Drying and gas or vapor contact with solids – Process – With nondrying treating of material
Reexamination Certificate
2000-12-28
2003-05-13
Lazarus, Ira S. (Department: 3749)
Drying and gas or vapor contact with solids
Process
With nondrying treating of material
C034S360000, C034S367000, C034S370000, C034S381000, C034S393000, C034S443000, C034S460000, C034S062000, C034S065000, C034S211000, C414S935000, C414S941000
Reexamination Certificate
active
06560896
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to cooling of wafers.
The treatment of semiconductor wafers generally takes place at a raised temperature. This temperature can have a different value for different treatment steps. There are treatment steps which are carried out at a temperature which does not differ significantly from the ambient temperature and there are also treatment steps which are carried out at a temperature from a couple of hundred degrees Celsius to 1200 degrees Celsius. In the treatment chamber in question, the wafer is brought up to the temperature needed for that process step. After the treatment step has finished, the wafer should be cooled down again before it can be transported within the treatment apparatus to the next station to undergo the next treatment step. The placing of a hot wafer in certain atmospheres can bring about undesirable and unintentional effects, which make the wafer unusable. To avoid these effects, the wafer should be cooled after a treatment step at a high temperature before the wafer is transported to the next treatment station. Moreover, after the last treatment step in the treatment system, the wafer should be cooled down before it can be placed in the plastic transport cassette.
This cooling down can take place in the treatment station itself by switching off the heating means. It can be a disadvantage to have the treatment station experience a range of temperatures during the treatment of a wafer, due to the loosening of deposited layers from the walls of the treatment station and the such like. In addition, depending on the design of the treatment station, it can cost a great deal of energy to continually expose the whole treatment station to a range of temperatures. Moreover, many treatment stations are better equipped to quickly heat the wafer than to quickly cool the wafer. The lower the temperature, the smaller the heat exchange through radiation and conductance. The quick cooling requires some special measures which are not always easy to integrate into the treatment stations themselves. For this reason, separate cooling stations are used in the prior art.
In EP 827.187A, a cooling station is described in working relationship with a multi-chamber treatment system wherein the treatment chambers and the wafer transport chambers are kept under vacuum conditions. Under vacuum conditions, heat transport by conduction via the present gas is practically non-existent. The heat contact between the wafer and the cooled plateau on which the wafer is placed is thus bad unless further measures are taken. In the European patent application mentioned, it is proposed to clamp the wafer electrostatically onto the cooled plateau which gives the possibility of introducing gas on the rear side of the wafer whereby the heat exchange between the wafer and plateau is significantly improved without the wafer being blown away and without the vacuum in the cooling station being significantly disturbed. A disadvantage of this method is that the heat removal takes place substantially to the side of the plateau while the opposite side is not made use of. Moreover, this one-sided cooling leads to significant thermal tensions with possible harmful consequences for the wafer. In addition the plateau with the electrostatic clamping provision comprises various synthetic parts which cannot withstand temperatures higher than a couple of hundred degrees Celsius.
During the thermal treatment of wafers at a high temperature, apart from the intended treatment at the desired temperature, an unintentional treatment also takes place during the heating up of the wafer to the treatment temperature and the cooling down of the wafer from the treatment temperature to the ambient temperature. Although during the design of an integrated circuit this unintentional thermal treatment is taken into account, there are still circumstances wherein the effect of these treatments are harmful. An example is the activating of doping electrons after implantation in the wafer; a high temperature step is needed to bring about the electrical activation of the implanted atoms. However, this high temperature step also has the consequence that, by diffusion, a spreading of the depth-concentration profile of the implanted atoms takes place. It appears that the most effective activation in combination with the most minimal spreading of the concentration profile occurs with as short as possible a heat treatment at high temperature. A treatment of 1 second at 1050° C. gives the same degree of activation but less spread than the treatment of 10 seconds at 1000° C., see M. A. Foad, G. de Cock, D. Jennings, T-S Wang and T. Cullis, Uniform Spike Anneals of Ultra Energy Boron Implants Using xR LEAP and RTP Xe
plus
Centura: Ramp Rate Effects Up to 150° C./sec (XIIth Ion Implantation Technology Conference, Kyoto 1998). For this, the realization of high heating up and cooling down speeds is of notable importance. In the prior art a Rapid Thermal Processing reactor is used for this purpose. This is a reactor where, in an otherwise cold surrounding, the wafer is heated by lamps. By putting a high lamp power into operation, a high heating up speed is possible, up to approximately 150° C./s. Cooling down is achieved by switching off the lamps and the wafer loses its heat again, substantially by radiation. From
FIG. 1
of the above-mentioned publication, it appears that the cooling speed of approx. 50° C./s is considerably smaller than the heating up speed. This is partly caused by the fact that, for a uniform heating up, mirrors are placed around the reactor chamber which reflect back part of the radiation energy given off by the wafer. With a free radiation in the area, without mirrors being present, a higher cooling down speed is achieved, but even then the cooling down speed remains limited to approximately 100° C./s at a temperature of 1000° C. while at lower temperatures the heat exchange by radiation decreases proportionally with the temperature to the fourth power.
In WO98/01890 a reactor is described for the treatment of wafers at a raised temperature. To do this a wafer is taken into an area bounded by two housing-parts whereby from each of the housing-parts a gas flow is supplied to the wafer. In this way, both the housing-parts and the gas have a raised temperature and heating of the wafer can take place in a particularly quick manner.
From the European application 829904 it is known to cool wafers in a separate station. To that end the wafer is spaced from two members with lifting pins. Cooling is realized by a flow of gas moving along the wafer, the gas being only provided for heat transport by conductance. From the PCT application WO98/01890 heating of the wafer in floating condition is known. In U.S. Pat. No. 5,974,682A a partially open ring for transporting of wafers is described.
SHORT DESCRIPTION OF THE INVENTION
It is the aim of the present invention to provide a cooling station wherein the wafer is cooled down on both sides by approximately equal amounts, evenly and quickly over the whole surface.
It is the aim of the present invention to provide a method for a thermal treatment wherein, after the treatment at high temperature, the wafer is placed in a cooling station and is cooled evenly on both sides and the occurrence of thermal tensions are avoided. It is also the aim of the invention to provide a method for thermal treatment wherein directly after the end of the high temperature step the wafer is transferred to the cooling station as quickly as possible. It is also the aim of the present invention to provide a method for the thermal treatment wherein after the treatment at high temperature, the wafer is placed in a cooling station that can withstand a wafer with a very high temperature being placed on it (1200° C.). A further aim of the invention is to provide a method for a thermal treatment wherein after the treatment at high temperature the wafer is placed in a cooling station and wherein the wafer is cooled down as quickly as possible. A further aim of th
Granneman Ernst Hendrik August
Kuznetsov Vladimir Ivanovich
Snijders Gert Jan
ASM International N.V.
Knobbe Martens Olson & Bear LLP
Lazarus Ira S.
Rinehart K. B.
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