JP2004177133A

JP2004177133A - Evaluation method and evaluation device for ferroelectric crystal

Info

Publication number: JP2004177133A
Application number: JP2002340177A
Authority: JP
Inventors: Fumiyuki Takahashi; 文之高橋; Hiroyuki Tsukahara; 博之塚原; Takashi Fuse; 貴史布施
Original assignee: Fujitsu Ltd
Current assignee: Fujitsu Ltd
Priority date: 2002-11-22
Filing date: 2002-11-22
Publication date: 2004-06-24

Abstract

<P>PROBLEM TO BE SOLVED: To evaluate the orientation angle in an area of a level of crystal grain in a ferroelectric crystal or smaller than it, by the near field Raman spectrometry. <P>SOLUTION: When a near field light is emitted to the area of the level of crystal grain in the ferroelectric crystal or smaller than it, and when Raman scattered light from the irradiation area is photoreceived and dispersed spectrally to detect photorception intensity, a polarization direction of the Raman scattered light is brought at first into a direction perpendicular to a polarization direction of the near field light (the first condition), then the polarization direction of the near field light is brought into a direction rotated by a prescribed angle ϕ' with respect to the same irradiation area, and the polarization direction of the Raman scattered light is brought into a direction rotated by a prescribed angle ϕ' +90° along the direction same to the rotation of the polarization direction of the near field light (the second condition). An evaluation value is computed based on a difference between the photoreception intensity of the Raman scattered light under the first condition and the photoreception intensity of the Raman scattered light under the second condition, and an orientation condition of the crystal is evaluated based thereon. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、近接場光を利用したラマン分光法による強誘電体結晶の評価方法および評価装置に関する。
【０００２】
近年、半導体メモリとして、不揮発性メモリの一種である強誘電体メモリが提案されている。強誘電体メモリは、ＰＺＴ（Ｐｂ（Ｚｒ，Ｔｉ）Ｏ_３）やＰＬＺＴ（Ｐｂ（Ｚｒ，Ｔｉ，Ｌａ）Ｏ_３）等からなる強誘電体膜の自発分極を利用して情報を記憶する。図１０は、ＰＺＴの結晶構造を示す図である。図１０に示すように、ＰＺＴはペロブスカイト型の結晶構造を有し、外部から電界が加えられると、酸素原子により配位されたＺｒまたはＴｉ原子が結晶主軸方向に変位する。その結果、ＰＺＴは、自発分極特性を示し、これを二値情報とすることにより記憶素子として利用される。
【０００３】
ＰＺＴ等を記憶素子として利用するにあたっては、情報を確実に保持することが重要であり、そのためにはＰＺＴ等の自発分極をできるだけ大きくする必要がある。自発分極を大きくするには、ＰＺＴ等の結晶主軸が強誘電体膜の主面に対してできるだけ垂直であるのが望ましい。このように、強誘電体膜中の結晶粒の配向方向を制御するため、結晶主軸が膜厚方向（空間固定座標系のｚ軸方向）に対してなす角、すなわち配向角θ（図１０参照）を強誘電体膜の面内で微細に計測することが必要となる。
【０００４】
【従来の技術】
従来より、可視光を利用することができる、試料の準備に特別な作業が不要である、非接触計測であるために試料を傷つけるおそれがない、などの特徴を有するラマン分光法が公知である。このラマン分光法により結晶の配向状態を評価する方法として、顕微ラマン分光法が提案されている（たとえば、特許文献１参照。）。
【０００５】
【特許文献１】
特開２０００−６８４６４号公報
【０００６】
ところで、メモリのセルは年々微小化しており、そのサイズは、近時、ミクロン以下になっている。そのため、セル内における結晶粒の配向状態を計測するには、１００ｎｍ程度の空間分解能が必要である。しかし、上記特許文献１によれば、顕微ラマン分光法の空間分解能は６００ｎｍであるため、最近の微細化されたメモリセル内の結晶配向状態を顕微ラマン分光法により計測することは困難である。
【０００７】
一方、非接触でかつ微小領域を計測する方法として、近接場光を利用する方法がある。近接場光を用いると、光の回折限界を超えた分解能で試料表面の微小領域の観測をおこなうことができる。そこで、この近接場光による計測とラマン分光法とを組み合わせることにより、結晶粒程度またはそれよりも微小な領域を計測対象とすることができるので、個々の結晶粒の物性を非接触で解析することが可能となる。
【０００８】
【発明が解決しようとする課題】
しかしながら、従来の近接場光を利用したラマン分光法（以下、近接場ラマン分光法とする）では、結晶分域の回転角φの状態によっては、求めるべき配向角θの値を特定することができないという問題点がある。その理由は、つぎのとおりである。
【０００９】
例として、上述したＰＺＴ薄膜について、ＰＺＴからのラマン散乱光のうち、Ａ１モードの振動に起因するラマンスペクトルに注目して、結晶分域の配向情報を求める場合について説明する。一般的に、ラマン散乱光の散乱強度Ｉは、ラマンテンソルＴを用いて、つぎの（１）式で表される。また、ラマンテンソルＴは、つぎの（２）式で表される。
【００１０】
【数１】

【００１１】
【数２】

【００１２】
ただし、上記（１）式において、Ｅ_ｉは、照射光の空間固定座標系（ｘ，ｙ，ｚ）における電場ベクトル方向の単位ベクトルである。また、Ｅ_ｓは、散乱光の空間固定座標系（ｘ，ｙ，ｚ）における電場ベクトル方向の単位ベクトルである。ここで、空間固定座標系のｚ方向を、試料（強誘電体膜）の膜厚方向とする。ラマンテンソルＴは、観測する物質に固有の形をしており、たとえば正方晶系のＰＺＴ結晶のＡ１モードの格子振動によるラマンテンソルＴは、結晶固定座標系（ｘ’，ｙ’，ｚ’）において、つぎの（３）式で表される（たとえば、非特許文献１参照）。
【００１３】
【数３】

【００１４】
【非特許文献１】
Ｒ．Ｌｏｕｄｏｎ著，“Ａｄｖ．Ｐｈｙｓ．１３”，１９６４年，ｐ．４２３
【００１５】
前記（１）式において、Ｒは、結晶固定座標系（ｘ’，ｙ’，ｚ’）を空間固定座標系（ｘ，ｙ，ｚ）に変換する行列であり、オイラー角γ、φおよびθを用いて、つぎの（４）式で表される。ただし、図１０に示すように、θはＰＺＴ結晶の配向角であり、φは空間固定座標系のｚ軸（ＰＺＴの膜厚方向）周りのＰＺＴ結晶回転角である。
【００１６】
【数４】

【００１７】
ここで、照射光と散乱光の偏光方向を制御して、Ｅ_ｉ＝（１，０，０）、Ｅ_ｓ＝（０，１，０）のように、照射光の偏光方向と垂直の散乱光のみを観測する偏光配置で散乱光を観測した場合、前記（１）式、前記（３）式および前記（４）式から計算される散乱強度Ｉはつぎの（５）式で表される。
【００１８】
【数５】

【００１９】
前記特許文献１では、上記（５）をφについて平均化して簡略化している。これは、図１１に示すように、顕微ラマン光学系の視野には、数百個程度の結晶粒が種々の回転角φで含まれるので、φの効果が平均化されるからである。それに対して、近接場ラマン光学系では、近接場光が照射される範囲は、近接場プローブの先端直径程度であり、たとえば先端径が１００ｎｍ程度のプローブを使用する場合には、近接場の照射（計測）範囲は結晶粒と同じかそれ以下の大きさとなる。したがって、近接場ラマン分光法では、回転角φについて平均化することができないので、観測される散乱強度は、回転角φの影響を受けてしまう。
【００２０】
仮に、近接場ラマン光学系の視野に１個の結晶粒が存在しているとする。この場合、配向角θが０°、５４．７°（［１１１］方向）および９０°について、回転角φを変化させたときの散乱強度の変化の様子を図５に示す。図５から明らかなように、計測範囲にある結晶粒の配向角θが異なっていても、回転角φが０°、９０°および１８０°のときに散乱強度が同一となるため、配向角θを特定することができない。
【００２１】
また、Ｅ_ｉ＝（１，０，０）、Ｅ_ｓ＝（１，０，０）のように、照射光の偏光方向と平行の散乱光のみを観測する偏光配置で散乱光を観測した場合、前記（１）式、前記（３）式および前記（４）式から計算される散乱強度Ｉはつぎの（６）式で表される。
【００２２】
【数６】

