JP2004254114A - Single crystal for piezoelectric substrate, surface acoustic wave filter using the same and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium tantalate signal crystal and a lithium niobate single crystal generating less static electricity due to the temperature variation and capable of promptly self-neutralizing the electric charge even when the electric charge is generated and to provide a surface acoustic wave filter using the single crystals as piezoelectric substrates and its manufacturing method. <P>SOLUTION: In the lithium tantalate single crystal and a lithium niobate single crystal, at least one or more kinds of additive elements to be selected from iron, copper, manganese, molybdenum, cobalt, nickel, zinc, carbon, magnesium, titanium, tungsten, indium, tin and a rare-earth element are made to be contained by 0.01 to 1.00wt%. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００５３】
まず、製造したＬＴ単結晶の組成の均一性について述べる。組成の均一性は、ＬＴ単結晶から切り出した結晶上部ウエーハのキュリー点と、結晶下部ウエーハのキュリー点との差（キュリー点上下差）で評価することができる。すなわち、単結晶の上部と下部とでキュリー点の差が小さいほど、単結晶の軸方向における組成は均一であるといえる。また、組成が均一であれば、添加元素の偏析や結晶欠陥も生じない。
【００５４】
表１に示すように、添加元素が含まれていない＃１１のＬＴ単結晶では、キュリー点上下差は０．５℃であった。つまり、単結晶の上下でキュリー点の差がほとんどないため、＃１１のＬＴ単結晶の組成は均一であることがわかる。一方、鉄の含有割合が１．２０ｗｔ％の＃１９のＬＴ単結晶では、キュリー点上下差が６．２℃であった。これより、＃１９のＬＴ単結晶では、上下で組成のばらつきがあるといえる。このことは、添加元素の偏析の有無等でも明らかである。添加元素が結晶中に均一に含まれていない場合には、添加元素の偏析が現れ、結晶欠陥が生じ易い。＃１９のＬＴ単結晶では、添加元素である鉄の偏析が観察され、結晶欠陥も生じていた。
【００５５】
また、鉄の含有割合が０．０１〜１．００ｗｔ％の＃１２〜＃１８のＬＴ単結晶では、キュリー点上下差は０．２〜３．５℃であった。これより、＃１２〜＃１８のＬＴ単結晶の組成は均一であることがわかる。加えて、＃１２〜＃１８のＬＴ単結晶では、鉄の偏析は観察されず、結晶欠陥も生じていなかった。このように、キュリー点上下差が上記範囲の単結晶は、組成が均一であるため、弾性表面波フィルタの圧電基板を作製するのに好適といえる。特に、鉄の含有割合が０．０１〜０．５０ｗｔ％の＃１２〜＃１７のＬＴ単結晶では、キュリー点上下差はより小さくなっていた。したがって、＃１２〜＃１７のＬＴ単結晶の組成は、より均一であり、弾性表面波フィルタの圧電基板を作製するのにより好適である。
【００５６】
さらに、＃１１および＃１５のＬＴ単結晶の結晶上部ウエーハおよび結晶下部ウエーハについて、上記（ａ）〜（ｅ）の測定位置におけるキュリー点の値を表２に示す。
【００５７】
【表２】

【００５８】
表２から明らかなように、両ＬＴ単結晶における各ウエーハでは、測定位置によるキュリー点の値の変動はほとんどなかった。これより、ウエーハ面においても、組成が均一であることがわかる。以上より、添加元素を０．０１ｗｔ％以上１．００ｗｔ％以下の割合で含む本発明のＬＴ単結晶は、組成が均一であることが確認された。
【００５９】
次に、クラックフリー率について述べる。添加元素を含まない＃１１のＬＴ単結晶では、クラックフリー率は９０％であった。また、鉄を０．０１〜０．０５ｗｔ％含む＃１２〜＃１７のＬＴ単結晶のクラックフリー率は、＃１１のＬＴ単結晶と同様、もしくはそれ以上となった。これらのＬＴ単結晶は、帯電し難いため、製造中におけるクラックの発生が抑制されたと考えられる。
【００６０】
次に、各ＬＴ単結晶から作製されたウエーハの表面電位について述べる。以下、便宜的に、各ＬＴ単結晶の番号をウエーハの番号として使用する。添加元素を含まない＃１１のウエーハでは、１５０℃での表面電位、すなわち表面電位の最高値が１４．５ｋＶであった。また、その後に降温され３０℃程度となっても、表面電位は７．８ｋＶ程度までしか低下しなかった。つまり、＃１１のウエーハは、降温された後も帯電し続けた。これに対し、添加元素を含む＃１２〜＃１９、＃２１〜＃２６のウエーハでは、添加元素の種類によらず、１５０℃での表面電位は６．２ｋＶ以下となった。特に、添加元素の含有割合が０．０２〜０．５０ｗｔ％である＃１３〜＃１７、＃２１〜＃２６のウエーハでは、表面電位がより低い値となった。また、降温された後は、表面電位は速やかに低下し、極めて低い値となった。特に、鉄を０．１０ｗｔ％以上含む＃１５〜＃１９のウエーハでは、表面電位が０ｋＶとなり、完全に電荷が除去された。
【００６１】
図４に、ウエーハの昇温・降温過程における表面電位の変化を示す。図４では、一例として、＃１１〜＃１６のウエーハについて示している。図４に示すように、温度の上昇に伴い、＃１１のウエーハの表面電位は高くなった。一方、＃１２〜＃１６のウエーハでは、温度が上昇しても、表面電位はあまり上昇しなかった。これより、＃１２〜＃１６のウエーハは、帯電し難いことがわかる。また、降温過程では、＃１１のウエーハの表面電位は、一旦低下するものの、高い値を維持し続けた。なお、＃１１のウエーハの表面電位は、４８時間経過した後も、０ｋＶにはならなかった。一方、＃１２〜＃１６のウエーハの表面電位は速やかに低下した。特に、＃１３〜＃１６のウエーハの表面電位は、降温過程に入った直後に、ほぼ０ｋＶとなった。これは、生じた電荷が速やかに除去されたことを示すものである。
