Device for electrolytic oxidation of silicon wafers

Details Device for electrolytic oxidation of silicon wafers Device for electrolytic oxidation of silicon wafers

1995-11-13

1998-03-10

Valentine, Donald R.

Chemistry: electrical and wave energy

Apparatus

Electrolytic

204268, C25D 1700, C25D 1706

Patent

active

057257426

DESCRIPTION:

BRIEF SUMMARY
This invention relates to a device for electrolytic oxidation of silicon wafers to be used as semiconductor components or integrated circuits.
The invention sets out from DE-A-1,496,883 and U.S. Pat. No. 3,419,480.
These publications describe electrolytic compartments which are separated by a wall, part of which is a silicon wafer, and which contain relatively small electrodes for producing a silicon oxide layer on one side of the silicon wafer (or on both sides thereof).
The problem to be solved by the invention resides in that the silicon oxide layers of the prior art do not have uniform thickness. This entails non-uniform electrical properties of the resulting oxidised silicon wafer, the semiconductor component or the integrated circuit.
The inventive concept aims to alleviate this problem. This has been achieved as recited in the appended claims.
According to the invention, the electrodes and the silicon wafer are horizontally arranged, resting on each other by the intermediary of spacers, and the electrodes are larger than the silicon wafer.
It is believed that the favourable effect of this design on the uniformity of the silicon oxide layer derives from the uniform electric field which is achieved by the gravity-warranted horizontal positioning and by the larger electrodes. Advantageously, the electrolyte is a buffer solution yielding substantially constant reaction kinetics, but it may also be of another type, e.g. weak HCl.
In practice, the invention ensures that the oxidation of silicon wafers, with resultant uniform silicon oxide layers, is made independent of the size of the silicon wafer.
By "uniform" silicon oxide thickness is here meant a silicon oxide thickness which at any rate is more uniform across the treated surface of the silicon wafer as compared with what is achievable by means of the small electrodes and larger silicon wafer of the prior art. Preferably, the uniformity of the oxide layer thickness is .+-.5 .ANG. in the thickness range of 200-2000 .ANG. of the silicon wafer, this range being at present technically acceptable for so-called high-integration circuits. In preferred embodiments of the invention, the above-mentioned ranges are determined by parameters recited in the appended claims and in the Examples below.
The invention will be described in more detail hereinbelow with reference to the accompanying drawings, in which FIG. 1 shows a preferred device according to the invention partly in section, and FIGS. 2 and 3 show the characteristics of a silicon oxide wafer obtained by means of the invention.
Between a cathode 1 and an anode 6 is provided a silicon wafer 4 (of which only the cathode-facing surface is to be oxidised). The components cathode, anode and silicon wafer are horizontally arranged. The cathode compartment 2 is defined by a silicon strand 3 shaped into a circle and disposed between and in direct engagement with the cathode and the silicon wafer. A similar arrangement may be used on the anode side as well, but in this Example it is preferred to use as anode-medium carrier a package of circular filter-paper sheets 5. The electrodes 1 and 6 are fixed on metallic holders 9 and 7, respectively, by bolts 8 and are essentially larger than the silicon wafer 4. Moreover, the cathode 1 and its holder 9 have a considerable weight, so that the assembly is able to compress the components 1, 3, 4, 5 and 6 into good physical and electrical contact with each other. The cathode and the anode terminals to a direct-current source (not shown) are designated 10 and 11. Here, the anode terminal 11 is shown to have a connection 12 with the bolt 8.


EXAMPLE

In the following Example, the parameters in anode oxidation of silicon wafers were the following, unless otherwise indicated. Electrode gap: 25 mm; starting voltage: 30 V; oxidation time: 10 min; electrolyte in both cathode and anode compartments: - 50 mM sodium phosphate - 2.1715 g of Na.sub.2 HPO.sub.4 +0.9358 g of NaH.sub.2 PO.sub.4 in 400 ml of distilled water - at a pH of 7.0.
The electrodes consisted of 170.times.175.times

REFERENCES:
patent: 3324015 (1967-06-01), Saia et al.
patent: 3419480 (1968-12-01), Schmidt
patent: 4043894 (1977-08-01), Gibbs
patent: 4288309 (1981-09-01), Cohen
patent: 5228966 (1993-07-01), Murata
patent: 5429733 (1995-07-01), Ishida
patent: 5437777 (1995-08-01), Kishi
patent: 5458755 (1995-10-01), Fujiyama et al.

Affiliated with

Also associated with

Rating

Device for electrolytic oxidation of silicon wafers does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Device for electrolytic oxidation of silicon wafers, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Device for electrolytic oxidation of silicon wafers will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-136282