JP3324824B2 - Cleaning equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cleaning apparatus for a semiconductor wafer, and more particularly to a cleaning apparatus for etching an SiO ₂ film on a semiconductor surface and cleaning the surface.

[0002]

2. Description of the Related Art In an IC manufacturing process, a cleaning process is becoming increasingly important. The cleaning step includes cleaning only contaminants on the surface and etching the substrate surface to remove contaminants on the surface together. SiO on Si substrate surface
Cleaning that exposes the cleaning surface by etching part or all of the _two films is often used.

The etching of the SiO ₂ film is usually performed by a wet process using a hydrofluoric acid aqueous solution or a dry process using plasma. However, these processes have problems such as addition of particles and addition of metal impurities. As a promising process that can solve these problems, a gas phase decomposition method using hydrogen fluoride gas is expected.

[0004] This vapor phase decomposition method is effective for cleaning semiconductor wafers because it can remove a surface layer and expose a clean surface by using a high-purity etching gas.

A semiconductor cleaning apparatus using this gas phase decomposition is as follows:
It is being developed by a joint development between Texas Institute of Technology and FSI (EXCALIBUR anhydrous hydrofluoric acid gas processing system).

[0006] The cleaning device includes a step of etching the SiO ₂ film of the object surface by supplying hydrogen fluoride gas anhydride, a mixed gas of N ₂ gas containing dry N ₂ gas and moisture to the object surface, A step of performing pure water rinsing and a step of subsequently drying the wafer can be performed.

FIG. 3 shows the impurity concentration on the wafer surface when a Si wafer is cleaned using this apparatus. In the figure, the left side shows the residual concentration of Cr, and the right side shows the residual concentration of Fe. The horizontal axis indicates the type of the sample before cleaning, the sample after etching the SiO ₂ film, and the sample after rinsing with pure water and drying.

As can be seen from the graph, even after rinsing with pure water and drying, impurity atoms of Cr and Fe remain on the wafer surface in the order of 10 ¹¹ cm ^-2 . This is presumably because the removed impurity atoms are reattached to the active Si surface and cannot be removed by pure water rinsing.

Further, it has been reported that even if hydrofluoric acid steam is sprayed on the wafer surface to decompose contaminants on the surface, impurity elements such as Cu and Au cannot be recovered by subsequent cleaning with pure water. (IEICE Technical Report S
DM91-159). It is reported that even if Cu, Au and the like can be decomposed, the ionization tendency is lower than that of Si, so that they reattach to the wafer surface and cannot be recovered by subsequent pure water washing or the like.

[0010]

In such a conventional wafer cleaning method, it is difficult to completely remove the decomposed metal element because the decomposed metal element adheres to the Si surface.

It is an object of the present invention to remove impurities such as metal elements decomposed by etching a SiO ₂ film on a wafer surface.
An object of the present invention is to provide a cleaning device that can be removed without reattaching to an i-surface.

[0012]

A cleaning apparatus according to the present invention comprises a filter including a hydrophobic porous membrane (4) capable of covering an opening (1) of a container (2) containing an aqueous solution of hydrofluoric acid (3). A member, a heating means (5) for heating the inside of the container (2), a cooling tank (7) for placing and cooling the object (6), and an opening of the container (2) (1) A gas supply system (8a) connected to an upper part of the filter member on the upper side, and a gas supply system (8a) connected to an upper part of the cooling tank (7), and the filter is connected to a container (2). Another gas supply system (8) for supplying steam supplied to the gas supply system (8a) via the member onto the object (6), and for rinsing and drying the object (6) Rinse drying means (1)
8, 20), a second gas discharging means (11, V1) for discharging gas from a space above the opening (1) of the gas supply system (8a), and the gas discharging means. Exhaust gas processing means (9, 10, 13).

[0013]

[Action] during SiO ₂ film etching the surface of the object by cooling the object, fine liquid droplets to the object on the surface adheres.

The impurity atoms in the SiO ₂ film decomposed by the hydrofluoric acid gas dissolve in the droplets. By flushing the droplet before the impurity atoms recombine with the activated object surface, the impurity atoms can be effectively removed.

In order to improve the etching rate of the SiO ₂ film, hydrofluoric acid gas is heated. The hydrofluoric acid gas obtained by heating in this way contains mist of a large diameter and has a low purity, but by cutting off the mist of a predetermined diameter or more by passing through a hydrophobic porous membrane, the hydrofluoric acid gas is removed. Purity can be improved.

