JP2000021779A - Manufacturing method of semiconductor element and semiconductor element manufacturing apparatus using the method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and apparatus for manufacturing a semiconductor element, wherein a semiconductor substrate is laid in a raw material gas atmosphere to deposit a product originating from the raw material gas on the semiconductor substrate surface, thereby forming a thin film on the substrate surface whereby it is possible to suppress the contamination of the semiconductor element with dust produced in the raw material gas atmosphere or byproducts deposited to a reactor chamber or pipings, and to improve the product yield and throughput. SOLUTION: In this semiconductor element manufacturing method in which a semiconductor substrate 3 is laid in a raw material gas atmosphere to deposit a product originating from the raw material gas on the semiconductor substrate 3 surface, thereby forming a thin film on the semiconductor substrate 3 surface, a gas capable of suppressing the adherence of byproducts which are produced with particles or in the raw material gas atmosphere to the apparatus walls is fed in a reaction system 2 to remove the byproducts produced in the atmosphere.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an apparatus and a method for manufacturing a semiconductor device. More specifically, the present invention relates to a method for forming a semiconductor element by forming a thin film on a substrate by a CVD method or the like, wherein a method for suppressing the generation of defects due to adhesion of by-products and the like on the thin layer and improving the yield. It is about.

[0002]

2. Description of the Related Art Conventionally, in the production of semiconductor devices, a gaseous raw material is supplied to a reaction chamber into which a substrate is inserted, and the raw material or a reaction product of the raw material is deposited on the substrate surface to process the surface shape of the substrate. May be used. According to this method, compared to other methods such as coating,
There is an advantage that the substrate surface can be processed uniformly.

[0003] However, the above method may cause a problem. For example, when monosilane is supplied as a raw material gas to a silicon substrate to form a silicon thin film on the substrate, fine granular products (silicon) may be generated in the gas phase. is there. The product is exhausted out of the system as an exhaust gas and adheres to the substrate and the piping.

Here, products generated in the gas phase have various sizes. Of these, large ones can often be removed by cleaning the substrate in a subsequent step, and are not likely to be a major problem. On the other hand, small dust, for example, dust smaller than 0.2 micron, is difficult to remove even by a cleaning process. As a result, small dust often remains on the substrate, and as a result, a defect may occur on the substrate and the product yield may be reduced.

In some cases, a source gas is chemically reacted and deposited on a substrate. In such a case, by-products other than the components of the thin film to be formed may be generated.

[0006] Usually, the substrate is heated to a specific temperature, and a desired reaction product is deposited on the substrate. However, by-products may be generated in a gas phase near the substrate. The by-product is generated in a gas, liquid, or solid state depending on the ambient temperature and pressure of the reaction gas, but usually, a gaseous by-product is generated near the substrate. This by-product, which was present as a gas on the substrate, is usually cooled after passing through a high-temperature portion near the substrate, and solidifies or liquefies when the pressure of the atmosphere exceeds the saturated vapor pressure of the generated gas. A part of the solidified or liquefied product is discharged out of the reaction chamber together with the gas flowing through the reaction chamber, but most of the product adheres to a gas retaining portion such as a reaction chamber wall or a reaction chamber having a low temperature. Also, by-products discharged from the reaction chamber may adhere to the piping downstream of the reaction chamber.

When the substrate is cooled after the step of forming the thin film on the semiconductor substrate is completed, or when the substrate is transported after the cooling, the pressure in the reaction chamber is changed due to the fluctuation of the pressure in the reaction chamber accompanying the exhaust of the reaction chamber. By-products adhering to the inner wall, the gas retaining portion, or the inner wall of the pipe may be scattered. The scattered by-products adhere to the substrate and may cause defects on the substrate, thereby lowering the product yield.

Conventionally, in order to prevent a decrease in product yield due to such reasons, when the amount of by-products adhered to the inner wall of a reaction chamber or a pipe increases, the operation of the apparatus is stopped to clean the entire apparatus. What has been done has been done.
However, the addition of the cleaning process lowers the operation rate of the apparatus and lowers the throughput of the product.

