JP2011216574A - Thin film transistor and method for manufacturing the same - Google Patents
Thin film transistor and method for manufacturing the same Download PDFInfo
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Images
Abstract
Description
本発明は、Ｉｎ−Ｇａ−Ｚｎ−Ｏ系アモルファス酸化物半導体膜をチャネル層とした薄膜
トランジスタ（ＴＦＴ）とその製造方法に関する。
The present invention relates to a thin film transistor (TFT) using an In—Ga—Zn—O-based amorphous oxide semiconductor film as a channel layer and a manufacturing method thereof.
近年、水素化アモルファスシリコン(ａ−Ｓｉ)及び多結晶シリコン(ｐｏｌｙ−Ｓｉ)に代
わり、低温で高い電子移動度を有する薄膜が作製できる酸化物半導体をチャネル層とする
薄膜トランジスタ(ＴＦＴ)の研究開発が活発に行われている[非特許文献１]。
In recent years, research and development of thin film transistors (TFTs) using oxide semiconductors as channel layers, which can produce thin films with high electron mobility at low temperatures, instead of hydrogenated amorphous silicon (a-Si) and polycrystalline silicon (poly-Si) Has been actively carried out [Non-Patent Document 1].
多くの酸化物半導体（例えば、酸化亜鉛など）は、高温・耐薬品性に優れていることに加
えて、光学バンドギャップが３．０ｅＶ以上を有することから、可視光領域の光を完全に
透過する。よって、透明酸化物半導体をＴＦＴのチャネル層として用いることにより、可
視光に対して光応答性を示さない透明ＴＦＴが作製できる。したがって、液晶ディスプレ
イにおける駆動スイッチング用ＴＦＴとして応用することにより、液晶素子の開口率の向
上、光遮断マスクが不要になるなどの利点が期待されている。
Many oxide semiconductors (for example, zinc oxide) have high temperature and chemical resistance, and have an optical band gap of 3.0 eV or more, so they completely transmit light in the visible light region. To do. Therefore, by using a transparent oxide semiconductor as a TFT channel layer, a transparent TFT that does not exhibit photoresponsiveness to visible light can be manufactured. Therefore, by applying it as a driving switching TFT in a liquid crystal display, there are expected advantages such as an improvement in the aperture ratio of the liquid crystal element and elimination of a light blocking mask.
しかし、酸化亜鉛などの代表的な酸化物半導体では、残留電子キャリア濃度の低減が困難
である。また、電子キャリア濃度が小さく、高品質の酸化物薄膜を得るためには、高価な
単結晶基板の使用や高温製膜プロセスが必要である[非特許文献２]。 加えて、酸化亜鉛
は低温（室温）製膜でもアモルファス状態にならず、多くの結晶粒界を含んだ多結晶状態
である。多結晶酸化物からなるチャネル層を用いたＴＦＴでは結晶粒界の欠陥によりＴＦ
Ｔ特性は極めて悪くなる。
However, in a typical oxide semiconductor such as zinc oxide, it is difficult to reduce the residual electron carrier concentration. Further, in order to obtain a high-quality oxide thin film with a low electron carrier concentration, it is necessary to use an expensive single crystal substrate or a high-temperature film forming process [Non-patent Document 2]. In addition, zinc oxide is not in an amorphous state even at low temperature (room temperature) film formation, and is in a polycrystalline state including many crystal grain boundaries. In a TFT using a channel layer made of a polycrystalline oxide, TF is caused by a defect in a crystal grain boundary.
T characteristics are extremely poor.
多結晶酸化物をチャネル層としたＴＦＴに共通的に発生する上記の課題を克服するため、
本発明者らは、２００４年にアモルファス酸化物半導体材料を開発し、それをチャネル層
としたＴＦＴを発表した[非特許文献３、特許文献１，２]。このＴＦＴのチャネル層は結
晶状態における組成が、例えば、（Ｉｎ1-xＭx）2Ｏ3(ＺｎＯ)m [mは、０又は６未満の数
又は自然数、Ｍは、Ｂ，Ａｌ，Ｇａ，Ｙ又はＬｕ]で表される化合物のモルファス状態の
金属酸化物である。
In order to overcome the above-mentioned problems that commonly occur in TFTs having a polycrystalline oxide channel layer,
In 2004, the present inventors developed an amorphous oxide semiconductor material and announced a TFT using it as a channel layer [
特に、アモルファスＩｎＧａＯ3(ＺｎＯ)m (以下、「ａ−ＩＧＺＯ」という)膜では、室
温堆積膜でも、ホール効果測定より求めた電子移動度が７ｃｍ2(Vs)-1以上の大きな値を
示し、電子キャリア濃度を再現性よく、安定に１０15〜１０20cm-3に制御することが可能
である[非特許文献４]。そのため、軟化点が３００℃以下のプラスチック基板上へもＴＦ
Ｔや電子回路を作製できる。
In particular, an amorphous InGaO 3 (ZnO) m (hereinafter referred to as “a-IGZO”) film shows a large value of an electron mobility of 7 cm 2 (Vs) −1 or more obtained from Hall effect measurement even in a room-temperature deposited film. The electron carrier concentration can be stably controlled to 10 15 to 10 20 cm −3 with good reproducibility [Non-Patent Document 4]. Therefore, TF is also applied to plastic substrates with a softening point of 300 ° C or lower.
T and electronic circuit can be produced.
