KR20080065587A - Ceramic target, film constituting zinc, gallium and boron oxide and method of manufacturing of the said film - Google Patents

Abstract

The invention relates to the field of opto-electronic technology and is intended to create transparent conducting layers. More particularly, the invention relates to the field of manufacturing of ceramic materials and is used in manufacturing of ceramic targets, which serve as a source of material in film application methods by magnetron sputtering, electronic beams, ionic beams and other film application methods in micro-, opto-and nano-electronics as well as to films produced from such ceramic target and to a manufacturing process of said films. Disclosed is a ceramic target containing zinc oxide alloyed by gallium and containing between 0.5 and 6 % of gallium atoms and between 0.1 and 2 % of boron atoms, wherein the gallium and boron part is contained in crystallites of zinc oxide as substitution impurity, and the boron and gallium remaining part is contained together with zinc in the amorphous intergranular phase. Disclosed is also a film containing zinc oxide with prevalent orientation (001), alloyed by gallium in the structure of which 0.1 to 2 % of zinc atoms are substituted by boron atoms and 0.5 to 6 % of zinc atoms are substituted by gallium atoms, as well as a corresponding manufacturing process.

Description

CERAMIC TARGET, FILM CONSTITUTING ZINC, GALLIUM AND BORON OXIDE AND METHOD OF MANUFACTURING OF THE SAID FILM}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the field of photovoltaic technology and to produce a transparent conductive layer.

More specifically, the present invention relates to the production of ceramic materials, which form magnetron, electron beam, ion beam and sputtering films in micro-, opto-, nanoelectronics technologies. It relates to the manufacture of a ceramic target for providing a raw material for another method applied, and also to a film produced from the ceramic target and a method of forming the film.

Synthetic methods consisting of a ceramic target and a preparation, compact and sintering process of a mixture are known [J.M. Tairov, V.F.Tsvetkov. See "Technology of semi-conducting and dielectric materials", Moscow, "Higher School" Publishing House, 1990, 423 pages].

Ceramic targets for magnetron sputtering are known.

The prior art most similar to the ceramic target and method for preparing according to the present invention is US Patent No. 5458753 published on October 17, 1995, which discloses a ceramic target composed of zinc oxide and gallium. It is starting.

A disadvantage of the target according to the prior art is that the density of the ceramic is insufficient. Inadequate ceramic density causes non-uniform sputtering of materials during film formation, creating fine particles on the target surface during sputtering, contamination of the growth surface by clusters and doping of the synthesized film. It becomes uneven.

Another subject of the present invention relates to a transparent conductive film formed by the ceramic target sputtering.

The inventors of WWWang, XGDio, Z.Wang, M.Yang, TMWang Z.Wu. under the heading "High Performance DC Magnetron Sputtered Zinc Oxide: Preparation and Characterization of Aluminum Films" for zinc oxide based transparent conductive films. The prior art published by 2005 is known [WWWang, XGDio, Z. Wang, M. Yang, TMWang Z. Wu. Preparation and characterization of highperformance directed current magnetron sputtered ZnO: Al films. Thin Solid Films 491 (2005) 54-60].

A disadvantage of these films is the absence of the doping mixture, which results in insufficient conductivity of the zinc oxide film.

A transparent conductive film based on gallium doped zinc oxide is known [P.K. Song, Watanabe, M. Kon, A. Mitsui, Y. Shigesato. "Electrical and optical properties of gallium-doped zinc oxide films deposited by DC magnetron sputtering. See Thin Solid Films 411 (2002) 82-86).

Disadvantages of the membranes are the reduction of carrier mobility and chemical resistance.

The prior art most similar to the present invention is a film based on gallium doped zinc oxide. Since the gallium ions are similar to those of zinc, gallium can be bonded to zinc oxide at substantial density [US 5,458,753, 17.10.1995].

A disadvantage of the membranes is that they provide columnar structures that degrade the properties of the membrane, in particular anisotropy.

Another subject of the present invention is a method for synthesizing the transparent conductive film described above.

Many synthetic methods are known for zinc oxide (gas-transport, pyrolitic and others). The most similar prior art is a method for synthesizing a film based on zinc oxide, with zinc oxide as the main material on the growth surface by magnetron sputtering of ceramic targets, and gallium applied as a doping mixture [P.K. Song, Watanabe, M.Kon, A. Mitsui, Y. Shigesato. "Electrical and optical properties of gallium-doped zinc oxide films deposited by DC magnetron sputtering. See Thin Solid Films 411 (2002) 82-86).

