JP2715299B2 - Method for forming Z-bottom nO film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for forming a ZnO film used for various uses such as an electronic element, a piezoelectric element, and an optical coating. (Prior Art) It can be said that almost all generally used film forming methods can be used for forming a metal oxide film. Various methods such as a sputtering method, a reactive sputtering method, a thermal CVD method, and a plasma CVD method have been put into practical use, even if only the method utilizing the vacuum technique is viewed. Common challenges in film formation are:
From the standpoint of industrial use, in particular, high speed and good film quality are required. In view of such a background, a method that utilizes the energy of an electromagnetic field has attracted attention as a method aiming at practical use. By this use, it is possible to discharge more efficiently than in a normal sputtering method, a plasma CVD method, or the like, and furthermore, there is a possibility that a high-quality film can be obtained at high speed because the pressure can be reduced (to a high degree of vacuum). (Problems to be Solved by the Invention) Among the problems in the case of using a gas source, the important ones are the completeness of decomposition of the organometallic gas or the state of the intermediate product, the organic and film crystallinity, Surface shape. The film is affected by its crystallinity, film structure, surface shape, and the like due to the presence of intermediate products and insufficient oxidation. For example, Zn
When the O film is used as a piezoelectric material, the disorder of the crystal structure causes a decrease in the piezoelectric characteristics. When the surface is rough, the propagation loss of the surface acoustic wave increases. Further, when a ZnO film is used as a transparent conductive film, there are drawbacks in that a desired electric resistance value cannot be obtained and a visible light transmittance is reduced. SUMMARY OF THE INVENTION An object of the present invention is to solve the conventional drawbacks, to suppress the occurrence of irregularities on the growth surface of a thin film, to improve the surface flatness, and to achieve excellent film quality such as surface acoustic wave propagation characteristics and visible light transmittance. An object of the present invention is to provide a method for forming a ZnO film. (Means for Solving the Problems) In order to achieve the above object, the present invention introduces a gas of an organic metal containing Zn and a gas containing oxygen into a vacuum chamber as raw material gases and converts them into plasma. A method of forming a ZnO film on a substrate, wherein during the formation of the ZnO film, different from the source gas, to accelerate the oxidation of the ZnO film and reduce intermediate products during the film formation. A method for forming a ZnO film, characterized by introducing a gas having an oxidizing effect of the above or a gas having a reducing effect for flattening the surface of the ZnO film by an etching reaction into the vacuum chamber. (Function) According to the above configuration, first, when a gas having an oxidizing action is introduced, promotion of decomposition of a gas of an organic metal containing Zn, reduction of an intermediate product, improvement of the degree of film oxidation, and the like are achieved. Therefore, the obtained ZnO film has improved crystallinity such as C-axis orientation, and has an improved surface shape and surface flatness, and excellent piezoelectric characteristics and excellent surface acoustic wave propagation characteristics can be obtained. Further, the visible light transmittance increases, and a transparent conductive film having an appropriate electric resistance value can be obtained. When a gas having a reducing action is introduced, the film forming reaction and the etching reaction proceed simultaneously, so that the surface of the ZnO film is flattened and the propagation characteristics of surface acoustic waves are improved. (Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings. Embodiment 1 FIG. 1 shows a schematic configuration of an ECR plasma CVD apparatus for forming a ZnO film according to an embodiment of the present invention. In FIG. 1, both a plasma chamber 1 and a film forming chamber 2 are evacuated to a pressure of 10 ⁻⁶ Torr or less by an exhaust system 3. As a source gas, for example, O ₂ and dimethyl zinc (hereinafter abbreviated as DMZ) are introduced into the plasma chamber 1 and microwave (2.45 G
Hz) The power of the oscillator 5 is turned on, a magnetic field is formed by the coil 6, and the state is changed to an electron cyclotron resonance state (ECR state). Plasma is generated efficiently by the action of high-energy electrons that move in a circular motion. The magnetic field is a divergent magnetic field that gradually weakens toward the film forming chamber, whereby ions are transported toward the substrate 7 and a ZnO film is formed on the substrate 7. When the film is formed only with O ₂ and DMZ, the surface of the formed ZnO film is easily roughened, and the surface of the film having a thickness of about 6 μm has surface irregularities of about 4000 ° observed with a scanning electron microscope. . In addition, since the crystal structure is disturbed, the resistance value tends to be low, and a high resistance of about 10 ⁶ Ω · cm or more required for obtaining desired piezoelectric characteristics cannot be obtained. In addition to O ₂ and DMZ, a small amount of an oxidizing gas such as N ₂ O or H ₂ O is introduced into the film formation chamber 2 from the preliminary introduction port 4. Since these gases have an action of promoting oxidation, the film can be sufficiently oxidized. As a result, the surface shape such as unevenness can be improved and flattened. In addition, when a gas having an oxidizing effect is introduced, an intermediate product generated when an organic metal gas such as DMZ is decomposed,
