Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2001-08-20
2004-11-30
Harlan, Robert D. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S229000, C526S250000, C526S253000, C526S254000
Reexamination Certificate
active
06825304
ABSTRACT:
The present invention relates to a dielectric (per)fluorinated material for the insulation of high frequency integrated circuits, under the form of films having a very good adhesion to the substratum and a thickness lower than 200 nm.
Specifically the invention relates to a dielectric perfluorinated material, for the insulation of high frequency integrated circuits, under the form of a homogeneous film, substantially without defects, obtained from a PTFE nanoemulsion having a particle diameter in the range 5-100 nm; the films of the invention are characterized by a very good adhesion to the substratum, a thickness lower than 200 nm, a dielectric strength higher than 4 MV/cm, and a weight loss at 425° C. comprised between about 0.0008%/minute and 0.02%/minute.
The modern high frequency integrated circuits contain ten millions of transistors placed on few square centimeters of silicon crystal and they work with frequencies of the order of 1,000 MHz. All the transistors of said integrated circuits must be connected each other by electricity conductors. The modern integrated circuits contain up to six layers of conductor elements. Owing to the sizes and the density of the transistor positioning, it is preferable that both the sizes of the conductor elements and the separation space among the conductors are reduced as much as possible. At present, integrated circuits are produced with conductors having a thickness of 180 nm and separation is lower than 200 nm. In next future the reduction of the conductor thickness is planned up to 100 nm.
The reduction of the conductor sizes and of the separation among conductors causes some problems. The main problem is due to an increase of the resistance-capacity delay (RC-delay), connected to the resistance increase due to a decrease of the conductor section and to the increase of the capacity due to the conductor approach. Besides, the capacity increase implies the decrease of the signal intensity due to the interference among conductors and the heat developed from the integrated circuit increases with consequent increase of the circuit energetic consumption. This makes it necessary a more intense cooling of the circuit.
These problems can be solved by reducing the capacity among the conductor elements by using an insulating material having a lower dielectric constant. At present as insulator among the conductor elements of the integrated circuits, silicon oxide is used, which however shows a high dielectric constant (∈=4.2). A lower dielectric constant is that of air (∈=1.01), which however does not guarantee the insulation of the conductors, since it shows unacceptable values of dielectric strength, lower than 0.01 MV/cm. The voltage used by modern integrated circuits is of 3.3 V, the distance among the conductors is of the order of 200 nm, wherefore 3.3/200 gives a value of 0.165 MV/cm or 16.5 V/&mgr;m. Therefore, the dielectric strength of the used dielectric material must be higher of at least one order of magnitude than this value. Besides, it is preferable to use an insulating material having a dielectric strength as high as possible, since in the case of porous dielectric material, the dielectric strength remains at acceptable values.
The film thickness of the dielectric material must be very low to guarantee high performances of the integrated circuits. Besides, in modern circuits thicknesses of about 500 nm are used and it is expected that the constant trend to miniaturization requires dielectric materials having a thickness lower than 200 nm.
The integrated circuits during the production process are subjected to various thermal treatments, and therefore, it is important that the dielectric material has a suitable thermal resistance so that it is not damaged during said treatments. In particular, the dielectric material must withstand for a short time temperatures higher than 350° C.
It is known that polytetrafluoroethylene (PTFE) has one among the lowest dielectric constants (∈=2,05) of the solid materials and absolutely the lowest one with respect to non porous solid materials which withstand temperatures higher than 350° C. Therefore it is the ideal material for the use as dielectric insulator for high frequency integrated circuits. The problem is to obtain a thin PTFE film without defects having a high dielectric strength.
In U.S. Pat. Nos. 5,889,104 and 6,071,600 it is described how to obtain a dielectric material for integrated circuits from PTFE aqueous dispersions by spin coating. In these patents there is described the obtainment of the dielectric material from PTFE dispersions with particles having a diameter lower than 100 nm. Tests carried out by the Applicant (see comparative Examples) show that said PTFE dispersions give films which show defects and unhomogeneity. These films therefore are not able to guarantee good electric properties. Besides in said patents no value of dielectric strength of the obtained films is reported.
In U.S. Pat. No. 5,928,791 a method for improving the dielectric strength of thin PTFE films used in integrated circuits is described. The method includes a quick cooling after the sintering film of PTFE. In the Examples PTFE dispersions with particles having an average diameter of the order of 200 nm are used and films are obtained having a dielectric strength lower than 4 MV/cm, of the order 3.25-3.5 MV/cm, but having a high thickness in the range 500 nm-1,000 nm. Said thickness of the film of the dielectric material results too high and therefore unsatisfactory to guarantee high performances of the integrated circuits.
The need was therefore felt to have available a dielectric material for integrated circuits, under the form of homogeneous film, substantially without defects, having the following combination of properties:
a very good adhesion to the substratum;
a high dielectric strength, higher than 4 MV/cm;
a thickness lower than 200 nm;
a weight loss at 425° C. comprised between about 0.0008%/minute and 0.02%/minute.
An object of the present invention is therefore a formulation based on polytetrafluoroethylene (PTFE), homopolymer or modified, comprising:
1) latex of said PTFE having a particle diameter between 5 and 100 nm, comprising an anionic fluorinated surfactant in an amount in the range 2-25% by weight based on the PTFE, preferably 3-20% by weight;
2) a non ionic fluorinated surfactant added to the PTFE latex in an amount in the range 18-60% by weight based on the PTFE, preferably 25-45% by weight.
The anionic fluorinated surfactants used during the polymerization for obtaining the PTFE-based dispersion of the invention, are selected from the following compounds:
T—O—R
f
—CFX—COOM (IA)
wherein: X═F, CF
3
; M=H, NH
4
, Na, Li, K;
T is a C
1
-C
3
(per) fluoroalkyl group, optionally containing one Cl atom; preferably it is selected from —CF
3
, —C
2
F
5
, —C
3
F
7
, —CF
2
Cl, —C
2
F
4
Cl, —C
3
F
6
Cl; optionally one or two F atoms can be replaced by H;
R
f
is a (per)fluoropolyoxyalkylene radical having a number average molecular weight M
n
in the range 200-2,000, preferably 350-1,000; R
f
is selected in particular from the following classes:
(a) —(CF
2
CF(CF
3
)O)
m
(CFXO)
n
—
wherein m and n are integers such that the n/m ratio is in the range 0.01-0.5 and the molecular weight is in the above range;
(b) —(CF
2
CF
2
O)
p
(CF
2
O)
q
—
wherein p and q are integers such that the q/p ratio is in the range 0.5-2 and the molecular weight is in the above range;
(c) —(CF
2
CF(CF
3
)O)
r
—(CF
2
CF
2
O)
s
—(CFX
II
O)
t
—
wherein r, s and t are integers such that r+s is in the range 1-50, the t/(r+s) ratio is in the range 0.01-0.05 and the molecular weight is in the above range;
(d) —(CF(CF
3
)CF
2
O)
u
—
wherein u is an integer such that the molecular weight is in the above range;
(e) —(CYZ—CF
2
CF
2
O)
v
—
wherein Y and Z, equal to or different from each other, are F, Cl or H; v is a number such that the molecular weight is in the above range;
(f) —(CF
2
CF
2
O)
w
—
w is a number such that the molecular weight is in the ab
Kapeliouchko Valery
Marchese Enrico
Temtchenko Tatiana
Ausimont S.p.A.
Harlan Robert D.
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