JP2004247685A

JP2004247685A - Method and device for forming transparent electrode thin film

Info

Publication number: JP2004247685A
Application number: JP2003038503A
Authority: JP
Inventors: Shin Shimozawa; 慎下沢; Shinji Fujikake; 伸二藤掛
Original assignee: Fuji Electric Holdings Ltd
Current assignee: Fuji Electric Co Ltd
Priority date: 2003-02-17
Filing date: 2003-02-17
Publication date: 2004-09-02
Anticipated expiration: 2023-02-17
Also published as: JP3846633B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a forming method and a device of a transparent electrode thin film by which the resistivity of the transparent electrode is reduced, the quality and the productivity of the film is improved by uniformizing the heating temperature of a substrate and shortening a heating time. <P>SOLUTION: A device for forming the transparent electrode thin film formed by sputtering or vapor deposition is provided with a generating source a3 of particles such as a sputtering target or a vapor depositing source opposite to a substrate a1 in a vacuum vessel a2, and heaters (h2s and h1) as heating means of the substrates on the both sides of a film forming surface side and a non-film forming surface side by sandwiching the substrate. The substrate is heated up to a prescribed temperature from the both sides of the film forming surface side and the non-film forming surface side of the substrate to form the film. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
この発明は、透明電極薄膜形成方法および装置、特に、フィルム基板にアモルファスシリコン，多結晶シリコン，微結晶シリコン等の薄膜太陽電池や薄膜トランジスタ（ＴＦＴ）等の薄膜半導体デバイスを形成する場合に、その基板上に、減圧下において、スパッタ法または蒸着法により透明電極薄膜を形成する透明電極薄膜形成方法および装置に関する。
【０００２】
【従来の技術】
一般的に、透明導電膜の作製方法には物理的作製法としてスパツタ法や蒸着法等があり、化学的作製法としてはスプレー法やディツプ法、ＣＶＤ法等が挙げられ、各研究機関等で種々の用途に適した膜を、種々の手法で透明電極の作製が試みられている。蒸着法としては、通常の真空蒸着（電子ビーム加熱、抵抗加熱）、イオンプレーティングなどがある。
【０００３】
上記各種方法において、真空装置内で、４０Ｐａ以下（スパッタ法または蒸着法等では２Ｐａ以下）の減圧下で透明電極を作製するような場合、装置内の熱伝導の悪さから目的の温度までの上昇、また装置内温度分布が均一になるまでに時間を要する。ここでは、そのような中で薄膜太陽電池に透明導電膜を形成する従来例について述べる（例えば、特許文献１および２参照）。
【０００４】
アモルファスシリコン（ａ‐Ｓｉ）や微結晶シリコンからなる薄膜非単結晶シリコンを用いた太陽電池は、薄膜、低温プロセス、大面積化が容易という特徴を持ち、低コスト太陽電池の本命として開発が進められている。この種の太陽電池はガラスやＰＥＴ等の透光性基板あるいはステンレスホイルやポリイミド等の非透光性基板を用い、光入射側から透明電極、非単結晶光電変換層、金属電極を順次積層した構造となっている。
【０００５】
具体的なプロセス手順の一例としては、基板上に金属電極を形成した後、プラズマＣＶＤ装置により非単結晶からなる薄膜のｐｉｎ型光電変換素子を堆積した後、透明電極としてＩＴＯをマグネトロンスパッタ法により製膜する。なお、マグネトロンスパッタ法としては、ＤＣマグネトロンスパッタ法またはＲＦマグネトロンスパッタ法があり、いずれでもよい。また、透明電極としては、ＩＴＯだけでなく、ＳｎＯ_２やＺｎＯ等、光電変換素子が吸収を生じる波長領域の波長を比較的透過し、かつ比較的低抵抗という特徴を有する薄膜であれば適用できる。
【０００６】
ＩＴＯを製膜するスパッタ装置は、真空装置内に主に基板を加熱するヒーターと、ヒーターと対向して平行に設置してあるＩＴＯターゲットから成る。ターゲットと基板間の距離は、３〜１０ｃｍ程度が一般的である。この製造装置内に、既に第一電極、ｐｉｎ型光電変換層を製膜した基板を、非製膜面側をヒーターに接触させた状態で設置し、真空引きを行った後、放電ガスとしてＡｒ＋Ｏ_２ガス（Ｏ_２濃度１〜５％）を導入し、装置内圧力を１〜２０Ｐａ程度に保持する。この時、ビーター温度は１００〜２００℃とする。
【０００７】
ヒーターによる基板の加熱は、生産性を考慮して１〜５分程度の比較的短時間の加熱とする。この時、基板にプラスチック基板やステンレス基板等の可とう性基板を適用した場合、基板の皺や反り等で実際の基板温度に分布が出る。例えば、ヒーター温度が２００℃の場合、基板温度はおよそ１２０℃土２０℃程度の分布が出る。これは、大面積基板になる程その影響が大きくなる。