In particular, it is possible to eliminate the influence of carbon, which is assumed to be due to hydrocarbons, so that problems such as disorder in C-axis orientation are eliminated, and crystallinity is improved. Further, since gases having a reducing action such as H ₂ O and alcohol have an effect of exerting an etching action on ZnO, it is necessary to add these gases during film formation, that is, the film forming reaction and the etching reaction are simultaneously performed. By creating a quasi-equilibrium condition that progresses, film formation can proceed while the surface is flattened. As described above, when a gas having an oxidizing action or a gas having a reducing action is used, the flatness of the surface of the formed ZnO film can be improved, and the unevenness can be suppressed to about 1000 mm or less. Since the crystallinity can be improved by using the gas having, high resistance and low surface acoustic wave propagation loss exhibiting the piezoelectric characteristics required as a surface acoustic wave element
A ZnO film could be formed. As an example, a resistance value of 1.3 × 10 ⁷ Ω · cm and an electromechanical coupling coefficient of 7.6% were obtained. Although the substrate temperature was set at about 170 ° C. during the above film formation, when the film was formed at room temperature, the surface looked rough, and the reproducibility of the resistance value was poor. Therefore, it is effective to heat the substrate. In the present embodiment, DMZ was used as a source gas, but another zinc-containing organometallic gas source such as diethyl zinc (DEZ) may be used. In the present invention, various gases such as CO ₂ can be used as a gas having an oxidizing action, and various gases can be used as a gas having a reducing action. Example 2 Using the same device as in Example 1, a laser beam 1 is guided into the film forming chamber 2 through a window 8 in the figure. As the window material, synthetic quartz was used so that short-wavelength light such as vacuum ultraviolet light could be used. There are roughly two ways of using laser light. Excitation in the gas phase by the energy of photons,
There are a method of causing decomposition and a method of directly irradiating the substrate and utilizing the thermal action. In forming a ZnO film using DMZ in this embodiment, these effects can be used. Excimer laser (KrF,
(Wavelength: 248 nm) was used so that it was horizontal to the substrate and did not directly hit the surface. At this time, the DMZ or the like that has not completely decomposed in the plasma chamber 1 and arrives in the film formation chamber 2 while remaining slightly is decomposed by the high energy of photons.
At the same time, carbon can be prevented from being taken into the film. By doing so, the C axis of the ZnO film is oriented without any problem. As laser light in the visible or infrared region, for example, YA
G-laser light is directly applied to the substrate surface. As a result, the propagation loss of the surface wavelength was reduced from 10.5 dB / cm to 4 db / cm as compared with the case without laser beam irradiation. This is presumably because the laser light irradiation improved the flatness of the ZnO film surface. (Effects of the Invention) As described above, according to the present invention, a gas having an oxidizing action or a gas having a reducing action is used in addition to using a gas of an organic metal containing Zn and a gas containing oxygen as raw materials. By introducing the ZnO film, a ZnO film having excellent crystallinity and a flat surface can be obtained as a result of an oxidizing action or a reducing action of these gases, or a combination thereof. Also, the resistance value,
The film properties such as piezoelectric characteristics and visible light transmittance are also improved, and can be effectively used for piezoelectric elements, optical coatings, and the like.
Furthermore, taking advantage of the high speed of film formation using a gas source,
A method for forming a ZnO film having excellent mass productivity can be provided, and its practical effect is great.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing a configuration of an ECR plasma CVD apparatus according to one embodiment of the present invention. DESCRIPTION OF SYMBOLS 1 ... Plasma chamber, 2 ... Film formation chamber, 3 ... Exhaust system, 4 ... Preliminary inlet, 5 ... Oscillator, 6 ... Coil, 7 ... Substrate, 8 ... Window.

   ────────────────────────────────────────────────── ─── Continuation of front page    (56) References JP-A-60-116118 (JP, A)                 JP-A-62-60876 (JP, A)                 JP-A-61-28156 (JP, A)                 Shokai Sho 59-209642 (JP, U)                 Shokai 17-179871 (JP, U)

Claims (1)

(57) [Claims] A method of forming a ZnO film on a substrate by introducing a gas of an organic metal containing Zn and a gas containing oxygen into a vacuum chamber as a raw material gas and forming a plasma to form a ZnO film on the substrate, It is different from the source gas,
For promoting oxidation of the ZnO film, for reducing intermediate products during film formation, a gas having an oxidizing effect, or a gas having a reducing effect for flattening the surface of the ZnO film by an etching reaction, A method for forming a ZnO film, wherein the method is introduced into a vacuum chamber. 2. 2. The method according to claim 1, wherein a laser beam is applied to the surface of the object to be processed when the ZnO film is formed.
A method for forming a ZnO film.