Accordingly, it becomes possible to supply a high-purity hydrofluoric acid gas onto the object, so that the object can be prevented from being contaminated by impurities in the hydrofluoric acid gas.

[0017]

FIG. 1 shows a basic configuration of a cleaning apparatus used in an embodiment of the present invention. This apparatus basically contains an ultra-high purity hydrofluoric acid gas generator and an object 6, and converts the hydrofluoric acid gas to SiO ₂
And a reaction vessel 16 for etching the SiO ₂ film on the surface of the object 6 and a rinse drying vessel 19 for rinsing and drying the object 6a.

In FIG. 1, a container 2 having an opening 1 is
The hydrofluoric acid aqueous solution 3 is stored. On the opening 1, a diameter of 50 μm
A hydrophobic porous membrane 4 such as a porous tetrafluoroethylene having a number of the following small holes is arranged and covers the opening 1.

A heating means 5 is arranged near the container 2.
The inside of the container 2 can be uniformly heated and maintained at a constant temperature. The hydrofluoric acid aqueous solution 3 in the container 2 is heated to a certain temperature and evaporates at a certain speed. The heating means 5 is preferably
The main surface of the container 2 can be uniformly heated, such as a ribbon heater or a rubber heater.

The hydrogen fluoride gas and water vapor (hereinafter referred to as hydrofluoric acid gas) generated in this manner are transferred to the hydrophobic porous membrane 4.
Through the gas supply system 8a. When hydrofluoric acid gas passes through the hydrophobic porous membrane 4, mist having a large particle diameter contained in hydrofluoric acid gas is cut off.

The impurities in the hydrofluoric acid aqueous solution 3 are wrapped in mist having a large particle diameter by heating and evaporate, but do not reach the gas supply system 8a because they are blocked by the hydrophobic porous membrane 4.

Therefore, the hydrofluoric acid gas supplied to the gas supply system 8a through the hydrophobic porous membrane 4 has a high purity. In addition, the whole opening 1 is not covered with the hydrophobic porous membrane 4,
A filter member having a hydrophobic porous membrane may be formed, and the opening 1 may be covered with the filter member.

In the reaction vessel 16 shown in the center of FIG. 1, the object 6 is arranged in contact with the cooling tank 7. The space surrounding the object 6 is connected to the gas supply system 8 and is substantially an airtight space. Preferably, the reaction vessel 16 is also heated uniformly so as to prevent liquefaction on the wall surface.

The cooling tank 7 is maintained at a temperature lower than the dew point in the reaction vessel 16 by, for example, passing cooling water. As the cooling unit, any unit other than the cooling water may be used as long as it can cool the object 6.

The reaction vessel 16 has a valve V4 and a pipe 12
And an exhaust system provided with
The hydrofluoric acid gas or the like that has completed the reaction with O ₂ is bubbled through the pipe 12 to the exhaust gas treatment liquid 9 in the exhaust gas treatment vessel 10.

An alkaline solution is used as the exhaust gas treatment liquid 9, and the acidic etching gas is neutralized by bubbling. The exhaust gas treated in this way is harmless and is discharged from the pipe 13 to the outside.

Also on the container 2 side containing the hydrofluoric acid aqueous solution 3, the pipes 11 and 14 are connected to the gas supply system 8a by valves V and V.
1 and V3. The pipe 11 is introduced into the exhaust gas treatment liquid 9 in the exhaust gas treatment container 10, and when the hydrofluoric acid gas is supplied, bubbling is performed in the exhaust gas treatment liquid 9.

The piping 14 can introduce a carrier gas such as N ₂ gas. Hydrofluoric acid aqueous solution 3 in container 2
Is heated and evaporated, and a carrier gas is introduced from the pipe 14, whereby a desired flow rate ratio of the hydrofluoric acid gas to the carrier gas can be realized. The etching gas having the desired flow ratio is supplied to the reaction vessel 16.

It is desirable that the gas supply systems 8 and 8a are heated by a ribbon heater or the like, and the entirety thereof together with the container 2 is maintained at a desired temperature. In this way, the reaction vessel 16 is supplied through the gas supply systems 8 and 8a without liquefying the hydrofluoric acid gas generated by the heating of the heating means 5.
Can be supplied to

Also in the reaction vessel 16, the pipe 15 is connected via the valve V2 and the gas supply system 8. The pipe 15 is used for introducing a gas such as an inert gas into the reaction vessel 16 and purging the inside of the reaction vessel 16.

If necessary, liquid drains 4 and 25 are provided above the reaction vessel 16 and the hydrophobic porous film of the gas supply system 8a.
It is desirable to be able to discharge from 4,25.

