JPH06148169A - Extracting method and extracting device for trace substance - Google Patents

Abstract

PURPOSE:To provide a super-high sensitivity extracting method and extracting device for trace substance with high processing speed and extremely low background impurity concentration in the super-high senstivity extraction of a trace material such as impurities present on a sample surface layer such as a semiconductor wafer. CONSTITUTION:A trace material extracting method and extracting device has a filter member containing a hydrophobic porous film 4 capable of covering the opening 1 of a vessel 2 for receiving a liquefied reagent 3; a heating means 5 for heating the inner part of the vessel 2; a cooling tank 7 for placing a sample 6 and cooling it; a gas feeding system 8 for connecting the filter member on the opening of the vessel 23 to the upper part of the cooling tank 7 and supplying the vapor supplied from the vessel 2 through the filter member onto the sample 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for ultrasensitive extraction of trace substances, and more particularly to a method and apparatus for ultratrace extraction of trace substances such as impurities present in a sample surface layer such as a semiconductor wafer. .

For example, in the semiconductor manufacturing technology, as the scale of semiconductor integrated circuits becomes larger and ultrafine processing progresses, it is required to control the quality of oxide films, nitride films, etc., which are the constituent elements of semiconductor devices, with high precision. ing.

[0003]

2. Description of the Related Art For example, the characteristics of a semiconductor insulating film are deteriorated by the inclusion of impurities. When alkali metal or heavy metal molecules are mixed in, the insulating property is significantly impaired. Further, the impurity ions drift in the insulating film when an electric field is applied, and segregate at the interface or defect site, deteriorating the device characteristics and sometimes causing the function of the integrated circuit to be lost.

Of course, the problem of impurity contamination is not limited to the insulating film. In the process of processing a semiconductor wafer, the impurity molecules attached to the surface layer enter the inside of the semiconductor due to diffusion or drift and deteriorate the characteristics of the semiconductor device. As the technology advances, trace amounts of impurities that have hitherto not been considered practically have become a problem.

In order to control the trace amount of impurities, it is necessary to detect the trace amount of impurities in order to specify the path and influence thereof. As a means for extracting trace impurities contained in an insulating film such as an oxide film or a nitride film formed on a semiconductor wafer, dissolution of the insulating film with an ultra-high purity reagent has been conventionally performed.

However, extraction by dissolution in a commercially available purified reagent has made it difficult to obtain sufficient sensitivity.
Further, as an effective method for extracting impurities with high sensitivity, a method using vapor of a purified reagent is disclosed.

FIG. 8 is a sectional view of the structure of a typical impurity extraction device by vapor phase decomposition. FIG. 8 (A) is an example utilizing the natural evaporation of the reagent disclosed in, for example, JP-A-60-69531, and FIGS. 8 (B) and 8 (C) are, for example, JP-A-60-164330. This is an example of using forced evaporation of a reagent disclosed in Proceedings 2C13 of 1992 Annual Meeting of Analytical Society.

In FIG. 8 (A), a semiconductor wafer 22 as a test object is vertically arranged in a sealed corrosion-resistant container 21. The insulating film 2 is formed on the surface of the semiconductor wafer 22.
3 is formed. The semiconductor wafer is, for example, a Si wafer, and the insulating film 23 is, for example, SiO ₂ .

At another place in the container 21, a high-purity liquid reagent 25 such as hydrofluoric acid is contained in a corrosion-resistant reagent container 24. The inner surface and the internal structure of the container 21 are formed of an acid resistant material such as tetrafluoroethylene. The upper portion of the reagent container 24 is open, and the liquid reagent 25 can freely evaporate.

Since the container 21 is sealed, the naturally evaporated reagent vapor 26 is confined in the container 21 and reaches the surface of the insulating film 23 via the partition wall 29 having a hole. As a result, for example, SiO ₂ is etched with hydrofluoric acid vapor. SiO
₂ Impurities contained in the film are droplets 27 of an aqueous solution of hydrofluoric acid.
Melts in.

Since the subject is held vertically, the droplet 2
7 drops down and is stored in the droplet reservoir 28. The impurity concentration can be fixed by collecting these droplets and performing atomic absorption analysis, for example.

According to this method, the concentration of impurities contained in the reagent vapor 26 naturally evaporated from the reagent container 24 at room temperature is extremely low. Therefore, the background of measurement becomes low, and the impurity concentration in the insulating film of the subject can be measured with extremely high sensitivity. For example, it is described that the Fe concentration can be detected with an accuracy of 5.5 × 10 ⁻¹⁰ g / cm ² . Subsequent advances have resulted in even higher measurement accuracy.

Although this method is highly accurate, since it uses the natural evaporation of the reagent at room temperature, the reagent evaporation supply amount is low, and it takes a relatively long time to extract impurities, that is, to dissolve the SiO ₂ film.

