JPH01156482A - Method for etching superconductor - Google Patents

Abstract

PURPOSE:To easily etch a superconductor made of a ceramic superconducting material by using bromine or a bromine compd. as an etchant for the superconductor. CONSTITUTION:At least bromine or a bromine compd. is used as an etchant for a superconductor made of a ceramic superconducting material. By using the etchant, the superconductor in the form of a bulk (solid) material, a thin film or the like can be subjected to etching for patterning, cleaning or flattening. Etching technique adopted is not especially restricted and may be conventional known etching technique such as wet, gas, plasma or radical etching, RIE, RIBE or photoetching.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an etching method used in the manufacturing process of compound semiconductor devices, and in particular, to a superconductor made of ceramic-based superconducting material. ! This invention relates to a method of etching a conductor.

[Conventional technology]

In the manufacturing process of a compound semiconductor device using lithography, when forming a pattern deposited on a substrate, any of the three prototypes shown in FIG. 2 is used. Among these, etching methods are divided into liquid phase etching method (wet etching method) and gas phase etching method (dry etching method).Furthermore, gas phase etching method involves sputtering using reactions caused by excited plasma radical groups and kinetic energy of particles. The technique can be divided depending on which side is the main body of etching,
There are etching methods that have only reactivity, only sputtering, or both reactivity and sputtering, and the main ones include gas etching, plasma etching, radical etching, and reactive ion etching (RrE etching).
), reactive ion beam etching (RIBE), and the like.

By the way, superconducting phenomenon refers to a phenomenon in which electrical resistance completely disappears below a certain temperature, and the temperature at which this superconducting phenomenon occurs (critical temperature) differs depending on the material. Since materials with high critical temperatures can be easily cooled, the development of materials with as high critical temperatures as possible has been particularly popular recently. In addition to a high critical temperature, the upper limit of current that can be passed in a superconducting state (critical current) is also an important point for the practical application of ceramic materials. To put this into practical use, ceramic materials must be shaped into plates (such as substrates), wires, or coils, but since the current that can be passed through ceramic materials per unit cross-sectional area is small, it is difficult to determine how high the critical current can be obtained. This is because this holds the key to practical application.

However, alloy-based and compound-based materials are well known as materials that cause superconductivity, and recently, the development of ceramic-based materials has been particularly advanced. The development of ceramic superconducting materials with high critical temperatures is progressing rapidly, but in order to put them into practical use, it is necessary to process the superconducting materials into plates (substrates), wires, tapes, coils, etc. In order to make a powerful electromagnet using the electric current that flows through it, it must be processed into a coil shape.However, ceramics, which are made by sintering powdered materials, are hard and brittle, so they cannot be bent like alloys or wound into a coil shape. Therefore, in order to overcome these drawbacks and bring them closer to practical use, progress is being made in the development of ceramic materials and processing methods.

One important point in the practical application of superconducting ceramic materials is how to make them into devices without degrading their superconducting properties.The key to this is the production of thin films of ceramic materials and their This is a thin film etching technology. In particular, the technology of epitaxially growing various compounds on a substrate and etching this grown layer is important in the manufacturing process of semiconductor devices. If etching technology for bodies is developed, it will be possible to fabricate various devices made of superconductors. Therefore, in order to overcome the processing difficulties of ceramic materials as mentioned above, and to apply superconducting to a wide range of fields such as energy, including the field of superconducting electronic devices, and also from the perspective of improving device productivity, superconducting ceramics have been developed. At present, we are competing in the development of etching methods for superconducting materials.

[Problem that the invention seeks to solve]

However, as mentioned above, various techniques for etching compound semiconductors have already been established, and for example, RIE is often used in the above-mentioned lift-off method with spacers, but there is still no method for etching superconductors made of ceramic superconducting materials. The reality is that it has not been sufficiently researched and developed.

Therefore, in view of the above discussion, an object of the present invention is to provide a method for etching a superconductor, which is one of the process techniques, in order to manufacture various devices composed of a superconductor made of a ceramic superconducting material. There is a particular thing.

[Means for solving problems]

In order to achieve the above object, the present inventor has made extensive research into what kind of material should be selected as an etchant for a superconductor made of ceramic-based superconducting materials. It was discovered that it is possible to etch superconductors by using this method.

