似しており、金の単結晶膜を形成できる可能性がある。
一方、SondheimerやMayadasらは、多結晶膜における電子の反射をモデル化した抵抗率の理論式で、結晶粒を大きくすることで抵抗率は低減できると述べている。そして、一般に方位の異なる結晶粒の界面では電子の散乱が生じるため、配向性を高くすれば抵抗率は低減できると考えられている（非特許文献１１、１２）。
Chopra et al. Formed a gold electrode film on mica or glass by vapor deposition and sputtering, and evaluated the film thickness dependence of the resistivity of the gold electrode film. It was shown that the resistivity is low (Non-Patent Document 9). Moreover, Ieki et al. Formed a single crystal aluminum electrode on an ST-cut (33.5 ° rotation Y-cut) quartz plate as a countermeasure against stress migration of the SAW resonator. It is described that a single crystal aluminum electrode film was obtained under the conditions of a substrate temperature of 150 ° C. and a deposition rate of 4 nm / s (Non-patent Document 3). From the viewpoint of the lattice constant, the relationship between the AT-cut quartz plate and the gold electrode film is similar to this combination, and there is a possibility that a gold single crystal film can be formed.
On the other hand, Sondheimer and Mayadas et al. Stated that the resistivity can be reduced by increasing the crystal grain in a theoretical equation of resistivity that models the reflection of electrons in a polycrystalline film. In general, since scattering of electrons occurs at the interface between crystal grains having different orientations, it is considered that the resistivity can be reduced by increasing the orientation (Non-Patent Documents 11 and 12).
Borgesらは、マイクロバランス用水晶振動子の研究を行い、ＡＴカット水晶板と平行に（111）面が配向した膜厚200 nmの金単層電極膜を形成した。成膜は基板温度が300℃、蒸着速度が0.5〜1 nm/sの条件で蒸着すると高配向の金電極膜が得られたと記している（非特許文献１３）。また、Kamijoらは、38°回転Yカット水晶板上に（111）面が配向した膜厚195 nmのアルミニウム電極膜を形成したと述べているが、これらの電極膜の抵抗率は明示されていない（非特許文献１４）。 Borges et al. Studied a quartz crystal resonator for microbalance and formed a gold single-layer electrode film with a thickness of 200 nm with the (111) plane oriented parallel to the AT-cut quartz plate. It is stated that a highly oriented gold electrode film was obtained when the film was deposited under conditions of a substrate temperature of 300 ° C. and a deposition rate of 0.5 to 1 nm / s (Non-patent Document 13). In addition, Kamijo et al. Stated that an aluminum electrode film with a film thickness of 195 nm with (111) orientation was formed on a 38 ° rotated Y-cut quartz plate, but the resistivity of these electrode films was clearly shown. No (Non-Patent Document 14).
膜厚が極めて薄い場合（20nm〜40nm）、金薄膜は島状構造から連続膜になる領域であり、大きな内部応力が残留することが知られている。この平均応力の最大値はスパッタ法よりも真空蒸着法の方が小さいと記されている。また、真空蒸着法は、スパッタ法のように不活性ガスを使用しないため、高配向の電極膜が得られ易いと考えられる（非特許文献１５、１６）。
水晶振動子のＱ値は発振器の位相雑音特性、ジッタ特性に影響を及ぼすので、６２２ＭＨｚの高周波の水晶振動子とはいえ高いＱ値が望まれる。
しかしながら、上記の文献を参照しても、３０ｎｍから１００ｎｍ程度の金単層膜の抵抗率がバルクのそれと同等になり、水晶振動子のＱ値をＱｍに近づける製造手段が未だ明らかでないという問題があった。
Since the Q value of the crystal resonator affects the phase noise characteristics and jitter characteristics of the oscillator, a high Q value is desired even for a high-frequency crystal resonator of 622 MHz.
However, even with reference to the above-mentioned literature, the resistivity of the gold single layer film of about 30 nm to 100 nm is equivalent to that of the bulk, and the manufacturing means for bringing the Q value of the crystal resonator close to Qm is still unclear. there were.
本発明は、水晶振動子のＱ値を改善するため、請求項１の発明は、真空装置内に基板をセットして該基板表面にボンバード処理を行った後に前記基板上に金単層膜を形成して金薄膜を製造することを特徴とする。
請求項２の発明は、真空装置内に基板をセットし、基板温度を２７０度に維持した状態で前記基板表面にボンバード処理を行った後に前記基板上に金単層膜を形成して金薄膜を製造することを特徴とする。
請求項３の発明は、真空装置内に基板をセットし、所定の真空度に排気し、酸素ガスあるいはアルゴンガスを導入してボンバード処理を行った後に、金単層膜を形成して金薄膜を製造することを特徴とする。
請求項４の発明は、前記真空装置の中の真空度を６Ｐａから１０Ｐａに維持したことを特徴とする請求項１乃至３のいずれかに記載の金薄膜の製造方法である。
請求項５の発明は、真空装置内部にプラズマを発生させるための直流電源出力を１９０Ｗから２５０Ｗに維持しボンバード処理を行ってから金単層膜を形成して金薄膜を製造することを特徴とする。
請求項６の発明は、真空装置の中でプラズマ状態を１５０秒から３００秒維持しボンバード処理を行ってから金単層膜を形成したことを特徴とする請求項１乃至５のいずれかに記載の金薄膜の製造方法である。
請求項７の発明は、真空中において基板の温度を１５０度から２７０度に保持し、金を蒸着することを特徴とする請求項１乃至６のいずれかに記載の金薄膜の製造方法である。
請求項８の発明は、真空中において基板の温度を１５０度から２７０度に保持し、毎秒１ナノ・メートルから３ナノ・メートルの範囲の蒸着速度で金を蒸着して金薄膜を製造することを特徴とする。
請求項９の発明は、ＡＴカット水晶基板上に請求項１乃至８のいずれかに記載の製造方法を用いて金薄膜による励振電極を構成した水晶振動子であることを特徴とする。
請求項１０の発明は、前記励振電極はＡＴカット水晶基板の端部に形成したパッド電極と導通しており、該パッド電極がニッケルまたはクロムを下地層とし、その上面に金層を備えた多層膜で形成されていることを特徴とする請求項９に記載の水晶振動子である。
請求項１１の発明は、前記パッド電極が前記励振電極より厚いことを特徴とする請求項１０に記載の水晶振動子である。
In order to improve the Q value of the crystal resonator according to the present invention, the invention according to claim 1 is characterized in that a gold single layer film is formed on the substrate after setting the substrate in a vacuum apparatus and performing bombarding on the substrate surface. It is characterized by forming a gold thin film.
