JP2015141815A - plasma processing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plasma processing apparatus performing effective surface modification and thin film formation, while preventing plasma damage on a substrate.SOLUTION: A plasma processing apparatus includes a vacuum vessel, a substrate holding mechanism provided in the vacuum vessel, a magnetron plasma electrode provided in the vacuum vessel oppositely to the substrate holding mechanism, and having a magnetron generating section on the side opposite from the substrate holding mechanism, and a metal plate having a gas supply port provided in the vacuum vessel while spaced apart from the magnetron plasma electrode, and surrounding the magnetron plasma electrode so as to cover a plasma generation surface.

Description

  The present invention relates to a plasma processing apparatus for surface treatment and thin film formation without damaging a substrate.

  Plasma treatment is widely used for surface modification of various substrates, functional thin film formation, and microfabrication. Plasma treatment is performed by decomposing a raw material gas according to the purpose under reduced pressure or atmospheric pressure, and charged particles (ions and electrons), radicals, and film-forming species in the generated plasma are applied to the substrate surface. Exposure and processing proceeds by its physical and chemical effects. It has been reported that charged particles in this plasma damage the substrate and thin film when the substrate is a polymer with a low melting point material or when a thin film such as amorphous silicon is formed. There is a problem of significantly reducing the function to be performed. Therefore, a method of separating the substrate and charged particles and treating the substrate surface with a chemical reaction from radicals or film-forming species has been studied.

  For example, Patent Document 1 shows an example of a plasma processing apparatus including a shield plate in which a plurality of through holes are formed between a plasma generation unit and a base material, and charged particles are captured by the shield plate. Discloses that plasma damage is suppressed and good quality can be obtained.

  Further, Patent Document 2 shows an example of a multi-hollow plasma processing apparatus in which a porous high-frequency electrode is sandwiched between porous ground electrodes, and the charged particles are localized in the hollow so as to be necessary for film formation. It discloses the transport of film species to form a thin film. Here, further, regarding the gas flow to be introduced, the substrate side is set upstream and the plasma generation unit is set downstream, whereby the cluster of film defect factors taken into the film is reduced and high quality amorphous silicon can be formed. .

  Either method is effective as a plasma processing apparatus that separates the base material from the charged particles and modifies and forms the base material surface only by a chemical reaction from radicals or film-forming species.

JP 2006-120974 A Japanese Patent Application No. 2006-531825

  However, the method of Patent Document 1 is effective as a method for suppressing damage caused by collision of charged particles against the substrate and charge accumulation by separating the substrate and charged particles, but neutrons having high energy or A sufficient effect cannot be obtained with respect to damage caused by electromagnetic waves generated from plasma. In addition, the generated radicals are lost when passing through the shield plate, and there is a problem that the processing speed cannot be obtained.

  The method of Patent Document 2 localizes plasma in a hollow to suppress collision of charged particles and charge accumulation on the base material, and to form a high-quality thin film without damaging the base material. This method is effective, but it is also not sufficient for damage caused by electromagnetic waves generated from neutrons or plasma having high energy. Moreover, since the base material side is set upstream with respect to the gas flow, only a small amount of film forming species necessary for film formation is supplied to the base material, and there is a problem that the processing speed is slow. Furthermore, since the plasma in the hole is greatly affected by the hole shape and gas conditions, it is difficult to generate plasma uniformly in all the holes, and the processing effect varies.

  An object of the present invention is made in view of the above-described problems, and is to provide a plasma processing apparatus for performing effective surface modification and thin film formation without causing plasma damage to a base material. is there.

The plasma processing apparatus of the present invention that achieves the above object provides:
A vacuum vessel;
A substrate holding mechanism provided in the vacuum vessel;
A magnetron plasma electrode provided in the vacuum container so as to face the substrate holding mechanism, and having a magnetron generation surface facing in a direction opposite to the substrate holding mechanism;
And a metal plate provided in the vacuum container at a distance from the magnetron plasma electrode, surrounding the magnetron plasma electrode so as to cover the magnetron generation surface, and provided with a gas supply port.

