DE1521728A1 - Process for polishing semiconductor crystals - Google Patents

Description

Dr. Ing.E. BERKENFELD, patent attorney, KOLN _# Universitätntraße 31 Attachment file number

to input · from l'J . March 1966 VA. Namid, Ann. DOW CORNING CORPORATION,

MIDLAND, MICHIGAN 48641, UNITED 3TATES OP AMERICA

Process for polishing the oüei'fiäofee of semiconductor crystals.

The present invention relates to methods of manufacture of semiconductor crystals and, in particular, on methods for achieving crystal surface qualities that are suitable for high-quality semiconductors rvorrichtungen are suitable, such. B. solar cells, diodes and transistors for electronic circuits.

Small blocks or sections of crystal in the form of cubes, plates, and disks are often used in the manufacture of semiconductor devices. These blocks or sections are generally cut from a larger crystal. Before they can be used, the surfaces of these sections must be tempered so that a smooth, mirror-like, almost perfect surface is produced. A problem that is well known to those skilled in this art is the removal of surface damage caused by the mechanical treatment of the semiconductor materials caused. Jiinc, such damage is caused by the cutting, sawing, and lapping operations necessary to make the units of crystalline material of the appropriate size, thickness, and geometric shape for making the devices. In order to achieve a working device, the semiconductor units must be treated in some way to avoid all foreign contamination and damage ^ qh-iah ^ n, y _; on their surfaces to remove. BAD ORIGINAL 909824/1193

According to the prior art, the semiconductor is lapped, mechanically polished and then etched in the reactor prior to application to obtain customization remove finished sections. When lapping z. B. the damaged layer is approximately half the diameter of the particle size the abrasive used. When using aluminum oxy / d with 2000 mesh for lapping, the damaged layer is about 5 microns thick. Mechanical polishing becomes part of this Area is removed and the section is then etched with a chemical etchant treated, which is generally a mixture of nitric acid and hydrofluoric acid and possibly additives such as acetic acid, bromine, iodine, sodium dichromate, oxides of nitrogen? Silver or mercury nitrates and even organic compounds that are occasionally used as wetting agents. In general the reaction is very quick and difficult to control.

An object of the present invention is to provide an improved method for polishing semiconductor crystal sections.

Another object is to develop a method for polishing of semiconductor crystal sections that do not require mechanical lapping or polishing.

To achieve these and other objects, the present invention provides an improved etching technique which makes use of the mechanisms associated with an oxidation-reduction reaction. This removes material layers from a semiconductor surface .

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Required and simple etching solutions that are considered unsuitable to this day for such work has been found to be practical for practicing the invention. Basically based the invention based on the knowledge that the structure of an essentially laminar flow of the etching solution over the surface of the semiconductor crystals leads to a perfecting of the surfaces, that can compete with the very best processes.

The following description serves to further explain the invention and is given in the appendix with the drawing. Where:

Fig. 1 is a perspective view of a typical disk from an i.i. Semiconductor material after cutting and before treatment and

Pig. Figure 2 is a partially sciiematioche view in perspective Eiii3S crfiniungsge.wet formed processing tanks, a piece broken out of 5 J-am to expose inner parts is.

Fig. 1 shows ο ine disk 11 made of semiconductor crystal material, v / ie z. 3. Silicon or germanium. When cutting the disc out of a larger crystal was made, the surface of the disc by saw marks 12 verioi'bon.

According to / L: r vorli jjenJ.jn invention ..er-lan discs 11 or blanks for solar οΛ-ar 3onnencells placed in iineii tank Iy (Fig. 2), which can be made from je-lon gejij ^ oten material that can commit does not react chemically with the ät :: solution to be used. In the tank Ij5 protrudes an lreli "':: ~' e ..- ^ 1Ij- ^; -4," Ie of einoi .: rotor Ib orljr like driven-

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will practice. At or near the bottom of the shaft is a Impeller 17 attached. The impeller contains several horizontal blades 18 and several vertical blades 19, which are vertically below run along the horizontal blades. However, it should make sense that impellers with other shapes can also be used effectively can.

The tank is up to a level above the impeller 17 with a caustic solution such as HF: ENT. or other known / itzlösungen filled. The impeller is rotated at slow to moderate speeds and thus results in an essentially laminar flow over and around the semiconductor wafers or the blanks for the solar or solar cells. The disks or blanks can rotate freely with the solution. A typical speed for an impeller in a 30.5 cm diameter tank is about 40 revolutions per minute. Modifications to this procedure have been attempted with varying degrees of success. Placing the disk in a static solution created problems in controlling the reaction and, at best, provided very poor surfaces. It was found that in some cases the reaction between the etching solution and the semiconductor was so slow that an oxide coating remained on the surface. In other cases it was so rapid that thermal runaway prevented any reasonable control of the process. Ultrasonic vibrations showed some advantages over static solutions. But they too led to a pretty bad surface. An attachment of the semiconductor wafers to a shaft or a?; .-. Paddling and turning the shaft or the paddle in the Xtz solutions led to a noticeable trace of the flow of fluid, since some surfaces of the disk are more pronounced than others.

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Static disks in a moving solution also fed Flow patterns or irregular etching on the edges of the disks or blanks.

Various types of impeller disks and propellers have been investigated. Two defining features were found. The speed of rotation must be sufficient to avoid convection currents in the etching solution and to keep the discs in constant motion. With convection currents Local temperature differences arose over the semiconductor wafers and these resulted from the different strengths Etching to surface fluctuations. But the speed of rotation must also be low enough to ensure minimal turbulence. That is, over the semiconductor surfaces a substantially laminar flow must be maintained. This speed depends of course on the shape and size of the impeller and dec tanks and the distance between the impeller and the tank away.

Various modifications and variations of the invention are possible and arise for professionals. It is therefore clear that the "irfinduns" also exercised differently within the framework of the following claims can be grounded as this has been described in detail.

Patent claims:

BATH

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Claims (2)

Dr. Ing. E. BERKENFELD, patent attorney, KQCN, UnivereitätMtraU · ~ λ Ante «· AkttfUNidwn zur EIn0Ob * vom Yf. Mar Z 1966 VA. Nam.d.Aiim. DOW CORNING CORPORATION, MIDLAND, MICHIGAN 48641, UNITED 3TATES OP AMERICA PATENT CLAIM 1. Process for polishing of semiconductor crystals, characterized in that that a substantially laminar flow of the chemical etching solution is generated over the surfaces of the crystals. 2. Process for polishing semiconductor crystals, characterized in that that the crystals are placed in a liquid chemical etching solution will and the etching solution is stirred at a rate that sufficient to create a flow of the over the surfaces of the crystals Generate A'tzlösung with a speed, which is large enough to avoid convectide currents in the A'tzlösung and around the To keep discs in constant motion, but also under the Velocity at which turbulence would occur in the flow on the crystal surfaces. 2. A method for polishing semiconductor crystals according to claim 2, characterized in that the stirring reads the turning of an impeller beneath the surface of the liquid chemical etching solution u:.; Fa.'3l ;. 909824/1193 _{BAD OW} QINAL