Temperature processing module

Details Temperature processing module Temperature processing module

1999-12-08

2002-03-05

Paik, Sang (Department: 3742)

Electric heating

Heating devices

Combined with container, enclosure, or support for material...

C118S725000

Reexamination Certificate

active

06353209

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
This invention relates generally to thermal processing of semiconductor substrates including wafers, quartz reticles and LCD flat panel displays. More particularly, it relates to an integrated procedure of baking and subsequently chilling a substrate coated with photoresist.
BACKGROUND
The lithography processing sequence for producing integrated circuit lines on semiconductor substrates such as semiconductor wafers, quartz photomask blanks, and LCD flat panel displays, involves coating the substrate with a thin photoresist film. The film is subsequently exposed according to a predefined pattern by an electron beam or optical tool and then chemically developed to produce integrated circuit features. Several of the photoresist processing steps consist of baking the photoresist-coated substrate and then chilling it back to ambient conditions. The bake step is performed for several applications including evaporation of solvent, removal of standing wave effects, hardening of the photoresist, and accelerating chemical reactions for acid catalyzed photoresist. In order to achieve uniform processing, it is essential that spatial temperature variations are minimal throughout the entire trajectory.
The conventional manner of performing the baking and chilling of a substrate is shown in FIG.
1
. An apparatus
20
includes a substrate
10
placed on a typically fixed-temperature hot plate
22
, where it is heated up to a temperature typically between 70° C. and 250° C. for a period of time typically between 3 and 8 minutes for quartz photomask substrates and 30 and 120 seconds for a semiconductor wafer. The transient time, or time it takes the substrate to reach its steady-state processing temperature, is substantially longer for a quartz photomask blank than a semiconductor wafer because of its larger thermal mass (a typical quartz blank is 6 inches square by 0.25 inches thick, whereas a semiconductor wafer is 8 or 12 inches in diameter and less than 0.040 inches thick). After the substrate reaches its processing temperature and is held for a predetermined time, it is then mechanically moved to a fixed-temperature cold plate
24
, where it is chilled to a temperature typically between 0 and 30° C.
There are several disadvantages to this method of processing substrates. First, the movement of the substrate through the air from the hot plate
22
to the cold plate
24
causes the substrate to experience uncontrolled and nonuniform temperature fluctuations that persist during the entire cool down step. Second, uncontrolled temperature nonuniformities during the bake or chill steps may arise due to nonuniform convection currents over the substrate, especially with a square geometry of a quartz photomask substrate or a large 300 mm diameter of a silicon wafer. Third, the time required to move the substrate between the plates prevents the realization of very short thermal transition times between the bake and chill steps. Fourth, the procedure requires two distinct processing modules leading to an increased equipment footprint and the inability to integrate the module within other processing modules, such as the exposure tool. Fifth, the mechanical movement of the hot substrate between the plates may contaminate or otherwise damage the substrate. Sixth, the substrate is initially placed on a hot plate thereby making inaccuracies of the substrate's temperature lowering mechanism inducing temperature nonuniformities that persist during the entire heating transient when one part of the substrate comes into proximity with the cold plate before another.
Referring to
FIG. 2
, a prior photoresist processing system
30
for silicon wafers, described in U.S. Pat. No. 5,431,700 by Sloan, discloses an apparatus where one of the plates, e.g., the hot plate
32
is placed upside down and directly above the other plate, e.g., cold plate
34
. A lifting mechanism moves the substrate
10
only a short distance between the two plates. This approach reduces the nonuniform temperature induced by the wafer movement. However, the substrate still needs to be placed on constant temperature plates and the movement of the substrate is still required leading to nonuniform temperature deviations.
Referring to
FIG. 3
, another prior art photoresist processing system
40
, described in U.S. Pat. No. 5,802,856 and incorporated herein by reference, includes a single integrated bake/chill plate
42
. A passage is formed through the plate
42
. To raise the temperature of the substrate
10
, a hot fluid (e.g. between 70° C. and 250° C.) from a hot fluid supply
46
is introduced through passage
44
via a pipe
45
. To lower the temperature of the substrate
10
, cold fluid (e.g. between 0° C. and 30° C.) from a cold fluid supply
48
is introduced through passage
44
. This system includes a resistive heat device
49
on the surface of the unit to improve temperature transients and steady-state holds. The resistive heater may be configured in a multizone arrangement to achieve improved temperature nonuniformity.
This system
40
eliminates the mechanical movement of the substrate during the temperature cycle and eliminates the placement of a cold substrate on a hot plate and vice versa. However, there are several disadvantages to the system. First, the entire apparatus is cycled in temperature. This procedure increases the energy requirements well beyond the theoretical minimum required to heat and cool the substrate. In addition, the hot fluid transportation through pipe
45
may pose a safety threat to personnel working close to the system in addition to nearby equipment that can become contaminated in case of a leak. Further, the fluid heat exchanger systems are bulky and expensive. In addition, the thin resistive heater placed on the surface of the exchanger, e.g. kapton, normally has operational limits of 200 to 250° C. that prevent the realization of higher operating temperatures.
OBJECTS AND ADVANTAGES OF THE INVENTION
It is a primary object of the present invention to provide an improved method and apparatus for the spatial temperature control of material substrates. The method and apparatus may include, but is not limited to, thermal cycling. Such material substrates are quartz photomask blanks and silicon wafers. In particular, it is an object of the present invention to provide a method and apparatus that reduces the energy requirements, provides exceptional multizone temperature control of the substrate, improves reliability and increases the upper limit on temperature processing. An additional advantage of the present invention is the reduction of thermal deflection of the heating elements because of the length to thickness aspect ratio of the heating elements. Further advantages of the invention will be apparent from the following description and drawings.
SUMMARY OF THE INVENTION
This invention is concerned with a module for the temperature control of a material substrate. The module includes a plurality of independent thermally-conductive heating elements arranged in a planar fashion. An air gap or other suitable resistive material separates each of the thermally-conductive heating elements. The upper surface of the thermally-conductive heating elements is in thermal contact with the substrate. The temperature of the thermally-conductive heating elements is raised by a resistive heating element in thermal contact with it. A support structure holds the thermally-conductive heating elements in a fixed position. A cooling plate may be located in close proximity to and in the backside of the thermally-conductive heating elements. In a preferred embodiment, the cooling plate may rest on top of the support structure, thereby maintaining the support structure at a cold temperature. If maximum cooling is desired, the cooling plate is raised by a lift mechanism to contact the backside of the thermally-conductive heating elements to lower the substrate temperature. Alternatively, because the support structure is itself in thermal contact with the thermally-conductive heating el

Affiliated with

Also associated with

Rating

Temperature processing module does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Temperature processing module, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Temperature processing module will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2871608