In the plasma processing apparatus of the present invention, the distance between the side surface of the magnetron plasma electrode and the metal plate is preferably 10 mm or more and 100 mm or less,
It is preferable that a plurality of magnetron plasma electrodes are adjacently surrounded by the metal plate, more preferably the distance between adjacent magnetron plasma electrodes is 10 mm or more and 100 mm or less,
A gas supply nozzle is preferably provided between the magnetron plasma electrode in the vacuum vessel and the substrate holding mechanism.

  The method for manufacturing a substrate with a thin film according to the present invention includes a film-forming species supplied from a gas supply port toward a magnetron generating unit surrounded by a metal plate using the plasma processing apparatus of the present invention as a plasma processing apparatus. The raw material gas containing the film-forming species supplied from the gas supply nozzle provided between the magnetron electrode and the substrate holding mechanism is radically decomposed by generating a radical by decomposing the raw material gas with plasma. A method for producing a substrate with a thin film, in which a film-forming species generated by the decomposition is deposited on the substrate.

  According to the present invention, as will be described below, it is possible to obtain a plasma processing apparatus for performing effective surface modification and thin film formation without damaging the substrate.

FIG. 1 is a schematic sectional view of an example of the plasma processing apparatus of the present invention. FIG. 2 is an enlarged schematic sectional view of a part of the plasma processing apparatus of the present invention. FIG. 3 is a schematic cross-sectional view of an example of the plasma processing apparatus of the present invention provided with a plurality of magnetron plasma electrodes adjacent to each other in a metal plate. FIG. 4 is a schematic cross-sectional view of an example of the plasma processing apparatus of the present invention provided with a gas supply nozzle between a substrate and a magnetron plasma electrode. FIG. 5 is a schematic cross-sectional view of an example of the plasma processing apparatus of the present invention in which the substrate holding mechanism is a rotating drum. FIG. 6 is a schematic view of another example of the plasma processing apparatus of the present invention in which the substrate holding mechanism is a rotating drum. FIG. 7 is a schematic cross-sectional view of an example of a conventional magnetron type plasma processing apparatus provided with a shield plate in which a plurality of through holes are formed between a plasma generation unit and a substrate. FIG. 8 is a schematic cross-sectional view of an example of a conventional plasma processing apparatus in which a second metal plate is provided between a base material and a magnetron plasma electrode.

  Hereinafter, an example of the best mode of the present invention will be described with reference to the drawings, taking the plasma processing apparatus of the present invention as an example.

  FIG. 1 is a schematic sectional view of an example of the plasma processing apparatus of the present invention. The plasma processing apparatus of the present invention includes a vacuum vessel 1, a gas exhaust mechanism 14, and a vacuum gauge 15. Inside the vacuum vessel 1, a magnetron plasma electrode 4, a metal plate 5 surrounding the magnetron plasma electrode 4, and a substrate holding mechanism 3 for holding the substrate 2 are provided. The magnetron plasma electrode 4 is provided so as to face the base material holding mechanism 3 (the base material 2 when the base material 2 is installed). The magnetron plasma electrode 4 is provided such that the magnetron generation surface 13 faces the side opposite to the substrate holding mechanism 3. The metal plate 5 is spaced from the magnetron plasma electrode 4 and surrounds the magnetron plasma electrode 4 so as to cover the magnetron generation surface 13. By disposing the magnetron electrode 4 and the metal plate 5 in this way, the region surrounded by the magnetron generation surface 13 and the metal plate 5 becomes the magnetron generation unit 12 in which the plasma 7 is generated.

  The width s of the base material 2 installed in the base material holding mechanism 3 is preferably smaller than the width x of the metal plate 5 in order to perform the processing uniformly.

  The shortest distance d1 between the metal plate 5 and the substrate holding mechanism 3 is preferably as close as possible to the substrate holding mechanism 3 so that a high concentration of radicals is transported toward the substrate 2. This is to prevent radical diffusion loss between the base material 2 and the magnetron electrode 4 at d2, and the treatment effect can be improved by transporting a high concentration of radicals in the vicinity of the substrate 2. Moreover, it is preferable because the gas flow can be defined in a certain direction regardless of the position of the exhaust mechanism 14.