【００６２】
ここで、各ウエーハにおける電荷中和時間について述べる。上述したように、電荷中和時間とは、ウエーハの昇温後、降温を開始してから、ウエーハの表面電位がほぼ０ｋＶになるまでの時間である。＃１１のウエーハでは、４８時間経過した後も表面電位が０ｋＶにならなかった。このため、表１では、＃１１のウエーハの電荷中和時間を「＞２８８０」と示している。これに対して、添加元素を含むすべてのウエーハでは、降温後、時間の経過とともに、表面電位がほぼ０ｋＶとなった。特に、鉄を０．０５ｗｔ％以上含む＃１４〜＃１９のウエーハでは、降温開始の数秒で表面電位がほぼ０ｋＶとなった。
【００６３】
このように、添加元素を０．０１ｗｔ％以上１．００ｗｔ％以下の割合で含む本発明のＬＴ単結晶は、温度が変化しても帯電し難いことが確認された。また、本発明のＬＴ単結晶は、電荷が生じた場合であっても、速やかに自己中和して除去できることが確認された。
【００６４】
なお、図５に、ＬＴ単結晶における鉄の含有割合に対する表面電位およびキュリー点上下差の関係を示す。図５における表面電位の値は、ウエーハが降温され、その温度が約３０℃になった時のウエーハの表面電位値である。図５に示すように、鉄の含有割合が大きくなると、ウエーハの表面電位は低くなる。一方、鉄の含有割合が大きくなると、キュリー点上下差も大きくなる。つまり、単結晶における組成の均一性が低下する。したがって、鉄の含有割合を０．０１ｗｔ％以上１．００ｗｔ％以下とすることで、降温後の表面電位が低く、かつ組成が均一なＬＴ単結晶を実現することが可能となる。
【００６５】
次に、各ウエーハの表面抵抗について述べる。添加元素を含む＃１４、＃１５、＃２１〜＃２６のウエーハでは、表面抵抗が９．５×１０^１３Ω以下の値であったのに対し、添加元素を含まない＃１１のウエーハでは、表面抵抗が測定範囲を超える大きな値（＞１．０×１０^１５Ω）であった。ウエーハの表面抵抗が小さいと、電荷が残存し難いため、電荷中和時間が短くなると考えられる。つまり、添加元素を０．０１ｗｔ％以上１．００ｗｔ％以下の割合で含む本発明のＬＴ単結晶は、表面抵抗値が小さいため、電荷が生じた場合であっても、速やかに自己中和して除去できると考えられる。
【００６６】
次に、上記ウエーハの昇温・降温過程における各ウエーハの静電気スパークの発生について述べる。添加元素を含まない＃１１のウエーハでは、降温過程において、合計３２回のスパークが観察された。これに対して、＃１２、＃２１〜＃２３、＃２５、＃２６の各ウエーハではスパークの発生は１〜３回であった。さらに、＃１３〜＃１９、＃２４のウエーハでは、スパークは全く発生しなかった。
【００６７】
図６に、ウエーハの昇温・降温過程における静電気スパークの発生回数を示す。図６では、一例として、＃１１〜＃１３のウエーハについて示している。図６に示すように、降温過程において、＃１１のウエーハでは、常にスパークが発生していた。一方、＃１２のウエハでは、降温開始後の直後に２回発生しただけであった。また、＃１３のウエーハでは、１回も発生しなかった。なお、上記ウエーハの昇温・降温を、昇温速度を２倍にし、ウエーハの最高温度を２００℃として行ったところ、＃１１のウエーハにはクラックが生じた。その結果、＃１１のウエーハは割れてしまった。一方、＃１２〜＃１９、＃２１〜＃２６のウエーハでは、クラックは生じなかった。このように、添加元素を０．０１ｗｔ％以上１．００ｗｔ％以下の割合で含む本発明のＬＴ単結晶は、静電気放電のおそれが少ないことが確認された。
【００６８】
なお、表１には示さなかったが、添加元素を含む＃１２〜＃１９、＃２１〜＃２６の各ウエーハにおける粒子の付着数は、添加元素を含まない＃１１のウエーハと比較して、１／１０程度であった。これより、添加元素を含むことにより、ウエーハ表面での静電気の発生が抑制されることがわかる。
【００６９】
以上まとめると、鉄等の添加元素を０．０１ｗｔ％以上１．００ｗｔ％以下の割合で含む本発明のＬＴ単結晶は、組成が均一である。また、温度が変化しても帯電し難く、電荷が生じた場合であっても、速やかに自己中和して除去できる。つまり、温度変化があっても静電気放電のおそれが少ない。したがって、本発明のＬＴ単結晶は、弾性表面波フィルタの圧電基板用に好適である。
【００７０】
【発明の効果】
本発明のタンタル酸リチウム単結晶およびニオブ酸リチウム単結晶は、ともに、所定の添加元素を０．０１ｗｔ％以上１．００ｗｔ％以下の割合で含有する。そのため、温度が変化しても電荷を生じ難く、仮に単結晶表面に電荷が発生しても速やかに自己中和して、電荷を除去することができる。したがって、本発明のタンタル酸リチウム単結晶またはニオブ酸リチウム単結晶から作製された圧電基板を用いて弾性表面波フィルタを製造すれば、除電設備等の設置が不要となり、コストが大幅に削減できる。また、除電のための製造工程も不要となるため、生産性が向上する。さらに、本発明の単結晶から作製された圧電基板を有する弾性表面波フィルタは、保管時や使用中においても静電気による不良の発生が少ない。
【図面の簡単な説明】
【図１】本実施形態の弾性表面波フィルタの一例を示す斜視図である。
【図２】ウエーハにおけるキュリー点の測定位置を示す。
【図３】表面電位測定装置の概略を示す。
【図４】ウエーハの昇温・降温過程における表面電位の変化を示す。
【図５】ＬＴ単結晶における鉄の含有割合に対する表面電位およびキュリー点上下差の関係を示す。
【図６】ウエーハの昇温・降温過程における静電気スパークの発生回数を示す。
【符号の説明】
１：弾性表面波フィルタ
２：ケース本体 ２１：入力端子 ２２：出力端子
３：チップ
３１：圧電基板
３２ａ、３２ｂ：入力側電極 ３２０ａ、３２０ｂ：導線
３３ａ、３３ｂ：出力側電極 ３３０ａ、３３０ｂ：導線
１００：表面電位測定装置
２００：ステージ ３００：絶縁ケース ４００：表面電位測定器
５００：非接触型放射温度計 ６００、６０１、６０２：ウエーハ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a lithium tantalate single crystal and a lithium niobate single crystal used as a piezoelectric substrate of a surface acoustic wave filter, and furthermore, a surface acoustic wave filter using a piezoelectric substrate manufactured from the single crystal, and a method of manufacturing the same. About.
