Coating processes – Measuring – testing – or indicating
Reexamination Certificate
1999-04-27
2001-07-31
Bareford, Katherine A. (Department: 1762)
Coating processes
Measuring, testing, or indicating
C427S240000, C118S052000, C118S688000, C118S712000
Reexamination Certificate
active
06268013
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of coating a film on an object such as a semiconductor wafer or an LCD substrate, an apparatus for coating a film on such an object, and an apparatus for counting particles existing in the coating liquid.
In the manufacture of a semiconductor device, a circuit pattern is formed by means of so-called photolithography. The photolithography comprises the steps of: coating a photoresist on a semiconductor wafer, exposing the photoresist to light by using a photomask, and developed the photoresist thus exposed to light.
In the photoresist-coating step, the resist liquid is applied on to the center part of the semiconductor wafer from a nozzle located above the wafer, while the wafer held on a spin chuck is spinning at high speed. The resist liquid thus applied spread by virtue of the centrifugal force the wafer exerts while spinning. As a result, a resist film having an uniform thickness is formed on the entire surface of the semiconductor wafer.
The semiconductor wafer with the resist film coated on it is subjected to heat treatment, light-exposure, development and etching. A circuit pattern is thereby formed on the semiconductor wafer. The circuit pattern may not be a desired one if the resist film contains particles.
To form a resist film containing as few particle as possible, a filter is interposed between the nozzle and the resist liquid source to filter out particles from the resist liquid. The efficiency of the filter gradually decrease with time. Hence, the filter may fail to filter out particles after a long use. Unless the filter is replaced with a new one, many particles will remain in the resist liquid.
To decide whether or not the filter should be replaced with a new one, it is necessary to determine how much the efficiency of the filter has decreased. To this end it is required that the particles in the resist liquid be counted before the liquid is applied to semiconductor wafers. It is proposed that the particle counters commercially available be used to count the particles in the resist liquid.
Here arises a problem. The conventional particle counters are designed to count particles existing in low-viscosity liquids such as pure water and hydrofluoric acid, not to count particles in a high-viscosity liquid such as resist liquid which has viscosity of several cP to several hundred cP. If a conventional particle counter is placed between the nozzle and the semiconductor wafer and used for a long time to count particles in the resist liquid applied from the nozzle, the resist liquid sticks to the inner wall of the optical cell of the counter. Much time and labor are required to wash the particle counter. In view of this, the conventional particle counter cannot be used in an in-line fashion as is employed to count particles existing in pure water or hydrofluoric acid.
The counter must therefore be located outside the line of manufacturing semiconductor devices. In this case, the resist liquid must be sampled, and samples must be supplied to the particle counter. This also requires much time and labor.
The conventional particle counter cannot be used to count particles in the resist liquid, for another reason. It applies a light beam, such as a laser beam, to a liquid to count particles existing in the liquid. When the conventional particle counter applies a light beam to the resist liquid, the resist liquid emits light. This makes it difficult for the counter to count particles in the resist liquid with a sufficiently high accuracy.
BRIEF SUMMARY OF THE INVENTION
The first object of the invention is to provide a method of coating a film on a substrate, in which before a coating liquid (e.g., a resist liquid) is applied to the substrate from a liquid-applying member such as nozzle, it is determined whether the coating liquid contains impurities (e.g., particles) in an amount so large as to lower the yield of products to be made by using the film.
The second object of the present invention is to provide an apparatus which performs the film-coating method described above.
The third object of this invention is to provide an apparatus for coating a film on a substrate, in which the particles in the coating liquid used can be counted in in-line fashion.
The fourth object of the present invention is to provide an apparatus for counting the particle in such a coating liquid, in in-line fashion.
A first coating method designed to attain the first object is a method of coating a film on a substrate by applying a coating liquid to the substrate located at a first position. The method comprises the steps of: applying the coating liquid at a second position (generally known as “dummy dispensing position”) before applying the coating liquid at the first position; and detecting impurities contained in the coating liquid applied at the second position.
In most cases, the first position is above the center of the substrate. It suffices to set the second position away from the first position. Preferably, the second position should be set in an area not above the substrate, so that the coating liquid applied at the second position may not be applied to the substrate. To detect impurities, if any, contained in the liquid applied at the second position, the liquid may be collected, and a device such as a particle counter may be used to detect the impurities in the collected liquid.
As described above, the coating liquid is applied at the second position before it is applied at the first position, and the impurities contained in the liquid applied in the second position are detected. Hence, before applying the coating liquid to the substrate it can be determined whether too many particles exist in the coating liquid. The impurities may be detected immediately before the liquid is applied in the first position, at regular intervals, or every time the liquid is applied a prescribed number of substrates.
A second coating method designed to attain the first object is a method of coating a film on a substrate by applying a coating liquid to the substrate located at a first position, from one of a plurality of liquid-applying members. This method comprises the steps of: selecting one of the liquid-applying members; applying the coating liquid from the selected liquid-applying member at a second position before applying the coating liquid at the first position; and detecting impurities contained in the coating liquid applied at the second position; and moving the selected liquid-applying member to the first position and applying the coating liquid from the selected liquid-applying member to the substrate, only when the impurities are contained in the liquid in an amount less than a reference value.
Since a plurality of liquid-applying members are used in the second method, any desired one can be selected and used to apply the coating liquid to the substrate.
In the second method, the selected liquid-applying member is moved to the first position and applies the coating liquid to the substrate, only when the impurities are contained in the liquid in an amount less than a reference value. Thus, it can be determined whether or not too many particles exist in the coating liquid, before the coating liquid is applied to the substrate, as in the first method. If the impurities are contained in the liquid in an amount equal to or greater than the reference value, the selected liquid-applying member is not moved to the first position and the coating liquid is not applied to the substrate at all.
A first coating apparatus designed to achieve the second object is an apparatus for coating a film on a substrate by applying a coating liquid from a liquid-applying member to the substrate located at a first position. The apparatus comprises: a receptacle located at a second position, for receiving the coating liquid applied from the liquid-applying member; and a detecting device for detecting impurities contained in the coating liquid applied into the receptacle.
Preferably, the receptacle is located not above the substrate. It may be one whi
Akimoto Masami
Sakamoto Kazuo
Semba Norio
Yoshioka Kazutoshi
Bareford Katherine A.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Tokyo Electron Limited
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