Apparatus for cleaning a wafer surface

A cleaning apparatus for cleaning with a mixture of various chemicals. The cleaning apparatus includes a compressor for compressing and transferring a solution medium, at least one jet pipe, one end of which is connected to the compressor and the other end of which is open, and a plurality of suction pipes, connected to the jet pipe at a specified interval, respectively. The apparatus further includes a plurality of chemical tanks with an open end of the suction pipe being inserted into each of the chemical tanks, respectively. The invention permits a number of objects to be cleaned sequentially without being contaminated by making use of the principal of aspiration. In addition, the compressor is used only to pass the solution medium therethrough inside of the compressor and is never corroded by the mixture of chemicals.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to cleaning equipment for cleaning a wafer 
surface with a mixture of various chemicals. 
2. Description of Related Art 
In conventional types of cleaning equipment, when it is necessary, for 
instance, to sequentially clean a number of objects (such as wafers), at 
first a mixture of chemicals is put in a vessel such as a beaker, and then 
an object to be cleaned is steeped in said mixture of chemicals, and after 
it is taken out from the mixture of chemicals, the next object to be 
cleaned is steeped in the mixture of chemicals, thus this step being 
repeated. 
With the construction based on prior art as described above, however, as 
objects to be cleaned are steeped sequentially in a mixture of chemicals, 
an object cleaned later in the mixture of chemicals is steeped in a more 
contaminated mixture of chemicals, which is not preferable. 
In this case, such a method as exhausting a mixture of various chemicals 
with a compressing means (a pump) for sequentially cleaning objects to be 
cleaned may be used. In this method, such problems as corrosion of the 
compressing means (a pump) may occur due to the chemicals. An object of 
the present invention is to provide, for the purpose to solve the problems 
as described above, a cleaning equipment in which objects to be cleaned 
can sequentially and repeatedly be cleaned without being contaminated and 
such problems as corrosion due to chemicals used for cleaning can be 
prevented. 
SUMMARY OF THE INVENTION 
To achieve the object as described above, an invention is characterized in 
that the construction according to the invention includes a compressing 
means to compress and transfer a solution medium, at least one jet pipe, 
one end of which is connected to an edge of the compressing means and 
another edge of which is open, a plurality of suction pipes connected to 
the jet pipe or jet pipes at a specified interval, each communicated to 
the jet pipe, and a plurality of chemical tanks with an open end of each 
suction pipe inserted to each of the chemical tanks respectively. 
An invention is characterized in that the aforesaid jet pipe has a heating 
means to improve the cleaning effect. 
An invention is characterized in that each of the aforesaid plurality of 
suction pipes has a flow rate control valve to change a composition ratio 
of each chemical. 
An invention is characterized in that a connecting section of the aforesaid 
jet pipe to each of the aforesaid suction pipes has a smaller diameter 
than that of other sections so that a mixing efficiency of a solution 
medium with chemicals will be furthermore improved. An invention is 
characterized in that the aforesaid chemical tank has a pressurizing means 
for pressing a chemical in the chemical tank with a gas to furthermore 
improve the mixing efficiency of chemicals. 
In accordance with an embodiment of the present invention, if a solution 
medium such as, for instance, pure water is compressed and transferred 
from one end to another end of a jet pipe with a pressurizing means, a 
chemical in each chemical tank is sucked up from the chemical tank into 
the solution medium flowing through the jet pipe, and a mixture of the 
solution medium and the chemicals is exhausted, as a mixture of chemicals, 
from an opening at another end of the jet pipe. 
In accordance with an alternative embodiment of the present invention, as a 
solution medium, which flows in a jet pipe, is heated by a heating means, 
the efficiency of processing with a mixture of chemicals and a solution 
medium can be improved. In yet another embodiment, the composition of the 
aforesaid mixture of chemicals can freely be changed by adjusting opening 
degrees of the flow rate control valves. 
According to one aspect of the present invention a flow velocity of a 
solution medium in a connecting section between a jet pipe and a suction 
pipe can be increased. 