[0002]
[Prior art]
A surface acoustic wave filter (SAW filter) using a surface acoustic wave is one in which fine comb-shaped electrodes are formed on the surface of a piezoelectric substrate, and is widely used in televisions, mobile phones, and the like. The surface acoustic wave filter is manufactured by forming an electrode thin film made of aluminum or the like on the surface of a piezoelectric substrate, and forming the electrode thin film into an electrode having a predetermined shape by photolithography. Specifically, first, an electrode thin film is formed on the surface of the piezoelectric substrate by a sputtering method or the like. Next, an organic resin as a photoresist is applied and prebaked at a high temperature. Subsequently, patterning of the electrode film is performed by exposure using a stepper or the like. Then, after post-baking at a high temperature, development is performed to dissolve the photoresist. Finally, wet or dry etching is performed to form an electrode having a predetermined shape.
[0003]
The material of the piezoelectric substrate is lithium tantalate (LiTaO). ₃ ) Single crystal or lithium niobate (LiNbO) ₃ ) Single crystals are often used. These single crystals have characteristics of a large pyroelectric coefficient and a high resistance. Therefore, electric charges are generated on the surface by a slight change in temperature. Then, the generated charge is accumulated, and the charged state continues unless the charge removing process is performed from the outside. Therefore, in the process of producing a wafer from these single crystals, there is a problem that chipping and chipping of the wafer surface and wafer edge are likely to occur due to electrostatic discharge, resulting in low productivity.
[0004]
Further, as described above, in the manufacturing process of the surface acoustic wave filter, there are processes involving several temperature changes, such as formation of an electrode thin film and prebaking and postbaking in photolithography. Therefore, when the above-mentioned lithium tantalate single crystal or the like is used as the piezoelectric substrate, generation of static electricity on the piezoelectric substrate becomes a problem in the process of manufacturing the surface acoustic wave filter. When the piezoelectric substrate is charged, electrostatic discharge occurs in the piezoelectric substrate, which causes cracks and cracks. Further, the formed electrodes may be short-circuited due to static electricity. Furthermore, fine metal powder, dust, dust, and the like generated during the manufacturing process may be attracted to the surface of the piezoelectric substrate by static electricity, causing the electrodes to be short-circuited or to be broken by the electrodes being opened. There is also.
[0005]
In order to suppress such charging of the piezoelectric substrate, various measures have been taken when manufacturing a surface acoustic wave filter. For example, installation of a static elimination facility such as an ionizer for neutralizing the electric charge on the surface of an electronic substrate, and installation of ancillary facilities such as a particle counter and a microscope for measuring particles such as dust are mentioned. Further, in the manufacturing process of the surface acoustic wave filter, before forming the electrode thin film, a conductive film forming step of previously forming a conductive film for the purpose of removing charge on the back surface of the piezoelectric substrate, or forming the electrode thin film A re-cleaning step of cleaning the piezoelectric substrate is added later. Further, a method has been disclosed in which a heating / cooling step of changing the temperature of a piezoelectric substrate by 50 ° C. or more is performed while removing charges charged on the piezoelectric substrate (for example, see Patent Document 1).
[0006]
[Patent Document 1]
JP-A-2002-9569
[0007]
[Problems to be solved by the invention]
In the method described in Patent Document 1, in the step of heating and cooling the piezoelectric substrate, the piezoelectric substrate and a sample stage on which the piezoelectric substrate is mounted are electrically connected, and the electric charge charged on the piezoelectric substrate is transferred to the ground potential. Have escaped to. However, in the method described in Patent Literature 1, an operation for removing static electricity is separately required, and the operation becomes complicated. In addition, it is not possible to suppress charging of the piezoelectric substrate other than in the heating / cooling step. On the other hand, installation of ionization equipment such as an ionizer is costly and has a space problem. In addition, when the number of manufacturing steps is increased, the work becomes complicated and productivity is reduced.
[0008]
The present invention has been made in view of such circumstances, and a lithium tantalate single crystal and a lithium niobate single crystal that generate less static electricity due to a temperature change and can quickly self-neutralize even if a charge is generated. The task is to provide. Another object of the present invention is to provide a surface acoustic wave filter in which the occurrence of defects due to static electricity is small even during use or the like by using such a single crystal as a piezoelectric substrate. It is still another object of the present invention to provide a method of manufacturing a surface acoustic wave filter which is less likely to cause defective products due to static electricity and has high productivity and safety.
[0009]
[Means for Solving the Problems]
The lithium tantalate single crystal of the present invention contains at least one additive element selected from iron, copper, manganese, molybdenum, cobalt, nickel, zinc, carbon, magnesium, titanium, tungsten, indium, tin, and rare earth elements. It is characterized by having a charge neutralization property of self-neutralizing and removing surface charges by containing it in a proportion of from 01 wt% to 1.00 wt%. Further, the lithium niobate single crystal of the present invention contains at least one or more additive elements selected from iron, copper, manganese, molybdenum, cobalt, nickel, zinc, carbon, magnesium, titanium, tungsten, indium, tin, and rare earth elements. It is characterized in that it is contained at a rate of 0.01% by weight or more and 1.00% by weight or less, and has a charge neutralizing property of self-neutralizing and removing surface charges.
[0010]
That is, both the lithium tantalate single crystal and the lithium niobate single crystal of the present invention (hereinafter, appropriately referred to as the “single crystal of the present invention”) contain a predetermined additive element in an amount of 0.01% by weight or more and 1.00% by weight or less. In the proportion of As will be described in detail later, the single crystal of the present invention hardly generates electric charge even when the temperature changes, and hardly generates static electricity by containing the predetermined additive element in the above ratio. Also, even if charges are generated on the single crystal surface, the charges can be quickly neutralized and removed. Here, the “charge neutralization characteristic” is a characteristic capable of self-neutralizing and removing the charge generated on the single crystal surface. The presence or absence of the charge neutralization characteristic can be confirmed, for example, by the following method. First, a predetermined single crystal or a wafer produced from the single crystal is heated to a predetermined temperature. After that, the single crystal or the wafer is cooled. When the surface potential of the single crystal or wafer becomes approximately 0 kV after the temperature is lowered, the single crystal is assumed to have charge neutralization characteristics.
[0011]
Therefore, the single crystal of the present invention has few cracks during its production. Also, when a wafer is produced from a single crystal, chipping or chipping of the wafer surface or the like due to electrostatic discharge is unlikely to occur, so that productivity is improved. Furthermore, since the single crystal of the present invention is hardly charged, it is easy to handle and has high safety. If a surface acoustic wave filter is manufactured using a wafer made of the single crystal of the present invention as a piezoelectric substrate, installation of static elimination equipment and the like becomes unnecessary, and the cost can be significantly reduced. In addition, since a manufacturing process for removing static electricity is not required, productivity is improved. Furthermore, by manufacturing a piezoelectric substrate from the single crystal of the present invention, a surface acoustic wave filter with less occurrence of defects due to static electricity even during storage or use can be configured.
