Patent Grant
8218284
The present invention relates generally to an apparatus for increasing electric conductivity to a wafer substrate when exposed to electron beam irradiation. More specifically, the present invention relates to significantly reducing damage on the backside of a wafer substrate.
During electron beam inspection or electron beam lithography process of the semiconductor device fabrication, the substrate surface, i.e. wafer surface, are irradiated with electron beam. If electric contact of the substrate or wafer is incomplete during irradiation of the electron beam onto an insulator film on the wafer, a charge-up of electrons occurs wherein electrons are accumulated on the interface between the wafer and the insulator film. The charging causes deflection of the electron beam during the irradiation thereof to deform the resultant pattern in the electron beam lithography process and the charge-up restrains the signal electrons emanating from the wafer surface thereof deform the image of surface in the electron beam inspection process.
There are many ways to prevent charge accumulation on wafer surface under electron irradiation. Control landing energy of the irradiating electrons, U.S. Pat. No. 6,734,429 of Takagi; eject rare gas molecules onto the wafer surface during electron irradiation, U.S. Pat. No. 6,465,795 of Madonado et al.; irradiate laser on the wafer surface simultaneously with electron irradiation, U.S. Pat. No. 6,753,524 of Matsui et al.; and the most common way utilize electric contact pins to conduct excess charge away, U.S. Pat. No. 6,068,964 of Komori. The electric contact pins make physical contact to the conductive layer on wafer backside (by means of mechanical punch through) or conductive path is formed between the pins and the conductive layer (by electrically breakthrough the insulator layer), stable potential can be obtained on the wafer conductive layer.
With a conventional electric contact pin housing design, the dimension of tolerance of the hole to let pin through is very tight. There is very little degree of freedom to let the pin move while the wafer slid in and the chucking force applied. Slide scratches within 20 to 30 micron level were found on the backside of wafer and became a particle source of other manufacturing processes. These slide scratches are believed scratched by the electric contact pin during the chucking and de-chucking process.
Accordingly, what is needed is a system and method to address the above-identified issues. The present invention addresses such a case.
This invention relates to an apparatus for increasing electric conductivity to a wafer substrate when exposures to electron beam irradiation. More specifically, a more free mechanical contact between a wafer and electric contact pins (within an electrostatic chuck) is provided to significantly reduce the scratch and damage on the wafer backside.
The embodiments of the present invention provide a plurality of electric contact pins that could be used to remove excessive charge with less back side scratch. Herein, the embodiments the shape of the electric contact pins is such that the contact area between the electric contact pin and the semiconductor is effectively increased to reduce scratch.
Other embodiments of the present invention provide some new distributions of electric contact pins, such that the damages induced by the scratch are decreased.
The present invention relates generally to an apparatus for increasing electric conductivity to a wafer substrate when exposures to electron beam irradiation. The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the preferred embodiment will be readily apparent to those skilled in the art and the generic principles herein may be applied to other embodiments. Thus, the present invention is not intended to be limited to the embodiment shown but is to be accorded the widest scope consistent with the principles and features described herein.
Reference will now be made in detail to specific embodiments of the invention. Examples of these embodiments are illustrated in the accompanying drawings. While the invention will be described in conjunction with these specific embodiments, it will be understood that it is not intended to limit the invention to these embodiments. In fact, it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. In the following description, numerous specific details are set forth in order to provide a through understanding of the present invention. The present invention may be practiced without some or all of these specific details. In other instances, well-known process operations are not described in detail in order not to obscure the present invention.
In most of the semiconductor industry, a semiconductor device is manufactured on a single crystal silicon substrate surface. Silicon will act as a conductor under certain conditions; however, the backside surface of the wafer has a layer of silicon oxide which is built up during the manufacturing process. The silicon oxide is an electrical insulator. The accumulated oxide layer usually has a thickness around 700 to 800 nanometers; however, sometimes it may be as thick as 2000 angstrom (0.2 micron). A conventional way to remove excess charge accumulating on the wafer is conducting the charge through electric contact pin(s). In order to conduct the charge away, the electric contact pin(s) needs to punch through the insulating layer to reach the conducting silicon crystal.
With a conventional electric contact pin housing design, the dimension of tolerance of the hole to let pin through is very tight. There is very little degree of freedom to let the pin 12 move while the wafer 16 is slid in and the chucking force is applied. Slide scratches within 20 to 30 micron level were found on the backside of wafer 16 and became a particle source of other manufacturing processes. These slide scratches are caused by the movement of electric contact pin 12 during the chucking and de-chucking process.
One embodiment to resolve the backside sliding scratches is to redesign the electric contact pin housing-hole.
Accordingly, an electric contact pin and an electrostatic chuck with a reconfigured pin housing hole form an apparatus for reducing charge density on a wafer. Herein, as disclosed by some embodiments, for each proposed pin housing hole, the opening of the pin housing hole is significantly wider than a corresponding portion of an electric contact pin located in a pin housing hole. For example, with a wide open housing-hole design, a 360 degree free rotation of the electric contact pin is provided. Of course, to achieve a 360 degree free rotation, the electric contact pin could be located on a spring. Moreover, the spring constant of the spring should be chosen to properly to control the motion of the electric contact pins to counteract the chucking and/or de-chucking force.
Other embodiments to resolve backside scratches is to redesign the shape of electric contact pin.
The other embodiment proposed to minimize backside scratches is to distribute the pin housing holes, (i.e. these electric contact pins) in a different position. In the embodiment, the pin housing holes are positioned on a minor area of the electrostatic chuck 14. Herein, the minor area means that the corresponding area of the wafer has less device pattern. For example, the minor area could correspond to an edge of the wafer. Herein, an example is shown in
Although the present invention has been described in accordance with the embodiments shown, one of ordinary skill in the art will readily recognize that there could be variations to the embodiments and those variations would be within the spirit and scope of the present invention. Accordingly, many modifications may be made by one of ordinary skill in the art without departing from the spirit and scope of the appended claims.
| Number | Name | Date | Kind |
|---|---|---|---|
| 5625526 | Watanabe et al. | Apr 1997 | A |
| 6068964 | Komori | May 2000 | A |
| 6465795 | Madonado et al. | Oct 2002 | B1 |
| 6511897 | Arima et al. | Jan 2003 | B2 |
| 6606234 | Divakar | Aug 2003 | B1 |
| 6665168 | Lin | Dec 2003 | B2 |
| 6734429 | Takagi | May 2004 | B2 |
| 6753524 | Matsui et al. | Jun 2004 | B2 |
| 7123350 | Akutsu et al. | Oct 2006 | B2 |
| 7408760 | Tanimoto et al. | Aug 2008 | B2 |
| 20070089672 | Shimamura et al. | Apr 2007 | A1 |
| 20080100983 | Purohit et al. | May 2008 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 20100019462 A1 | Jan 2010 | US |