ａ−ＩＧＺＯをチャネル層としたＴＦＴ(以下、「ａ−ＩＧＺＯ-ＴＦＴ」という)では、
チャネル中の伝導キャリアの動き易さを表す電界効果移動度が約１０cm2(Vs)-1、閾値電
圧付近におけるゲート電圧の変動に対するドレイン電流の変化の度合いを示すサブスレシ
ョルド(subthreshold)値が約０．２V/decade、電流オン・オフ（On/Off）比が約１０8以
上という優れたトランジスタ特性を示す[非特許文献５]。また、ＴＦＴのチャネル層が、
結晶粒界を一切含まないアモルファス状態であることから、トランジスタ特性に優れ、Ｔ
ＦＴ素子間のトランジスタ特性のばらつきが少ない [非特許文献６]。したがって、大面
積でも特性が均一なＴＦＴが作製できるので、大面積平面ディスプレイ用の駆動スイッチ
ングＴＦＴとしての応用を目指した開発が精力的に進められている。
In a TFT using a-IGZO as a channel layer (hereinafter referred to as “a-IGZO-TFT”),
The field-effect mobility representing the mobility of the conduction carriers in the channel is about 10 cm 2 (Vs) −1 , and the subthreshold value indicating the degree of change in the drain current with respect to the fluctuation of the gate voltage near the threshold voltage is about Excellent transistor characteristics of 0.2 V / decade and current on / off ratio of about 10 8 or more are shown [Non-Patent Document 5]. Moreover, the channel layer of TFT is
Since it is in an amorphous state that does not contain any crystal grain boundaries, it has excellent transistor characteristics, and T
Little variation in transistor characteristics between FT elements [Non-Patent Document 6]. Accordingly, since TFTs having uniform characteristics even in a large area can be manufactured, development aimed at application as a driving switching TFT for a large area flat display has been vigorously advanced.
現在までに、ｎ型アモルファス酸化物半導体として、ａ−ＩＧＺＯ以外に２成分系Ｉｎ−
Ｚｎ−Ｏ、Ｉｎ−Ｇａ−Ｏ、Ｚｎ−Ｓｎ−Ｏ、３成分系Ｓｎ−Ｇａ−Ｚｎ−Ｏなどが報告
されている[非特許文献７]。これらの金属酸化物も室温堆積膜はアモルファス状態であり
、ＴＦＴのｎチャネル層へ適用できる。これらの金属酸化物では、伝導帯を構成する電子
軌道は金属のｎｓ軌道であることから、軌道半径の大きな５ｓ軌道を有するＩｎやＳｎを
多く含んだ組成系で、高い飽和移動度が得られる[非特許文献８]。しかしながら、デバイ
ス特性の再現性・安定性の観点からは、Ｉｎ−Ｇａ−Ｚｎ３成分系アモルファス酸化物の
方が、２成分系アモルファス酸化物よりも、優れた性能、特に閾値電圧、電界効果移動度
の長期安定性を示すことが知られている。
To date, as an n-type amorphous oxide semiconductor, in addition to a-IGZO, two-component In-
Zn—O, In—Ga—O, Zn—Sn—O, ternary Sn—Ga—Zn—O, and the like have been reported [Non-patent Document 7]. These metal oxides also have a room temperature deposited film in an amorphous state and can be applied to the n-channel layer of the TFT. In these metal oxides, the electron orbits constituting the conduction band are metal ns orbitals, and therefore high saturation mobility can be obtained with a composition system containing a large amount of In and Sn having a 5s orbital with a large orbital radius. [Non-Patent Document 8]. However, from the viewpoint of reproducibility and stability of device characteristics, In-Ga-Zn ternary amorphous oxides have superior performance, especially threshold voltage, field effect mobility, than binary amorphous oxides. It is known to exhibit long-term stability.
よって、アモルファス酸化物半導体の中でも、特に３成分系のａ−ＩＧＺＯが広く研究さ
れている。現在までに、ａ−ＩＧＺＯ-ＴＦＴ を用いた発振回路（リングオシレータ）に
おいて４１０ｋＨｚで動作することなどが実証されている[非特許文献９]。また、画素と
駆動回路のスイッチング素子用ＴＦＴとしてａ−ＩＧＺＯ-ＴＦＴを用いた１９インチア
クティブマトリクス方式の有機ＥＬディスプレイ（ＡＭＯＬＥＤ）や３７インチアクティ
ブマトリクス方式の液晶ディスプレイ（ＡＭＬＣＤ）などが 実用試作ディスプレイとし
て開発されている[非特許文献１０，１１]。
Therefore, among the amorphous oxide semiconductors, ternary a-IGZO is particularly widely studied. To date, it has been demonstrated that an oscillation circuit (ring oscillator) using an a-IGZO-TFT operates at 410 kHz [Non-Patent Document 9]. In addition, 19-inch active matrix organic EL displays (AMOLED) and 37-inch active matrix liquid crystal displays (AMLCD) using a-IGZO-TFTs as switching element TFTs for pixels and drive circuits are practical prototype displays. It has been developed [
ＡＭＯＬＥＤでは発光部位に自発光型エレクトロルミネセンス（ＥＬ）素子を用いること
から、高輝度・高解像度・高応答性に加えて低消費電力・省スペース化などの有利性から
次世代ディスプレイとして期待されている。ＡＭＯＬＥＤにおける発光素子制御用ＴＦＴ
としては主に二つの条件が要求される。第一の条件は、電流を注入することで得るエレク
トロルミネッセンスを取り出す電流注入型有機発光ディスプレイであることから、高輝度
・高応答性を実現するためには、高移動度・低サブスレッショルド値を示すＴＦＴが望ま
しいことである。第二の条件は、大面積デバイス特性の均一性とデバイス特性、特に長時
間駆動に対する閾値電圧の安定性が必要なことである。
Since AMOLED uses a self-luminous electroluminescence (EL) element in the light emitting part, it is expected to be a next generation display due to advantages such as low power consumption and space saving in addition to high brightness, high resolution and high response. ing. Light emitting element control TFT in AMOLED
There are two main requirements. The first condition is a current injection type organic light emitting display that takes out electroluminescence obtained by injecting current. Therefore, in order to achieve high brightness and high responsiveness, high mobility and low subthreshold values are required. The TFT shown is desirable. The second condition is that uniformity of large area device characteristics and device characteristics, in particular, threshold voltage stability with respect to long-time driving is required.