[0012]
The surface acoustic wave filter of the present invention comprises at least one additive element selected from iron, copper, manganese, molybdenum, cobalt, nickel, zinc, carbon, magnesium, titanium, tungsten, indium, tin, and rare earth elements in an amount of 0.01 wt. % Or more and 1.00 wt% or less, and has a piezoelectric substrate made of a lithium tantalate single crystal or a lithium niobate single crystal having a charge neutralization property of self-neutralizing and removing a surface charge. And
[0013]
That is, the surface acoustic wave filter of the present invention is one in which a piezoelectric substrate is manufactured from one of the above-described lithium tantalate single crystal and lithium niobate single crystal of the present invention. As described above, in the single crystal of the present invention, charge generation due to temperature change is small, and the generated charge is quickly removed. Therefore, such a surface acoustic wave filter in which a piezoelectric substrate is manufactured from the single crystal of the present invention generates little static electricity even during storage or use, and has little risk of electrode breakdown.
[0014]
The method for producing a surface acoustic wave filter according to the present invention comprises: iron, copper, manganese, molybdenum, cobalt, nickel, zinc, carbon, magnesium, titanium, tungsten, indium, tin, and at least one additional element selected from rare earth elements. A piezoelectric substrate prepared from a lithium tantalate single crystal or a lithium niobate single crystal having a charge neutralization property of containing 0.01 wt% or more and 1.00 wt% or less and having a charge neutralizing property of self-neutralizing and removing surface charges is prepared. A step of preparing a piezoelectric substrate, a step of forming an electrode thin film on the surface of the piezoelectric substrate, and a step of forming the electrode thin film into an electrode having a predetermined shape by photolithography.
[0015]
That is, in the method for manufacturing a surface acoustic wave filter of the present invention, a piezoelectric substrate manufactured from any one of the lithium tantalate single crystal and the lithium niobate single crystal of the present invention is used, and an electrode is formed on the surface of the piezoelectric substrate. Form. By using the piezoelectric substrate manufactured from the single crystal of the present invention, there is no need for a static elimination facility in any process that handles the piezoelectric substrate, such as transport, storage, and inspection, as well as the electrode forming process. In addition, a process for removing static electricity is not required. Specifically, before forming the electrode thin film, a conductive film forming step of forming a conductive film on the back surface of the piezoelectric substrate in advance for the purpose of removing charge, or cleaning the piezoelectric substrate after forming the electrode thin film. The washing step and the like can be omitted. As described above, since a static elimination facility and a process for eliminating static electricity are not required, manufacturing cost can be significantly reduced, and productivity can be improved. In addition, cracks and cracks in the piezoelectric substrate due to electrostatic discharge, destruction of formed electrodes, and the like are also suppressed, so that the defective rate is reduced and productivity is improved.
[0016]
Further, in the conventional manufacturing method, in order to suppress the charging of the piezoelectric substrate due to a rapid temperature change, the rate of temperature rise / fall in a process involving a temperature change is slowed. That is, since the heating and cooling of the piezoelectric substrate are performed slowly, the process in the step requires time. In the manufacturing method of the present invention, since a piezoelectric substrate that is difficult to be charged is used, the rate of temperature rise / fall in a step involving a temperature change can be increased. As a result, the processing speed of this step is increased, and a surface acoustic wave filter can be efficiently produced.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the lithium tantalate single crystal, the lithium niobate single crystal, the surface acoustic wave filter, and the method of manufacturing the same according to the present invention will be described in detail. The lithium tantalate single crystal, lithium niobate single crystal, surface acoustic wave filter, and the method of manufacturing the same according to the present invention are not limited to the following embodiments. The lithium tantalate single crystal, the lithium niobate single crystal, the surface acoustic wave filter, and the method of manufacturing the same according to the present invention may be modified or modified by those skilled in the art without departing from the scope of the present invention. It can be implemented in the form.
[0018]
<Lithium tantalate single crystal and lithium niobate single crystal>
Both lithium tantalate single crystal and lithium niobate single crystal of the present invention are selected from iron, copper, manganese, molybdenum, cobalt, nickel, zinc, carbon, magnesium, titanium, tungsten, indium, tin, and rare earth elements. It contains at least one or more additional elements at a ratio of 0.01 wt% or more and 1.00 wt% or less, and has a charge neutralizing property of self-neutralizing and removing surface charges.
[0019]
That is, the single crystal of the present invention contains the predetermined additional element at a rate of 0.01 wt% or more and 1.00 wt% or less. The additive element may be any one of iron, copper, manganese, molybdenum, cobalt, nickel, zinc, carbon, magnesium, titanium, tungsten, indium, tin, and rare earth elements. You may. Among them, iron, copper, cobalt, nickel, manganese, yttrium, and titanium are preferred.
[0020]
The content ratio of the additional element is the mass ratio of the additional element when the total mass of the lithium tantalate single crystal or the lithium niobate single crystal of the present invention is 100 wt%. When the content ratio of the additional element is less than 0.01% by weight, the charge suppressing effect is low. From the viewpoint of further increasing the charge suppression effect, the content ratio of the additional element is desirably 0.02 wt% or more. On the other hand, when the content ratio of the additional element exceeds 1.00 wt%, the additional element segregates in the crystal, and crystal defects are likely to occur. Further, the composition tends to be non-uniform. From the viewpoint of obtaining a single crystal having a more uniform composition, the content ratio of the additional element is desirably 0.50 wt% or less.
[0021]
The method for producing a single crystal of the present invention is not particularly limited. It may be manufactured according to a known method such as the Czochralski method. That is, after mixing and firing a predetermined raw material to form a raw material mixture, the raw material mixture is melted, a seed crystal is immersed in the melt, and then pulled up to obtain a single crystal.
[0022]
<Surface acoustic wave filter>
The surface acoustic wave filter of the present invention is one in which a piezoelectric substrate is manufactured from any one of the above-described lithium tantalate single crystal and lithium niobate single crystal of the present invention. Regardless of which single crystal is used, the ratio of the additional element in the single crystal is desirably 0.02 wt% or more and 0.50 wt% or less. Hereinafter, a surface acoustic wave filter according to an embodiment of the present invention will be described.
[0023]
First, the configuration of the surface acoustic wave filter according to the present embodiment will be described. FIG. 1 is a perspective view illustrating an example of the surface acoustic wave filter according to the present embodiment. As shown in FIG. 1, the surface acoustic wave filter 1 includes a case main body 2 and a chip 3.
[0024]
The case body 2 is made of ceramics and has a rectangular parallelepiped box shape with an open upper surface. The case body 2 is hermetically closed by covering the opening on the upper surface with a lid (not shown).