【００２３】
再び、近接場ラマン光学系の視野に１個の結晶粒が存在していると仮定して、配向角θが０°、５４．７°および９０°について、回転角φを変化させたときの散乱強度の変化の様子を図１２に示す。図１２から明らかなように、この場合も回転角φが９０°のときに散乱強度が一致してしまうため、配向角θを特定することができない。
【００２４】
本発明は、上記問題点に鑑みてなされたものであって、近接場ラマン分光法により、強誘電体結晶の結晶粒程度またはそれよりも小さい領域の配向角を評価することができる強誘電体結晶の評価方法を提供することを目的とする。また、本発明は、近接場ラマン分光法により、強誘電体結晶の結晶粒程度またはそれよりも小さい領域の配向角を評価するための装置を提供することを目的とする。
【００２５】
【課題を解決するための手段】
上記目的を達成するため、本発明は、強誘電体結晶の結晶粒程度またはそれよりも小さい微小領域に近接場光を照射し、その照射領域からのラマン散乱光を受光し、分光してその受光強度を検出するにあたって、まず、ラマン散乱光の偏光方向を、近接場光の偏光方向に対して垂直な方向とし（第１の状態）、つづいて、同じ照射領域に対して、近接場光の偏光方向を所定角φ’だけ回転させた方向にするとともに、ラマン散乱光の偏光方向を、近接場光の偏光方向の回転と同じ方向にφ’＋９０°だけ回転させた方向とする（第２の状態）ことを特徴とする。
【００２６】
そして、第１の状態におけるラマン散乱光の受光強度と、第２の状態におけるラマン散乱光の受光強度とに基づいて、評価値を演算して求め、照射領域を含まれる結晶の配向状態を評価する。Ａ１モードの振動に起因するラマンスペクトルに注目して、結晶分域の配向情報を求める場合には、φ’を４５°とする。
【００２７】
この発明によれば、ラマン散乱光の偏光方向が、近接場光の偏光方向に対して垂直な方向であるとき（第１の状態）に、異なる配向角θに対して散乱強度が同じになる回転角φの値と、近接場光の偏光方向を所定角φ’だけ回転させた方向にするとともに、ラマン散乱光の偏光方向を、近接場光の偏光方向の回転と同じ方向にφ’＋９０°だけ回転させた方向にしたとき（第２の状態）に、異なる配向角θに対して散乱強度が同じになる回転角φの値とがずれる。
【００２８】
【発明の実施の形態】
以下に、本発明の実施の形態について図面を参照しつつ詳細に説明する。図１は、本発明方法を実施するための光学系の要部の一例を示す図である。図１に示すように、この評価装置の光学系は、近接場光照射手段を構成する散乱型近接場プローブ２、および近接場プローブ２と試料１に外側から照射されるレーザ光（入射光）の偏光方向を制御する第１の偏光制御手段としてのλ／２板６を備えている。レーザ光の照射により、近接場プローブ２の先端において近接場光が生じる。ラマン散乱光は、近接場光が試料１と相互作用することにより生じる。
【００２９】
また、この光学系は、ラマン散乱光の検出偏光方向を制御する第２の偏光制御手段としての偏光板１１、受光したラマン散乱光を分光する手段としての分光器１４、および偏光板１１により偏光制御されたラマン散乱光を分光器１４に導くミラー２１を備えている。なお、ミラー２１はなくてもよい。
【００３０】
図２は、本発明方法を実施するための評価装置の全体構成を示す図である。図２に示すように、この評価装置は、上述した光学系のほかに、近接場光照射手段としてレーザ光を射出するレーザ光源４、レーザ光源４から射出されたレーザ光（入射光）の強度を調整するＮＤ（ＮｅｕｔｒａｌＤｅｎｓｉｔｙ）フィルタ５、ＮＤフィルタ５およびλ／２板６を順次通った入射レーザ光を試料１側へ導くミラー７、ミラー７により導かれたレーザ光を試料１側と光量、周波数検出器１８側ヘ分岐させて導くとともに、試料１からのラマン散乱光を受光光学系へ導くためのハーフミラー８、ハーフミラー８により試料１側へ導かれたレーザ光を試料１および近接場プローブ２に結像させるとともに、ラマン散乱光を集光する対物レンズ９を備えている。
【００３１】
また、評価装置の受光系は、対物レンズ９により集光されたラマン散乱光に対して迷光を除去するための空間フィルタ１０、分光器１４の偏光依存性の影響を除去するための偏光解消板１２、レーリー散乱光を除去するホログラフィックノッチフィルタ１３から構成され、空間フィルタ１０、偏光板１１、偏光解消板１２およびホログラフィックノッチフィルタ１３を順次透過し、分光器１４で分光された光の散乱強度を検出する光強度検出手段としての冷却ＣＣＤ１５を備えている。
【００３２】
また、評価装置は、複数の偏光状態において検出された散乱強度に基づいて、評価値を演算して求める演算手段であるとともに、その評価値に基づいて、近接場光の照射領域内の結晶の配向状態を評価する評価手段でもあるＣＰＵ１７、所望の偏光状態を得るために、λ／２板６および偏光板１１を後述する決められた手順にしたがって回転制御する偏光コントローラ１６を備えている。
【００３３】
また、光量、周波数検出器１８は、入射レーザ光の強度および周波数を逐次検出する。この検出結果に基づいて、ＣＰＵ１７は、冷却ＣＣＤ１５から得られた散乱強度を補正する。このような補正をおこなう理由は、つぎのとおりである。すなわち、前記（１）式、前記（５）式および前記（６）式の定数Ａは入射レーザ強度に比例し、かつ入射レーザ周波数の４乗に比例する。したがって、結晶の配向状態をより正確に評価するためには、入射レーザ強度や入射レーザ周波数の変動など、配向情報以外の散乱強度の変動要因を除去するのが望ましいからである。
【００３４】
また、近接場プローブ２のシアフォース制御をおこなうプローブ操作ヘッド３が設けられている。近接場プローブ２は、プローブ操作ヘッド３により、計測中に試料１との距離が一定となるよう制御される。また、プローブ操作ヘッド３にはＰＺＴステージが搭載されており、近接場プローブ２の位置を試料１上で操作することにより、２次元的にデータを取得できる構成となっている。なお、図２では、ミラー２１は図示省略されている。
【００３５】
ここで、図１に示す光学系に代えて、図３に示すように、λ／２板６により偏光方向が制御された入射レーザ光を、たとえば開口型の近接場プローブ２２内に導入し、プローブ先端の開口部に発生する近接場光を試料１に照射する構成の光学系を用いてもよい。また、特に図示しないが、近接場ファイバープローブとして偏光状態の保存が可能なファイバーを用いてもよい。この場合には、入射レーザ光を近接場ファイバープローブ内に導入するとともに、試料１からのラマン散乱光も近接場ファイバープローブ内を通して受光系に導く構成とすることができる。
【００３６】
つぎに、上述した構成の評価装置を用いて強誘電体結晶の配向角を評価する際の、λ／２板６および偏光板１１の各偏光方向の制御手順について、図４を参照しながら説明する。ここでは、試料１からのラマン散乱光のうち、Ａ１モードの振動に起因するラマンスペクトルに注目する場合を例にして説明する。
【００３７】
まず、Ｅ_ｉ＝（１，０，０）、Ｅ_ｓ＝（０，１，０）とし、入射レーザ光の偏光方向と垂直のラマン散乱光のみを観測する偏光配置とする。これを第１の状態とする。このときのλ／２板６および偏光板１１は、それぞれ図４（ａ）に示す偏光方向となる。この偏光配置でもってラマン散乱光の強度を観測する。得られる散乱強度と回転角φとの関係を図５に示す。図５に示すように、回転角φが０°、９０°および１８０°のときに、配向角が０°、５４．７°および９０°での散乱強度が一致する。なお、図５において、縦軸は、配向角θが０°のときの散乱強度をゼロとしたときの相対強度である。
【００３８】
つづいて、図４（ａ）に片矢印で示すように、偏光板１１を９０°回転させる。これによって、図４（ｂ）に示すように、Ｅ_ｉ＝（１，０，０）、Ｅ_ｓ＝（１，０，０）の偏光配置、すなわち入射レーザ光の偏光方向に平行なラマン散乱光のみを観測する偏光配置となる。さらに、この状態から、図４（ｂ）にそれぞれ片矢印で示すように、λ／２板６および偏光板１１をφ’だけ回転させ、図４（ｃ）に示す偏光配置とする。これを第２の状態とする。この偏光配置でもってラマン散乱光の強度を観測する。
【００３９】
図６に、配向角θが０°のときの散乱強度を１としたときの相対的な散乱強度と回転角φとの関係を示す。図６に示すように、回転角φが１３５°のときに、配向角が０°、５４．７°および９０°での散乱強度が一致する。なお、説明の便宜上、図４（ｂ）の状態を示したが、実際には図４（ａ）に示す第１の状態から図４（ｃ）に示す第２の状態に直接移行する。また、λ／２板６および偏光板１１の回転方向は同じ方向とする。
【００４０】
このようにして得られた第１の状態での散乱強度信号と第２の状態での散乱強度信号とを演算し、配向角の評価をおこなう。具体的には、たとえば第２の状態での散乱強度信号から、第１の状態での散乱強度信号を減算した結果を評価値とする。図５および図６に示す散乱強度に基づいて求めた評価値と回転角φとの関係を図７に示す。図７より、回転角φの値にかかわらず、配向角θが０°の場合と、配向角θが５４．７°または９０°の場合とを、適当な閾値を用いて分離できることがわかる。
【００４１】
なお、上述した第１の状態でラマン散乱光を観測する際の入射レーザ光の強度を、第２の状態でラマン散乱光を観測する際の入射レーザ光の強度のｎ倍としてもよい。ｎは１よりも大きい数である。このようにすれば、配向角θが０°の結晶粒に対する評価値と、それ以外の配向角度を有する結晶粒の評価値とをさらに分離させることができるので、容易かつより正確に配向角を評価することができる。
【００４２】
たとえば、第１の状態でラマン散乱光を観測する際の入射レーザ光の強度を、第２の状態でラマン散乱光を観測する際の入射レーザ光の強度の４倍とし、配向角θが０°のときの散乱強度をゼロとしたときの相対的な散乱強度と回転角φとの関係を図８に示す。この図８に示す散乱強度を図６に示す散乱強度から減算して求めた評価値と回転角φとの関係を図９に示す。図７と比べて明らかなように、図９の方が、配向角θが０°の結晶粒に対する評価値と、それ以外の配向角度を有する結晶粒の評価値との分離度が高いことがわかる。
【００４３】
ここで、Ａ１モードの場合には、配向角θが０°のときとそれ以外のときを分離するための最適な入射光強度の倍率ｎが４付近であることは、前記（５）式および前記（６）式から解析的に導き出すことができる。つまり、前記（５）式における散乱強度Ｉの最大値および前記（６）式における散乱強度Ｉの最大値は、ａとｂの値にもよるが、それぞれＡ／４およびＡとなることがあると考えられる。したがって、第１の状態のときの入射光強度を４倍にすれば、配向角θが０°のときの散乱強度とそれ以外のときの散乱強度とが、より分離されると考えられる。