According to a second aspect of the present invention, a gold thin film is formed by setting a substrate in a vacuum apparatus, performing a bombarding process on the substrate surface in a state where the substrate temperature is maintained at 270 degrees, and forming a gold single layer film on the substrate. It is characterized by manufacturing.
According to the invention of claim 3, a gold thin film is formed by setting a substrate in a vacuum apparatus, evacuating to a predetermined degree of vacuum, introducing oxygen gas or argon gas and performing bombarding, and then forming a gold single layer film. It is characterized by manufacturing.
A fourth aspect of the present invention is the method for producing a gold thin film according to any one of the first to third aspects, wherein the degree of vacuum in the vacuum apparatus is maintained from 6 Pa to 10 Pa.
The invention of claim 5 is characterized in that a gold thin film is manufactured by forming a gold single layer film after performing a bombarding process while maintaining a DC power output for generating plasma in a vacuum apparatus from 190 W to 250 W. To do.
The invention of claim 6 is characterized in that the gold single layer film is formed after the plasma state is maintained for 150 seconds to 300 seconds in the vacuum apparatus and bombarding is performed. This is a method for producing a gold thin film.
The invention according to claim 7 is the method for producing a gold thin film according to any one of claims 1 to 6, wherein the temperature of the substrate is maintained at 150 to 270 degrees in vacuum and gold is deposited. .
The invention of claim 8 is to produce a gold thin film by depositing gold at a deposition rate in the range of 1 nanometer to 3 nanometers per second while maintaining the substrate temperature at 150 to 270 degrees in a vacuum. It is characterized by.
A ninth aspect of the invention is a crystal resonator in which an excitation electrode made of a gold thin film is formed on an AT-cut quartz substrate using the manufacturing method according to any one of the first to eighth aspects.
According to a tenth aspect of the present invention, the excitation electrode is electrically connected to a pad electrode formed at an end portion of the AT-cut quartz crystal substrate, the pad electrode is made of nickel or chromium as a base layer, and a multi-layer including a gold layer on the upper surface The crystal unit according to claim 9, wherein the crystal unit is formed of a film.
An eleventh aspect of the present invention is the crystal resonator according to the tenth aspect, wherein the pad electrode is thicker than the excitation electrode.
本発明の水晶振動子とその電極膜の製造方法は、金単層膜電極の抵抗率をバルクのそれに近づけたため、水晶振動子の抵抗値が小さくなり、Ｑ値を大きく改善できたので、本発明の水晶振動子を基準信号用発振器に用いれば性能を大幅に向上させるという利点がある。 Since the crystal resonator of the present invention and the electrode film manufacturing method brought the resistivity of the gold single-layer film electrode close to that of the bulk, the resistance value of the crystal resonator was reduced and the Q value was greatly improved. The use of the crystal unit of the invention for a reference signal oscillator has the advantage of greatly improving performance.
図１は本発明に係る水晶振動子の実施の形態を示す図であって、同図（ａ）は斜視図、同図（ｂ）は平面図、同図（ｃ）はＱ−Ｑにおける断面図である。水晶基板１はフォトリソグラフィ技法とエッチング手法とを用いて、ＡＴカット水晶基板１の一方の主面の中央より少し離れた位置に凹陥部２を形成し、該凹陥部２の薄い平板を振動部３とすると共に、水晶基板１の平坦側に電極４を形成し、電極４からリード電極５を水晶基板１の端部まで延在し、端部に設けたパッド電極６と接続する。そして、凹陥部２側の振動部３と、該振動部３に連なる４面の傾斜部７とに電極４と対向して電極８を形成し、該電極８からリード電極９を延在し、端部のパッド電極１０と接続して、水晶振動素子を構成する。そして、端部には２箇所にリード電極配線用の貫通穴が設けられ、一方の水晶基板面のみで電極の導通が図られるようになっている。パッド電極６、１０と水晶基板との接着度は、電極部よりも強固なことが必要なので、予めニッケル、またはクロムを下地とした金の電極を形成し、その上に上記電極４、８及びリード電極５、９を形成する。 FIG. 1 is a diagram showing an embodiment of a crystal resonator according to the present invention. FIG. 1 (a) is a perspective view, FIG. 1 (b) is a plan view, and FIG. FIG. The quartz substrate 1 uses a photolithography technique and an etching method to form a recessed portion 2 at a position slightly away from the center of one main surface of the AT-cut quartz substrate 1, and the thin flat plate of the recessed portion 2 is formed as a vibrating portion. 3, the electrode 4 is formed on the flat side of the quartz substrate 1, the lead electrode 5 extends from the electrode 4 to the end of the quartz substrate 1, and is connected to the pad electrode 6 provided at the end. Then, an electrode 8 is formed opposite to the electrode 4 on the vibrating portion 3 on the recessed portion 2 side and the four inclined portions 7 connected to the vibrating portion 3, and the lead electrode 9 is extended from the electrode 8, It connects with the pad electrode 10 of an edge part, and comprises a crystal oscillator. Further, through holes for lead electrode wiring are provided at two positions on the end portion, and conduction of the electrodes is achieved only on one crystal substrate surface. Since the degree of adhesion between the pad electrodes 6 and 10 and the quartz substrate needs to be stronger than the electrode part, a gold electrode with nickel or chromium as a base is formed in advance, and the electrodes 4, 8 and Lead electrodes 5 and 9 are formed.
本発明の特徴は電極４、８及びこれと連結するリード電極５、９の成膜方法にある。即ち、水晶基板の温度を１５０度から２７０度の範囲に維持し、例えば、真空度10 Pa、直流電源の出力を220 Wとして酸素プラズマによるボンバードを行ってから、金の蒸着速度を毎秒１nmから３nmの範囲で蒸着して金の単層膜を形成して水晶振動子を構成することにある。 A feature of the present invention resides in a method of forming the electrodes 4 and 8 and the lead electrodes 5 and 9 connected thereto. That is, the temperature of the quartz substrate is maintained in the range of 150 to 270 ° C., for example, the degree of vacuum is 10 Pa, the output of the DC power source is 220 W, and bombarding with oxygen plasma is performed, and then the gold deposition rate is from 1 nm per second It is to form a quartz crystal unit by forming a gold single layer film by vapor deposition in the range of 3 nm.
以下、配向性が高く、抵抗率がバルクのそれに近い金の単層膜が得られるまでの実験過程を詳細に説明する。
抵抗加熱蒸着法を用いて薄膜を作ると、被蒸着物質の電極材料が加熱ボートと直接接触して加熱されるため、ボート材料と電極材料とが反応するという問題がある。一方、電極材料に電子ビームを当て加熱・溶融する電子ビーム蒸着法は、上記の問題がなく、純度の高い蒸着膜が得られるものと考えられるのでこの方法を採用することにした。
従来から被蒸着基板は薄膜の密着性、内部応力の減少のために予め所定の温度で加熱しておくことが必要であるので、加熱源としてハロゲンヒータとシースヒータとを用いることにした。また、電極材料を入れる坩堝の上方には膜厚分布を均一にするための補正板を設け、真空槽の排気系はクライオポンプを用いた。
Hereinafter, an experimental process until a gold single layer film having high orientation and resistivity close to that of a bulk is obtained will be described in detail.