[0009] Such substrate contamination by by-products,
In order to solve the dilemma of lowering the throughput due to the trouble of cleaning the device to prevent this, conventionally, a method of heating the piping downstream of the reaction chamber so as not to lower the temperature of the gas discharged to the outside of the reaction chamber is known. Has been taken. Thereby, the by-product adhering to the inner wall of the reaction chamber or the pipe is heated, vaporized and discharged, and the gaseous by-product is prevented from being cooled and deposited. However, in this method, since the pipe temperature cannot be set higher than the heat-resistant temperature of the organic polymer rubber used for the pipe connection and the gas seal of the pressure regulating valve, it is impossible to completely remove liquid and solid by-products. It was possible.

[0010]

In view of the above, there has been a demand for a method of discharging dust or by-products generated in forming a semiconductor thin film from a reaction chamber in the manufacture of a semiconductor device.

[0011]

[Summary of the Invention] <Summary> According to a first method for manufacturing a semiconductor device of the present invention, a semiconductor substrate is placed in a source gas atmosphere, and the surface of the semiconductor substrate is derived from a source gas. A method for manufacturing a semiconductor device, comprising depositing a product to form a thin film on the substrate surface, comprising supplying fine particles into the source gas atmosphere and removing by-products generated in the atmosphere. It is assumed that.

In a first semiconductor device manufacturing apparatus according to the present invention, a reaction chamber in which a substrate can be disposed and a source gas (this source gas itself or a reaction product thereof can be deposited on the substrate) are subjected to the reaction. A semiconductor device manufacturing apparatus comprising: a supply device for supplying a gas to a chamber; and an exhaust device for discharging a gas from the reaction chamber, wherein the fine particles are supplied to any position of a gas flow path of the manufacturing device. Further comprising a fine particle supply device.

According to a second method of manufacturing a semiconductor device of the present invention, a semiconductor substrate is placed in a source gas atmosphere, and a product derived from the source gas is deposited on the surface of the semiconductor substrate by a predetermined reaction. A method of manufacturing a semiconductor device, comprising: forming a thin film on a substrate; and supplying a gas for suppressing adhesion of by-products generated in the source gas atmosphere to a reaction system.

According to a second semiconductor device manufacturing apparatus of the present invention, a reaction chamber in which a substrate can be disposed and a source gas (the source gas itself or a reaction product thereof can be deposited on the substrate) are supplied to the reaction chamber. A semiconductor device manufacturing apparatus comprising: a supply device that supplies gas to the reaction chamber; and an exhaust device that discharges gas from the reaction chamber, wherein the source gas is disposed at any position in a gas flow path of the manufacturing device. The apparatus further includes a device for supplying a gas that suppresses adhesion of by-products generated in the atmosphere.

<Effects> According to the present invention, in the manufacture of a semiconductor device in which a semiconductor substrate is placed in a source gas atmosphere and a product derived from the source gas is deposited on the surface of the semiconductor substrate to form a thin film on the substrate surface, It is possible to suppress contamination of the semiconductor element by dust generated in a source gas atmosphere and by-products attached to a reaction chamber or a pipe, and to improve product yield and throughput.

[Specific description of the invention] <Particle supply method> When a semiconductor substrate is placed in a source gas atmosphere and a product derived from the source gas is deposited on the surface of the semiconductor substrate to form a thin film on the substrate surface, It is estimated that the mechanism of dust generation in a gas atmosphere is roughly as follows. 1. A molecule A having high reaction activity is generated in the source gas atmosphere. 2. The molecules A collide with each other and aggregate to form an aggregate (or molecule) A ₂ . 3. Aggregate A _n (n is an integer of 1 or more) is by colliding aggregate aggregates A _m (m is an integer of 1 or more), to produce a larger aggregate A _{n + m.} 4.2. Or 3. Is repeated to form larger aggregates. 5. When the molecule A in the gas disappears, the growth of the aggregate stops.

According to such a process, an aggregate in which a plurality of A are aggregated is finally formed. If the aggregate has a size that is difficult to remove in a washing step after the thin film forming step, The aggregates may remain on the thin film and cause defects. Aggregates of such a size are called dust.

The method of manufacturing a semiconductor device according to the present invention is characterized in that fine particles are supplied into a source gas atmosphere in which a molecule A having high reaction activity is generated.

