Wafer transfer system with temperature control apparatus

Details Wafer transfer system with temperature control apparatus Wafer transfer system with temperature control apparatus

2002-05-13

2004-01-20

Jiang, Chen Wen (Department: 3744)

Refrigeration

Using electrical or magnetic effect

Thermoelectric; e.g., peltier effect

C136S201000

Reexamination Certificate

active

06679064

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a wafer transfer system, and more particularly to a wafer transfer system with a temperature control apparatus for controlling the temperature of the wafer.
BACKGROUND OF THE INVENTION
In 1821 Thomas Seebeck discovered that an electric circuit would flow continuously in a closed circuit made up of two dissimilar metals (conductors) if the junctions of the metals (conductors) or maintained at two different temperatures. In 1834, a French watch maker and part-time physicist Jean Peltier discovered that an electrical circuit would produce a temperature gradient at the junction of two dissimilar metals (conductors). Stated another way, Peltier discovered that passing current through two dissimilar electrical conductors caused heat to be either emitted or absorbed at the junctions of the conductors. Twenty years later Thomas (Lord Calvin) issued a comprehensive explanation of the Seebech and Peltier Effects and described their interrelationship.
It was only after the mid 20
th
-Century advancements in semiconductor technology that practical applications for thermoelectric devices became feasible. With such modern techniques, thermoelectric modules can be produced that deliver efficient solid state heat pumping for both cooling and heating. Many of these thermoelectric modules or units can be used to generate DC power in certain circumstances (that is conversion of waste heat).
A detailed description of the thermoelectric technologies can be found at http://www.naijiw.com/peltier/peltier. The following description of thermoelectric technology, components and uses is derived from or is a restatement of the disclosure that appears at the above web site.
The Peltier Effect occurs whenever electrical current flows through two dissimilar conductors. Dependent upon the direction to current flow, the junction of the conductors will either absorbed or release heat. Today, semiconductors, usually bismuth telluride, are the materials of choice for producing the Peltier Effect. The semiconductor materials can be more easily optimized for heat pumping, and designers can control the type of charge carrier employed within the conductor as will be described hereafter. Using this type of material a Peltier device for thermoelectric modules can be constructed.
FIG. 1
illustrates a basic thermoelectric module
10
useful in the present invention. A thermoelectric module
10
includes at least a single pellet or structure
12
of an electrically conductive material which is secured by solder (not shown) to an electrically conductive material
14
(usually plated copper) at each end of the pellet
12
. In this most simplistic configuration, the second dissimilar material (metal) required for the Peltier effect is actually the copper connection paths
16
to the power supply
18
. In this configuration, heat will be moved or pumped in the direction of the charge carrier movement throughout the circuit. It is actually the charge carriers that transfer this heat. For example, when a “N-type” semiconductor material is used for the pellet
12
, the pellet includes electrons (with a negative charge, usually due to the addition of P atoms into the base semiconductor material) that will be the charge carriers utilized to create the transfer of heat. With a DC voltage source
18
connected as shown, electrons will be repelled by he negative pole and attracted by the positive pole of the a DC voltage supply
18
. This produces electron flow in a clock wise direction. With electrons flowing through the N-type material of the pellet
12
from the bottom
20
to the top
22
of the pellet
12
so that heat is absorbed at the bottom junction
24
(top surface of plated copper
14
) and pumped by the charge carriers through the semiconductor pellet
12
to be dissipating at the top junction
26
(bottom surface of plated copper
14
).
FIG. 2
illustrates another embodiment of a thermoelectric device useful in the present invention. In this embodiment, and “P-type” semiconductor pellets
12
′ are utilized. The P-type pellets are manufactured so that the charge carriers in the material are positive, also known electronics as “holes”. These “holes” are typically created by the addition of B atoms into the base semiconductor material. The “holes” allow electrons to flow through the material when a voltage is applied. These positive charge carriers are repelled by the positive pole of the DC voltage supply
18
and attracted by the negative pole. The “hole” flow is in the opposite direction of the electron flow. The “holes” flow from the top
22
of the P-type pellet
12
′ to the bottom
20
of the pellet
12
′. The use of P-type materials results in heat being drawn toward the negative pole of the power supply
18
and away from the positive pole of the power supply
18
. Thus, heat is absorbed at the junction
26
(top surface of plated copper
14
) travels through the pellet
12
′ and is dissipating at junction
24
(bottom surface of plated copper
14
). In this embodiment, the direction of flow of the “holes” and the heat is in a counter clock wise direction. However, single pellet embodiments of thermoelectric devices as shown in
FIGS. 1-2
are not sufficient to remove a substantial quantity of heat and therefore more complicated structures are required.
FIG. 3
illustrates another embodiment of a thermoelectric device
10
useful in the present invention. In this embodiment the thermoelectric device
10
includes a plurality of pellets
12
(N-type) arranged both electrically and thermally in parallel. This arrangement produces a greater amount of heat simply because there are more pellets
12
. However, there is a problem with this type of arrangement in that each pellet
12
is typically rated for only a small voltage, often less than 10 millivolts but draws a substantial amount of current. A single pellet in a typical thermoelectric device might draw 5 A or more with only 60 millivolt supplied. When a number of such pellets are arranged in parallel, the current draw typically becomes impractical.
FIG. 4
illustrates another embodiment of a thermoelectric device useful in the present invention. In this embodiment, a number of N-type pellets
12
are arranged thermally in parallel but electrically in series. To accomplish this, electrical connection
28
is provided and connected at one end at the plated copper
14
near the top
22
of the pellet
12
and connected at the other end to the plated copper
14
at the bottom
20
at the next adjacent positioned pellet
12
. Although this arrangement is plausible, electrical shorts may occur between pellets.
FIG. 5
illustrates another embodiment of the thermoelectric device
10
useful in the present invention. In this embodiment, a N-type electrically conductive material
12
and a spaced apart P-type electrically conductive material
12
′ are arranged to form a junction between them with a plated copper pad
14
. This arrangement allows the electrically conductive materials
12
,
12
′ to be arranged electrically in series and thermally in parallel. In this embodiment negative charge carriers in the N-type material or pellet
12
flow from the bottom
20
of the pellet
12
to the top
22
of the pellet
12
. Likewise, the heat flows in the same direction through the N-type pellet. The positive charge carriers or “holes” flow from the bottom
20
of the P-type material or pellet
12
′ to the top
22
of the P-type pellet
12
′. Likewise the heat flows in the same direction as the “holes” flow through the P-type pellet
12
′. In this arrangement the electrons flow continuously from the negative pole of the voltage supply, through the N-type pellet
12
, through the copper plated junction
14
, through the P-type pellet
12
′ and back to the positive pole of the supply
18
.
FIG. 6
illustrates another embodiment of a thermoelectric device
10
useful in the present invention. In this embodiment, a plurality of N-type and P-type pellet couples
12
,
12
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