When a thin film is formed using the resistance heating vapor deposition method, there is a problem that the boat material and the electrode material react with each other because the electrode material of the deposition target material is heated in direct contact with the heating boat. On the other hand, the electron beam vapor deposition method in which an electron beam is heated and melted by applying an electron beam to the electrode material does not have the above-mentioned problems, and it is considered that a high-purity vapor deposition film can be obtained.
Conventionally, it is necessary to heat the deposition target substrate at a predetermined temperature in order to reduce the adhesion of the thin film and the internal stress. Therefore, a halogen heater and a sheath heater are used as a heating source. In addition, a correction plate for making the film thickness distribution uniform was provided above the crucible containing the electrode material, and a cryopump was used as the exhaust system of the vacuum chamber.
坩堝は回転式で10 ccと40 ccの２種類の容量のものを用いた。そして、蒸着速度の再現性を考慮し、１回のプロセス毎に金ササブキ（粒状の金）を補充して金インゴットと金ササブキの総重量が同一になるようにした。電極材料の金に電子ビームを当てることにより発生する二次電子は、蒸着速度に影響を及ぼすばかりではなく、散乱した場合には周りの物体を溶融するおそれがあるので、電子ビームのパワーが高い場合、吸収板のみでは二次電子を十分に処理できないため、坩堝自体を接地することにした。 The crucible used was a rotary type with two capacities of 10 cc and 40 cc. In consideration of the reproducibility of the deposition rate, gold sasabaki (granular gold) was replenished for each process so that the total weight of the gold ingot and the gold sasabaki was the same. Secondary electrons generated by applying an electron beam to the gold electrode material not only affect the deposition rate, but if scattered, the surrounding objects may melt, so the electron beam power is high. In this case, since the secondary electrons cannot be sufficiently processed with the absorption plate alone, the crucible itself was grounded.
真空蒸着法で成膜する場合、主な蒸着パラメータは基板の加熱温度と蒸着速度とである。基板温度は基板に到達した金原子の基板表面での動き易さを決定し、蒸着速度は金原子の基板への供給量を決定する。この２つの組合せで結晶性が変化するので、蒸着パラメータの最適条件を見出すために、基板温度を広温度範囲、蒸着速度を色々変えて評価することにした。
そこで、基板温度を制御するため基板表面に熱電対を取付けた。ハロゲンヒータとシースヒータの設定温度は個別に決められるが、ここでは同一とした。図２はヒータの設定温度と基板温度との関係を示す図である。○印はハロゲンヒータの電流値が35 A、シースヒータの電流値が50 Aの場合で、基板温度の最高到達点は240℃であった。これに対し、●印はハロゲンヒータの電流値が70 A、シースヒータの電流値が85 Aの場合で、基板温度の最高到達点は270℃であった。この結果、ハロゲンヒータの電流値を70 A、シースヒータの電流値を85 Aとし、基板温度を制御することにした。
When a film is formed by vacuum vapor deposition, the main vapor deposition parameters are the substrate heating temperature and the vapor deposition rate. The substrate temperature determines the ease of movement of gold atoms that have reached the substrate on the substrate surface, and the deposition rate determines the amount of gold atoms supplied to the substrate. Since the crystallinity changes depending on the combination of the two, in order to find the optimum conditions for the deposition parameters, it was decided to evaluate the substrate temperature in a wide temperature range and various deposition rates.
Therefore, a thermocouple was attached to the substrate surface in order to control the substrate temperature. The set temperatures of the halogen heater and the sheath heater are individually determined, but here they are the same. FIG. 2 is a diagram showing the relationship between the set temperature of the heater and the substrate temperature. The circle indicates that the current value of the halogen heater is 35 A and the current value of the sheath heater is 50 A, and the maximum temperature of the substrate temperature is 240 ° C. On the other hand, the mark ● shows the case where the current value of the halogen heater is 70 A and the current value of the sheath heater is 85 A, and the highest substrate temperature reached 270 ° C. As a result, the current value of the halogen heater was set to 70 A, the current value of the sheath heater was set to 85 A, and the substrate temperature was controlled.
蒸着速度の制御には5 MHzの水晶振動子膜厚計を用いることにした。電子ビームの最大パワーは、装置の規格から坩堝容量が10 ccの場合6 kW、40 ccの場合10 kWに制限されている。図３は電子ビームのパワーと蒸着速度との関係を示す図で、○印が10 ccの坩堝を、●印が40 ccの坩堝を用いた場合である。坩堝容量10 ccの場合、金インゴットの冷却効率が高く電子ビームのパワーを上げても蒸着速度は最高で1.0 nm/sであった。これに対し、坩堝容量40 ccの場合、蒸着が開始するパワーは4 kWと大きいが、電子ビームのパワー6.6 kWで蒸着速度は2.6 nm/sに達することが分かった。この結果、坩堝容量40 ccを用いて蒸着速度を制御することにした。 A 5 MHz quartz resonator film thickness meter was used to control the deposition rate. The maximum power of the electron beam is limited to 6 kW when the crucible capacity is 10 cc and 10 kW when it is 40 cc. FIG. 3 is a graph showing the relationship between the power of the electron beam and the vapor deposition rate, where a circle indicates a 10 cc crucible and a circle indicates a 40 cc crucible. In the case of a crucible capacity of 10 cc, the cooling efficiency of the gold ingot was high, and the deposition rate was 1.0 nm / s at the maximum even if the electron beam power was increased. In contrast, in the case of a crucible capacity of 40 cc, the power at which vapor deposition started was as high as 4 kW, but it was found that the vapor deposition rate reached 2.6 nm / s with an electron beam power of 6.6 kW. As a result, the deposition rate was controlled using a crucible capacity of 40 cc.
各種条件による抵抗率及び結晶性の評価は、ポリッシュ仕上げした水晶基板（ＡＴカット基板）の片面全面に蒸着した金薄膜について行った。ポリッシュ基板の外形寸法は25 mm (X)×20 mm (Z')×0.08 mm (Y') で、蒸着領域は 23 mm (X)×18 mm (Z')とした。蒸着は次の手順で行った。
１．基板洗浄
２．真空槽排気（基板洗浄後１５分以内に開始、３時間排気、到達真空度6 (×10−5 Pa)
３．基板予備加熱（１時間）
４．蒸着
Evaluation of resistivity and crystallinity under various conditions was performed on a gold thin film deposited on the entire surface of a polished quartz substrate (AT cut substrate). The external dimensions of the polished substrate were 25 mm (X) × 20 mm (Z ′) × 0.08 mm (Y ′), and the deposition area was 23 mm (X) × 18 mm (Z ′). Vapor deposition was performed according to the following procedure.
