JP4265042B2 - Capacitors - Google Patents

Description

【００２９】
上記表１に示すように、Ｌａはイオン半径がＰｂのものと近似しており、Ｎｂ及びＢｉは電気陰性度がＰｂのものと近似している。一方、Ｌｉの電気陰性度及びイオン半径はＰｂのそれらと著しく相違する。このように、Ｌｉの添加元素としての性質は従来の添加元素と比して著しく相違するものである。また、ＦｅはＰｂと同程度の電気陰性度を有するが、標準生成エネルギはＬｉの方がＦｅよりも低く、酸化物はＬｉ酸化物の方がより安定に存在する。
【００３０】
次に、上述のような組成を有する誘電体薄膜をキャパシタ絶縁膜として備えた本発明の実施例を適用した誘電体メモリを製造する方法について説明する。図１（ａ）及び（ｂ）並びに図２（ａ）乃至（ｃ）は本発明の実施例を適用した誘電体メモリを製造する方法を工程順に示す断面図である。
【００３１】
図１（ａ）に示すように、従来の方法と同様の方法により、膜厚が、例えば、０．６ｍｍのシリコン基板１の表面又は表面上にゲート酸化膜２、ゲート電極３、ソース４ａ及びドレイン４ｂを形成する。更に、全面に膜厚が、例えば、４５０ｎｍの第１のＳｉＯ₂膜８を層間絶縁膜として形成する。
【００３２】
次いで、図１（ｂ）に示すように、全面に第１の導電膜５ａ、前述の組成を有し膜厚が、例えば、２００ｎｍの誘電体膜６及び第２の導電膜５ｂを順次形成する。なお、誘電体膜６の具体的な形成方法については後述する。また、第１の導電膜は、例えば、膜厚が２０ｎｍのＴｉ膜及び膜厚が２０００ÅのＰｔ膜からなる。更に、第２の導電膜は、例えば、Ｐｔ膜からなる。
【００３３】
次に、図２（ａ）に示すように、キャパシタが形成される予定の所定の領域にのみ残るように第２の導電膜５ｂ、誘電体膜６及び第１の導電膜５ａをイオンミリング等によりパターニングする。これにより、第１の導電膜５ａから下部電極が構成され、誘電体膜６からキャパシタ絶縁膜が構成され、第２の導電膜５ｂから上部電極が構成される。
【００３４】
その後、図２（ｂ）に示すように、全面に第２のＳｉＯ₂膜９を層間絶縁膜として形成する。次いで、第２の導電膜５ｂ、ソース４ａ及びドレイン４ｂの各拡散層まで到達するコンタクトホール１０を第１のＳｉＯ₂膜８及び第２のＳｉＯ₂膜９に形成する。
【００３５】
そして、図２（ｃ）に示すように、Ａｌ膜を全面に形成しパターニングすることにより、コンタクトホール１０内にＡｌ配線層７を埋設する。このとき、第２の導電層５ｂとドレイン４ｂとがＡｌ配線層７により接続されるようにする。これにより、１個のトランジスタ１１及び１個のキャパシタ１２が形成される。
【００３６】
図３は本発明の実施例を適用した誘電体メモリを示す等価回路図である。上述のようにして構成された誘電体メモリセルは、図３に示すように、１個のトランジスタ１１と１個のキャパシタ１２から構成される。そして、この誘電体メモリに１ビットの情報が記憶される。
【００３７】
次に、誘電体膜６の形成方法について具体的に説明する。誘電体膜６は種々の方法により形成することが可能であるが、ここではその一例として、ゾルゲル液を使用する形成方法について説明する。先ず、２０．９ｇの２酢酸鉛・３水和物を溶媒である７０ミリリットルのメトキシエタノールに入れた後、８００℃で３０乃至６０分間加熱攪拌することにより、２酢酸鉛・３水和物を溶解させる。このとき、鉛酸化物は０．０５モルの１．１倍使用されている。これは、加熱時のＰｂの蒸発、電極中への拡散及びＰｂの純度が９９．９％であるための補正を考慮したものである。
【００３８】
次に、溶液を反応器に移し、更に溶媒を加えて全量を２００ミリリットルとする。そして、１２４℃で１２時間の加熱攪拌により脱水を行う。
【００３９】
次いで、反応系の温度を６０℃まで降温した後、８．６９１ｇのテトライソプロポキシジルコニウム（０．０２６モル、純度９８％補正済み）及び７．１４４ミリリットルのテトライソプロポキシチタン（０．０２４モル、純度９９．９９９％補正済み）を反応系に加える。更に、０．３３３ｇのイソプロポキシリチウム（０．００５モル、純度９９．９％補正済み）を反応系に加え、１２４℃で６時間の加熱攪拌を行う。
【００４０】
そして、攪拌終了後に溶液をメスシリンダに移し、溶媒を更に加えて全量を１００ミリリットルとする。これにより、リチウムを含有するＰＺＴゾルゲル液が作製される。０．０５モルの液が１００ミリリットルの液中にあるので、その濃度は０．５モル／リットルとなる。
【００４１】
なお、全ての加熱攪拌は窒素気流下で行われる。
【００４２】
次に、上述のように作製されたリチウムを含有するＰＺＴゾルゲル液を第１の導電膜５ａ上に３０００ｒｐｍの回転数で１０秒間スピンコーティングする。そして、１５０℃で５分間のプリベーク及び４００℃で１０分間のプリベークの２段階のプリベークをホットプレートを使用して行う。以降、スピンコーティング及び２段階のプリベークを４回繰り返す。これにより、アモルファス状の膜が第１の導電膜５ａ上に形成される。
【００４３】
次いで、酸素雰囲気の６００℃のオーブン中で１時間のアニールを行うか、又は、酸素雰囲気の６００℃の赤外線イメージ炉（ＲＴＡ）中で１分間のアニールを行う。これにより、アモルファス状の膜が結晶化し、誘電体膜６が形成される。なお、前述のように、誘電体膜６の形成方法はゾルゲル液を使用する方法に限定されるものではなく、スパッタリング法又はＣＶＤ法等によっても形成可能である。また、ゾルゲル液の作製に使用される薬品の量等も上述の数値に限定されるものではない。
【００４４】
なお、上述の形成方法においては、誘電体膜６をキャパシタ絶縁膜として２００ｎｍ形成したが、キャパシタ絶縁膜の膜厚はこれに限定されるものではなく、２００乃至３０００Åであればよい。
【００４５】
キャパシタ絶縁膜として誘電体膜を使用する場合、その膜厚が２００Å未満であると、均一な膜を得られず、リーク電流が増大し、歩留まりが悪くなる。一方、膜厚が３０００Åを超えると、微細加工が困難となり、歩留まりが著しく悪くなる。従って、キャパシタ絶縁膜としての誘電体膜の膜厚は２００乃至３０００Åとする。但し、誘電体膜の膜厚が５００Å未満であると、均一な膜が得にくくなり、歩留まりが低下する。一方、膜厚が２０００Åを超えると、キャパシタンス（静電容量）が低くなり、誘電率を有効に生かすことができなくなる。従って、キャパシタ絶縁膜としての誘電体膜の膜厚は５００乃至２０００Åであることが望ましい。
【００４６】
【実施例】
以下、本発明の実施例について、その特許請求の範囲から外れる比較例と比較して具体的に説明する。
【００４７】
第１実施例
先ず、下記表３に示す基板上に表３に示す下部電極をスパッタ法により形成した。なお、実施例１並びに比較例２及び３の基板表面には、膜厚が２４５００ÅであるＳｉＯ₂膜が熱酸化により形成されている。次いで、下部電極上に下記表２に示すキャパシタ絶縁膜を形成した。キャパシタ絶縁膜の形成の際には、スピンコート等の後に７００℃の電気炉内に１時間保持することによりアニールを施した。その後、キャパシタ絶縁膜上に膜厚が１０００ÅのＰｔ電極を上部電極として形成することにより、キャパシタを作製した。
【００４８】
【表２】

