JPS5812722B2 - Sankabutsu Handout Taihakumakuno Seizouhouhou - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing an oxide semiconductor thin film.

In general, oxide semiconductors such as Zn (LTt02pSn02) are materials that have a wide range of uses, such as transparent electrodes, fluorescent materials, and thermistors, and various thin film techniques have been provided and put into practical use.

ZnO, TiO2, etc. are known as n-type semiconductors, and are generally known to be produced when metal or metal ions are in excess in an ionic crystal that deviates from the stoichiometric composition.

Therefore, it is theoretically possible to create a semiconductor thin film by thinning it using a vacuum evaporation method.

That is, when powders of oxides such as ZnO and TiO2 are evaporated by known evaporation methods such as electron beam heating and resistance heating, a metal-excess state can be created by causing thermal dissociation.

However, in reality, it is difficult to achieve this and to provide sufficient controllability for practical use, and a method of valence control is usually used.

The best known SnO2 is 2-3% Sb203
By including , it becomes a transparent semiconductor with a low sheet resistance of several Ω/cIL, and this is used as a transparent electrode.

However, this manufacturing method is called a spray method, in which Sn, sb, and
This method involves spraying a chloride solution, and it is impossible to use a low melting point material such as plastic for the substrate.

Depending on the conditions, plastic can also be used as the substrate.

Oxygen evaporation method and heat treatment method are methods for producing semiconductor thin films at relatively low temperatures.

That is, metals such as Sn and In are slowly evaporated in about 10 mm of oxygen, and then 15 mm is heated in an oxygen atmosphere.
This is a method of making a semiconductor thin film with relatively low resistance by performing heat treatment at about 0°C to 200°C.

This method of controlling valence is binary vapor deposition, in which, for example, Sn*Sb is placed on separate boats and heated by a separate power source, but control is extremely difficult and reproducibility is difficult. Poor.

An object of the present invention is to provide a method for obtaining a semiconductor thin film with good reproducibility and having a desired resistance value over a wide range from low resistance to high resistance.

Specifically, by using N atoms for valence control,
This invention relates to a method for controlling conductivity.

A description will be given below using SnO2 as an example of an oxide semiconductor.

The drawing shows an example of an apparatus for carrying out the present invention, in which a substrate 2 and an evaporation source 3 are disposed facing each other in a vacuum container 1.

The evaporation source 3 is a known electron beam evaporation source, a resistance heating evaporation source,
Although it may be configured with any type of induction heating evaporation source, the explanation was given using resistance heating.

That is, an evaporated substance placed on a boat 3' made of a high-melting point metal such as Ta or MotW, or Sn metal particles 3 in the case of Sn02.
An evaporation source was provided in which the boat 3' was evaporated by heating the boat 3' under the control of the heating power source 4 via the insulated introduction terminal 14.

Although one end of the evaporation source is DC grounded, this is not necessarily the case, and it may be grounded via a capacitor.

Although the base 2 is shown to be held by the substrate holder 5, for example, when forming a Sn02 thin film on a plastic film, the film winding mechanism may be used instead. In this case, measures such as arranging an electrode with openings such as a mesh on the front surface of the substrate facing the evaporation source are carried out depending on the type and shape of the substrate, but the explanation of the present invention is most I went to a simple case.

An electrode 6 for plasma formation is provided in the space between the evaporation source 3 and the substrate 2.

Plasma generation methods can be broadly divided into high-frequency glow and DC glow, but DC glow uses hot shade! Including plasma.

The drawing shows the simplest case of using high frequency glow, which is capable of generating and maintaining plasma in a relatively high vacuum region, and is composed of a high frequency power source 7 and a west frequency electrode 6.

The high frequency electrode 6 often has a spiral structure such as an aluminum or copper pipe, but the shape may be cylindrical or otherwise designed as appropriate.

The vacuum container 1 is made of glass, stainless steel, or the like, and is connected to a vacuum exhaust system 8 that includes, for example, an oil diffusion pump, a water-cooled trap, and an oil rotary pump.

Further, leak bars 9 and 10 are connected to the vacuum vessel 1 and connected to a source of gas 11 and 12.

Note that the substrate 2 is biased to a ground potential or a negative potential by a DC power supply 13.

A relative! When making it into a plate, use the mesh electrode as described above,
This gives the substrate potential.

An example of creating Sn02 on a glass substrate using this apparatus will be explained.

The inside of the vacuum container 1 is made up of l×l by the vacuum evacuation system 8 in advance.
Exhausted to Q-5 mmHg to 1 x 10-6 wlHg.

Although the degree of vacuum of ζ is not uniquely determined, the higher the vacuum, the better, but the practical difference is recognized at 10-
This is a case where the exhaust is only about 4maHg, and IX
There is no particular problem if the value is IO-51 mHg or less.