1. 1. Substrate cleaning Vacuum chamber exhaust (start within 15 minutes after substrate cleaning, exhaust for 3 hours, ultimate vacuum 6 (× 10 −5 Pa)
3. Substrate preheating (1 hour)
4). Vapor deposition
基板温度と蒸着速度とを図２、３に示した曲線に基づいて制御し、成膜の結晶性及び抵抗率を評価した。金単層膜の膜厚は、非特許文献２より抵抗率が最小値に飽和する100 nmに設定することにした。また、抵抗率はピン径0．5 mm、ピンピッチ1．5 mmのプローブを用いた四探針法により測定した。測定箇所は、23 mm (X) ×18 mm (Z')の蒸着領域の中央1点とした。抵抗率（体積抵抗率）ρＶは次式で表される。
ρＶ＝Ｒ×α×ｔ （２）
ここで、Ｒは抵抗、αは測定位置で決まる補正係数、ｔは膜厚である。なお、ρＶと膜厚によって変わる表面抵抗率ρＳとの関係は次のとおりである。
ρＳ＝ρＶ／ｔ （３）
図４は、蒸着速度が2 nm/sのとき、抵抗率と基板温度との関係を示す図である。この図より明らかなように270℃のとき抵抗率が最も低く、2.24×10−8 Ωmであり、バルクの抵抗率2．2×10−8 Ωmとほぼ同等の値が得られた。図５は基板温度が270℃のとき、抵抗率と蒸着速度との関係を示す図である。この図より抵抗率は、蒸着速度が2 nm/sのとき最も低い抵抗率を示している。
The substrate temperature and the deposition rate were controlled based on the curves shown in FIGS. 2 and 3, and the crystallinity and resistivity of the film formation were evaluated. According to Non-Patent Document 2, the thickness of the gold monolayer film is set to 100 nm at which the resistivity is saturated to the minimum value. The resistivity was measured by a four probe method using a probe having a pin diameter of 0.5 mm and a pin pitch of 1.5 mm. The measurement location was one central point in the deposition area of 23 mm (X) × 18 mm (Z ′). The resistivity (volume resistivity) ρ V is expressed by the following equation.
ρ V = R × α × t (2)
Here, R is a resistance, α is a correction coefficient determined by a measurement position, and t is a film thickness. The relationship between the surface resistivity [rho S vary according to [rho V and film thickness are as follows.
ρ S = ρ V / t (3)
FIG. 4 is a graph showing the relationship between the resistivity and the substrate temperature when the deposition rate is 2 nm / s. As is apparent from this figure, the resistivity is lowest at 270 ° C., which is 2.24 × 10 −8 Ωm, which is almost the same as the bulk resistivity of 2.2 × 10 −8 Ωm. FIG. 5 is a graph showing the relationship between resistivity and vapor deposition rate when the substrate temperature is 270 ° C. From this figure, the resistivity shows the lowest resistivity when the deposition rate is 2 nm / s.
次に、金単層膜の結晶性の評価として、Ｘ線回折(X-ray Diffraction、ＸＲＤ)を用いて調べた。図６（ａ）は、最も小さな抵抗率が得られた条件、即ち基板温度が270℃、蒸着速度が2 nm/sの条件で成膜した金薄膜のX線回折パターンを示す図である。また、図６（ｂ）は比較として、前述したニッケル7 nmを下地とした金100 nm（Ａｕ／Ｎｉ；100 nm／7 nm）の電極膜のX線回折パターンを示す図である。図６（ａ）から分かるように、水晶（SiO2）のピークとAu(111)ピークのみが検出され、金は単配向していると言える。また、図６（ａ）のAu(111)ピークは、図６（ｂ）に示したAu(111)ピークと比較して、X線強度は極めて大きいことが分かる。図７（ａ）は、図６（ａ）のAu(111)ピークのX線ロッキングカーブを示す図である。図７（ｂ）は、Ａｕ／Ｎｉ；100 nm／7 nmの電極膜のX線ロッキングカーブを示す図である。図７（ａ）のロッキングカーブ半値全幅(Full Width at Half Maximum、ＦＷＨＭ)は0.65°であり非常に高い配向性を示している。このＦＷＨＭ値は、Kamijoらが非特許文献７で示したアルミニウム電極の(111)面のＦＷＨＭ値2.0°よりもかなり小さい。なお、図７（ｂ）に示したＡｕ／Ｎｉ；100 nm／7 nm膜のロッキングカーブはブロードとなり、正確なＦＷＨＭ値を求めることができなかった。 Next, X-ray diffraction (XRD) was used to evaluate the crystallinity of the gold single layer film. FIG. 6A is a diagram showing an X-ray diffraction pattern of a gold thin film formed under the condition that the smallest resistivity is obtained, that is, the substrate temperature is 270 ° C. and the deposition rate is 2 nm / s. FIG. 6B shows an X-ray diffraction pattern of an electrode film of 100 nm gold (Au / Ni; 100 nm / 7 nm) with nickel 7 nm as a base, as a comparison. As can be seen from FIG. 6A, only the peak of quartz (SiO 2 ) and the Au (111) peak are detected, and it can be said that gold is unidirectionally oriented. Further, it can be seen that the X-ray intensity of the Au (111) peak in FIG. 6 (a) is extremely large as compared with the Au (111) peak shown in FIG. 6 (b). Fig.7 (a) is a figure which shows the X-ray rocking curve of the Au (111) peak of Fig.6 (a). FIG. 7B is a diagram showing an X-ray rocking curve of an electrode film of Au / Ni; 100 nm / 7 nm. The full width at half maximum (FWHM) of the rocking curve in FIG. 7A is 0.65 °, indicating a very high orientation. This FWHM value is much smaller than the FWHM value of 2.0 ° of the (111) plane of the aluminum electrode shown by Kamijo et al. In addition, the rocking curve of the Au / Ni; 100 nm / 7 nm film shown in FIG. 7B was broad, and an accurate FWHM value could not be obtained.
