Method to reduce contaminants from semiconductor wafers

Details Method to reduce contaminants from semiconductor wafers Method to reduce contaminants from semiconductor wafers

1999-08-03

2002-06-18

El-Arini, Zeinab (Department: 1746)

Cleaning and liquid contact with solids

Processes

Including use of vacuum, suction, or inert atmosphere

C134S037000, C015S302000

Reexamination Certificate

active

06406553

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to method and apparatus for purging and cleansing of contaminants such as air-borne particles, moisture, etc., from semiconductor wafers prior to their being fabricated into integrated circuits.
BACKGROUND OF THE INVENTION
Present day integrated circuits (ICs) may have many millions of devices (e.g., memory cells) per square centimeter of chip area The devices themselves may have line widths and other surface dimensions considerably smaller than a micron (micrometer). As a consequence cleanliness and freedom from contamination of the ICs before and between the various processing steps during their manufacture is now more important than ever before.
It has long been known that dust, smoke, and similar air-borne particles (some too small to see with the unaided eye), and contaminants such as moisture and organic vapors are very harmful to ICs during manufacturing. Accordingly, semiconductor manufacturing plants have elaborate air filtering systems and are as clean if not cleaner than surgical operating rooms. The operators and technicians who run a semiconductor manufacturing plant are required to wear elaborate clean-room garb including face masks and in some cases self-contained breathing units. Even so contamination of semiconductor wafers continues to be a problem, particularly before or between processing steps where the semiconductor wafers are handled by human operators in the course of moving the wafers from one piece of equipment to another. This is especially true where IC device density is so great and device size so small. The present invention is intended to help further eliminate contamination of semiconductor wafers during their manufacture into ICs.
SUMMARY OF THE INVENTION
In accordance with the invention in one aspect thereof, semiconductor processing equipment is provided with an input-output (I-O) chamber which may be hermetically sealed from the remainder of the equipment whenever desired. The I-O chamber is easily opened to permit an operator to insert a cassette or cassettes containing semiconductor wafers for processing at a station or stations provided by the equipment. After a cassette containing semiconductor wafers has been placed in the I-O chamber, it is closed and hermetically sealed and the following sequence of events in accordance with the invention are carried out. A dry, inert purge gas, such as nitrogen, is flowed into the chamber near the top thereof through a diffuser in close proximity to the cassette and semiconductor wafers. The gas forms a covering blanket blowing over and around the wafers and helps eliminate residual contamination which may be present. The purge gas with any trapped contaminants is exhausted during an initial phase at a relatively slow rate down and out of the chamber. During this initial gas flow and slow pump-down of gas pressure, contaminants such as minute particles, moisture (e.g., from atmospheric humidity), residual organic vapor (e.g., from a previous processing step), etc. are swept off of and down away from the wafers. While gas is still being admitted into the chamber, gas pressure is reduced within the chamber to a pre-determined intermediate value below which pressure remaining atmospheric moisture within the chamber will no longer condense on the wafers. When this intermediate pressure is reached (e.g., typically in about 1 minute) the incoming gas is turned off and the pressure within the chamber is then rapidly reduced to a vacuum base pressure (e.g., a fraction of a Torr). As soon as vacuum base pressure is reached (e.g., after about 2 minutes or less of fast-pump gas exhaust) the I-O chamber may be opened to the remainder of the equipment to permit processing of the semiconductor wafers.
In accordance with another aspect of the invention there is provided a method to help purge residual contamination from semiconductor wafers during their manufacture into integrated circuits (ICs). The method comprises the steps of placing one or more wafers in an input-output (I-O) chamber; sealing the chamber; flowing a dry inert purge gas into the chamber in close proximity to the wafers to form a covering blanket of purge gas flowing over and around the wafers to help eliminate contaminants from the wafers; exhausting the purge gas and residual contamination away from the wafers and out of the chamber; relatively slowly reducing the pressure within the chamber to an intermediate pressure level; and thereafter relatively rapidly reducing the gas pressure within the chamber to a low base value to permit the wafers to go through a step or steps of processing into ICs.
In accordance with yet another aspect of the invention there is provided apparatus for helping in processing semiconductor wafers into integrated circuits (ICs) in a processing line.
The apparatus comprises an input-output (I-O) chamber adjacent the processing line for helping eliminate contamination of the wafers before they are processed in the line, the I-O chamber being hermetically sealable from the processing line so that the chamber can be opened to the atmosphere and thereafter closed to permit semiconductor wafer to be placed into the chamber for subsequent processing; a gas supply for supplying dry, inert gas to form a gas blanket over and around the wafers to help purge them of contaminants such as minute foreign particles, atmospheric moisture, and residual organic vapors; and a pump for pumping the purge gas, residual moisture and purged contaminants away from the wafers, the pump being controlled during an initial period to relatively slowly exhaust purge gas and contaminants and reduce the pressure within the chamber to an intermediate level, the gas supply being turned off when the intermediate pressure level is reached, and thereafter the pump relatively rapidly exhausting the gas in the chamber to a base level at which pressure the I-O chamber can be opened to the processing line for processing of the wafers therein.
Viewed from a first apparatus aspect, the present invention is directed to apparatus comprising an input-output (I-O) chamber, a gas supply line, and a pump. The input-output (I-O) chamber I-O chamber is hermetically sealable so that the chamber can be opened to the atmosphere and thereafter closed. The gas supply line supplies dry, inert gas to form a gas blanket over and around at least one semiconductor wafer in the chamber to remove therefrom contaminants such as minute foreign particles, atmospheric moisture, and residual organic vapors. The pump pumps the purge gas, and any residual moisture and purged contaminants away from the at least one semiconductor wafer. The pump is controlled during an initial period to relatively slowly exhaust purge gas and contaminants and reduce the pressure within the chamber to an intermediate pressure level. A gas supplied to the gas supply line is turned off when the intermediate pressure level is reached. Thereafter the pump relatively rapidly exhausting the gas in the chamber to a lower base pressure level.
Viewed from a second apparatus aspect, the present invention is directed to apparatus for processing semiconductor wafers into integrated circuits (ICs). The apparatus comprises a processing line, an input-output (I-O) chamber, a gas supply line for supplying dry inert purge gas to the chamber, a diffuser in the chamber, a pump, and control circuitry. The input-output (I-O) chamber is adjacent the processing line for reducing contamination of the semiconductor wafers before they are processed in the line and is hermetically sealable from the line so that the chamber can be opened to the atmosphere to permit placement into the chamber of semiconductor wafers to be processed in the line. The diffuser disperses the purge gas as a blanket over and around the semiconductor wafers to help purge them of contaminants such as minute foreign particles, atmospheric moisture, and organic vapors. The pump pumps the purge gas and residual contaminants away from the semiconductor wafers. The control circuitry turns on a gas supply coupled to the

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