JPS6041803B2 - compound - Google Patents

Description

[Detailed description of the invention] This invention relates to transparent conductive material systems.

Electrically conductive metal oxide layers, coatings and thin films are well known. These are widely used in display device applications, such as, for example, liquid crystal displays, where some of the electrodes impair the viewing ability of the viewer of the displayed information. Transparency is required to avoid leakage. For an example of this application, see Schindler, US Pat. No. 3,814,501. The most frequently encountered metal oxides used for this purpose are indium, tin oxide, and indium and tin oxide (indium-tin oxide or ITO).
It is. Schlndler describes the use of transparent materials in liquid crystal displays in which the conductive material is indium oxide or tin oxide or a combination of these materials. A pattern of clear, electrically conductive material is disclosed. Other applications for transparent electrical conductors include electrodes for gate structures constructed on semiconductor devices such as charge coupled imagers.

It is practiced in both imager and display applications to form conductive patterns as separate, discontinuous entities.

Typically, the pattern is formed by forming the metal oxide material and then using photolithographic techniques to conform the metal oxide to the desired conductor pattern, although various other approaches, such as printing, are also used. It was formed by As an example for printing, LaLlr'
See West German Publication No. 24118η of Ie. For example, where the ITO conductive pattern is formed as a separate entity on the imager or display device, at least two different types of paths are created for light incident on the device.

In one type of path, the light beam passes through a thickness of 1T0 once or twice depending on whether it is reflected or not. In other types of paths, which do not pass through a layer of ITO, the light typically travels a longer distance through an air-filled space. The difference between the refractive indices of air and ITO and the number of boundaries that the light beam has traversed based on the path traveled results in a distortion of the detected or reflected image. The present invention greatly reduces these differences and reduces the distortion caused by them. U.S. Patent No. 2932 to Barrett et al.
No. 590 discloses the controlled formation and subsequent thermal oxidation of metallic indium and tin to create thin, transparent, electrically conductive coatings. However, the Barrett et al. patent does not disclose the formation of patterns of electrical conductors included in the insulating film disclosed herein. The invention provides a pattern of transparent electrically conductive material formed on a substrate, semiconductor device, etc., wherein the pattern of electrically conductive material is the same as the electrically conductive material. otherwise continuous layers of transparent insulating material having a substantially index of refraction, said layers having substantially the same thickness throughout.

Similar optical distances are given for light passing through a conductive material and for light passing through an insulating material. Because 2
This is because the length and propagation time differences for light rays passing through different types of materials are reduced. In a preferred embodiment, the insulator material is indium oxide, more particularly indium sesquioxide (In2O3).

The insulating indium oxide is preferably relatively impurity-free and substantially stoichiometric in order to provide a high ratio of the resistivity of the insulator material to the resistivity of the conductor material. Impurities and deficiencies in oxygen ions provide free charge carriers and are therefore undesirable. Regions of the layer of insulating material are modified to make them electrically conductive in a pattern that matches the desired conductor pattern.

In a preferred embodiment, tin is used as a dopant to modify the insulator material. Both tin and indium are first formed in elementary or metallic form on a substrate or device.

The tin is conformed to the desired pattern for the electrical conductors. The tin is then diffused or alloyed with indium and the material system is oxidized. The basic materials are obtained in much higher purity than, for example, in metal oxides.

By first working with the metals tin and indium, the purity of the materials used in implementing the invention can be matched with the requirements of semiconductor technology, where even small amounts of contamination degrade the parameters of the device. It is known. As another advantage of the present invention, it will become apparent that smaller electrical conductor line widths can be realized in the present invention than could be conveniently realized in the prior art.

This is because the conductor pattern is formed of a thin layer of modified material, such as the tin mentioned above, which is much thinner than the final formed conductor. Thin layers can be etched to smaller line widths since the time required for etching is reduced and the cutout is greatly reduced. Referring first to FIG. 1A, a base 10 is shown upon which a layer 12 of modified material is formed.

The base 10 may be, for example, a glass substrate used as a cover plate for liquid crystal displays where transparent electrodes are desired. As another example, base 1
0 may be a semiconductor integrated circuit device such as a CCD imager where a transparent conductor is used in the gate structure. In a preferred embodiment, the formed modification material is metallic tin. High purity tin may be preferred for use where the base is a semiconductor device, such as those mentioned above, and where the properties of the semiconductor device may be adversely affected by impurities in the tin. do not have. Metallic tin with purity as high as 99.999% is readily obtained and used in the practice of this invention.

In a preferred embodiment, the tin metal is preferably formed using standard sputtering techniques well known to those skilled in the art. A suitable power level for tin d-sputtering is about 150 watts. A suitable atmospheric pressure for the argon contained in the sputtering chamber is 8±2 microns. However, in lieu of sputtering, any of a variety of other standard techniques for metal formation may be used, if desired.
It may also be used for forming the tin layer 12.