現在まで、ＡＭＯＬＥＤ用のＴＦＴのチャネル材料として高移動度を示すpｏｌｙ−Ｓｉ
ＴＦＴが検討されているが、多結晶状態による素子間におけるＴＦＴ特性のばらつきが大
きく、大面積化が非常に困難である[非特許文献１２]。よって、大面積ディスプレイ作製
においてはａ−Ｓｉの方が有利であるが、トランジスタが流せる電流量の指標である移動
度が２ｃｍ2／Ｖｓ以下と小さいなどの問題がある[非特許文献１３]。現在、この問題は
電極幅の大きいａ−Ｓi ＴＦＴ構造を使うことなどで回避されているが、移動度の大きい
ＴＦＴを使えば開口率の増大や高速動作の面で大きな利点となる。
Up to now, poly-Si which shows high mobility as a channel material of TFT for AMOLED
Although TFTs have been studied, variation in TFT characteristics between elements due to the polycrystalline state is large, and it is very difficult to increase the area [Non-Patent Document 12]. Therefore, although a-Si is more advantageous in manufacturing a large area display, there is a problem that mobility, which is an index of the amount of current that can be passed through a transistor, is as small as 2 cm 2 / Vs or less [Non-patent Document 13]. At present, this problem is avoided by using an a-Si TFT structure having a large electrode width. However, using a TFT having a high mobility is a great advantage in terms of increase in aperture ratio and high speed operation.
ａ−ＩＧＺＯ−ＴＦＴでは、チャネル層がアモルファス状態であることから多結晶半導体
デバイスと異なりＴＦＴ素子間特性の均一性に優れている。また、ａ−ＩＧＺＯ-ＴＦＴ
ではａ−Ｓｉ−ＴＦＴと比較して、１０倍以上の電界効果移動度、低サブスレショルド値
を有する高性能ＴＦＴが作製できる。よって、ＡＭＯＬＥＤ用のスイッチングＴＦＴとし
てａ−ＩＧＺＯ−ＴＦＴが特に有望である。
Since the channel layer is in an amorphous state, the a-IGZO-TFT has excellent uniformity of characteristics between TFT elements unlike a polycrystalline semiconductor device. Moreover, a-IGZO-TFT
Then, a high-performance TFT having a field effect mobility of 10 times or more and a low subthreshold value can be manufactured as compared with an a-Si-TFT. Therefore, an a-IGZO-TFT is particularly promising as a switching TFT for AMOLED.
現在までに、ａ−ＩＧＺＯ−ＴＦＴにおける電界効果移動度及びサブスレッショルド値な
どのデバイス特性改善・向上において、ａ−ＩＧＺＯ薄膜を３００℃以上で熱処理するこ
とが非常に有効であることが知られている。容量−電圧（C-V）測定より、ａ−ＩＧＺＯ
薄膜中のサブギャップ準位は約１０17ｃｍ-3程度であり、このサブギャップ準位は熱処理
により低減され、ＴＦＴ特性は向上する[非特許文献１４]。また、Nomura et al.,は、露
点温度３０〜９５℃の水蒸気を含んだ酸素（湿潤酸素）雰囲気中で３００℃でａ−ＩＧＺ
Ｏ薄膜の熱処理を行うことにより、ａ−ＩＧＺＯ−ＴＦＴの移動度、サブスレショルド値
を向上させ、安定性も改善できると報告している [非特許文献１５]。
To date, it is known that it is very effective to heat-treat an a-IGZO thin film at 300 ° C. or higher in improving and improving device characteristics such as field effect mobility and subthreshold value in an a-IGZO-TFT. Yes. From the capacitance-voltage (CV) measurement, a-IGZO
The subgap level in the thin film is about 10 17 cm −3 , and this subgap level is reduced by heat treatment, and the TFT characteristics are improved [Non-Patent Document 14]. Nomura et al., A-IGZ at 300 ° C. in an oxygen (wet oxygen) atmosphere containing water vapor with a dew point temperature of 30-95 ° C.
It has been reported that by performing heat treatment of the O thin film, the mobility and subthreshold value of the a-IGZO-TFT can be improved and the stability can be improved [Non-patent Document 15].
現在まで、ａ−ＩＧＺＯ−ＴＦＴの特性改善を目的としたａ−ＩＧＺＯ薄膜の熱処理にお
ける熱処理雰囲気は、大気中、酸素ラジカル、オゾン、水蒸気、窒素中、乾燥酸素中、又
は湿潤酸素中で実施されている（特許文献３〜５）。しかし、ａ−ＩＧＺＯを含む多くの
酸化物半導体では、熱処理による材料特性及びＴＦＴ特性に及ぼす影響は非常に大きいと
考えられる。既に、乾燥酸素や湿潤酸素雰囲気中での熱処理によるＴＦＴ特性の改善に関
してはいくつかの報告はあるが、２００℃以下での熱処理では大きな移動度の改善が得ら
れないこと、閾値電圧が大きく負にシフトすることなどが問題となっている[非特許文献
１６，１７]。
To date, the heat treatment atmosphere in the heat treatment of the a-IGZO thin film aimed at improving the characteristics of the a-IGZO-TFT has been carried out in the air, oxygen radical, ozone, water vapor, nitrogen, dry oxygen, or wet oxygen. (
２００４年に、本発明者らがＩｎ−Ｇａ−Ｚｎ−Ｏ系アモルファス酸化物をチャネル層と
する薄膜トランジスタを報告して以来、そのＴＦＴ特性・安定性の改善、向上に関する研
究が活発に研究されている。
Since 2004, when the present inventors reported a thin film transistor having an In—Ga—Zn—O-based amorphous oxide as a channel layer, research on improvement and improvement of TFT characteristics and stability has been actively conducted. Yes.