[0025]
The chip 3 is housed inside the case body 2. The chip 3 includes a piezoelectric substrate 31, input electrodes 32a and 32b, and output electrodes 33a and 33b. The piezoelectric substrate 31 has a flat plate shape. The piezoelectric substrate 31 is made of a lithium tantalate single crystal containing iron at a rate of 0.10 wt%.
[0026]
The input-side electrodes 32a and 32b are made of aluminum and have a comb shape. The input-side electrodes 32a and 32b are arranged on the surface of the piezoelectric substrate 31 so as to face each other in the lateral direction such that their teeth mesh with each other. The input-side electrodes 32a and 32b are electrically connected to the input terminal 21 embedded in the case main body 2 through conductors 320a and 320b.
[0027]
Similarly, the output side electrodes 33a and 33b are made of aluminum and have a comb shape. The output-side electrodes 33a and 33b are arranged on the surface of the piezoelectric substrate 31 so as to face each other in the lateral direction such that their teeth mesh with each other. The output electrodes 33a and 33b are arranged to face the input electrodes 32a and 32b in the longitudinal direction. The output-side electrodes 33a and 33b are electrically connected to the output terminal 22 embedded in the case main body 2 via conductors 330a and 330b.
[0028]
Next, the operation of the surface acoustic wave filter according to the present embodiment will be described. First, a voltage is applied from the input terminal 21 to the input-side electrodes 32a and 32b via the conductors 320a and 320b. Then, due to the piezoelectric effect, opposite phase distortions are generated between the input-side electrodes 32a and 32b, and surface acoustic waves are excited. This surface acoustic wave propagates on the surface of the piezoelectric substrate 31. Distortion occurs on the surface of the piezoelectric substrate 31 due to the propagated surface acoustic waves. An electric charge is generated by the distortion. The generated charges are extracted from the output-side electrodes 33a and 33b as electrical signals via the conductors 330a and 330b and the output terminal 22.
[0029]
According to the present embodiment, the following effects can be obtained. That is, the piezoelectric substrate 31 is made of a single crystal of lithium tantalate containing iron. This single crystal is less likely to generate electric charge even when the temperature changes, and even if electric charge is generated, it can be quickly neutralized and removed. Therefore, the surface acoustic wave filter of the above-described embodiment generates less static electricity during storage and use, and has less risk of electrode breakdown due to electrostatic discharge.
[0030]
In the above embodiment, the piezoelectric substrate was made of a lithium tantalate single crystal containing iron. However, the additive element contained is not limited to iron, and may be appropriately selected from the above-described elements. Further, the piezoelectric substrate may be made of a lithium niobate single crystal containing a predetermined additive element. Further, the material of the input side electrode and the output side electrode is not limited to aluminum, and a metal such as an aluminum alloy, copper, or gold can be used. In the above embodiment, the case body made of ceramics is used. However, the case body may be formed of another insulating material such as a resin.
[0031]
<Production method of surface acoustic wave filter>
The method for manufacturing a surface acoustic wave filter according to the present invention includes a piezoelectric substrate preparing step, an electrode thin film forming step, and an electrode forming step. Hereinafter, each step will be described.
[0032]
(1) Piezoelectric substrate preparation process
In this step, at least one or more additive elements selected from iron, copper, manganese, molybdenum, cobalt, nickel, zinc, carbon, magnesium, titanium, tungsten, indium, tin, and rare earth elements are contained in an amount of 0.01 wt% or more and 1.00 wt %, Which is a step of preparing a piezoelectric substrate made of a lithium tantalate single crystal or a lithium niobate single crystal having a charge neutralization property of self-neutralizing and removing surface charges.
[0033]
For example, a wafer may be prepared by cutting out a predetermined thickness from either the lithium tantalate single crystal or the lithium niobate single crystal of the present invention, and mirror-polishing both surfaces thereof to form a wafer. . Regardless of which single crystal is used, the ratio of the additional element in the single crystal is desirably 0.02 wt% or more and 0.50 wt% or less. In this step, cleaning of the surface of the piezoelectric substrate, surface treatment of the piezoelectric substrate, or the like may be performed as pretreatment of a subsequent step.
[0034]
(2) Electrode thin film forming process
This step is a step of forming an electrode thin film on the surface of the piezoelectric substrate. As a material for the electrode thin film, a metal such as aluminum, an aluminum alloy, copper, or gold may be used. A metal as a material is formed on the surface of the piezoelectric substrate to form an electrode thin film. As a film formation method, a known method such as a sputtering method, a vacuum evaporation method, and a chemical vapor deposition method (CVD method) may be used.
[0035]
Note that, before this step, a conductive film forming step of forming a conductive film for the purpose of removing charge on the back surface of the piezoelectric substrate may be included. In this manufacturing method, the conductive film forming step is unnecessary. However, when the present manufacturing method includes the conductive film forming step, the charging of the piezoelectric substrate can be more effectively suppressed. Furthermore, after this step, a re-cleaning step of cleaning the piezoelectric substrate may be included. Also in this case, similarly to the above, charging of the piezoelectric substrate can be more effectively suppressed.
[0036]
(3) Electrode formation process
In this step, the electrode thin film formed on the surface of the piezoelectric substrate is formed into an electrode having a predetermined shape by photolithography. Photolithography may follow a commonly performed procedure. For example, first, an organic resin as a photoresist is applied on the electrode thin film. Then, prebaking is performed at a temperature of about 70 to 90 ° C. Next, the photoresist is exposed using a photomask or the like on which a pattern such as a metal electrode is formed. Subsequently, post baking is performed at about 130 ° C. Thereafter, development is performed to remove the exposed areas of the photoresist. Finally, wet or dry etching is performed to form an electrode having a predetermined shape.
[0037]
After the electrodes are formed in this step, the piezoelectric substrate may be cut into a predetermined size and housed in a case. Then, a predetermined terminal and an electrode may be connected, and the case may be hermetically closed to form a surface acoustic wave filter.
[0038]
【Example】
Various lithium tantalate single crystals of the present invention were manufactured based on the above embodiment. As a comparative example, lithium tantalate single crystals having different content ratios of the additional elements were manufactured. Then, various measurements were performed on the manufactured lithium tantalate single crystal to evaluate the chargeability and the like. Hereinafter, production of lithium lithium tantalate single crystal, various measurements, and evaluation of chargeability and the like will be described. Hereinafter, the lithium tantalate single crystal is abbreviated as “LT single crystal” as appropriate.
