JPH06191844A - Electric conductive transparent oxide - Google Patents

Abstract

PURPOSE:To obtain an electric conductive transparent oxide having excellent electric conductivity and transmitting UV. CONSTITUTION:This electric conductive transparent oxide is a solid soln. having a spinel type crystal structure and contg. an oxide contg. magnesium oxide and aluminum oxide and oxide of at least one selected among Zn, Cd, In, Tl, Sn, Pb, Sb and Bi.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transparent conductive oxide having transparency in the ultraviolet region and electrical conductivity, and particularly KrF.
The present invention relates to a transparent conductive oxide that can be applied to a mask or the like in lithography using excimer laser light (wavelength 248 nm).

[0002]

2. Description of the Related Art So-called transparent conductive materials which are transparent in the visible light region and have electrical conductivity are liquid crystal displays,
Used as various displays such as EL displays and transparent electrodes for solar cells, anti-fog heaters for freezer showcases, heat ray reflection films for window glass of buildings and automobiles, and as a coating for antistatic and electromagnetic shielding of transparent materials. Has been done.

A metal oxide semiconductor is generally used as a transparent conductive material of this type, and tin oxide (SnO ₂ ),
Indium oxide (ITO) doped with tin, CdSn
Various proposals have been made for ₂ O ₄ , ZnCd ₂ O _4, and among these, ITO is widely used. ITO has an optical absorption edge near 370 nm, and is not only transparent over almost the entire region except the region on the shortest wavelength side of the visible region, but also has a carrier concentration comparable to that of metal and is relatively large as an oxide. It has carrier mobility and high electrical conductivity.

[0004]

With the development of lithography technology, a material having both transparency and electric conductivity in a wavelength range shorter than that of a conventional transparent conductive material has been demanded. In a DRAM of 64 to 256 MB which is the memory element of the next to the next generation, the line width is 0.25.
An exposure technique of .about.0.2 .mu.m is required, and a phase shift mask and an exposure technique using a 248 nm light of a KrF excimer laser having a shorter wavelength than the current i-line (365 nm) have been proposed. In the case of a phase shift mask, when a pattern for phase inversion is directly drawn by an electron beam, it is expected that the glass substrate will be charged up, and it is necessary to form an electrically conductive layer on the mask substrate. In addition, regardless of the exposure method, preventing charging of the mask that leads to dust adsorption is a common problem, and it is still necessary to form an electrically conductive layer on the mask. Such an electrically conductive layer must be transparent to the exposing light during the actual exposure stage. However, there has been no substance that is transparent to light having a wavelength of 365 nm or 248 nm, which is a shorter wavelength, and has electrical conductivity. 37
Many oxides such as Al ₂ O ₃ and MgO are known as substances having transparency to light with a wavelength shorter than 0 nm, and all of them are good-quality electrically insulating materials. It is not a material that can meet the demands of. Under such circumstances, new materials having both transparency in the ultraviolet region and electrical conductivity are desired.

[0005]

As a result of studies to solve such a problem, the present inventor has found that Mg having a spinel structure is used.
Al ₂ O ₄ Mg is Zn, Cd, In, Tl, Sn, P
It has been found that an oxide having a transparent and electrically conductive property in the ultraviolet region can be obtained by partially substituting with a metal element selected from b, Sb and Bi.

That is, according to the present invention, an oxide containing magnesium oxide and aluminum oxide, Zn, Cd, I
A transparent conductive oxide characterized by being a solid solution having a spinel type crystal structure, containing at least one oxide selected from n, Tl, Sn, Pb, Sb and Bi, and more preferably general. Formula M _x Mg _1-x Al ₂ O
_{4- (1-m / 2) x} (where M is Zn, Cd, In, Tl, S
at least one element selected from n, Pb, Sb and Bi, X is 0.01 ≦ X ≦ 0.2, and m is M
The transparent conductive oxide is a solid solution having a spinel type crystal structure.