現在までに、電界効果移動度やサブスレッショルド値などのＴＦＴ特性及びその安定性の
向上に関して、３００℃以上における空気中又は乾燥酸素雰囲気中でのａ−ＩＧＺＯ薄膜
の熱処理が有効なことがよく知られている。また、湿潤酸素雰囲気中での３００〜５００
℃の範囲におけるａ−ＩＧＺＯ薄膜の熱処理では、さらにＴＦＴ特性を改善できるが、２
００℃以下におけるａ−ＩＧＺＯ薄膜の熱処理では移動度の改善は８ｃｍ2／Ｖｓ程度に
限られること、閾値電圧が−１５Ｖ以下と大きく負の値にシフトしてしまう問題がある。
ＯＬＥＤディスプレイや８０インチ以上の画面サイズ・２４０Ｈｚ以上のフレームレート
・フルハイビジョン解像度の液晶ディスプレイには電界効果移動度が５ｃｍ2／Ｖｓ以上
が必要である。また、閾値電圧シフトを大幅に低減する必要がある。
To date, it is well known that heat treatment of an a-IGZO thin film in air or in a dry oxygen atmosphere at 300 ° C. or higher is effective for improving TFT characteristics such as field effect mobility and subthreshold value and stability thereof. It has been. Also, 300 to 500 in a wet oxygen atmosphere
The heat treatment of the a-IGZO thin film in the range of ° C. can further improve the TFT characteristics.
In the heat treatment of the a-IGZO thin film at 00 ° C. or lower, the improvement in mobility is limited to about 8 cm 2 / Vs, and there is a problem that the threshold voltage is greatly shifted to a negative value of −15 V or lower.
A field effect mobility of 5 cm 2 / Vs or more is required for an OLED display, a screen size of 80 inches or more, a frame rate of 240 Hz or more, and a liquid crystal display with full high-definition resolution. Moreover, it is necessary to significantly reduce the threshold voltage shift.
また、プラスチック基板上にディスプレイや電子回路を作製するためには、デバイス作製
プロセスの最高温度をプラスチック基板の軟化点よりも低く抑える必要があり、例えば、
ポリイミド基板の場合で３００℃、ポリエチレンテレフタラート（ＰＥＴ）基板の場合で
１５０℃以下に抑える必要がある。
In addition, in order to produce a display or electronic circuit on a plastic substrate, it is necessary to keep the maximum temperature of the device production process lower than the softening point of the plastic substrate.
In the case of a polyimide substrate, it is necessary to suppress the temperature to 300 ° C. or 150 ° C. or less in the case of a polyethylene terephthalate (PET) substrate.
プラスチック基板上にアクティブマトリクス方式の液晶ディスプレイ及び有機ＥＬディス
プレイを形成するためには、３００℃以下の、より好ましくは、２００℃以下のデバイス
作製プロセスとする必要がある。本発明者は、２００℃以下の低温における熱処理によっ
て、処理後のａ−ＩＧＺＯ薄膜の閾値電圧が０±５Ｖ以内、ＴＦＴの移動度が５ｃｍ2／
Ｖｓ以上となる条件を見出した。
In order to form an active matrix liquid crystal display and an organic EL display on a plastic substrate, it is necessary to use a device manufacturing process of 300 ° C. or lower, more preferably 200 ° C. or lower. The present inventor conducted a heat treatment at a low temperature of 200 ° C. or lower, the threshold voltage of the a-IGZO thin film after the treatment was within 0 ± 5 V, and the mobility of the TFT was 5 cm 2 /
The condition which becomes Vs or more was found.
すなわち、本発明は、基板と、ゲート電極と、ゲート絶縁膜と、チャネル層とを含み、該
チャネル層としてＩｎ−Ｇａ−Ｚｎ−Ｏ系アモルファス酸化物半導体膜を用いた薄膜トラ
ンジスタにおいて、オゾンを含む乾燥酸素ガス雰囲気による熱処理後のａ−ＩＧＺＯ薄膜
の閾値電圧が０±５Ｖ以内、電界効果移動度が５ｃｍ2／Ｖｓ以上であることを特徴とす
る薄膜トランジスタ、である。
That is, the present invention includes ozone in a thin film transistor including a substrate, a gate electrode, a gate insulating film, and a channel layer, and using the In—Ga—Zn—O amorphous oxide semiconductor film as the channel layer. The thin film transistor is characterized in that the a-IGZO thin film after heat treatment in a dry oxygen gas atmosphere has a threshold voltage of 0 ± 5 V or less and a field effect mobility of 5 cm 2 / Vs or more.
また、本発明は、基板と、ゲート電極と、ゲート絶縁膜と、チャネル層とを含み、該チャ
ネル層としてＩｎ−Ｇａ−Ｚｎ−Ｏ系アモルファス酸化物半導体膜を用いた薄膜トランジ
スタの製造方法において、該半導体膜を製膜した後、乾燥酸素中にオゾンを１．０容積％
以下０．０１容積％以上含む乾燥酸素ガス雰囲気中で該半導体膜を１００〜２００℃の温
度範囲内で１〜１２０分間、熱処理することを特徴とする薄膜トランジスタの製造方法、
である。
Further, the present invention relates to a method of manufacturing a thin film transistor including a substrate, a gate electrode, a gate insulating film, and a channel layer, and using an In—Ga—Zn—O-based amorphous oxide semiconductor film as the channel layer. After depositing the semiconductor film, 1.0% by volume of ozone in dry oxygen
A method for producing a thin film transistor, wherein the semiconductor film is heat-treated in a temperature range of 100 to 200 ° C. for 1 to 120 minutes in a dry oxygen gas atmosphere containing 0.01% by volume or more;
It is.
本発明の製造方法によって、特に、アクティブマトリクス方式の液晶ディスプレイ及び有
機ＥＬディスプレイのバックプレーンとして、実用可能なＴＦＴ特性を実現することがで
きる。
By the manufacturing method of the present invention, practical TFT characteristics can be realized particularly as a backplane of an active matrix liquid crystal display and an organic EL display.
本発明によれば、チャネル層としてａ−ＩＧＺＯ薄膜を用いるＴＦＴにおいて、製膜後に
酸化性雰囲気中で熱処理する場合の問題であった閾値電圧が大きく負にシフトしてしまう
問題とデバイス作製プロセスの最高温度をプラスチック基板の軟化点よりも低く抑えると
い問題を、従来の製造プロセスを変更することなく熱処理雰囲気の制御と加熱温度の低温
化により同時に解決することができる。
According to the present invention, in a TFT using an a-IGZO thin film as a channel layer, the threshold voltage, which has been a problem when heat-treating in an oxidizing atmosphere after film formation, greatly shifts to a negative value. The problem of keeping the maximum temperature lower than the softening point of the plastic substrate can be solved simultaneously by controlling the heat treatment atmosphere and lowering the heating temperature without changing the conventional manufacturing process.