As a method for shortening the impurity extraction time,
For example, a method of forced evaporation of a reagent shown in FIGS. 8B and 8C has been proposed. The method shown in FIG. 8 (B) heats the reagent to increase the vapor pressure. As in FIG. 8A, the reagent container 24 and the droplet reservoir 28 are arranged in the container 21, but the reagent container 24 is wrapped in the heater 30, and the droplet reservoir 28 is cooled by the cooling tank 3.
Surrounded by 1.

The liquid reagent 25 in the reagent container 24 is attached to the heater 3
By heating at 0, the amount of reagent vapor evaporated from reagent 25 increases. The higher the heating temperature, the larger the amount of reagent vapor generated. In this way, the amount of reagent vapor supplied to the surface of the semiconductor wafer 22 can be significantly increased.

Further, since the periphery of the droplet reservoir 28 is surrounded by the cooling tank 31, the droplets that have fallen down along the surface of the semiconductor wafer 22 are cooled by the cooling tank 31, and re-evaporation is suppressed. Therefore, it is possible to prevent a change in the amount of liquid droplets in the liquid droplet reservoir 28 due to re-evaporation, and it is possible to prevent mixing of liquid between different tanks of the liquid droplet reservoir 28 due to re-evaporation-recondensation.

However, if the reagent container 24 is overheated,
The generated reagent vapor 26 also becomes high in temperature, and the semiconductor wafer 22
Although it reacts with the insulating film 23 on the surface, the droplet 27 is not formed and the surface of the semiconductor wafer 22 is in a dry state. Therefore, in order to form the droplet 27, the reagent 2
The heating temperature of 5 is limited.

A method has also been proposed in which nitrogen gas is supplied onto the heated reagent, the reagent vapor is transported, and the reagent gas is sprayed onto the semiconductor wafer (SDM91-15).
9). According to this method, the reaction between the reagent and the surface of the semiconductor occurs on the semiconductor wafer, but no droplet is generated. The reaction refined product is obtained by dropping a recovery liquid such as pure water on the wafer and recovering the decomposed product on the wafer with the recovery liquid.

According to this method, even if the purity of the reagent sprayed on the semiconductor wafer is sufficiently increased, the purity of the recovered liquid needs to be sufficiently high in order to obtain sufficiently high measurement accuracy.

In the method shown in FIG. 8C, a carrier gas, for example, nitrogen (N ₂ ) is sent to the two reagent containers 24a and 24b and bubbled in the liquid reagents 25a and 25b to generate a reagent vapor together with the carrier gas. It is to be provided on the subject. By adopting bubbling, the amount of reagent vapor can be increased and the extraction time can be shortened.
Depending on the type of the insulating film 23, the reagents 25a and 25b can be mixed and used.

[0021]

In such a conventional ultra-sensitive impurity extraction method, the natural evaporation method of the reagent of FIG. 8 (A) can suppress the background impurity concentration to a very low level. The pressure is low and it takes time to extract impurities.

In the method of FIGS. 8B and 8C, the impurities can be extracted in a short time, but the extraction accuracy is lowered. When heating or bubbling is performed, high kinetic energy is given to the vaporized reagent vapor, and not only a single reagent molecule but also a mist (particles) having a diameter exceeding 10 μm is generated. Generally, when it is wrapped in a large mist, F in the reagent
Impurities such as e also evaporate.

In other words, if the reagent is evaporated by heating or bubbling, there is a strong possibility that the high purity obtained by quiet natural evaporation will be lost. Furthermore, if the reagent vapor temperature is high,
The reaction product of the reagent and the insulating film does not take the form of droplets but tends to be dried. To collect the dried reaction product,
A method such as dissolution in a liquid is required, and the extraction accuracy depends on the purity of the recovered liquid.

An object of the present invention is to provide an ultrasensitive extraction method or extraction apparatus for a trace substance having a high processing speed and a very low background impurity concentration.

[0025]

The trace substance extraction method of the present invention comprises an evaporation step of heating and evaporating a liquid reagent capable of decomposing a target substance, and vaporizing the vaporized reagent vaporized into a hydrophobic porous material. A purification process in which mist with a certain diameter or more is blocked through a membrane to obtain high-purity reagent vapor, and the purified reagent vapor is supplied onto a cooled target object to decompose the target object and liquefy the vapor to form droplets. And a reaction step of

Further, the trace substance extracting apparatus of the present invention comprises a filter member including a hydrophobic porous membrane capable of covering the opening of the container for containing the liquid reagent, and a heating means for heating the inside of the container. , A cooling tank for placing and cooling the sample, the filter member above the opening of the container and the upper part of the cooling tank are connected, and vapor supplied from the container via the filter member is connected to the sample. And a gas supply system for supplying the