【０００８】
その後、ターゲット〜基板間に直流、もしくは高周波電力を印加し、放電させることによってスパッタを行う。スパッタの際、マグネツトは固定式を採用しても製膜は行えるが、ターゲット寿命の長期化、また面内膜厚均一性の向上のためにマグネットを可動式にする方が好ましい。また、ＤＣ放電の場合、放電の持続性を向上させるために、基板とターゲットの間にアノード電極一個、もしくは複数個を挿入しても良い。アノード電極を固定すると、固定されたアノード電極とターゲット間で放電が集中してしまい、ターゲットの短寿命化をもたらす。また、ステッピングロール装置等の基板を固定した製膜を行う際、薄膜の不均一性が問題となる。上記のような方法を用いて得られるＩＴＯ膜は、アモルファスもしくは結晶率の比較的低い微結晶状態であり、透明電極としての重要な機能の一つである抵抗率は結晶化したＩＴＯ膜に劣る。
【０００９】
前記薄膜の不均一性の問題を解決するために、例えば、前記特許文献１に開示される発明のように、アノード電極を可動させる可動部を設ける。アノード電極は、ターゲットから１〜２ｃｍの距離に設置する。
【００１０】
また、ＩＴＯは光電変換層の直上に製膜することから、特許文献２に開示されたようなステッピングロール装置のように、光電変換層の製膜を行う装置と同真空装置内でスパッタを行うことが好ましい。光電変換層を製膜するプラズマＣＶＤ装置と、ＩＴＯを製膜するスパッタ装置が異なる装置の場合には、光電変換層を製膜後、一度エアーブレイクする必要があり、その際にパーティクルが薄膜表面に付着し、リークの原因となる他、生産性の低下に繋がる。
【００１１】
【特許文献１】
特開平９−２６８３６９号公報（第３−５頁、図１，２）
【特許文献２】
特開平６−２９１３４９号公報（第４−６頁、図１，図５−１７）
【００１２】
【発明が解決しようとする課題】
ところで、生産性を考慮して、基板および製膜装置内の所要部分等の加熱時間が十分に取れない場合、基板等の温度を十分に上昇させることができなくなり、透明電極の膜質の劣化等が生ずる。
【００１３】
また、ｎｉｐ型光電変換層上にＩＴＯ薄膜を形成する際、基板加熱用ヒーターのみで基板の加熱を行う場合であって、特に、基板がフィルム基板やステンレス基板等の場合、フィルムの皺や反り等でヒーターによる加熱が均一に行われず、その結果膜質等の均一性が損なわれて分布が生じ、抵抗率が増大して太陽電池の特性が低下する問題がある。
【００１４】
さらに、ヒーターによる加熱時間を長くすると、生産性を低下させてしまう。また、ヒーターの温度を上げすぎると、光電変換素子部分の温度が高くなり、例えばｎｉｐ型光電変換層中のｐ層にドーピングされたボロンがｉ層中に拡散してしまい、光電変換素子の性能が大きく低下してしまう問題がある。
【００１５】
上記のような加熱に関わる問題は、特に、スパッタリングや蒸着のように製膜時の圧力が２Ｐａ以下と低い場合に、ガスの熱伝導によって均熱性を保つことが困難なために、より大きな問題となる。
【００１６】
この発明は、上記のような問題点を解消するためになされたもので、本発明の課題は、基板の加熱温度の均一化および加熱時間の短縮化を図り、もって透明電極の抵抗率の低減と膜質の向上並びに生産性の向上を図った透明電極薄膜の形成方法と装置を提供することにある。
【００１７】
【課題を解決するための手段】
前述の課題を解決するため、この発明においては、薄膜半導体デバイスの基板上に、減圧下において、スパッタ法または蒸着法により透明電極薄膜を形成する方法において、前記基板の製膜面側および非製膜面側の両側から基板を所定温度に加熱して製膜する（請求項１の発明）。これにより、基板の加熱温度の均一化および加熱時間の短縮化を図ることができる。
【００１８】
また、前記発明の実施態様としては、下記請求項２ないし５の発明が好ましい。即ち、請求項１に記載の薄膜形成方法において、前記基板の所定温度は、１５０〜２００℃とする。基板の温度は、サブストレート型太陽電池の場合、下地のデバイスの熱劣化を防ぐために２００〜２５０℃以下に設定する必要がある。また、基板にプラスチックフィルムを用いる場合には、サブストレート型、スーパーストレート型に関係なく耐熱温度の関係で３００℃以下とする必要があり、ポリエチレンテレフタレート（ＰＥＴ），ポリエチレンナフタレート（ＰＥＮ），ポリエーテルサルフォン（ＰＥＳ）等のフィルムを用いる場合には、１５０〜２００℃とする必要がある。この発明は、基板温度の上限が２００℃程度に設定されるような微細な制御が必要な場合に、特に有効である。
【００１９】
また、請求項１または２に記載の薄膜形成方法において、前記薄膜形成時の圧力は、２Ｐａ以下とする（請求項３の発明）。この発明は、前述のように、ガスの熱伝導によって均熱性を保つことが困難な２Ｐａ以下の場合に有効である。
【００２０】
さらに、請求項１ないし３のいずれか１項に記載の薄膜形成方法において、前記基板は、樹脂フィルム基板やステンレススティールフィルム基板等の可とう性基板とする（請求項４の発明）。さらにまた、請求項１ないし４のいずれか１項に記載の薄膜形成方法において、前記透明電極薄膜は、薄膜太陽電池用の透明電極薄膜とする（請求項５の発明）。
【００２１】
また、上記発明の方法を実施するための装置としては、下記請求項６の発明が好ましい。即ち、請求項１ないし５のいずれか１項に記載の透明電極薄膜形成方法を実施するためのスパッタまたは蒸着による薄膜形成装置であって、真空容器内に、基板に対面して、スパッタターゲットまたは蒸着源を有し、かつ基板を挟んでその製膜面側および非製膜面側の両側に基板の加熱手段を備えるものとする。
【００２２】
前記請求項６の発明の実施態様としては、下記請求項７ないし９の発明が好ましい。即ち、請求項６に記載の透明電極薄膜形成装置において、前記製膜面側の加熱手段は、基板の製膜面に対向して複数個の開口を有する棒状，網目状もしくは平板状のヒーターとする（請求項７の発明）。複数個の開口は、スパッタターゲットまたは蒸着源と基板との間を閉塞しないようにするための開口である。
【００２３】
また、請求項７に記載のスパッタによる透明電極薄膜形成装置において、前記製膜面側の加熱手段としてのヒーターの外殻部材は金属とし、前記ヒーターはアノード電極を兼ねる構成とする（請求項８の発明）。これにより、ヒーターにアノード電極としての機能を付与できる。
【００２４】
さらに、請求項８に記載のスパッタによる透明電極薄膜形成装置において、前記アノード電極を兼ねる構成のヒーターは、基板の製膜面と平行に可動させる可動装置を備えるものとする（請求項９の発明）。面内膜厚均一性の向上のために、ヒーターを可動式にする方が好ましい。