【００４４】
また、ｎ＝４付近が最適であることは、図５と図６を比較することからも容易に導き出せる。すなわち、第１の状態（図５参照）では、入射光強度の倍率をどのような値にしても、回転角φが９０°のときには配向角θによらず、相対強度がゼロとなる。したがって、回転角φが９０°のときには、第１の状態での入射光強度の倍率を上げても、配向角θが５４．７°に対する評価値の値は変化しない。
【００４５】
そこで、配向角θが５４．７°に対する評価値（図７参照）に関して、回転角φが１３５°のときの評価値を、そのピークを下げて、回転角φが９０°のときの評価値と同程度にすれば、配向角θが０°のときの散乱強度とそれ以外のときの散乱強度との分離度がより高くなる。そのためには、回転角φが１３５°のときの、第１の状態における配向角θが５４．７°と０°との相対散乱強度の差分はおおよそ０．１５であり（図５参照）、第２の状態における配向角θが５４．７°と０°との相対散乱強度の差分がおおよそ０．６である（図６参照）ことから、ｎ＝４が導き出される。ここで、配向角θが５４．７°と０°との相対散乱強度の差分に着目するのは、図５および図６より明らかなように、配向角θが５４．７°の方が９０°よりも、０°との分離度が低いからである。
【００４６】
また、Ａ１モードの場合に、前記φ’の最適値が４５°であることは、図５および図１２より容易に導き出せる。すなわち、図５に示すように、入射レーザ光の偏光方向と垂直のラマン散乱光のみを観測する偏光配置の場合には、回転角φが１３５°のときに、配向角θが０°のときの散乱強度とそれ以外のときの散乱強度との差分が最大となる。一方、図６に示すように、入射レーザ光の偏光方向に対して平行なラマン散乱光のみを観測する偏光配置の場合には、回転角φが９０°のときに、配向角θが０°のときの散乱強度とそれ以外のときの散乱強度との差分が最小となる。
【００４７】
そこで、入射レーザ光の偏光方向に対して平行なラマン散乱光のみを観測する偏光配置からさらに４５°だけ回転した偏光配置にすれば、配向角θが０°のときの散乱強度とそれ以外のときの散乱強度との差分が最小となるときの各相対散乱強度から、配向角θが０°のときの散乱強度とそれ以外のときの散乱強度との差分が最大となるときの各相対散乱強度を減算することになるので、各配向角θに対して、分離度の高い評価値が得られる。
【００４８】
Ａ１モード以外の振動モードに起因するラマンスペクトルに着目する場合には、その振動モードに適した回転角φ’および入射強度倍率ｎをあらかじめ求めておくとよい。その求め方は、たとえば前記（３）式のラマンテンソルＴを注目する振動モードに対応するものに置き換え、前記（５）式および前記（６）式に相当する、２つの偏光条件に対応する２つの散乱強度式を算出する。そして、２つの散乱強度式のうち、一方のφを（φ＋α）と置き換え、αを所定角ずつ３６０°変えながら（たとえば、０．５°ステップで３６０°までとすれば十分である）、各配向角θにおける散乱強度を求め、２つの偏光条件における散乱強度の差が、区別したい配向角間において最大となるαをφ’とする。また、一方のφを（φ＋φ’）とした条件で，一方の散乱強度をβ倍（たとえば、０．２倍ステップで５倍程度まで）しながら、２つの偏光条件における散乱強度の差が、区別したい配向角間において最大となるβをｎとする。
【００４９】
ところで、上述した説明および添付図面では、ラマン散乱光強度は、Ｅ_ｉ＝（１，０，０）、Ｅ_ｓ＝（１，０，０）の偏光配置でもってラマン散乱光を観測したときに得られる最大強度（配向角θ＝０°の結晶から得られる強度）を１とした相対強度である。したがって、実際には、あらかじめＥ_ｉ＝（１，０，０）、Ｅ_ｓ＝（１，０，０）の偏光配置でもって、試料の広い範囲について計測をおこない、最大強度を求めておく必要がある。そして、その最大強度と上述した評価値との差分量の絶対値を求め、その絶対値があらかじめ決められてなる閾値よりも大きいか、それとも小さいかによって、結晶の配向状態を評価すればよい。
【００５０】
上述した実施の形態によれば、前記第１の状態における散乱強度と前記第２の状態における散乱強度との差分をとり、それを評価値とすることによって、強誘電体結晶の回転角φによらず、強誘電体結晶の結晶粒程度またはそれよりも小さい領域の配向角を評価することができる。したがって、強誘電体メモリの性能をより正確に評価することが可能となり、製品状態の事前チェックや、メモリ性能を向上させるための研究効率や、正確性が著しく向上する。
【００５１】
（付記１）強誘電体結晶の結晶粒程度またはそれよりも小さい微小領域に、第１の偏光方向の近接場光を照射し、第１の偏光方向の近接場光が照射された照射領域からの第２の偏光方向のラマン散乱光を受光し、分光して前記第２の偏光方向のラマン散乱光の受光強度を検出する工程と、
前記照射領域に、第３の偏光方向の近接場光を照射し、第３の偏光方向の近接場光が照射された照射領域からの第４の偏光方向のラマン散乱光を受光し、分光して前記第４の偏光方向のラマン光の受光強度を検出する工程と、
前記第２の偏光方向のラマン散乱光の受光強度および前記第４の偏光方向のラマン散乱光の受光強度に基づいて、評価値を演算して求める工程と、
前記評価値に基づいて、前記照射領域を含む結晶の配向状態を評価する工程と、
を含むことを特徴とする強誘電体結晶の評価方法。
【００５２】
（付記２）前記第１の偏光方向と前記第２の偏光方向とは垂直であり、前記第３の偏光方向は前記第１の偏光方向を所定角φ’だけ回転させた方向であり、前記第４の偏光方向は、前記第１の偏光方向から前記第３の偏光方向への回転方向と同じ方向に、前記第２の偏光方向をφ’＋９０°だけ回転させた方向であることを特徴とする付記１に記載の強誘電体結晶の評価方法。
【００５３】
（付記３）あらかじめ、近接場光の偏光方向とラマン散乱光の偏光方向が水平となる条件でもって、試料の複数箇所の強誘電体結晶に対して、結晶粒程度またはそれよりも小さい微小領域に、近接場光を照射し、前記近接場光が照射された照射領域からのラマン散乱光を受光し、分光して前記ラマン散乱光の受光強度を検出し、ラマン散乱光強度の最大値を求めておくことを特徴とする付記２に記載の強誘電体結晶の評価方法。
【００５４】
（付記４）前記評価値と前記ラマン散乱光強度の最大値を差分した値の絶対値の大小に基づいて、結晶の配向状態を評価することを特徴とする付記３に記載の強誘電体結晶の評価方法。
【００５５】
（付記５）Ａ１モードの振動に起因するラマンスペクトルに対して、前記第４の偏光方向のラマン散乱光の受光強度から前記第２の偏光方向のラマン散乱光の受光強度を減算することにより、前記評価値を求めることを特徴とする付記２〜４のいずれか一つに記載の強誘電体結晶の評価方法。
【００５６】
（付記６）前記φ’は４５°であることを特徴とする付記５に記載の強誘電体結晶の評価方法。
【００５７】
（付記７）前記第１の偏光方向の近接場光を発生させるための入射レーザ光の強度を、前記第３の偏光方向の近接場光を発生させるための入射レーザ光の強度のｎ倍とすることを特徴とする付記５または６に記載の強誘電体結晶の評価方法および評価装置。
【００５８】
（付記８）前記近接場光を発生させるための入射レーザ光の強度および周波数を検出し、検出された強度および周波数に基づいて、前記ラマン散乱光の受光強度を補正しながら、強誘電体結晶の評価をおこなうことを特徴とする付記１〜７のいずれか一つに記載の強誘電体結晶の評価方法。
【００５９】
（付記９）任意の振動モードに起因するラマンスペクトルに対して、前記φ’をあらかじめ求めておくことを特徴とする付記２に記載の強誘電体結晶の評価方法。
【００６０】
（付記１０）任意の振動モードに起因するラマンスペクトルに対して、前記第１の偏光方向の近接場光を発生させるための入射レーザ光の強度を、前記第３の偏光方向の近接場光を発生させるための入射レーザ光の強度のｎ倍とし、前記第４の偏光方向のラマン散乱光の受光強度から前記第２の偏光方向のラマン散乱光の受光強度を減算することにより、前記評価値を求めることを特徴とする付記２〜４のいずれか一つに記載の強誘電体結晶の評価方法。
【００６１】
（付記１１）強誘電体結晶の結晶粒程度またはそれよりも小さい微小領域に近接場光を照射する近接場光照射手段と、
前記近接場光の偏光方向を、第１の偏光方向と、前記第１の偏光方向を所定角φ’だけ回転させた第３の偏光方向とに可変制御する第１の偏光制御手段と、前記近接場光の照射領域からのラマン散乱光を受光し、分光して前記ラマン散乱光の受光強度を検出する光強度検出手段と、
前記近接場光が前記第１の偏光方向であるときには、前記第１の偏光方向に垂直な第２の偏光方向とし、前記近接場光が前記第３の偏光方向であるときには、前記第１の偏光方向から前記第３の偏光方向への回転方向と同じ方向に、前記第２の偏光方向をφ’＋９０°だけ回転させた第４の偏光方向となるように、前記ラマン散乱光の偏光方向を可変制御する第２の偏光制御手段と、
前記第２の偏光方向のラマン散乱光の受光強度および前記第４の偏光方向のラマン散乱光の受光強度に基づいて、評価値を演算して求める演算手段と、
前記評価値に基づいて、前記照射領域を含む結晶の配向状態を評価する評価手段と、
を具備することを特徴とする強誘電体結晶の評価装置。
【００６２】
（付記１２）前記近接場光を発生させるための入射レーザ光の強度および周波数を検出する光量、周波数検出手段をさらに具備し、前記演算手段は、光量、周波数検出手段により検出された入射レーザ光の強度および周波数に基づいて、前記評価値の補正をおこなうことを特徴とする付記１１に記載の強誘電体結晶の評価装置。
【００６３】
【発明の効果】
本発明によれば、ラマン散乱光の偏光方向が、近接場光の偏光方向に対して垂直な方向であるとき（第１の状態）に、異なる配向角θに対して散乱強度が同じになる回転角φの値と、近接場光の偏光方向を所定角φ’だけ回転させた方向にするとともに、ラマン散乱光の偏光方向を、近接場光の偏光方向の回転と同じ方向にφ’＋９０°だけ回転させた方向にしたとき（第２の状態）に、異なる配向角θに対して散乱強度が同じになる回転角φの値とがずれる。したがって、第１の状態における散乱強度と第２の状態における散乱強度との差分をとり、それを評価値とすることによって、強誘電体結晶の回転角φによらず、強誘電体結晶の結晶粒程度またはそれよりも小さい領域の配向角を評価することができる。
【図面の簡単な説明】
【図１】本発明方法を実施するための光学系の要部の一例を示す図である。
【図２】本発明方法を実施するための評価装置の全体構成を示す図である。
【図３】本発明方法を実施するための光学系の要部の他の例を示す図である。
