WO1995003622A1

WO1995003622A1 - Methods and apparatus for water desorption of vacuum chambers

Info

Publication number: WO1995003622A1
Application number: PCT/US1994/008185
Authority: WO
Inventors: Frank Scuotto
Original assignee: Materials Research Corporation
Priority date: 1993-07-22
Filing date: 1994-07-20
Publication date: 1995-02-02
Also published as: AU7401294A

Abstract

Methods and apparatus used particularly in the field of sputter coating and etching which include the use of ultra-violet (UV) light to cause faster evacuation or pump-down of vacuum chambers and to reduce the base pressure of such vacuum chambers. One or more UV lamps (24) are mounted within the main vacuum chamber (12a) of a sputter coating and etching machine (10). The UV light causes moisture on the inside walls of the chamber (12a) to be desorbed from the walls by exciting the water molecules and causing their bonds with the walls to be broken. As the water molecules are desorbed, a pump is used to evacuate them from the chamber until the pressure in the chamber (12a) reaches an optimum base pressure. In other aspects of the invention UV light sources (24) are also used in the individual vacuum process chambers (20, 21, 22, 23) within the main vacuum chamber (12a) to further reduce the moisture content of the vacuum system and thus reduce the predominant source of partial pressure in such systems.

Description

Methods and Apparatus for

Water Desorption of Vacuum Chambers

Background of the Invention

The present invention relates to pressure sealed chambers and more particularly to methods and apparatus for removing moisture and other contaminants from a vacuum chamber after the chamber has been exposed to atmosphere.

In the manufacture of semiconductor devices and other articles through coating or etching processes performed on wafers and other substrates, processing apparatus such as sputter coating or sputter etching machines typically process the substrate in an isolated and usually near vacuum environment. Such machines generally have a main vacuum chamber or plenum which communicates with several individual process vacuum chambers or pods which receive the substrates and carry out the processing operations. The main vacuum chamber or plenum is usually provided with one or more chamber doors located in the wall of the chamber

through which, for example, wafer substrates are introduced for

processing and then removed by various types of transfer mechanisms which allow vacuum pressure to be maintained in the plenum during the wafer transfer.

Wafer processing machines that process wafers in a vacuum environment most often maintain a constant vacuum environment so that processing upon some wafers can be carried out in the process chambers as other wafers are being inserted into or removed from the chamber. To this end, such machines have an intermediate chamber or load lock at an entry to the main vacuum chamber that alternately communicates with the external environment through the entry and, when the entry is sealed, with the internal environment of the plenum or main vacuum chamber through another sealable entry thereto. The load lock is alternately pumped to the vacuum level of the internal environment of the main vacuum chamber or plenum and vented to the external environment so that the pressure of the load lock matches that of the environment with which it communicates while the wafers are being

introduced into and removed from the plenum. With such a load lock, the internal portion of the plenum where processes are carried out may be maintained continuously at a specific vacuum pressure and may be used additionally for the processing of other wafers while wafers are being introduced into and removed from the load lock chamber.

Other types of processing machines, such as batch processing machines may have no load lock, but are instead opened to the external environment and loaded with the objects to be processed. In such machines, the entire vacuum processing chamber or plenum is repeatedly vented, opened and pumped down

to a vacuum or near vacuum level.

Prior processing machines of the above type have also generally included a means for accessing the inside of the plenum, for example, to enable preventative maintenance to be performed on the processing equipment inside the plenum, to retrieve broken wafer substrates, or to repair or replace other processing components contained in the plenum. As a result, the plenum is exposed to atmospheric contaminants and moisture on a regular basis. Moisture and other contaminants also enter each processing

chamber if the plenum is opened to atmosphere.

The presence of moisture and contaminants in both the main vacuum chamber and the process chambers can cause contamination of the substrates which may result in defective processing. Also, atmospheric moisture is the predominant source of partial pressure in the vacuum chambers of these processing machines and, as is well known in the art, partial pressure in the plenum reduces the efficiency of the processing machine. Previous methods of evacuating moisture and other contaminants from the main vacuum chamber or plenum have

included "vacuum baking" wherein the plenum is heated with, for example, external heaters as the plenum is "pumped down" or evacuated to a near vacuum level and moisture and other contaminants contained therein are simultaneously pumped out of the plenum. This is a relatively time consuming process, usually taking 24 hours or more depending on the machine, and therefore requires the machine to be idle for a significant amount of time after the plenum has been exposed to atmosphere for one reason or another. Thus, after exposing the plenum to atmosphere during repairs, preventative maintenance, etc., many machine operators forego the time consuming vacuum baking process and relatively quickly pump down the plenum without applying any heat and thus leave a significant amount of moisture and other contaminants in the plenum as a source of partial pressure.