【００２５】
【発明の実施の形態】
図面に基づき、本発明の実施の形態について以下に述べる。
【００２６】
図１は、本発明の実施の形態に関わる基本的な透明電極薄膜形成装置の模式的概略構成図を示す。図１に示すように、真空容器ａ２内に基板ａ１を挟んで非製膜面側のヒーターｈ１と製膜面側ヒーターｈ２を一個、または複数個配置する。また、スパッタターゲツトや蒸発源等の透明電極を形成する粒子の発生源ａ３を、製膜面側ヒーターｈ２の反基板側に設け、粒子の基板ａ１への流れを塞がないように、製膜面側ヒーターｈ２の形状は、例えば、複数個の開口を有する棒状、網目状、平板状、あるいはリング状にする。また、スパッタ法を用いて製膜を行う場合には、製膜面側ヒーターｈ２の外部材質を金属として、アノード電極を兼用する。また、製膜面側ヒーターｈ２には、基板ａ１と平行方向に可動させる図示しない駆動装置を取り付ける。
【００２７】
図２は、本発明に関わる装置のうち、スパッタ法を用いて透明電極膜を形成する装置の実施の形態の模式的概略構成図を示す。図中、真空容器ａ２内にヒーターｈ１、スパッタターゲツトａ３１、マグネットａ４が設置してあり、ヒーターｈ１上に基板ａ１が設置してある。スパッタターゲツトａ３１には、ＤＣ電源が接続され、スパッタターゲツトとしてはＩＴＯを用い、基板ａ１には可とう性基板のポリイミド基板を適用した。
【００２８】
また、基板ａ１とスパッタターゲツトａ３１との間には、リング状の棒状ヒーターｈ２１が取り付けてある。リング状の棒状ヒーターｈ２１は、マグネットａ４の外周の寸法とほぼ同寸法のヒーターとした。図２の実施例では、棒状ヒーターｈ２１を一つ設けた例を示すが、例えば、図３に示すように、ヒーターを複数個上下２段に配置し、加熱効果を高めることも出来る。
【００２９】
棒状ヒーターｈ２１は外部材質が金属であるヒーターを用い、電位的に接地電位となるような電気的接続を施した。この場合、棒状ヒーターｈ２１には、アノード電極としての役割も付与するが、棒状ヒーターｈ２１の材質は、絶縁物でも加熱機能を有していれば良い。また、基板１ａとスパッタターゲツトａ３１との距離は、５ｃｍで、スパッタターゲツトａ３１と棒状ヒーターｈ２１との距離は１ｃｍとした。棒状ヒーターｈ２１は、加熱効果を向上させるために基板ａ１側に近づけても良い。この場合、棒状ヒーターｈ２１のアノード電極としての効果は小さくなる。
【００３０】
マグネットａ４および棒状ヒーターｈ２１は、ターゲットの利用効率向上と薄膜の面内均一性向上のため、基板と平行に稼動する可動式を用いた。棒状ヒーターｈ２１およびマグネットａ４は、製膜室外の図示しないモーターによって駆動される駆動軸によって往復運動する移動台に固定されている。また、棒状ヒーターｈ２１は、移動台を介して外部ヒーター電源まで接続されており、電源を調整することにより温度を制御できる。
【００３１】
図１に示す製膜面側ヒーターｈ２は、図２に示した棒状の他に、平板状や網目状等でも良いが、透明電極を形成する粒子を発生させる機能を有する粒子の発生源ａ３と基板ａ１との間を塞がないように、開口を有する必要がある。図４に、網目状ヒーターｈ３を用いた場合の一例を示す。図４では、網目状ヒーターｈ３を、基板ａ１〜網目状ヒーターｈ３間距離より基板ａ１〜粒子の発生源ａ３間距離が小さくなるように設置したが、加熱効果を向上させるために網目状ヒーターｈ３を基板ａ１に近づけても良い。この場合、網目状ヒーターｈ３のアノード電極としての効果は小さくなる。
【００３２】
【実施例】
次に、図２の実施の形態のスパッタ装置により製膜した場合の実施例について、以下に述べる。図２におけるヒーターｈ１と棒状ヒーターｈ２１とは、それぞれ独立に温度制御機構を有しており、それぞれ独立に温度を設定できる。このような設備を有する透明電極スパッタ室を、前記特許文献２に開示されたような、光電変換層を形成するプラズマＣＶＤ室と連結させたステッピングロール方式の装置であって、各層の製膜を行い、かつ真空を保ったまま製膜面を搬送できる装置を用いて製膜を行った。
【００３３】
実施例に用いた装置は、４０ｃｍ×８０ｃｍの比較的大面積の光電変換素子を一度で作製できる機能を有する。このような装置を用いて、サブストレート型光電変換素子を作製した。ポリイミド基板上に既に金属電極の製膜を終了した基板をステッピングロール方式の装置に入れ、真空引き後、搬送を行いながら光電変換層の各層をプラズマＣＶＤ法を用いて製膜を行った後、透明電極スパッタ室まで搬送した。透明電極を製膜する直前までで、基板１ａ上には既に金属電極、ｐｉｎ型光電変換層が製膜してある。光電変換層としては、ａ‐Ｓｉシングルセルとａ‐ＳｉＧｅシングルセルとを直列に接続したａ‐Ｓｉ／ａ‐ＳｉＧｅタンデムセルを作製した。
【００３４】
透明電極の製膜条件としては、ヒーターｈ１を２００℃、棒状ヒーターｈ２１を非加熱および３００℃の２通りの条件で製膜を行った。事前に、棒状ヒーターｈ２１の各温度条件において熱電対を用いた基板温度の測定を行ったところ、非加熱の場合、４０ｃｍ×８０ｃｍの面内において１２０℃±２０℃程度の温度分布が存在していたのに対し、３００℃（基板と平行に棒状ヒーターｈ２１を可動させた状態）では、１７０℃土５℃となり、基板温度の高温化と温度の均一性向上が図られていることが分かった。
【００３５】
スパッタ室まで搬送後、スパッタ室内を外部と隔離して真空引きを行った後、ＡｒとＯ_２の混合ガスをスパッタ室内に入れ、２Ｐａに保持した。この作業中からマグネットａ４、棒状ヒーターｈ２１を基板ａ１と平行方向に可動させ始めた。Ｏ_２の流量は、各条件でＩＴＯの膜中酸素濃度が約１．２％程度になるような流量を用いた。その後、圧力安定と基板加熱のため、約１分その状態を保持した後、ＤＣ電源からＤＣを５００Ｗ印加した。事前に調べてある製膜レートから、透明電極の膜厚が約８０ｎｍ程度になるようにスパッタ時間を調節した。
【００３６】
製膜終了後、完成した光電変換素子を真空容器から取り出し、モジュール化工程を経て太陽電池の作製を終了した。今回は、製膜条件の全く同じセルを各２サンプル以上作製し、そのうち１サンプルはモジュール化工程を行わず、透明電極のシート抵抗評価用サンプルとした。
【００３７】
各条件で作製した太陽電池の特性を調べるため、モジュール化した太陽電池を用いて白色光下（１００ｍＷ／ｃｍ^２）でのＩＶ特性を測定した。測定の際、面積を正確にするため、既知の面積を有するマスクを太陽電池上に覆った状態で測定した。また、測定したデータは温度補正で２５℃相当の値に補正した。測定した結果を表１に示す。
【００３８】
【表１】