The rinse drying container 19 and the reactor 16 shown on the left side of FIG. 1 are separated by a shutter 21 so that the sealed state in each container is maintained. By opening the shutter 21, the object 6 on the cooling tank 7 is moved to the spinner 18 in the rinsing drying container 19 using the object transfer machine 17.
Can be placed on the

At the upper part of the spinner 18, pure water introducing means 2 is provided.
0 is connected via a valve V8. The pure water introducing means 20 can supply pure water onto the target object 6 a placed on the spinner 18.

A valve V is provided on the bottom of the rinsing drying vessel 19.
6, the drain 23 is connected. Object 6a
The waste liquid after rinsing is discharged through the drain 23.

The washing and drying container 19 has a valve V9.
Gas introduction means 24 is connected through
The gas exhaust means 22 is connected via 7. The gas introduction unit 24 and the gas exhaust unit 22 are used for introducing a gas such as a dried inert gas into the rinse drying container 19, purging the rinse drying container 19, and drying the object 6a. .

In the following, a thickness of 1 was formed on a Si wafer by thermal oxidation.
The object on which the SiO ₂ film of 2,000 mm is formed is
The case where the surface of the Si wafer is cleaned will be described as an example.
The Si wafer 6 is placed on the cooling bath 7. Cooling water of, for example, 7 ° C. is passed through the cooling tank 7 to cool the Si wafer 6.
Here, the temperature of the cooling water may be a temperature other than 7 ° C. as long as it is 0 ° C. or higher and is equal to or lower than the dew point in the reaction vessel 16.

The reaction vessel 16 is preheated to 80.degree. The valve V2 is opened to introduce the dried N ₂ gas into the reaction vessel 16, and the valve V4 is opened to exhaust. At this time, the shutter 21 is closed to keep the inside of the reaction vessel 16 almost airtight. Thus, the inside of the reaction vessel 16 is set to the N ₂ gas atmosphere.

At the same time, the container 2 is heated, and the hydrofluoric acid aqueous solution 3 is heated to 120 ° C. The evaporated hydrofluoric acid gas is purified by the hydrophobic porous membrane 4 and supplied to the gas supply system 8a. At this time, the valves V1 and V3 are opened and the valve V5 is closed.

A dry N ₂ gas at a flow rate of 0.8 l / min is introduced from the pipe 14, hydrofluoric acid gas and N ₂ gas are mixed in the gas supply system 8 a, and the mixture is exhausted through the pipe 11. Bubble. This process is continued for a certain period of time, and the mixed gas (etching gas) of hydrofluoric acid gas and N ₂ gas is brought into a steady state at 120 ° C. At this time, the flow ratio of the hydrofluoric acid gas to the N ₂ gas is 0.4.

In this embodiment, the temperature of the hydrofluoric acid aqueous solution is set to 120 ° C., and the flow rate of the N ₂ gas is set to 0.8 l / min. By changing the temperature of the hydrofluoric acid aqueous solution, the Si
Since the etching rate of the O ₂ film changes, it is preferable to set the temperature so as to obtain an appropriate etching rate.

After the steady state, the valves V1 and V2 are closed and the valve V5 is opened to supply the etching gas to the reaction vessel 16 through the gas supply system 8. The SiO ₂ film on the surface of the Si wafer 6 in the reaction vessel 16 is etched by the etching gas supplied through the gas supply system 8.

After part or all of the SiO ₂ film has been removed, the surface of the Si wafer 6 is kept below the dew point.
A mist droplet adheres to the surface. Since the impurity element such as a metal is dissolved in the mist-like droplet, it is possible to prevent the impurity element from re-adhering to the active Si wafer surface after removing the SiO ₂ film.

After etching for a predetermined time, the valve V5 is closed, the valve V2 is opened, and the hydrofluoric acid gas in the reaction vessel 16 is exhausted, and the valve V1 is opened to exhaust the hydrofluoric acid gas in the vessel 2 through the pipe 11. I do. At the same time, the valve V
7, V9 is opened, and N ₂ gas is introduced into the rinsing drying container 19 to make an N ₂ gas atmosphere.

Next, the shutter 21 that shuts off the reaction container 16 and the washing and drying container 19 is opened, and the object transfer machine 1 is opened.
7 moves the Si wafer from above the cooling bath 7 to above the spinner 18.

