Apparatus for plasma etching circuit boards or the like

The circuit board plasma etching apparatus includes a preheating chamber, a plasma reaction chamber and a cooling chamber for etching circuit boards with plasma in a quasi continuous operation. The plasma reaction chamber is sealed by a gas-tight preheating sealing slide adjacent the preheating chamber and by a gas-tight cooling sealing slide adjacent the cooling chamber. A preheating door selectively closes the preheating entry end and a cooling door selectively closes the cooling chamber exit end. Boards to be etched are placed in printed circuit board cages supported by a guide rail within the chambers. The guide rail is separable into a preheating segment, a reaction chamber segment and a cooling segment contained within the respective chambers. A preheating chamber bellows allows axial movement of the preheating door, as does a cooling chamber bellows for the cooling chamber door. Axial displacement of the doors allows selective segmentation of the guide rail. A bypass conduit selectively allows gas exhausted from the cooling chamber to be fed to the preheating chamber.

The invention relates to an apparatus for plasma etching circuit boards or 
the like, comprising a closable chamber for receiving the circuit boards 
to be treated. 
When circuit boards are plasma etched, they are placed into a reactor 
chamber (cf. e.g. U.S. Pat. No. 4 285 800 or U.S. Pat. No. 4 289 598), a 
gas plasma being generated by introducing a gas and by means of electric 
discharges. The plasma reacts with the surface of the circuit boards, 
whereby above all organic impurities are etched away from the circuit 
board surfaces. More details on the general problems of the plasma etching 
of circuit boards are described e.g. in German Offenlegungsschrift 30 41 
551. 
Known reactors for plasma etching circuit boards have, in addition to a 
limited throughput quantity, above all the disadvantage of relatively long 
idle times arising as a result of loading and unloading between the 
individual treatment cycles. This not only increases the processing time 
of the circuit boards, but also unduly lowers the chamber temperature 
required for the process so that special heating cycles between the 
individual treatment cycles are required which further reduce the 
availability of the reactor. First a continuous processing plant presents 
itself as alternative, but it has become apparent that such a plant does 
not offer an economical solution because of the very high additional 
design expenditure, while the throughput quantity is not particularly 
increased. 
In connection with the treatment of wafers with gaseous carbon 
tetrachloride a continuous apparatus has become known (JP-A-161 065), 
comprising a gas treatment chamber and a lock chamber in front of and a 
lock chamber behind such gas treatment chamber. The wafers may be moved on 
conveyor belts through these chambers which are obviously arranged 
horizontally. A part of the chamber cross section may be opened or closed 
by shut-off means. Since wafers are smaller in size than circuit boards by 
orders of magnitude, since no plasma is generated and since no preheating 
or cooling is provided, this known apparatus could never be used for 
plasma etching circuit boards or the like. 
It should also be mentioned that JP-A-53-114 744 discloses an apparatus 
comprising two chambers, wherein a semiconductor substrate is "exposed" to 
electron or ion beams in a first chamber and this substrate is immediately 
etched with a reactive gas, such as hydrogen fluoride, in an adjacent 
chamber which is separable in a gas-tight manner. The problems underlying 
the present invention are not dealt with. The same applies to an even 
greater extent to the apparatus disclosed by JP-A-57-104 669, wherein 
wafers are immersed one after the other by grip arms in various liquid 
vessels for chemical treatment. 
It is an object of the present invention to provide an apparatus for plasma 
etching in particular circuit boards, which guarantees a high throughput 
and great economic efficiency at low design expenditure. 
This object may be achieved with an apparatus of the type mentioned above, 
in which the chamber is tubular and is arranged preferably horizontally, 
which comprises two outer zones and one center zone, the center zone being 
the plasma reaction chamber and being separable in a gas-tight manner from 
the two outer zones constituting the preheating and cooling chambers, 
respectively, by means of slides or the like, and the two outer zones each 
being closable by a door. 
The solution according to the invention offers the possibility of loading 
and preheating a second charge during the plasma treatment of one charge, 
and at the same time cooling and unloading a third charge. The idle times 
due to the loading and unloading of known reactor chambers are avoided and 
there remains more time for the loading and unloading operations without 
impairing the process flow, which results in a longer life of the 
mechanical parts and offers the possibility of automating the loading and 
unloading operations. Moreover, the handling of hot parts can largely be 
avoided and disturbing residual gases are not present during loading and 
unloading. 
An advantageous further embodiment of the invention is characterized by the 
tubular chamber comprising rails extending substantially along the entire 
length thereof for guiding a cage, container or the like receiving the 
circuit boards or the like. Loading and unloading as well as the 
throughput of the parts to be treated through the apparatus is 
substantially facilitated thereby. 
If the rails are separable from one another or slidable into one another in 
the region of the slides, a gas-tight separation of the individual zones 
may be achieved in a simple manner without the disturbing influence of the 
rails. 
In this case it is of particular advantage if the rails are capable of 
being connected with the doors and if the doors, when closed, are slidable 
axially, while the tightness is maintained, to an extent which permits 
separation of the rails in the region of the slides so that the individual 
chambers can be sealed from each other by means of the slides. In this way 
the rails may be separated from one another in a simple manner and 
subsequently the slides may be closed while the apparatus is completely 
tightly closed. 
The doors are provided with a bellow-type seal to ensure that they are 
slidable. 
In the apparatus according to the invention the heat balance may be 
improved in a simple manner by providing the preheating chamber with a 
heating gas (air) inlet and the cooling chamber with a cooling gas (air) 
inlet, at least a part of the cooling gas (air) leaving the cooling 
chamber being capable of being fed to the preheating chamber through a 
bypass conduit.

According to FIG. 1 the apparatus according to the invention comprises a 
tubular chamber 1 having e.g. circular cross section and being arranged 
preferably horizontally. The chamber comprises two outer zones 2, 3 as 
well as a center zone 4. The center zone 4 of the chamber 1 constitutes 
the plasma reaction chamber 5 and may be separated in a gas-tight manner 
from the two outer zones 2, 3 which constitute the preheating chamber 6 
and the cooling chamber 7, respectively, by means of two slides 8, 9. The 
chamber 1 may be closed by doors 10 and 11, respectively, at its two ends. 
The doors 10, 11 are designed in such a manner that on the one hand they 
can be opened completely so that substantially the entire chamber cross 
section is open, but they may also be moved in the closed, tight state in 
the axial direction of the tubular chamber 1, as is indicated by the 
arrows a. In order to make this movement possible, each door comprises 
bellows 12 and 13, respectively. 
Rails 14, in which cages 15 or similar containers are guided in a suspended 
manner, extend along the entire length of the chamber 1. The circuit 
boards or other objects to be etched are arranged in these cages 15. In 
order to allow sealing of the individual chambers by means of the slides 
8, 9 despite the rails, the rails may be separated from one another in 
this region, which is possible in the following manner. In the region 
where the rails are separated, i.e. in the region of the slides 8, 9, the 
rails are slidable into one another or may be pulled apart so that the 
required separation is possible. In the region of the plasma reactor 
chamber 5 the rails are rigidly secured to the chamber wall in an 
appropriate manner, whereas the rails in the region of the front chamber 6 
and the cooling chamber 7, respectively, are slidable in the logitudinal 
direction and may be secured with their outer ends to the doors 10 and 11, 
respectively. Thereby it is possible to separate the rails in the region 
of the slides 8 and 9, respectively, by moving the doors 10 and 11, 
respectively, in the sealing state to a certain extent outwards, the rails 
14 in the region of the preheating chamber 6 and the cooling chamber 7, 
respectively, thus being capable of being pulled out of the rails in the 
region of the plasma reaction chamber 5 and the slides 8, 9 now being 
closable without impediment. 
The plasma reaction chamber 5 is provided in a known manner with an inlet 
16 and an outlet 17 for the plasma gas. The conduits are connected to the 
respective supply and vacuum systems. The electrodes required to generate 
the plasma are not shown. The preheating chamber 6 comprises an inlet 18 
for the heating gas or the heating air, respectively, a heat exchanger 19, 
heater or the like being provided in the inlet. The air leaving the 
chamber 6 is removed through a conduit 20. In a similar manner cooling air 
or a cooling gas, respectively, is fed to the cooling chamber 7 through a 
conduit 21 and sucked off by means of a blower 22 through a conduit 23 
from the chamber 7 again. At least a part of the heated air leaving the 
cooling chamber 7 may be fed to the preheating chamber 6 again through a 
bypass conduit 24. 
Starting from a chamber which is completely empty at first, the 
quasi-continuous operation of the apparatus according to the invention is 
carried out as follows. The door 10 of the preheating chamber 6 is opened 
and a cage 15 with circuit boards to be treated is placed on the rails 14. 
The door 10 which is axially slidable owing to the bellow-type seal 12 is 
in its outermost position so that the rails 14 are separated in the region 
of the slide 8 and the slide 8 may be closed. After completion of the 
preheating step the slide 8 is opened, the door 10 is moved together with 
the rails 14 in the direction of the chamber so that the rails 14 are 
again connected in the region of the slide 8 and now the cage 15 with the 
circuit boards may be moved into the plasma reaction chamber 5. Now both 
slides 8 and 9 are closed and the etching operation in the plasma reaction 
chamber 5 may be performed. Independent thereof the door 10 may now be 
opened again and a new cage 15 with circuit boards may be placed into the 
preheating chamber. After completion of the etching step, the slide 9 is 
opened and a cage 15 is moved from the reaction chamber 5 into the cooling 
chamber 7. At the same time another cage 15 may be moved from the 
preheating chamber 6 into the reaction chamber 5. When the circuit boards 
in the cooling chamber 7 are sufficiently cooled, the door 11 may be 
opened and the cage 15 with the treated circuit boards is taken out. The 
connection of the rails in the region of the slide 9 is effected in the 
same manner by means of the axially slidable door 11 as described above in 
connection with the preheating chamber. An advance means 25 having e.g. a 
hydraulic or pneumatic drive may be provided to move the cages 15 along 
the rails 14, which is only suggested in the drawing and not described in 
greater detail. 
It is shown that the apparatus according to the invention allows a 
quasi-continuous operation which avoids the relatively long idle times 
required so far. The entire heat balance is substantially more favourable 
than with the known systems. Loading and unloading of the apparatus may be 
effected in a simple manner and may, moreover, be automated with little 
expenditure. Although the drawing shows heating in the preheating chamber 
by means of hot air, the circuit boards may be heated in the preheating 
chamber also by infrared radiation.