表１には、開放電圧，短絡電流密度，曲線因子，変換効率および直列抵抗の測定値に関し、棒状ヒーターｈ２１の非加熱および加熱温度３００℃について、それぞれ示す。表１の結果から明らかなように、棒状ヒーターｈ２１の温度を３００℃に設定した場合、太陽電池の直列抵抗成分が低減し、太陽電池の特性が向上していることが分かる。
【００３９】
また、シート抵抗について、モジュール化工程を行わなかったセルに関し、四端子法を用いて測定を行った。各条件で作製した太陽電池の透明電極のシート抵抗の測定結果を表２に示す。
【００４０】
【表２】

表２の結果から明らかなように、棒状ヒーターｈ２１の温度を３００℃に設定した場合、太陽電池の透明電極シート抵抗は、非加熱に設定した太陽電池のシート抵抗に比べ低下していることが分かる。
【００４１】
【発明の効果】
前述のように、この発明によれば、スパッタまたは蒸着による透明電極薄膜形成装置において、真空容器内に、基板に対面して、スパッタターゲットまたは蒸着源を有し、かつ基板を挟んでその製膜面側および非製膜面側の両側に基板の加熱手段を備えるものとし、基板の製膜面側および非製膜面側の両側から基板を所定温度に加熱して製膜することとしたので、
基板の加熱温度の均一化および加熱時間の短縮化を図り、もって透明電極の抵抗率の低減と膜質の向上並びに生産性の向上を図ることができる。特に、薄膜太陽電池に適用した場合、太陽電池の直列抵抗成分が低減し、太陽電池の特性が向上する効果が得られる。
【図面の簡単な説明】
【図１】この発明の基本的な透明電極薄膜形成装置の実施の形態の模式的概略構成図
【図２】図１の装置をスパッタ装置に適用した場合の実施の形態の模式的概略構成図
【図３】図２とは異なるスパッタ装置の実施の形態の模式的概略構成図
【図４】図１とは異なる透明電極薄膜形成装置の実施の形態の模式的概略構成図
【符号の説明】
ａ１：基板、ａ２：真空容器、ａ３：粒子の発生源、ａ４：マグネット、ａ３１：スパッタターゲット、ｈ１：非製膜面側ヒーター、ｈ２：製膜面側ヒーター、ｈ３：網目状ヒーター、ｈ２１：棒状ヒーター。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for forming a transparent electrode thin film, and particularly to a method for forming a thin film solar cell such as amorphous silicon, polycrystalline silicon, or microcrystalline silicon or a thin film semiconductor device such as a thin film transistor (TFT) on a film substrate. The present invention also relates to a transparent electrode thin film forming method and apparatus for forming a transparent electrode thin film by sputtering or vapor deposition under reduced pressure.
[0002]
[Prior art]
In general, methods for producing a transparent conductive film include a spattering method and a vapor deposition method as a physical production method, and a spraying method, a dipping method, a CVD method, and the like as chemical production methods. Production of transparent electrodes by various methods using films suitable for various uses has been attempted. Examples of the vapor deposition method include ordinary vacuum vapor deposition (electron beam heating, resistance heating), and ion plating.
[0003]
In the above-mentioned various methods, when a transparent electrode is produced under a reduced pressure of 40 Pa or less (2 Pa or less in a sputtering method or a vapor deposition method) in a vacuum device, the temperature rises to a target temperature due to poor heat conduction in the device. In addition, it takes time until the temperature distribution in the apparatus becomes uniform. Here, a conventional example in which a transparent conductive film is formed on a thin film solar cell in such a situation will be described (for example, see Patent Documents 1 and 2).
[0004]
Solar cells using amorphous silicon (a-Si) or thin-film non-single-crystal silicon made of microcrystalline silicon have the features of thin film, low-temperature process, and easy area enlargement, and are being developed as a favorite for low-cost solar cells. Have been. This type of solar cell uses a translucent substrate such as glass or PET or a non-translucent substrate such as stainless steel foil or polyimide, and sequentially laminates a transparent electrode, a non-single-crystal photoelectric conversion layer, and a metal electrode from the light incident side. It has a structure.
[0005]
As an example of a specific process procedure, after a metal electrode is formed on a substrate, a thin-film pin-type photoelectric conversion element made of a non-single crystal is deposited by a plasma CVD apparatus, and ITO is then formed as a transparent electrode by magnetron sputtering. Form a film. As the magnetron sputtering method, there are a DC magnetron sputtering method and an RF magnetron sputtering method, and any of them may be used. In addition, as the transparent electrode, not only ITO but also a thin film such as SnO ₂ or ZnO can be used as long as it is a thin film having a characteristic of relatively transmitting a wavelength in a wavelength region where the photoelectric conversion element absorbs and having a relatively low resistance. .
[0006]
A sputtering apparatus for forming an ITO film includes a heater for mainly heating a substrate in a vacuum apparatus, and an ITO target which is installed in parallel with the heater. The distance between the target and the substrate is generally about 3 to 10 cm. In this manufacturing apparatus, a substrate on which a first electrode and a pin-type photoelectric conversion layer were already formed was placed in a state where the non-film-forming surface side was in contact with a heater, and after evacuation, Ar + O was used as a discharge gas. ₂ gas (O ₂ concentration 1-5%) is introduced, and the pressure in the apparatus is maintained at about 1-20 Pa. At this time, the beater temperature is set to 100 to 200 ° C.
[0007]
The heating of the substrate by the heater is performed for a relatively short time of about 1 to 5 minutes in consideration of productivity. At this time, when a flexible substrate such as a plastic substrate or a stainless steel substrate is applied to the substrate, the actual substrate temperature has a distribution due to wrinkles or warpage of the substrate. For example, when the heater temperature is 200 ° C., the substrate temperature has a distribution of about 120 ° C. and about 20 ° C. This has a greater effect on larger substrates.
[0008]
Thereafter, direct current or high-frequency power is applied between the target and the substrate, and sputtering is performed by discharging. At the time of sputtering, film formation can be performed by using a fixed magnet, but it is preferable to make the magnet movable so as to extend the life of the target and improve the uniformity of the in-plane film thickness. In the case of DC discharge, one or more anode electrodes may be inserted between the substrate and the target in order to improve the sustainability of the discharge. When the anode electrode is fixed, discharge concentrates between the fixed anode electrode and the target, and the life of the target is shortened. Further, when a film is formed by fixing a substrate such as a stepping roll device, nonuniformity of a thin film becomes a problem. The ITO film obtained by the above method is in an amorphous or microcrystalline state having a relatively low crystallinity, and the resistivity, which is one of the important functions as a transparent electrode, is inferior to the crystallized ITO film. .
[0009]
In order to solve the problem of the non-uniformity of the thin film, for example, a movable part for moving an anode electrode is provided as in the invention disclosed in Patent Document 1. The anode electrode is placed at a distance of 1 to 2 cm from the target.
[0010]
Further, since ITO is formed directly on the photoelectric conversion layer, sputtering is performed in the same vacuum apparatus as the apparatus for forming the photoelectric conversion layer, such as a stepping roll apparatus disclosed in Patent Document 2. Is preferred. If the plasma CVD device for forming the photoelectric conversion layer and the sputtering device for forming the ITO film are different from each other, it is necessary to air-break once after forming the photoelectric conversion layer. , Which may cause a leak and reduce productivity.
[0011]
[Patent Document 1]
JP-A-9-268369 (pages 3 to 5, FIGS. 1 and 2)
[Patent Document 2]