That is, the etching method of the present invention is characterized in that at least bromine or a bromine compound is used as an etchant for a superconductor made of a ceramic superconducting material, and a bulk material (
It is an etching technology for patterning, cleaning, and flattening superconductors such as solid state) or thin films.
This is an important technology in the manufacturing process for realizing various devices made of superconductors.

The etching techniques employed include the previously known wet etching method, gas etching method, plasma etching method, radical etching method, RrE, RrBE,
Alternatively, a technique such as a photoetching method may be used without any particular limitation, and etching may be carried out by a conventional method using bromine or a bromine compound as an etchant.

There are no particular limitations on the bromine or bromine compound used as an etchant, as long as it can supply bromine during etching. Br0I 5) IBrOsC÷H! 0), HBr
+ HzO, Br(CHzOH), Br(C1li
OH) + HtO, etc., gas etching, RIE, R
For gases such as IBE, HBr, HBr0i,
Brt, BrC1, BrF, BrF5, BrF5 (
However, for BrF3 and BrF5, raw materials are heated and extracted as gas).

In the present invention, the superconducting ceramic material or the mixture of its raw materials constituting the superconductor to be etched is not particularly limited as long as it is a ceramic-based superconducting material.
In particular, a ceramic material containing an oxide of a rare earth element is preferable.

Existing materials may be used as such materials, but for example, barium, yttrium, copper, etc.
Oxygen, barium/lanthanum/copper/oxygen, strontium/lanthanum/copper/oxygen, barium/scandium/copper/
There are ceramics having a composition of oxygen, calcium, lanthanum, copper, and oxygen, and preferably a material having a composition of barium, yttrium, copper, and oxygen, which is an yttrium-based material that is becoming mainstream in ceramic materials. Furthermore, when using this yttrium-based superconducting material, the preferred blending ratio is Ha:Y:Cu:
0=11:3:6-7.

A ceramic superconducting material having such a composition is usually used as a superconductor. The method of manufacturing the material is
Any conventionally known method may be used, and there are no particular limitations.
In the case of a superconducting material of yttrium, copper, and oxygen, it may be manufactured by a solid-state process that includes mixing of barium carbonate, yttrium oxide, copper oxide, etc. → sintering → re-powdering of the sintered body.

The form of superconductors made of ceramic-based superconducting materials is usually 5rTiO, BaTi, etc., since thinning is important in the application of superconductors to electronic devices.
Examples include those in which a thin film is formed on a substrate made of Os, MgO, sapphire, or the like.

Next, we will outline the apparatus used in the etching method of the present invention and the etching method based on the apparatus. Techniques applicable to the etching method of the present invention include wet etching, gas etching, plasma etching, radical etching, and RIE. , RIBE, and photoetching methods, but there are no particular limitations on the equipment used for each etching method, and the equipments used for these etching techniques are well known, so only their basic structures will be explained below. The details will be omitted.

First, in wet etching, a superconductor sample made of a ceramic superconducting material is immersed in a solution containing bromine as a component element in a container such as a beaker. It is preferable to immerse the solution while heating the container as this will increase the etching rate.Furthermore, it may be done while stirring the solution to increase the uniformity of etching.The liquid to be used can be selected from any of the above examples. do it.

In gas etching, a reactive gas containing bromine as a component element is passed into a reaction vessel, and the inside of the reaction vessel is heated to a high temperature using a high-frequency heating furnace, an infrared heating furnace, a resistance heating furnace, etc. placed around the outside of the reaction vessel. By doing this, the sample placed in the reaction vessel is etched. In addition to using the gas containing bromine as the main reaction gas in the previous example,
If necessary, H2,08, oto (uto is mixed in as water vapor), Ars Nzs He, etc. are mixed and used as appropriate.

The equipment used for plasma etching basically consists of a reaction tank to maintain the plasma state, a pair of electrodes placed around the outside of the reaction tank, a high-frequency power source for plasma generation, a gas introduction system, and an oil rotary pump. There is. The sample is etched using the reactive components in the gas plasma by causing an electric discharge in the reaction tank using an electrode.
The gas pressure is set at about 0.1 to 10 orr,
The ionosphere of atoms or molecules in the reactor is low (, most of them are neutral atoms and molecules. Most of these neutral atoms and molecules are in an excited state and have high chemical activity. Plasma etching utilizes these active atoms and molecules, and while the gas etching described above uses heat to cause a reaction, plasma etching uses electrical discharge and heat to perform etching.The general conditions for plasma etching are as follows: Gas pressure = 0.1 to 10 Torr, substrate temperature: room temperature to 5
00℃, power density = 104~100 +w14/ai,
Gas flow rate: 10 to 101,000 sc.