【００４９】
【表３】

【００５０】
そして、各実施例及び比較例について、キャパシタ絶縁膜の比誘電率を測定した。この結果を下記表４に示す。なお、比誘電率の測定に使用したインピーダンスアナライザの測定周波数は１０ｋＨｚに設定した。
【００５１】
【表４】

【００５２】
上記表４に示すように、ＰｂＺｒ_0.4Ｔｉ_0.6Ｏ₃に１モル％のＬｉが添加された実施例１においては、高い比誘電率が得られた。
【００５３】
一方、比較例２及び３においては、Ｌｉが添加されていないので、十分な比誘電率は得られなかった。
【００５４】
また、比較例４においては、高い比誘電率が得られたものの、Ｌｉが添加されておらず、単結晶ＭｇＯ基板等を使用しているため、コストが高かった。
【００５５】
第２実施例
先ず、ＰｂＺｒ_0.4Ｔｉ_0.6Ｏ₃に０．０００５モル％、０．００１モル％、１モル％、１０モル％、２０モル％又は３０モル％のＬｉを添加した誘電体膜及びＬｉを全く添加しない誘電体膜を作製した。膜厚は、１００Å、３００Å、５００Å、１０００Å、２０００Å、５０００Å、６０００Å又は１００００Åとした。そして、各試料について比誘電率を測定した。この結果を図４に示す。図４は横軸に誘電体膜の膜厚をとり、縦軸に比誘電率をとって両者の関係を示すグラフ図である。なお、図４において、●印及び実線で示すものはＬｉを添加していないもの（比較例９）、●印及び破線で示すものはＬｉを０．０００５モル％添加したもの（比較例１０）、■印及び実線で示すものはＬｉを０．００１モル％添加したもの（実施例５）、■及び破線で示すものはＬｉを１モル％添加したもの（実施例６）、▲印及び実線で示すものはＬｉを１０モル％含むもの（実施例７）、▲印及び破線で示すものはＬｉを２０モル％含むもの（実施例８）、◆及び実線で示すものはＬｉを３０モル％添加したもの（比較例１１）である。
【００５６】
図４に示すように、Ｌｉの添加量が本発明（請求項１）の範囲内にある実施例５乃至８においては、３００Å以上の膜厚で２０００以上の比誘電率を得ることができた。また、膜厚が１００Åであっても、１５００以上の比誘電率を得ることができた。
【００５７】
一方、比較例９においては、Ｌｉが添加されておらず、比較例１０においては、Ｌｉの添加量が本発明範囲の下限未満であるので、膜厚が５０００Åを超えなければ２０００以上の比誘電率を得ることができなかった。また、比較例１１においては、Ｌｉの添加量が本発明範囲の上限を超えているので、十分な比誘電率を得ることができなかった。
【００５８】
図５は横軸に誘電体膜へのＬｉ添加量をとり、縦軸に誘電率をとって両者の関係を示すグラフ図であり、図６は図５の横軸を対数表示したグラフ図である。なお、図５及び図６において、●印で示すものは、膜厚が５０００Åであるもの、■印で示すものは、膜厚が２０００Åであるものである。また、図６においては、対数表示であるため、Ｌｉが添加されていないものをＬｉが極微量（０．０００１モル％）添加されているものとして示してある。
【００５９】
図５及び図６に示すように、Ｌｉ添加量が０．００１モル％未満となるか、又は２０モル％を超えると、比誘電率が２０００よりも低くなった。
【００６０】
第３実施例
ＰｂＺｒ_0.4Ｔｉ_0.6Ｏ₃にＬｉを１モル％添加して形成した膜をキャパシタ絶縁膜とするキャパシタを作製した。このときの上部電極及び下部電極の材料及びその格子定数及びその配向状態を下記表５に示す。
【００６１】
【表５】