As a surface of a chemical is pressurized by the pressurizing means, the 
efficiency in mixing the chemical with a solution medium can furthermore 
be raised.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG.1 shows a first embodiment of the cleaning system of the present 
invention, wherein a compressing pump 2 as a compressing means is arranged 
at an edge (the right edge in the figure) of a horizontal jet pipe 1 and 
the compressing pump 2 has a solution medium storage tank 3, in its 
upstream side, in which a solution medium is stored. To the aforesaid jet 
pipe 1 are connected at a specified interval, for instance, 2 suction 
pipes 4a and 4b, each communicated to said jet pipe 1, and the suction 
pipes 4a and 4b are inserted into chemical tanks 5a and 5b respectively 
with various types of chemical being stored in the chemical tanks 5a and 
5b. 
And, one end (the left edge in FIG. 1) of the aforesaid jet pipe 1 is 
tapered with an opening at its tip, so that an object to be cleaned is 
placed against the end opening. 
As the first embodiment has the construction as described above, when the 
compressing pump 2 is driven, the solution medium sucked up from the 
solution medium storage tank 3 flows in the jet pipe 1 along its 
longitudinal direction. Then, chemicals stored in the chemical tanks 5a 
and 5b respectively are sucked up from the chemical tanks because of the 
principle of aspirator, namely due to a jet of the solution, and mixed 
with the solution medium in the jet pipe 1, and exhausted from the end 
opening of the jet pipe 1. And, an object to be cleaned is cleaned by this 
exhausted mixture of chemicals. Herein, the compressing pump 2 may be 
either of the type that feeds a chemical either at a constant rate or of 
the type that feeds a chemical spasmodically like a diaphragm. Also a 
plurality of jet pipe 1 may be used in the construction according to the 
present invention. 
FIG. 2 shows a second embodiment of the present invention, wherein suction 
pipes 4c and 4d and chemical tanks 5c and 5d are added to the construction 
according to the aforesaid first embodiment, a branch pipe 9 having a flow 
rate control valve 8 is arranged in the downstream from the compressing 
pump 2, and furthermore, for instance, heating means 10 and 11 comprising 
an electrothermal coil respectively at, for instance, the upstream end or 
the downstream end. Also pressurizing means 13a to 13d, which supply an 
inactive gas to the chemical in each of the aforesaid chemical tanks 5a to 
5d through gas supply pipes 14a to 14d respectively, are arranged. 
With the construction according to the second embodiment of the present 
invention, when it is necessary, for instance, to carry out so-called RCA 
cleaning, the following sequence is employed. 
At first, pure water is stored in the solution medium tank 3, and H.sub.2 O 
liquid, NH.sub.4 OH liquid, HCl liquid, and HF liquid are stored in the 
chemical tanks 5a to 5d respectively. 
In a first cleaning process, at first the two flow rate control valves 7c 
and 7d are fully closed so that only the two chemicals (NH.sub.4 OH, 
H.sub.2 O.sub.2) are sucked up, and the mixture of chemicals obtained 
through the operation described above is exhausted against a wafer 6. In 
this case, in order to adjust the mixing ratio of the solution medium 
(H.sub.2 O) vs the two chemicals (H.sub.2 O.sub.2, NH.sub.4 OH) to, for 
instance, 1:1:5, opening degrees of the flow rate control valves 7a and 7b 
area adjusted, and if the opening degree is insufficient, a quantity of a 
chemical to be sucked up is adjusted by using the pressurizing means 13a 
or 13b to push down the level of the chemical with a gas which is inactive 
to the chemical (for instance, N, gas). Furthermore, the heating means 10 
and 11 are run to heat the mixture of chemicals up to, for instance, the 
boiling state. 
Then, in a second cleaning process, each of the flow rate control valves 7a 
to 7d is completely closed, and the wafer 6 is cleaned only by the pure 
water sucked up from the solution tank 3. 
Then, in a third cleaning process, the two flow rate control valves 7b and 
7d are fully closed so that the two types of chemicals (H.sub.2 O.sub.2, 
HCl) are sucked up and the ratio of H.sub.2 O vs H.sub.2 O.sub.2 VS HCL is 
adjusted to 5:1:1. Also in this process, like in the aforesaid first 
process, the heating means 10 and 11 are run to clean wafers with the 
heated mixture of chemicals. 
Then, in a fourth cleaning process, like in the aforesaid second process, 
each of the flow rate control valves 7a to 7d is completely closed, and 
cleaning with only pure water is carried out. 