In radical etching, the equipment used is different from the plasma etching equipment described above, in cases where a high etching rate is not desired or in order to prevent damage caused by ion irradiation caused by placing the sample directly in the plasma. It has a structure in which the chamber and the radical generation chamber are separated, and this makes it possible to etch the sample without significantly changing its physical properties. The general conditions are the same as those for plasma etching, but the reaction area is
In this case, damage caused by ion irradiation to the substrate is reduced.

RIE is electric field (cathode drop caused by asymmetric electrode structure)
This method performs etching by reacting with the material on the surface of the sample using active ions accelerated by ions. Furthermore, by heating the electrode on which the sample is placed, it is possible to increase the reactivity and increase the etching rate, as well as to smooth the bottom and sides of the etched surface. The general conditions are gas pressure in the reaction tank = 1
01~to-'Torr, substrate temperature: room temperature~500"C
1 power density: 1~800+m11/C4, gas flow rate: 1~100 secm.

RIBE is essentially an apparatus that uses an ECR ion source that generates highly ionized plasma. The ECR ion source extracts ions into a beam and irradiates the sample to perform etching. The general conditions are: gas pressure in the reaction tank: 10-' to 10-'' Torr, substrate temperature: room temperature to 5
00℃, ion extraction voltage; 100-100OV, gas flow! =1 to 50 seconds.

Furthermore, in optical etching, the structure of the device is similar to that of gas etching, in which a reactive gas is passed through a light-transparent reaction vessel, and the sample is irradiated with mainly ultraviolet or infrared rays from outside the reaction vessel. For etching, the light sources used are Suigotsu lamps, xenon lamps, excimer lasers, etc. for ultraviolet rays, and C08 lasers for infrared rays, and the light from these light sources may be focused and applied.
Two light sources may be used to irradiate the top and side of the sample, respectively, or ultraviolet and infrared light sources may be used to irradiate the sample at the same time.General conditions are gas etching. Same as, but the laser power is 1~
10' J/cd.

In this way, if a superconductor made of ceramic superconducting material is etched using bromine or a bromine compound as an etchant, the bromine compound produced by the material components of the superconductor and bromine has a low boiling point and is easily vaporized. ,−
As an example, the boiling point of a bromine compound for each element of the ceramic superconducting material constituting a superconductor is shown as follows: Element: Bromine compound → boiling point (°C) La
: La(BrOs)'9H! 0 -
7Hz0,100Y: Y(Br(h)s
'9HzO→ 6H20,100Ba:
BaBrx ・2HzO→ −2H,0,12
0Sr: 5r(BrOi)z ・HlO
→ 240Sr: 5rBrz ・6
HzO → 6HJ, >180Ca: C
aBrz ・6HzO→149Cu: C
uBrz ・3Cu(HzO) -240~250
It can be seen that all temperatures are below 250°C. Therefore, superconductors can be easily etched.

According to the etching method of the present invention, particularly in the field of superconducting electronic devices, it is possible to easily pattern a thin film as a superconductor made of ceramic superconducting material into a device, and it is also easy to miniaturize it by microfabrication. be.

In addition, it is possible to perform cleaning to improve the characteristics of the element, cleaning as a pre-stage for forming electrodes on the element, or replenishing 02 defects along with cleaning.
A reduction in contact resistance and an improvement in adhesion between the element and the electrode are achieved. Furthermore, if roughness occurs on the surface of the element,
In other words, if the surface has irregularities, it is preferable that the surface be as flat as possible in the subsequent manufacturing process, and this can also be applied to flattening the surface of this element, or it can be It is also useful for separating devices.

[Example/Experiment example]

Hereinafter, the etching method of the present invention will be specifically explained using Examples and Experimental Examples.

Examples and experimental examples include R as a representative example of etching technology.
We will perform etching using IE.

