Semiconductor device manufacturing: process – Chemical etching – Liquid phase etching
Reexamination Certificate
2000-02-18
2001-05-01
Powell, William (Department: 1765)
Semiconductor device manufacturing: process
Chemical etching
Liquid phase etching
C156S345420, C216S091000, C216S092000, C438S748000
Reexamination Certificate
active
06225235
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention concerns a method and a device for cleaning and etching disc-shaped substrates (wafers) using wet chemistry, for the production of micro-electronic components.
In addition to physical cleaning methods (e.g. brush cleaning, megasonic vapor cleaning), cleaning of wafers, i.e. elimination of contaminants (e.g. organic particle metal-ion contaminants) and natural oxides from the wafer surface, is carried out with high concentration chemicals such as H
2
SO
4
, H
2
O
2
, HF, NF, NH
4
OH, DI—H
2
O (de-ionized water) etc. or with a
mixture of chemicals for e.g. RCA, SC1, SC2 methods. Dipping installations are preferably used for chemical treatment using highly aggressive chemicals, wherein the wafers are dipped into processing basins filled with chemicals.
Dipping installations have the advantage that the wafer is chemically treated on both sides in a bath and the throughput is relatively high due to dipping of several commonly borne substrates in one step.
Disadvantageously, such installations consume-large amounts of chemicals and therefore require a large chemical supply and a large amount of space in the clean room, and are also expensive. Moreover, the treatment of several substrates in one step is only possible due to the long processing times associated with the dipping method.
The larger the component integration on a wafer and the larger the wafer diameters, the greater is the need for reproducible processing of each individual wafer in exactly the same manner. This cannot be reliably achieved in dipping installations.
Spraying and etching systems of conventional construction, e.g. continuous spraying systems, cannot be used, since very aggressive chemicals are required and since the substrate must be treated uniformly on both sides. Moreover, there are extremely strict processing parameter requirements with respect to uniformity of the chemical action, freedom from particles, from metal-ion contamination etc., such that the processing chamber must be constructed in a very specific manner.
Spin processors are sometimes used with which an individual wafer is rotated on a support (chuck) and simultaneously sprayed with chemicals. Disadvantageously thereby is that simultaneous, uniform treatment of the front and rear sides is not possible due to the substrate support. The substrate must be turned in the support and the front and rear sides must be treated, one after the other. If several sequential processes are carried out, the processing time per wafer of spin processors is unacceptably long, resulting in low throughput. Moreover, the required material chemical resistance precludes combination in an installation together with physical cleaning methods.
When several spin processors are used, the plant is unacceptably expensive, excessively large. In addition, handling between the processors is unacceptably demanding and expensive.
It is therefore the underlying purpose of the invention to provide a method and a device for wet chemical cleaning and etching of disc-shaped substrates (wafers) which permits simultaneous processing of several wafers, wherein individual substrates can be processed simultaneously, on both sides, using chemical methods.
SUMMARY OF THE INVENTION
This object is solved in accordance with the invention with a method and a device as claimed.
The object is solved in accordance with the inventive device and method, wherein the wafer to be treated is held vertically in a support at the edge area (3 points). The support can be rotated by a drive. This rotating support is disposed in a processing chamber comprising two parts, which is opened for loading the wafer. The treatment chemicals are sprayed onto the substrate from both sides with the processing chamber closed. The substrate is rotated during spraying. This effects uniform distribution of the medium on the surface as well as centrifugation of the chemicals, already active on the surface and therefore depleted. Chemical treatment is followed by rinsing of the substrate with water. The substrate can also be spin-dried for further transport. After rinsing, the processing chamber is opened, the substrate is removed from the substrate support via a gripping device and e.g. passed, via a transport means or a handling robot, to the next processing chamber of identical construction for further chemical treatment, or loaded into a centrifuge for drying. By providing several processing chambers, the substrates which are each transported from chamber to chamber can be processed simultaneously in the respective chamber to effect a correspondingly high throughput.
A substantial advantage of the invention is the high etching rate homogeneity due to the uniform chemical action, the small amount of particles generated and the low metal-ion contamination. Moreover, the throughput is high, a combination of physical and chemical cleaning methods, within an installation, is easy to realize and the required space for the installation in the clean room is low for the ever increasing substrate sizes (e.g. 300 mm, 400 mmm etc.).
The processing chamber is constructed symmetrically with respect to rotation to minimize turbulences of the rotating substrate. In addition to the rotationally symmetric construction of the substrate support and the processing chamber, the shape and surface characteristics of all parts in the chamber is selected to facilitate simple but highly thorough rinsing and therefore automatic cleaning of the processing chambers which also minimizes particle contamination in the processing chamber.
The very simple construction of the processing chamber and the substrate support permits manufacture from plastic materials resistant to the aggressive chemicals used to thereby also satisfy the high requirements for low metal contamination.
The closed processing chamber allows use of aggressive chemicals without having to take costly precautions for the entire installation with respect to material resistance and safety. Vertical processing of the wafer facilitates construction of an installation which is small in size. The sprayed and centrifuged chemicals are collected in the processing chamber via an outlet and are regenerated. This ensures minimum use of chemicals and a steady etching rate homogeneity from substrate to substrate, since each substrate is processed under the same conditions (constant chemical concentration).
To optimize processing of each individual wafer, end point detectors can also be used to allow optimum processing control for each wafer without having to e.g. precisely keep the media parameters (temperature, concentration, sprayed amount etc.) constant from wafer to wafer, since processing is controlled by the detector.
To avoid cross contamination throughout the installation, a reciprocating wafer transport system is used which transports each wafer from only one processing station to the next and, after transport, returns to the initial position. This prevents transport of particles, as can occur e.g. with a continuous conveyer belt.
The nozzles for spraying the chemicals are cleaned by subsequent spraying of rinsing media (in most cases water) between the processing steps. This is achieved by connecting the spraying nozzle to a valve battery to allow different chemicals to be sprayed, one after another, and also to allow the spray nozzle to be rinsed with water.
The chemicals can be supplied using a combined valve battery and mixing device to define a mixing ratio of the etching solution composition, optionally, directly before spraying. This is particularly important when chemical mixtures are used which tend to decompose and can therefore not be stored in the form of a mixture for long periods of time.
Spraying of different processing chemicals from various nozzles is also possible, with the chemicals first being mixed together on the substrate surface.
In accordance with the invention, some or all cleaning, etching and spraying processes can be carried out sequentially in a processing chamber, e.g. in laboratories. Rinsing and, optionally, clean
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