The shutter 21 and the valves V9 and V7 are closed, the valve V6 is opened, and the Si wafer is set at 1000 rpm.
Rotate at the speed of At the same time, the valve V8 is opened to supply pure water onto the Si wafer 6a, and rinse with pure water for about 1 minute.

Next, the valves V8 and V6 are closed, and the valves V9 and V7 are opened. While flowing dry N ₂ gas into the cleaning / drying container 19, the rotation speed of the Si wafer 6a is set to 3
000 rpm, and the Si wafer 6a is dried.

FIG. 2 is a graph showing the impurity concentration on the surface of the Si wafer whose surface has been cleaned by the above embodiment and the conventional example. Using the total reflection X-ray fluorescence, the F
The residual concentrations of e and Cu were measured.

FIG. 2 shows the measurement results of the control wafer before cleaning, the measurement results obtained when the apparatus used in the present embodiment was used to clean the Si wafer without cooling, and the measurement result obtained in the case of cleaning according to the present embodiment. .

The surface concentration of Fe was lower than the detection limit both in the case where the Si wafer was washed without cooling and in the case where the Si wafer was washed according to the present embodiment. The surface concentration of Cu is S
If the i-wafer is cleaned without cooling, it is still 10 ¹⁰
cm ^-2 order. This is considered to be because Cu has a lower ionization tendency than Si, and thus is strongly bonded to the active Si wafer surface.

In the case of cleaning according to this embodiment, Cu
Was also below the detection limit. This is SiO ₂
It is considered that since fine droplets adhere to the surface of the Si wafer during etching, Cu atoms dissolve in the droplets and are washed away by washing before recombining with the surface of the Si wafer.

In the present embodiment, SiO ₂
Although pure water rinsing is performed immediately after the film is etched, a mixed gas of hydrochloric acid gas and N ₂ gas may be supplied onto a cooled Si wafer before pure water rinsing.

By supplying hydrochloric acid gas, fine droplets of hydrochloric acid are generated on the surface of the Si wafer, and the effect of removing metal elements such as Cu and Ni can be further enhanced. The same effect can be obtained even when the supply of the hydrochloric acid gas is performed simultaneously with the supply of the hydrofluoric acid gas.

FIG. 4 shows the basic structure of a cleaning apparatus capable of supplying hydrochloric acid gas after supplying hydrofluoric acid gas or simultaneously with supplying hydrofluoric acid gas. The cleaning apparatus shown in FIG. 4 includes another container 2b similar to the container 2 of FIG. 1, another hydrophobic porous membrane 4b similar to the hydrophobic porous membrane 4, and another heating unit 5b similar to the heating unit 5. have. The container 2b contains hydrochloric acid 3b.

The upper part of the hydrophobic porous membrane 4b is covered by a gas supply system 8c, and the gas supply system 8c is connected to the gas supply system 8b via a valve V5b. Gas supply system 8
b is connected to the upper part of the reaction vessel 16 and can supply the hydrochloric acid gas evaporated from the vessel 2b into the reaction vessel 16.

The gas supply system 8c includes pipes 11b and 1
4b is connected via valves V1b and V3b. The pipe 11b is introduced into the exhaust gas treatment liquid 9 in the exhaust gas treatment container 10, and is introduced into the exhaust gas treatment liquid 9 when hydrochloric acid gas is supplied.

Further, the carrier gas such as N ₂ gas can be introduced into the pipe 14b. Hydrochloric acid 3b in container 2b
Is heated and evaporated, and a carrier gas is introduced from the pipe 14b, whereby a hydrochloric acid gas having a desired flow ratio to the carrier gas can be supplied into the reaction vessel 16.

A pipe 15b is connected to the gas supply system 8b via a valve V2b. The pipe 15b is used for introducing and purging a gas such as an inert gas into the gas supply system 8b and the reaction vessel 16.

If necessary, the gas supply systems 8a, 8a
a liquid drain 2 at the top of the hydrophobic porous membrane in c.
It is desirable to provide liquids 4 and 24b so that when liquid is generated, the liquid can be discharged from the drains 24 and 24b.

The cleaning device used in the above-described embodiment is a Si device.
Since the decomposition of the O ₂ film, the formation of droplets of hydrofluoric acid and hydrochloric acid, washing with water, and drying are performed in a closed system separated from the environment,
No pollution from the environment.

In the above-described embodiment, N ₂ gas is used as the carrier gas and the purge gas. However, the present invention is not limited to the N ₂ gas, and other inert gases may be used. Further, in the above-described embodiment, the case where the reaction container and the rinsing drying container are separated from each other is described. However, a rinsing drying unit may be provided in the reaction container. In this case, Si
There is no need to move the target when moving from the O ₂ film etching process to the pure water rinsing process.