The base material of the transparent conductive oxide of the present invention is aluminum-magnesium-spinel, Mg.
Al ₂ O ₄ . MgAl ₂ O ₄ has an absorption edge wavelength of about 16
It has a band gap of about 7.8 eV corresponding to 0 nm, and there is almost no carrier excitation from the valence band to the conduction band at around room temperature, and the conduction band is empty, so that it has no electrical conductivity. I can't expect. However, from the theoretical calculation results of its electronic structure, it is expected that the mobility in the conduction band is relatively high (Proceedings of the 1992 conference of the Ceramic Society of Japan, p. 283), and carriers are injected without impairing the original transparency. If it is possible, a material having transparency in the ultraviolet region and electrical conductivity should be feasible.

As a general method for injecting carriers in an oxide, a method in which the composition is shifted from the stoichiometric ratio by oxidation-reduction, doping with ions having different valences, or the like is generally used. _The oxidation states of Mg ²⁺ and Al ³⁺ , which are the cations of ₂ O ₄ , are divalent and 3 respectively.
It is not easy to redox it because it is very stable in value. Therefore, although the method of imparting electric conductivity by the method of impurity doping is adopted, in the present invention, the doping must be performed so as to replace Mg instead of Al for the following reason.

MgAl ₂ O ₄ is a substance having a crystal structure known as a spinel structure. For its structure,
For example, “Illustrated Fine Ceramics Crystal Chemistry”
(FS Galassau, translated by Seiji Kato, translated by Keizo Uematsu, published by Agne Technical Center (1984)) and the like, but has the following structure. The chemical formula of a substance having a spinel structure is generally represented by AB ₂ O ₄ (A and B represent two kinds of cations). The unit cell of spinel is a cubic type, and 32 oxygen ions are contained in one unit cell, and the oxygen ions are closest packed in the <111> direction. By the cubic closest packing of oxygen ions,
There are 64 tetrahedral coordination sites and 32 octahedral coordination sites in one unit lattice. Of these, 1/8 of the tetrahedral coordination sites and 1/2 of the octahedral coordination sites are positive. It is occupied by ions, and one unit cell contains eight AB ₂ O ₄ . The spinel structure is further divided into two types. A ion occupies the tetrahedral coordination site, and B ion occupies the octahedral coordination site. A positive spinel, half of the B ion is the tetrahedral coordination site, and the other half is the B ion. And the case where A ions occupy the octahedral coordination site is called reverse spinel. MgAl ₂ O ₄
Is a positive spinel, Mg ²⁺ ions are located at the tetrahedral coordination site, and Al ³⁺ is located at the octahedral coordination site. In the theoretical calculation cited above, it is said that the bottom of the conduction band, that is, the lowest energy part of the conduction band is mainly formed by the s orbital of Al. Therefore, if Al ³⁺ is replaced with another element and electrons serving as carriers are supplied to the conduction band, the presence of impurity ions in the conduction electron path causes scattering of conduction electrons, trapping, etc. Mobility will decrease. In contrast, in the case of replacing the Mg ²⁺ is, different sites and Mg ²⁺ is Al ³⁺ in the crystal lattice, i.e. to positions in tetrahedral coordination sites rather than octahedral coordination sites, this Substitution with other ions does not significantly disturb the structure of the conduction band, and it is expected that the mobility will not be significantly reduced. For this reason, it is considered to be practical if the doping of impurities in a manner of substituting Mg of MgAl ₂ O ₄ is not performed to impart electric conductivity, 10 ⁰ /
The electrical conductivity of Ω · cm or more cannot be realized.

Next, the element M for substituting Mg has an ionic radius close to that of Mg ²⁺ when it becomes a cation, carriers are injected by the substitution, and the band gap of MgAl ₂ O ₄ is not reduced so much. There must be.
It is Zn, Cd, and I that satisfy all of these requirements.
There are only n, Tl, Sn, Pb, Sb and Bi, and at least one selected from these must replace Mg. If other elements are used, the difference in ionic radius from Mg ²⁺ is too large to replace Mg in the first place.If Mg is replaced, the band gap becomes smaller, the absorption edge appears in the visible light region, and the ultraviolet transparency is lost. There are problems such as being told.