In the growth process of the above-mentioned aggregate, the larger the aggregate, the larger the cross-sectional area of collision with another aggregate or a single molecule, and the smaller the aggregate or the single molecule becomes. Therefore, by supplying fine particles having a large particle diameter that can be removed in a subsequent washing step into the source gas atmosphere in which the molecule A is generated, the molecule A having high reaction activity can be collected on the fine particles. As a result, the generation of aggregates, that is, dust, having a size that is difficult to remove in the cleaning step is suppressed. For example, when forming a Si film on a substrate,
When Si is used as the fine particles to form a SiO ₂ film, it is optimal to use SiO ₂ . The fine particles for forming the Si film only need to contain at least Si, and the SiO ₂ film may also contain at least SiO ₂ .

Part of the supplied fine particles is discharged to the outside of the reaction chamber together with the flow of the gas, and the particles remaining in the reaction chamber can be easily removed by the washing step, so that generation of defects in the semiconductor element is suppressed.

The size of the fine particles to be supplied is generally such that the generated molecules can be taken in and discharged from the reaction chamber by the flow of gas.
Thicknesses of 1000 μm, more preferably 1 to 100 μm are used.

When a semiconductor element is manufactured, an alignment mark may be formed on the substrate surface, but it is preferable that the alignment mark be larger than this size (the size of the alignment mark is generally 10 to 100 μm). This makes it possible to suppress the removal of fine particles from entering the gaps between the alignment marks, making it difficult to remove the fine particles, thereby increasing the efficiency of removal by cleaning.

As the fine particles to be supplied, any type can be used as long as they can capture molecules having high reaction activity generated in the raw material gas atmosphere, and the same components as the aggregates generated in the raw material gas atmosphere can be used. It is preferable that This is because the same element is more likely to be agglomerated in the agglomeration process of the agglomerate than the dissimilar elements, or new impurities are not introduced into the reaction chamber.

The fine particles to be supplied are preferably fine particles having voids therein. Generally supplied fine particles tend to settle in the reaction chamber due to the influence of gravity. Although it can be easily removed by washing, it is more preferable that the gas is discharged out of the reaction chamber together with the gas.

Fine particles having voids therein, that is, fine particles having a small apparent density, can be made lighter fine particles as compared with dense fine particles of the same material while keeping the same size. As a result, the fine particles can be easily discharged out of the reaction chamber together with the gas flow without lowering the collection efficiency of small aggregates or single molecules.

The position at which the fine particles are supplied is arbitrary as long as dust can be removed, but may be located downstream of the substrate in the gas flow direction. This can reduce the adhesion of particles on the substrate. The removal time by washing can be reduced.

One embodiment of the semiconductor device manufacturing apparatus of the present invention is for manufacturing a semiconductor device by using the above-described semiconductor device manufacturing method. A semiconductor comprising: a supply device for supplying a gas (this raw material gas itself or a reaction product thereof can be deposited on the substrate) to the reaction chamber; and an exhaust device for discharging the gas from the reaction chamber. An element manufacturing apparatus, further comprising a fine particle supply device for supplying fine particles to any position in a gas flow path of the manufacturing apparatus.

FIG. 1 is a schematic sectional view of an example of the semiconductor manufacturing apparatus. A substrate 3 is provided in the reaction chamber 2. The reaction chamber 2 has a gas supply pipe 1 and an exhaust pipe 4.
And are connected. A heater 10 is provided around the reaction chamber 2. The gas supplied from the gas supply pipe 1 to the reaction chamber 2 passes through the connection part 7, the exhaust pipe 4, and the pressure regulating valve 6, and is discharged out of the system by the pump 8. The substrate 3 is provided in the reaction chamber 2 by the transfer device 5. Further, the semiconductor manufacturing apparatus of the present invention further includes a fine particle supply device 9.

In a conventional semiconductor manufacturing apparatus having no fine particle supply device, as shown in FIG.
And the dust 21 may accumulate in the concave portion of the pipe 4. On the other hand, in the semiconductor manufacturing apparatus of the present invention, dust is removed by the fine particles and discharged outside the system.

The fine particle supply device 9 can be provided at an arbitrary position in the flow path of the raw material gas. However, by providing the fine particle supply device 9 downstream of the substrate 3 in the reaction chamber 2, adhesion of the fine particles to the substrate 3 is suppressed. Is preferred. FIG. 3 is a schematic cross-sectional view of a semiconductor device manufacturing apparatus including the fine particle supply device 9 on the downstream side of the substrate 3 as described above.