A disadvantage of the synthesis method according to the prior art is the generation and maintenance of membrane columnar tissue, which impairs the incompleteness of the formed membrane, that is, the characteristics of the membrane as described above.

An object of the present invention is to qualitatively improve the properties of zinc oxide based gallium doped transparent conductive films by increasing the structural completion according to the process occurring on the growth surface. The preparation of such films requires a high density, corresponding ceramic material of a sputtering nonuniformity and a structure that prevents macrostructure formation on the ceramic surface during sputtering.

The above object can be achieved by proposing a ceramic target having a composition in which boron is added to zinc oxide and gallium.

In particular, the target according to the present invention contains 0.5 to 6 atomic percent of gallium and 0.1 to 2 atomic percent of boron together with zinc oxide. At the same time, the doping mixture comprises a zinc oxide crystal lattice and a mixture of zinc, gallium, boron and grain boundaries in the form of an amorphous phase comprising an oxide in the mixture as a substituting admixture. do.

It is another object of the present invention to increase the carriers' mobility, to reduce the deterioration of characteristics due to the external environment of a device including such membranes, and to allow film properties to be predicted and calculated. This is to increase the crystallinity of.

This object can be achieved by providing a polycrystalline film based on zinc oxide doped with gallium in a mixture containing boron.

Another object of the present invention is to increase structural completion, in particular by preventing columnar tissue formation of the membrane.

This object can be achieved by providing a method for synthesizing a film to which boron is applied as an element which increases the mobility of atoms adsorbed on the growth surface in addition to the main material (zinc oxide) and the doping mixture (gallium) on the growth surface of the film. Can be.

One subject of the invention is a ceramic target. The target provides a liquid state of gallium before grinding the mixture of zinc oxide powder, metal gallium and boron-containing material, pressing and then covering the zinc oxide particles with the mixture of liquid gallium and boron-containing material. It is prepared by sintering under temperature. The component amount of the component is determined according to the composition of the ceramic.

The composition of the synthesized ceramic comprises 0.5-6 atomic% gallium and 0.1-2 atomic% boron together with zinc oxide, a part of gallium and boron present in the crystal lattice of zinc oxide as a substitution mixture, gallium and The remainder of boron is contained at grain boundaries in the form of an amorphous phase with zinc oxide.

1 illustrates different patterns of ZnO: Ga: B ceramic targets. From these different patterns it can be seen that there is no structureless band corresponding to the amorphous phase present at the grain boundaries.

By grinding the zinc oxide powder containing liquid metal gallium [RU2004105169], all of the zinc oxide particles can be covered with a gallium layer, which is difficult to achieve by other methods (for example, impossible by sputtering). The method provides a uniform gallium distribution through the ceramic volume, resulting in a uniform gallium distribution through the volume of the film sputtered from the ceramic. The zinc oxide particles can then be derived into boric acid particles (aqueous solutions, powders and slightly dried or directly pressurized forms) by grinding into boron oxide or a composition that forms boron oxide (eg, boric acid) in an annealing process. ) Can be covered. Boron oxide formed in the ceramic dissolves gallium oxide formed from gallium upon heating and then zinc oxide forms a liquid surface phase on the particles during sintering. Upon heating, liquid gallium worsens the material than other liquid metals (see Chemical Encyclopedia, "Sovetskaya Encyclopedia" Publishing House, Moscow, 1988, page 935); therefore, zinc oxide particles are also subject to gallium deterioration and subsequent boron oxide Dissolution in it also increases the uniformity of the ceramic.

FIG. 2 shows component analysis data according to X-ray emission characteristics using a LEO 1450 type scanning electron microscope (SEM), showing the evenness of the ceramic obtained.

Thus, grinding of gallium-containing zinc oxide powders increases the distribution uniformity of gallium through the volume of ceramics and membranes, and the addition of boron interacts with zinc oxide particles deteriorated by gallium and oxides with gallium at high temperatures. This increases the uniformity of distribution of the mixture in the volume. In the absence of gallium, boron oxide is not very uniformly distributed, whereas in the absence of boron, the distribution uniformity of gallium is increased, and it is impossible to obtain the properties of the film obtained when gallium and boron are present in both. On the other hand, gallium cannot be substituted in the ceramic, so it is necessary to form a film therefrom. Since the properties of gallium can be applied to the surface of the zinc oxide particles by the aforementioned method, the uniformity of gallium distribution through the volume of the ceramic and the film is increased. Let's do it. Gallium also worsens zinc oxide, which has the same effect. On the other hand, during sintering of the ceramic, boron oxide dissolves gallium oxide so that zinc oxide forms a liquid phase instead of the zinc oxide particles produced by gallium at the boundary of the particles. This increases the density and conductivity of the ceramic and further increases the distribution uniformity of the mixture.