The distance d2 between the substrate 2 and the magnetron electrode 4 is preferably set to a distance that can suppress processing unevenness. This distance d2 can be determined according to the electrode width e [mm] and the radical diffusion angle θ [deg]. According to the knowledge of the present inventor, the diffusion angle θ varies depending on the degree of vacuum. Therefore, it is preferable to experimentally derive the diffusion angle θ according to the degree of vacuum used. For example, in the apparatus shown in FIG. 1, when discharging was performed at a vacuum degree of 0.1 Pa, the distance d2 at which the processing unevenness was 5% or less at this vacuum degree was derived. As a result, a distance of 50 mm or more was required. . In addition, the process nonuniformity with respect to a base material can be judged from a film thickness if it is source gas containing film-forming seed | species. On the other hand, in the case of a source gas that does not contain a film-forming species, it can be determined from the surface condition such as the contact angle and surface roughness of the substrate. Then, based on the derived distance d2, as shown in FIG. 2, the center of the base material was connected by a line and the angle was defined as the diffusion angle θ, and the result was 45 °. The relational expression (1) is shown below.
Distance d2 [mm] ≧ (tan (90 ° −θ) × e) / 2 (1)
When the diffusion angle θ = 45 °, the distance d2 [mm] ≧ 0.5 × e.

  The metal plate 5 is provided with a gas supply port 8 for supplying a source gas, and the source gas is ejected from the gas supply port 8 toward the magnetron generation surface 13 and the magnetron generation unit 12.

  The magnetron plasma electrode 4 is connected to a DC power source, a DC pulse power source, a high frequency power source, or the like as a power source 6 for applying a voltage. The metal plate 5 is electrically insulated from the magnetron plasma electrode 4 connected to the power source 6 and has a ground potential.

  In the plasma treatment, a raw material gas containing a film-forming species or a material gas not containing a film-forming species is introduced from a gas supply port 8 according to the purpose under vacuum, and then a voltage is applied between the magnetron plasma electrode 4 and the metal plate 5. Is applied to generate plasma 7, and the surface of the substrate 2 is treated by transporting radicals and film-forming species in the plasma 7 to the surface of the substrate 2 by gas flow. At this time, the gas introduced from the gas supply port 8 may be a single gas or a mixture of a plurality of source gases. Further, it is preferable to introduce gas through the mass flow controller 16 in order to control the gas amount.

  Here, the source gas containing a film-forming species refers to a gas that can form a polymer such as a thin film or fine particles by the combination of active species generated by being decomposed by the plasma 7 alone. Specific examples of such reactive gases include silane, disilane, TEOS (tetraethoxysilane), TMS (tetramethoxysilane), HMDS (hexamethyldisilazane), HMDSO (hexamethyldisiloxane), methane, ethane, Examples thereof include, but are not limited to, ethylene and acetylene. In addition, the gas that does not include the film-forming species is a gas that does not form a polymer by combining active species generated by decomposition with the plasma 7 by the gas alone. Specific examples of such a gas that does not include a film-forming species include, but are not limited to, rare gases such as helium and argon, and gases such as nitrogen, oxygen, and hydrogen.

  The magnetron plasma electrode 4 is provided with an internal magnet for forming a magnetron (E × B drift). Since the magnet may be demagnetized by the heat generated when the plasma 7 is generated, it is preferable to provide the cooling water channel 18 inside the magnetron plasma electrode 4. Moreover, it is preferable to cover the peripheral part of the magnetron plasma electrode 4 other than the magnetron generating surface 13 with a dielectric member in order to suppress abnormal discharge. The shape of the magnetron plasma electrode 4 may be circular or rectangular.

  The connection between the magnetron plasma electrode 4 and the power source 6 may be fixed to any one of the magnetron plasma electrodes 4, but the radicals flow onto the magnetron generation surface 13 so that the radicals flow uniformly from the gap between the magnetron electrode 4 and the metal plate 5. It is preferable to fix. At that time, in order to suppress damage to the power supply 6 cable due to the plasma 7, it is preferable to cover with a ceramic or the like. Similarly, it is preferable that the flow path 18 of the cooling water flowing to the magnetron plasma electrode 4 is also provided on any of the magnetron generation surfaces 13.