【００６２】
そして、各実施例及び比較例について、キャパシタ絶縁膜の比誘電率を測定した。この結果を下記表６に示す。
【００６３】
【表６】

【００６４】
上記表６に示すように、実施例１２及び１３においては、電極材料の格子定数が本発明範囲内にあるので、基板との整合により（００１）配向が得られ、高い比誘電率が得られた。
【００６５】
一方、比較例１４乃至１６においては、電極材料の格子定数が本発明範囲からはずれているので、基板との整合がとれず、ランダム配向となって比誘電率が低いものとなった。
【００６６】
第４実施例
ＰｂＺｒ_0.4Ｔｉ_0.6Ｏ₃にＬｉを１モル％添加して形成した膜をキャパシタ絶縁膜とするキャパシタを作製した。このときの上部電極及び下部電極は厚さが１０００ÅのＰｔ電極である。キャパシタ絶縁膜の厚さを下記表７に示す。
【００６７】
【表７】

【００６８】
そして、各実施例及び比較例について、微細加工性の評価及びリーク電流の測定を行った。なお、微細加工性の評価は、歩留りよく加工できる最小線幅の測定により行った。これらの結果を下記表８に示す。なお、総合評価の欄において、◎は極めて良好であることを示し、○は良好であることを示し、△はやや不良であることを示し、×は不良であることを示している。
【００６９】
【表８】

