Coating processes – Centrifugal force utilized
Reexamination Certificate
1999-09-08
2001-05-29
Beck, Shrive (Department: 1762)
Coating processes
Centrifugal force utilized
C427S425000, C118S052000, C118S320000
Reexamination Certificate
active
06238735
ABSTRACT:
BACKGROUND OF THE INVENTION
The manufacture of integrated circuits involves the transfer of geometric shapes on a mask to the surface of a semiconductor wafer. Thereafter the semiconductor wafer corresponding to the geometric shapes or corresponding to the areas between the geometric shapes is etched away. The transfer of the shapes from the mask to the semiconductor wafer typically involves a lithographic process. This includes applying a photosensitive pre-polymer solution to the semiconductor wafer. The solvent in the pre-polymer solution is removed by evaporation, and the resulting polymer film is then baked. The film is exposed to radiation, for example ultraviolet light, through a photomask supporting the desired geometric patterns. The images in the photosensitive material are then developed by soaking the wafer in a developing solution. The exposed or unexposed areas are removed in the developing process, depending on the nature of the photosensitive material. Thereafter the wafer is placed in an etching solution which etches away the areas not protected by the photosensitive material. Due to their resistance to the etching process, the photosensitive materials are also known as photoresists. These may for instance be sensitive to ultraviolet light, electron beams, x-rays, or ion beams.
The high cost of the photoresist pre-polymer solutions makes it desirable to devise methods of improving the efficiency of the coating process so as to minimize the polymer solution's consumption. Furthermore, thickness uniformity of the photoresist layer is an important criterion in the manufacture of integrated circuits. It ensures satisfactory reproduction of the geometric patterns on the semiconductor wafer.
The solvent in the photoresist tends to evaporate during application, increasing the viscosity of the polymer solution and inhibiting the leveling of the resulting film. This produces thickness non-uniformities. It is therefore desirable to be able to control the rate of evaporation of solvent from the polymer solution.
Environmental humidity is one of the factors affecting the thickness of the photoresist layer. Typically photoresist coating uniformity of the order of 15 to 20 angstroms within a wafer and 20 to 25 angstroms from one wafer to the next and from batch to batch and from day to day is required. This is less than the effect of a 1% difference in relative humidity. Furthermore, in commonly used positive photoresists employing photosensitive diazoquinone compounds, some water content is required to react with products of the photolytic reaction to form required water-soluble carboxylic acids.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the invention to provide a method of and an apparatus for improving the thickness uniformity of a polymer solution applied to a surface of a substrate such as a semiconductor wafer.
It is a further object of the invention to improve the consumption of polymer solutions such as photoresist pre-polymer solutions used in the coating of substrates.
According to the invention there is provided a method of coating a surface of a substrate with a polymer solution which includes mounting the substrate inside an enclosed housing, passing a control gas into the housing through an inlet, depositing the polymer solution onto the surface of the substrate in the housing, spinning the substrate, and exhausting the control gas and any solvent vapour and particulate contaminants suspended in the control gas from the housing through an outlet.
The control gas can be a solvent vapour-bearing gas or a solvent-free gas.
The step of exhausting the control gas and any solvent vapour and contaminants can be performed before, during, or after the deposition step.
The solvent vapor-bearing gas is typically produced by bubbling a gas through a solvent and can include the step of controlling the solvent vapor concentration of the solvent vapor-bearing gas by controlling the temperature of the solvent. The solvent vapor concentration of the solvent vapor-bearing gas can also be controlled by controlling the temperature of the housing or by mixing the solvent vapor-bearing gas with a second gas having a different solvent vapor concentration.
The solvent vapor-bearing gas typically comprises air or an inert gas such as nitrogen.
The control gas can be passed into the housing through a showerhead dispenser located directly above the substrate to ensure continuous, controlled, laminar gas flow over the wafer.
The polymer solution can contain a photoresist polymer, for example, a deep-ultraviolet photoresist polymer.
The method can include the step of passing temperature controlled solvent-free, dry, filtered gas over the coated substrate. The method can also include the step of passing solvent-free, humid gas over the coated substrate; the humidity of the humid gas can be controlled to have the relative humidity required by the polymer solution. The relative humidity lies typically in the range of 40% to 45%. The temperature of the humid gas can also be controlled by means of a temperature and humidity controller.
The step of mounting the substrate in the housing can include securing the substrate to a rotatable chuck, for example, by establishing a vacuum between the substrate and the chuck.
The substrate typically comprises a semiconductor wafer and the solute content in the polymer solution is typically 10% to 50% by weight.
Further, according to the invention there is provided a coating apparatus for coating a surface of a substrate with a polymer solution which includes an enclose housing, a rotatable chuck mounted in the housing for supporting the substrate, a depositing means for depositing the polymer solution onto the surface of the substrate in the housing, a control gas supply means connected in flow communication with the housing for supplying a control gas to the housing, and an exhaust means connected to the housing for exhausting the control gas and any solvent vapour and particulate contaminants from the housing.
The depositing means can include a dispensing head means mounted above the chuck for dispensing a stream of the polymer solution onto the surface of the substrate, the dispensing head means being moveable relative to the substrate. If the substrate has a substantially circular shape, the dispensing head means is typically moveable substantially radially across the surface of the substrate. The depositing means can instead comprise a film extruding means having an extrusion head mounted above the chuck for dispensing a stream of the polymer solution onto the surface of the substrate. In this case, if the substrate is substantially circular in shape, the extrusion head is typically mounted above the chuck for dispensing a radially extending stream of the polymer solution onto the surface of the substrate.
The rotatable chuck is typically connected to a variable speed motor, and the coating apparatus can include a controlling means for controlling the speed of the variable speed motor.
The housing can have an upstream side and a downstream side; the solvent vapor-bearing gas supply means can include an inlet to the housing mounted at the upstream side of the housing, and the exhaust means can include an outlet mounted at the downstream side of the housing. The control gas supply means can include conduits connected in flow communication with the housing , and electrically-controlled valves in at least one of the conduits for controlling the rate of control gas flowing into the housing and the composition of the control gas. The exhaust means can also include a valve means for controlling the exhaustion of the gas and any contaminants from the housing. The solvent vapor-bearing gas supply means can include a clean, dry, filtered gas source and a bubbler connected in flow communication with the housing.
The coating apparatus can, further, include a temperature and humidity controlled gas source connected in flow communication with the housing. The temperature and humidity controlled gas source can include a temperature control means
Dettes Ted C.
Grambow James C.
Gurer Emir
Mandal Robert P.
Sauer Donald R.
Beck Shrive
Calcagni Jennifer
Silicon Valley Group Inc.
Wilson Sonsini Goodrich & Rosati
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