Thereafter, 02 is introduced through the i nodes of the barrier pull leak valves 9 and 10 to a partial pressure of, for example, 8×10 −4′ mHg.

Meanwhile, N2 is introduced at IX10-4 mmHg.

The pressure in the system is then 9×10 −4 mmHg.

The purity of the introduced gases 0211 and N212 is sufficient when they are directly introduced from a commercially available pressure cylinder via a pressure reducing valve and a tank reservoir, and there is no need to add any particular purification equipment.

In this state, the high frequency power supply 7 is operated to generate high frequency glow discharge.

Although the glow depends on the mixing ratio of 02/N2, pink excited light emission can be observed.

In the vicinity of the high-frequency electrode 6, a dark area where no light emission is observed is formed due to the ion sheath.

The pink tray is in a plasma state, and the key point is to expose the metal vapor described below in this region, so it is natural that the geometry, slits, etc. for this purpose must be devised.

The Sn3 grains placed on the tungsten boat 3l are vaporized by adjusting the external heating power source 4.

As a result of interaction with the plasma, this vapor flow forms a SnO2 film on the substrate 2, and N atoms are included in an appropriate amount by adjusting the O2/N2 ratio, which become donors and improve the conductivity. Therefore, the desired oxide semiconductor thin film can be changed.

In addition to Sn02, Pb02tSin2tTi02pZrO
2.HiO.

Similarly, in order to increase the adhesion between the substrate and the film, it is better to have it as high as IKV or higher, rather than limiting the conductivity (of course, it varies depending on the material, but 3 to 4K
If V is exceeded, a phenomenon in which the adhesion force decreases is observed.

), the damage to the film increases and adversely affects the physical properties of the semiconductor, so it is appropriate to apply a voltage of 200 V to 500 V (a negative value with respect to the evaporation source).

Note that the higher the partial pressure of N2 and 02 is, the higher the partial pressure of N2 and 02 (at most 5×10 −3 Torr).

), it is necessary to increase the N2 partial pressure (experimentally, this is approximately 1/5 of the time).

) When the 02 partial pressure is lower than that, N2 needs to be maintained at 1/5 or less.

Next, a comparison between the conventional method and the method of the present invention is as follows.

Conventional method: After Sn vapor deposition on a 2 mm glass substrate, 5
When heat treated at 50C for 2 hours, the film thickness was 2000A, the transparency was 75% to 80% in the visible range, and the resistance value was IKΩlcA2.

Method 2 of the present invention High frequency power = 350W (2
．． When a film was formed at 5KVp anode voltage), substrate applied voltage: DC-300V, 02:8×10-4 TorrpN2:IXlO-4 Torr, the film thickness was 2000X, transparency was 80% to 85%, and resistance was 50Ω. /cA2 to 300 Ω/cm2.

Next, a comparison of the reproducibility of semiconductor control is as follows.

Conventional method: Sn was evaporated by resistance heating using a tungsten boat, and sb was evaporated by heating using an indirect heating filament. The resistance value of the SnO2 (sb) film was ioΩ/cft to 500KΩ/
It was cA2.

Resistance value when manufactured under the same condition settings Variations can be made with low resistance, but are they large? It was.

Invention method: High frequency power: 400W (2KVp anode voltage)
The resistance values for the following gas pressures were as follows.

(i) 02:5X10-4Torr+N2:7X10-
5 Torr Resistance value of SnO2N film: 200Ω/cf2~700Ω/
cm2 (2) 02:6X10-4 TorrtN2:6X10-
5Torr SnO2N film resistance value: 800Ω/cyR ~ 1.2KΩ
/ctA (3)02:8X10-”forrtN2:IX10-
'Torr Resistance value of Sn02N film = 70Ω/cIt ~ 18oΩ/d
m2 The variation in resistance value was small.

As described above, according to the present invention, it is possible to form a thin film with good reproducibility, and it has great practical value.It is noteworthy that no heating of the substrate is required in any case. It can contribute to the application and practical use of electrodes, EL, etc., and its industrial potential is great.

[Brief explanation of the drawing]

The drawing is a schematic cross-sectional front view of an apparatus used to carry out the manufacturing method of the present invention. 1... Vacuum container, 2... Substrate, 3.3
'・・・Evaporation sources (evaporation substances and boats), 4...
... Heating power supply, 6 ... High frequency electrode, 7 ...
...High frequency power supply, 11...Oxygen gas, 12...
...Nitrogen gas.

Claims (1)

[Claims] 1 A substrate and an evaporation source are arranged facing each other in a vacuum container, a mixed gas plasma of oxygen and nitrogen is formed in the space between them, and a vapor flow generated from the evaporation source is exposed to the plasma, and the vaporization source and the evaporation source are exposed to the plasma. 1. A method for producing an oxide semiconductor thin film, which comprises forming an oxide semiconductor thin film whose valence is controlled by nitrogen on a substrate placed at a high potential or a negative potential.