[0027]

Function The amount of reagent vapor can be increased by heating and evaporating the reagent. The reagent vapor thus formed has a low purity including a mist of a large diameter, but the purity of the reagent vapor can be improved by blocking the mist having a predetermined diameter or more by passing through the hydrophobic porous membrane. You can

The high-purity reagent vapor thus obtained is
By supplying onto the cooled object, the reaction product with the object can be obtained as droplets. If the droplets are collected, a sample in which a trace substance is extracted can be obtained.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the basic structure of a trace substance extracting apparatus according to an embodiment of the present invention. This apparatus is basically divided into an ultrahigh-purity purified gas generator and a gas phase decomposer for containing the sample 6 and reacting the purified gas with the sample to extract a trace substance in the sample 6.

In FIG. 1, a container 2 having an opening 1 is
A liquid reagent 3 is contained. A hydrophobic porous membrane 4 is arranged on the opening 1 and covers the opening 1. A heating means 5 is arranged near the container 2 to heat the inside of the container 2. The reagent 3 in the container 2 is heated to increase the evaporation amount.

The reagent vapor thus generated is supplied to the gas supply system 8 through the hydrophobic porous membrane 4. When the reagent vapor passes through the hydrophobic porous membrane 4, the mist having a large particle size contained in the reagent vapor is blocked.

The impurities in the reagent 3 are wrapped in mist having a large particle diameter by heating and evaporate, but the hydrophobic porous membrane 4
The gas supply system 8 is not reached because it is cut off by. Therefore, the reagent vapor supplied to the gas supply system 8 through the hydrophobic porous film 4 has high purity. The opening 1 may not be entirely covered with the hydrophobic porous film 4, but a filter member having a hydrophobic porous film may be formed and the opening 1 may be covered with the filter member.

In the gas phase decomposer shown on the left side of the drawing,
The sample 6 is placed in contact with the cooling tank 7. The space surrounding the sample 6 is connected to the gas supply system 8 and is a substantially airtight space.

The reagent vapor supplied from the gas supply system 8 is
It is provided on the surface of the sample 6 and reacts with the sample 6 to form a reaction product. At this time, since the sample 6 is cooled by the cooling tank 7, the reagent vapor is liquefied on the sample 6 to form droplets.

The cooling tank 7 is maintained at a temperature below room temperature by passing cooling water, for example. As the cooling means, other than cooling water may be used as long as it can cool the sample 6.

The gas phase decomposer is provided with an exhaust system having a valve V2 and a pipe 12, and the reagent vapor and the like which have reacted with the sample 6 pass through the pipe 12 and the exhaust gas treatment container 10
Bubble in the exhaust gas treatment liquid 9 therein.

When a reagent such as an acid is used, an alkaline solution is used as the exhaust gas treatment liquid 9 and the acidic reagent is neutralized by bubbling. The exhaust gas treated in this way becomes harmless and is discharged from the pipe 13 to the outside.

Also on the side of the container 2 for containing the reagent 3, pipes 11 and 14 are connected to the gas supply system 8 via valves V1 and V3. The pipe 11 is introduced into the exhaust gas treatment liquid 9 in the exhaust gas treatment container 10, and when reagent vapor is supplied, the pipe 11 bubbles through the exhaust gas treatment liquid 9.

A carrier gas such as an inert gas can be introduced into the pipe 14. By heating and evaporating the reagent 3 in the container 2 and introducing a carrier gas from the pipe 14, a reagent vapor having a desired concentration can be supplied to the gas phase decomposer.

It is desirable that the gas supply system 8 and the container 2 as a whole be maintained at a desired temperature. In this way, the reagent vapor generated by the heating of the heating means 5 can be supplied to the gas phase decomposer through the gas supply system 8 without being liquefied.

Also in the gas phase decomposer, in addition to the pipe 12, the pipe 15 is connected via the valve V4. Piping 15
Is used for introducing a gas such as an inert gas into the gas phase decomposer and purging the inside of the gas phase decomposer.

A liquid drain is preferably provided above the hydrophobic porous film of the gas phase decomposer and the gas supply system 8 if necessary so that when the liquid is generated, it can be discharged from the drain. .

When extracting a trace substance from the sample 6, first, the gas supply system 8 is closed by a valve or the like (not shown), the valve V1 is opened, and the generated reagent vapor is guided to the exhaust gas treatment container 10 until a steady state is reached. It is preferable. After reaching the steady state, the reagent vapor is supplied to the gas phase decomposer through the gas supply system 8 for a predetermined time.

