JPH0515313B2 - - Google Patents
Info
- Publication number
- JPH0515313B2 JPH0515313B2 JP61079139A JP7913986A JPH0515313B2 JP H0515313 B2 JPH0515313 B2 JP H0515313B2 JP 61079139 A JP61079139 A JP 61079139A JP 7913986 A JP7913986 A JP 7913986A JP H0515313 B2 JPH0515313 B2 JP H0515313B2
- Authority
- JP
- Japan
- Prior art keywords
- oxide film
- thickness
- barrier layer
- lower electrode
- substrate
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
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Classifications
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N60/00—Superconducting devices
- H10N60/80—Constructional details
- H10N60/81—Containers; Mountings
- H10N60/815—Containers; Mountings for Josephson-effect devices
Landscapes
- Superconductor Devices And Manufacturing Methods Thereof (AREA)
- Containers, Films, And Cooling For Superconductive Devices (AREA)
Description
【発明の詳細な説明】
〔産業上の利用分野〕
本発明はトンネル障壁層の厚みを制御するのに
好適なトンネル障壁層膜厚制御用開口部を設けた
ジヨセフソン素子用基板に関する。DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a substrate for a Josephson device provided with an opening for controlling the thickness of a tunnel barrier layer suitable for controlling the thickness of a tunnel barrier layer.
トンネル型ジヨセフソン接合素子は、上部電極
と下部電極との間に厚さ数nmのトンネル障壁層
を挟んだ構造である。トンネル障壁層としては、
熱酸化法、高周波プラズマ酸化法等の手段を用い
て、下部電極膜の表面に形成した極薄の酸化膜が
主として用いられる。例えば、Nb系の場合Nb2
O5，Pb系の場合PbO等である。ジヨセフソン接
合素子の動作の基本となる超電導トンネル電流を
所望とする値に揃えるためには、トンネル障壁層
となる下部電極膜の酸化膜の厚みを酸化工程で正
確に制御する必要がある。従来のプラズマ酸化工
程では、酸素圧力と超電導トンネル電流の関係を
求め、所望とする電流値に対応する酸素圧力で酸
化を行つていた。しかし、この方法では、酸化前
の自然酸化膜厚が異つた場合や、酸化条件が変動
した場合、作製した素子の超電導トンネル電流値
が大きく変動し再現性のないという問題があつ
た。直接、極薄の酸化膜の厚みを測定する方法と
しては、エリプソメータを用いる方法が知られて
いる。エリプソメータを用いた酸化膜厚の測定に
ついては、“エス・バサバイヤ、ジエイ・エツ
チ・グライナ：「接合容量とエリプソメータで求
めた窒化ニオブ−酸化物−鉛ジヨセフソン・トン
ネル接合の酸化膜厚」、ジヤーナル・オブ・アプ
ライド・フイズイツクス、47巻、９月、1976年”、
S.Basavaiah and J.H.
Greiner：“Capacitance and
Ellipsometrically determind oxide thickness
of NbN−oxide−Pb Josephson tunnel
Junctions”，Journal of Applied Physics，
Vol.47，No.９，September，（1976）と題する文
献において論じられている。
A tunnel-type Josephson junction device has a structure in which a tunnel barrier layer with a thickness of several nm is sandwiched between an upper electrode and a lower electrode. As a tunnel barrier layer,
An extremely thin oxide film formed on the surface of the lower electrode film using a thermal oxidation method, a high frequency plasma oxidation method, or the like is mainly used. For example, for Nb series, Nb 2
In the case of O 5 and Pb, it is PbO, etc. In order to adjust the superconducting tunnel current, which is the basis of the operation of the Josephson junction element, to a desired value, it is necessary to accurately control the thickness of the oxide film of the lower electrode film, which becomes the tunnel barrier layer, in the oxidation process. In conventional plasma oxidation processes, the relationship between oxygen pressure and superconducting tunneling current is determined, and oxidation is performed at an oxygen pressure that corresponds to a desired current value. However, this method has a problem in that when the thickness of the natural oxide film before oxidation differs or when the oxidation conditions change, the superconducting tunnel current value of the fabricated device varies greatly and is not reproducible. A method using an ellipsometer is known as a method for directly measuring the thickness of an extremely thin oxide film. Regarding the measurement of oxide film thickness using an ellipsometer, see “Junction Capacitance and Oxide Thickness of Niobium Nitride-Oxide-Lead Josefson Tunnel Junction Determined with an Ellipsometer” by S. Basabaiya and G.H. Greiner, Journal. of Applied Physics, Volume 47, September 1976”,
S. Basavaiah and J. H. Greiner: “Capacitance and Ellipsometrically determined oxide thickness
of NbN−oxide−Pb Josephson tunnel Junctions”, Journal of Applied Physics,
Vol. 47, No. 9, September, (1976).
ここでは、エリプソメータに用いた基板と、実
際に作製したジヨセフソン接合素子の基板が同一
ではない。したがつて、下部電極膜の自然酸化膜
厚が異なる。さらに酸化工程において直接酸化膜
厚を測定し、その値に応じて酸化条件を変化さ
せ、所望とする超電導トンネル電流値に対応する
酸化膜厚に一致させることは難しい。すなわち、
一般に大気中で生成した自然酸化膜を除去し、新
たに制御された雰囲気、エネルギーのもとで極薄
の酸化膜を形成している。従つて、接合を形成す
る部分の酸化膜が個々の基板によつて異なつた場
合は自然酸化膜を除去するための条件も異り、新
たに形成する酸化膜も異なるという問題がある。
このような理由から、超電導トンネル電流を再現
性良く制御することは極めて困難であつた。
Here, the substrate used for the ellipsometer and the substrate for the Josephson junction element that was actually produced are not the same. Therefore, the natural oxide film thickness of the lower electrode film is different. Furthermore, it is difficult to directly measure the oxide film thickness in the oxidation process, change the oxidation conditions according to the measured value, and match the oxide film thickness to a value corresponding to a desired superconducting tunnel current value. That is,
The natural oxide film that normally forms in the atmosphere is removed, and an extremely thin oxide film is formed under a newly controlled atmosphere and energy. Therefore, if the oxide film in the portion where the junction is to be formed differs depending on the individual substrates, the conditions for removing the natural oxide film will also differ, and the oxide film to be newly formed will also be different.
For these reasons, it has been extremely difficult to control superconducting tunneling current with good reproducibility.
本発明の目的は、超電導トンネル電流を再現性
良く制御するため、トンネル障壁層となる酸化膜
を均一な膜厚となるように形成することにある。 An object of the present invention is to form an oxide film serving as a tunnel barrier layer to have a uniform thickness in order to control superconducting tunnel current with good reproducibility.
本発明はジヨセフソン接合素子と同一基板上に
トンネル障壁層膜厚制御用開口部を設けたことを
特徴とする。
The present invention is characterized in that an opening for controlling the thickness of the tunnel barrier layer is provided on the same substrate as the Josephson junction element.
超電導トンネル電流を所望とする値に揃えるた
めには、トンネル障壁層となる下部電極膜上の酸
化膜厚を正確に制御する必要がある。特に、酸化
膜厚の変化要因である下部電極膜の自然酸化膜厚
は各プロセスでの履歴によつて変化する。本発明
は図１に示したようなジヨセフソン・デバイス領
域３と同一基板１上にエリプソメータによる酸化
膜厚測定用領域２を形成して酸化時の酸化膜厚を
制御することで、超電導トンネル電流値の制御性
を向上させた点に特徴がある。すなわち、同一基
板上にエリプソメータの光学スポツト程度の下部
電極膜を露出させた酸化膜厚測定用領域を形成し
ておく。この領域はジヨセフソン接合と同一基板
上であるため下部電極膜は同質であり、自然酸化
膜の形成およびその後に行なわれるプロセスの履
歴が同じである。そのようなことから酸化工程に
おいて形成される酸化膜の厚さの変化をエリプソ
メータで測定し、所望とする超電導トンネル電流
に対応する厚みとなるように酸化膜厚をリアルタ
イムで調整することができる。これによつて歩留
り良くジヨセフソン素子を作製するとができる。
In order to adjust the superconducting tunnel current to a desired value, it is necessary to accurately control the thickness of the oxide film on the lower electrode film that becomes the tunnel barrier layer. In particular, the natural oxide film thickness of the lower electrode film, which is a factor in changing the oxide film thickness, changes depending on the history of each process. The present invention forms an oxide film thickness measuring region 2 using an ellipsometer on the same substrate 1 as the Josephson device region 3 shown in FIG. It is characterized by improved controllability. That is, on the same substrate, a region for measuring the oxide film thickness is formed in which the lower electrode film is exposed to the extent of an optical spot of an ellipsometer. Since this region is on the same substrate as the Josephson junction, the lower electrode film is of the same quality, and the history of the formation of the native oxide film and the subsequent processes are the same. For this reason, it is possible to measure changes in the thickness of the oxide film formed in the oxidation process using an ellipsometer, and adjust the oxide film thickness in real time so that the thickness corresponds to the desired superconducting tunnel current. Thereby, Josephson devices can be manufactured with high yield.
以下、本発明の一実施例を第１図および第２図
を用いて説明する。寸法２インチのシリコンウエ
ハ４を真空装置中の基板ホルダに設置して、直流
マグネトロンスパツタ法によりNb膜５を200nm
堆積する。引き続いて、下部電極に対応するレジ
ストパターン６を形成する（第２図ａ）。この後、
CF4を用いたプラズマエツチング法により下部電
極７のパターンを形成した（同ｂ）。次に、トン
ネル障壁層の形成面積を規定するための開口部形
成用レジスト・パターン８と、エリプソメータに
よる測定用パターンに対応するレジスト・パター
ン９を形成する（同ｃ）。この後、SiO膜を
300nm蒸着し、リフトオフ法によりレジストを除
去すると絶縁膜１０が形成される。次に上部電極
形成用のレジスト・パターン１１を形成する。こ
の時点で、トンネル障壁層を形成する下部電極領
域１２と、エリプソメータによつて酸化膜厚を測
定するための下部電極領域１３は確保される（同
ｄ）。次にエリプソメータのレーザーの光軸１４
が測定用パターンの下部電極領域１３で反射され
るように基板を蒸着装置の基板ホルダーに設置す
る。こののち、露出した下部電極領域１２，１３
の表面をrfスパツタ・エツチングにより清浄化し
た後、プラズマ酸化法によつてNb2O5を形成しト
ンネル障壁層１５を形成する（同ｅ）。このとき
同時に形成される酸化膜厚測定用パターンのNb2
O5の膜厚をエリプソメータによつて測定し、酸
化膜厚が2nmに達したところで酸化を終えた。こ
の後、PbInAuからなる上部電極１６を450nm形
成する。リフトオフ法によつてレジストを除去す
ると素子が完成する（同ｆ）。
An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. A silicon wafer 4 with a size of 2 inches is placed on a substrate holder in a vacuum device, and a Nb film 5 of 200 nm is coated using the DC magnetron sputtering method.
accumulate. Subsequently, a resist pattern 6 corresponding to the lower electrode is formed (FIG. 2a). After this,
A pattern for the lower electrode 7 was formed by plasma etching using CF 4 (see b). Next, a resist pattern 8 for forming an opening for defining the formation area of the tunnel barrier layer and a resist pattern 9 corresponding to a pattern for measurement by an ellipsometer are formed (c). After this, the SiO film is
The insulating film 10 is formed by depositing the resist to a thickness of 300 nm and removing the resist using a lift-off method. Next, a resist pattern 11 for forming an upper electrode is formed. At this point, the lower electrode region 12 for forming the tunnel barrier layer and the lower electrode region 13 for measuring the oxide film thickness with an ellipsometer are secured (d). Next, the optical axis 14 of the laser of the ellipsometer
The substrate is placed on a substrate holder of a vapor deposition apparatus so that the light is reflected by the lower electrode area 13 of the measurement pattern. After this, the exposed lower electrode regions 12, 13
After cleaning the surface by RF sputter etching, Nb 2 O 5 is formed by plasma oxidation to form the tunnel barrier layer 15 (see e). Nb 2 of the oxide film thickness measurement pattern formed at the same time.
The O 5 film thickness was measured using an ellipsometer, and oxidation was terminated when the oxide film thickness reached 2 nm. After this, an upper electrode 16 made of PbInAu is formed to a thickness of 450 nm. The device is completed by removing the resist by a lift-off method (see f).
従来、所望とする超電導トンネル電流値、例え
ば100μAの場合、20〜500μAの範囲でばらついて
いたが、本実施例によれば70〜130μAの範囲で制
御することができた。 Conventionally, in the case of a desired superconducting tunneling current value of 100 μA, for example, it varied in the range of 20 to 500 μA, but according to this embodiment, it was possible to control it in the range of 70 to 130 μA.
〔発明の効果〕
本発明によれば、ジヨセフソン・デバイスと同
一基板上にエリプソメータによる酸化膜厚測定用
領域を形成することができるので、酸化工程で酸
化膜厚の変化をエリプソメータで測定し、所望と
する超電導トンネル電流値に対応する厚みとなる
ように酸化条件を制御することができる。すなわ
ち、従来所望とする超電導トンネル電流値に対し
て作製した素子の電流値が1/5〜５倍も変動して
いたが、本発明によれば再現性良く±30％以内に
そのばらつきを低減することができた。したがつ
て、所望とする超電導トンネル電流値のジヨセフ
ソン素子を歩留り良く作製できる効果がある。ま
た、酸化工程前のrfスパツタ・エツチングで下部
電極表面の自然酸化膜をわずかに残した場合、ジ
ヨセフソン接合の接合特性が著しく改善される効
果があることも明らかとなつた。[Effects of the Invention] According to the present invention, it is possible to form a region for measuring the oxide film thickness using an ellipsometer on the same substrate as the Josephson device, so that changes in the oxide film thickness during the oxidation process can be measured using the ellipsometer, and desired results can be obtained. The oxidation conditions can be controlled so that the thickness corresponds to the superconducting tunnel current value. In other words, conventionally, the current value of the fabricated device varied by 1/5 to 5 times relative to the desired superconducting tunnel current value, but according to the present invention, this variation can be reduced to within ±30% with good reproducibility. We were able to. Therefore, there is an effect that a Josephson device having a desired superconducting tunneling current value can be manufactured with a high yield. It has also been found that if a small amount of natural oxide film is left on the surface of the lower electrode by RF sputter etching before the oxidation process, the bonding characteristics of Josephson junctions can be significantly improved.
第１図は酸化膜厚測定用パターン領域とジヨセ
フソン接合素子形成領域を示す図、第２図ａ〜ｆ
は酸化膜厚測定用パターンの作製工程を示すジヨ
セフソン接合素子の縦断面図である。
１……基板Si、２……酸化膜厚測定用パターン
形成領域、３……ジヨセフソン接合素子形成領
域、４……基板Si、５……Nb膜、６……レジス
ト、７……下部電極、８……開口部形成用レジス
ト・パターン、９……酸化膜厚測定用パターンに
対応するレジスト・パターン、１０……絶縁膜、
１１……レジスト、１２……トンネル障壁層を形
成する下部電極領域、１３……酸化膜厚を測定す
るための下部電極領域、１４……レーザの光軸、
１５……Nb2O5、１６……上部電極。
Figure 1 is a diagram showing the pattern area for measuring oxide film thickness and the Josephson junction element formation area, Figure 2 a to f
1 is a longitudinal cross-sectional view of a Josephson junction element showing a process of manufacturing a pattern for measuring oxide film thickness. DESCRIPTION OF SYMBOLS 1...Substrate Si, 2...Pattern formation area for oxide film thickness measurement, 3...Josephson junction element formation area, 4...Substrate Si, 5...Nb film, 6...Resist, 7...Bottom electrode, 8... Resist pattern for forming an opening, 9... Resist pattern corresponding to a pattern for measuring oxide film thickness, 10... Insulating film,
11...Resist, 12...Lower electrode region for forming a tunnel barrier layer, 13...Lower electrode region for measuring oxide film thickness, 14...Optical axis of laser,
15...Nb 2 O 5 , 16... Upper electrode.
Claims (1)
次形成するトンネル型ジヨセフソン素子用の基板
において、基板の中央部に少なくとも光学スポツ
トの大きさの膜厚測定用トンネル障壁層と、基板
の上記中央部以外の所定部分にジヨセフソン接合
を形成するためのトンネル障壁層とを備えたこと
を特徴とするジヨセフソン素子用基板。1. In a substrate for a tunnel type Josephson device in which a tunnel barrier layer and an upper electrode are sequentially formed on a lower electrode, a tunnel barrier layer for film thickness measurement having at least the size of an optical spot is provided in the center of the substrate, and 1. A substrate for a Josephson device, comprising a tunnel barrier layer for forming a Josephson junction in a predetermined portion other than the above.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP61079139A JPS62237777A (en) | 1986-04-08 | 1986-04-08 | Substrate for josephson element |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP61079139A JPS62237777A (en) | 1986-04-08 | 1986-04-08 | Substrate for josephson element |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS62237777A JPS62237777A (en) | 1987-10-17 |
| JPH0515313B2 true JPH0515313B2 (en) | 1993-03-01 |
Family
ID=13681623
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP61079139A Granted JPS62237777A (en) | 1986-04-08 | 1986-04-08 | Substrate for josephson element |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS62237777A (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH02112289A (en) * | 1988-10-21 | 1990-04-24 | Agency Of Ind Science & Technol | Device for manufacture of tunnel type josephson junction |
-
1986
- 1986-04-08 JP JP61079139A patent/JPS62237777A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| JPS62237777A (en) | 1987-10-17 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EXPY | Cancellation because of completion of term |