JP-A-6-291349 (page 4-6, FIGS. 1, 5-17)
[0012]
[Problems to be solved by the invention]
By the way, in consideration of the productivity, when the heating time of the substrate and the required portion in the film forming apparatus cannot be sufficiently taken, the temperature of the substrate or the like cannot be sufficiently increased, and the film quality of the transparent electrode deteriorates. Occurs.
[0013]
Also, when the ITO thin film is formed on the nip type photoelectric conversion layer, the substrate is heated only by the substrate heating heater. In particular, when the substrate is a film substrate, a stainless steel substrate, or the like, the film is wrinkled or warped. As a result, heating by a heater is not performed uniformly, and as a result, uniformity such as film quality is impaired, distribution occurs, and there is a problem that the resistivity increases and the characteristics of the solar cell deteriorate.
[0014]
Further, if the heating time by the heater is lengthened, the productivity is reduced. Further, if the temperature of the heater is too high, the temperature of the photoelectric conversion element portion increases, and for example, boron doped in the p-layer in the nip type photoelectric conversion layer diffuses into the i-layer, and the performance of the photoelectric conversion element increases. Is greatly reduced.
[0015]
The problem related to the heating described above is a larger problem, particularly when the pressure during film formation is as low as 2 Pa or less, such as sputtering or vapor deposition, because it is difficult to maintain uniform heat due to heat conduction of the gas. It becomes.
[0016]
The present invention has been made to solve the above problems, and an object of the present invention is to make the heating temperature of the substrate uniform and to shorten the heating time, thereby reducing the resistivity of the transparent electrode. Another object of the present invention is to provide a method and an apparatus for forming a transparent electrode thin film in which the film quality and productivity are improved.
[0017]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention provides a method for forming a transparent electrode thin film on a substrate of a thin film semiconductor device by sputtering or vapor deposition under reduced pressure. The substrate is heated to a predetermined temperature from both sides on the film surface side to form a film (the invention of claim 1). Thereby, the heating temperature of the substrate can be made uniform and the heating time can be shortened.
[0018]
As embodiments of the invention, the following inventions 2 to 5 are preferable. That is, in the thin film forming method according to the first aspect, the predetermined temperature of the substrate is set to 150 to 200 ° C. In the case of a substrate type solar cell, the temperature of the substrate needs to be set to 200 to 250 ° C. or lower in order to prevent thermal deterioration of the underlying device. Further, when a plastic film is used for the substrate, the temperature must be 300 ° C. or less regardless of the substrate type or the superstrate type in relation to the heat resistance temperature, and polyethylene terephthalate (PET), polyethylene naphthalate (PEN), When a film such as ether sulfone (PES) is used, the temperature needs to be 150 to 200 ° C. The present invention is particularly effective when fine control is required such that the upper limit of the substrate temperature is set to about 200 ° C.
[0019]
Further, in the thin film forming method according to claim 1 or 2, the pressure at the time of forming the thin film is 2 Pa or less (the invention of claim 3). As described above, the present invention is effective when the pressure is 2 Pa or less where it is difficult to maintain the uniform temperature due to the heat conduction of the gas.
[0020]
Furthermore, in the thin film forming method according to any one of claims 1 to 3, the substrate is a flexible substrate such as a resin film substrate or a stainless steel film substrate (the invention of claim 4). Furthermore, in the thin film forming method according to any one of claims 1 to 4, the transparent electrode thin film is a transparent electrode thin film for a thin film solar cell (the invention of claim 5).
[0021]
Further, as an apparatus for carrying out the method of the present invention, the following invention of claim 6 is preferable. That is, a thin film forming apparatus by sputtering or vapor deposition for performing the method for forming a transparent electrode thin film according to any one of claims 1 to 5, wherein a sputtering target or A deposition source is provided, and heating means for the substrate is provided on both sides of the substrate on the film forming side and the non-film forming side.
[0022]
As an embodiment of the invention of claim 6, the following inventions of claims 7 to 9 are preferable. That is, in the transparent electrode thin film forming apparatus according to claim 6, the heating means on the film forming surface side is a rod-shaped, mesh-shaped or plate-shaped heater having a plurality of openings facing the film forming surface of the substrate. (The invention of claim 7). The plurality of openings are openings for preventing a gap between the substrate and the sputter target or the evaporation source from closing.
[0023]
In the apparatus for forming a transparent electrode thin film by sputtering according to claim 7, the outer shell member of the heater as the heating means on the film forming surface side is made of metal, and the heater also serves as the anode electrode. Invention). Thereby, the function as an anode electrode can be given to the heater.
[0024]
Further, in the apparatus for forming a transparent electrode thin film by sputtering according to claim 8, the heater configured to also serve as the anode electrode includes a movable device that can move in parallel with the film formation surface of the substrate (the invention according to claim 9). ). In order to improve the in-plane film thickness uniformity, it is preferable to make the heater movable.
[0025]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0026]
FIG. 1 is a schematic diagram illustrating a basic apparatus for forming a transparent electrode thin film according to an embodiment of the present invention. As shown in FIG. 1, one or a plurality of heaters h1 on the non-film-forming side and heaters h2 on the film-forming side are arranged in a vacuum vessel a2 with the substrate a1 interposed therebetween. Further, a source a3 of particles for forming a transparent electrode such as a sputter target or an evaporation source is provided on the side opposite to the substrate on the side of the heater h2 on the film-forming side, so that the flow of the particles to the substrate a1 is not blocked. The shape of the surface side heater h2 is, for example, a bar shape having a plurality of openings, a mesh shape, a flat shape, or a ring shape. When a film is formed by using the sputtering method, the external material of the film forming surface side heater h2 is a metal, and the anode is also used. Further, a driving device (not shown) that is movable in a direction parallel to the substrate a1 is attached to the film forming surface side heater h2.