FIG. 2 shows an apparatus for extracting impurities on a semiconductor surface according to an embodiment of the present invention. The impurity extraction device roughly includes a purified gas generator 40, a gas phase decomposer 50, and an exhaust gas treatment device 60. The impurities to be extracted are the impurities in the insulating film formed on the surface of the semiconductor wafer.

In the purified gas generator 40, a reagent container 42 such as a commercially available reagent container is placed on a support, and the container 41 is fitted on the reagent container 42 with the lid of the reagent container 42 removed. . The reagent container 42 is wound with a rubber heater 45, and the whole is heated to a predetermined temperature. The rubber heater 45 is connected to the temperature controller 46 and can heat the rubber heater 45 to a predetermined temperature.

The temperature controller 46 can set an arbitrary temperature according to the type and conditions of the reagent. Container 41
Has gas lines 47, 49 and a drain 48.
Valves V48 and V49 are connected to the drain 48 and the gas pipe 49. An inert gas source having a valve is connected to the gas pipe 47.

With such a configuration, the reagent in the reagent container 42 is heated to a predetermined temperature and the generated reagent vapor is purified, and then the gas pipe 49 is connected to the gas pipe 7 via the valve V49.
Supply 0 or 71.

The vapor phase decomposer 50 stores a semiconductor wafer from which impurities are to be extracted in a container 51. Gas pipes 55, 56, 57 are connected to the container 51, and a drain 58 is further connected.
Have.

Valves V55, V57 and V58 are connected to the gas pipes 55 and 57 and the drain 58, respectively. An inert gas source having a valve is connected to the gas pipe 56. In the configuration shown in the figure, the valve V49 of the purified gas generator 40 and the valve V5 of the gas phase decomposer 50 are used.
7 is connected to the gas pipe 70.

The containers 41, 51, or at least the inner surface thereof, is made of a material such as tetrafluoroethylene which is not attacked by a reagent. Further, the gas pipe 70 is formed by a deformable free tube such as tetrafluoroethylene.

The exhaust gas treatment device 60 has gas inlets 63, 64.
And a container 61 having a gas outlet 65. The gas inlets 63 and 64 are connected to valves V49 and V via free tubes 71 and 72 made of tetrafluoroethylene or the like, respectively.
Connected to 55. Before and after the decomposition of the sample is started, the valve V49 is connected to the gas pipe 71, and the generated reagent vapor is processed by the exhaust gas processing device 60.

After the sample is disassembled, the valve V57 is closed and the valve V55 is opened, and the gas pipe 56 is opened.
The inert gas is supplied from above to purge the inside of the container 51 of the gas phase decomposer 50.

The container 51 of the gas phase decomposer 50 is further provided with a cooling water inlet 67 and a cooling water outlet 68,
Cooling water is supplied to the cooling tank provided in the container 51. The drains 48 and 58 are for draining the liquid when the liquid is accumulated in the containers 41 and 51. Hereinafter, each part of the impurity extraction device will be described in more detail with reference to cross-sectional views.

FIG. 3 shows the structure of the purified gas generator. The reagent container 42 is, for example, a commercially available reagent container or a dedicated container for transferring a reagent from the commercially available reagent container,
The outside of the upper opening is threaded. A rubber heater 45 is wound around the reagent container 42 so that the whole can be heated to a substantially uniform temperature.

The lower member 41b of the container is fitted with this threaded portion. The upper member 41a of the container is fitted with the lower member 41b to form a substantially airtight structure. Lower part of container 4
A hydrophobic porous film 44 made of tetrafluoroethylene or the like is bonded to 1b, and vapor generated from the reagent container 42 cannot escape to the upper portion unless it passes through the hydrophobic porous film. Has been done.

Gas pipes 47, 49 and a drain 48 are formed in the upper member 41a arranged so as to surround the hydrophobic porous film 44. The drain 48 is for taking out the liquid reagent when the reagent vapor passing from the reagent container 42 to the outside through the hydrophobic porous film 44 is liquefied.

The gas pipe 47 is a pipe for introducing a carrier gas, and the gas pipe 49 is a pipe for leading the generated reagent vapor together with the carrier gas to the outside.
A three-way cock type valve V49 is connected to the gas pipe 49.

Although the gas pipe 47 has a shape without a valve, a valve such as a two-way cock may be connected to the gas pipe 47. The container 41 and the piping for carrying the purified gas are all heated to a predetermined temperature by a rubber heater, a ribbon heater or the like.

FIG. 4 shows another form of the purified gas generator. In this configuration, the gas pipe 47 is inserted deep inside the reagent container 47. Also, the container 41
Of the hydrophobic porous membrane 44 connected to the lower member 41b of
It is composed of two sheets with different pore sizes.