The equipment used for RIE may be any equipment used in normal RIE, and Figure 1 shows a schematic diagram of an example of the equipment used in RIE. This apparatus consists of a reaction chamber (reactor) A for performing etching, a vacuum gauge B, an etching gas introduction system C1, a high vacuum evacuation system, and an etching gas exhaust system E. In such an apparatus, it is sufficient to apply the etching conditions such as gas pressure, gas flow rate, and power density that are generally adopted in normal RIE, but in order to obtain a greater etching effect, it is necessary to increase the gas pressure to 10%. ~100
Xl0-'Torr, preferably 20-50 X 1
0-”Torr, more preferably 30X10-’T
orr, gas flow rate from 1 to loosccm, preferably 2
0~40sccn+, high frequency power density 1~800+m
W/+j, good mashi<ha2oo~4ooIIIW/etj
Set to . Furthermore, the temperature increases as bromine compounds (La(Br03)s H9HJ, Y(BrO
s)s ・9H! 0, BaBrt ・2HtO1Sr(
BrOs)t ・HzO, 5rBrt ・61110
, Carry ・6HzO1CuBrt ・3Cu(H
zO), etc.). Also,
It is preferable that the inside of the reaction chamber A be kept in a vacuum state as much as possible.

Examples 1 to 4/Experimental Example 1 Using the above-mentioned apparatus and using Mar as the main reaction gas for RIE, for example, the following procedure is carried out:
For etching, the inside of reaction chamber A was heated to 4.0×10-'Tor.
After evacuation using a high vacuum evacuation system until the degree of vacuum reaches r or less, operate the etching gas introduction system C to introduce HBr gas into the reaction chamber A, and adjust the conductance valve of the etching gas evacuation system E. desired pressure (e.g. 3
The sample was set at 5r Torr.
A superconducting thin film made of the ceramic superconducting material mentioned above is formed by sputtering on a substrate 1 made of TiO=. Note that a mask is used for actual etching such as patterning or miniaturizing a thin film, and the materials for this mask include resists such as PMMA and Si-containing PMMA, Ti, Cr, Ag, W, ^u,
AI, Zn5Pt, C, Ni, Ta, FeXCu
, metals such as Mo, or 81201, BN, TiN
,Cr,O,,5iNxs sio,,5ili,o
, , Ti(h, ZrO2, TaN % Taxes
, (:r=C2% CrN% TiN or other compounds may be selected arbitrarily. Here, SiO□ is used as a mask. In other words, SiO is deposited on the substrate 1 by sputtering.
O□ is approximately 0.27. The substrate 1 is patterned by photolithography, and then the SiO□ is wet-etched using a hydronic acid-based Banfa etching solution. Using this 5iO1 as a mask, R of the substrate 1 is
I did IB.

Substrate materials, ceramic materials that make up superconducting thin films,
Main reaction gas, etching conditions (gas pressure, total gas flow rate,
High frequency power density) and substrate temperature were set as shown in Table 1, and the etching rate for the superconducting thin film, which is a superconductor, on the substrate 1 was measured under those conditions.
Shown in the table.

Margin below c] [Effects of the invention] As is clear from the above, the etching method of the present invention has the following effects:
By using bromine or a bromine compound as an etchant, it is possible to easily etch superconductors made of ceramic-based superconducting materials. It can be applied to devices in all fields, including devices in the electronics field, and mass production of these devices is also possible.As an etching technology used in the device manufacturing process, it is an important step in the practical application of ceramic superconducting materials. It is extremely useful.

[Brief explanation of the drawing]

FIG. 1 shows R as one technique of the etching method of the present invention.
FIG. 2 is a schematic diagram showing an example of the configuration of an apparatus used for IB; FIG. 2 is an explanatory diagram showing three prototypes used when forming a pattern deposited on a substrate in the manufacturing process of a compound semiconductor device using beam lithography. A: Reaction chamber B; Vacuum gauge C: Etching gas introduction system D: High vacuum exhaust system E: Etching gas exhaust system 1: Substrate

Claims (2)

[Claims] (1) An etching method for a superconductor made of a ceramic superconducting material, characterized in that bromine or a bromine compound is used as an etchant. (2) The components of the ceramic superconducting material are barium, yttrium, copper, oxygen, barium, lanthanum, copper,
The method of etching a superconductor according to claim 1, wherein the etching method is oxygen, strontium/lanthanum/copper/oxygen, barium/scandium/copper/oxygen, or calcium/lanthanum/copper/oxygen.