【図４】照射光および散乱光の偏光方向の制御手順を説明するための模式図である。
【図５】配向角θが０°、５４．７°および９０°について、照射光の偏光方向に対して垂直な偏光方向の散乱光を観測したときの散乱強度と回転角φとの関係を示す図である。
【図６】配向角θが０°、５４．７°および９０°について、照射光の偏光方向に対して平行な偏光方向の散乱光を、入射光および散乱光の偏光方向をともに４５°回転させて観測したときの散乱強度と回転角φとの関係を示す図である。
【図７】図５および図６に示す散乱強度に基づいて求めた評価値と回転角φとの関係を示す図である。
【図８】配向角θが０°、５４．７°および９０°について、入射光強度を４倍して、照射光の偏光方向に対して垂直な偏光方向の散乱光を観測したときの散乱強度と回転角φとの関係を示す図である。
【図９】図８および図６に示す散乱強度に基づいて求めた評価値と回転角φとの関係を示す図である。
【図１０】ＰＺＴの結晶構造を示す図である。
【図１１】近接場ラマン法と顕微ラマン法の計測範囲の違いを模式的に示す図である。
【図１２】配向角θが０°、５４．７°および９０°について、照射光の偏光方向に対して平行な偏光方向の散乱光を観測したときの散乱強度と回転角φとの関係を示す図である。
【符号の説明】
１試料
２，２２近接場光照射手段（散乱型近接場プローブ）
４近接場光照射手段（レーザ光源）
６第１の偏光制御手段（λ／２板）
１１第２の偏光制御手段（偏光板）
１４光強度検出手段（分光器）
１５光強度検出手段（冷却ＣＣＤ）
１７演算手段、評価手段（ＣＰＵ）[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for evaluating a ferroelectric crystal by Raman spectroscopy using near-field light.
[0002]
In recent years, a ferroelectric memory, which is a type of nonvolatile memory, has been proposed as a semiconductor memory. Ferroelectric memory is composed of PZT (Pb (Zr, Ti) O ₃ ) Or PLZT (Pb (Zr, Ti, La) O ₃ ) Is used to store information by utilizing spontaneous polarization of the ferroelectric film. FIG. 10 is a diagram showing a crystal structure of PZT. As shown in FIG. 10, PZT has a perovskite crystal structure, and when an electric field is applied from the outside, Zr or Ti atoms coordinated by oxygen atoms are displaced in the main crystal axis direction. As a result, PZT exhibits spontaneous polarization characteristics, and is used as a storage element by converting this into binary information.
[0003]
When using PZT or the like as a storage element, it is important to securely retain information, and for that purpose, it is necessary to maximize the spontaneous polarization of PZT or the like. In order to increase spontaneous polarization, it is desirable that the crystal main axis of PZT or the like be as perpendicular to the main surface of the ferroelectric film as possible. As described above, in order to control the orientation direction of the crystal grains in the ferroelectric film, the angle formed by the crystal main axis with respect to the film thickness direction (the z-axis direction of the space fixed coordinate system), that is, the orientation angle θ (see FIG. ) Must be finely measured in the plane of the ferroelectric film.
[0004]
[Prior art]
Conventionally, Raman spectroscopy is known which has features such as being capable of utilizing visible light, requiring no special work for sample preparation, and having no risk of damaging the sample due to non-contact measurement. . Micro Raman spectroscopy has been proposed as a method for evaluating the orientation state of crystals by Raman spectroscopy (for example, see Patent Document 1).
[0005]
[Patent Document 1]
JP-A-2000-68464
[0006]
By the way, memory cells are miniaturized year by year, and their size has recently become smaller than a micron. Therefore, in order to measure the orientation state of the crystal grains in the cell, a spatial resolution of about 100 nm is required. However, according to Patent Document 1, since the spatial resolution of the micro-Raman spectroscopy is 600 nm, it is difficult to measure the crystal orientation state in recent miniaturized memory cells by the micro-Raman spectroscopy.
[0007]
On the other hand, as a method of measuring a minute area without contact, there is a method of using near-field light. When near-field light is used, a minute region on the sample surface can be observed with a resolution exceeding the diffraction limit of light. Therefore, by combining this near-field measurement and Raman spectroscopy, it is possible to measure a crystal grain or a region smaller than that, so that the physical properties of individual crystal grains are analyzed in a non-contact manner. It becomes possible.
[0008]
[Problems to be solved by the invention]
However, in the conventional Raman spectroscopy using near-field light (hereinafter, referred to as near-field Raman spectroscopy), the value of the orientation angle θ to be obtained may be specified depending on the state of the rotation angle φ of the crystal domain. There is a problem that can not be. The reason is as follows.
[0009]
As an example, a case will be described in which the orientation information of the crystal domain is obtained by focusing on the Raman spectrum caused by the A1 mode vibration among the Raman scattered light from the PZT in the above-described PZT thin film. Generally, the scattering intensity I of Raman scattered light is expressed by the following equation (1) using a Raman tensor T. The Raman tensor T is expressed by the following equation (2).
[0010]
(Equation 1)

