GB2119970A - Film deposition equipment - Google Patents

Abstract

This film deposition equipment is arranged so that metal 4 is evaporated in atmosphere including reactive gas introduced in a vacuum, and pressure variation of the reactive gas caused by the metal evaporation is detected at 17 to know and control metal evaporation amount, by varying the power to the evaporator at 5. <IMAGE>

Description

SPECIFICATION Film deposition equipment This invention relates to a film deposition equipment ensuring deposition of film with constantcomposi- tion.

In fields of electricity and chemistry, various conductive or insulative films are used. Particularly in electronic field which is text to realize films with always constant quality so as to be used for electronic devices.

Reactive high frequency (RF) ion plating is known as one of film deposition methods to satisfy the above-mentioned requirement. Figure 1 shows an equipment to be used for said reactive RF ion plating. Reference numeral 1 designates a vacuum, 2 refers to a substrate holder, 3 to a substrate to be provided with film thereon, 4 to evaporation source metal, 5 to an evaporating power source, 6 to an RF power source, 7 to a matching circuit, 8 to an acceleration DC power source, 9 to an RF discharge electrode, 10 to a reactive gas inlet, 11 to a reactive gas outlet, 12 to a valve, 13 to a crystal oscillator, 14 to a film thickness monitor, 15 to an evaporating speed monitor, and 16 to a controller.

With this equipment, glow discharge is caused by the RF discharge electrode 9 within the vacuum 1.

The metal 4 is evaporated in the atmosphere including reactive gas introduced through the reactive gas inlet 10. Thereby, the reactive gas and the metal components react and the resulting compound forms film on the substrate 3. In this case, since plasma is generated due to glow discharge, the reactive gas and the metal particles become radical or ionized so as to be chemically active. Therefore, it is possible to make film with excellent crystallization on substrate at a considerably low temperature as compared to other vacuum evaporating deposition methods.

If ions are accelerated and bombard the substrate 3 by applying DC voltage between the evaporation source metal 4 and the substrate 3 by means of the acceleration DC power source 8 (minus Vat the substrate 3 and 0 to several kV at the metal 4), chemical activity is further improved. Further, since the reactive RF ion plating uses RF electric field, glow discharge is maintained even when pressure in the vacuum 1 is very low (-5x10-5 TORR). As the result, fine, even and plane film can be provided. Further, since increase of temperature of the surface of the substrate 3 due to striking or radiation energy of ions is not so large, it is easy to control temperature of the substrate 3.

To ensure and maintain evenness of film quality, constant conditions must be maintained throughout the entire process of film deposition.

Particularly when film is made by chemical reaction between more than two kinds of elements such as said reactive gas and the metal, it is important to precisely control amount of the respective elements in order to maintain stoichiometric chemical composition of the film.

Substrate temperature, RF power, acceleration voltage, gas pressure, metal evaporating speed are parameters for deposition of desired film. However, it is most important to reliably control metal evaporating speed.

To this end, there is used a crystal oscillation monitoring method as shown in Figure 1 in which the crystal oscillator 13 is disposed within the vacuum 1 to detect metal evaporating speed. More specifically, since the crystal oscillator 13 has such a nature that its resonance frequency varies in proportion to amount of film deposited thereon, metal evaporating speed is controlled by the following manner: thickness of film deposited on the crystal oscillator 13 is measured by the film thickness monitor 14; the resulting output signal from the monitor 14 is differentiated by the speed monitor 15 to detect variation of resonance frequency i.e. vapor deposition speed; and in response to the detection result; output signal to maintain constant vapor deposition speed is fed back to the evaporating power source.

However, the crystal oscillation monitoring method has the following drawbacks: (1 ) when temperature of the crystal oscillator 13 increases due to radiation heat from the evaporation source (metal) and plasma, variation of resonance frequency becomes irregular, causing measurement error; (2) there is upper limitation to thickness of film which the crystal oscillator 13 can detect; (3) since film adheres on the RF discharge electrode 9 and along the inner periphery of the vacuum 1 during film deposition for a long time, matching of RF power disorders little by little to change discharge condition, and noise is caused by the change and appears at the film thickness monitor 14; (4) since the noise appearing at the film thickness monitor 14 is promoted by differential of the speed monitor 15, it becomes larger;; (5) since it takes relatively long time from detection of resonance frequency variation to feedback to evaporation speed control, evaporation speed cannot be immediately controlled.

Therefore, it is difficult to provide, by the prior-art method, film with even and constant quality.

It is therefore an object of the present invention to maintain substantially constant evaporation speed of metal in order to make film with even thickness and quality.

In accordance with the present invention, variation of reaction gas pressure caused by evaporation of metal is detected by use of stoichiometric correlation between the reactive gas and the metal upon gettering action, and metal evaporating amount is controlled in response to the detection result.

Examples of the present invention are now described with reference to the accompanying drawings, in which Figure 1 is schematic view of a conventional equipment; Figure 2 is a schematic view of an embodiment of the equipment according to the present invention; and Figure 3 shows the relation between gas pressure variation and vapor deposition speed obtained by the present invention.

The phenomenon that when metal with strong activity is evaporated within a vacuum wherein reactive gas remains, the remaining reactive gas is taken up by the evaporated metal to increase vacuum degree is well known as gettering action.