Another subject of the invention relates to a transparent polycrystalline film prepared from a ceramic target according to the invention and a method of synthesizing said film.

The membrane according to the present invention comprises a polycrystalline membrane based on zinc oxide having a gallium doped (001) preferred orientation, which additionally contains boron, in which 0.1 to 2% of zinc atoms are substituted with boron atoms in the construction of the membrane. 0.5-6% of the zinc atoms are replaced with gallium atoms.

Sputtering of the membrane is carried out in magnetron sputtering equipment (high frequency or direct current equipment). As the target, the target according to the present invention is used. The film is applied on a substrate, in particular a glass substrate. The sputtering is performed at room temperature to 350 ° C. in an argon atmosphere.

During the sputtering, the presence of boron in the film is important because boron increases the mobility of atoms adsorbed on the substrate of the growing film, and the mobility of the atoms affects the film's structural completeness and properties (optical, electrical and stability). Increase substantially. At the same time, for example, usually do not generate columnar tissue of the membrane, increase the conductivity and the like (there are electrophotographic and other confirmatory tools). Boron that performs this action remains in the zinc oxide crystals that displace zinc and create donor centers and, similar to gallium (elements of the same group), that is, boron does not contaminate the membrane and negatively affect other properties of the membrane. Don't. When boron is used instead of zinc, boron alone cannot be used as a mixture because the ion radius of boron is substantially smaller than the ion radius of zinc, and lattice strains occur when zinc is replaced with boron. The necessity of introducing gallium is related to the ion radius of gallium being similar to that of zinc and that no structural deformation in the lattice occurs even when zinc is replaced with gallium. Thus, sufficient levels of gallium can be introduced for the required conductivity.

On the other hand, since the gallium ion radius is similar to that of zinc, gallium cannot be substituted in the membrane, so gallium can be introduced in an amount sufficient for the required conductivity without substantially increasing deformation in the lattice.

As in the prior art, gallium in the film according to the invention displaces zinc in the form of a zinc oxide lattice, produces donor levels that do not cause substantial lattice deformation, and boron prevents deterioration of membrane quality and columnar tissue formation. . Boron also substitutes zinc in the form of a zinc oxide lattice to produce donor levels, but the boron's ion radius is essentially different from the zinc's ion radius, and the high doping levels of boron lead to structural and strain lattice deformations as well as electrical and optical properties. Therefore, high conductivity may not be obtained when boron is used as a sole donor.

3 shows a cross-sectional electrophotograph of a ZnO: Ga: B film synthesized at a substrate temperature of T = 200 ° C. FIG.

4 shows a cross-sectional electrophotograph of a ZnO: Ga film synthesized at a substrate temperature of T = 200 ° C. FIG.

Comparing the data of FIGS. 3 and 4, it can be seen that the ZnO: Ga: B layer does not exhibit any significant relief of cleavage unlike the films in the prior art.

4 shows that the ZnO: Ga film has a typical columnar structure due to the low mobility of the reactants deposited on the surface during synthesis. At the same time the layer has a protruding surface that impairs optical and electrical properties.

The presence of the developed relief as well as grain boundaries (circumferential boundaries) increases the etching rate as well as the selective etching of the film, which reduces the chemical stability of the film.

Table 1 shows that at a predetermined temperature, the specific resistance of the layer does not change substantially with the thickness of the layer. This is evidence that there is no incomplete transition layer on the boundary film substrate.

                                                            Table 1

Resistivity according to the thickness of ZnO: Ga: B layer synthesized at various temperatures

50 nm (Ω.㎝) 100 nm (Ω.㎝) 150 nm (Ω.㎝) 25 ℃ 3 x 10 ^-3 2.5 x 10 ^-3 1.2 x 10 ^-3 120 ℃ 1.08 x 10 ^-3 1.00 x 10 ^-3 7.8 x 10 ^-4 200 ℃ 4.50 x 10 ^-4 4.50 x 10 ^-4 4.50 x 10 ^-4

  It can be seen from Table 2 that the electrical properties of the ZnO: Ga: B layer do not substantially change during the heat treatment at a temperature of about 200 ° C.