【００７０】
上記表８に示すように、実施例１７乃至２０においては、誘電体膜からなるキャパシタ絶縁膜の膜厚が本発明の範囲内にあるので、微細加工性が高く、また、リーク電流が低かった。
【００７１】
一方、比較例２１及び２２においては、キャパシタ絶縁膜の膜厚が本発明範囲の上限を超えているので、微細加工性が低くかった。また、比較例２３においては、キャパシタ絶縁膜の膜厚が本発明範囲の下限未満であるので、リーク電流が大きいか、又は短絡が生じた。
【００７２】
【発明の効果】
以上詳述したように、本発明によれば、ＰＺＴ系誘電体材料にＬｉを含有させているので、Ｏ₂の欠損を抑制することができる。このため、単結晶基板を使用したり、又は特別な方法を採用する必要がないので、低コストで薄膜化しながら誘電率を著しく向上させることができる。また、このような誘電体膜をキャパシタ絶縁膜として使用すれば、静電容量が大きいキャパシタを得ることができる。
【図面の簡単な説明】
【図１】 （ａ）及び（ｂ）は本発明の実施例を適用した誘電体メモリを製造する方法を工程順に示す断面図である。
【図２】 （ａ）乃至（ｃ）は、同じく、誘電体メモリを製造する方法を示す図であって、図１（ａ）及び（ｂ）に示す工程の次工程を工程順に示す断面図である。
【図３】 本発明の実施例を適用した誘電体メモリを示す等価回路図である。
【図４】 誘電体膜の膜厚と誘電率との関係を示すグラフ図である。
【図５】 誘電体膜へのＬｉ添加量と誘電率との関係を示すグラフ図である。
【図６】 図５の横軸を対数表示したグラフ図である。
【符号の説明】
１；シリコン基板、 ２；ゲート酸化膜、 ３；ゲート電極、 ４ａ；ソース、 ４ｂ；ドレイン、 ５ａ、５ｂ；導電膜、 ６；誘電体膜、 ７；Ａｌ配線層、 ８、９；ＳｉＯ₂膜、 １０；コンタクトホール、 １１；トランジスタ、 １２；キャパシタ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a preferred key Yapashi data in a semiconductor device, particularly, relates to a key Yapashi data permittivity is improved.
[0002]
[Prior art]
Conventionally, as a ferroelectric material used for a ferroelectric film in a ferroelectric random access memory (FRAM), a lead-based oxide ferroelectric material and a bismuth layered structure ferroelectric material have been used. Yes. Examples of the former lead-based oxide ferroelectric material include PZT (Pb (Zr, Ti) O ₃ ) -based ferroelectric material having a perovskite crystal structure and lead titanate (PbTiO ₃ ). PZT-based ferroelectric materials and lead titanate (PbTiO ₃ ) thin films are expected to be applied to infrared sensor materials, microactuator materials, memory materials, and the like.
[0003]
However, these thin films are known to have a significant decrease in dielectric characteristics, particularly dielectric constant, when the film thickness is 1 μm or less, regardless of the manufacturing method. It is a big obstacle.
[0004]
In order to improve such a decrease in dielectric constant, various methods for producing thin films and additives have been studied so far. Among them, it is known that a dielectric property can be improved by using a (Pb, La) TiO ₃ thin film (PLT thin film) in which a part of Pb in the lead titanate crystal lattice is replaced with La.
[0005]
These ferroelectric thin films are usually formed on the lower electrode provided on the Si wafer by sputtering or sol-gel method.
[0006]
[Problems to be solved by the invention]
However, when the PZT-based ferroelectric thin film is formed on the lower electrode provided on the Si wafer by sputtering or sol-gel method, if the film thickness is 1 μm or less, in the vicinity of the interface between the thin film and the lower electrode There is a problem in that the loss of O ₂ occurs and the dielectric constant decreases.
[0007]
If a single crystal Pt electrode is formed as a lower electrode on a single crystal substrate such as Mg having a mirror index of (100) on the surface, and a PZT layer is epitaxially grown thereon by metal organic CVD (MOCVD) or the like, defects A thin film having a high dielectric constant can be obtained, but the cost is extremely high.
[0008]
The present invention has been made in view of such problems, and an object of the present invention is to provide a capacitor that includes a dielectric film having a film thickness of 0.5 μm or less and a high dielectric constant and can be manufactured at low cost. To do.
[0011]
In the present invention, since the PZT ferroelectric material contains Li, the standard generation energy is large and oxygen escape is prevented. This makes it possible to increase the dielectric constant while reducing the film thickness without using a single crystal substrate or adopting a special method.
[0012]
[Means for Solving the Problems]
A capacitor according to the present invention includes a lower electrode, a dielectric film formed on the lower electrode, and an upper electrode formed on the dielectric film, wherein the dielectric film is Pb _x Zr. _(1-y) having a composition containing Ti _y O ₃ and Li, the value of x being 0.9 to 1.3, and the value of y being 0.3 to 0.7, The content of Li is 0.001 to 20 mol% with respect to the content of Pb _x Zr _(1-y) Ti _y O ₃ , the thickness of the dielectric film is 200 to 3000 mm, and the upper electrode And at least one of the lower electrodes is a Pt electrode.
[0013]
Another capacitor according to the present invention is a capacitor having a lower electrode, a dielectric film formed on the lower electrode, and an upper electrode formed on the dielectric film, wherein the dielectric film is Pb. _x Zr _(1-y) Ti _y O ₃ and a composition containing Li, the value of x being 0.9 to 1.3, and the value of y being 0.3 to 0.7, The Li content of the film is 0.001 to 20 mol% with respect to the content of Pb _x Zr _(1-y) Ti _y O ₃ , and the film thickness of the dielectric film is 200 to 3000 mm, The lattice constant of the conductive material constituting the upper electrode and the lower electrode is 3.5 to 4.3 cm or 5.0 to 6.1 cm.
[0014]