Vacuum baking has also been employed as a step during the manufacture of these processing machines. Generally, the machines are shipped from the manufacturing plant with the plenums already pumped down to a near vacuum level. To obtain as low a base pressure as possible, contaminants and moisture must be removed from the plenum during this pump down process, however, as noted above, the "vacuum baking" process is very time consuming and therefore decreases productivity and increases manufacturing costs associated with the machines.

Accordingly, there is a need to decrease the pump down time necessary for the plenum or main vacuum chamber to reach an optimum base pressure or a near vacuum level by removing

substantially all of the moisture and other contaminants from the interior of the main vacuum chamber or plenum after it has been exposed to the atmosphere. In addition, there is a need for a fast,

efficient method of removing moisture and other contaminants from

the processing chambers as they are being pumped down to an optimum base pressure after exposure to atmosphere at the load lock station. Summary of the Invention

It has been a primary objective of the present invention to significantly reduce the amount of time needed to reach an optimum base pressure in a vacuum system.

Another objective of the invention has been to lower the base pressure of a vacuum chamber such as the main vacuum chamber or one of the processing chambers of, for example, a coating and/or etching machine and thereby increase the productivity of each processing operation.

According to the principles of the present invention, one or more of the vacuum chambers of a processing machine is exposed to ultra-violet (UV) light during the "pump-down" operation during which air, moisture or water vapor, and other contaminants are pumped out of the chamber until the chamber reaches an optimum base pressure. In implementing the concepts of the

present invention one or more UV light sources are preferably mounted within at least the main vacuum chamber or plenum of a sputter coating and etching machine. The light sources are turned on before and/or during the "pump-down" procedure wherein the vacuum chamber or plenum is pumped to a near vacuum level. The UV light excites water molecules which have bonded to the interior walls of the vacuum chamber thus causing the bonds to be broken and allowing the molecules to be easily pumped out of the chamber.

In other aspects of the invention UV light sources may be operatively coupled to the apparatus so as to expose the interior walls of the individual process chambers within the main vacuum chamber or plenum to UV light as these process chambers are pumped down to a pressure essentially equal to the pressure within the main vacuum chamber. As previously mentioned, this pump- down procedure occurs in a typical sputter coating and etching machine at the load lock station of the machine after a wafer or other substrate has been transferred into the process chamber. As with the UV light sources used in the main vacuum chamber or

plenum, the UV lights sources used for desorbing water from the process chambers are preferably mounted within the process chambers.

While a preferred embodiment of the invention is described with respect to machines for coating or etching semiconductor wafers, the principles of the invention are applicable to machines and processes wherein other objects such as lenses, or magnetic, optical or magneto-optical disks or other substrates are coated, etched or otherwise processed in vacuum chambers.

One advantage of the methods and apparatus contemplated by present invention is that the time necessary to

pump-down the main vacuum chamber or plenum and the individual

process chambers of a processing machine to an optimum base pressure has been significantly reduced as compared to prior pump- down methods.

Another advantage is that the methods and apparatus of the invention reduce the ultimate base pressure of the vacuum chambers of a processing machine as compared to prior pump-down methods by removing comparatively more moisture content and, as a result, significantly increase the productivity of vacuum runs

conducted within the plenum.

These and other advantages of the invention will become more readily apparent to those of ordinary skill in the art from the following detailed description taken in conjunction with the

accompanying drawings and examples. Brief Description of the Drawings

Fig. 1 is a schematic perspective view of a wafer processing mac ιe of the present invention with certain elements of the machine not shown so as to clearly illustrate the vacuum

chambers utilized in the machine;

Fig. 2 is a cross sectional view of the wafer processing machine taken along line 2-2 of Fig. 1 and again omitting certain elements of the machine for clarity. Detailed Description of the Preferred Embodiments

One preferred embodiment of the present invention is particularly suitable for use in conjunction with a wafer processing apparatus such as the sputter coating and sputter etching apparatus disclosed in the commonly assigned U.S. Patent Nos. 4,909,695 and 4,915,564, both entitled "METHOD AND APPARATU&FOR HANDLING AND PROCESSING WAFER-LIKE MATERIALS," both of which are hereby expressly incorporated by reference herein.

