Heating – Processes of heating or heater operation – Including preparing or arranging work for heating
Reexamination Certificate
2002-05-16
2004-06-08
Wilson, Gregory (Department: 3749)
Heating
Processes of heating or heater operation
Including preparing or arranging work for heating
C219S490000, C414S161000, C414S294000
Reexamination Certificate
active
06746237
ABSTRACT:
PRIORITY INFORMATION
This application claims the priority under 35 U.S.C. § 119 of Dutch Patent Application No. 1018086, filed May 16, 2001; the disclosure of this application is hereby incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to reactors for treating substrates. More particularly, the invention relates to reactors that process wafers and a method of operating such a reactor.
2. Description of the Related Art
When processing a substrate, such as a semiconductor wafer, the substrate is often heated with a heating means within a body of a furnace. It is customary that the energy supply to the heating means is controlled such that the measured temperature of the furnace body is substantially constant and has a desired value. When a number of substrates are subjected to a heat treatment one after the other, heat is withdrawn from the furnace body on the side of the furnace body adjacent to the substrate. Over the course of time a fall in the temperature of the furnace body will be detected by the temperature sensor. As a response to this, the energy supply to the heating means will be increased to such an extent that the furnace body again reaches the desired temperature. In view of the relatively high thermal capacity of the furnace body, this is a process that proceeds slowly and it can be some time before stable conditions have been established, in particular in those cases where the thermal capacity of the furnace body is so high and the treatment time so short that the temperature of the furnace body has still not been restored at the end of the treatment of a substrate. When a subsequent substrate has been loaded, heat is again withdrawn from the furnace body and in this way the temperature deviation can become increasingly greater for an initial number of substrates to be treated before it is finally restored as a result of the slow progression of the control process. The substrates subjected to treatment during this period will have received a non-uniform heat treatment.
These differences in heat treatment can be even greater than appears from the measured values produced by the temperature sensor. The temperature sensor is usually located within the furnace body, some distance away from the surface of the furnace body that is adjacent to the substrate. The heat, on the other hand, is withdrawn via the surface of the furnace body adjacent to the substrate. Decreases in the temperature of the furnace body of 10° C. or more are possible at the surface or in the immediate vicinity of the surface. This is, of course, undesirable.
In the case of some heat treatments according to the prior art, after the substrate has been positioned in the vicinity of the furnace body, there is a waiting period until a stable, desired temperature has been established, after which the actual treatment, for example the deposition of a layer with the aid of plasma enhanced chemical vapor deposition, starts. However, in some heat treatments (e.g., annealing), the entire temperature-time-profile (i.e., the “thermal budget”) plays an important role in the treatment, especially when the treatment temperature is higher than approximately 500° C. Imposing a particular thermal budget on the substrates can even be the sole purpose of the treatment (e.g., without the formation of a layer on the substrate during the treatment). In such cases controlled and reproducible heating of the substrates is just as important as the final treatment temperature. In other words, it is important to achieve a thermal budget that is identical for all substrates when subjecting substrates to heat treatment. In principle, positioning the substrates in the vicinity of a relatively massive, heated furnace body is an extremely suitable method for this purpose, provided the disadvantages described above can be avoided.
SUMMARY OF THE INVENTION
A need therefore exists for a method and a device for heat treatment of substrates which avoid the disadvantages described above and which can achieve an identical heat treatment for successive substrates.
In one embodiment, a method for the successive heat treatment of a series of flat substrates comprises placing a substrates adjacent to, and essentially parallel to, a heating body having a flat boundary surface facing the substrate. The temperature in said heating body is measured at a location therein that is so close to the boundary surface that after the substrate has been placed in position the withdrawal of heat from the heating body by the substrate is measured at that location. The substrate is placed in the vicinity of said heating body, only after a desired temperature measured in the location has been reached. An amount of heat is supplied to said heating body such that the temperature measured at said location during the successive heat treatment of the series of substrates has an essentially constant value averaged over time. The substrate is removed from said heating body before said desired temperature, measured at said location, is reached again.
In this way an identical starting situation can be achieved for each substrate to be treated, which appreciably increases the reproducibility of the treatment. In a modified embodiment of the invention, after the substrate has been moved some distance away from the heated furnace body on completion of the heat treatment, it is moved into the vicinity of an essentially flat cooling body, so that cooling also takes place in a rapid and controlled manner.
The method described above can be carried out in various ways, in particular with regard to the control of the power supply to the heating means. For instance, it is possible in so-called “open loop control” to supply a constant power to the heating means and, at the point in time when the treatment of substrates starts, to increase the power supply in order to compensate for the heat withdrawn from the furnace body by the substrates. It is also possible in “closed loop control” to control the power supply in such a way that the temperature measured by the temperature sensor is constant. Both in the case of “open loop control” and in the case of “closed loop control” the control can be adjusted so that during the treatment of substrates the average temperature measured over time is somewhat higher than that in a state of rest. The result of this is that, following treatment and removal of a substrate, the temperature sensor indicates the desired temperature again within a shorter period and the introduction of the following substrate can start at an earlier point in time.
The method described above is particularly suitable for subjecting substrates to a heat treatment in a so-called “floating wafer reactor,” as described in U.S. Pat. No. 6,183,565, which is hereby expressly incorporated by reference herein. In this floating wafer reactor flat substrates are brought one by one and successively between two essentially flat furnace bodies parallel to the substrate, after which the furnace bodies are moved towards one another and positioned a short distance away from the wafer. Preferably, the wafer is supported and held in place by gas streams, directed in opposing directions, issuing from these furnace bodies, without mechanical contact. With floating wafer reactors of this type it has proved possible to provide very rapid heating or cooling of the wafers without the wafers being damaged. As a result of the very rapid heating, wafers can also be treated very rapidly in succession.
According to another embodiment of the invention, substrates are treated in a treatment chamber in which, in addition to the heat treatment chamber, there is also a cooling station and a transport system for the substrate. The temperature of the substrate is lowered very rapidly in the cooling station under controlled conditions.
Yet another modified embodiment relates to a device for the heat treatment of a series of substrates. The device comprises a heating body with a flat surface for accommodating the subs
Bast Ronald
Kuznetsov Vladimir Ivanovich
Storm Arjen
Zinger Jan
ASM International N.V.
Knobbe Martens & Olson Bear LLP.
Wilson Gregory
LandOfFree
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