The dielectric film preferably has a thickness of 500 to 2000 mm.
[0015]
In the present invention, since the dielectric film having a high dielectric constant as described above serves as the capacitor insulating film, a high capacitance can be ensured.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
The inventors of the present invention have conducted extensive experimental studies to solve the above problems, and as a result, Pb _x Zr _(1-y) Ti _y O ₃ , which is a PZT-based ferroelectric material, contains Li. It has been found that a sufficiently high dielectric constant can be obtained even if the film thickness is reduced to 5 μm or less.
[0018]
Hereinafter, the chemical components contained in the dielectric film according to the present invention and the reasons for limiting the composition thereof will be described.
[0019]
Li is an element having a large standard generation energy of Pb _x Zr _(1-y) Ti _y O ₃ and a high bonding force with O. Therefore, the decrease of the polarization amount is prevented by preventing the oxygen loss, and the dielectric constant is remarkably improved.
[0020]
In Pb _x Zr _(1-y) Ti _y O ₃ , the value of x is 0.9 to 1.3, and the value of y is 0.3 to 0.7.
[0021]
If the value of x is less than 0.9, Pb is insufficient and the spontaneous polarization tends to be low. On the other hand, if the value of x exceeds 1.3, the leakage current tends to increase due to excess Pb. If the value of y is less than 0.3, Ti is insufficient and the spontaneous polarization of the ferroelectric material tends to be low. On the other hand, if the value of y exceeds 0.7, Ti becomes excessive and the leakage current of the ferroelectric material tends to increase. Therefore, the value of x is 0.9 to 1.3, and the value of y is 0.3 to 0.7.
[0022]
The Li content is 0.001 to 20 mol% with respect to the Pb _x Zr _(1-y) Ti _y O ₃ content.
[0023]
When the content of Li is less than 0.001 mol% with respect to the content of Pb _x Zr _(1-y) Ti _y O ₃ , the effect of containing Li is low and the improvement of the dielectric constant is small. On the other hand, when the Li content exceeds 20 mol%, the leakage current increases. In addition, the dielectric constant decreases. Therefore, the content of Li is set to 0.001 to 20 mol% with respect to the content of Pb _x Zr _(1-y) Ti _y O ₃ .
[0024]
The film thickness of the dielectric film is 5000 mm or less.
[0025]
If the film thickness of the dielectric film exceeds 5000 mm, fine processing of 1 μm or less becomes difficult. Therefore, the film thickness of the dielectric film is 5000 mm. However, if the film thickness is less than 200 mm, a sufficient dielectric constant may not be obtained. On the other hand, when the film thickness exceeds 3000 mm, fine processing of 1 μm or less is possible, but the yield is lowered. Accordingly, the thickness of the dielectric film is desirably 200 to 3000 mm. Furthermore, if the film thickness is less than 2000 mm, it may be difficult to perform film formation stably. Therefore, the thickness of the dielectric film is more desirably 2000 mm or more.
[0026]
When a dielectric film having such a composition is used as a capacitor insulating film, an electrode that can be easily formed, such as a Pt electrode or an Ir electrode, can be used as a capacitor electrode. The PZT crystal belongs to the tetragonal system, and its a-axis length is 3.9３. The dielectric constant of PZT is most effectively increased when its c-axis is oriented perpendicular to the substrate. For this reason, it is also possible to use a conductive material having a lattice constant of 3.5 to 4.3 mm or 5.0 to 6.1 mm as the upper electrode or the lower electrode. When the lattice constant of the conductive material is less than 3.5 mm, more than 4.3 mm and less than 5.0 mm, or more than 6.1 mm, the c-axis of the crystal lattice of the conductive material is oriented perpendicular to the substrate. It disappears and the dielectric constant decreases. Therefore, the lattice constant of the conductive material used as the upper electrode or the lower electrode is set to 3.5 to 4.3 mm or 5.0 to 6.1 mm. The range of 3.5 to 4.3 mm is within ± 10% of the length of the a-axis (3.9 mm), and the range of 5.0 to 6.1 mm is the length of the a-axis 2 is a range within ± 10% of ^half the ones (length of the diagonal line of the bottom surface of the unit cell (5.52Å)).
[0027]
Note that Li is an element that is significantly different in properties as an additive element from an element added to a conventional PZT-based ferroelectric material. As described above, La, Nb, Bi, or the like is conventionally added to the PZT-based ferroelectric material in order to prevent O from coming out of the film made of the PZT-based ferroelectric material. is there. Since these additive elements act as substitution elements for Pb, their electronegativity or ionic radius is close to that of Pb. Table 1 below shows the electronegativity and ionic radius of various elements.
[0028]
[Table 1]