An inert gas such as nitrogen gas or argon gas supplied from the gas pipe 47 bubbles in the reagent in the reagent container 42 and passes through the hydrophobic porous film 44 in a form containing the reagent vapor. It is supplied upward from the gas pipe 49.
The other points are the same as those of the purified gas generator shown in FIG.

FIG. 5 shows the structure of the gas phase decomposer 50. The container 51 has a cooling tank 52 in which cooling water flows. The cooling tank 52 has an upper plate of a tetrafluoroethylene sheet for mounting a sample, a cooling water inlet 67, and a cooling water outlet 68.

A semiconductor wafer 53 is placed in close contact with the tetrafluoroethylene sheet which is the upper plate of the cooling tank 52. A sample holder 54 is arranged on the semiconductor wafer 53 to expose a predetermined area of the semiconductor wafer 53.

The container 51 has gas pipes 55, 56, 57.
And the drain 58 are connected. Gas pipe 55,
57 includes valves V55 and V57 formed by a two-way cock
Are connected. Further, a valve V58 formed of a two-way cock is connected to the drain 58.

One of the gas pipes 55 and 57 is used as a reagent gas introduction pipe, and the other is used as a reagent gas discharge pipe. The gas pipe 56 is a pipe for introducing a purge gas after sample decomposition. The gas pipe 56 may also be provided with a valve such as a two-way cock.

In the impurity extraction apparatus described above, the surface that comes into contact with the liquid reagent or the vaporized reagent is preferably made of a corrosion resistant material such as tetrafluoroethylene or acid resistant polyethylene.

Although the case where the reagent container 42 is wound with a rubber heater to heat the reagent has been described, another heating method may be used. For example, the reagent container may be placed in a closed container and the reagent container may be heated from below. The entire container may be heated.

It is desirable that the reagent vapor evaporated from the liquid reagent is not liquefied until it comes into contact with the sample. For this reason,
It is preferable that all the gas passages from the portion on the reagent container to the position where the sample of the gas phase decomposer 50 is placed are heated to a predetermined temperature.

The exhaust gas treatment device 60 is for neutralizing a reagent such as an acid to produce a harmless gas. For example, an alkaline solution is contained in the acid of the reagent, the exhaust gas is bubbled and then discharged. Let

The corrosion-resistant hydrophobic porous membrane of the purified gas generator is, for example, a tetrafluoroethylene membrane having a large number of small holes having a diameter of about 10 to 100 μm. The membrane need not be single and may also vary in shape.

As is well known, the hydrophobic porous membrane has a function of allowing vapor consisting of fine reagent particles and a carrier gas to pass through, but blocking mist of large particles containing impurity atoms.

Therefore, even if the high-density reagent vapor is vaporized by bubbling or heating the carrier gas, the gas after passing through the hydrophobic porous membrane has a very high purity as in the natural vaporization.

Even if the ultrahigh-purity reagent gas comes into contact with the surface of the sample in the "heated" state, the sample is cooled by the cooling bath, and is cooled on the surface of the sample to form droplets. Further, since the droplet temperature is low, excessive etching of the sample surface is prevented.

FIG. 6 is a schematic sectional view for explaining the function of the embodiment shown in FIGS. The extraction device includes a purified gas generator 40, a gas phase decomposer 50, and an exhaust gas treatment device 6
0 and gas pipes 70, 71, 72.

The purified gas generator 40 comprises a corrosion-resistant container 41.
A reagent container 42 and a cylindrical tetrafluoroethylene porous film 44 covering the container hole are housed inside. The reagent container 42 is also usually made of tetrafluoroethylene and is a liquid reagent 4.
3 are stored.

A heater 45 for heating is arranged in the reagent container 42. The heater 45 is maintained at a predetermined temperature by the temperature control device 46. The heater 45 may be any heater as long as the temperature can be adjusted.

The container 41 has a carrier gas (usually ultra-high purity nitrogen or argon) inlet 47 and a gas outlet 49.
And a drain 48. Valves made of tetrafluoroethylene V47, V49, V in each passage
48 are arranged.

The valve V49 has a role of switching the gas from the container 41 to the exhaust gas treatment device 60 or the gas phase decomposer 50. It is also possible to use two 2-way cock types instead of the 3-way cock type.

The vapor phase decomposer 50 has a cooling tank 52 and a sample holder 54 placed thereon in a corrosion-resistant container 51. The container 51 includes a gas pipe 56 provided with a valve V56 for introducing a purge gas (usually ultra-high purity nitrogen or argon), a gas pipe 55 for reagent gas provided with a valve V55,
It has an exhaust gas pipe 57 equipped with a valve V57 and a drain 58 equipped with a two-way cock type valve V58. Cooling water is normally flowed in the cooling tank 52 to cool the sample 53 via the upper plate.