本発明者は、基板と、ゲート電極と、ゲート絶縁膜と、チャネル層とを含み、該チャネル
層としてＩｎ−Ｇａ−Ｚｎ−Ｏ系アモルファス酸化物半導体膜を用いた薄膜トランジスタ
において、オゾンを含む乾燥酸素ガス雰囲気による熱処理後のａ−ＩＧＺＯ薄膜の閾値電
圧が０±５Ｖ以内、電界効果移動度が５ｃｍ2／Ｖｓ以上である薄膜トランジスタを実現
した。
The present inventor has disclosed that a thin film transistor including a substrate, a gate electrode, a gate insulating film, and a channel layer and using an In—Ga—Zn—O-based amorphous oxide semiconductor film as the channel layer is dried with ozone. A thin film transistor was realized in which the threshold voltage of the a-IGZO thin film after heat treatment in an oxygen gas atmosphere was within 0 ± 5 V and the field effect mobility was 5 cm 2 / Vs or more.
図４に、本発明のＴＦＴの一例である基板１上に形成した熱酸化膜ＳｉＯ2をゲート絶縁
層２とするボトムゲート構造のトランジスタの模式図を示しているが、本発明のＴＦＴは
、ボトムゲート構造に限らない。ソース電極４、ドレイン電極５、ゲート電極６の形成は
通常採用されている材料、方法を用いればよい。
FIG. 4 shows a schematic diagram of a bottom-gate transistor in which the
本発明のＴＦＴのチャネル層３は、真空容器中で、例えば、ＩｎＧａＺｎＯ4焼結体又は
Ｉｎ2Ｏ3−Ｇａ2Ｏ3−ＺｎＯを含む３成分酸化物焼結体をターゲットとして用いて、ＰＬ
Ｄ 法やスパッタ法などで堆積させる製膜工程により形成できる。例えば、ＲＦマグネト
ロンスパッタリング（ＲＦＭＳ）法を用いる場合は、容量結合型プラズマを用いてＩｎＧ
ａＺｎＯ4焼結体のターゲットをスパッタリングし、加熱していない基板上に電源出力３
０〜７０Ｗ、基板−ターゲット間距離４０〜９０ｍｍ、プラズマガスはＡｒとＯ2の混合
ガス、全圧を０．１〜１Ｐａ、酸素分圧を０．０１〜０．１Ｐａで行うことが好ましい。
基板は１００〜２００℃の温度範囲の熱処理に耐え得る材料であれば制限されない。製膜
工程は酸素分圧を制御できれば、ＰＬＤ法やスパッタ法など制限されない。
The
It can be formed by a film forming process that is deposited by a D method or a sputtering method. For example, when the RF magnetron sputtering (RFMS) method is used, a capacitively coupled plasma is used for InG.
Sputtering target of aZnO 4 sintered body,
It is preferable to perform 0 to 70 W, a substrate-target distance of 40 to 90 mm, a plasma gas at a mixed gas of Ar and O 2 , a total pressure of 0.1 to 1 Pa, and an oxygen partial pressure of 0.01 to 0.1 Pa.
The substrate is not limited as long as it can withstand heat treatment in a temperature range of 100 to 200 ° C. As long as the oxygen partial pressure can be controlled, the film forming process is not limited to a PLD method or a sputtering method.
ａ−ＩＧＺＯ薄膜の製膜工程では、残留電子キャリア濃度を１０15〜１０20ｃｍ-3で制御
する目的で製膜室内雰囲気の酸素分圧を適正な範囲に設定する。なお、酸素分圧とは、流
量制御装置により製膜室内に意図的に導入された酸素ガスの分圧のことを意味する。酸素
分圧は、通常０．０１〜１Ｐａ程度とする。酸素分圧が小さいときは、酸素欠損を多く含
む伝導性薄膜が作製される。また、酸素分圧を大きくすることにより、半導体及び半絶縁
体薄膜に変化する。
In the film-forming process of the a-IGZO thin film, the oxygen partial pressure in the film-forming room atmosphere is set to an appropriate range for the purpose of controlling the residual electron carrier concentration at 10 15 to 10 20 cm −3 . The oxygen partial pressure means the partial pressure of oxygen gas intentionally introduced into the film forming chamber by the flow control device. The oxygen partial pressure is usually about 0.01 to 1 Pa. When the oxygen partial pressure is small, a conductive thin film containing many oxygen vacancies is produced. Moreover, it changes into a semiconductor and a semi-insulator thin film by making oxygen partial pressure large.
ａ−ＩＧＺＯ薄膜を製膜した後、加熱装置に移して酸化性雰囲気中で熱処理する。紫外線
（ＵＶ）ランプ及びプラズマオゾン発生器により発生させたオゾンを１．０容積％以下、
０．０１容積％以上添加した乾燥酸素ガスとなるように両者の流量を調整して連通接続し
た供給管を通して加熱装置に導入する。熱処理雰囲気は大気圧下が好ましいが、必要に応
じて減圧下、又は加圧下でもよい。酸素雰囲気中に水分を含むとオゾンと反応してオゾン
含有の効果が減殺されるので乾燥酸素を用いる。オゾン含有量が０．０１容積％未満の場
合はオゾン濃度が十分でなく、良好な結果が得られない。また、１．０容積％超では理由
は定かでないがＴＦＴ特性の改善効果が乏しい。より好ましくは０．０５〜０．５容積％
とする。
After forming an a-IGZO thin film, it transfers to a heating apparatus and heat-processes in an oxidizing atmosphere. 1.0 vol% or less of ozone generated by an ultraviolet (UV) lamp and a plasma ozone generator;
The flow rate of both is adjusted so that it becomes dry oxygen gas added 0.01 volume% or more, and it introduce | transduces into a heating apparatus through the supply pipe | tube connected in communication. The heat treatment atmosphere is preferably under atmospheric pressure, but may be under reduced pressure or under pressure as necessary. If moisture is included in the oxygen atmosphere, dry oxygen is used because it reacts with ozone to reduce the effect of ozone. When the ozone content is less than 0.01% by volume, the ozone concentration is not sufficient, and good results cannot be obtained. On the other hand, if it exceeds 1.0% by volume, the reason is not clear, but the effect of improving TFT characteristics is poor. More preferably 0.05 to 0.5% by volume
And
乾燥酸素ガスは、工業用乾燥酸素ガスを用いる。乾燥酸素ガスは水蒸気分圧が１０-3Ｐａ
以下が好ましい。オゾン発生装置は、ＵＶランプ単独、プラズマオゾン発生器単独、これ
らの組み合わせなど制限されない。加熱装置は、抵抗加熱炉、赤外線加熱炉など制限され
ない。炉内温度が熱処理温度になるように制御する。
Industrial dry oxygen gas is used as the dry oxygen gas. Dry oxygen gas has a water vapor partial pressure of 10 −3 Pa.