For example, these other techniques include plating, plasma coating, vacuum phase deposition, pyrolytic coating, thermal evaporation, electron beam evaporation. The preferred thickness of the completed layer of transparent material formed in accordance with this invention is about 1000 Angstroms.

This thickness provides a suitably high electrical conductivity for the conductive regions of the completed layer and a suitably high resistivity for the insulating regions of the completed layer in electronic applications such as displays or imaging devices, along with high light transmission. Indicates a compromise point. 100
For a finished layer thickness of 0 angstroms, the preferred thickness of tin formed layer 12 is 75±25 angstroms.

Thus, in a preferred embodiment layer 12 of modified material
is found to have a thickness of 10% or less of the thickness of the finished layer. After a layer 12 of modified material is formed over the base 10 as shown in FIG. 1A, the layer 12 is patterned or looped to accommodate the desired pattern for electrical conductors. .

The result is shown in FIG. 1B, where individual elements 14 of modified material are shown formed on the base 10 and positioned at the desired locations for the conductors. A plurality of individual elements 14 are shown in FIG. 1B for illustrative purposes only. It will be appreciated by those skilled in the art that the present invention is equally applicable where the desired conductor pattern has only one unitary conductor structure. 2
When the modified material is tin, the individual elements 14 are preferably adapted to the desired conductor pattern by standard photolithographic techniques well known to those skilled in the art.

For example, a suitable photoresist for this purpose is Eastman Kodak, Rottsiesta, New York.
Manufactured and sold under the registered trademark Kodak #809 by Co., Ltd. The photoresist is preferably baked at a relatively low temperature, eg, no higher than about 90° C., to prevent diffusion of tin into the photoresist. A suitable etchant for tin is a mixture of 12.5y ammonium fluoroborate, 2.25 liters concentrated nitric acid, 0.2 liters fluoroboric acid, and 150 liters deionized water. Using this etchant, element 14 can be formed in tin in 120 seconds. It is well known that patterns delineated by photolithographic techniques are limited in their definition due to the cutouts created by the etching material.

However, in the method of forming the desired electrical conductor pattern described herein, the pattern is formed of the completed layer of transparent material that the pattern for electrical conductors will ultimately include, as described below. The layer 12 is formed to have a thickness of 10% or less. and,
Conductor patterns (with finer definition than can be made if required so that the pattern is formed in a layer with a greater thickness of the finished layer of transparent material)
(smaller line widths and smaller interline spacings) can be photolithographically created in accordance with the practice of this invention. The former case represents the prior art case in which a layer of conductive metal oxide is etched to form the desired pattern of electrical conductors. ing.
Although photolithographic techniques are preferred for forming elements 14 into the desired conductive pattern, other approaches may be used consistent with the present invention.

For example, modified materials are mass! 1B, thus immediately forming element 14 of FIG. 1B. This approach may be more desirable if the element 14 is to be established on a base with sharp corners or steps required to fit. As yet another example, the modified material may be placed in ink that is screen printed onto the base in the desired pattern. Using either of these two techniques to form element 14 does not require the formation of an uncirculated layer of modified material such as layer 12 of FIG. The result is a reduction in the number of steps required to form the layer. As shown in FIG. 1C, after the element 14 of modified material is formed, a layer 16 of material 16 is formed.
This layer 16 of material is one that can be oxidized to a transparent insulating material when relatively pure and can be oxidized to a transparent conductive material when combined with a suitable modifying material.

At least 99. Metallic indium having a purity of 100% is the preferred oxidizable material for use with tin in implementing this invention. The greater purity for indium used to form the layer 12 of modified material in FIG. It is preferred for use in cases where Metallic indium having high purity, such as 99.99 percent heel weight, is readily obtained and used in the practice of this invention.

There are other reasons for using relatively high purity indium.

The oxidized indium is to serve as an insulator for the completed layer of transparent material suitable for this invention. Indium impurities tend to give up free charge carriers and thereby reduce the electrical resistivity of indium oxide.
The extent to which the reduced resistivity of insulating indium oxide due to impurities is a problem depends, in part, on the application in which the invention is practiced. If the finished material system is relatively large, and the desired pattern for its conductive areas gives relatively large conductors spaced relatively far apart, then satisfactory performance will depend on the resistivity of the insulating material and the conductive material. can be obtained with a relatively low ratio of resistivity to . On the other hand,
For applications involving microcircuits and precision small conductor definition, it is preferred that the ratio to the resistivity of the insulating material be as high as practicable. In the latter case, the higher the purity of the metal indium used, the higher the resistivity ratio tends to be. A ratio of the resistivity of the insulating material to the resistivity of the conductive material as high as 1σ has been obtained in the practice of this invention using indium having a purity of about 99.99 weight percent.