<Adhesion Suppressing Gas Supply Method> On the other hand, by-products may be generated in the form of adhering to the inside of the reaction chamber or piping for dust generated in a form floating in the atmosphere.

For example, when a thin film of Si ₃ N ₄ (silicon nitride) is to be formed on the substrate 3, the source gas is Si
Using H ₂ Cl ₂ and NH ₃ , Si ₃ N
Generate ₄ . 3SiH ₂ Cl ₂ + 10NH ₃ → Si ₃ N ₄ + 6NH ₄ C
1 + 6H ₂ Here, NH ₄ Cl is produced as a by-product.

In the formation of such Si ₃ N ₄ , for example, the pressure in the reaction chamber 2 is about 1 torr and the temperature in the reaction chamber 2 is 70
Conditions around 0 ° C. are selected. Here, NH ₄ Cl has a low vapor pressure, and is about 0.00001 torr at room temperature.
Even at 0 ° C., the pressure is about 0.01 torr, and precipitation is easy at a low temperature. Therefore, there is a possibility that the precipitate may be deposited on a low-temperature portion of the inner wall of the reaction chamber 2 or on an inner wall of the pipe 4 downstream of the reaction chamber 2.

According to another method of manufacturing a semiconductor device of the present invention, a gas capable of suppressing the adhesion of by-products generated in a raw material gas atmosphere to a vessel wall (reaction chamber wall, pipe inner wall). (Hereinafter referred to as an adhesion suppressing gas) to the reaction system. Here, the reaction system refers to a process in which the raw material gas is supplied, causes a chemical reaction, and is discharged by the pump 8.

As the adhesion suppressing gas, any gas can be used according to the purpose, but a gas which does not hinder the production of the desired compound or cause a defect in the semiconductor element is preferable. The gas that can be used depends on the raw material gas, the by-products to be generated, and the like. However, a gas obtained by vaporizing a solvent that can dissolve the by-products to be generated is preferable. For example, when H ₂ O gas is introduced as an adhesion suppressing gas into a system in which NH ₄ Cl is generated as a by-product, NH ₄ C
l is decomposed into NH ₃ and HCl, and is discharged out of the system as a gas. A specific example of a gas that can be used is H
₂ O, CH ₃ OH, C ₂ H ₅ OH, C ₃ H ₇ OH, (CH ₃ ) ₂
CO, (CH ₃ ) ₂ O, (C ₂ H ₅ ) ₂ O, and those obtained by vaporizing a mixture thereof.

The introduction of the adhesion suppressing gas is optional in a method of manufacturing a semiconductor device in which a semiconductor substrate is placed in a source gas atmosphere, and a product derived from the source gas is deposited on the semiconductor substrate surface to form a thin film on the substrate surface. Can be done at the time. However, it is preferable to perform the process only before forming the thin film and / or after forming the thin film because the adhesion suppressing gas can be saved.

At the same time as introducing the adhesion suppressing gas, the entire reaction chamber 2 and the piping are heated to a predetermined temperature, for example, 100 to 2
Since the decomposition or vaporization of by-products can be promoted by heating to 00 ° C. or discharging in a pipe, it is preferable to combine heating or discharging with the introduction of the adhesion suppressing gas.

Further, another apparatus for manufacturing a semiconductor device according to the present invention is for manufacturing a semiconductor device using the above-described method for manufacturing a semiconductor device, and comprises: a reaction chamber in which a substrate can be disposed; A semiconductor comprising: a supply device that supplies a source gas (this source gas itself or a reaction product thereof can be deposited on a substrate) to the reaction chamber; and an exhaust device that discharges the gas from the reaction chamber. An element manufacturing apparatus, further comprising an apparatus for supplying a gas for suppressing adhesion of a by-product generated in the raw material gas atmosphere to any position of a gas flow path of the manufacturing apparatus. It is.