The following is preferred. The ozone generator is not limited to a UV lamp alone, a plasma ozone generator alone, or a combination thereof. The heating device is not limited, such as a resistance heating furnace or an infrared heating furnace. The furnace temperature is controlled to be the heat treatment temperature.
加熱温度が９０℃以下ではＴＦＴ特性に変化は認められず、また、加熱温度が２５０℃以
上ではオゾンが自己分解して、オゾンを含有させる効果がなくなるとともに、３００℃以
上ではチャネル層の抵抗が大きくなりすぎ、ＴＦＴ動作しない。そのため、加熱温度は１
００℃〜２００℃が好ましく、１００℃〜１５０℃がより好ましい。加熱時間が１分以内
ではＴＦＴ特性に変化は認められず、また、１２０分以上では処理に要する時間（タクト
タイム）が長くなる。好ましくは１０分〜６０分とする。
When the heating temperature is 90 ° C. or lower, no change is observed in the TFT characteristics. When the heating temperature is 250 ° C. or higher, ozone self-decomposes and the effect of containing ozone is lost. It becomes too large and TFT operation does not work. Therefore, the heating temperature is 1
00 ° C to 200 ° C is preferable, and 100 ° C to 150 ° C is more preferable. When the heating time is within 1 minute, no change is observed in the TFT characteristics, and when the heating time is 120 minutes or longer, the time required for processing (tact time) becomes long. Preferably, it is 10 minutes to 60 minutes.
上記の熱処理により、ａ−ＩＧＺＯ薄膜のバンドギャップ内の欠陥準位密度が減り、ＴＦ
Ｔのサブスレッショルド値を減少させると共に、閾値電圧が大きな負の値にシフトするこ
とを防ぐことができる。よって、熱処理後のａ−ＩＧＺＯ薄膜の閾値電圧が０±５Ｖ以内
、電界効果移動度が５ｃｍ2／Ｖｓ以上である薄膜トランジスタが得られる。
The above heat treatment reduces the density of defect states in the band gap of the a-IGZO thin film, and TF
The subthreshold value of T can be reduced and the threshold voltage can be prevented from shifting to a large negative value. Therefore, a thin film transistor in which the threshold voltage of the a-IGZO thin film after heat treatment is within 0 ± 5 V and the field effect mobility is 5 cm 2 / Vs or more can be obtained.
さらに詳しく、本発明を実施例に基いて説明する。 In more detail, this invention is demonstrated based on an Example.
a−ＩＧＺＯ薄膜をチャネル層として、図４に示す構造のボトムゲート型ＴＦＴを作製し
た。初めに、ＴＦＴのチャネル層として、ｎ+-Ｓｉ基板１上に製膜したＳｉＯ2熱酸化膜
２上に厚さ３０ｎｍのa−ＩＧＺＯ層３を製膜した。
Using the a-IGZO thin film as a channel layer, a bottom gate type TFT having the structure shown in FIG. 4 was produced. First, a SiO 2 thermal oxide film formed on an n + -
An
ａ−ＩＧＺＯ薄膜層３はＲＦマグネトロンスパッタリング（ＲＦＭＳ）法により堆積した
。ＲＦＭＳ装置としては、ＣＡＮＯＮ ＡＮＥＬＶＡ社製ＲＦＭＳ製膜装置を用いた。平
行平板電極に１３．５６ＭＨｚのラジオ波電力を引加する容量結合型プラズマを用いてＩ
ｎＧａＺｎＯ4焼結体のターゲットをスパッタリングし、加熱していないＳｉＯ2熱酸化膜
２上にａ−ＩＧＺＯ薄膜を製膜した。ＲＦ電源出力は３０〜７０Ｗ、基板−ターゲット間
距離は４０〜９０mm、プラズマガスはＡｒとＯ2の混合ガス、全圧を０．１〜１Ｐａ、酸
素分圧を０．０１〜０．１Ｐａの範囲とした。
The a-IGZO
An nGaZnO 4 sintered target was sputtered to form an a-IGZO thin film on the unheated SiO 2
製膜後に試料をＲＦＭＳ装置から取り出し、サムコ社製ＵＶオゾンクリーナー（型式 Ｕ
Ｖ−１）に搬送した。次に、１気圧のオゾン含有乾燥酸素（オゾン含有量０．５容積％）
雰囲気中で１００℃（実施例１−１）、１３０℃（実施例１−２）、１５０℃（実施例１
−３）、で各１５分の熱処理を行った。乾燥酸素は工業用酸素を上記装置に供給し、ＵＶ
ランプ及びプラズマオゾン発生器を用いてオゾンを生成した。試料温度はヒーターによる
基板加熱機構により上記温度に設定した。
After film formation, the sample was taken out from the RFMS apparatus, and UV ozone cleaner (model U
V-1). Next, 1 atmosphere of ozone-containing dry oxygen (ozone content 0.5% by volume)
100 ° C. (Example 1-1), 130 ° C. (Example 1-2), 150 ° C. (Example 1) in the atmosphere
-3), heat treatment was performed for 15 minutes each. Dry oxygen supplies industrial oxygen to the above equipment, UV
Ozone was generated using a lamp and a plasma ozone generator. The sample temperature was set to the above temperature by a substrate heating mechanism using a heater.