図８は金単層膜（蒸着速度2 nm/s、膜厚100 nm）のＦＷＨＭ値と基板温度との関係を示す図である。また、図９は金単層膜（基板温度270℃、膜厚100 nm）のＦＷＨＭ値と蒸着速度との関係を示す図である。ＦＷＨＭ値の基板温度依存性、蒸着速度依存性ともＦＷＨＭ値と抵抗率との間に完全な相関はないが、図８、９より基板温度270℃、蒸着速度2 nm/sの条件の場合、ＦＷＨＭ値と抵抗率がともに最小になることが判明した。 FIG. 8 is a graph showing the relationship between the FWHM value of the gold single layer film (deposition rate 2 nm / s, film thickness 100 nm) and the substrate temperature. FIG. 9 is a diagram showing the relationship between the FWHM value of the gold single layer film (substrate temperature 270 ° C., film thickness 100 nm) and the deposition rate. Although there is no perfect correlation between the FWHM value and the resistivity depending on the substrate temperature dependency and the deposition rate dependency of the FWHM value, the substrate temperature is 270 ° C. and the deposition rate is 2 nm / s from FIGS. It has been found that both the FWHM value and the resistivity are minimized.
次に、FE-SEM（Field Emission Scanning Electron Microscope）とAFM（Atomic Force Microscope）とを用いて金薄膜表面の状態を観察した。FE-SEMによる評価では、試料を前処理をすることなく0．2 kVの低加速電圧で、極表面の二次電子像を撮影することができた。観察領域は4.0μｍ×6.0μｍである。AFMによる評価では、三次元像と表面粗さの定量値を得た。三次元像の観察領域は5.0μｍ×5.0μｍであり、この中の2.5μｍ×2.5μｍの領域を表面粗さを求める対象領域とした。図１０（ａ）、（ｂ）、（ｃ）は蒸着速度を2nm/s、基板温度をそれぞれ150℃、200℃及び270℃に設定して成膜した金薄膜のFE-SEM像の写真である。これらの写真を比較すると、基板温度の増加に伴って結晶粒が大きくなり、特に基板温度を270℃に設定した場合、150℃、200℃の場合の結晶粒の大きさとの差が明確であった。結晶粒が大きくなると抵抗率が低くなるという観点から、図４の基板温度と抵抗率との相関が得られる。また、基板温度をそれぞれ150℃、200℃及び270℃に設定した金薄膜のAFM像（図示しない）についても撮影し、それぞれ算術平均表面粗Raも評価したが、Raに大きな差はなかった。 Next, the state of the gold thin film surface was observed using FE-SEM (Field Emission Scanning Electron Microscope) and AFM (Atomic Force Microscope). In the evaluation by FE-SEM, it was possible to take a secondary electron image of the pole surface at a low acceleration voltage of 0.2 kV without pre-processing the sample. The observation area is 4.0 μm × 6.0 μm. In the evaluation by AFM, a three-dimensional image and a quantitative value of the surface roughness were obtained. The observation area of the three-dimensional image is 5.0 μm × 5.0 μm, and the area of 2.5 μm × 2.5 μm among these is the target area for determining the surface roughness. Figures 10 (a), (b), and (c) are photographs of FE-SEM images of gold thin films deposited at a deposition rate of 2 nm / s and substrate temperatures of 150 ° C, 200 ° C, and 270 ° C, respectively. is there. When these photographs are compared, the crystal grains become larger as the substrate temperature increases. In particular, when the substrate temperature is set to 270 ° C., the difference between the crystal grain sizes at 150 ° C. and 200 ° C. is clear. It was. The correlation between the substrate temperature and the resistivity in FIG. 4 is obtained from the viewpoint that the resistivity decreases as the crystal grain size increases. Further, AFM images (not shown) of gold thin films with the substrate temperatures set to 150 ° C., 200 ° C., and 270 ° C., respectively, were photographed and the arithmetic average surface roughness Ra was also evaluated, but there was no significant difference in Ra.
基板温度が270℃、蒸着速度をそれぞれ1 nm/s、2 nm/s及び3 nm/sと変化させて成膜した金の単層膜のFE-SEM像（図示しない）を撮影して結晶粒の大きさを比較した。その結果、蒸着速度が2 nm/sの場合に結晶粒が最も大きいことが判明した。また、蒸着速度が3 nm/sの場合、結晶粒が小さくなる理由は、基板への金原子の供給量が多くなり、十分に結晶の成長が追いつけないものと考えられる。基板温度と同様に、蒸着速度と結晶粒との関係から結晶粒の大きさと抵抗率との間には図５に示すような相関がほぼ得られると考えられる。
また、蒸着速度3 nm/sの場合のFE-SEM像（図示しない）及びAFM像（図示しない）を撮影したが、表面粗さは小さいが、抵抗率は大きい。従って、抵抗率は結晶粒の外表面より内表面（側面）の状態が大きく影響するものと考えられる。
これらと比較するため、前述したニッケル7 nmを下地とした金100 nm（Ａｕ／Ｎｉ；100 nm／7 nm）の電極膜の表面状態のFE-SEM像及びAFM像写真を撮影した。図１１はこのときのFE-SEM像写真である。結晶粒は非常に細かく、表面粗さは小さいことが分かった。表面粗さが小さい方が、電子の散乱が少なく抵抗率は小さくなると考えられるが、この電極の抵抗率は前述したように、基板温度270℃、蒸着速度2 nm/sの金単層電極のそれの1．7倍であった。
FE-SEM images (not shown) of gold monolayer films deposited with substrate temperature of 270 ° C and deposition rates of 1 nm / s, 2 nm / s, and 3 nm / s, respectively, were crystallized. The size of the grains was compared. As a result, it was found that the crystal grains were the largest when the deposition rate was 2 nm / s. In addition, when the deposition rate is 3 nm / s, the reason why the crystal grains are small is considered that the supply amount of gold atoms to the substrate increases and the crystal growth cannot sufficiently catch up. Similar to the substrate temperature, from the relationship between the deposition rate and the crystal grains, it is considered that a correlation as shown in FIG. 5 is obtained between the crystal grain size and the resistivity.
Further, FE-SEM images (not shown) and AFM images (not shown) at a deposition rate of 3 nm / s were taken, but the surface roughness was small but the resistivity was large. Therefore, it is considered that the resistivity is more influenced by the state of the inner surface (side surface) than the outer surface of the crystal grains.
For comparison with these, FE-SEM images and AFM image photographs of the surface state of the electrode film of gold 100 nm (Au / Ni; 100 nm / 7 nm) with the above-mentioned nickel 7 nm as a base were taken. FIG. 11 is a FE-SEM image photograph at this time. It was found that the crystal grains were very fine and the surface roughness was small. The smaller the surface roughness, the smaller the electron scattering and the lower the resistivity. However, as described above, the resistivity of this electrode is that of a gold single layer electrode with a substrate temperature of 270 ° C and a deposition rate of 2 nm / s. It was 1.7 times that.
