Compositions: ceramic – Ceramic compositions – Glass compositions – compositions containing glass other than...
Utility Patent
1999-03-16
2001-01-02
Group, Karl (Department: 1755)
Compositions: ceramic
Ceramic compositions
Glass compositions, compositions containing glass other than...
C501S069000, C501S070000, C428S428000
Utility Patent
active
06169047
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to alkali-free glasses which are suitable as substrate glasses for various displays or photomasks and which are essentially free from alkali metal oxides and can be formed by float process, and flat panel displays employing them.
2. Discussion of Background
Heretofore, the following properties have been required for substrate glasses for various displays, particularly for the ones intended to form a thin film of a metal or oxide on their surface.
(1) They are essentially free from alkali metal oxides. If an alkali metal oxide is contained, the alkali metal ion tends to diffuse in the thin film, whereby the film properties will deteriorate.
(2) They have high strain points, so that when they are exposed to a high temperature during the process for forming a thin film, deformation of the glass and shrinkage due to stabilization of the glass structure are suppressed to the minimum levels.
(3) They have adequate chemical durability against various reagents to be used for forming semiconductors. Particularly, they have durability against hydrofluoric acid used for etching SiO
x
or SiN
x
or against a buffered hydrofluoric acid (BHF) containing ammonium fluoride and hydrofluoric acid as the main components.
(4) They have no internal or surface defects (such as bubbles, striae, inclusions, pits or scratch marks).
Heretofore, Corning code 7059 glass is widely employed as a substrate glass for various displays or photomasks. However, this glass has the following deficiencies for displays.
(1) The strain point is as low as 593° C., and preliminary heat treatment to reduce the shrinkage of glass has to be carried out prior to a process for preparing the displays.
(2) The amount of elution into hydrochloric acid used for etching a metal electrode or a transparent conductive film (such as ITO) is substantial, and the eluted substance tends to recrystallize during the process for preparing displays, whereby it becomes difficult to prepare the displays.
In addition to the above requirements, the following two points have been additionally required along with the trend for large sized displays in recent years.
(1) The above-mentioned code 7059 glass has a density of 2.76 g/cc, and a glass having a smaller density is required to meet a requirement for light weight.
(2) The above code 7059 glass has a coefficient of thermal expansion of 46×10
−7
/° C., and a glass having a smaller coefficient of thermal expansion is required to increase the rate of temperature increase for the preparation of displays and thus to increase the throughput.
With respect to B
2
O
3
, JP-A-1-160844 discloses a glass product containing from 20 to 23 cation % of B
2
O
3
, but the amount of B
2
O
3
is so large that the strain point is not sufficiently high. JP-A-61-281041 discloses a product containing from 0.1 to 4 wt % of B
2
O
3
, JP-A-4-175242 discloses a product containing from 0.1 to 5 mol % of B
2
O
3
, and JP-A-4-325435 discloses a product containing from 0 to 3 wt % of B
2
O
3
. However, in each of them, the amount of B
2
O
3
is so small that the durability against BHF is not sufficient.
With respect to BaO, JP-A-4-325434 discloses a glass product containing from 10 to 20 wt % of BaO, JP-A-63-74935 discloses a product containing from 10 to 22 wt % of BaO, and JP-A-59-169953 discloses a product containing from 15 to 40 wt % of BaO. However, in each of them, BaO is so large that the coefficient of thermal expansion is large, and the density is high.
With respect to MgO, JP-A-61-132536 discloses a glass product containing from 6.5 to 12 wt % of MgO, JP-A-59-116147 discloses a product containing from 5 to 15 wt % of MgO, JP-A-60-71540 discloses a product containing from 5 to 17 wt % of MgO, and JP-A-60-42246 discloses a product containing from 10 to 25 mol % of MgO. However, such glass containing a large amount of MgO tends to undergo phase separation.