[0011]
(Equation 2)

[0012]
However, in the above equation (1), E _i Is a unit vector in the electric field vector direction in the spatial fixed coordinate system (x, y, z) of the irradiation light. Also, E _s Is a unit vector in the electric field vector direction in the spatial fixed coordinate system (x, y, z) of the scattered light. Here, the z direction of the space fixed coordinate system is defined as the thickness direction of the sample (ferroelectric film). The Raman tensor T has a shape peculiar to the substance to be observed. For example, the Raman tensor T due to the lattice vibration of the A1 mode of the tetragonal PZT crystal is expressed in a crystal fixed coordinate system (x ′, y ′, z ′). Is expressed by the following equation (3) (for example, see Non-Patent Document 1).
[0013]
[Equation 3]

[0014]
[Non-patent document 1]
R. Loudon, "Adv. Phys. 13", 1964, p. 423
[0015]
In the above equation (1), R is a matrix for converting the crystal fixed coordinate system (x ′, y ′, z ′) into the space fixed coordinate system (x, y, z), and includes Euler angles γ, φ, and θ. And is expressed by the following equation (4). Here, as shown in FIG. 10, θ is the orientation angle of the PZT crystal, and φ is the rotation angle of the PZT crystal around the z-axis (PZT film thickness direction) of the space fixed coordinate system.
[0016]
(Equation 4)

[0017]
Here, by controlling the polarization directions of the irradiation light and the scattered light, E _i = (1,0,0), E _s = (0,1,0), when the scattered light is observed in a polarization arrangement that observes only the scattered light perpendicular to the polarization direction of the irradiation light, the expressions (1), (3), and ( The scattering intensity I calculated from the equation (4) is expressed by the following equation (5).
[0018]
(Equation 5)

[0019]
In Patent Document 1, the above (5) is averaged for φ to simplify it. This is because, as shown in FIG. 11, since the field of view of the microscopic Raman optical system contains about several hundred crystal grains at various rotation angles φ, the effect of φ is averaged. On the other hand, in the near-field Raman optical system, the irradiation range of the near-field light is about the tip diameter of the near-field probe. For example, when a probe having a tip diameter of about 100 nm is used, the near-field irradiation is performed. The (measurement) range is equal to or smaller than the crystal grain. Therefore, in the near-field Raman spectroscopy, since the rotation angle φ cannot be averaged, the observed scattering intensity is affected by the rotation angle φ.
[0020]
It is assumed that one crystal grain exists in the visual field of the near-field Raman optical system. In this case, FIG. 5 shows how the scattering intensity changes when the rotation angle φ is changed when the orientation angle θ is 0 °, 54.7 ° ([111] direction), and 90 °. As is clear from FIG. 5, even if the orientation angles θ of the crystal grains in the measurement range are different, the scattering intensity becomes the same when the rotation angle φ is 0 °, 90 °, and 180 °. Can not be identified.
[0021]
Also, E _i = (1,0,0), E _s = (1,0,0), when the scattered light is observed in a polarization arrangement that observes only the scattered light parallel to the polarization direction of the irradiation light, the expressions (1), (3), and ( The scattering intensity I calculated from the equation (4) is expressed by the following equation (6).
[0022]
(Equation 6)