Then, in a fifth cleaning process, the flow rate control valves 7a to 7c 
are closed so that only one chemical (HF) will be sucked up and the ratio 
of solution medium (H.sub.2 O) and chemical (HF) will be adjusted to, for 
instance, 50:1. 
Finally, in a sixth cleaning process, like in the aforesaid second and 
fourth processes, cleaning with only pure water is carried out, and then a 
drying process is started. 
To carrying out this drying process, it is necessary to stop operation of 
the compressing pump 2 and fully open, for instance, a flow rate control 
valve 9 for a branch pipe 8 and to send N.sub.2 gas (or Ar gas) into the 
jet pipe 1 with the pressurizing means 13a to 13d by driving the heating 
means 10 and 11 and exhaust the gas from the end of the jet pipe 1. With 
this construction, the necessity to arrange a drying means separately is 
eliminated. 
It should be noted that, with the branch pipe 8 arranged in the 
construction, a flow rate of the compressing pump 2 can be controlled by 
adjusting an opening degree of the flow rate control valve 9. Also it 
should be noted that, although a case of scrubbing wafers by means of RCA 
scrubbing as described as an example of application of this invention, the 
present invention is also applicable to other forms of cleaning such as 
cleaning after separating resist by using a mixture of, for instance, 
alcohol as a solution medium and acetone and trichloroethane as chemicals. 
FIG. 3 shows other embodiment of the jet pipe 1, and in the connecting 
section between the jet pipe 1 and the suction pipe 4a , a diameter of the 
jet pipe is smaller that that in other sections. Other sections of this 
construction are the same as those in the second embodiment. With this 
construction, a flow velocity of a solution medium in the aforesaid 
connecting section increases, and the sucking rate of a chemical the 
chemical tank 4a also increases in proportion to the increase of flow 
velocity above. 
FIG. 4 shows other embodiment of the end opening of the jet pipe 1, and 
this embodiment has the construction wherein said end opening is branched 
to two branch pipes, exhaust nozzles 1c.sub.1 and 1c.sub.2 are arranged 
facing tips of the branch pipes 1b.sub.1 and 1b.sub.2 respectively, and an 
object to be cleaned is placed between the two exhaust nozzles 1c.sub.1 
and 1c.sub.2. 
In this construction, the object to be cleaned can be cleaned from both 
sides, which contributes to improvement of the cleaning efficiency. 
If a material with a surface finished to a mirror-like state by means of, 
for instance, electrolytic compound polishing and oxidized film 
passivation formed on it by supplying high purity oxygen under a high 
temperature (around 400.degree. C.) is used for internal surface (which is 
contacted by a liquid) of such sections as the jet pipe through which the 
solution medium flows, elution of metallic components can be prevented. 
An embodiment of the present invention comprises a compressing means to 
compress and transfer a solution medium, at least one jet pipe, one end of 
which is connected to the compressing means and other end of which is 
open, a plurality of suction pipes connected to the jet pipe at a 
specified interval, each communicated to each jet pipe, and a plurality of 
chemical tanks with an open end of each suction pipe inserted into each 
chemical tank respectively, so that a large number of objects to be 
cleaned can sequentially be cleaned without being contaminated by making 
use of the principle of aspirator. Also, as the compressing means is used 
only to pass a solution medium, inside of the compressing means is never 
corroded by a mixture of chemicals. 
The aforesaid jet pipe has a heating means additionally arranged in the 
construction, so chemicals can easily be mixed and such a processing as 
boiling the mixture of chemicals can be made, which contributes to 
improvement of the cleaning efficiency. 
The aforesaid plurality of suction pipes has a flow rate control valve 
respectively, so a mixing ratio of chemicals to be mixed together can be 
changed arbitrarily by adjusting opening degrees of the flow rate control 
valves, and also types of chemicals to be mixed together can arbitrarily 
be changed by opening or closing the flow rate control valves. 
According to the present invention, it is possible to increase a quality of 
any chemical to be sucked up by making higher the jet velocity of a 
solution medium. 
With the invention according to claim 5, in the construction as claimed in 
claim 1, the aforesaid chemical tank has a compressing means to push up a 
level of the chemical by using a gas, the sucking rate of the chemical 
into the jet pipe can easily be increased, and at the same time the gas 
can be exhausted from an end of the jet pipe by discharging the chemical 
and pressurizing only the gas.