[0039]
<Production of lithium tantalate single crystal>
(1) Iron-containing LT single crystal
Nine kinds of LT single crystals were manufactured by the Czochralski method using iron (Fe) as an additive element and containing 0 to 1.20 wt%. First, iron oxide (Fe ₂ O ₃ ) And lithium carbonate (Li ₂ CO ₃ ) And tantalum pentoxide (Ta) as a tantalum source ₂ O ₅ ) Were mixed in predetermined amounts and calcined at 1000 ° C. for 10 hours to obtain a raw material mixture. The lithium carbonate and tantalum pentoxide used had a purity of 99.99%. Next, the raw material mixture was put in a crucible made of iridium and melted by high-frequency induction heating. The melting temperature was 1700 ° C. A seed crystal cut in a predetermined orientation was immersed in the melt of the raw material mixture and pulled up at a rotation speed of 10 rpm and a pulling speed of 5 mm / hr to obtain a single crystal having a diameter of about 80 mm and a length of about 60 mm. The obtained LT single crystals were numbered as LT single crystals # 11 to # 19 in ascending order of iron content.
[0040]
(2) LT single crystal containing additional elements other than iron
Copper (Cu), cobalt (Co), nickel (Ni), manganese (Mn), yttrium (Y), and titanium (Ti) are used as the additional elements, and six types of LT single crystals having different additional elements are used as iron-containing elements. It was manufactured in the same manner as the LT single crystal. The content ratio of the additional element in each LT single crystal was 0.10 wt%. The obtained LT single crystals were numbered as LT single crystals of # 21 to # 26.
[0041]
<Various measurements on LT single crystal and evaluation of chargeability, etc.>
With respect to the manufactured LT single crystals # 11 to # 19 and # 21 to # 26, crystal blocks each having a thickness of 1 mm were cut out from positions 5 mm and 60 mm from the upper end of the single crystal. Note that the upper end of the single crystal means an end of the single crystal on the seed crystal side in the axial direction, that is, an end on the side pulled up earlier. Next, one side of the cut crystal block was mirror-polished to produce a wafer. That is, for each of the manufactured LT single crystals, two types of wafers having different cutout positions at the upper portion and the lower portion were manufactured. In addition, the one where the cut-out position is upper is the upper crystal wafer and the lower one is the lower crystal wafer. Various measurements were performed using the upper crystal wafer and the lower crystal wafer prepared for each LT single crystal. First, the measured items will be described, and then the measurement results and evaluation will be described.
[0042]
(1) Curie point measurement
The Curie points of the upper crystal wafer and the lower crystal wafer were measured by a differential thermal analyzer (DTA). FIG. 2 shows the measurement position of the Curie point on the wafer. As shown in FIG. 2, the Curie points were measured at the central part (a) of the wafer 600 and at four places (b) to (e) at the inner periphery of 5 mm from the wafer edge, for a total of five places. The difference between the Curie point of the upper crystal wafer and the Curie point of the lower crystal wafer was calculated. The value measured at the center of each wafer was used to calculate the Curie point difference.
[0043]
(2) Presence or absence of segregation of added elements
The presence or absence of segregation of the additional element in the upper crystal wafer and the lower crystal wafer (hereinafter simply referred to as “wafer”) was visually observed. In addition, under a white fluorescent lamp, the inside and the outer periphery of the wafer were visually observed, and the presence or absence of crystal defects such as cracks, bubbles, twins, etc. was examined.
[0044]
(3) Crack-free rate
In producing the LT single crystal, it was investigated how much cracks occurred. 100 pieces of LT single crystals of # 11 to # 19 were produced in the same manner as above, and the ratio of those in which no crack was generated was calculated to be the crack-free rate (%).
[0045]
(4) Measurement of surface potential
With respect to the wafer produced from each of the LT single crystals, the change in the wafer surface potential due to the temperature change was measured. The measurement of the wafer surface potential was performed using a surface potential measurement device. FIG. 3 schematically shows a surface potential measuring device. As shown in FIG. 3, the surface potential measuring device 100 includes a stage 200, an insulating case 300, a surface potential measuring device 400, and a non-contact radiation thermometer 500.
[0046]
The upper surface of the stage 200 can be adjusted to various temperatures. On an upper surface of the stage 200, wafers 601 and 602 to be measured are placed via an insulating case 300 described later. The insulating case 300 is made of Teflon (registered trademark: manufactured by DuPont) and is placed on the upper surface of the stage 200. The charge generated from the wafers 601 and 602 is insulated by the insulating case 300. The surface potential measuring device 400 is disposed above the wafers 601 and 602. The distance between the surface potential measuring device 400 and the wafers 601 and 602 is 50 mm. The surface potential of the wafers 601 and 602 is measured by the surface potential measuring device 400. The non-contact radiation thermometer 500 is disposed above the wafers 601 and 602. The temperature of the wafers 601 and 602 is measured by the non-contact radiation thermometer 500.
[0047]
The surface potential of the wafers 601 and 602 was measured by the following procedure. First, by adjusting the temperature of the stage 200, the temperatures of the wafers 601 and 602 mounted on the upper surface of the stage 200 were raised from room temperature to about 150 ° C. in about 48 minutes. Next, the wafers 601 and 602 were allowed to cool to a temperature of about 30 ° C. During this time, the surface potentials of the wafers 601 and 602 were measured at predetermined time intervals.
[0048]
(5) Observation of electrostatic spark phenomenon
In the same manner as in the measurement of the wafer surface potential in the above (4), the temperature of the wafer was changed, and it was observed whether or not sparks due to static electricity were generated, and the number of occurrences was counted. The observation was performed in a dark room at 20 ° C.
[0049]
(6) Measurement of surface resistance
With respect to the wafer produced from each LT single crystal, the resistance value of the wafer surface at 25 ° C. was measured by a surface resistance meter.
[0050]
(7) Ease of particle adhesion
The ease with which particles such as dust and dirt adhere to the wafer was measured. In a clean room, the wafer was placed in a vertical wafer cassette, and left for 10 hours with the upper part of the wafer cassette opened. Thereafter, the number of particles attached to each wafer was measured with a microscope.
[0051]
(8) Measurement results and evaluation
Table 1 shows the measurement and observation results of the above (1) to (6). In Table 1, “Surface potential: 150 ° C.” is a surface potential value when the temperature of the wafer is increased to about 150 ° C. This value is the highest value of the surface potential measured on each wafer. “Surface potential: 30 ° C.” is a surface potential value when the temperature of the wafer is lowered to about 30 ° C. Further, the “charge neutralization time” is the time from when the temperature of the wafer is raised and after the temperature is started to when the surface potential of the wafer becomes almost 0 kV.