In a preferred embodiment, indium metal is preferably formed using standard sputtering techniques well known to those skilled in the art.

A suitable power level for indium gospattering is approximately 175±25 watts. A suitable atmospheric pressure for the argon contained in the sputtering chamber is 8±2 microns. However, in lieu of sputtering, any of a variety of other standard techniques for metal formation may be used to form the layer of indium 16, if desired. As discussed above with respect to the discussion of techniques for forming tin, these other techniques include, for example, plating, plasma coating, vacuum phase deposition, pyrolytic coating, thermal evaporation, and electron beam evaporation. The finished amount of transparent material has a thickness of about 1000 angstroms and the tin layer 12 has a thickness of 75±, as shown in FIG. 1A.
For the preferred embodiment, which is 25 angstroms thick, the preferred thickness for the indium layer 16 is about 700 angstroms.

The layer of indium 16 must cover the entire area of the base 10 where it is desired to have a coating of transparent material.

Due to the formation of the layer 16 of indium, since there are portions of the base 10 covered where no coating of transparent material is desired, photolithographic formation techniques are used to remove the indium from these portions. Good too. Access to the top pads of the underlying semiconductor device may be required or in such circumstances to be made available for connection to interface circuitry not provided by the procedures of this invention. Dew. In this case, the layer of indium 16 is preferably formed using the same photoresist and the same etchant described above with respect to the discussion of forming element 14 shown in FIG. 1B. This indium layer 16 is etched using the etching material described above.
Approximately 2 minutes are required to etch the . After the element 14 of modified material is covered with a coating of oxidizable material 16 as shown in FIG. 1C, the modified material is diffused into the oxidizable material. This may be accomplished in a furnace with an inert fog surround or a reducing fog surround. When the material is the preferred dopant, i.e., tin, and the preferred oxidizable material, i.e., indium, the diffusion or alloying is preferably carried out by heating in a reducing fog atmosphere of about 85% nitrogen and 15% hydrogen. will be achieved. 1st
Figure D shows the result of diffusing indium hetin in region 18 through the depth of layer 20.

Regions 18 of layer 20 are suitable for the desired pattern for electrical conductors, while the remaining portions of layer 20 are intended to be occupied by insulating material. The definition of the conductor pattern that may be required for the region 18 of alloyed material to fit is limited by the need to maintain some minimum spacing for insulation between the conductors.

The resulting spacing between the regions 18 of alloyed material is the first
Element 1 of the modified material shown in Figure B and Figure 1C
4 and the manner in which the diffusion of the modified material into the oxidizable material was carried out. As shown in Figures 1B and 1C, the spacing between adjacent edges of elements 14 of modified material is preferably at least 10@ of the thickness at which layer 16 of oxidizable material is formed. For example, for layer 16 having a thickness of 700 Angstroms, the preferred spacing between elements 14 is:
Preferably it is at least 7000 angstroms, or about 1 micron. This lower spacing limit corresponds to the smallest line-to-line spacing that can reasonably be obtained for a 700 angstrom layer by photolithographic techniques. The extent to which the modified material diffuses into the oxidizable material is determined in part by the parameters of the heating operation used to generate the diffusion.

In a preferred embodiment, alloying of tin and indium is accomplished at a temperature of 200±20° C. at a temperature of 30±1. Heating for a very long time or at a very high temperature, or both, will eventually result in conductors with little spacing between them, or as a result of the entire layer of Figure 1D. Diffusion must be limited so as to result in a uniformly distributed modified material throughout. In either case, the desired conductor pattern will be effectively removed. Heating at a lower temperature or for a shorter time, or both, adequately prevents good mixing of indium and tin in region 18 of layer 20. 1st D
It will be apparent to those skilled in the art that the procedures described above for making the material system illustrated in the figures are preferred but not limiting.

For example, a layer of indium 16 may first be formed directly on the base 10 before being formed on the tin layer 12. After the indium layer 16 is formed, a tin layer 12 is deposited on top of the indium layer 16 using the well-known lift-off (1ift-0ff) technique and using a photoresist mask to protect the indium from the etchant. It may also be formed using photolithography technology. Once the tin is diffused into the indium, the result is as shown in Figure 1D. The structure illustrated in FIG. 1D is converted to that shown in FIG. 1E by heating layer 20 in oxygen or air to oxidize layer 20. The unmodified oxidizable material is converted to the transparent insulating material of the completed layer 22 of FIG. 1E. The modified material in region 18 of FIG. 1D is converted to a transparent electrically conductive material in region 24 of FIG. 1E. When the oxidizable material is the preferred metal indium, the formed transparent insulating material is indium oxide. Complete oxidation to make stoichiometric indium sesquioxide appears to be preferred due to the higher resistivity that can be obtained. When the modified material is tin, the indium-tin alloy is the well-known transparent electrical conductor indium-tin oxide (ITO).
in which the tin serves as a dopant for the otherwise insulating indium oxide. It is believed that the stoichiometry of the indium sesquioxide is ensured by heating at a sufficiently high temperature for a sufficient period of time.