Details of the gettering action is complicate. However, it is generally considered that since evaporated metal i.e. metal vapor reacts on remaining gas in gas phase to take up the gas and the metal component continues to take up the remaining gas even after it is deposited on inner surface of the vacuum, pressure of the remaining gas decreases, thereby improving vacuum degree. Further, it is considered that when plasma is generated due to discharge, this tendency is further promoted and the gettering action becomes remarkable. Therefore, the gettering action might become particularly remarkable in reactive RF ion plating.

If it is assumed that flow amount of reactive gas introduced after discharge speed of the vacuum is fixed constant, gas pressure is kept constant. This gas pressure expressed by P1. When the metal is thereafter evaporated within the vacuum, the gas pressure decreases. The decreased gas pressure is designated by P2. The decrease expressed by P1 - P2 = AP depends on metal evaporating speed and RF power.

Since film deposition is carried out underthe gas pressure P2, the pressure P2 must be stabilized. That is, it is desired to stabilize the pressure decrease AP.

One of the two parameters, RF power, can be relatively easily controlled. However, it is difficult to reliably control the other parameter i.e. metal evaporating speed.

The fact that the reactive gas and the metal react on each other with a determined stoichiometric correlation upon gettering action, however, makes it possible to reliably control gas pressure variation AP.

Figure 2 shows a schematic view of a reactive RF plating equipment which is an embodiment of the film deposition equipment according to this invenzion. In this Figure, elements and parts corresponding those of Figure 1 are designated by the same reference numerals. Reference numeral 17 refers to a vacuum gauge, 18 to a DC converter, 19 to a DC amplifier, and 20 to a PID regulator.

With this arrangement, after air in the vacuum 1 is discharge to lower the pressure to about 1 x 10-6 TORR, reactive gas i.e. oxygen gas, for example, is introduced through the reactive gas inlet 10 so as to maintain gas pressure of 8 x 10-4 TORR, aproximately.

Next, glow discharge is caused within the vacuum 1 due to RF electric field. After discharge and the said gas pressure reach predetermined values, evaporation source metal 4 i.e. zinc, for example, is heated and evaporated by the evaporating power source 5.

Along with metal evaporation, gas pressure within the vacuum 1 decreases (vacuum degree increases) due to gettering action, thereby representing certain value in response to metal evaporatiing speed.

The value of gas pressure is detected by the vacuum gauge 17 and the detection output is converted to DC voltage by the DC converter 18. The DC voltage is amplified by the DC amplifier 19 and is applied to the PID regulator 20. The PID regulator compares the DC voltage to reference voltage value which is previously set in response to the determined gas pressure, and applies output equal to the reference voltage value to the evaporating power source 5.

The evaporating power source 5 accordingly controls metal evaporating amount to select evaporation speed corresponding to DC voltage of the value equal to the value of the reference setting value.

Therefore, by detecting variation of gas pressure, metal evaporating speed is controlled to be stable.

Oxygen which is the reactive gas and zinc which is the evaporation source metal 4 react to form zinc oxide ZnO and ZnO film is deposited on the substrate 3.

The ZnO film is even and constant in its composition.

When the evaporating speed changes, the change AP is immediately detected and evaporating speed is controlled until the variation AP is stabilized.

Figure 3 shows a characteristic between evaporation speed V, abscissa, and gas pressure variation AP, ordinate, which is obtained by the present invention. As apparent from the Figure, both factors are substantially correlated so that metal vapor deposition speed V can be controlled by adjusting the gas pressure variation AP. It should be noted that this characteristic is obtained under the conditions: material of the substrate 3: (Ill)-oriented silicon; substrate temperature: ordinary room temperature, ZnO film thickness: 4,am; evaporating source boat: tantalum; RF power: 100W; and DC bias: OV.

Films obtained by this embodiment were submitted to measurement of film crystallization film construction by means of X-ray diffraction and scanning electronic microscope. As the result, it was assured that films deposited at a same evaporating speed have a same quality.

As described in the above, since the present invention does not require crystal oscillation monitoring method to detect and control evaporating speed, detection is never prevented by film thickness and immediate reflection of the detection result to evaporating speed control can be expected. Further, omission of expensive crystal monitoring equipment leads to cost reduction.

This invention is not restricted to deposition of ZnO film and is also effective for film deposition of other compounds i.e. TiO2, ln203, Al2O3, SiO2, TiN, AIN, for example.

Claims (3)

1. Afilm deposition equipment wherein metal is evaporated in atmosphere including reactive gas introduced in a vacuum for deposition of film on a substrate disposed within the vacuum, said equipment further including a metal evaporating means to evaporate said metal, a detecting means to detect variation of pressure of said reactive gas within said vacuum due to metal evaporation, and a control means responsive to detection signal of said detecting means to control metal evaporating amount by said metal evaporating means.

2. Afilm deposition equipment as setforth in Claim 1 wherein said detecting means comprises a vacuum gauge to detect reactive gas pressure within said vacuum, a DC converter to convert output of said gauge to DC voltage, a DC amplifier to amplify said DC voltage, and a PID regulator responsive to output of said amplifier to control metal evaporation source,

3. A film deposition equipment substantially as herein described with reference to Figures 2 and 3.