[0052]
[Table 1]

[0053]
First, the uniformity of the composition of the manufactured LT single crystal will be described. The uniformity of the composition can be evaluated by the difference between the Curie point of the upper crystal wafer cut out of the LT single crystal and the Curie point of the lower crystal wafer (curie point vertical difference). In other words, it can be said that the smaller the difference between the Curie points of the upper portion and the lower portion of the single crystal, the more uniform the composition of the single crystal in the axial direction. Further, if the composition is uniform, neither segregation of additional elements nor crystal defects occur.
[0054]
As shown in Table 1, in the LT single crystal of # 11 containing no added element, the Curie point vertical difference was 0.5 ° C. That is, since there is almost no difference in the Curie points between the upper and lower portions of the single crystal, it can be seen that the composition of the # 11 LT single crystal is uniform. On the other hand, the # 19 LT single crystal having an iron content of 1.20 wt% had a Curie point vertical difference of 6.2 ° C. From this, it can be said that the # 19 LT single crystal has a variation in composition between the upper and lower parts. This is clear from the presence or absence of segregation of the added element. If the additional element is not uniformly contained in the crystal, segregation of the additional element appears, and crystal defects are likely to occur. In the # 19 LT single crystal, segregation of iron as an additional element was observed, and crystal defects also occurred.
[0055]
In addition, in the LT single crystals of # 12 to # 18 having an iron content of 0.01 to 1.00 wt%, the difference between the Curie points was 0.2 to 3.5 ° C. This indicates that the compositions of the LT single crystals of # 12 to # 18 are uniform. In addition, in the LT single crystals of # 12 to # 18, no segregation of iron was observed, and no crystal defects occurred. As described above, since the single crystal having the Curie point vertical difference in the above range has a uniform composition, it can be said that it is suitable for producing a piezoelectric substrate of a surface acoustic wave filter. In particular, in the LT single crystals of # 12 to # 17 in which the iron content ratio was 0.01 to 0.50 wt%, the difference between the Curie points in the upper and lower directions was smaller. Therefore, the compositions of the LT single crystals of # 12 to # 17 are more uniform, and are more suitable for producing a piezoelectric substrate of a surface acoustic wave filter.
[0056]
Further, Table 2 shows the Curie point values at the measurement positions (a) to (e) for the upper crystal wafer and the lower crystal wafer of the LT single crystals # 11 and # 15.
[0057]
[Table 2]

[0058]
As is evident from Table 2, there was almost no change in the Curie point value depending on the measurement position in each wafer in both LT single crystals. This shows that the composition is uniform even on the wafer surface. From the above, it was confirmed that the LT single crystal of the present invention containing the additive element at a ratio of 0.01 wt% or more and 1.00 wt% or less has a uniform composition.
[0059]
Next, the crack-free rate will be described. With the # 11 LT single crystal containing no additional element, the crack-free ratio was 90%. Further, the crack free ratio of the LT single crystals # 12 to # 17 containing 0.01 to 0.05 wt% of iron was similar to or higher than that of the LT single crystal of # 11. It is considered that the generation of cracks during the production was suppressed because these LT single crystals were hardly charged.
[0060]
Next, the surface potential of a wafer manufactured from each LT single crystal will be described. Hereinafter, for convenience, the number of each LT single crystal will be used as the number of the wafer. For the wafer # 11 containing no added element, the surface potential at 150 ° C., that is, the maximum value of the surface potential was 14.5 kV. Further, even when the temperature was lowered to about 30 ° C., the surface potential was reduced only to about 7.8 kV. That is, the wafer # 11 continued to be charged even after the temperature was lowered. On the other hand, in the wafers # 12 to # 19 and # 21 to # 26 containing the additional element, the surface potential at 150 ° C. was 6.2 kV or less regardless of the type of the additional element. In particular, in the wafers # 13 to # 17 and # 21 to # 26 in which the content ratio of the additional element was 0.02 to 0.50 wt%, the surface potential was lower. After the temperature was lowered, the surface potential immediately decreased to a very low value. In particular, for wafers # 15 to # 19 containing 0.10 wt% or more of iron, the surface potential was 0 kV, and the charge was completely removed.
[0061]
FIG. 4 shows changes in the surface potential during the process of raising and lowering the temperature of the wafer. FIG. 4 shows wafers # 11 to # 16 as an example. As shown in FIG. 4, as the temperature rose, the surface potential of wafer # 11 increased. On the other hand, in the wafers # 12 to # 16, the surface potential did not increase so much even when the temperature increased. This indicates that the wafers # 12 to # 16 are hardly charged. In the temperature decreasing process, the surface potential of the wafer # 11 once decreased, but continued to maintain a high value. The surface potential of the wafer # 11 did not become 0 kV even after 48 hours. On the other hand, the surface potentials of the wafers # 12 to # 16 rapidly decreased. In particular, the surface potentials of the wafers # 13 to # 16 became almost 0 kV immediately after entering the cooling process. This indicates that the generated charges were quickly removed.
[0062]
Here, the charge neutralization time in each wafer will be described. As described above, the charge neutralization time is the time from when the temperature of the wafer is raised and after the temperature is started to when the surface potential of the wafer becomes substantially 0 kV. For the wafer # 11, the surface potential did not become 0 kV even after 48 hours. Therefore, in Table 1, the charge neutralization time of the wafer # 11 is indicated as “> 2880”. On the other hand, in all the wafers containing the added elements, the surface potential became almost 0 kV over time after the temperature was lowered. In particular, in the wafers # 14 to # 19 containing 0.05 wt% or more of iron, the surface potential became almost 0 kV in a few seconds after the start of the temperature drop.
[0063]
As described above, it was confirmed that the LT single crystal of the present invention containing the additive element at a ratio of 0.01 wt% or more and 1.00 wt% or less is hardly charged even when the temperature changes. It was also confirmed that the LT single crystal of the present invention could be quickly self-neutralized and removed even when a charge was generated.
[0064]
FIG. 5 shows the relationship between the surface potential and the Curie point vertical difference with respect to the iron content in the LT single crystal. The value of the surface potential in FIG. 5 is the value of the surface potential of the wafer when the temperature of the wafer is lowered to about 30 ° C. As shown in FIG. 5, as the content ratio of iron increases, the surface potential of the wafer decreases. On the other hand, when the iron content ratio increases, the difference between the upper and lower Curie points increases. That is, the composition uniformity in the single crystal is reduced. Therefore, by setting the iron content to 0.01 wt% or more and 1.00 wt% or less, it becomes possible to realize an LT single crystal having a low surface potential after temperature drop and a uniform composition.