The exhaust gas treatment device 60 contains a treatment liquid 62 in a corrosion-resistant container 61 made of vinyl chloride or the like, and is provided with exhaust gas inlets 63, 64 and an exhaust port 65. The exhaust gas inlets 63 and 64 are connected to the container 61 as shown.
A pipe is inserted deep inside to allow the exhaust gas to bubble through the treatment liquid 62.

FIG. 7 shows an enlarged view of the structure of the sample holder 54 and the method of introducing the carrier gas into the purified gas generator 40. FIG. 7A shows a sectional structure of the sample holder 54. The sample holder 54 includes a threaded fitting portion 54b made of tetrafluoroethylene and a fixed base 5 made of tetrafluoroethylene.
4c and. The threaded fitting portion 54b has an opening 54a having a predetermined shape and size in the central portion.

As shown in the drawing, the opening is formed in the fixed base 5.
The bottom of 4c penetrates to the surface of the sample (semiconductor wafer) 53 directly mounted on the cooling tank 52. Therefore, the purified reagent gas is supplied to the sample 53 only in this opening 54a.
Contact and react with.

On the other hand, FIGS. 7B and 7C show a method of introducing a carrier gas into the purified gas generator 40. Figure 7
(B) shows that nitrogen gas captures and transports the vapor of the reagent 43 generated by heating outside the reagent container 42.

Further, FIG. 7C shows that the nitrogen gas is supplied to the reagent container 4.
2 shows the state in which the reagent 43 of No. 2 is sent below the liquid surface, and vapor is forcibly generated and conveyed by bubbling. Either method can be adopted. The gas pipe 70 and the container 5
The upper part of 1 is heated and kept warm by, for example, a ribbon heater (not shown).

Next, an example of extracting and analyzing impurities in the oxide film formed on the Si wafer will be described. A sample 53 having a SiO ₂ film with a thickness of 1000 Å formed on a Si wafer by a thermal oxidation method is placed on a cooling tank 52 with a sample holder 54.

Cooling water is caused to flow in the cooling tank 52 and the gas pipe 7
0 and the upper portion of the container 51 are heated, and nitrogen gas is introduced into the container 41 through the two-way cock valve V47. In this case, 50% hydrofluoric acid is used as the reagent 43.
Further, the valve V56 is opened to introduce the nitrogen gas into the container 51.

In this gas replacement step, the heater 45
Off. Further, the three-way cock type valve V49 is connected to the exhaust gas treatment device 60. Further, the two-way cock type valve V57 is opened to remove the gas in the container 51 from the exhaust gas treatment device 60.
Lead to.

The exhaust gas treating device 60 is filled with a caustic soda solution. When the gas in the gas pipe 70 is replaced, the two-way cock type valve V55 may be opened to allow the nitrogen gas to flow backward, and the nitrogen gas may be connected to the exhaust gas treatment device 60 via the three-way cock type valve V49.

After the gas replacement is completed, the heater 45 is heated.
The hydrofluoric acid vapor generated until the heating temperature reaches 80 ° C. is made to flow to the exhaust gas treatment device 60 side. When the temperature of the heater 45 becomes stable, the three-way cock type valve V49 is switched, and the generated hydrofluoric acid vapor and nitrogen carrier gas are introduced from the valve V49 to the gas phase decomposer 50 through the gas pipe 70. At this time, the two-way cock type valves V55 and V57 are opened, and the two-way cock type valves V56 and V58 are closed.

When the hydrofluoric acid vapor passes through the tetrafluoroethylene porous film 44, mist having a diameter of tens of μm to several tens of μm or more is removed and is supplied to the surface of the sample 53 in an extremely high purity state. After introducing the reagent gas for 10 minutes, operate the 3-way cock type valve V49 to remove the hydrofluoric acid vapor into the exhaust gas treatment device 6
Flow to the 0 side. At the same time, the two-way cock type valve V55 is closed.

Next, the two-way cock valve V56 is opened to introduce the nitrogen gas into the container 51, and the residual gas components are purged from the exhaust gas pipe 57 through the gas pipe 72 to the exhaust gas processor 60.

Thereafter, two-way cock type valves V56, V5
When 7 is closed and the container 51 is opened, droplets are formed on the surface of the sample 53. Collect this with a micropipette. As a result of examination with an ellipsometer, S from the Si wafer
It was found that the iO ₂ film had completely disappeared. When the inflow time of the reagent gas introduced into the vapor phase decomposer 50 was changed and examined, it was found that the thermally oxidized SiO ₂ film having a thickness of 1000 Å was completely etched off in 3 minutes. Thermal oxide SiO ₂ with the same thickness as compared with the case of using a natural evaporation type gas phase decomposition apparatus
It can be seen that the processing time required for film etching is significantly reduced.

