Chemistry of inorganic compounds – Carbon or compound thereof – Oxygen containing
Reexamination Certificate
1999-09-17
2001-09-11
Hendrickson, Stuart L. (Department: 1754)
Chemistry of inorganic compounds
Carbon or compound thereof
Oxygen containing
Reexamination Certificate
active
06287532
ABSTRACT:
This invention relates to hydrotalcite compounds of low uranium (U) content and processes for their preparation. More particularly, the invention concerns hydrotalcite compounds which are useful as ion scavenger or various stabilizers for epoxy resins used for sealing large-capacity, high-integration memory semiconductor devices, without impairing reliability of the devices against soft errors.
Hydrotalcites having concurrently the various properties required for an inorganic powder additive for resins, such as good dispersibility and processability and no deteriorating effect on the products' appearance were disclosed in Japanese Patent KOKAI No. 80447/80A. The hydrotalcites shown in this publication are actually used in many synthetic resins as heat-stabilizers of PVC, stabilizers for polyolefins and the like.
Whereas, semiconductor devices such as transistor, IC, LSI and the like need to be sealed, for protection and insulation from contact, contamination and moisture from outside. Presently, resin sealing methods are advantageous from the standpoints of productivity and economy, and are widely practiced. In particular, epoxy resins are used for sealing semiconductor devices because of their favorable electrical characteristics, moisture resistance and adherability. Hydrotalcite compounds are used as ion scavenger or the like in such epoxy resin sealing material for semiconductor devices to perform the roles and functions of prevention of corrosion and improvement in moisture resistance of wiring.
With the still larger capacities and higher integration given to recent semiconductor memories, occurrence of soft errors caused by alpha ray emitted upon decay in radioactive substances such as uranium, thorium, etc. which are contained in the sealing resin compositions begins to create problems. For example, the content of uranium and thorium is required not to exceed 1 ppb (ng/g) for 4M bit memories, and not to exceed 0.1 ppb (ng/g) for 4-16M bit memories, in order to secure reliability against soft errors. In consequence, hydrotalcite compounds, which are blended in the epoxy resin sealant in such a small (minor) amount as not more than a few percent to said resin, are also required to contain not more than micro-level of radioactive substances.
An object of the present invention is to provide hydrotalcite compounds which are useful as ion scavengers for epoxy resin compositions serving as sealant for memory semiconductor devices in which capacity increase and raise in integration level are highly advanced, and which possess high reliability against soft errors. This object can be fulfilled by provision of high purity hydrotalcite compounds whose radioactive substance content, i.e., that of uranium and thorium, is exceeding low. Thus, the theme of the present invention is to provide hydrotalcite compounds which possess the properties required for additives to resin and have extremely low uranium content, and processes for their preparation.
The hydrotalcite compounds of the present invention are characterized in that they have the composition expressed by the formula (1) below:
M
1−X
2+
Al
X
(OH)
2
A
2−
X/2
2
·mH
2
O (1)
[in which
M
2+
is at least one of Mg
2+
and Zn
2+
,
x is a positive number of 0.2≦x≦0.5,
A is at least one of CO
3
2−
and SO
4
2−
, and
m is a number of 0 to 2],
have a uranium (U) content not more than 10 ppb, an average secondary particle size not more than about 3 &mgr;m and a BET specific surface area of not more than 30 m
2
/g.
The hydrotalcite compounds of the present invention are preferably those that are surface-treated with at least one surface-treating agent selected from the group consisting of higher fatty acid, anionic surfactant, silane-containing coupling agent, titanate-containing coupling agent, aluminium-containing coupling agent and phosphoric acid ester of higher alcohol.
Of those, particularly the hydrotalcite compounds which are surface-treated with not more than 3% by weight thereof of a silane-containing coupling agent are preferred.
The hydrotalcite compounds of the present invention are conveniently used as additives and fillers for synthetic resin.
Of the hydrotalcite compounds of above formula (1) of the present invention, particularly those whose A
2−
is CO
3
2−
are preferred. Whereas, those in which a part of CO
3
2−
is replaced with the other anion, eg., those containing not more than ⅕ mol of Al (not more than 40 mol % of —CO
3
2−
), in particular, not more than {fraction (1/10)} mol of Al (not more than 20 mol % of —CO
3
2−
), of SO
4
2−
are also preferred.
The hydrotalcite compounds of low uranium content according to the invention can be prepared through the steps of
(1) coprecipitation reaction of aqueous solution of a water-soluble aluminium compound with aqueous solution of a water-soluble magnesium compound and/or a water-soluble zinc compound under alkaline condition, at a composition of the starting materials satisfying the molar ratio in the range defined by the formula (2) below:
0.15
≦
at
least
one
of
CO
3
2
-
and
SO
4
2
-
M
2
+
+
Al
3
+
≦
1.25
(
2
)
[in which M
2+
stands for at least one of Mg
2+
and Zn
2+
], at temperatures ranging 10-50° C. and under stirring [hereafter may be referred to as step (1)], and
(2) hydrothermal reaction of the resultant coprecipitation reaction product in the form of the suspension as formed in the step (1) reaction, at temperatures in the range of 90-200° C. for at least 0.5 hour [hereafter may be referred to as step (2)], in which occasion
(3) adjusting the reaction conditions so that pH of the reaction suspension after the hydrothermal reaction falls within the range of 7.0 to 13.5.
In the production process according to the invention, it is particularly preferred to carry out the coprecipitation reaction (1) of aqueous solution of a water-soluble aluminium compound with aqueous solution of a water-soluble magnesium compound and/or water-soluble zinc compound under alkaline condition at the composition of the starting materials satisfying the molar ratio in the range defined by the formula (2-a) below:
0.15
≦
CO
3
2
-
M
2
+
+
Al
3
+
≦
1.25
(2-a)
[in which M
2+
stands for at least one of Mg
2+
and Zn
2+
],
at temperatures ranging 10-50° C. and under agitation.
In the present invention, it is also preferred to carry out the hydrothermal reaction of the coprecipitation reaction product which is obtained in said step (1), leaving said product in the state of suspension in the mother liquor of the reaction, at temperatures of 90-200 C. for at least 0.5 hour, preferably for 0.5-24 hours, while so adjusting the reaction conditions that pH of the reaction suspension after the hydrothermal reaction falls within the range of 7.0-13.5 [the step (2)], and then
(4) to suspend the hydrothermal reaction product which has been washed with water, in an aqueous solution of ammonium carbonate and/or alkali (hydrogen)carbonate and to stir the suspension at temperatures of 10-100° C. for 1-24 hours (an eluting treatment).
Preferred concentration of ammonium carbonate and/or an alkali carbonate or alkali hydrogencarbonate in the aqueous solution used in (4) above is from 0.1 to 3.0 mols/liter.
While the pH value of the suspension after the hydrothermal reaction of step (2) in the production process of the present invention is an important condition which controls the elimination ratio of uranium, basically it may be the one sufficient for UO
2
2+
ions to take a form of such complex ions as UO
2
(OH)
3
, UO
2
(CO
3
)
2
2−
, UO
2
(CO
3
)
3
4−
and the like in the aqueous solution, i.e., 7.0 or higher. At exceedingly high pH region, surface charge of the hydrotalcite compounds reverses to negative level and ele
Okada Akira
Shimizu Koji
Yamashita Satoko
Hendrickson Stuart L.
Kyowa Chemical Industry Co Ltd
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