The substitution amount X of Mg ²⁺ by ions of these elements is preferably 0.01 or more and 0.2 or less with respect to Mg. If X is less than 0.01, the doping amount is not sufficient, and it is difficult to achieve an electrical conductivity of 10 ⁰ / Ω · cm or more. When X exceeds 0.2, the absorption edge is 240 nm.
At the same time as moving to the longer wavelength side, the effect of absorption due to plasma resonance begins to appear in the visible range, so the transparency in the visible range also drops sharply, so the desired transparency in the ultraviolet range can be realized. It gets harder. A particularly preferable substitution amount X is 0.02 to 0.1.

[0012]

EXAMPLES Next, the present invention will be described in more detail by way of examples.

Examples 1 to 8 and Comparative Examples 1 to 2 Aluminum oxide powder having a purity of 99.99% or more, magnesium carbonate powder, and various oxide powders shown in Table 1 as compounds of metal M substituting Mg (Example 1 ~ 8) as the composition of the spinel solid solution is M _0.05 Mg _0.95 Al ₂ O
_{Blend to 4-0.05 (1-m / 2)} and mix powder in air 10
It was calcined at 00 ° C. for 24 hours. Each of the obtained calcined bodies was roughly pulverized, and then wet pulverized in a ball mill for 24 hours using alcohol as a solvent, dried and pulverized to obtain a raw material powder having an average particle size of 1.5 to 2 μm. This powder was die-molded at a pressure of about 70 MPa into a disk having a diameter of 20 mm and a thickness of about 2 mm, and this was sintered in air at 1400 ° C. for 5 hours. When the sintered body was ground and the generated phase was identified by the X-ray diffraction method, it was confirmed that all were MgAl ₂ O ₄ solid solution. The surface was polished, the absorption spectrum in the ultraviolet to visible region was measured by the diffuse reflection method, and the electrical conductivity at room temperature was measured by the van der Pauw method. The results are shown in Table 1. For comparison, aluminum oxide powder, magnesium carbonate powder, TiO ₂ , F
The same measurement was performed for a system in which eO (Comparative Examples 1 and 2) was added and mixed.

[0014]

[Table 1] From Table 1, the transparent conductive oxides of Examples 1 to 8 have an absorption edge of 2
It was 20 to 235 nm, it was transparent in the ultraviolet region, and the electric conductivity was 1.8 to 3.8 × 10 ¹ / Ω · cm, which revealed that the electric conductivity was excellent. On the other hand, in Comparative Examples 1 and 2, the absorption edge was 360 to 37.
It was 0 nm, and transparency in the ultraviolet region could not be achieved.

Examples 9 to 11 The same aluminum oxide powder, magnesium carbonate powder, and indium oxide powder as in Example 3 were used, and Examples 1 to 8 were used so that the spinel solid solution having the composition shown in Table 2 was obtained by changing the compounding ratio. A sintered body was prepared and evaluated in the same manner as in. The results are shown in Table 2.

[0016]

[Table 2] From Table 2, the transparent conductive oxides of Examples 9 to 11 were also transparent in the ultraviolet region and had excellent electrical conductivity.

[0017]

The transparent conductive oxide of the present invention is transparent to ultraviolet light and has excellent electric conductivity.

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Claims (2)

[Claims] 1. An oxide containing magnesium oxide and aluminum oxide, and Zn, Cd, In, Tl, Sn, P.
A transparent conductive oxide, which is a solid solution having a spinel type crystal structure, containing at least one kind of oxide selected from b, Sb and Bi. 2. The general formula M _x Mg _1-x Al ₂ O
_{4- (1-m / 2) x} (where M is Zn, Cd, In, Tl, S
at least one element selected from n, Pb, Sb and Bi, X is 0.01 ≦ X ≦ 0.2, and m is M
Is the oxidation number of).
The transparent conductive oxide according to.