FIG. 4 is a schematic sectional view of an example of the semiconductor manufacturing apparatus. A substrate 3 is provided in the reaction chamber 2. The reaction chamber 2 has a gas supply pipe 1 and an exhaust pipe 4.
And are connected. The gas supplied from the gas supply pipe 1 to the reaction chamber 2 passes through the connection part 7, the exhaust pipe 4, and the pressure regulating valve 6, and is discharged out of the system by the pump 8. The substrate 3 is disposed in the reaction chamber 2 by the transfer device 5. The semiconductor manufacturing apparatus of the present invention further includes an adhesion suppressing gas supply device 41.

In the conventional semiconductor manufacturing apparatus not provided with the adhesion suppressing gas supply apparatus, as in the conventional semiconductor element manufacturing apparatus not provided with the fine particle supply apparatus, as shown in FIG. In some cases, by-products adhered to the pipes and the concave portions of the pipes 4. On the other hand, in the semiconductor manufacturing apparatus of the present invention, the by-products are suppressed or vaporized by the adhesion suppressing gas and discharged out of the system.

The semiconductor device manufacturing apparatus of the present invention may be combined with a means for heating a pipe or the like. For example, pipes have a hollow structure, and water, oil,
Air or other fluid may be supplied, or a heater 51 may be wound around the pipe as shown in FIG.

Further, the semiconductor device manufacturing apparatus of the present invention may be combined with a means for causing discharge in a pipe. Specifically, a discharge electrode 61 can be provided as shown in FIG.

[0043]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following examples serve to illustrate the invention. However, the following examples are only for illustrating specific examples of the technical idea of the present invention, and do not limit the present invention to the following. The invention is capable of numerous modifications within the scope of the appended claims.

Embodiment 1 FIG. 1 shows an example of an apparatus for manufacturing a semiconductor device having the structure of the present invention.

When growing a polysilicon thin film, SiH ₄ (silane) is supplied as a source gas from a gas supply pipe 1 toward a substrate 3 installed in a reaction chamber 2. The supplied silane is represented by the following reaction. Decomposition of supplied silane: SiH ₄ → SiH ₂ + H ₂ Formation of polysilicon by reaction between generated SiH ₂ and substrate 2: SiH ₂ + substrate → Si (polysilicon) 10 H ₂

The above-mentioned SiH ₂ generates polysilicon by the reaction with the substrate 3 and, at the same time, is further decomposed by the following reaction to generate Si having high reaction activity. Decomposition of _{SiH 2: SiH 2 → Si +} H 2

The dust which has been a problem in the past is generated as a result of the molecular weight gradually increasing due to repeated aggregation of Si generated by the decomposition of SiH ₂ . Specifically _{Si + Si → Si 2 Si 2} + Si → Si 3 subsequent reaction continues Si _n ten Si → Si _{n + 1} (Dust)

After the completion of the reaction, the reaction gas is discharged out of the system through the exhaust pipe 4. After the formation of the thin film is completed, the substrate 3
Is transported out of the reaction chamber 2 using the transport device 5. Reaction chamber 2
A pressure regulating valve 6 is provided to regulate the pressure of the pressure. In the present invention, as an example, silane gas to be supplied is mixed with fine particles (Si) from a fine particle supply device 9, and the mixed gas is supplied from a gas supply pipe 1. The supplied particles trap high-active molecules Si that cause dust generation in the reaction vessel 2 by the following reaction. Si _N (particles) 10 Si → Si _{N + 1} (particles)

In the above example, by supplying Si particles, molecules having high reaction activity could be efficiently collected on the particles, and the generation of dust could be suppressed.

Embodiment 2 FIG. 4 shows an example of a semiconductor device manufacturing apparatus having the structure of the present invention.

When a thin film of Si ₃ N ₄ (silicon nitride) is to be grown, a reaction tube 2 is supplied from a gas supply tube 1 using SiH ₂ C ₁₂ (dichlorosilane) and NH ₃ (ammonia) as source gases.
It is supplied to the substrate 3 installed in the inside. The supplied dichlorosilane and ammonia produce silicon nitride Si ₃ N ₄ by the following reaction. 3SiH ₂ C ₁₂ + 10NH ₃ → Si ₃ N ₄ + 6NH ₄ C1 +
6H ₂

The generated Si ₃ N ₄ is the target thin film. Simultaneously formed NH ₄ Cl and H ₂ are by-products of the reaction. After the completion of the reaction, the reaction gas is discharged out of the system through the exhaust pipe 4. After the formation of the thin film is completed, the substrate 3 is transferred to the outside of the reaction chamber 2 using the transfer device 5. A pressure adjusting valve 6 is provided for adjusting the pressure of the reaction chamber 2. Usually, this thin film growth is performed at a reaction chamber pressure of about 1 torr and a reaction chamber temperature of about 700 ° C.