基板温度が270℃、蒸着速度が2 nm/s の蒸着条件が、抵抗率が最も低く、かつ高い配向性を示す金の単層膜を作る最適設定条件であり、電子デバイスに応用する更に薄い金単層膜、例えば36 nmの抵抗率及び結晶性を評価することにした。図１２は膜厚と抵抗率との関係を示す図で、●印は金単層膜で膜厚は36 nmと100 nmの場合を示す。比較としてニッケル7 nmを下地とした金30 nmの電極膜（Ａｕ／Ｎｉ；30 nm／7 nm）及びニッケル7 nm、金100 nmの電極膜（Ａｕ／Ｎｉ；100 nm／7 nm）の抵抗率を▲印で示している。図１２から明らかなように、36nmの金単層電膜の抵抗率は3．29×10−8Ωmで、ニッケルを下地とした金30 nmの薄膜の抵抗率は6．20×10−8Ωm であるから、金単層膜の抵抗率はニッケルを下地とした金薄膜のそれの約１／２であった。
また、36nmの金単層膜の抵抗率は、ニッケルを下地とした金100 nmの薄膜のそれよりも低く、またChopraらが非特許文献２で示した、マイカ上に形成した同等膜厚の単結晶金電極膜の4．0×10−8Ωm よりも低く、良好な結果であると言える。
The deposition conditions with a substrate temperature of 270 ° C and a deposition rate of 2 nm / s are the optimum setting conditions for producing a gold monolayer film with the lowest resistivity and high orientation, and are thinner for electronic devices. It was decided to evaluate the resistivity and crystallinity of a gold monolayer film, for example 36 nm. FIG. 12 is a diagram showing the relationship between the film thickness and the resistivity. The black circles indicate the cases where the gold single layer film has a film thickness of 36 nm and 100 nm. For comparison, the resistance of gold 30 nm electrode film (Au / Ni; 30 nm / 7 nm) and nickel 7 nm, gold 100 nm electrode film (Au / Ni; 100 nm / 7 nm) with nickel 7 nm as the base The rate is indicated by ▲. As is clear from FIG. 12, the resistivity of the 36 nm gold single-layer electrode film is 3.29 × 10 −8 Ωm, and the resistivity of the gold 30 nm thin film with nickel as the base is 6.20 × 10 −8. Since it was Ωm, the resistivity of the gold single layer film was about ½ that of the gold thin film with nickel as a base.
In addition, the resistivity of the 36 nm gold single layer film is lower than that of the 100 nm gold thin film with nickel as the base, and the equivalent film thickness formed on mica as shown in Non-Patent Document 2 by Chopra et al. The result is lower than 4.0 × 10 −8 Ωm of the single crystal gold electrode film, which is a good result.
図１３は膜厚36 nmの金単層膜の結晶性を評価したXRDパターンを示す図である。図６（ａ）に示した膜厚100 nmの金単層膜と比較するとX線強度は小さくなるが、Au(111)ピークのみが検出されており単配向していることが分かる。また、図１４はAu(111)ピークのロッキングカーブを示す図で、ＦＷＨＭ値は0．82°であり高い配向性を示していることが分かる。
次に、膜厚36 nmの金単層膜の表面状態をFE-SEM像を撮影して調べると、金単層膜は完全な連続膜にはなっていないことが分かった。また、膜厚36 nmの金単層膜のAFM像から、36 nmの金単層膜が100 nmの薄膜の結晶成長の途中であるとすると、表面粗さは成長初期には小さいことも分かった。
FIG. 13 is a diagram showing an XRD pattern in which the crystallinity of a gold single layer film having a thickness of 36 nm is evaluated. Compared with the 100 nm-thick gold single-layer film shown in FIG. 6A, the X-ray intensity is small, but only the Au (111) peak is detected, indicating that the film is unidirectionally oriented. Moreover, FIG. 14 is a figure which shows the rocking curve of an Au (111) peak, and it turns out that FWHM value is 0.82 degrees and has shown high orientation.
Next, when the surface state of the 36 nm-thick gold monolayer film was examined by photographing an FE-SEM image, it was found that the gold monolayer film was not a complete continuous film. Also, from the AFM image of the 36 nm thick gold monolayer, if the 36 nm gold monolayer is in the middle of crystal growth of a 100 nm thin film, the surface roughness is small at the beginning of growth. It was.
金単層膜を電子デバイスに応用するにあたり、環境試験に耐える必要があるので、高温放置試験を行った。36 nmの金単層膜は連続膜ではないことから、熱処理により結晶性が変わり、抵抗率が変化することも考えられるので、熱処理による抵抗率の変化を評価した。熱処理は真空中で熱処理温度は120℃、270℃とし、それぞれ４時間行った。図１５の●印は36 nmの金単層膜、▲印は100 nmの金単層膜でそれぞれ熱処理前後の抵抗率を示す。金単層膜の場合、いずれの膜厚でも120℃の熱処理前後で抵抗率の変化はみられなかった。次いで、これらの試料を更に270℃で処理した場合も、いずれの膜厚の金単層膜とも抵抗率の変化はみられなかった。
比較するため、図１５にＡｕ／Ｎｉ；30 nm／7 nm及びＡｕ／Ｎｉ；100 nm／7 nmの薄膜の抵抗率をそれぞれ○印、△印で重ね書きしたが、Ａｕ／Ｎｉ；30 nm／7 nmの薄膜は抵抗率が増加することが分かった。これは、前述したように、ニッケルと金との相互拡散によるものであると考えられる。
図１６に金単層膜36 nm、100 nmの熱処理前後のＦＷＨＭ値を示す。前述の条件の熱処理によるＦＷＨＭ値の変化はなく、結晶性は変わらず金単層膜は熱に対し安定であると言える。
In order to apply the gold monolayer film to an electronic device, it is necessary to withstand an environmental test, so a high temperature storage test was performed. Since the 36 nm gold monolayer film is not a continuous film, the crystallinity may change due to the heat treatment, and the resistivity may change. Therefore, the change in resistivity due to the heat treatment was evaluated. The heat treatment was performed in a vacuum at 120 ° C. and 270 ° C. for 4 hours, respectively. In FIG. 15, the ● marks indicate the resistivity before and after the heat treatment for the 36 nm gold single layer film and the ▲ marks indicate the 100 nm gold single layer film, respectively. In the case of the gold single layer film, no change in resistivity was observed before and after the heat treatment at 120 ° C. at any film thickness. Next, when these samples were further treated at 270 ° C., no change in resistivity was observed in any single-layer gold film.
For comparison, the resistivity of the thin film of Au / Ni; 30 nm / 7 nm and Au / Ni; 100 nm / 7 nm is overwritten in FIG. / 7 nm thin film was found to increase resistivity. As described above, this is considered to be due to the mutual diffusion of nickel and gold.
FIG. 16 shows the FWHM values before and after the heat treatment of the gold single layer films 36 nm and 100 nm. It can be said that the FWHM value is not changed by the heat treatment under the above conditions, the crystallinity is not changed, and the gold single layer film is stable to heat.