With respect to CaO, JP-A-63-176332 discloses a glass product containing from 11 to 25 wt % of CaO, JP-A-58-32038 discloses a product containing from 7 to 20 mol % of CaO, JP-A-2-133334 discloses a product containing from 8 to 15 wt % of CaO, JP-A-3-174336 discloses a product containing from 7 to 12 wt % of CaO, JP-A-6-40739 discloses a product containing from 10 to 12 wt % of CaO, and JP-A-5-201744 discloses a product containing at least 18 cation % of CaO. However, if CaO is contained in a large amount, the coefficient of thermal expansion tends to be too large.
With respect to Al
2
O
3
, JP-A-61-236631 discloses a glass product containing from 22.5 to 35 wt % of Al
2
O
3
, but the amount of Al
2
O
3
is so large that elution to a chemical reagent such as hydrochloric acid is substantial.
With respect to P
2
O
5
, JP-A-61-261232 and JP-A-63-11543 disclose those containing P
2
O
5
. However, they are not desirable, since they tend to deteriorate the semiconductor properties of thin films.
Further, glass having a strain point of at least 640° C. and a relatively small coefficient of thermal expansion is disclosed in JP-A-4-160030 or JP-A-6-263473. However, such glass contains a substantial amount of BaO as an essential element, whereby it is difficult to satisfy the requirements for low density and small thermal expansion coefficient simultaneously. Accordingly, it does not fully satisfy the demand of the age for large sized panels.
It is an object of the present invention to solve the above drawbacks and to provide alkali-free glasses which have strain points of at least 640° C. and small coefficients of thermal expansion and small densities and are free from forming of turbidity by BHF and which are excellent in the durability against reagents such as hydrochloric acid, are easy to melt and shape and can be formed by float process.
SUMMARY OF THE INVENTION
The present invention provides an alkali-free glass consisting essentially of, by wt %, from 58.4 to 66.0% of SiO
2
, from 15.3 to 22.0% of Al
2
O
3
, from 5.0 to 12.0% of B
2
O
3
, from 0 to 8.0% of MgO, from 0 to 9.0% of CaO, from 3.0 to 12.5% of SrO, from 0 to less than 2.0% of BaO, and from 9.0 to 18.0% of MgO+CaO+SrO+BaO and having a strain point of at least 640° C.
Also, the present invention provides an alkali-free glass consisting essentially of, by wt %, from 58.4 to 66.0% of SiO
2
, from 15.3 to 22.0% of Al
2
O
3
, from 5.0 to 12.0% of B
2
O
3
, from 0 to 6.5% of MgO, from 0 to 7.0% of CaO, from 4.0 to 12.5% of SrO, from 0 to less than 2.0% of BaO, and from 9.0 to 18.0% of MgO+CaO+SrO+BaO and having a strain point of at least 640° C.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The alkali-free glasses of the present invention are essentially free from alkali metal oxides (such as Na
2
O or K
2
O). Specifically, the total amount of alkali metal oxides is preferably not higher than 0.5 wt %, more preferably not higher than 0.2 wt %.
Now, the reasons for defining the compositional ranges of the respective components as mentioned above, will be described.
If the content of SiO
2
is too small, it tends to be difficult to increase the strain point sufficiently, and the chemical durability tends to deteriorate and the coefficient of thermal expansion tends to increase. Preferably, it is at least 59.0 wt %. If it is too large, the melting property tends to be poor, and the liquidus temperature tends to increase. Preferably, it is at most 65.0 wt %, more preferably at most 62.7 wt %.
Al
2
O
3
suppresses phase separation of glass, reduces the coefficient of thermal expansion and increases the strain point. If its content is too small, no adequate effects can be obtained. Preferably, it is at least 15.3 wt %. If it is too large, the melting property of glass tends to be poor. Preferably, it is at most 21.1 wt %.
B
2
O
3
serves to prevent formation of turbidity by BHF and is effective to lower the coefficient of thermal expansion and the density without increasing the viscosity at a high temperature. If its content is too small, the BHF property tends to deteriorate. Preferably,
Nakao Yasumasa
Nishizawa Manabu
Asahi Glass Company Ltd.
Group Karl
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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