[0023]
Again, assuming that one crystal grain exists in the visual field of the near-field Raman optical system, when the rotation angle φ is changed for the orientation angles θ of 0 °, 54.7 ° and 90 °. FIG. 12 shows how the scattering intensity changes. As is clear from FIG. 12, in this case as well, when the rotation angle φ is 90 °, the scattering intensities match, so that the orientation angle θ cannot be specified.
[0024]
The present invention has been made in view of the above-mentioned problems, and a ferroelectric material capable of evaluating the orientation angle of a crystal grain of a ferroelectric crystal or a region smaller than the crystal grain by near-field Raman spectroscopy. An object of the present invention is to provide a method for evaluating a crystal. Another object of the present invention is to provide an apparatus for evaluating the orientation angle of a region of about the size of a ferroelectric crystal or smaller than that by a near-field Raman spectroscopy.
[0025]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is to irradiate near-field light to a microscopic region of a ferroelectric crystal grain size or smaller, receive Raman scattered light from the irradiated region, and spectrally divide the light. In detecting the received light intensity, first, the polarization direction of the Raman scattered light is set to a direction perpendicular to the polarization direction of the near-field light (first state). Is rotated by a predetermined angle φ ′, and the polarization direction of the Raman scattered light is rotated by φ ′ + 90 ° in the same direction as the rotation of the polarization direction of the near-field light (No. 2).
[0026]
Then, an evaluation value is calculated and obtained based on the received light intensity of the Raman scattered light in the first state and the received light intensity of the Raman scattered light in the second state to evaluate the orientation state of the crystal including the irradiation region. I do. When the orientation information of the crystal domain is obtained by focusing on the Raman spectrum caused by the A1 mode vibration, φ ′ is set to 45 °.
[0027]
According to the present invention, when the polarization direction of the Raman scattered light is perpendicular to the polarization direction of the near-field light (first state), the scattering intensity becomes the same for different orientation angles θ. The value of the rotation angle φ and the polarization direction of the near-field light are rotated by a predetermined angle φ ′, and the polarization direction of the Raman scattered light is changed to φ ′ + 90 in the same direction as the rotation of the polarization direction of the near-field light. When the direction is rotated by an angle of ° (the second state), the value of the rotation angle φ at which the scattering intensity becomes the same for different orientation angles θ deviates.
[0028]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing an example of a main part of an optical system for carrying out the method of the present invention. As shown in FIG. 1, the optical system of this evaluation apparatus includes a scattering type near-field probe 2 constituting a near-field light irradiating unit, and a laser beam (incident light) that irradiates the near-field probe 2 and the sample 1 from outside. Λ / 2 plate 6 as first polarization control means for controlling the polarization direction of the light. By the irradiation of the laser light, near-field light is generated at the tip of the near-field probe 2. Raman scattered light is generated when near-field light interacts with the sample 1.
[0029]
This optical system is polarized by a polarizing plate 11 as second polarization control means for controlling the detection polarization direction of the Raman scattered light, a spectroscope 14 as a means for dispersing the received Raman scattered light, and a polarizing plate 11. A mirror 21 is provided to guide the controlled Raman scattered light to the spectroscope 14. Note that the mirror 21 may not be provided.
[0030]
FIG. 2 is a diagram showing the overall configuration of an evaluation device for implementing the method of the present invention. As shown in FIG. 2, in addition to the above-described optical system, this evaluation apparatus includes a laser light source 4 that emits laser light as a near-field light irradiation unit, and the intensity of laser light (incident light) emitted from the laser light source 4. (Neutral Density) filter 5, which adjusts the wavelength, mirror 7 for guiding the incident laser light passing through ND filter 5 and λ / 2 plate 6 to sample 1 side, and the laser light guided by mirror 7 to the sample 1 side and light intensity And a half mirror 8 for guiding the Raman scattered light from the sample 1 to the light receiving optical system while branching it to the frequency detector 18 side. An objective lens 9 that forms an image on the field probe 2 and condenses Raman scattered light is provided.
[0031]
The light receiving system of the evaluation device includes a spatial filter 10 for removing stray light from the Raman scattered light condensed by the objective lens 9 and a depolarizing plate for removing the polarization dependency of the spectroscope 14. 12, a holographic notch filter 13 for removing Rayleigh scattered light, which sequentially transmits through the spatial filter 10, the polarizing plate 11, the depolarizing plate 12, and the holographic notch filter 13 and scatters light dispersed by the spectroscope 14. A cooling CCD 15 is provided as light intensity detecting means for detecting the intensity.
[0032]
In addition, the evaluation device is an arithmetic unit that calculates and calculates an evaluation value based on scattering intensity detected in a plurality of polarization states, and based on the evaluation value, a crystal of the crystal in the near-field light irradiation region. The CPU 17 also serves as an evaluation means for evaluating the alignment state, and a polarization controller 16 for controlling the rotation of the λ / 2 plate 6 and the polarizing plate 11 in accordance with a predetermined procedure described later to obtain a desired polarization state.
[0033]
The light quantity and frequency detector 18 sequentially detects the intensity and frequency of the incident laser light. Based on this detection result, the CPU 17 corrects the scattering intensity obtained from the cooled CCD 15. The reason for performing such correction is as follows. That is, the constant A in the equations (1), (5) and (6) is proportional to the incident laser intensity and is proportional to the fourth power of the incident laser frequency. Therefore, in order to more accurately evaluate the orientation state of the crystal, it is desirable to remove a variation factor of the scattering intensity other than the orientation information, such as a variation of the incident laser intensity or the incident laser frequency.
[0034]
Further, a probe operation head 3 for performing shear force control of the near-field probe 2 is provided. The near-field probe 2 is controlled by the probe operation head 3 so that the distance from the sample 1 during measurement is constant. Further, a PZT stage is mounted on the probe operation head 3, and data can be acquired two-dimensionally by operating the position of the near-field probe 2 on the sample 1. In FIG. 2, the mirror 21 is not shown.
[0035]
Here, instead of the optical system shown in FIG. 1, as shown in FIG. 3, an incident laser beam whose polarization direction is controlled by the λ / 2 plate 6 is introduced into, for example, an aperture type near-field probe 22, An optical system configured to irradiate the sample 1 with near-field light generated in the opening at the tip of the probe may be used. Although not particularly shown, a fiber capable of preserving the polarization state may be used as the near-field fiber probe. In this case, the configuration can be such that the incident laser light is introduced into the near-field fiber probe, and the Raman scattered light from the sample 1 is guided to the light receiving system through the near-field fiber probe.
[0036]
Next, a control procedure of each polarization direction of the λ / 2 plate 6 and the polarizing plate 11 when evaluating the orientation angle of the ferroelectric crystal using the evaluation device having the above-described configuration will be described with reference to FIG. I do. Here, a case will be described as an example in which, among the Raman scattered lights from the sample 1, attention is paid to a Raman spectrum caused by vibration in the A1 mode.
[0037]
First, E _i = (1,0,0), E _s = (0,1,0), and the polarization arrangement is such that only the Raman scattered light perpendicular to the polarization direction of the incident laser light is observed. This is referred to as a first state. At this time, the λ / 2 plate 6 and the polarizing plate 11 have the polarization directions shown in FIG. With this polarization arrangement, the intensity of the Raman scattered light is observed. FIG. 5 shows the relationship between the obtained scattering intensity and the rotation angle φ. As shown in FIG. 5, when the rotation angles φ are 0 °, 90 °, and 180 °, the scattering intensities at the orientation angles of 0 °, 54.7 °, and 90 ° match. In FIG. 5, the vertical axis indicates the relative intensity when the scattering intensity when the orientation angle θ is 0 ° is zero.
[0038]
Subsequently, as shown by a single arrow in FIG. 4A, the polarizing plate 11 is rotated by 90 °. As a result, as shown in FIG. _i = (1,0,0), E _s = (1,0,0), that is, a polarization arrangement for observing only Raman scattered light parallel to the polarization direction of the incident laser light. Further, from this state, the λ / 2 plate 6 and the polarizing plate 11 are rotated by φ ′ as indicated by single arrows in FIG. 4B, respectively, to obtain the polarization arrangement shown in FIG. 4C. This is a second state. With this polarization arrangement, the intensity of the Raman scattered light is observed.
[0039]
FIG. 6 shows the relationship between the relative scattering intensity and the rotation angle φ when the scattering intensity when the orientation angle θ is 0 ° is 1. As shown in FIG. 6, when the rotation angle φ is 135 °, the scattering intensities at the orientation angles of 0 °, 54.7 ° and 90 ° match. Although the state shown in FIG. 4B is shown for convenience of description, the state directly shifts from the first state shown in FIG. 4A to the second state shown in FIG. 4C. The rotation directions of the λ / 2 plate 6 and the polarizing plate 11 are the same.
[0040]
The scattered intensity signal in the first state and the scattered intensity signal in the second state thus obtained are calculated, and the orientation angle is evaluated. Specifically, for example, the result of subtracting the scattered intensity signal in the first state from the scattered intensity signal in the second state is used as the evaluation value. FIG. 7 shows the relationship between the evaluation value obtained based on the scattering intensity shown in FIGS. 5 and 6 and the rotation angle φ. From FIG. 7, it can be seen that, regardless of the value of the rotation angle φ, the case where the orientation angle θ is 0 ° and the case where the orientation angle θ is 54.7 ° or 90 ° can be separated using an appropriate threshold value.
[0041]
Note that the intensity of the incident laser light when observing the Raman scattered light in the first state may be n times the intensity of the incident laser light when observing the Raman scattered light in the second state. n is a number greater than one. In this way, the evaluation value for a crystal grain having an orientation angle θ of 0 ° and the evaluation value for a crystal grain having another orientation angle can be further separated, so that the orientation angle can be easily and more accurately determined. Can be evaluated.
[0042]
For example, the intensity of the incident laser light when observing the Raman scattered light in the first state is four times the intensity of the incident laser light when observing the Raman scattered light in the second state, and the orientation angle θ is 0. FIG. 8 shows the relationship between the relative scattering intensity and the rotation angle φ when the scattering intensity at ° is zero. FIG. 9 shows the relationship between the evaluation value obtained by subtracting the scattering intensity shown in FIG. 8 from the scattering intensity shown in FIG. 6 and the rotation angle φ. As is apparent from comparison with FIG. 7, FIG. 9 shows that the degree of separation between the evaluation value for a crystal grain having an orientation angle θ of 0 ° and the evaluation value for a crystal grain having another orientation angle is higher. Understand.
[0043]
Here, in the case of the A1 mode, the optimal incident light intensity magnification n for separating the case where the orientation angle θ is 0 ° and the other cases is around 4, which is expressed by the above equation (5). It can be analytically derived from the above equation (6). That is, the maximum value of the scattering intensity I in the above equation (5) and the maximum value of the scattering intensity I in the above equation (6) may be A / 4 and A, respectively, depending on the values of a and b. it is conceivable that. Therefore, if the incident light intensity in the first state is quadrupled, it is considered that the scattering intensity when the orientation angle θ is 0 ° and the scattering intensity in other cases are more separated.
[0044]
Further, the fact that n = 4 is optimal can be easily derived from a comparison between FIG. 5 and FIG. That is, in the first state (see FIG. 5), the relative intensity is zero regardless of the orientation angle θ when the rotation angle φ is 90 °, regardless of the value of the magnification of the incident light intensity. Therefore, when the rotation angle φ is 90 °, the value of the evaluation value for the orientation angle θ of 54.7 ° does not change even if the magnification of the incident light intensity in the first state is increased.
[0045]
Therefore, as for the evaluation value for the orientation angle θ of 54.7 ° (see FIG. 7), the evaluation value when the rotation angle φ is 135 ° is reduced to the evaluation value when the rotation angle φ is 90 °. When the orientation angle is about the same as above, the degree of separation between the scattering intensity when the orientation angle θ is 0 ° and the scattering intensity when the orientation angle θ is other than that is higher. For this purpose, when the rotation angle φ is 135 °, the difference in relative scattering intensity between the orientation angle θ of 54.7 ° and 0 ° in the first state is approximately 0.15 (see FIG. 5), Since the difference in relative scattering intensity between the orientation angle θ of 54.7 ° and 0 ° in the second state is approximately 0.6 (see FIG. 6), n = 4 is derived. Here, paying attention to the difference in relative scattering intensity between the orientation angle θ of 54.7 ° and 0 °, it is clear that the orientation angle θ of 54.7 ° is 90%, as is clear from FIGS. This is because the degree of separation from 0 ° is lower than 0 °.
[0046]