金単層膜の抵抗率は基板の表面粗さの影響を受ける可能性がある。そこで、予め厚さ220μmから83μmまでエッチングした基板を用いて実験した。この場合、片面の総エッチング量は約70μmになる。この基板上に36 nmの金単層膜を形成して抵抗率を測定した。図１７に抵抗率とウェハエッチング量との関係を示す。エッチング量73μmの抵抗率は3．11×10−8Ωmであり、エッチング量4．2μm の抵抗率より低い。図１８は基板のエッチング量と基板の表面粗さとの関係を示す図である。エッチング量が多い方が表面粗さは小さいことから、ウェハの表面が平滑な方が抵抗率を低減できると考える。 The resistivity of the gold single layer film may be affected by the surface roughness of the substrate. Therefore, an experiment was performed using a substrate which was previously etched to a thickness of 220 μm to 83 μm. In this case, the total etching amount on one side is about 70 μm. A 36 nm gold monolayer film was formed on this substrate, and the resistivity was measured. FIG. 17 shows the relationship between resistivity and wafer etching amount. The resistivity when the etching amount is 73 μm is 3.11 × 10 −8 Ωm, which is lower than the resistivity when the etching amount is 4.2 μm. FIG. 18 is a diagram showing the relationship between the etching amount of the substrate and the surface roughness of the substrate. Since the surface roughness is smaller when the etching amount is larger, it is considered that the resistivity can be reduced when the wafer surface is smoother.
上記で得られた金単層膜を水晶振動子へ適用した場合の効果を調べるため、図１に示す構造の水晶振動子Ｂａ、即ち水晶基板Ｂ（水晶基板寸法0.85 mm (X) ×1.25 mm (Z') ×0.07 mm (Y')）を用い、楕円電極（寸法長軸200μm (X)、短軸158μm (Z')）を金の単層薄膜（片面36 nm）で試作した。この水晶振動子Ｂａの諸定数を測定した結果、共振抵抗は52 Ωとなり、Q値の改善が見られなかった。 In order to investigate the effect when the gold single layer film obtained above is applied to a crystal resonator, the crystal resonator Ba having the structure shown in FIG. 1, that is, the crystal substrate B (crystal substrate size 0.85 mm (X) × 1.25 mm) (Z ') x 0.07 mm (Y')), and an elliptical electrode (dimension major axis 200μm (X), minor axis 158μm (Z ')) was fabricated as a gold single layer thin film (36 nm on one side). As a result of measuring various constants of the crystal resonator Ba, the resonance resistance was 52 Ω, and no improvement in the Q value was observed.
そこで、Ｑ値が改善できない要因について検討した結果、水晶基板Ｂの振動部と金単層電極との密着性が主要因であると推定し、金電極の密着性を改善すべく、酸素プラズマによるボンバード処理を行うことにした。ボンバード処理は、酸素イオンが水晶基板板へ衝突することによるクリーニング効果と加熱効果とで、薄膜と基板との密着性が高まるからである。特に、622 MHz基本波水晶振動子のように、微小な電極パターンの蒸着マスクを使用する場合、基板の大部分が露出しないため加熱の補助としも有効であると考えられる。酸素プラズマは、酸素ガス流入量と排気量とのバランスによる真空度と、直流電源出力とにより制御し、実験での一例をあげると真空度は10 Pa、直流電源出力は220 Wである。また、アルゴンの場合の一例をあげると、真空度は6 Pa、直流電源出力は250 Wであった。 Therefore, as a result of examining factors that cannot improve the Q value, it is estimated that the adhesion between the vibrating portion of the quartz substrate B and the gold single layer electrode is the main factor, and in order to improve the adhesion of the gold electrode, oxygen plasma is used. We decided to perform bombarding. This is because the bombarding treatment improves the adhesion between the thin film and the substrate due to the cleaning effect and heating effect caused by the collision of oxygen ions with the quartz substrate plate. In particular, when a vapor deposition mask with a minute electrode pattern is used, such as a 622 MHz fundamental wave crystal resonator, it is considered that the substrate is not exposed and is effective as a heating aid. The oxygen plasma is controlled by the degree of vacuum based on the balance between the oxygen gas inflow and the amount of exhaust, and the DC power supply output. As an example in the experiment, the vacuum degree is 10 Pa and the DC power supply output is 220 W. Further, as an example in the case of argon, the degree of vacuum was 6 Pa and the DC power output was 250 W.
ボンバード処理を含む蒸着は次の手順で行った。なお、蒸着条件は基板温度270℃、蒸着速度2 nm/sとした。
1) 真空槽排気 （３時間、到達真空度6×10−5 Pa．）
2) 基板予備加熱 (１時間)
3) ボンバード処理 （各面150秒）
4) 真空度、基板温度回復 (15分)
5) 蒸着
Vapor deposition including bombardment was performed according to the following procedure. The deposition conditions were a substrate temperature of 270 ° C. and a deposition rate of 2 nm / s.
1) Vacuum chamber exhaust (3 hours, ultimate vacuum 6 × 10 −5 Pa.)
2) Substrate preheating (1 hour)
3) Bombard processing (150 seconds for each side)
4) Vacuum degree, substrate temperature recovery (15 minutes)
5) Evaporation
ボンバード処理を行った膜厚36 nmの金単層電極の抵抗率と結晶性を評価した。図１９は酸素ガスあるいはアルゴンガスを用いてボンバード処理を行った金単層膜電極と、ボンバード処理を行わなかった金単層膜電極との抵抗率をそれぞれ比較した図で、この図から酸素ガスでボンバード処理を行った金単層膜電極の抵抗率は2.87×10−8Ωmであり、行わない場合と比べて非常に低い値を示した。
次に、図２０はＸ線回折パターンを示す図である。図中に水晶基板のSiO2 (101)、SiO2 (202)のピーク以外に、Au(111)ピークのみが検出されているがX線強度は、図１３と比較すると小さい。図２１はAu(111)ピークのロッキングカーブを示す図であるが、ロッキングカーブはブロードとなり、正確なロッキングカーブ半値全幅(ＦＷＨＭ)を求めることができなかった。酸素ガスボンバード処理により金単層電極の配向性は著しく低下していると考えられる。
The resistivity and crystallinity of a 36 nm thick gold single layer electrode subjected to bombarding were evaluated. FIG. 19 is a graph comparing the resistivity of a gold single-layer film electrode that has been bombarded with oxygen gas or argon gas, and a gold single-layer film electrode that has not been bombarded. The resistivity of the gold single-layer film electrode subjected to the bombarding treatment was 2.87 × 10 −8 Ωm, which was a very low value compared to the case where the bombarding treatment was not performed.