TABLE 2

After heat treatment and synthesis for 1 hour at 200 ℃ in vacuum and air

Resistivity comparison between ZnO: Ga and ZnO: Ga: B layers

ZnO: Ga 25 ° C 150 nm ZnO: Ga 200 ° C 150 nm ZnO: Ga: B 25 ° C. 150 nm ZnO: Ga: B 200 ° C. 150 nm ρ (Ω x cm) 1.2 x 10 ^-3 4.5 x 10 ^-4 6.75 x 10 ^-4 3.0 x 10 ^-4 ρ _vacuum (Ω x ㎝) 1 x 10 ^-3 4.0 x 10 ^-4 4.50 x 10 ^-4 4.50 x 10 ^-4 ρ _air (Ω x ㎝) 8.4 x 10 ^-3 6.0 x 10 ^-4 1.13 x 10 ^-3 3.3 x 10 ^-4

Table 3 shows the etch rate comparison values of the ZnO: Ga layer and ZnO: Ga: B layer in 0.1 mol (M) oxalic acid.

TABLE 3

ZnO: Ga and ZnO: Ga: B Layers at 0.1 mol (M) Oxalic Acid

Etch Rate Comparison

ZnO: Ga ZnO: Ga: B T _room 5 nm / sec 4 nm / sec 200 ℃ 2 nm / sec 1.5 nm / sec

Thus, the authors note that the presence of boron increases the migration rate of atoms adsorbed on the zinc oxide surface, thereby uniformizing the distribution of atoms on the zinc oxide surface and preventing columnar formation. For the first time, it was found that it increases the degree of completeness of the crystals, thereby increasing the mobility and conductivity of the carrier. The solution to this claimed problem is not apparent to those skilled in the art.

Obtaining zinc oxide ceramics containing gallium and boron involves the idea of the mutual strengthening of the uniformity by boron and gallium and the distribution uniformity of gallium through the volume of the ceramic: Gallium is a particle of zinc oxide powder depending on their defects and nonuniformities. Boron oxide is dissolved in gallium oxide and zinc oxide to ameliorate these adverse effects. It has also been exploited that gallium containing boron does not interact chemically (unlike oxides) and does not form clusters that remain on the growth surface during sputtering. These two situations are not at all apparent to those skilled in the art before the present invention is read.

The present invention will also be described as examples, which illustrate only the essential points of the invention and do not limit the nature of the invention.

1 is a view showing a ZnO: Ga: B ceramic target of different patterns,

2 is a diagram illustrating elemental analysis data according to X-ray emission characteristics using a scanning electron microscope (SEM),

3 is a cross-sectional electrophotograph of a ZnO: Ga: B film synthesized at a substrate temperature of T = 200 ° C.

4 is a cross-sectional electrophotograph of a ZnO: Ga film synthesized at a substrate temperature of T = 200 ° C. FIG.

An example of the proposed target is a target prepared from gallium doped zinc oxide. Take 100 g of zinc oxide powder, introduce 2.7 g of metal gallium (about 3 atomic%), and then grind the mixture completely into powder in a ceramic dish until gallium is completely transferred to the zinc oxide particle surface. . After grinding, 0.8 g (about 1 atomic%) of aqueous boric acid solution is introduced into the prepared mass. The mixture is ground into a powder, dried in a drying chamber and pressurized to a pressure of 1000 kg / cm 2 and then sintered at a temperature of 1200 ° C. for 10 hours.

The density of the synthesized ceramic is 5.65 g / cm 3, which corresponds to 99% of the theoretical ceramic density.

A particular embodiment of the proposed invention is a (001) orientation zinc oxide polycrystalline film doped with gallium (3 atomic%) and boron (1 atomic%), wherein the film is gallium (3 atomic%) and boron (1 atomic%). Synthesized by magnetron sputtering from a ceramic target based on zinc oxide containing oxides. The ceramic target is synthesized by pulverizing zinc oxide powder, gallium or gallium oxide and boric acid solution at a temperature of 30 ° C., pressing at a pressure of 1000 kg / cm 2, and sintering at a temperature of 1200 ° C. for 10 hours.

The density of the synthesized ceramic is 5.65 g / cm 3, which corresponds to 99% of the theoretical ceramic density.

Claims (3)

5 to 6 atomic% gallium and 0.1 to 2 atomic% boron, part of the gallium and boron is included in the zinc oxide microcrystals as a substitution mixture, the remainder of gallium and boron in the form of amorphous grain boundaries on zinc Ceramic target based on gallium doped zinc oxide. Oxides of gallium doped (001) preferred orientation containing boron, in which the composition contains 0.1 to 2 atomic percent zinc atoms substituted with boron atoms and 0.5 to 6 atomic percent zinc atoms substituted with gallium atoms. Polycrystalline film based on zinc. A method for synthesizing a polycrystalline film composed of a film to which the magnetron sputtering method of the ceramic target according to claim 1 is applied.

Images