[0027]
FIG. 2 shows a schematic configuration diagram of an embodiment of an apparatus for forming a transparent electrode film using a sputtering method among apparatuses according to the present invention. In the figure, a heater h1, a sputter target a31, and a magnet a4 are installed in a vacuum vessel a2, and a substrate a1 is installed on the heater h1. A DC power supply was connected to the sputter target a31, ITO was used as the sputter target, and a flexible polyimide substrate was used as the substrate a1.
[0028]
Further, a ring-shaped rod-shaped heater h21 is attached between the substrate a1 and the sputter target a31. The ring-shaped rod-shaped heater h21 was a heater having substantially the same dimensions as the outer dimensions of the magnet a4. In the embodiment of FIG. 2, an example in which one bar-shaped heater h21 is provided is shown. However, for example, as shown in FIG. 3, a plurality of heaters may be arranged in upper and lower two stages to enhance the heating effect.
[0029]
The rod-shaped heater h21 was a heater whose external material was metal, and was electrically connected so as to be ground potential. In this case, the rod-shaped heater h21 is also provided with a role as an anode electrode, and the rod-shaped heater h21 may be made of an insulating material as long as it has a heating function. The distance between the substrate 1a and the sputter target a31 was 5 cm, and the distance between the sputter target a31 and the rod-shaped heater h21 was 1 cm. The rod-shaped heater h21 may be close to the substrate a1 to improve the heating effect. In this case, the effect of the rod-shaped heater h21 as an anode electrode is reduced.
[0030]
For the magnet a4 and the rod-shaped heater h21, a movable type operating in parallel with the substrate was used in order to improve the use efficiency of the target and to improve the in-plane uniformity of the thin film. The rod-shaped heater h21 and the magnet a4 are fixed to a movable table that reciprocates by a drive shaft driven by a motor (not shown) outside the film forming chamber. Further, the rod-shaped heater h21 is connected to an external heater power supply via a movable base, and the temperature can be controlled by adjusting the power supply.
[0031]
The film-forming-surface-side heater h2 shown in FIG. 1 may be in the form of a flat plate or a mesh in addition to the rod shape shown in FIG. 2, but may have a particle generation source a3 having a function of generating particles forming a transparent electrode. It is necessary to have an opening so as not to block between the substrate a1. FIG. 4 shows an example in the case of using the mesh heater h3. In FIG. 4, the mesh heater h3 is installed so that the distance between the substrate a1 and the particle generation source a3 is smaller than the distance between the substrate a1 and the mesh heater h3. However, the mesh heater h3 is used to improve the heating effect. May be brought closer to the substrate a1. In this case, the effect of the mesh heater h3 as the anode electrode is reduced.
[0032]
【Example】
Next, an example in which a film is formed by the sputtering apparatus of the embodiment of FIG. 2 will be described below. The heater h1 and the rod-shaped heater h21 in FIG. 2 each have a temperature control mechanism independently, and can set the temperature independently. A stepping roll type apparatus in which a transparent electrode sputtering chamber having such equipment is connected to a plasma CVD chamber for forming a photoelectric conversion layer, as disclosed in Patent Document 2, wherein the film formation of each layer is performed. The film formation was performed using a device capable of transporting the film formation surface while maintaining the vacuum.
[0033]
The device used in the example has a function of manufacturing a photoelectric conversion element having a relatively large area of 40 cm × 80 cm at a time. Using such an apparatus, a substrate-type photoelectric conversion element was manufactured. After placing the substrate on which a metal electrode has already been formed on the polyimide substrate into a stepping roll type apparatus, and after evacuation, forming each layer of the photoelectric conversion layer using a plasma CVD method while transporting the film, It was transported to the transparent electrode sputtering chamber. Immediately before forming a transparent electrode, a metal electrode and a pin-type photoelectric conversion layer have already been formed on the substrate 1a. As the photoelectric conversion layer, an a-Si / a-SiGe tandem cell in which an a-Si single cell and an a-SiGe single cell were connected in series was manufactured.
[0034]
The transparent electrode was formed under the following two conditions: 200 ° C. for the heater h1, 200 ° C. for the bar-shaped heater h21, and 300 ° C. for the transparent electrode. In advance, when the substrate temperature was measured using a thermocouple under each temperature condition of the rod-shaped heater h21, a temperature distribution of about 120 ° C. ± 20 ° C. was present in a plane of 40 cm × 80 cm in the case of non-heating. On the other hand, at 300 ° C. (in a state in which the rod-shaped heater h21 was moved in parallel with the substrate), the temperature was 170 ° C. and 5 ° C., indicating that the substrate temperature was increased and the temperature uniformity was improved. .
[0035]
After being transported to the sputtering chamber, the inside of the sputtering chamber was evacuated while being isolated from the outside, and then a mixed gas of Ar and O ₂ was put into the sputtering chamber and kept at 2 Pa. During this operation, the magnet a4 and the rod-shaped heater h21 were started to move in the direction parallel to the substrate a1. The flow rate of O ₂ was such that the oxygen concentration in the ITO film under each condition was about 1.2%. Then, after maintaining the state for about 1 minute for pressure stabilization and substrate heating, 500 W of DC was applied from a DC power supply. The sputtering time was adjusted so that the film thickness of the transparent electrode was about 80 nm from the film formation rate checked in advance.
[0036]
After the formation of the film, the completed photoelectric conversion element was taken out of the vacuum vessel, and a solar cell was completed through a modularization process. In this case, two or more samples each having exactly the same film forming conditions were prepared, and one of the samples was used as a sample for evaluating the sheet resistance of the transparent electrode without performing the modularization process.
[0037]
In order to investigate the characteristics of the solar cell manufactured under each condition, the IV characteristics under white light (100 mW / cm ² ) were measured using the modularized solar cell. At the time of measurement, in order to make the area accurate, the measurement was performed with a mask having a known area covered on the solar cell. The measured data was corrected to a value equivalent to 25 ° C. by temperature correction. Table 1 shows the measurement results.
[0038]
[Table 1]