The above-incorporated patents describe, in pertinent part, methods and apparatus for processing wafers, particularly for the sputter coating and etching of semiconductor wafers, in a vacuum environment maintained within a main vacuum chamber or plenum of the apparatus. In these apparatus, wafers may be simultaneously and sequentially processed at a plurality of processing stations in the main vacuum chamber. Within the main vacuum chamber, the wafers are held in a rotatable plate which sequentially indexes them to a plurality of angularly spaced stations, including a plurality of processing stations and a single ioadlock station. The Ioadlock allows the wafers to be transported between the main vacuum chamber and the external environment. The Ioadlock is sealable both from the main vacuum chamber and from

the external environment of the machine.

The above-incorporated patents also disclose a transfer mechanism for transporting unprocessed semiconductor wafers from the external environment into a holder within the Ioadlock, and removing processed wafers from the Ioadlock to the external

environment. These patents explain in detail the operation of the

wafer handling mechanism, the structure and operation of the Ioadlock, the structure and operation of the mechanism for moving a wafer supported ir a holder between the Ioadlock and stations within the main vacuum chamber, and the structure for isolating the Ioadlock from the main vacuum chamber. As these detai do not form part of the present invention, and since they are detailed in the incorporated patents mentioned above, they will not be described in detail below.

Figs. 1 and 2 illustrate one use of the methods and apparatus of the present invention embodied in a wafer processing machine 10 which may be, for example, a sputter coating or sputter etching machine. The frame to which the wafer processing apparatus 10 is normally attached has been omitted in the drawings for clarity. The wafer processing apparatus 10 includes a main

vacuum chamber or plenum 12 comprised of two half sections 14, 16. The two half sections 14, 16 generally define a main plenum area 12a, shown in greater detail in Fig. 2. Four work stations 20,

21 , 22, 23 are disposed at generally equal angular intervals about

the center of the main vacuum chamber 12. Work station 20 is a Ioadlock station used for the entry and removal of processed or unprocessed wafers from the main vacuum chamber 12 and work stations 21 , 22 and 23 each comprise processing stations at which

various processing steps, such as etching and sputtering, may be performed on the wafers. The Ioadlock station 20 further includes a Ioadlock door 25 which is actuated into open and closed positions by a door operating mechanism 19 to allow articles to be inserted and removed from the Ioadlock station 20.

The wafer processing apparatus 10 further includes a plurality of vacuum pumps 30, 31 , 32, 33, which may be cryogenic vacuum pumps, for providing the proper base vacuum levels in each of the volumes of the respective work stations 20, 21 , 22, 23. Each of the work stations, 20, 21, 22, 23 may be isolated from the main vacuum chamber 12a during processing operations. Vacuum pumps 30, 31 , 32, 33 are coupled to the respective work stations 20, 21 , 22, 23 by respective manifold members 40, 41 , 42, 43. Before the cryogenic vacuum pumps 30, 31 , 32, 33 are activated,

separate mechanical vacuum pumps (not shown) are activated to evacuate the respective chambers to a level close to the desired base vacuum level. The cryogenic pumps 30, 31 , 32, 33 are then activated to bring the vacuum in the process vacuum chambers which comprise each work station down to an optimum base pressure level. An optimum base pressure level may be, for example, 5 x 10^*7 Torr. The fittings and connections necessary for the operation of the various pumps are described in greater detail in U.S. Patent No. 4,909,695 (the '695 patent), which has been inc. porated by reference herein.

Fig. 2 shows the Ioadlock station 20 with the Ioadlock

door 25 in a closed position. The index plate 15 is rotatably

mounted within the main vacuum chamber 12a which is defined by chamber halves 14, 16. The front plane device 27 at Ioadlock station 20 may comprise a motor or hydraulically or air actuated member 300 mounted to a support 308. As further shown in Fig. 2,

and more specifically detailed in the above incorporated U.S. Patent No. 4,909,695, the Ioadlock area 330 is defined by the cup shaped member 304, ring shaped member 220 and extending member 320 of chamber half 14. In the present invention, however, the Ioadlock area further includes at least one and preferably more than one, UV light source 24. These UV light sources 24 are operatively connected to the control system of the apparatus such that they are turned on during the "pump down" process during which a mechanical vacuum pump and a cryogenic vacuum pumr are used to equalize the vacuum level in the Ioadlock area 330 with that of the main chamber 12a. Activation of the UV light sources 24 during this pump down process causes water and other contaminants to more rapidly desorb from the inner walls of the area 330 such that they

may be readily evacuated from the area 330.

