Patent Application
20070182948
1. Field of the Invention
The present invention relates to a semiconductor exposure process. More particularly, the present invention relates to a semiconductor exposure method and a method of controlling a semiconductor exposure apparatus.
2. Description of the Related Art
With our increasing demand for higher level of integration in integrated circuits, the size of circuit devices continues to decrease. In the semiconductor manufacturing, the process most sensitive to device miniaturization is photolithography. In particular, the wafer exposure process in photolithography is one of the most important processes that have a direct effect on the pattern fidelity.
As semiconductor production enters the nanometer era, the resolution of the older generation of exposure apparatus has become severely inadequate. To resolve this problem, a technique called immersion exposure has been developed. In the immersion exposure process, the wafer is exposed through pure wafer. The advantage of this type of exposure apparatus can be realized using the following formula:
Resolution=k×λ/NA (1),
where k s a processing constant, λ is the wavelength of the light source in the exposure, NA is the numerical aperture. Furthermore, the numerical aperture can be represented by the following formula:
NA=n×sin θ, (2)
where n is the refractive index when the exposure light source passes through the dielectric, and θ is the incident angle of the exposure light source.
Therefore, with the same lens and under the same exposure light source condition, reducing the resolvable minimum distance or minimal resolution demands an increase in the NA value. To increase NA, one method is to increase the value of the refractive index n. For example, if the exposure light source is ArF, then using a medium having a refractive index larger than air (generally not greater than 1) such as a pure wafer (n is about 1.4) can reduce the minimal resolution.
When this type of exposure apparatus is used to carry out an exposure, the supporting platform 102 is frequently moved to adjust the expose region of the wafer 110. Thus, before carrying out each exposure, the supporting platform 102 must be aligned to ensure the accuracy of the subsequent exposure location. However, because the supporting platform 102 contains pure water, the alignment accuracy provided by a conventional light source may be compromised due to the presence of wafer.
Accordingly, at least one objective of the present invention is to provide a semiconductor exposure method that allows a supporting platform to be precisely aligned.
At least a second objective of the present invention is to provide a method of operating a semiconductor exposure apparatus that can precisely control the location of a supporting platform inside an immersion exposure apparatus.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a semiconductor exposure method suitable for exposing a wafer through an exposure apparatus. The semiconductor exposure apparatus comprises at least an exposure lens, a platform for supporting the wafer and a liquid-circulating device. The liquid-circulating device supplies a liquid to the space between the wafer and the exposure lens during exposure. One major feature of the present invention is that at least one alignment light source is used to perform an alignment operation for aligning the supporting platform before the actual exposure. The alignment light source has a particular wave length in which the effect on the alignment light source due to the evaporation of liquid is minimized to prevent the liquid from affecting the alignment operation.
According to the aforementioned semiconductor exposure method in the preferred embodiment of the present invention, the alignment operation includes aligning the light source with the X-axis and the Y-axis of the supporting platform.
According to the aforementioned semiconductor exposure method in the preferred embodiment of the present invention, the liquid-circulating device provides a liquid including pure water, glycerin or perfluoro polymer.
According to the aforementioned semiconductor exposure method in the preferred embodiment of the present invention, the light source for performing the alignment includes a XeCl, N2, XeF, pulsed dye laser or a continuous wave (CW) laser.
According to the aforementioned semiconductor exposure method in the preferred embodiment of the present invention, the particular wavelength of the light source ranges between 300 nm and 450 nm.
According to the aforementioned semiconductor exposure method in the preferred embodiment of the present invention, the exposure apparatus includes a stepper exposure machine.
According to the aforementioned semiconductor exposure method in the preferred embodiment of the present invention, the exposure light source used in the exposure apparatus includes a laser.
The present invention also provides a method of operating a semiconductor exposure apparatus such as an exposure machine. The exposure machine includes at least an exposure lens, a platform for supporting a wafer and a liquid-circulating device. The liquid-circulating device supplies a liquid to the space between the wafer and the exposure lens during exposure. One major feature of the method is that at least one alignment light source is used to control the position of the supporting platform. The alignment light source has a particular wavelength, in which the effect on the light source due to the evaporation of liquid is minimized to prevent the liquid from affecting the positioning of the supporting platform.
According to the aforementioned method of operating the semiconductor exposure apparatus in the preferred embodiment of the present invention, the step for controlling the position of the supporting platform includes emitting a light beam from a first interferometer to detect the X-axis of the supporting platform and then emitting a light beam from a second interferometer to detect the Y-axis of the supporting platform.
According to the aforementioned method of operating the semiconductor exposure apparatus in the preferred embodiment of the present invention, the liquid-circulating device provides a liquid including pure water, glycerin or perfluoro polymer.
According to the aforementioned method of operating the semiconductor exposure apparatus in the preferred embodiment of the present invention, the above particular wavelength ranges between about 300 to 540 nm.
According to the aforementioned method of operating the semiconductor exposure apparatus in the preferred embodiment of the present invention, the light source includes a XeCl, N2, XeF, pulsed dye laser or a continuous wave (CW) laser.
According to the aforementioned method of operating the semiconductor exposure apparatus in the preferred embodiment of the present invention, the exposure apparatus includes a stepper exposure machine.
According to the aforementioned method of operating the semiconductor exposure apparatus in the preferred embodiment of the present invention, the exposure light source used in the exposure apparatus includes a laser.
In the present invention, a light source having a wavelength set within a specified range is used to align or control the position of the supporting platform of the exposure apparatus. Hence, the liquid contained within the supporting platform is prevented from affecting the aligning operation. Consequently, the accuracy of the pattern transfer after the exposure process is improved.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.
In step 210, the wafer is placed on a supporting platform containing a liquid inside an exposure apparatus. The exposure apparatus of the present embodiment includes at least an exposure lens, a platform for supporting the wafer and a liquid-circulating device. The liquid-circulating device supplies the aforementioned liquid to the space between the wafer and the exposure lens during exposure. The liquid such as pure water, glycerin or perfluoro polymer described in
Because the wafer is disposed on the supporting platform, an alignment operation using at least a pair of aligning light sources is carried out to align the supporting platform in step 220 so that the wafer is precisely aligned with respect to the exposure lens. The aligning light source has a particular wavelength in which the effect on the aligning light source due to the evaporation of liquid is minimized. Further, the particular wavelength of the aligning light source is selected to be within a range that is the least interfered by the evaporation of liquid in the environment. In other words, the particular wavelength of the aligning light source is selected to be within a range that is less likely to be absorbed by the liquid to prevent the liquid from affecting the alignment operation. For example, when the liquid is pure water, the particular wavelength of the aligning light source is set within the 300˜540 nm range. The light source for performing the alignment includes, for example, XeCl, N2, XeF, pulsed dye laser or a continuous wave (CW) dye laser. The aforementioned aligning operation includes aligning the aligning light source with the X-axis and Y-axis of the supporting platform.
In step 230, an exposure of the wafer is carried out using a laser as the light source. In the present embodiment, if the exposure apparatus is a stepper exposure machine, then the control is returned to step 220 after the first exposure to perform another alignment of the supporting platform and get ready for the next exposure. This process is repeated until the exposure for the entire wafer is completed.
In summary, the present invention uses a light source having a wavelength set within a specified range to align or control the position of the supporting platform of the exposure apparatus. Hence, the liquid contained within the supporting platform is prevented from affecting the aligning operation. Consequently, the accuracy of the pattern transfer after the exposure process is improved. In other words, the method in the present invention is advantageous to the fabrication of nanometer grade semiconductor devices.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.