Table 1 shows the measured values of the open-circuit voltage, the short-circuit current density, the fill factor, the conversion efficiency, and the series resistance for the non-heating and heating temperatures of 300 ° C. of the rod-shaped heater h21. As is clear from the results in Table 1, when the temperature of the rod-shaped heater h21 is set to 300 ° C., the series resistance component of the solar cell is reduced, and the characteristics of the solar cell are improved.
[0039]
Further, the sheet resistance was measured using the four-terminal method for the cells not subjected to the module forming step. Table 2 shows the measurement results of the sheet resistance of the transparent electrode of the solar cell manufactured under each condition.
[0040]
[Table 2]

As is clear from the results in Table 2, when the temperature of the rod-shaped heater h21 is set to 300 ° C., the sheet resistance of the transparent electrode of the solar cell is lower than the sheet resistance of the solar cell set to non-heating. I understand.
[0041]
【The invention's effect】
As described above, according to the present invention, in a transparent electrode thin film forming apparatus by sputtering or vapor deposition, in a vacuum vessel, a sputtering target or vapor deposition source is provided facing a substrate, and the film is formed with the substrate interposed therebetween. Since the heating means for the substrate is provided on both the surface side and the non-film-forming surface side, and the substrate is heated to a predetermined temperature from both sides on the film-forming surface side and the non-film-forming surface side, the film is formed. ,
The heating temperature of the substrate is made uniform and the heating time is shortened, so that the resistivity of the transparent electrode can be reduced, the film quality can be improved, and the productivity can be improved. In particular, when applied to a thin-film solar cell, the effect of reducing the series resistance component of the solar cell and improving the characteristics of the solar cell is obtained.
[Brief description of the drawings]
FIG. 1 is a schematic schematic configuration diagram of an embodiment of a basic transparent electrode thin film forming apparatus of the present invention. FIG. 2 is a schematic schematic configuration diagram of an embodiment in which the device of FIG. 1 is applied to a sputtering device. FIG. 3 is a schematic schematic configuration diagram of an embodiment of a sputtering apparatus different from FIG. 2; FIG. 4 is a schematic schematic configuration diagram of an embodiment of a transparent electrode thin film forming device different from FIG. 1;
a1: substrate, a2: vacuum vessel, a3: particle generation source, a4: magnet, a31: sputter target, h1: non-film-forming surface heater, h2: film-forming surface heater, h3: mesh heater, h21: Bar heater.

