Semiconductor Device Manufacturing Unit

The present invention relates to a semiconductor device manufacturing unit which is used to form plasma CVD films on semiconductor wafers.

In manufacturing semiconductor devices such as integrated circuits, vacuum evaporation, sputtering, plasma CVD (chemical vapor deposition), or electrolytic oxidation is usually employed for formation of films. Among these methods, the plasma CVD method is of particular interest because with it films can be achieved at low temperatures and the quality of the films thus deposited is most suitable for dry processes.

FIG. 1 shows a conventional parallel flat plate type semiconductor device manufacturing unit which implements the plasma CVD method. In FIG. 1, reference numeral 1 designates a chamber, 2 an RF (high frequency) electrode provided in the chamber 1, and 3 a susceptor. The electrode 2 generates a plasma gas a by which CVD films are formed on semiconductor wafers 4 on the susceptor 3.

The conventional unit is disadvantageous in the following points. As the flow of plasma gas a is not uniform, the formed CVD films are not uniform. In addition the number of semiconductor wafers processable in one batch is small. As the density of the plasma gas a is low, the speed of deposition of the CVD film is low and accordingly the time required for processing each batch of semiconductor wafers is long. Furthermore, it is difficult to control the temperature in the chamber 1 and hence the quality of the CVD films is unstable. As the temperature distribution is not uniform, flakes are liable to be formed on the electrode. Also, it requires much time to clean the electrode of the flakes. Moreover, as the flakes fall on the main surfaces of the wafers, it is difficult to obtain stable films which are of excellent quality.

Accordingly, an object of the invention is to provide a semiconductor device manufacturing unit in which the plasma gas is maintained sealed in a quartz tube with a magnet disposed outside the quartz tube to make the density of the plasma gas high and uniform thereby improving the quality of the CVD films formed by the gas and reducing the time required for processing semiconductor wafers. A wafer holder is moved through the magnet to effectively achieve the deposition of the CVD films.

More specifically, a semiconductor device manufacturing unit of the invention includes a quartz tube and a wafer holder which is movably mounted in the quartz tube. A support bar is provided for moving the wafer holder with the support bar additionally serving as a ground electrode. An RF electrode and a magnet are disposed outside the quartz tube. The wafer holder preferably is constructed so as to arrange the semiconductor wafers longitudinally in the wafer holder with respect to the quartz tube.

FIG. 1 is a sectional view of a conventional semiconductor device manufacturing unit; and

FIG. 2 is a sectional view of a semiconductor device manufacturing unit according to the invention.

A preferred embodiment of the invention will be described with reference to FIG. 2 which shows a diffusion furnace type semiconductor device manufacturing unit constructed according to the invention. The unit, as shown in FIG. 2, includes a quartz tube 5, inlets 6 for introducing the gas which is used to produce the plasma gas, an outlet 7 for discharging the gas, a flange 8, a shielding O-ring 9, a semi-cylindrical wafer holder 10 for holding semiconductor wafers 11 which is made of graphite or aluminum and is movable longitudinally in the quartz tube 5, and a metal support bar 12 coupled directly to the wafer holder 10. The wafer holder 10 is moved by operating the support bar 12. The support bar 12 is grounded and accordingly the wafer holder 10 is grounded. The unit further includes a flexible bellows 13 adapted to isolate the interior of the quartz tube 5 from the external atmosphere while the support bar 12 can be moved longitudinally, a cylindrical RF (high frequency) electrode 14 in close contact with the outer wall of the quartz tube 5, a permanent magnet or electromagnet 15 which is ring-shaped and surrounds the quartz tube 5, and a heater 16 including a heat insulating material. In FIG. 2, the magnet 15 is shown as being outside the RF electrode 14 although the magnet 15 may be provided inside the electrode 14 if desired.

In the unit thus constructed, the magnet 15 is disposed outside the quartz tube 5. Accordingly, even under a low pressure, for instance 1.times.10.sup.-2 Torr, the plasma gas is maintained sealed in the quartz tube 5 for a long period of time and the gas density is increased. Accordingly, the speed of formation of a CVD film on the semiconductor wafers is increased, that is, the processing time per batch is reduced. As the semiconductor wafers are moved through the field of the magnet 15, the plasma gas is uniformly distributed over the semiconductor wafers as a result of which the CVD films thus formed are substantially uniform in thickness. Furthermore, the temperature in the quartz tube 5 can be readily controlled and accordingly the films have a quite stable quality and the temperature distribution in the quartz tube is uniform with the result that few if any flakes are formed on the electrode.

As shown in FIG. 2, the semiconductor wafers are arranged longitudinally in the wafer holder 10. Therefore, the distance of movement of the wafer holder is short and accordingly the unit can be made small in size. In addition, the unit is advantageous in that flakes formed on the electrode cannot fall on the wafers.

As is clear from the above description, with the semiconductor device manufacturing unit according to the invention, the quality of the CVD film is improved with respect to that of prior art units and the processing time is reduced.