Next, FIG. 20 is a diagram showing an X-ray diffraction pattern. In the figure, only the Au (111) peak is detected in addition to the peaks of SiO 2 (101) and SiO 2 (202) of the quartz substrate, but the X-ray intensity is smaller than that in FIG. FIG. 21 is a diagram showing a rocking curve of the Au (111) peak, but the rocking curve was broad, and an accurate rocking curve full width at half maximum (FWHM) could not be obtained. It is considered that the orientation of the gold single layer electrode is remarkably lowered by the oxygen gas bombardment treatment.
次に、ボンバード処理した金単層電極のFE-SEM像とAFM像とを撮影した。図２２は表面状態を示すFE-SEM像である。この図よりボンバード処理した金単層電極は連続膜になっていることが分かる。
以上の実験結果から、ボンバード処理を行った金単層電極は、配向性は低下しているにもかかわらず、抵抗率が低くなることが判明した。これは、連続膜になったことに起因しているものと思われる。
Next, an FE-SEM image and an AFM image of a gold single layer electrode subjected to bombarding were taken. FIG. 22 is an FE-SEM image showing the surface state. From this figure, it can be seen that the gold single layer electrode subjected to the bombarding process is a continuous film.
From the above experimental results, it was found that the gold single layer electrode subjected to the bombardment treatment has a low resistivity even though the orientation is lowered. This seems to be due to the fact that it became a continuous film.
水晶基板Ｂに酸素ガスあるいはアルゴンガスを用いてボンバード処理した膜厚36nmの金の単層膜を形成した周波数622 MHzの水晶振動子Ｂｂ１、Ｂｂ２の諸特性を、インピーダンスアナライザを用いて測定した。図２３は、水晶振動子Ｂｂ１、Ｂｂ２、Ｂｎ（ボンバード処理なし）のアドミッタンス円を示す図である。図２３から酸素ガスを用いてボンバード処理を行った水晶振動子Ｂｂ１のアドミッタンス円は大きくなり、Ｑ値が大幅に改善されていることが分かる。
図２４はボンバード処理をした水晶振動子Ｂｂ１の諸定数を示す図である。アドミッタンス円が良好であるため、Butterworth-Van Dyke(BVD)集中4定数回路での表記が可能となる。また、参考として、エネルギ閉じ込め解析による容量比から各定数を求めた計算値（Calculated）を並記する。計算値では、共振抵抗は固有限界値Qmをもとに算出した。図２４より共振抵抗は17.6 Ω、Q値は8400となり、固有限界値Qmの約60%まで改善した。
Various characteristics of quartz resonators Bb1 and Bb2 having a frequency of 622 MHz, in which a single-layer gold film having a thickness of 36 nm formed by bombarding with oxygen gas or argon gas on a quartz substrate B, were measured using an impedance analyzer. FIG. 23 is a diagram illustrating admittance circles of the crystal resonators Bb1, Bb2, and Bn (without bombarding). It can be seen from FIG. 23 that the admittance circle of the crystal resonator Bb1 subjected to the bombard process using oxygen gas is increased, and the Q value is greatly improved.
FIG. 24 is a diagram showing various constants of the quartz resonator Bb1 subjected to the bombard process. Since the admittance circle is good, it can be expressed in a Butterworth-Van Dyke (BVD) lumped four-constant circuit. For reference, the calculated values (Calculated) obtained from the constants based on the capacity ratio by the energy confinement analysis are also listed. In the calculated value, the resonance resistance was calculated based on the intrinsic limit value Qm. As shown in FIG. 24, the resonance resistance is 17.6 Ω and the Q value is 8400, which is improved to about 60% of the intrinsic limit value Qm.
図２５は上記水晶振動素子Ｂｂ１をパッケージに実装した後のアドミッタンス円を示す図であり、図２６は諸定数の一覧表である。また、比較として電極をＡｕ／Ｎｉ；30 nm／7 nmで形成した水晶振動子Ｂのアドミッタンス円及び諸定数の一覧表をそれぞれ図２５、２６に重ね書き及び並記した。水晶振動子Ｂに比較して、酸素ガスでボンバード処理した金単層電極の水晶振動子Ｂｂ１のFigure of Meritは1.7倍、Q値は2.1倍に改善した。 FIG. 25 is a diagram showing an admittance circle after the crystal resonator element Bb1 is mounted on a package, and FIG. 26 is a list of various constants. For comparison, a list of admittance circles and various constants of the quartz resonator B in which the electrodes were formed of Au / Ni; 30 nm / 7 nm was overwritten and written in FIGS. 25 and 26, respectively. Compared to the quartz resonator B, the figure of Merit of the quartz resonator Bb1 of gold single layer electrode bombarded with oxygen gas was improved 1.7 times and the Q value was improved 2.1 times.
図２７は、水晶振動子２Ｂ１のインピーダンス特性を示す図である。１次非調和振動S1の共振抵抗は、主振動S0のそれの５倍となった。一方、図２９に示したインピーダンス特性のS0、S1の共振抵抗比R1／R0は１．９倍であり、大幅に改善された。 FIG. 27 is a diagram illustrating impedance characteristics of the crystal resonator 2B1. The resonance resistance of the primary anharmonic vibration S 1 is five times that of the main vibration S 0 . On the other hand, the resonance resistance ratio R 1 / R 0 of the impedance characteristics S 0 and S 1 shown in FIG. 29 is 1.9 times, which is greatly improved.
１ 水晶基板
２ 凹陥部
３ 振動部
４、８ 電極
５、９ リード電極
６、１０ パッド電極
７ 傾斜部
DESCRIPTION OF SYMBOLS 1 Crystal substrate 2 Recessed part 3 Vibrating part 4, 8 Electrode 5, 9 Lead electrode 6, 10 Pad electrode 7 Inclined part
Claims (11)
The crystal unit according to claim 10, wherein the pad electrode is thicker than the excitation electrode.
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| JP2007205806A (en) * | 2006-01-31 | 2007-08-16 | Kyocera Kinseki Corp | Method for manufacturing sensor element for measurement of very small mass and its element |
| JP2009044237A (en) * | 2007-08-06 | 2009-02-26 | Epson Toyocom Corp | Frequency adjustment method of piezoelectric device, and piezoelectric device and mask for frequency adjustment |
| JP2013034217A (en) * | 2012-09-14 | 2013-02-14 | Seiko Epson Corp | Frequency adjusting method of vibrating device, vibrating device and electronic device |
| US8963402B2 (en) | 2010-11-30 | 2015-02-24 | Seiko Epson Corporation | Piezoelectric vibrator element, piezoelectric module, and electronic device |
| JPWO2021045094A1 (en) * | 2019-09-04 | 2021-03-11 |
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