[0029]
As shown in Table 1 above, La approximates that of an ion radius of Pb, and Nb and Bi approximate that of an electronegativity of Pb. On the other hand, the electronegativity and ionic radius of Li are significantly different from those of Pb. Thus, the properties of Li as an additive element are significantly different from those of conventional additive elements. Fe has an electronegativity comparable to that of Pb, but the standard generation energy of Li is lower than that of Fe, and the oxide of Li oxide exists more stably.
[0030]
Next, a method for manufacturing a dielectric memory to which an embodiment of the present invention provided with a dielectric thin film having the above composition as a capacitor insulating film will be described. 1A and 1B and FIGS. 2A to 2C are cross-sectional views showing a method of manufacturing a dielectric memory to which an embodiment of the present invention is applied in the order of steps.
[0031]
As shown in FIG. 1A, a gate oxide film 2, a gate electrode 3, a source 4a, and a surface of a silicon substrate 1 having a thickness of, for example, 0.6 mm are formed by a method similar to the conventional method. A drain 4b is formed. Further, a first SiO ₂ film 8 having a thickness of, for example, 450 nm is formed as an interlayer insulating film on the entire surface.
[0032]
Next, as shown in FIG. 1B, a first conductive film 5a, a dielectric film 6 having the above-described composition and a film thickness of, for example, 200 nm, and a second conductive film 5b are sequentially formed on the entire surface. . A specific method for forming the dielectric film 6 will be described later. The first conductive film is made of, for example, a 20 nm thick Ti film and a 2000 mm thick Pt film. Furthermore, the second conductive film is made of, for example, a Pt film.
[0033]
Next, as shown in FIG. 2A, the second conductive film 5b, the dielectric film 6 and the first conductive film 5a are ion milled or the like so as to remain only in a predetermined region where a capacitor is to be formed. To pattern. Thus, the first conductive film 5a forms a lower electrode, the dielectric film 6 forms a capacitor insulating film, and the second conductive film 5b forms an upper electrode.
[0034]
Thereafter, as shown in FIG. 2B, a second SiO ₂ film 9 is formed as an interlayer insulating film on the entire surface. Next, contact holes 10 reaching the diffusion layers of the second conductive film 5b, the source 4a, and the drain 4b are formed in the first SiO ₂ film 8 and the second SiO ₂ film 9.
[0035]
Then, as shown in FIG. 2C, an Al wiring layer 7 is embedded in the contact hole 10 by forming and patterning an Al film on the entire surface. At this time, the second conductive layer 5 b and the drain 4 b are connected by the Al wiring layer 7. Thereby, one transistor 11 and one capacitor 12 are formed.
[0036]
FIG. 3 is an equivalent circuit diagram showing a dielectric memory to which an embodiment of the present invention is applied. The dielectric memory cell configured as described above is composed of one transistor 11 and one capacitor 12 as shown in FIG. Then, 1-bit information is stored in the dielectric memory.
[0037]
Next, a method for forming the dielectric film 6 will be specifically described. The dielectric film 6 can be formed by various methods. Here, as an example, a formation method using a sol-gel solution will be described. First, 20.9 g of lead diacetate trihydrate was placed in 70 ml of methoxyethanol as a solvent, and then heated and stirred at 800 ° C. for 30 to 60 minutes to obtain lead diacetate trihydrate. Dissolve. At this time, lead oxide is used 1.1 times as much as 0.05 mol. This takes into account the correction for evaporation of Pb during heating, diffusion into the electrode, and the purity of Pb being 99.9%.
[0038]
Next, the solution is transferred to a reactor and further solvent is added to make a total volume of 200 milliliters. Then, dehydration is performed by heating and stirring at 124 ° C. for 12 hours.
[0039]
Then, after the temperature of the reaction system was lowered to 60 ° C., 8.691 g of tetraisopropoxyzirconium (0.026 mol, corrected for 98% purity) and 7.144 ml of tetraisopropoxytitanium (0.024 mol, Purity 99.999% corrected) is added to the reaction system. Further, 0.333 g of isopropoxylithium (0.005 mol, purity corrected to 99.9%) is added to the reaction system, and the mixture is heated and stirred at 124 ° C. for 6 hours.
[0040]
And after completion | finish of stirring, a solution is moved to a graduated cylinder, and a solvent is further added to make the whole quantity 100 ml. Thereby, a PZT sol-gel solution containing lithium is produced. Since 0.05 mol of liquid is in 100 ml of liquid, the concentration is 0.5 mol / liter.
[0041]
All heating and stirring is performed under a nitrogen stream.
[0042]
Next, the PZT sol-gel solution containing lithium prepared as described above is spin-coated on the first conductive film 5a for 10 seconds at a rotational speed of 3000 rpm. Then, pre-baking at 150 ° C. for 5 minutes and pre-baking at 400 ° C. for 10 minutes are performed using a hot plate. Thereafter, spin coating and two-stage pre-baking are repeated four times. Thereby, an amorphous film is formed on the first conductive film 5a.
[0043]
Next, annealing is performed in an oxygen atmosphere at 600 ° C. for 1 hour, or in an oxygen atmosphere at 600 ° C. in an infrared image furnace (RTA) for 1 minute. Thereby, the amorphous film is crystallized and the dielectric film 6 is formed. As described above, the method of forming the dielectric film 6 is not limited to the method using a sol-gel solution, and can be formed by a sputtering method or a CVD method. Further, the amount of chemicals used for preparing the sol-gel liquid is not limited to the above-mentioned numerical values.
[0044]
In the above-described forming method, the dielectric film 6 is formed with a thickness of 200 nm as the capacitor insulating film. However, the thickness of the capacitor insulating film is not limited to this, and may be 200 to 3000 mm.
[0045]
When a dielectric film is used as the capacitor insulating film, if the film thickness is less than 200 mm, a uniform film cannot be obtained, the leakage current increases, and the yield deteriorates. On the other hand, when the film thickness exceeds 3000 mm, fine processing becomes difficult and the yield is remarkably deteriorated. Therefore, the film thickness of the dielectric film as the capacitor insulating film is 200 to 3000 mm. However, when the film thickness of the dielectric film is less than 500 mm, it is difficult to obtain a uniform film and the yield decreases. On the other hand, when the film thickness exceeds 2000 mm, the capacitance (capacitance) becomes low, and the dielectric constant cannot be utilized effectively. Therefore, the thickness of the dielectric film as the capacitor insulating film is desirably 500 to 2000 mm.
[0046]
【Example】
Examples of the present invention will be specifically described below in comparison with comparative examples that depart from the scope of the claims.
[0047]
First Example First, a lower electrode shown in Table 3 was formed on a substrate shown in Table 3 below by a sputtering method. Note that a SiO ₂ film having a thickness of 24500 mm is formed by thermal oxidation on the substrate surfaces of Example 1 and Comparative Examples 2 and 3. Next, a capacitor insulating film shown in Table 2 below was formed on the lower electrode. When forming the capacitor insulating film, annealing was performed by holding in an electric furnace at 700 ° C. for 1 hour after spin coating or the like. Thereafter, a Pt electrode having a thickness of 1000 mm was formed as an upper electrode on the capacitor insulating film, thereby manufacturing a capacitor.
[0048]
[Table 2]

