Device for one-sided etching of a semiconductor wafer

Details Device for one-sided etching of a semiconductor wafer Device for one-sided etching of a semiconductor wafer

1993-02-01

1994-06-28

Valentine, Donald R.

Chemistry: electrical and wave energy

Apparatus

Electrolytic

204297R, C25D 1706, C25F 700

Patent

active

053244109

DESCRIPTION:

BRIEF SUMMARY
PRIOR ART

The invention relates to a device for one-sided etching of semiconductor wafers (silicon wafers), which is constructed like an etching box. Such a device is known from the journal Vacuum Science Technology, issue of July/August 1985, pages 1015 ff., G. Kaminsky, "Micro-machining of silicon mechanical structures". Described therein is an etching mount for silicon wafers in the form of a Teflon plate at the edge of which there is arranged in a groove a O-ring on which the wafer to be etched is supported. The wafer is mounted on the Teflon plate by a ring made from Teflon, which is connected to the base plate by means of nylon screws. Etching solution reaches the surface of the wafer through the Teflon ring. The O-ring prevents etching solution from reaching the rear. However, the etching solution can wet the edge of the wafer on both sides up to the contact zone between the wafer and 0-ring. The mechanical stability is therefore diminished in the edge region of the wafer, and in addition possibilities for machining the wafer after the etching process are restricted. During the etching operation, the pressure of the air situated under the wafer rises as a consequence of the high etching temperatures. The risk of breakage therefore increases, particularly at the edge region of the wafer, where it rests on the O-ring. A device for pressure compensation for the air space produced under the wafer is not provided. Again, the possibility of electrical contacting of the wafer in order to be able to carry out an electrochemical etching stop is not provided.
Furthermore, as basic material, Teflon has a dimensional stability which is too low at high etching temperatures for the envisaged application. In solutions, Teflon varies its volume by swelling, and thus its shape. An etching mount made from Teflon therefore cannot be multiply used.
It is the object of the invention to specify a device for the one-sided etching of silicon wafers which imposes a low mechanical stress on the wafer to be etched, ensures complete protection of the wafer edges, and permits an electrochemical etching stop.
The object is achieved according to the invention by the characterising features of claim 1. In this case, use is made of a mount like an etching box having an open upper part which is provided with two O-rings between which the wafer is clamped and which are arranged such that the etching solution can reach only the inner region, situated inside the O-ring, which is on the lid side, of the side of the wafer to be etched. The cavity produced under the wafer backside is connected to the external environment via a bore which adjoins a tube or a hose. The production of an overpressure under the wafer is thereby excluded. Guided simultaneously through the bore is the lead for the electrical contacting of the wafer which is required for the electrochemical etching stop.


ADVANTAGES OF THE INVENTION

The device according to the invention has the advantage that the wafer edge is protected absolutely securely against contact with the etching solution. The O-rings holding the wafer are arranged precisely one above the other, so that both sides of the wafer are subjected to symmetrical holding forces. Due to the fact that it is mounted only via O-rings, the wafer is elastically supported. It is contacted electrically from the backside in a manner protected against the etching solution. Even at high temperatures of the etching solution, no overpressure is produced in the cavity under the wafer backside because of the connection to the external environment. The device therefore permits maximum safety against breakage. The good dimensional stability of the materials proposed permits multiple use of the etching box. The electrical contacting of the wafer is advantageously performed by spring contacts.
Further advantageous developments of the device follow from the measures specified in the subclaims.
When producing the etching box from a polyvinylidene fluoride (PVDF) plastic, it is expedient respectively to provide in the lid and base

REFERENCES:
patent: 4043894 (1977-08-01), Gibbs
patent: 4696729 (1987-09-01), Santini
patent: 5126031 (1992-06-01), Gordon et al.
Kaminsky, "Micromachining of Silicon Mechanical Structures", J. Vac. Sci. Technol., vol. 3, No. 4, Jul./Aug. 1985, pp. 1015-1024.
Joseph T. Kung et al, "A compact, inexpensive apparatus for one-sided etching in KOH and HF", Sensors and Actuators, vol. 29, (1991), pp. 209-215.

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