In a like manner, and as shown in both Figs. 1 and 2, the main vacuum chamber 12a also includes a plurality of UV light sources 24 which are activated during the pump down process during which the main vacuum chamber is evacuated to a near

vacuum level. The pump down process of the main vacuum chamber 12a occurs any time the main vacuum chamber has been exposed to atmosphere. That is, any time the chamber halves 14, 16 have been separated from one another, or have otherwise been exposed to atmosphere or other contaminated air, the main vacuum chamber 12a must be evacuated to a near vacuum level or optimum pressure level after the chamber halves 14, 16 have been closed to prepare the apparatus 10 for operation. Therefore, for example, before the apparatus 10 is shipped from the manufacturing facility, the main vacuum chamber 12a is pumped down to a near vacuum level while the UV light sources 24 contained therein are turned on. In addition, any time the main vacuum chamber 12a has been

exposed to atmosphere due to maintenance of the inner workings of the device, retrieval of a broken substrate, or other reasons, the

main vacuum chamber 12a must again be pumped down to a near vacuum level while the UV light sources 24 in the main vacuum chamber 12a are turned on.

Fig. 2 further shows process station 22 in which like components have bet provided with like reference numerals for station 20 and 22, with the exception that the reference numerals for like already introduced elements of station 22 are provided with primes. As more specifically detailed in the '695 patent, the back plane device 47 operates to displace member 304' to bear against ring shaped member 220' which in turn bears against chamber half 16, thereby sealing volume 350 from the main vacuum chamber

12a. As with the Ioadlock area 330, chamber volume 350 also

includes at least one and preferably more than one UV light source 24 for the purpose of desorbing water from the inner chamber walls of the volume 350 during the pump down process of station 22. That is, while the mechanical vacuum pump (not shown) and the cryogenic vacuum pump 32 are activated to provide the proper base vacuum level in the volume 350, the UV light sources 24 contained therein are turned on to cause water and other contaminants to desorb from the inner walls of the volume 350 to achieve base vacuum levels lower than those that would be possible without the UV light sources.

It will be appreciated that, as shown in Fig. 1 , the process stations 21 and 23 may be provided with UV light sources 24 in their respective vacuum chambers in a like manner and for like purposes to the incorporation of UV lights sources 24 in process

stations 20 and 22. Each of the UV light sources are preferably 16 Watt ultraviolet lamps. The following data represents test results from four hour UV treatments of 14 test plenums utilizing two 16

Watt UV lamps placed within each test plenum:

TIME TO REACH BASE PRESSURE OF 5 X 10^"7 TORR (HOURS)

Plenum Without UV With 4 Hour UV Treatment Treatment

1 30 8

2 22 9

3 26 16

4 13 7

5 35 17

6 16 8

7 15 8

8 28 13

9 33 20

10 33 18

11 29 9

12 36 16

13 99 48

14 42 18

The above data shows that the UV treatment reduced pump down or evacuation time, i.e., the time necessary to evacuate the plenum to a base pressure of 5.0 x 10^"7, by approximately 56%

on average as compared to pump down durations for the same plenums but not using UV lamps. Generally, it has been found that a plenum or vacuum chamber having an inside wall surface area of approximately 23,000 cm² benefits from the use of dual 16 Watt UV

lamps while the process "pods" or process vacuum chambers utilized at the process stations need only one 16 Watt UV lamp as they have inner wall surface areas in the range of 6,400 cm² to 7200 cm².

Accordingly, the present invention decreases the time necessary to pump down the main vacuum chamber or plenum as well as the individual process vacuum chambers of a processing machine to an optimum base pressure. Additionally, the methods and apparatus of the present invention reduce the ultimate base

pressure of the various vacuum chambers in a processing machine

such as described above as compared to prior pump down methods not utilizing UV sources for directing UV light at the inner walls of the vacuum chambers. As is well known in the art, reduction of the L.timate base pressure of the vacuum chambers in a processing

machine increases the productivity and efficiency of processes conducted within the vacuum chambers.

Although a preferred embodiment of the present invention has been described above, it will be appreciated that the artisan of ordinary skill will readily recognize further modifications thereof. For example, while the present invention has been described in conjunction with a specific processing machine used for processing wafer like substrates, it will appreciated that the teachings of the present invention may be easily used in conjunction with other apparatus which utilize vacuum chambers needing to be

"pumped down" or evacuated to near vacuum levels. In this regard, the use of UV light in accordance with the present invention during the evacuation of such chambers for whatever reason will result in significant improvements directed to time savings and lower base

pressure levels.

As many modifications and uses of the present invention will become readily apparent to those of ordinary skill without departing from the scope of the invention, Applicant intends to be bound only by the claims appended hereto.

Claims

What is claimed is:

1. A process apparatus comprising: a main vacuum chamber for receiving substrates to be processed; a primary vacuum pump connected to said main vacuum chamber to first vacuum pump means for evacuating said

main vacuum chamber and reducing the pressure in said main

vacuum chamber to a predetermined base pressure; and, a first ultra-violet light source operatively coupled to said apparatus for exposing the interior of said main vacuum chamber to ultra-violet light as said first vacuum pump reduces the pressure within said main vacuum chamber to said predetermined base pressure.

2. The apparatus of claim 1 wherein said ultra-violet light source comprises at least one ultra-violet light mounted within said main vacuum chamber to direct ultra-violet light at the interior walls of said main vacuum chamber.

3. The process apparatus of claim 1 further

comprising:

at least one process vacuum chamber disposed within said main vacuum chamber for receiving said substrates while a process operation is performed thereon; a secondary vacuum pump connected to said process vacuum chamber for evacuating said process vacuum chamber; and, a second ultra-violet light source operatively coupled to said apparatus for exposing the interior of said process vacuum chamber to ultra-violet light as said secondary vacuum pump evacuates said process vacuum chamber.

4. The apparatus of claim 3 wherein said ultra-violet light source further comprises at least one ultra-violet light mounted within said process vacuum chamber for directing ultra-violet light at the interior walls of said process vacuum chambers.

5. A process apparatus comprising: a main vacuum chamber; a load lock chamber for allowing substrates to be transferred between an external environment and said main vacuum chamber; a plurality of process vacuum chambers disposed within said main vacuum chamber for receiving substrates to be processed; vacuum pumps connected to said main vacuum

chamber, said load lock chamber and each of said process vacuum chambers for evacuating said main vacuum chamber, said load lock chamber, and said process vacuum chambers; and, an ultra-violet light source operatively coupled to said

apparatus for directing ultraviolet light at the interior walls of at least one of said main vacuum chamber, said plurality of process vacuum chambers, and said load lock chamber as one of said vacuum pumps evacuates said one of said main vacuum chamber, said plurality of process vacuum chambers, and said load lock chamber.

6. The apparatus of claim 5 wherein said ultra-violet light

source is operatively coupled to said apparatus for exposing the

interior of said main vacuum chamber to ultra-violet light as one of said vacuum pumps evacuates said main vacuum chamber.

7. The apparatus of claim 5 wherein said ultra-violet light

source is operatively coupled to said apparatus for exposing the interiors of said plurality of process vacuum chambers to ultra-violet light as vacuum pumps evacuate said process vacuum chambers.

8. The apparatus of claim 5 wherein said ultra-violet light source is operatively coupled to said apparatus for exposing the interior of said load lock chamber to ultra-violet light as said vacuum pump evacuates said load lock chamber.

9. A iTu iod of reducing the pressure in a vacuum chamber to a predetermined base pressure by removing water molecules bonded to interior walls of said vacuum chamber, the method comprising the steps of: exposing said inner walls of said vacuum chamber to ultra-violet light sufficient to break the bonds between said water molecules and S inner walls; and,

while exposing said inner walls to ultra violet light,

pumping air and said water molecules out of said vacuum chamber until the pressure in said vacuum chamber reaches said predetermined base pressure.

10. A process apparatus comprising:

a vacuum chamber for receiving substrates to be

processed; a connection on said vacuum chamber for allowing the attachment of a vacuum pump to said vacuum chamber for evacuating said main vacuum chamber and reducing the pressure in said main vacuum chamber to a predetermined base pressure; and, a first ultra-violet light source operatively coupled to said apparatus for exposing the interior of said main vacuum chamber to ultra-violet light as said vacuum pump reduces the pressure within said main vacuum chamber to said predetermined base pressure.