In the case of the A1 mode, the fact that the optimum value of φ ′ is 45 ° can be easily derived from FIGS. That is, as shown in FIG. 5, in the case of the polarization arrangement in which only the Raman scattered light perpendicular to the polarization direction of the incident laser light is observed, when the rotation angle φ is 135 ° and the orientation angle θ is 0 ° Is the largest. On the other hand, as shown in FIG. 6, in the case of the polarization arrangement in which only the Raman scattered light parallel to the polarization direction of the incident laser light is observed, when the rotation angle φ is 90 °, the orientation angle θ is 0 °. The difference between the scattering intensity at the time of and the scattering intensity at other times is minimized.
[0047]
Therefore, if the polarization arrangement rotated only 45 ° is changed from the polarization arrangement observing only the Raman scattered light parallel to the polarization direction of the incident laser light, the scattering intensity when the orientation angle θ is 0 ° and the other The relative scattering intensity when the difference between the scattering intensity when the orientation angle θ is 0 ° and the relative scattering intensity when the difference between the scattering intensity when the orientation angle θ is not 0 ° and the scattering intensity when the orientation angle θ is 0 ° is the maximum. Since the intensity is subtracted, an evaluation value with a high degree of separation is obtained for each orientation angle θ.
[0048]
When paying attention to a Raman spectrum caused by a vibration mode other than the A1 mode, a rotation angle φ ′ and an incident intensity magnification n suitable for the vibration mode may be obtained in advance. The method of obtaining the value is, for example, replacing the Raman tensor T in the expression (3) with the one corresponding to the vibration mode of interest, and corresponding to the two polarization conditions corresponding to the expressions (5) and (6). Calculate the two scattering intensity equations. Then, of the two scattering intensity expressions, one φ is replaced with (φ + α), and α is changed by 360 ° by a predetermined angle (for example, it is sufficient to set it to 360 ° in 0.5 ° steps). The scattering intensity at the orientation angle θ is determined, and α at which the difference between the scattering intensities under the two polarization conditions is maximum between the orientation angles to be distinguished is φ ′. Further, under the condition that one φ is (φ + φ ′), while the scattering intensity of one is β times (for example, up to about 5 times in 0.2 times steps), the difference between the scattering intensities under the two polarization conditions is: The maximum β between the orientation angles to be distinguished is n.
[0049]
Incidentally, in the above description and the accompanying drawings, the Raman scattered light intensity is E _i = (1,0,0), E _s = (1, 0, 0) is a relative intensity with the maximum intensity (intensity obtained from a crystal having an orientation angle θ = 0 °) obtained when Raman scattered light is observed with a polarization arrangement of 1 being 1. Therefore, in practice, E _i = (1,0,0), E _s With a polarization arrangement of = (1,0,0), it is necessary to measure over a wide range of the sample to obtain the maximum intensity. Then, the absolute value of the difference between the maximum intensity and the above-described evaluation value is obtained, and the orientation state of the crystal may be evaluated based on whether the absolute value is larger or smaller than a predetermined threshold value.
[0050]
According to the above-described embodiment, the difference between the scattered intensity in the first state and the scattered intensity in the second state is obtained, and the difference is used as an evaluation value. Regardless, it is possible to evaluate the orientation angle of a region of about the size of the ferroelectric crystal grains or smaller. Therefore, it is possible to more accurately evaluate the performance of the ferroelectric memory, and the pre-check of the product state, the research efficiency for improving the memory performance, and the accuracy are remarkably improved.
[0051]
(Supplementary Note 1) Irradiating near-field light in a first polarization direction to a minute region about or smaller than a crystal grain of a ferroelectric crystal, and irradiating the near-field light in the first polarization direction from the irradiation region Receiving the Raman scattered light in the second polarization direction, and detecting the received light intensity of the Raman scattered light in the second polarization direction;
The irradiation region is irradiated with near-field light in a third polarization direction, and Raman scattered light in a fourth polarization direction from the irradiation region irradiated with the near-field light in the third polarization direction is received and separated. Detecting the received light intensity of the Raman light in the fourth polarization direction by
Calculating and calculating an evaluation value based on the received light intensity of the Raman scattered light in the second polarization direction and the received light intensity of the Raman scattered light in the fourth polarization direction;
Based on the evaluation value, the step of evaluating the orientation state of the crystal including the irradiation region,
A method for evaluating a ferroelectric crystal, comprising:
[0052]
(Supplementary Note 2) The first polarization direction and the second polarization direction are perpendicular to each other, and the third polarization direction is a direction obtained by rotating the first polarization direction by a predetermined angle φ ′. The fourth polarization direction is a direction obtained by rotating the second polarization direction by φ ′ + 90 ° in the same direction as the rotation direction from the first polarization direction to the third polarization direction. 2. The method for evaluating ferroelectric crystals according to Supplementary Note 1.
[0053]
(Supplementary Note 3) Under a condition that the polarization direction of the near-field light and the polarization direction of the Raman scattered light are horizontal in advance, a micro-area of about a crystal grain or smaller than a plurality of ferroelectric crystals in the sample. Irradiates near-field light, receives the Raman scattered light from the irradiation area irradiated with the near-field light, detects the received light intensity of the Raman scattered light, and detects the maximum value of the Raman scattered light intensity. The method for evaluating a ferroelectric crystal according to Supplementary Note 2, wherein the evaluation is performed in advance.
[0054]
(Supplementary note 4) The ferroelectric crystal according to supplementary note 3, wherein the orientation state of the crystal is evaluated based on the magnitude of the absolute value of the difference between the evaluation value and the maximum value of the Raman scattered light intensity. Evaluation method.
[0055]
(Supplementary Note 5) By subtracting the received light intensity of the Raman scattered light in the second polarization direction from the received light intensity of the Raman scattered light in the fourth polarization direction with respect to the Raman spectrum caused by the vibration in the A1 mode, The method for evaluating a ferroelectric crystal according to any one of supplementary notes 2 to 4, wherein the evaluation value is obtained.
[0056]
(Supplementary Note 6) The method for evaluating a ferroelectric crystal according to Supplementary Note 5, wherein φ ′ is 45 °.
[0057]
(Supplementary Note 7) The intensity of the incident laser light for generating the near-field light in the first polarization direction is n times the intensity of the incident laser light for generating the near-field light in the third polarization direction. 7. The method and apparatus for evaluating a ferroelectric crystal according to Supplementary Note 5 or 6, wherein:
[0058]
(Supplementary Note 8) The ferroelectric crystal detects the intensity and frequency of the incident laser light for generating the near-field light, and corrects the received light intensity of the Raman scattered light based on the detected intensity and frequency. 8. The method for evaluating a ferroelectric crystal according to any one of supplementary notes 1 to 7, wherein the evaluation is performed.
[0059]
(Supplementary note 9) The method for evaluating a ferroelectric crystal according to supplementary note 2, wherein φ ′ is determined in advance for a Raman spectrum caused by an arbitrary vibration mode.
[0060]
(Supplementary Note 10) For a Raman spectrum caused by an arbitrary vibration mode, the intensity of the incident laser light for generating the near-field light in the first polarization direction is determined by the near-field light in the third polarization direction. The evaluation value is obtained by subtracting the received light intensity of the Raman scattered light in the second polarization direction from the received light intensity of the Raman scattered light in the fourth polarization direction with n times the intensity of the incident laser light to be generated. 3. The method for evaluating a ferroelectric crystal according to any one of supplementary notes 2 to 4, wherein
[0061]
(Supplementary Note 11) Near-field light irradiating means for irradiating near-field light to a minute region about or smaller than a crystal grain of a ferroelectric crystal,
A first polarization control unit that variably controls a polarization direction of the near-field light to a first polarization direction and a third polarization direction obtained by rotating the first polarization direction by a predetermined angle φ ′; Light intensity detection means for receiving the Raman scattered light from the irradiation region of the near-field light, spectrally detecting the received light intensity of the Raman scattered light,
When the near-field light is the first polarization direction, the second polarization direction is perpendicular to the first polarization direction. When the near-field light is the third polarization direction, the first polarization direction is the first polarization direction. The polarization direction of the Raman scattered light so as to be the fourth polarization direction obtained by rotating the second polarization direction by φ ′ + 90 ° in the same direction as the rotation direction from the polarization direction to the third polarization direction. Second polarization control means for variably controlling
Calculating means for calculating and calculating an evaluation value based on the received light intensity of the Raman scattered light in the second polarization direction and the received light intensity of the Raman scattered light in the fourth polarization direction;
Evaluation means for evaluating the orientation state of the crystal including the irradiation region, based on the evaluation value,
An apparatus for evaluating a ferroelectric crystal, comprising:
[0062]
(Supplementary Note 12) The apparatus further includes a light quantity and frequency detecting means for detecting the intensity and frequency of the incident laser light for generating the near-field light, and the calculating means includes an incident laser light detected by the light quantity and frequency detecting means. 12. The apparatus for evaluating a ferroelectric crystal according to claim 11, wherein the evaluation value is corrected based on the intensity and frequency of the ferroelectric crystal.
[0063]
【The invention's effect】
According to the present invention, when the polarization direction of the Raman scattered light is a direction perpendicular to the polarization direction of the near-field light (first state), the scattering intensity becomes the same for different orientation angles θ. The value of the rotation angle φ and the polarization direction of the near-field light are rotated by a predetermined angle φ ′, and the polarization direction of the Raman scattered light is changed to φ ′ + 90 in the same direction as the rotation of the polarization direction of the near-field light. When the direction is rotated by an angle of ° (the second state), the value of the rotation angle φ at which the scattering intensity becomes the same for different orientation angles θ deviates. Therefore, by taking the difference between the scattering intensity in the first state and the scattering intensity in the second state and using the difference as an evaluation value, the crystal of the ferroelectric crystal can be obtained regardless of the rotation angle φ of the ferroelectric crystal. It is possible to evaluate the orientation angle in a region of a grain size or smaller.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of a main part of an optical system for carrying out a method of the present invention.
FIG. 2 is a diagram showing an overall configuration of an evaluation device for implementing the method of the present invention.
FIG. 3 is a diagram showing another example of a main part of an optical system for carrying out the method of the present invention.
FIG. 4 is a schematic diagram for explaining a control procedure of a polarization direction of irradiation light and scattered light.
FIG. 5 shows the relationship between the scattering intensity and the rotation angle φ when observing scattered light in a polarization direction perpendicular to the polarization direction of irradiation light when the orientation angle θ is 0 °, 54.7 °, and 90 °. FIG.
FIG. 6 rotates the scattered light in the polarization direction parallel to the polarization direction of the irradiation light by 45 ° for both the incident light and the scattered light when the orientation angle θ is 0 °, 54.7 °, and 90 °. FIG. 6 is a diagram showing a relationship between the scattering intensity and the rotation angle φ when observed by observing the laser beam.
FIG. 7 is a diagram showing a relationship between an evaluation value obtained based on the scattering intensity shown in FIGS. 5 and 6 and a rotation angle φ.
FIG. 8 shows the scattering when the incident light intensity is quadrupled and the scattered light in the polarization direction perpendicular to the polarization direction of the irradiation light is observed for the orientation angles θ of 0 °, 54.7 ° and 90 °. FIG. 4 is a diagram illustrating a relationship between intensity and rotation angle φ.
FIG. 9 is a diagram showing a relationship between an evaluation value obtained based on the scattering intensity shown in FIGS. 8 and 6 and a rotation angle φ.
FIG. 10 is a diagram showing a crystal structure of PZT.
FIG. 11 is a diagram schematically showing a difference in a measurement range between the near-field Raman method and the microscopic Raman method.
FIG. 12 shows the relationship between the scattering intensity and the rotation angle φ when observing scattered light in a polarization direction parallel to the polarization direction of irradiation light when the orientation angle θ is 0 °, 54.7 °, and 90 °. FIG.
[Explanation of symbols]
1 sample
2,22 Near-field light irradiation means (scattering near-field probe)
4 Near-field light irradiation means (laser light source)
6 First polarization control means (λ / 2 plate)
11 Second polarization control means (polarizing plate)
14. Light intensity detection means (spectrometer)
15 Light intensity detection means (cooled CCD)
17 Calculation means, evaluation means (CPU)