The present invention has been described in connection with the preferred embodiments.
The present invention is not limited to these. For example,
It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0062]

As described above, according to the present invention,
It is possible to obtain a highly clean wafer with extremely little metal contamination.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a basic configuration of a cleaning apparatus used in an embodiment of the present invention.

FIG. 2 is a graph showing an impurity concentration on a wafer surface after cleaning a Si wafer according to an embodiment of the present invention.

FIG. 3 is a graph showing an impurity concentration on a wafer surface after cleaning a Si wafer according to a conventional example.

FIG. 4 is a conceptual diagram showing a basic configuration of a cleaning apparatus used in another embodiment of the present invention.

[Explanation of symbols]

 1, 1b opening 2, 2b container 3 aqueous solution of hydrofluoric acid 3b hydrochloric acid 4, 4b hydrophobic porous membrane 5, 5b heating means 6, 6a object 7 cooling tank 8, 8a, 8b, 8c gas supply system 9 exhaust gas treatment liquid 10 Exhaust gas treatment vessel 11, 11b, 12, 13 Piping 14, 14b, 15, 15b, 24 Gas introduction means 16 Reaction vessel 17 Object transfer machine 18 Spinner 19 Rinse drying vessel 20 Pure water introduction means 21 Shutter 22 Gas exhaust means 23 , 24, 24b, 25 Drain V valve

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kaoru Nozaki 1-6-6 Matsuzakadaira, Yamato-cho, Kurokawa-gun, Miyagi Prefecture In-house Fujifilm Micro Devices Co., Ltd. (72) Inventor Norihiko Kato 1-chome Matsuzakadaira, Yamato-cho, Kurokawa-gun, Miyagi 6 Fujifilm Micro Devices Co., Ltd. In-house (56) References JP-A-4-97526 (JP, A) JP-A-62-213127 (JP, A) JP-A-2-237029 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 21/304 H01L 21/306

Claims (11)

(57) [Claims] 1. A container (2) for containing a hydrofluoric acid aqueous solution (3).
Hydrophobic porous membrane (4) that can cover the opening (1)
And a heating means (5) for heating the inside of the container (2).
And a cooling tank (7) for placing and cooling the object (6)
A gas supply system (8a) connected to the upper part of the filter member on the opening (1) of the container (2); and connecting the gas supply system (8a) to the upper part of the cooling tank (7). And another gas supply system (8) for supplying steam supplied from the container (2) to the gas supply system (8a) through the filter member onto the object (6); Rinsing and drying means (18, 20) for rinsing and drying (6), and second gas discharging means (for discharging gas from the space above the opening (1) of the gas supply system (8a) 11, V
1) and exhaust gas treatment means (9, 1) connected to the gas discharge means.
0, 13). 2. The rinsing drying means is provided in another container (19) separated from a space above the cooling bath (7) by a shutter (21).
The cleaning device according to the above. 3. The rinse drying means includes a pure water introduction means (20) provided on the object (6) and the object (6).
3. The cleaning device according to claim 1, further comprising a spinner (18) capable of rotating the fixed member. 4. The rinsing drying means includes a first rinsing means capable of introducing a dry inert gas into a space in which the object (6) is placed.
Gas introducing means (24, V9) and first gas discharging means (22, V7) for discharging gas from the space
The cleaning device according to claim 1, comprising: 5. The cleaning according to claim 2, further comprising an object transfer machine (17) capable of moving an object placed on the upper part of the cooling tank (7) into the another container (19). apparatus. 6. The cleaning apparatus according to claim 1, further comprising a second gas introduction unit (14, V3) for introducing an inert gas into the gas supply system (8a). 7. A gas discharge means (12, V4) for discharging gas from a space above an object (6) of said another gas supply system (8). The cleaning device according to any one of the above. 8. A third gas supply system for introducing an inert gas into a space above an object (6) of the other gas supply system (8).
The cleaning apparatus according to claim 7, further comprising a gas introduction means (15, V2). 9. The cleaning apparatus according to claim 1, further comprising heating means for heating the gas supply system (8a) and another gas supply system (8). 10. A valve (V) that connects the gas supply system (8a) to another gas supply system (8) and opens and closes.
The cleaning device according to any one of claims 1 to 9, further comprising (5). 11. The cleaning apparatus according to claim 1, wherein at least one of the gas supply system (8a) and the other gas supply system (8) has a drain for discharging a liquid.