[0065]
Next, the surface resistance of each wafer will be described. In the wafers # 14, # 15 and # 21 to # 26 including the additional element, the surface resistance is 9.5 × 10 ^Thirteen In contrast to the value of Ω or less, in the case of the wafer # 11 containing no added element, the surface resistance was large (> 1.0 × 10 ^Fifteen Ω). If the surface resistance of the wafer is small, the charge is unlikely to remain, so that the charge neutralization time is considered to be short. In other words, the LT single crystal of the present invention containing the additive element at a ratio of 0.01 wt% or more and 1.00 wt% or less has a small surface resistance value, and therefore quickly self-neutralizes even if a charge is generated. Can be removed.
[0066]
Next, the generation of electrostatic spark of each wafer in the process of raising and lowering the temperature of the wafer will be described. In the # 11 wafer containing no added element, a total of 32 sparks were observed during the cooling process. On the other hand, in each of the wafers # 12, # 21 to # 23, # 25, and # 26, the occurrence of the spark was 1 to 3 times. Further, sparks did not occur at all in the wafers # 13 to # 19 and # 24.
[0067]
FIG. 6 shows the number of occurrences of electrostatic sparks in the process of raising and lowering the temperature of the wafer. FIG. 6 shows wafers # 11 to # 13 as an example. As shown in FIG. 6, during the cooling process, spark was always generated on the wafer # 11. On the other hand, in the case of the wafer # 12, the temperature occurred only twice immediately after the start of cooling. In the case of wafer # 13, no occurrence occurred. When the temperature was raised and lowered by doubling the temperature raising rate and setting the maximum temperature of the wafer to 200 ° C., cracks occurred in the wafer # 11. As a result, the wafer # 11 was broken. On the other hand, cracks did not occur in the wafers # 12 to # 19 and # 21 to # 26. As described above, it was confirmed that the LT single crystal of the present invention containing the additive element at a rate of 0.01 wt% or more and 1.00 wt% or less has a low possibility of electrostatic discharge.
[0068]
Although not shown in Table 1, the number of particles attached to each of the wafers # 12 to # 19 and # 21 to # 26 containing the additive element was smaller than that of the wafer # 11 containing no additional element. It was about 1/10. This indicates that the presence of the additional element suppresses the generation of static electricity on the wafer surface.
[0069]
In summary, the LT single crystal of the present invention containing an additive element such as iron at a ratio of 0.01 wt% or more and 1.00 wt% or less has a uniform composition. Further, even if the temperature changes, it is hard to be charged, and even if a charge is generated, it can be quickly neutralized and removed. That is, even if there is a temperature change, there is little possibility of electrostatic discharge. Therefore, the LT single crystal of the present invention is suitable for a piezoelectric substrate of a surface acoustic wave filter.
[0070]
【The invention's effect】
Both the lithium tantalate single crystal and the lithium niobate single crystal of the present invention contain a predetermined additive element in a ratio of 0.01 wt% or more and 1.00 wt% or less. Therefore, even if the temperature changes, electric charge is hardly generated, and even if electric charge is generated on the single crystal surface, self-neutralization can be quickly performed and the electric charge can be removed. Therefore, if a surface acoustic wave filter is manufactured using the piezoelectric substrate made of the lithium tantalate single crystal or the lithium niobate single crystal of the present invention, installation of static elimination equipment and the like becomes unnecessary, and the cost can be significantly reduced. In addition, since a manufacturing process for removing static electricity is not required, productivity is improved. Furthermore, the surface acoustic wave filter having the piezoelectric substrate manufactured from the single crystal of the present invention has less occurrence of defects due to static electricity even during storage or use.
[Brief description of the drawings]
FIG. 1 is a perspective view illustrating an example of a surface acoustic wave filter according to an embodiment.
FIG. 2 shows a measurement position of a Curie point on a wafer.
FIG. 3 schematically shows a surface potential measuring device.
FIG. 4 shows a change in surface potential during a process of raising and lowering the temperature of a wafer.
FIG. 5 is a graph showing the relationship between the surface potential and the Curie point vertical difference with respect to the iron content in an LT single crystal.
FIG. 6 shows the number of occurrences of electrostatic sparks in the process of raising and lowering the temperature of the wafer.
[Explanation of symbols]
1: Surface acoustic wave filter
2: Case body 21: Input terminal 22: Output terminal
3: Chip
31: Piezoelectric substrate
32a, 32b: input electrode 320a, 320b: conducting wire
33a, 33b: output electrode 330a, 330b: conducting wire
100: Surface potential measuring device
200: Stage 300: Insulating case 400: Surface potential measuring instrument
500: Non-contact radiation thermometer 600, 601, 602: Wafer

Claims (6)

A ratio of at least one additional element selected from iron, copper, manganese, molybdenum, cobalt, nickel, zinc, carbon, magnesium, titanium, tungsten, indium, tin, and rare earth elements in a range of 0.01 wt% to 1.00 wt%. And a charge neutralizing lithium tantalate single crystal which self-neutralizes and removes surface charges. The lithium tantalate single crystal according to claim 1, wherein the content ratio of the additional element is 0.02 wt% or more and 0.50 wt% or less. A ratio of at least one additional element selected from iron, copper, manganese, molybdenum, cobalt, nickel, zinc, carbon, magnesium, titanium, tungsten, indium, tin, and rare earth elements in a range of 0.01 wt% to 1.00 wt%. A lithium niobate single crystal having a charge neutralizing property of self-neutralizing and removing surface charges. The lithium niobate single crystal according to claim 3, wherein the content ratio of the additional element is 0.02 wt% or more and 0.50 wt% or less. A ratio of at least one additional element selected from iron, copper, manganese, molybdenum, cobalt, nickel, zinc, carbon, magnesium, titanium, tungsten, indium, tin, and rare earth elements in a range of 0.01 wt% to 1.00 wt%. A surface acoustic wave filter having a piezoelectric substrate made of a lithium tantalate single crystal or a lithium niobate single crystal having a charge neutralizing property of self-neutralizing and removing surface charges. A ratio of at least one additional element selected from iron, copper, manganese, molybdenum, cobalt, nickel, zinc, carbon, magnesium, titanium, tungsten, indium, tin, and rare earth elements in a range of 0.01 wt% to 1.00 wt%. A piezoelectric substrate preparing step of preparing a piezoelectric substrate made of lithium tantalate single crystal or lithium niobate single crystal having a charge neutralizing property of self-neutralizing and removing surface charge,
An electrode thin film forming step of forming an electrode thin film on the surface of the piezoelectric substrate,
An electrode forming step of forming the electrode thin film into an electrode having a predetermined shape by photolithography,
A method for manufacturing a surface acoustic wave filter comprising:

Images