[0049]
[Table 3]

[0050]
And about each Example and the comparative example, the dielectric constant of the capacitor insulating film was measured. The results are shown in Table 4 below. The measurement frequency of the impedance analyzer used for measuring the relative dielectric constant was set to 10 kHz.
[0051]
[Table 4]

[0052]
As shown in Table 4 above, in Example 1 in which 1 mol% of Li was added to PbZr _0.4 Ti _0.6 O ₃ , a high relative dielectric constant was obtained.
[0053]
On the other hand, in Comparative Examples 2 and 3, since Li was not added, a sufficient dielectric constant could not be obtained.
[0054]
In Comparative Example 4, although a high relative dielectric constant was obtained, Li was not added and a single crystal MgO substrate or the like was used, so that the cost was high.
[0055]
The second embodiment <br/> First, PbZr _0.4 Ti _0.6 O ₃ to 0.0005 mol%, 0.001 mol%, 1 mol%, 10 mol%, the dielectric with the addition of 20 mol% or 30 mol% of Li A body film and a dielectric film to which no Li was added were prepared. The film thickness was 100 mm, 300 mm, 500 mm, 1000 mm, 2000 mm, 5000 mm, 6000 mm, or 10,000 mm. And the relative dielectric constant was measured about each sample. The result is shown in FIG. FIG. 4 is a graph showing the relationship between the dielectric film thickness on the horizontal axis and the relative dielectric constant on the vertical axis. In FIG. 4, the solid circles and solid lines indicate that no Li is added (Comparative Example 9), and the solid circles and broken lines indicate that 0.0005 mol% Li is added (Comparative Example 10). , ▪ and solid lines indicate that 0.001 mol% Li is added (Example 5), ■ and dotted lines indicate that 1 mol% Li is added (Example 6), ▲ marks and solid lines The one shown in FIG. 5 contains 10 mol% of Li (Example 7), the one shown by ▲ and the broken line contains 20 mol% Li (Example 8), the one shown by ◆ and the solid line shows 30 mol% Li. It is what was added (Comparative Example 11).
[0056]
As shown in FIG. 4, in Examples 5 to 8 in which the addition amount of Li is within the range of the present invention (Claim 1), a relative dielectric constant of 2000 or more was obtained with a film thickness of 300 mm or more. . Further, even when the film thickness was 100 mm, a relative dielectric constant of 1500 or more could be obtained.
[0057]
On the other hand, in Comparative Example 9, Li was not added, and in Comparative Example 10, the amount of Li added was less than the lower limit of the range of the present invention, so that the relative dielectric constant was 2000 or more unless the film thickness exceeded 5000 kg. The rate could not be obtained. In Comparative Example 11, the amount of Li added exceeded the upper limit of the range of the present invention, so that a sufficient dielectric constant could not be obtained.
[0058]
FIG. 5 is a graph showing the relationship between the horizontal axis with the amount of Li added to the dielectric film and the vertical axis with the dielectric constant. FIG. 6 is a graph showing the logarithm of the horizontal axis in FIG. is there. In FIGS. 5 and 6, those indicated by ● are those having a thickness of 5000 mm, and those indicated by ■ are those having a thickness of 2000 mm. Moreover, in FIG. 6, since it is a logarithmic display, the thing which Li is not added is shown as what Li is added in a trace amount (0.0001 mol%).
[0059]
As shown in FIGS. 5 and 6, the relative dielectric constant was lower than 2000 when the Li addition amount was less than 0.001 mol% or more than 20 mol%.
[0060]
Third Example A capacitor having a capacitor insulating film formed by adding 1 mol% of Li to PbZr _0.4 Ti _0.6 O ₃ was fabricated. Table 5 below shows the materials of the upper electrode and the lower electrode, the lattice constants thereof, and the orientation states thereof.
[0061]
[Table 5]

[0062]
And about each Example and the comparative example, the dielectric constant of the capacitor insulating film was measured. The results are shown in Table 6 below.
[0063]
[Table 6]

[0064]
As shown in Table 6 above, in Examples 12 and 13, since the lattice constant of the electrode material is within the range of the present invention, (001) orientation is obtained by matching with the substrate, and a high relative dielectric constant is obtained. It was.
[0065]
On the other hand, in Comparative Examples 14 to 16, since the lattice constant of the electrode material deviated from the range of the present invention, the alignment with the substrate was not achieved, and the orientation was random and the relative dielectric constant was low.
[0066]
Fourth Example A capacitor having a film formed by adding 1 mol% of Li to PbZr _0.4 Ti _0.6 O ₃ as a capacitor insulating film was produced. In this case, the upper electrode and the lower electrode are Pt electrodes having a thickness of 1000 mm. The thickness of the capacitor insulating film is shown in Table 7 below.
[0067]
[Table 7]

