Semiconductor device manufacturing: process – Chemical etching – Vapor phase etching
Reexamination Certificate
1998-06-04
2001-01-23
Dang, Thi (Department: 1763)
Semiconductor device manufacturing: process
Chemical etching
Vapor phase etching
C438S906000, C134S001200, C156S345420
Reexamination Certificate
active
06177356
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods and apparatus for cleaning semiconductor wafers generally and to such methods and apparatus utilizing thermoemission in particular.
BACKGROUND OF THE INVENTION
The steps of the production of semiconductor silicon integrated circuits must be very clean, because even small amounts of undesirable contaminating impurities can cause complete degradation or malfunction of integrated circuits. Thus, semiconductor silicon wafers must be cleaned between processing steps.
There exist many cleaning processes used in silicon semiconductor production. Wet cleaning processes usually remove contaminants from the silicon wafer surface with special chemical solutions as part of a separate production step. Dry cleaning processes usually remove contaminants by etching the contaminants from the wafer surface within some gas or gas mixture or within a plasma environment. Gettering processes utilize the tendency for contaminants to move towards special traps inside the silicon wafer (areas with a high density of such traps are called “getters”) and to stay stable within the traps.
However, wet and dry cleaning processes can only remove contaminants from the silicon wafer surface. Gettering processes can be used only for some types of contaminants (such as iron, copper, nickel etc.).
European Patent Publication EP-A-0749153, assigned to the common owners of the present application, describes a cleaning method which utilizes an electric field in the presence of heat to move positively charged impurity ions from the semiconductor wafer surface and above it towards a negatively charged electrode (called the “collector”).
The apparatus of European Patent Publication EP-A-0749153 is schematically illustrated in
FIG. 1
to which reference is now briefly made. The electric field is created between the electrodes, one of which, labeled
10
, is attached to the wafer
12
to be cleaned. The other electrode (the “collector”), labeled
14
, is placed at a distance therefrom. Wafer electrode
10
is connected to a voltage source output Vb and the electrode
14
is connected to another source output Vc, where the potential Vc is more electronegative than the potential Vb. Thus, an electric field is created to move positive ions, labeled
16
, from the wafer area toward the collector electrode
14
, where positive ions will be absorbed (captured). Typically, the apparatus is placed in a vacuum or in presence of a gas mixture and heated to initiate ion emission from the wafer surface. EP Publication EP-A-0749153, also describes utilizing a plasma between the two electrodes
10
and
14
to strengthen the electric field over the wafer surface.
SUMMARY OF THE PRESENT INVENTION
It is an object of the present invention to provide methods and apparatus for batch cleaning of semiconductor wafers using thermoemission. These methods and apparatus can be utilized, in particular, within high temperature ovens, reactors or rapid thermal tools such as are common in the semiconductor manufacturing process.
There is therefore provided, in accordance with a preferred embodiment of the present invention, a collector electrode formed of semiconductor wafer. The semiconductor wafer can have an unpolished surface, a rough surface or an oxidized surface.
There is also provided, in accordance with a preferred embodiment of the present invention, a wafer transfer device or boat having a first unit with a plurality of first slots for receiving a first group of semiconductor wafers and a second unit with a plurality of slots for receiving a second group of semiconductor wafers. The first slots alternate with the second slots. The first unit is connectable to a first voltage source and the second unit is connectable to a second voltage source. The second voltage source is more electronegative than the first one. Typically, the first group of semiconductor wafers have impurities therein which are to be removed and the second group of semiconductor wafers are to receive the impurities.
Additionally, in accordance with a preferred embodiment of the present invention, the first unit is a lower layer of conductive material and the second unit is an upper layer of conductive material. The second unit has a plurality of third slots, aligned with the first slots and the third slots are wider and longer than the first slots.
Moreover, in accordance with a second preferred embodiment of the present invention, the first unit is a first support wall formed of alternating conductive and isolating supports and the second unit is a second support wall formed of alternating isolating and conductive supports. Each semiconductor wafer is supported horizontally by one conductive and one isolating support.
Further, in accordance with a third preferred embodiment of the present invention, the wafer transfer device additionally includes two support rods of isolating material. The first unit is a first rod of conductive material and the second unit is a second rod of conductive material. The first rod has alternating small and large slots and the second unit has alternating large and small slots such that each semiconductor is held by one small slot and floats in one large slot.
Additionally, in accordance with a preferred embodiment of the present invention, the first semiconductor wafers are to be cleaned and the second semiconductor wafers are collector electrodes.
There is further provided, in accordance with a preferred embodiment of the present invention, a semiconductor cleaning unit including a heatable reaction core, a core collector electrode and a wafer transfer device. The core collector electrode is mounted to the reaction core and is connectable to a first, core voltage source Va. The wafer transfer device transfers at least one semiconductor wafer to be cleaned to within the reaction core. The wafer transfer device is connectable to at least a second, wafer voltage source Vb. Va is more electronegative than Vb.
Moreover, in accordance with a preferred embodiment of the present invention, the core collector electrode is mounted to the outside of the reaction core.
Further, in accordance with a preferred embodiment of the present invention, the wafer transfer device has a first unit receives a first group of semiconductor wafers and a second unit which receives a second group of semiconductor wafers. The first unit has slots which alternate with slots of the second unit. The first unit connectable to the wafer voltage source Vb and the second unit connectable to a third, collector voltage source Vc. The collector voltage source Vc is more electronegative than Vb.
Still further, in accordance with a preferred embodiment of the present invention, the first semiconductor wafers are to be cleaned and the second semiconductor wafers are collector electrodes.
There is alternatively provided, in accordance with a preferred embodiment of the present invention, a semiconductor cleaning unit which includes a heatable reaction core and a wafer transfer device. The latter transfers a plurality of semiconductor wafers to within the reaction core and has a first slotted unit for receiving a first group of semiconductor wafers to be cleaned and a second slotted unit for receiving a second group of semiconductor wafers forming collector electrodes. The slots of the first unit alternate with the slots of the second unit. The first unit is connectable to a first voltage source Vb and the second unit is connectable to a second voltage source Vc.
Finally, there is provided, in accordance with a preferred embodiment of the present invention, a reaction core cleaning unit including a heatable reaction core, a core collector electrode and a conductive element. The core collector electrode is mounted to the reaction core and is connectable to a first, core voltage source Va. The conductive element is locatable within the reaction core and is connectable to at least a second voltage source having a voltage level greater than the voltage level of the core voltage source. The core collector electrode can be mo
Rapoport Igor
Raskin Yosef
Sergienko Alex
Zaidman Solomon
Zinman Yosef
Dang Thi
Darby & Darby
Sizary Ltd.
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