The heating by the heater 45 is limited to 80 ° C.
It is not fixed. If the temperature is above room temperature and below the boiling point of the reagent,
It is possible to choose the temperature. The collected droplet is black
Quantitative analysis was performed by a lead furnace polarized Zeeman atomic absorption method. So
As a result, Fe and Ni are 3 to 5 × 10.^-13g / cm², C
u and Cr are 2 to 10 × 10 ^-14g / cm²Measured with accuracy
I knew I could do it. Minimize background impurity concentration
It can be suppressed to a low level.

L as sample 53 under the same equipment and under the same conditions
When using the thickness 1000Å to deposited the Si ₃ N ₄ film on the Si wafer surface by a PCVD method, within 10 minutes Si ₃ N
_{The 4} membranes could be completely dissolved.

After the extraction experiment, the two-way cock valves V48 and V58 are opened to drain the drainage collected at the bottoms of the containers 41 and 51, respectively.
Discharge from. Hydrofluoric acid and S introduced into the exhaust gas treatment device 60
Since the i-fluoride is neutralized by caustic soda, the carrier gas discharged from the exhaust port 65 is rendered harmless.

Next, another embodiment for detecting the type and concentration of fine dust (particles) floating in the clean room by using such an ultrasensitive trace substance extraction apparatus will be described.

The mirror-like Si wafer whose surface has been cleaned is left at a predetermined position in a clean room. A natural oxide film (50 to 100Å) is formed on the surface of the Si wafer.
After a sufficient time has passed, the sample 53 is placed on the cooling tank 52 by the sample retainer 54 with the particle adhering surface facing upward.

When extracting a trace substance from the surface of this sample, a 61% HNO ₃ solution is used as the reagent 43. The exhaust gas treatment liquid 62 may be a caustic soda aqueous solution. As in the previous embodiment, the purified gas generator 40, the gas phase decomposer 50 and the gas pipe 70 are replaced with nitrogen gas, the cooling tank 52 is cooled with water, the gas pipe 70 and the gas phase decomposer 50 are heated, and then the reagent 43. The nitric acid aqueous solution is heated.

Until the temperature of the aqueous nitric acid solution rises, the generated reagent vapor and nitrogen carrier gas are guided to the exhaust gas treatment unit 60 from the exhaust gas outlet 49b through the gas pipe 71 by the operation of the three-way cock type valve V49 as in the previous embodiment. Get burned.

After the temperature of the reagent 43 is stabilized, the three-way cock type valve V49 is operated to introduce the nitric acid vapor and the nitrogen carrier gas into the gas phase decomposer 50 from the reagent gas outlet 49c through the gas pipe 70.

After 5 minutes, the three-way cock type valve V4 is again used.
9 is operated to switch the gas path from the exhaust gas outlet 49b to the exhaust gas processing device 60. At the same time, two-way cock type valve V
55 is closed and the two-way cock type valve V56 is opened to purge the gas remaining in the container 51 of the gas phase decomposer 50 with nitrogen gas.

After that, the gas phase decomposer 50 is opened, and the droplets of the nitric acid aqueous solution formed on the surface of the Si wafer are collected with a micropipette. Since SiO ₂ is stable against nitric acid solution,
The Si wafer is not dissolved, only the particles deposited on the wafer are dissolved in the droplets.

The collected liquid was quantitatively analyzed by a graphite furnace polarized Zeeman atomic absorption method. As a result, Na and K in the particles could be analyzed with an accuracy of ² to 5 × 10 ⁻¹³ g / cm ² .

As described above, the trace substance extraction device is functionally separated into a purified gas generator and a gas phase decomposer, and in the former case, reagent heating is used to generate a high density reagent gas, which is then treated with a hydrophobic porous material. Ultra high purification by filtering with a quality membrane.

In the latter case, the sample gas is cooled by the cooling bath to cause the reagent gas in the "temperature rising" state to condense on the surface,
The extracted trace material is dissolved and included in the ultrapure droplets. Further, by cooling on the surface of the sample, the reactivity of the reagent gas is lowered to prevent excessive etching. By separating the functions, it is possible to easily attach the sample, replace the gas inside, and take out the sample, and improve the reproducibility of the experiment.

In addition, it becomes possible to extract ultra-sensitive impurities from the surface layer of the substrate in a very short time. Its accuracy is Fe,
3-6 × 10 ^-13 g / cm ^{2 for} Ni, ² for Cu and Cr
10 × 10 ⁻¹⁴ g / cm ² , ² to 5 × 10 ¹³ with Na and K
It can be about g / cm ² .

Furthermore, the safety of the experiment is kept high by adopting the gas replacement and the exhaust gas treatment device. In particular, it is useful for extracting a trace amount of impurities on the surface of a semiconductor wafer. Such extraction of trace substances can also be used for detecting trace contaminants on the surface of other floppy disks, laser disks, and the like.

