Gas separation – Combined or convertible – In environmental air enclosure
Reexamination Certificate
2002-12-27
2004-09-28
Copenheaver, Blaine (Department: 1724)
Gas separation
Combined or convertible
In environmental air enclosure
C055SDIG001, C055SDIG002, C055SDIG007, C454S049000, C454S056000, C454S059000, C454S184000, C454S187000, C454S188000, C454S189000
Reexamination Certificate
active
06797029
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a configuration of at least two physical units in a process facility for processing at least one semiconductor wafer in which the process units each have a reduced density of contaminating particles with respect to the surrounding area in the process facility, and also to a method of operating the configuration.
Such configurations are known from semiconductor fabrication shops, in which the clean room conditions of the halls are subject to increased requirements. Both the hall itself and the individual process facilities are in this case subject to strict specifications with regard to the maintenance of temperature, humidity, air pressure, air flow velocity, the density of contaminating particles, etc. Typical clean room plant systems therefore include sensors for measuring the appropriate parameters, which in a control loop, provide their data to the corresponding ventilation, cooling or heating and recirculation systems. The permissible variation ranges for the respective parameters are in this case mostly very small.
With the decreasing structure sizes on the semiconductor wafers, the range of sizes of contaminating particles, which can lead to damage to the integrated circuit on the wafer, becomes wider and wider. In this document, however, contaminating particles should be understood to mean macroscopic particles, which can settle out of the air onto an integrated circuit on the semiconductor wafer, and also chemical substances such as solutions, amines or other reactive substances. These can attack the wafers, often covered with sensitive layers, and therefore chemically change the surface. For example, in lithographic exposure facilities, the acids liberated by an acid former as a result of exposure can attack the sensitive resist surface of the still unexposed, following semiconductor wafers and therefore disadvantageously attenuate the photoactivity of the resist. On the other hand, the object lens can also be attacked as a result, which can lead to lens degradation, so that the lens either has to be cleaned more often—with the result of lower productivity—or the lenses have to be replaced after shorter intervals, as a result of a shorter lifetime, with the result of higher production costs.
In the aforementioned example, the cause is contamination within a reduced-contamination physical unit belonging to a lithographic exposure facility. It is in precisely such a facility, however, that the objective is normally to keep the level of contamination, that is to say the density of contaminating particles in the physical unit, particularly low as compared with the surrounding units. For the aforementioned case, therefore, effective protection can consist only in a particularly suitable plant for producing the mini environment, as it is known, in the aforementioned physical unit.
On the other hand, a typical problem is represented by the contamination source in the physical units surrounding the particularly sensitive physical unit of the exposure facility and belonging to what is known as the lithographic track. On automated transport paths, the semiconductor wafers pass through various stations such as a hot plate, cool plate, varnishing, pre-bake, etc. In the process, first the mechanical abrasion of the transport systems has a contaminating effect, but second, the processing of the substrate surface also acts as a contamination source. Many of these stations have their own physical units with their own devices for reducing the density of contaminating particles, that is to say plants for maintaining a respective mini environment. Of course, in this example the requirement on the reduced-contamination physical unit of the exposure facility is at its greatest with respect to the clean room parameters.
For the transfer of a semiconductor wafer from one physical unit to the next, a direct opening is needed between the physical units. In order nevertheless to be able to maintain the differentiated conditions, care is additionally taken that there is a slightly greater pressure in the physical unit having the more sensitive conditions—for example, an exposure facility—than in the adjacent physical unit, for example, a physical unit belonging to the lithographic track in the aforementioned example. Under this assumption, a minimum air flow leads through the opening out of the more sensitive physical unit, so that no new contaminating particles can penetrate.
The clean room conditions in the reduced-contamination physical units are also ensured, inter alia, by producing a laminar flow. For this purpose, the device for reducing the density of contaminating particles has a suitable ventilation system that produces a suitable flow with a flow velocity which is sufficiently low, for example 0.3 m/s, so that no turbulence is produced. As a result, contaminating particles once produced drift with the flow from an air inlet opening in the direction of an air outlet opening and are filtered there or are otherwise disposed of. It is important in this case that the air flow be oriented substantially parallel to the opening area of the opening leading to the adjacent physical unit. Therefore, between the physical units, no air exchange takes place directly as a result of the laminar flow, but only a minimum air flow which results from the pressure equalization. As a result of the only minimal permitted pressure differences between the two physical units, however, the problem can then arise that, as a result of sudden pressure changes or air movements—for example, during the transport of a wafer into the vicinity of the opening—the air flow can be deflected in the opposite direction. As a result, contaminating particles pass into the more sensitive of the two physical units.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a process facility and a method for operating the process facility, which overcome the above-mentioned disadvantages of the prior art apparatus and methods of this general type.
In particular, it is an object of the invention to insure a lower density of contaminating particles in the more sensitive of two physical units in a process facility for semiconductor fabrication.
With the foregoing and other objects in view there is provided, in accordance with the invention, a process facility including: a first physical unit including a first device for reducing a density of contaminating particles therein with respect to an area surrounding the first physical unit, the first device providing a first laminar air flow at a first flow velocity; a second physical unit including a second device for reducing a density of contaminating particles therein with respect to an area surrounding the second physical unit, the second device providing a second laminar air flow at a second flow velocity; and a third physical unit formed with a first opening leading to the first physical unit and formed with a second opening leading to the second physical unit. The third physical unit forms a connection for transferring at least one semiconductor wafer between the first physical unit and the second physical unit. The third physical unit is formed with an air inlet slot and an air outlet slot. The third physical unit includes a third device for reducing a density of contaminating particles therein. The third device provides a third laminar air flow at a third flow velocity. The first laminar air flow and the second laminar air flow are aligned parallel with each other. The third laminar air flow is oriented substantially at right angles to the first laminar air flow and the second laminar air flow.
In accordance with an added feature of the invention, the third flow velocity is slightly larger than the first flow velocity and slightly larger than the second flow velocity such that near the first opening and near the second opening, no turbulence is produced as a result of a pressure difference established between the first physical unit and the third physical unit and a pressur
Hornig Steffen
Lederer Kay
Copenheaver Blaine
Greenberg Laurence A.
Infineon - Technologies AG
Locher Ralph E.
Pham Minh-Chau T.
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