その後、フォトリソグラフィーと電子線蒸着法によりＡｕ(３０ｎｍt) /Ｔｉ(５ｎｍt)
層からなるソース電極４及びドレイン電極５を作製した。また、基板１にＡｌ層からなる
ゲート電極６を作製した。チャネル長(L)及びチャネル幅(W)はＬ／Ｗ＝５０／３００μｍ
とした。
［比較例１、２］
Thereafter, Au by photolithography and electron beam deposition (30nm t) / Ti (5nm t)
A
It was.
[Comparative Examples 1 and 2]
実施例１と同じ方法でａ−ＩＧＺＯ層を製膜した。次に、オゾンを含まない１気圧の乾燥
酸素中で１００℃（比較例１−１）、１５０℃（比較例１−２）、２００℃（比較例１−
３）の温度で熱処理を行った。また、１気圧、露点温度５０℃の湿潤酸素中で１００℃（
比較例２−１）、１５０℃（比較例２−２）、２００℃（比較例２−３）の温度で熱処理
を行ってａ−ＩＧＺＯ薄膜をチャネル層とするボトムゲート型ＴＦＴを作製した。なお、
加熱条件は加熱雰囲気を変更した以外は、実施例１と同じ条件である。
An a-IGZO layer was formed in the same manner as in Example 1. Next, 100 ° C. (Comparative Example 1-1), 150 ° C. (Comparative Example 1-2), and 200 ° C. (Comparative Example 1-) in 1 atmosphere of dry oxygen not containing ozone.
Heat treatment was performed at the temperature of 3). Also, 100 ° C. in wet oxygen with 1 atm and dew point temperature of 50 ° C.
Comparative Example 2-1), 150 ° C. (Comparative Example 2-2), and 200 ° C. (Comparative Example 2-3) were heat-treated to produce a bottom gate TFT having an a-IGZO thin film as a channel layer. In addition,
The heating conditions are the same as in Example 1 except that the heating atmosphere is changed.
作製したＴＦＴは大気中、暗所にて、出力特性、伝達特性の解析を行った。図１に、実施
例１のＴＦＴの伝達特性を示す。比較のために、１５０℃で０．５分の短時間熱処理した
結果の伝達特性を図１に示す。実施例１−１のＴＦＴの移動度は６．７ｃｍ2／Ｖｓ、閾
値電圧は１．５Ｖであったが、サブスレッショルド値は０．７８Ｖ／ｄｅｃａｄｅであっ
た。実施例１−２のＴＦＴの移動度は８．９ｃｍ2／Ｖｓ、閾値電圧は０．３Ｖであり、
サブスレッショルド値も０．４Ｖ／ｄｅｃａｄｅへ改善した。実施例１−３のＴＦＴの移
動度は１０．３ｃｍ2／Ｖｓ、サブスレッショルド値は０．２６Ｖ／ｄｅｃａｄｅであり
、閾値電圧−２．０Ｖが得られた。実施例１では、閾値電圧は０±２Ｖの範囲にあること
が分かる。
The produced TFTs were analyzed for output characteristics and transfer characteristics in the air and in a dark place. FIG. 1 shows the transfer characteristics of the TFT of Example 1. For comparison, FIG. 1 shows transfer characteristics as a result of a short heat treatment at 150 ° C. for 0.5 minutes. The mobility of the TFT of Example 1-1 was 6.7 cm 2 / Vs and the threshold voltage was 1.5 V, but the subthreshold value was 0.78 V / decade. The mobility of the TFT of Example 1-2 is 8.9 cm 2 / Vs, the threshold voltage is 0.3 V,
The subthreshold value was also improved to 0.4 V / decade. The mobility of the TFT of Example 1-3 was 10.3 cm 2 / Vs, the subthreshold value was 0.26 V / decade, and a threshold voltage of −2.0 V was obtained. In Example 1, it can be seen that the threshold voltage is in the range of 0 ± 2V.
図２に、比較例１のａ−ＩＧＺＯ薄膜をチャネル層としたＴＦＴの伝達特性を示す。比較
例１−１のＴＦＴの移動度は４．１ｃｍ2／Ｖｓ、サブスレッショルド値は０．５３Ｖ／
ｄｅｃａｄｅ、比較例１−２のＴＦＴの移動度は８．９ｃｍ2／Ｖｓ、サブスレッショル
ド値は０．３８Ｖ／ｄｅｃａｄｅと、実施例１のＴＦＴよりも悪い。また、閾値電圧は、
比較例１−１では８．８Ｖ、比較例２−１では−５Ｖとなり、大きく負の値にシフトした
。比較例１−３のＴＦＴの移動度は１１ｃｍ2／Ｖｓ、サブスレッショルド値は０．２９
Ｖ／ｄｅｃａｄｅであったが、閾値電圧は−１０Ｖと、やはり大きく負の値にシフトした
。
FIG. 2 shows the transfer characteristics of a TFT using the a-IGZO thin film of Comparative Example 1 as a channel layer. The mobility of the TFT of Comparative Example 1-1 was 4.1 cm 2 / Vs, and the subthreshold value was 0.53 V /
The mobility of TFT of comparative example 1-2 is 8.9 cm 2 / Vs, and the subthreshold value is 0.38 V / decade, which is worse than the TFT of example 1. The threshold voltage is
In Comparative Example 1-1, the voltage was 8.8 V, and in Comparative Example 2-1, it was −5 V, which was greatly shifted to a negative value. The mobility of the TFT of Comparative Example 1-3 is 11 cm 2 / Vs, and the subthreshold value is 0.29.
Although it was V / decade, the threshold voltage was -10V, which was also greatly shifted to a negative value.
