Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Reexamination Certificate
2001-05-31
2002-12-17
Walberg, Teresa (Department: 3742)
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
C219S405000, C219S411000, C118S724000, C118S725000, C392S416000, C392S418000
Reexamination Certificate
active
06495802
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to controlling the temperature of partial areas of a substantially flat object. More particularly, the present invention relates to a temperature-controlled chuck to hold a substantially flat object. With such a temperature-controlled chuck the temperature distribution of the substantially flat object can be sensed or measured, and due to temperature influencing elements the temperature of partial areas of said object's back side can be altered to obtain a more uniform temperature distribution. Furthermore, the present invention relates also to a temperature-controlled wafer chuck and a method for controlling the temperature of a substantially flat object such as a wafer. Finally, the invention relates also to a pre-align station of an exposure tool for wafers comprising a temperature-controlled wafer chuck, and relates to an exposure wafer chuck in an exposure tool for wafers comprising a wafer chuck with which the temperature of a wafer can be measured and influenced as desired.
BACKGROUND OF THE INVENTION
Integrated circuits are typically constructed by depositing a series of individual layers of predetermined materials on a wafer-shaped semi-conductor substrate, or “wafer”. The individual layers of the integrated circuit are in turn produced by a series of manufacturing steps. For example, in forming an individual circuit layer on a wafer containing a previously formed circuit layer, an oxide such as silicon dioxide is deposited over the previously formed circuit layer to provide an insulating layer for the circuit. A pattern for the next circuit layer is then formed on the wafer using a radiation alterable material, known as photoresist.
Photoresist materials are generally composed of a mixture of organic resins, sensitizers and solvents. Sensitizers are compounds such as diazonaphthaquinones, that under go a chemical change upon exposure to radiant energy, such as visible and ultraviolet light. The irradiated sensitizer material has different solution characteristics with respect to various solvents than the non-irradiated material allowing for selective removal of the photoresist. Resins are used to provide mechanical strength to the photoresist and the solvents serve to lower the viscosity of the photoresist so that it can be uniformly applied to the surface of the wafers.
After a photoresist layer is applied to the wafer surface, the solvents are evaporated and the photoresist layer is hardened, usually by heat treating the wafer. The photoresist layer is then selectively irradiated through the use of a radiation opaque mask. The mask contains transparent portions that define the pattern for the next circuit layer. The mask is placed over the photoresist layer and the photoresist covered by the transparent portion is irradiated. The wafer is removed and the photoresist layer is exposed to a process liquid, known as developer. The developer selectively solubilizes and removes either the irradiated or the nonirradiated photoresist exposing portions of the underlying insulating layer.
The exposed portions of the insulating layer can be selectively removed using an etchant to expose corresponding sections of the underlying circuit layer. In this process, the photoresist should be more resistant to the etchant than the insulating layer to limit the attack of the etchant to only the exposed portions of the insulating layer. Alternatively, the exposed underlying layer(s) can be implanted with ions which do not penetrate the photoresist layer thereby selectively penetrating only those portions of the underlying layer not covered by the photoresist. The remaining photoresist is then stripped using either a solvent, or a strong oxidizer in the form of a liquid or a gas in the plasma state. The next layer is then deposited and the process is repeated until fabrication of the semiconductor device is complete.
Thermal gradients in wafers during lithography exposure create linear pattern transfer effects due to expansion or contraction. Wafers can have temperature instability due to previous processing from a photoresist track hot plate. If this bake is non-uniform or the cooling prior to wafer transfer into the exposure tool is not complete, non-linear effects will occur. During the transfer from the track to the exposure tool there may not be adequate time for the wafer to thermally stabilize prior to exposure. This effect causes pattern transfer errors, seen as overlay or grid distortion and chip magnification errors. Other sources of non-linear errors can occur outside of lithography processing. These sources include rapid thermal processing such as anneal (RTA), film deposition processing (such as diffusion or chemical vapor deposition-CVD), and chemical mechanical polishing (CMP). These non-linear errors are variable across the wafer and are difficult to correct when severe.
A temperature difference as small as 0.1° C. can affect overlay. Wafers can only equilibrate through conduction with the exposure tool environment or contact with non-temperature regulated surfaces, so-called chucks. There are defects during lithography processing known as “banana effect” problems due to wafer contact non-uniformity on the track hotplate that cause significant temperature gradients over the wafer that result in overlay issues in these areas. Banana effect non-linear errors typically occur on the edge regions of the wafer in a semicircle pattern that resembles a banana shape. The magnitude of these non-linear errors varies significantly across the effected region, and therefore are difficult to correct using normal lithography processing.
Thus, it is apparent that a need exists for an improved chuck to hold a substantially flat object such as a wafer and a method for controlling the temperature of a wafer in a pre-align station or an exposure tool, which overcomes, among other things, the above-discussed problems to produce a more uniform temperature distribution over the surface of the wafer.
Furthermore, it is an object to provide an improved chuck with which the temperature of localized areas of a generally flat object, particularly a wafer, can be influenced in a desired manner to reduce significant temperature gradients over the wafer or to use defined temperature peaks or temperature depths in localized areas of a wafer to reduce or eliminate distortions of the wafer grid.
BRIEF SUMMARY OF THE INVENTION
The above objects and others are accomplished by a temperature-controlled chuck and a method for controlling the temperature of a substantially flat object such as a semiconductor wafer, in accordance with the present invention. The temperature-controlled chuck according to the invention comprises a chuck body having an object support side and a back side, said object support side holding a substantially flat object having a front side and a back side on said back side of said object. A plurality of temperature sensing elements is distributed on said object support side to measure the temperature distribution of said object. A plurality of individual temperature influencing elements is distributed on said object support side to face said back side of said flat object, each of said temperature influencing elements being arranged to influence the temperature of a partial area of said object's back side as desired.
A temperature-controlled chuck according to the invention provides the possibility to influence the temperature of a wafer, particularly the back side of a wafer, in a partial area in a manner as desired. For example, by use of an inventive temperature-controlled chuck the temperature can be varied precisely in tenths of a degree centigrade and be controlled overall to ±1° C. Hence, a good temperature uniformity across the whole wafer would be provided. It is also possible to provide local modification to correct process distortions on a wafer. If, for example, the temperature in partial areas of the wafer can be precisely controlled, then it is also possible to use a variation of the chuck temper
Charles Alain B.
Maltabes John G.
Mautz Karl E.
Fuqua Shawntina T.
Walberg Teresa
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