Claims

Irradiating near-field light in a first polarization direction to a crystal region about the size of a ferroelectric crystal or a small region smaller than the crystal grain, and irradiating the near-field light in the first polarization direction from the irradiation region. Receiving Raman scattered light in a second polarization direction, spectrally detecting the received light intensity of the Raman scattered light,
The irradiation region is irradiated with near-field light in a third polarization direction, and Raman scattered light in a fourth polarization direction from the irradiation region irradiated with the near-field light in the third polarization direction is received. Detecting the received light intensity of the Raman scattered light in the fourth polarization direction,
Calculating and calculating an evaluation value based on the received light intensity of the Raman scattered light in the second polarization direction and the received light intensity of the Raman scattered light in the fourth polarization direction;
Based on the evaluation value, the step of evaluating the orientation state of the crystal including the irradiation region,
A method for evaluating a ferroelectric crystal, comprising:

The first polarization direction is perpendicular to the second polarization direction, the third polarization direction is a direction obtained by rotating the first polarization direction by a predetermined angle φ ′, and the fourth polarization direction is the fourth polarization direction. The direction is a direction obtained by rotating the second polarization direction by φ ′ + 90 ° in the same direction as the rotation direction from the first polarization direction to the third polarization direction. 2. The method for evaluating a ferroelectric crystal according to item 1.

In advance, under the condition that the polarization direction of the near-field light and the polarization direction of the Raman scattered light are horizontal, the near-field Irradiating light, receiving Raman scattered light from the irradiation area irradiated with the near-field light, detecting the received light intensity of the Raman scattered light, and obtaining the maximum value of the Raman scattered light intensity. 3. The method for evaluating a ferroelectric crystal according to claim 2, wherein:

4. The method for evaluating a ferroelectric crystal according to claim 3, wherein an orientation state of the crystal is evaluated based on a magnitude of an absolute value of a difference between the evaluation value and a maximum value of the Raman scattered light intensity. .

Near-field light irradiating means for irradiating near-field light to a minute region about or smaller than a crystal grain of a ferroelectric crystal,
First polarization control means for variably controlling the polarization direction of the near-field light to a first polarization direction and a third polarization direction obtained by rotating the first polarization direction by a predetermined angle φ ′,
Light intensity detecting means for receiving Raman scattered light from the irradiation region of the near-field light, spectrally detecting the received light intensity of the Raman scattered light,
When the near-field light is the first polarization direction, the second polarization direction is perpendicular to the first polarization direction. When the near-field light is the third polarization direction, the first polarization direction is the first polarization direction. The polarization direction of the Raman scattered light so as to be the fourth polarization direction obtained by rotating the second polarization direction by φ ′ + 90 ° in the same direction as the rotation direction from the polarization direction to the third polarization direction. Second polarization control means for variably controlling
Calculating means for calculating and calculating an evaluation value based on the received light intensity of the Raman scattered light in the second polarization direction and the received light intensity of the Raman scattered light in the fourth polarization direction;
Evaluation means for evaluating the orientation state of the crystal including the irradiation region, based on the evaluation value,
An apparatus for evaluating a ferroelectric crystal, comprising: