NL9000214A - Superconducting layer application method - releasing material to be deposited with oxygen in plasma state transported along lines of flux over substrate - Google Patents

Abstract

The method comprises the steps of releasing part of a material to be applied in an enviroment of underpressure using a laser bundle and bringing oxygen into a plasma state close to the substrate. The material to be applied is YlBa2Cu3O7-delta and a magnetic field is applied of a value such that close to the edges of the substrate the oxygen is ionised to enter into a plasma state. The plasma is subsequently transported over the substrate along field lines of the magnetic field. The apparatus has a substrate holder and an entrance for the laser bundle and entrance port for the material.

Description

Method for applying a layer of superconducting material and a suitable device.

The world is looking for a method for applying superconducting layers with a high critical temperature, which can also be combined with other micro-electronic layers. Sputtering, vapor deposition, molecular beam deposition and laser ablation are the main known techniques for this. These are mainly ortho-rhombic substances such as Ba2 CU3 O7 .- &, in which an additional oxygen treatment after precipitation is often applied and annealing steps are used at high temperatures (± 900 ° C), the disadvantage of these known techniques includes diffusion and / or chemical reactions between substrate and the superconducting layer to be deposited thereon, especially with semiconductor substrates such as gallium arsenide (GaAs) and silicon (Si). The difference in expansion coefficient between the different materials can also give rise to grating errors.

The present invention aims to improve the above techniques and provides a method according to claim 1 for this purpose.

The present invention furthermore provides a device according to claim 5, in which other micro-electronic layers, such as conductive layers and the like, can also be applied in a simple manner. The (dry) etching of layers can also take place in such a device.

Further advantages, features and details of the present inventions are elucidated on the basis of a description of a preferred embodiment thereof with reference to the accompanying figure.

A device 1 comprises a chamber 2 in which a substrate S is arranged on a substrate holder 3. A laser beam B is directed via an entrance or window 4 onto a superconducting piece of material M according to the ablation technique known per se, so that material can be released therefrom onto the substrate S. A holder 5 for the material M is preferably made rotatable, so that overheating thereof is avoided. A schematically indicated microwave system 6 is included on either side of the chamber 2 and comprises two solenoids (7,8).

Preferably, the magnetic field generated by the solenoids 7,8 is dimensioned such that the field strength near the edges of the substrate S is such that the released superconducting material there enters a plasma state and is transported along the magnetic field lines over the substrate. Furthermore, oxygen is preferably introduced from the microwave system in a manner not shown, into the plasma region, so that the oxygen also enters plasma mode. For this purpose, the magnetic field preferably has a value of 875 Gauss at the edges of the substrate.

The microwave system shown here avoids the use of a separate discharge cell or an additional quartz tube to keep the plasma away from the walls of a room.

In the manner not shown, the chamber 2 is maintained at underpressure, for example, from 1.0 "9" Torr using a Balzer ™ pump (not shown).

The device 1 is furthermore for applying other layers, preferably provided with Knudsen or effusion cells (9,11).

: A YAG laser (12) is preferably galvanically controllable, so that patterns can be written on a substrate.

Furthermore, the chamber 2 is preferably provided, in a manner not shown, with a photomultiplier directed at the substrate S in order to make measurements thereon.

It should be understood that the device shown allows for a method in which GaAs or Si substrates can be applied in different layers at low temperature, (about 400 ° C) involving interactions, i.e. diffusion or reactions, between substrate and layers to be applied are avoided as much as possible, and an efficient transport of the oxygen-containing plasma over the substrate takes place along the magnetic field lines, because of the dimensioning of that magnetic field. Even at a pressure of only 10 "5 - 10" 7 Torr, the plasma will ignite. Any passivation of a superconducting layer using an oxide layer can be that oxygen is withdrawn from the superconducting layer, since sufficient oxygen can be introduced into the plasma.

Both using plasma etching and writing patterns using the laser will be possible with the device shown, avoiding having to take the substrate out of a vacuum chamber and thus also avoiding impurities and the like thereon.

Claims (8)

Method for applying a layer of superconducting material to a substrate, comprising the following steps: - releasing at least a part of the material to be applied in an environment of underpressure by means of a laser beam; and - bringing the released material into a plasma state near the substrate. The method of claim 1, wherein the material Y1 is Ba2 Cu3 07_ &. The method of claim 1 or 2, wherein oxygen is added near the substrate in the plasma state. The method of claim 3, wherein a magnetic field is applied near the plasma of such a value that the oxygen is ionized near the edges of the substrate and then transported across the substrate along magnetic field fields. Device for applying one or more layers to a substrate, comprising: - a substrate holder; - an input for a laser beam; - an entrance port for material to be irradiated with the laser beam; two substantially opposite sole-noides for generating a magnetic field near the substrate holder; and - means for generating an underpressure in the device. Apparatus according to claim 5, provided with a quaterine pool for residual gas analysis. Device as claimed in claim 5 or 6, comprising one or more Knudsen cells for introducing material to be deposited into the chamber. 8. Device as claimed in claim 5,6 or 7, provided with a photomultiplier.