It seems that satisfactory results can be obtained by heating 30 to 12 degrees Celsius in air at 480±20°C.

The transparent layer 22 of metal oxide material grows in thickness as it is oxidized.

The oxide layer 22 of FIG. 1E will be about 1000 angstroms thick, with the metal layer initially being about 700-800 angstroms thick. The metal to metal oxide film is grown by a factor of about 1.35 to about 1.45. After processing, IT is about 90 mole percent indium oxide and 10 mole percent tin oxide.
The objective is to control the thickness of indium and tin in order to achieve a composition of O.

This is the commonly accepted composition for most conductive 1T0. Typical measurements obtained for the refractive index of indium oxide ranged from 1.7 to 1.8.

Measured values for the refractive index of ITO ranged from 1.9 to 2.0. Measured values for the resistivity of indium oxide range from 1000 Ω-α to 10000 Ω-d, while the resistivity at n°C made by this invention is 0.01 Ω.
It ranged from 1α to 0.02Ω-G. Although the invention has been described in terms of preferred embodiments, the terms used are words of description rather than limitation, and changes within the scope of the appended claims do not reflect the true scope of the invention in its broader perspective. It will be understood that this can be done without departing from the spirit.

For example, tin, when relatively pure, may be used as an oxidizable material to form a transparent insulator material. Antimony may be used as a dopant to modify the tin oxide so that it is a conductive material. As another example, cadmium as a modifying material may be diffused into tin, which acts as an oxidizable material. Oxidation of cadmium-tin alloys creates cadmium stannate compounds (Cd2SrO4), which are known to be highly conductive. Furthermore, those skilled in the art will appreciate that the present invention is not limited to a single layer of transparent material containing regions of conductive material. A plurality of such layers may be formed in a stack if desired. It may be desirable to separate layers containing conductive material by other layers of only insulating material.

[Brief explanation of drawings]

Figures 1A-1E schematically illustrate, in cross-sectional views, steps in forming a conductor in accordance with a preferred embodiment of the invention. In the figure, 10 is a base, 12 is a layer of modified material, 14
is an element, 16 is a layer, 18 is a region of modified material, 20
indicates a layer, and 22 indicates a transparent layer.

Claims (1)

Claims: 1. An integrated circuit device comprising: 1 an integrated circuit device of semiconductor material; and a substantially continuous layer of transparent material formed on the integrated circuit device, wherein the layer of transparent material includes a first layer of insulating material.
and a second region of conductive material, said second region diffusing a modified material into a portion of a first metal layer formed on said integrated circuit device, thereby said a first metal is alloyed with the modified material;
The insulating material is an oxide of the first metal formed by oxidation of unalloyed portions of the layer of first metal, and the conductive material is an alloy of the layer of first metal. wherein the first metal of the layer has a purity of at least 99.9% by weight and the insulating material has a resistivity of at least 1000 ohm-cm. A compound that is a substantially pure and stoichiometric oxide of one metal. 2. The composite of claim 1, wherein the ratio of the resistivity of the insulating material to the resistivity of the conductive material is at least 50,000. 3. The composite according to claim 2, wherein the first metal is indium and the modified material is tin. 4. The composite of claim 2, wherein the first metal is tin and the modified material is antimony. 5. Claim 2, wherein the conductive material is a compound of the first metal and the modified material, and the compound is formed by oxidation of an alloy of the first metal with the modified material. Compounds described in Section. 6. The composite of claim 5, wherein the first metal is tin and the modified material is cadmium. 7. A method of forming a desired pattern of transparent electrical conductors on a base, the method comprising: selecting a first material oxidizable to form a transparent insulating material; selecting a modified material capable of bonding with one material, said second material being oxidizable to form a transparent electrical conductor material, in a pattern matching said desired pattern of transparent electrical conductor; forming a layer of the modified material on the base, forming a layer of the first material adjacent to the layer of modified material on the base, and forming the modified material to form the second material; into the first material to form a substantially continuous layer of oxidized material having transparent conductor regions and transparent insulator regions conforming to the desired pattern. The method further comprising oxidizing the second material. 8. The method of claim 7, wherein the modified material and the first material are metals. 9. The method of claim 8, wherein the modified material is tin and the first material is indium. 10. The method of claim 8, wherein the modified material is selected from the group consisting of antimony and cadmium, and the first material is tin.