図３に、比較例２のａ−ＩＧＺＯ薄膜をチャネル層としたＴＦＴの伝達特性を示す。比較
例２−１のＴＦＴの移動度は４．１ｃｍ2／Ｖｓ、サブスレッショルド値は０．５３Ｖ／
ｄｅｃａｄｅ、比較例２−２のＴＦＴの移動度は８．９ｃｍ2／Ｖｓ、サブスレッショル
ド値は０．４Ｖ／ｄｅｃａｄｅと、実施例１のＴＦＴよりも悪い。また、閾値電圧は、比
較例２−１では−３．１Ｖ、比較例２−２では−４０Ｖとなり、大きく負の値にシフトし
た。比較例２−３では閾値電圧は−５０Ｖ以下となり、ＴＦＴの移動度もサブスレッショ
ルド値も測定不能であった。よって、ＴＦＴ特性は、実施例１のＴＦＴでは比較例１、２
よりも大幅に改善され、特に、閾値電圧を−２ 〜 ２Ｖの範囲で制御できたことが分かる
。
FIG. 3 shows the transfer characteristics of a TFT using the a-IGZO thin film of Comparative Example 2 as a channel layer. The mobility of the TFT of Comparative Example 2-1 is 4.1 cm 2 / Vs, and the subthreshold value is 0.53 V /
Decade, the mobility of the TFT of Comparative Example 2-2 is 8.9 cm 2 / Vs, and the subthreshold value is 0.4 V / decade, which is worse than the TFT of Example 1. Further, the threshold voltage was −3.1 V in Comparative Example 2-1, and −40 V in Comparative Example 2-2, and was greatly shifted to a negative value. In Comparative Example 2-3, the threshold voltage was −50 V or less, and neither the mobility of the TFT nor the subthreshold value could be measured. Therefore, the TFT characteristics of the TFT of Example 1 are Comparative Examples 1 and 2.
It can be seen that the threshold voltage can be controlled in the range of −2 to 2 V, in particular.
実施例及び比較例の結果を表１にまとめて示す。 The results of Examples and Comparative Examples are summarized in Table 1.
本発明によれば、熱処理の影響による閾値電圧シフトを低減して、Ｉｎ−Ｇａ−Ｚｎ−Ｏ
系アモルファス酸化物半導体膜を用いた薄膜トランジスタにおいて、ａ−ＩＧＺＯ薄膜の
閾値電圧 が０±５Ｖ以内、電界効果移動度が５ｃｍ2／Ｖｓ以上であるＴＦＴを提供でき
る。また、大面積有機ＬＥＤ（ＯＬＥＤ）ディスプレイ及び液晶ディスプレイにおいて、
ＴＦＴ作製プロセスの低温化は、廉価なガラス基板を使用できる、昇温・降温時間の低減
、熱コストの削減、熱膨張によるパターン合わせ精度の低下の抑制など、メリットが多い
。また、プラスチック基板上にこれらディスプレイや電子回路を作製する場合は、軟化点
の高いポリイミドを使っても３００℃、軟化点の低いＰＥＴを使う場合は１５０℃以下に
することが必要である。本発明の方法は、ａ−ＩＧＺＯ薄膜を１００〜２００℃で熱処理
することによって、製作したＴＦＴの閾値電圧を０Ｖ近辺で制御できることにより、単純
な回路を用い、ＴＦＴがオフ時の印加電圧を下げることが可能となる。
According to the present invention, the threshold voltage shift due to the influence of heat treatment is reduced, and In—Ga—Zn—O
In a thin film transistor using an amorphous oxide semiconductor film, a TFT in which a threshold voltage of an a-IGZO thin film is within 0 ± 5 V and field effect mobility is 5 cm 2 / Vs or more can be provided. In large area organic LED (OLED) displays and liquid crystal displays,
Lowering the temperature of the TFT fabrication process has many advantages such as the ability to use an inexpensive glass substrate, reduction in temperature rise / fall time, reduction in thermal cost, and suppression of deterioration in pattern alignment accuracy due to thermal expansion. Further, when these displays and electronic circuits are produced on a plastic substrate, it is necessary that the temperature be 300 ° C. even when polyimide having a high softening point is used, and 150 ° C. or lower when PET having a low softening point is used. The method of the present invention uses a simple circuit to lower the applied voltage when the TFT is turned off, because the threshold voltage of the fabricated TFT can be controlled around 0 V by heat-treating the a-IGZO thin film at 100 to 200 ° C. It becomes possible.
Claims (2)
−Ｇａ−Ｚｎ−Ｏ系アモルファス酸化物半導体膜を用いた薄膜トランジスタにおいて、オ
ゾンを含む乾燥酸素ガス雰囲気による熱処理後のａ−ＩＧＺＯ薄膜の閾値電圧が０±５Ｖ
以内、電界効果移動度が５ｃｍ2／Ｖｓ以上であることを特徴とする薄膜トランジスタ。 The substrate includes a substrate, a gate electrode, a gate insulating film, and a channel layer.
In a thin film transistor using a —Ga—Zn—O-based amorphous oxide semiconductor film, the threshold voltage of the a-IGZO thin film after heat treatment in a dry oxygen gas atmosphere containing ozone is 0 ± 5 V
And a field effect mobility of 5 cm 2 / Vs or more.
−Ｇａ−Ｚｎ−Ｏ系アモルファス酸化物半導体膜を用いた薄膜トランジスタの製造方法に
おいて、該半導体膜を製膜した後、乾燥酸素中にオゾンを１．０容積％以下０．０１容積
％以上含む乾燥酸素ガス雰囲気中で該半導体膜を１００〜２００℃の温度範囲内で１〜１
２０分間、熱処理することを特徴とする薄膜トランジスタの製造方法。 The substrate includes a substrate, a gate electrode, a gate insulating film, and a channel layer.
In the method for manufacturing a thin film transistor using a —Ga—Zn—O-based amorphous oxide semiconductor film, after the semiconductor film is formed, the dry oxygen containing 1.0% by volume or less and 0.01% by volume or more ozone in dry oxygen The semiconductor film is placed in a temperature range of 100 to 200 ° C. in an oxygen gas atmosphere.
A method of manufacturing a thin film transistor, characterized by performing a heat treatment for 20 minutes.
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| KR20220009453A (en) | 2019-06-28 | 2022-01-24 | 가부시키가이샤 아루박 | Sputtering target and manufacturing method of sputtering target |
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