In the semiconductor device manufacturing apparatus of the present invention,
H ₂ O, CH ₃ OH, C ₂ H ₅ O
One of H, C ₃ H ₇ OH, acetone, methyl ether, ethyl ether or a mixture thereof is added in a gaseous state. Ammonium chloride is decomposed by these chemicals by the following reaction to form gaseous ammonia and hydrogen chloride. NH ₄ Cl → NH ₃ + HC1

In this example, N is introduced by introducing an adhesion suppressing gas.
H ₄ Cl was efficiently decomposed, and adhesion of by-products to the inside of the pipe could be reduced.

[0055]

According to the present invention, in the manufacture of a semiconductor device in which a semiconductor substrate is placed under a source gas atmosphere and a product derived from the source gas is deposited on the surface of the semiconductor substrate to form a thin film on the substrate surface, It is possible to suppress contamination of the semiconductor element by dust generated in a gas atmosphere and by-products attached to a reaction chamber or a pipe, and to improve product yield and throughput.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of an example of a first semiconductor manufacturing apparatus of the present invention.

FIG. 2 is a schematic view of a conventional semiconductor manufacturing apparatus.

FIG. 3 is a schematic cross-sectional view of an example of the first semiconductor manufacturing apparatus of the present invention.

FIG. 4 is a schematic cross-sectional view of an example of a second semiconductor manufacturing apparatus of the present invention.

FIG. 5 is a schematic sectional view of an example of the first semiconductor manufacturing apparatus of the present invention.

FIG. 6 is a schematic sectional view of an example of the first semiconductor manufacturing apparatus of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Gas supply pipe 2 Reaction pipe 3 Substrate 4 Exhaust pipe 5 Transport device 6 Pressure control valve 7 Connection part 8 Pump 9 Particle supply device 21 Dust or by-product 41 Adhesion suppressing gas

Claims (6)

[Claims] 1. A method for manufacturing a semiconductor device, comprising: placing a semiconductor substrate under a raw material gas atmosphere, depositing a product derived from the raw material gas on the surface of the semiconductor substrate, and forming a thin film on the substrate surface. A method for manufacturing a semiconductor device, comprising supplying fine particles to a gas atmosphere and removing by-products generated in the atmosphere. 2. A reaction chamber capable of disposing a substrate, a supply device for supplying a source gas (this source gas itself or a reaction product thereof can be deposited on the substrate) to the reaction chamber,
An exhaust device for discharging gas from the reaction chamber, further comprising a fine particle supply device for supplying fine particles to any position of a gas flow path of the manufacturing device. A semiconductor device manufacturing apparatus characterized by comprising: 3. A method for manufacturing a semiconductor device, comprising: placing a semiconductor substrate under a raw material gas atmosphere, depositing a product derived from the raw material gas on the surface of the semiconductor substrate by a predetermined reaction, and forming a thin film on the surface of the substrate. A method for manufacturing a semiconductor device, characterized in that a gas for suppressing adhesion of by-products generated in the source gas atmosphere is supplied to a reaction system. 4. The method of manufacturing a semiconductor device according to claim 3, wherein the gas for suppressing the adhesion of the by-product is obtained by vaporizing a solvent capable of dissolving the by-product. 5. A reaction chamber in which a substrate can be disposed, a supply device for supplying a source gas (this source gas itself or a reaction product thereof can be deposited on the substrate) to the reaction chamber, and the reaction chamber And a gas exhaust device for discharging gas from the semiconductor device manufacturing apparatus, wherein by-products generated in the source gas atmosphere are attached to any position of a gas flow path of the manufacturing apparatus. An apparatus for manufacturing a semiconductor device, further comprising an apparatus for supplying a gas that suppresses the occurrence of gas. 6. The semiconductor device manufacturing apparatus according to claim 5, wherein the gas for suppressing the adhesion of the by-product is obtained by vaporizing a solvent capable of dissolving the by-product.