Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Including integrally formed optical element
Reexamination Certificate
1998-12-10
2001-07-17
Le, Vu A. (Department: 2824)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Including integrally formed optical element
C438S166000, C438S463000, C438S487000
Reexamination Certificate
active
06261856
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of producing thin film patterns on a glass substrate.
Photolithography is a well-known technique for producing patterns in thin films formed on substrates. This technique is convenient and advantageous, having regard to the desirability of removing portions of the thin film to be processed without causing damage to the underlying surface. However, a somewhat large number of steps is necessary for completing patterning procedure in accordance with this method. Namely, after forming the thin film to be treated on a substrate, a photoresist film is formed and patterned; the thin film is subjected to an etchant through the patterned photoresist film as a mask and then the photoresist film is removed.
Laser scribing techniques are well known in the art as a low cost patterning method capable of carrying out the scribing at a high speed. YAG laser (IR light, 1.06 microns) is a representative laser which has been generally used for this purpose. Since the optical energy of this laser is only 1.23 eV, however, tin oxide, indium oxide (or ITO), ZnO or so forth having optical energy gaps of about 3 to 4 eV are not effectively processed by the YAG laser. While transparent conductive oxide (CTO) films are generally made of this class.
This laser scribing method has another shortcoming. When portions of a transparent conductive film formed over a soda-lime glass substrate with an ion blocking film therebetween is removed in order to produce electrode patterns thereon, the ion blocking film and the glass substrate are partially eliminated together, and therefore the surface of the glass substrate is exposed. Eventually, in case of liquid crystal device manufacture, the liquid crystal material contained in the device is contaminated by sodium ions introduced from the glass substrate. Furthermore, the scribing makes the upper surface thereof uneven as well as residue remaining on the edges of the removal portions, the residue is piled as high as 0.5 to 1 micron. The unevenness is undesirable not only in regard to the application to liquid crystal devices but also to the manufacture of general electric devices including laminating process. The uneven surface might may be the cause of electrical shorting between different levels of the laminate and disconnection of the electrical patterns superimposed thereon.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a thin film pattern formed on a glass substrate in order that little contaminant is leaked from the substrate.
In accordance with a preferred embodiment, a glass substrate is covered with an alkali ion blocking film made of silicon oxide by sputtering, followed by forming an ITO (indium tin oxide) film. The ITO film is then treated by laser scribing in order to produce a pattern of the ITO film. In this connection, there are several key points for improving the configuration of the pattern as follow.
The heat transmission is an obstacle to the formation of clear edges of grooves. While laser irradiated portions are heated to its boiling point, the adjacent portions are necessarily heated, reflow and form swollen edges adjacent to the grooves. In order to minimize the formation of the swollen portions which cause disconnection of an overlying film coated thereon, it is necessary to elevate the temperature of the portions to be removed to the boiling point in advance of substantially heating the adjacent portions of the ITO film. This is accomplished by making use of a laser beam having a short wavelength and a short pulse width. The wavelength is selected to be not longer than 400 nm (3.1 eV). The pulse length is not longer than 50 nanoseconds. YAG lasers, which have been broadly used in the field, can not emit such a power concentrated laser pulse. The applicant found that eximer lasers could be used for this purpose. In this regards, the damage of the ion blocking film during laser scribing largely depends on the thermal conductivity thereof. As the thermal conductivity is low, the elevation speed of the ion blocking film becomes low and suffers little influence of heat from the overlying ITO film.
The melting points of the ion blocking film and the ITO film are very important. If the ion blocking film is easily molten, there is a chance that openings is formed in the blocking film so that the glass surface is exposed through the grooves. In this regards, the choice of ITO and non-doped SiO
2
is desirable since the melting points of the former and the latter are 890° C. and 1700° C. respectively. The melting point of the SiO
2
film is in turn substantially higher than that of the glass substrate. The energy gaps of them are also suitable for this purpose. SiO has an energy gap of 7 to 8 eV and therefore absorbs little portion of the eximer laser beam of a short wavelength, while ITO has an energy gap of 3 eV.
The method in which only the ITO film is selectively removed by the laser scribing is advantageous having regards to the desirability of smooth and level surface of patterns. Even in accordance with the present invention, residue remains after removal of the ITO film. The residue, however, can be easily eliminated by HC
1
etch since it is composed of InO
x
and SnO
x
of porous structure. Unlike this, in accordance with prior art methods utilizing YAG lasers in which the SiO
2
film is eventually partially removed, the residue is formed somewhat integrally with the remaining portions of the ITO and composed of an indium or tin alloy which is mixed with silicon contained in the underlying ion blocking film. The residue can not be eliminated by HCI etch and requires HF etch. Even if HF etch is used, the residue can not be selectively removed independent of the remaining portion of ITO film, which tends to be partially removed together with the overlying ITO film by HF etch.
The ion blocking film is not limited to SiO
2
film formed by sputtering but may be made from other materials as long as the above listed conditions are satisfied. For example, the blocking film can be formed by CVD of SiO
2
or Si
3
N
4
films, sputtering of a target of heat resistant glass, such as quartz. Anyway, the formation should be carried out under the softing temperature of the glass substrate.
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Shinohara Hisato
Sugawara Akira
Le Vu A.
Lebentritt Michael S.
Nixon & Peabody LLP
Robinson Eric J.
Semiconductor Energy Laboratory Co,. Ltd.
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