  In the magnetron plasma, charged particles are captured by the magnetron magnetic field formed on the magnetron generation surface 13, so that high-density plasma 7 is locally obtained in the magnetron portion. Therefore, a large amount of radicals necessary for the treatment can be generated, and an effective treatment can be performed. Moreover, since the magnetron plasma electrode 4 is provided between the base material 2 and the magnetron generating part 12, the base material 2 and the plasma 7 are separated, and damage due to charged particles is suppressed. Further, in the configuration of the present invention, since the plasma 7 cannot be seen from the base material 4, it is not affected by electromagnetic waves generated from the plasma 7. In addition, since the magnetron production | generation surface 13 may be damaged by sputtering by the high-density plasma 7, and the plasma 7 may become unstable, it is preferable to comprise the magnetron production | generation surface 13 with a material with a low sputtering rate like Ti. . High energy neutrons such as sputtered atoms sputtered out by this sputtering and neutral particles that neutralize and bounce off when colliding with the magnetron plasma electrode 4 travel toward the metal plate 5 facing the magnetron generating surface 13. Does not cause damage.

  The shape of the gas supply port 8 is preferably a slit shape in order to prevent clogging when a source gas containing a film-forming species is used. The material of the gas supply port 8 is preferably composed of a dielectric such as polytetrafluoroethylene (PTFE) or nylon so that the plasma 7 does not enter the gas supply port 8 in order to prevent clogging.

The distances w1 and w2 between the side surface of the magnetron plasma electrode 4 and the metal plate 5 are preferably 10 mm or more and 100 mm or less. This is because when the distance is less than 10 mm, radicals that are attached and lost on the side surfaces of the magnetron electrode 4 and the surface of the metal plate 5 increase when the distances w1 and w2 pass, and the treatment effect decreases. On the other hand, when the thickness exceeds 100 mm, leakage of charged particles due to plasma 7 diffusion damages the base material 2. The leakage of the charged particles can be confirmed by measuring plasma 7 emission spectroscopy just above the magnetron plasma electrode 4 openings w1 and w2. According to the inventor's knowledge, in the apparatus shown in FIG. 1, when a mixed gas of HMDSO and O ₂ was introduced from the gas supply port 8 to form a SiO ₂ film on the substrate 2, openings w1 and w2 were formed. When the thickness exceeds 100 mm, the plasma 7 emission spectrum appears remarkably, and the film quality deteriorates.

  FIG. 3 is a schematic cross-sectional view of an example of a plasma processing apparatus in which a plurality of magnetron plasma electrodes 4 are provided adjacent to each other in a metal plate. When the processing area for the base material 2 is enlarged, if a plurality of magnetron electrodes 4 surrounded by the metal plate 5 are provided adjacent to each other, streaks are generated between the base material 2 and the metal plate 5, so that a plurality of magnetron plasma electrodes are provided. More preferably, 4 is provided inside the metal plate 5.

  Further, when the width x of the metal plate 5 is fixed, the distance d2 can be shortened by increasing the number of electrodes and reducing the electrode width e from the equation (1). Thereby, the adhesion loss of the radical in the metal plate 5 and the loss by recombination can be suppressed, and the processing effect with respect to the base material 2 can be improved. Furthermore, by individually controlling the processing conditions of the plurality of magnetron plasma electrodes 4, it is possible to further improve the uniformity of the in-plane processing effect on the substrate 2. Further, when the base material holding mechanism 3 is movable and the base material 2 is transported, an inclination process to the base material 2 is also possible.

  Moreover, it is preferable to provide the space | interval w3 so that the magnetic field of the magnetron production | generation part 12 may not interfere between the adjacent magnetron plasma electrodes 4, and it is preferable that the space | interval w3 shall be 10 mm or more and 100 mm or less. This is because the treatment effect is enhanced by setting the distance between the magnetron plasma electrode 4 and the metal plate 5 to 10 mm or more and 100 mm or less, similarly to the intervals w1 and w2.

