Drying and gas or vapor contact with solids – Apparatus – For diverse operations on treated material
Reexamination Certificate
1999-11-11
2001-04-03
Ferensic, Denise L. (Department: 3749)
Drying and gas or vapor contact with solids
Apparatus
For diverse operations on treated material
C034S391000, C034S430000, C034S433000, C034S062000
Reexamination Certificate
active
06209220
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to methods and devices for cooling bodies such as semiconductor substrates after they are heated. More particularly, the invention relates to cooling a substrate by heat transfer between the substrate and a heat sink prior to handling the substrate.
Semiconductor wafers or other such substrates are subjected to very high treatment or processing temperatures. For example, in certain chemical vapor deposition (CVD) processes, the temperatures can approach 1,200° C. In a typical cycle, a wafer is transferred from a room temperature cassette by a robotic wafer handler into a processing or reaction chamber, where it is subjected to a high temperature treatment and is then transferred by the wafer handler from the high temperature processing chamber back to the same cassette or a separate cassette for processed wafers.
In many high temperature processes encountered in semiconductor processing, the wafer has to cool from the processing temperature to a much lower temperature before it can be placed or picked up by a wafer handler. For example, in an epitaxial silicon deposition reactor, processing temperatures in the reaction chamber are typically in the range of 1,000-1,200° C., while the maximum temperature that the robotic wafer handler can handle is only about 900° C. Furthermore, at high temperatures, the wafer is more vulnerable to physical damage which can be caused by the wafer handler during transportation. Therefore, the wafer must be allowed to cool down from the processing temperature (e.g., to about 900° C.) before it can be handled and transferred by standard handling equipment. Similarly, the wafer must be cooled down to even lower temperatures for safe handling by other types of wafer handlers (e.g., paddles), and for storage in low cost cassettes.
The time required to cool down the wafer to handling temperatures can be very costly to the integrated circuit manufacturer. Cool down rates depend in part upon the mass of the system being cooled, and have been measured at about 45 seconds from 1,200° C. to 900° C. for a 200 mm wafer on typical susceptor. This cool down adds to the total cycle time for each wafer and hence decreases the throughput of the system. This will increase the cost of wafer processing.
Because of the high cost of semiconductor wafer processing equipment, it is critically important from a competitive standpoint to be able to keep the expensive equipment in continued use, allowing increased throughput. At the same time, the wafer cooling technique employed must be compatible with the environment of the CVD processing apparatus and stringent purity requirements. Additionally, the cost of the technique must itself be low enough that there is a net reduction in the per-wafer cost of processing.
It is therefore an object of the present invention to provide a method and apparatus to cool down a wafer quickly and in a uniform fashion from a high processing temperature to a temperature at which the wafer can be picked up using a wafer handler and placed in wafer storage cassette.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, a method is provided for treating substrates in a processing chamber. The method includes loading a substrate onto a support structure within the chamber. The substrate is heated to a treatment temperature and treated at that temperature. After the substrate has been treated, an element is moved within the chamber to bring the substrate and a cooling surface of a heat sink into a cooling position. The substrate and cooling surface are maintained at the cooling position, in which the substrate loses heat to the cooling surface.
In accordance with another aspect of the present invention, a method is provided for cooling a substrate after heating to a processing temperature. The method includes moving the substrate from a first position to a second position in proximity to a cold element. The substrate is maintained at the second position while heat transfers from the substrate to the cold element until it cools to a handling temperature which is lower than the processing temperature.
In accordance with another aspect of the present invention, a method is provided for cooling a semiconductor substrate from a first temperature to a second temperature. The method includes moving a cooling member from a retracted position to a location adjacent and spaced from the substrate. In the retracted position, the cooling member has a third temperature which is lower than the second temperature. The cooling member is maintain in the adjacent position until the substrate cools to the second temperature. The substrate is then lifted with substrate handling device.
In accordance with still another aspect of the present invention, a processing reactor is provided for treating substrates at high temperatures. The reactor includes a heat source and a plurality of walls which define a process chamber. A substrate support structure is housed within the chamber. The reactor further includes a heat sink and a movable element. A drive mechanism moves the movable element from a first position to a second position. In the first position, a substrate (supported by the support structure within the chamber) can be treated. In the second position, the heat sink is spaced from the substrate by a distance sufficiently small to enable heat transport between the cold element and the substrate.
In accordance with yet another aspect of the present invention, a substrate processing system is provided with a high temperature processing chamber, a substrate holder positioned within the chamber, a cooling member, and a cooling shelter. The shelter is configured to shield the cooling member from heat during high temperature processing. A moveable arm, supporting the cooling member, is connected to a drive mechanism which can extend the moveable arm and cooling member from a first position to a second position. In the first position, the cooling member is proximate the cooling shelter, while in the second position, the cooling member is proximate the substrate holder.
In accordance with another aspect of the invention, a cooling mechanism is provided in a substrate processing system. The mechanism includes a support structure configured to support a substrate, a first cooling element and a second cooling element. These components are relatively movable between a cooling position and a substrate load position. In the cooling position, the substrate is proximate and spaced between each of the first and second cooling elements. In the substrate load position, a wafer handler can place the substrate upon the support structure. Advantageously, the illustrated embodiments facilitate conductively cooling a substrate, thus cooling the substrate significantly faster than by radiation alone. As the cooling methods and mechanisms do not require handling the substrate with a pick-up device, down time (specifically that caused by waiting for substrate to reach a temperature at which it can be safely handled) is significantly reduced. Additionally, the substrate can be cooled before moving it from the support structure within the process chamber, in accordance with certain of the above-noted aspects. Few moving parts are required to adapt the invention to existing reactors designs. The faster cool down process will allow a wafer or other substrate to be picked up from or placed on a susceptor in a shorter time, which enhances wafer throughput and ultimately decreases cost of wafer processing.
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patent:
ASM America Inc.
Ferensic Denise L.
Joyce Andrea M.
Knobbe Martens Olson & Bear LLP
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