[0068]
And about each Example and the comparative example, evaluation of fine workability and the measurement of leak current were performed. The fine workability was evaluated by measuring the minimum line width that can be processed with a high yield. These results are shown in Table 8 below. In the comprehensive evaluation column, ◎ indicates extremely good, ◯ indicates good, Δ indicates slightly poor, and x indicates poor.
[0069]
[Table 8]

[0070]
As shown in Table 8 above, in Examples 17 to 20, since the film thickness of the capacitor insulating film made of the dielectric film is within the range of the present invention, the fine workability is high and the leakage current is low. .
[0071]
On the other hand, in Comparative Examples 21 and 22, since the film thickness of the capacitor insulating film exceeded the upper limit of the range of the present invention, the fine workability was low. Moreover, in Comparative Example 23, since the film thickness of the capacitor insulating film was less than the lower limit of the range of the present invention, the leakage current was large or a short circuit occurred.
[0072]
【The invention's effect】
As described above in detail, according to the present invention, since PZT-based dielectric material contains Li, it is possible to suppress O ₂ deficiency. For this reason, it is not necessary to use a single crystal substrate or adopt a special method, so that the dielectric constant can be remarkably improved while reducing the film thickness at low cost. Further, if such a dielectric film is used as a capacitor insulating film, a capacitor having a large capacitance can be obtained.
[Brief description of the drawings]
FIGS. 1A and 1B are cross-sectional views showing a method of manufacturing a dielectric memory to which an embodiment of the present invention is applied in order of steps.
FIGS. 2A to 2C are views showing a method for manufacturing a dielectric memory, and are cross-sectional views showing the next steps of the steps shown in FIGS. 1A and 1B in order of steps; It is.
FIG. 3 is an equivalent circuit diagram showing a dielectric memory to which an embodiment of the present invention is applied.
FIG. 4 is a graph showing a relationship between a film thickness of a dielectric film and a dielectric constant.
FIG. 5 is a graph showing the relationship between the amount of Li added to the dielectric film and the dielectric constant.
6 is a graph in which the horizontal axis of FIG. 5 is displayed logarithmically.
[Explanation of symbols]
1; silicon substrate, 2; gate oxide film, 3: a gate electrode, 4a; source, 4b; drain, 5a, 5b; conductive, 6; a dielectric layer, 7; Al wiring layer, 8, 9; SiO ₂ film , 10; contact hole, 11; transistor, 12; capacitor

Claims (5)

In a capacitor having a lower electrode, a dielectric film formed on the lower electrode, and an upper electrode formed on the dielectric film, the dielectric film is Pb _x Zr _(1-y) Ti _y It has a composition containing O ₃ and Li, the value of x is 0.9 to 1.3, the value of y is 0.3 to 0.7, and the Li content of the dielectric film is Pb _x Zr _(1-y) Ti _y O ₃ content is 0.001 to 20 mol%, the dielectric film has a thickness of 200 to 3000 mm, and at least of the upper electrode and the lower electrode One of the capacitors is a Pt electrode. In a capacitor having a lower electrode, a dielectric film formed on the lower electrode, and an upper electrode formed on the dielectric film, the dielectric film is Pb _x Zr _(1-y) Ti _y It has a composition containing O ₃ and Li, the value of x is 0.9 to 1.3, the value of y is 0.3 to 0.7, and the Li content of the dielectric film is Pb _x Zr _(1-y) Ti _y O ₃ content is 0.001 to 20 mol%, the dielectric film has a thickness of 200 to 3000 mm, and at least of the upper electrode and the lower electrode One of the capacitors is an Ir electrode. In a capacitor having a lower electrode, a dielectric film formed on the lower electrode, and an upper electrode formed on the dielectric film, the dielectric film is Pb _x Zr _(1-y) Ti _y It has a composition containing O ₃ and Li, the value of x is 0.9 to 1.3, the value of y is 0.3 to 0.7, and the Li content of the dielectric film is Pb _x The content of Zr _(1-y) Ti _y O ₃ is 0.001 to 20 mol%, the thickness of the dielectric film is 200 to 3000 mm, and constitutes the upper electrode and the lower electrode A capacitor characterized in that the lattice constant of the conductive material is 3.5 to 4.3 Å. In a capacitor having a lower electrode, a dielectric film formed on the lower electrode, and an upper electrode formed on the dielectric film, the dielectric film is Pb _x Zr _(1-y) Ti _y It has a composition containing O ₃ and Li, the value of x is 0.9 to 1.3, the value of y is 0.3 to 0.7, and the Li content of the dielectric film is Pb _x The content of Zr _(1-y) Ti _y O ₃ is 0.001 to 20 mol%, the thickness of the dielectric film is 200 to 3000 mm, and constitutes the upper electrode and the lower electrode A capacitor characterized in that the conductive material has a lattice constant of 5.0 to 6.1 Å. 5. The capacitor according to claim 1, wherein the dielectric film has a thickness of 500 to 2000 mm.

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