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

[0108]

As described above, according to the present invention, trace substances can be extracted at high speed and with high accuracy.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a basic configuration of a trace substance extraction device according to an embodiment of the present invention.

FIG. 2 is a schematic side view showing an impurity extraction device according to an embodiment of the present invention.

3 is a partially cutaway side view showing a purified gas generator of the impurity extraction apparatus shown in FIG.

FIG. 4 is a partially cutaway side view of another example of the purified gas generator of the impurity extraction device shown in FIG.

5 is a partially cutaway side view of a gas phase decomposer of the impurity extraction apparatus shown in FIG.

FIG. 6 is a schematic sectional view for explaining the function of the embodiment shown in FIGS.

FIG. 7 is a schematic cross-sectional view for explaining the functions of some elements of the embodiment shown in FIGS.

FIG. 8 is a cross-sectional view showing an ultrahigh-purity impurity extraction device according to a conventional example.

[Explanation of symbols]

 1 Opening 2 Container 3 Reagent 4 Hydrophobic Porous Membrane 5 Heating Means 6 Sample 7 Cooling Tank 8 Gas Supply System 9 Exhaust Gas Treatment Liquid 10 Exhaust Gas Treatment Containers 11, 12, 13 Pipes 14, 15 Gas Introducing Means 21 Container 22 Semiconductor Wafer 23 Insulating film 24 Reagent container 25 Liquid reagent 26 Reagent vapor 27 Droplet 28 Droplet reservoir 29 Perforated partition wall 30 Heater 31 Cooling tank 40 Purified gas generator 41 Container 42 Reagent container 43 Reagent 44 Hydrophobic porous film 45 Heater 46 Temperature control device 47, 55, 56, 57 Gas piping 48, 58 Drain 50 Gas phase decomposer 51 Container 52 Cooling tank 53 Sample 54 Sample holder 60 Exhaust gas processor 61 Container 62 Processing liquid 63, 64 Gas inlet 65 Gas outlet 70, 71, 72 Gas piping V valve

Claims (14)

[Claims] 1. An evaporation step of heating and evaporating a liquid reagent capable of decomposing a target substance, and a vapor of the evaporated reagent is passed through a hydrophobic porous membrane to block mist having a diameter larger than a predetermined value to obtain high purity. And a reaction step of supplying the purified reagent vapor onto a cooled target object, decomposing the target object, and liquefying the vapor to form droplets. 2. The trace substance extraction method according to claim 1, further comprising a mixing step of mixing an inert gas with the vapor of the reagent. 3. A filter member including a hydrophobic porous membrane (4) capable of covering an opening (1) of a container (2) containing a liquid reagent (3), and heating the inside of the container (2). Heating means (5)
A cooling tank (7) for placing and cooling the sample (6), and connecting the filter member above the opening (1) of the container (2) and the upper part of the cooling tank (7). And a gas supply system (8) for supplying the vapor supplied from the container (2) through the filter member onto the sample (6), the trace substance extraction device. 4. The trace substance extraction device according to claim 3, further comprising gas introduction means (14, V3) for introducing an inert gas into the container (2) or the gas supply system (8). 5. The trace substance extraction according to claim 3, further comprising gas discharge means (11, V1) for discharging gas from the space above the opening (1) of the gas supply system (8). apparatus. 6. Further gas discharging means (1) for discharging gas from the space above the sample of said gas supply system (8).
The trace substance extraction device according to any one of claims 3 to 5, which has V2). 7. The trace substance extraction apparatus according to claim 6, further comprising another gas introduction means (15, V4) for introducing an inert gas into the space above the sample of the gas supply system (8). 8. The trace substance extraction apparatus according to claim 3, further comprising another heating means for heating the gas supply system (8). 9. The gas discharging means (11, V
The trace substance extraction apparatus according to claim 5, further comprising an exhaust gas treatment means (10) connected to 1). 10. The other gas discharging means (1)
7. The trace substance extraction device according to claim 6, further comprising an exhaust gas treatment means (10) connected to V2, V2). 11. A filter means comprising said hydrophobic porous membrane (4), another filter means comprising another hydrophobic porous membrane similar to said heating means, and another heating means. 10. The trace substance extraction device according to any one of 10 to 10. 12. A holding means for holding a sample (6) on the cooling tank (7), further comprising:
1. The trace substance extraction device according to any one of 1. 13. The trace substance extracting apparatus according to claim 12, wherein the holding means has a mechanism for exposing only a predetermined area of the sample. 14. The trace substance extraction device according to claim 3, wherein said gas supply system (8) has a drain for discharging a liquid.