Wafer handling system and wafer handling method

Details Wafer handling system and wafer handling method Wafer handling system and wafer handling method

2002-07-01

2004-07-27

Hess, Douglas (Department: 3651)

Material or article handling

Apparatus for moving material between zones having different...

C414S936000, C414S939000, C414S941000

Reexamination Certificate

active

06767170

ABSTRACT:

BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to a wafer handling system including a wafer holder and a wafer chuck. The wafer holder has a set of minimum contact wafer support members predefining support member contacting portions on a planar wafer surface of a wafer. The wafer chuck has a wafer support region for supporting the wafer. The wafer support region is constructed for contacting the planar wafer surface. The wafer holder and the wafer chuck have a relative position to each other which includes a distance extending in a horizontal direction.
The invention further refers to a wafer handling method for moving a wafer between a wafer holder and a wafer chuck.
In semiconductor product manufacturing, semiconductor wafers are processed in order to form integrated circuits thereon. A single wafer is subjected to about a few hundred processing steps that are performed in several processing tools.
Wafer processing requires the wafer to be positioned very precisely during some process steps that define an integrated circuit structure. Especially during lithographic exposure, it is very important that the wafer is very precisely positioned in a lithography tool to achieve sufficient alignment with integrated structures already existing on the wafer.
Wafer positioning includes correctly laterally adjusting the wafer position. This is commonly accomplished by steppers used for multiple exposure in lithography tools.
Furthermore, precise wafer positioning requires the wafer position in the direction perpendicular to the planar wafer surface to be sufficiently controlled. As each wafer is exposed to exposure light from this direction during a lithography step, the distance between the wafer and the exposure beam source, or if the wafer is oriented horizontally during exposure, the vertical position of the wafer, has a great influence on focus control. Any deviation of the vertical position of the upper wafer surface, which is being exposed, from the required position leads to defocusing and as a consequence, to the production of lithographic structures of minor quality. Wafers exposed in such a way often are rejected because of a bad critical dimension or misalignment with existing integrated structures.
Due to progressing miniaturization and integration, the exposure wavelength and as a consequence, the depth of focus achievable with the respective wavelength has decreased. Current lithography tools generate exposure light of a wavelength of 248 or 193 nm in the UV-range. Operating in this sub-&mgr;-range requires the wafer to be highly precisely positioned in the direction perpendicular to the plane of the wafer surface.
In a lithography tool, a wafer chuck supports the backside of the wafer from below and thereby adjusts the height of the upper-wafer surface that will be exposed. The wafer chuck has a wafer support region for receiving the wafer and is constructed for contacting the lower planar wafer surface. The cross section of the wafer support region is substantially equal to the circumference of the planar wafer surface of the wafers that will be supported.
When a wafer is resting on the wafer chuck, the height of the wafer in general is predefined by the height of the chuck or its wafer support region, respectively. However, often the back surface of the wafer has microscopic protrusions or elevations unintentionally produced during preceding processing steps. There may be various processing steps leading to such irregularities. Predominantly hot diffusion and deposition processes performed in high temperature furnaces cause these elevations.
There are at least two effects producing elevations on the contacted lower surface of a wafer in a high temperature furnace.
First, the speed of deposition of substances that will be deposited onto a wafer that is accessible from both sides is increased in the direct vicinity of the support member contacting portions of the backside of the wafer. Adjacent to these support member contacting portions of the wafer and support members supporting the wafer at these contacting portions, process gas flow is inhibited by the presence of a finger-like quartz support member, for instance. This may lead to an increased deposition rate near the contact area.
Second, the thermal expansion of the silicon wafers themselves relative to the quartz fingers may lead to the production of scratches from the lateral movement of the quartz finger tips relative to the lower wafer surface. Current hot diffusion processes require temperatures of 1000° C. and above, thereby producing a comparatively large movement due to thermal expansion. Furthermore, current 300 mm-wafers are rather heavy and because of their weight produce a high pressure onto the quartz finger tips. When the position of a wafer is displaced relative to a quartz finger due to thermal expansion, the movement of the quartz finger relative to the lower wafer surface produces scratches surrounded by elevating walls on both sides of the scratches. The weight of a 300 mm-wafer leads to the quartz finger tip providing a relatively high pressure onto the lower wafer surface, and as a consequence, to deeper scratches and higher adjacent elevating walls.
These irregularities deteriorate the planarity of the back surface of the wafer, and when the wafer is resting on the wafer chuck, lead to misalignments of the wafer position in the direction perpendicular to the wafer surface. As a consequence, defocusing is caused during lithographic exposure.
Whereas overall deviations from the height of a wafer supported by a wafer chuck may be corrected by appropriate wafer chuck positioning, local misalignments of the wafer position cannot be corrected in this way.
Due to the elasticity of the wafer material (like silicon or another metal) a wafer having microscopic elevations on its lower wafer surface is resting slightly deformed on the wafer chuck. In those surface regions covered with microscopic elevations and in their vicinity, the upper surface of the wafer is slightly elevated compared to surrounding portions of the upper wafer surface.
Hence the elevations on the lower wafer surface are locally lifting the wafer from the wafer chuck, whereas remote from these elevations the wafer surface is slightly concavely deformed and resting on the wafer chuck in direct contact to the wafer support region of the chuck.
Thereby local regions of defocussing, so-called focus spots, are caused at the lateral position of the backside elevations when a wafer is exposed to exposure light. In the area of the focus spots, the upper wafer surface is located out of the depth of focus. Thereby wafer surface is wasted because some semiconductor products produced will be rejected.
There are various attempts to overcome this problem by cleaning the wafer backside. However, all of these cleaning methods do not successfully remove the elevations from the back surface of the wafers.
It has been recognized that sometimes the focus spot vanishes after rotating the wafer on the wafer chuck. In the case of a vacuum chuck, for example, a ring chuck or a pin chuck, the wafer support region of the chuck has a multitude of pins or concentric rings forming the contact area for contacting the backside of a wafer. If a wafer is resting on such a vacuum chuck and an elevation is located on one of the pins or rings, the focus spot appears. In the case that the elevation is located just between adjacent pins or rings, the focus spot vanishes.
However, according to this method there is only an accidental chance of overcoming the problem of local wafer lifting in this way and additional efforts for surveying the appearance of focus spots are required.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a wafer handling system and a method for moving a wafer between a wafer holder and a wafer chuck which overcomes the abovementioned disadvantages of the prior art apparatus and methods of this general type.
In particular, it is an object of the invention to reliably avoid the appearan

Affiliated with

Also associated with

Rating

Wafer handling system and wafer handling method does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Wafer handling system and wafer handling method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Wafer handling system and wafer handling method will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3257358