Claims

In a method of forming a transparent electrode thin film on a substrate of a thin film semiconductor device by sputtering or vapor deposition under reduced pressure, the substrate is heated to a predetermined temperature from both the film forming side and the non-film forming side of the substrate. A method for forming a transparent electrode thin film, comprising:

2. The method according to claim 1, wherein the predetermined temperature of the substrate is 150 to 200 [deg.] C.

3. The method according to claim 1, wherein the pressure at the time of forming the thin film is 2 Pa or less.

4. The method according to claim 1, wherein the substrate is a flexible substrate such as a resin film substrate or a stainless steel film substrate.

5. The method according to claim 1, wherein said transparent electrode thin film is a transparent electrode thin film for a thin-film solar cell.

A thin film forming apparatus by sputtering or vapor deposition for performing the method for forming a transparent electrode thin film according to any one of claims 1 to 5, wherein a sputtering target or a vapor deposition source is provided in a vacuum vessel facing the substrate. And a heating means for the substrate on both sides of the film forming surface side and the non-film forming surface side of the substrate.

7. The transparent electrode thin film forming apparatus according to claim 6, wherein the heating means on the film forming surface side is a rod-shaped, mesh-shaped or plate-shaped heater having a plurality of openings facing the film forming surface of the substrate. An apparatus for forming a transparent electrode thin film, comprising:

8. The transparent electrode thin film forming apparatus according to claim 7, wherein the outer shell member of the heater as the heating means on the film forming surface side is made of metal, and the heater also serves as an anode electrode. Electrode thin film forming equipment.

9. The transparent electrode thin film forming apparatus according to claim 8, wherein the heater configured to also serve as the anode electrode includes a movable device that moves in parallel with a film forming surface of the substrate.