  FIG. 4 is a schematic cross-sectional view of an example of a plasma processing apparatus provided with a gas supply nozzle 9 between the substrate holding mechanism 3 and the magnetron plasma electrode 5. In the case of forming a thin film using a source gas containing a film-forming species, a gas supply nozzle 9 is provided between the magnetron plasma electrode 4 and the substrate holding mechanism 3 in order to prevent contamination of the magnetron plasma electrode 4 and the metal plate 5. It is more preferable. This is because the source gas containing the film-forming species is introduced from the gas supply nozzle 9 and the material gas not containing the film-forming species is introduced separately from the gas supply port 8, thereby preventing electrode contamination from the material gas containing the film-forming species. This is to prevent and maintain the plasma 7 more stably. The substrate holding mechanism 3 may be a drum shown in FIG. 5 instead of a flat plate as shown in FIGS. When it is desired to perform plasma processing on the surface of the long base material 2, the plasma processing can be continuously performed by transporting the base material 2 with a rotating drum.

  FIG. 5 is a schematic view of another example of the plasma processing apparatus of the present invention in which the substrate holding mechanism 3 is a rotating drum. The gaps w <b> 1 and w <b> 2 between the side surface of the magnetron plasma electrode 4 and the metal plate 5 may be closed with the cover plate 17 on one side. In this case, it is preferable to provide the gas supply port 8 on the metal plate 5 side where the cover plate 17 is provided. This is because the decomposition of the source gas is promoted by increasing the residence time of the source gas in the plasma 7. Moreover, it is preferable to provide the cover plate 17 and the gas exhaust mechanism 14 so that a gas flow can be performed in the conveyance direction of the base material 2. This can be expected to improve the treatment effect by lengthening the residence time of radicals on the substrate 2.

  The results of film formation experiments using the plasma processing apparatus described above will be described.

Example 1
The plasma processing apparatus itself has the structure shown in FIG. 1, and uses a mixed gas of HMDSO gas containing film-forming species and O ₂ gas not containing film-forming species as a raw material gas, and the substrate 2 is a polymer material having a width of 100 mm. PET base material 2 was obtained. An SiO ₂ thin film was formed on the PET substrate 2 by plasma CVD.

  The magnetron plasma electrode 4 has a rectangular shape with an electrode width of 100 mm. The material of the magnetron generating surface 13 was Ti having a low sputtering rate in order to prevent sputtering, and the side and back surfaces of the magnetron plasma electrode 4 other than the magnetron generating surface 13 were covered with a PTFE plate having a thickness of 10 mm. The connection between the PTFE plate and the magnetron plasma electrode 4 was fixed with a resin screw. A water channel for circulating the cooling water was provided on the side surface of the magnetron plasma electrode 4.

A 100 KHz AC power source was used as the power source 6 and fixed to the magnetron generating surface 13 via a matching box.
The distances w1 and w2 between the metal plate 5 and the side surface of the magnetron plasma electrode 4 are designed to be 150 mm, the thickness of the metal plate 5 is 5 mm, and the material is SUS430.
The shortest distance d1 between the metal plate 5 and the base material holding mechanism 3 is 10 mm, the distance d2 between the base material 2 and the magnetron electrode 4 is 120 mm based on the above formula (1), and the magnetron generating surface 13 and the metal plate 5 facing it are The distance d3 was 50 mm.

  The gas supply port 8 attached to the metal plate 5 has a slit structure made of PTFE, and the distance between the slits is 1 mm. The attachment position of the gas supply port 8 was provided in the longitudinal direction of the center of the magnetron plasma electrode 4. The gas supply port 8 was attached to the metal plate 5 by providing a hole for the gas supply port 8 in the metal plate 5 and fitting into the hole.

The influence of plasma damage was judged from the film density of the SiO ₂ film obtained by the X-ray reflectivity measurement method (XRR). The film density is considered to increase as the plasma damage increases and the number of defects in the film (dangling bonds) increases and the density decreases.

Using the plasma processing apparatus described above, HMDSO gas 0.1 g / min and O ₂ gas 200 sccm are introduced, the pressure inside the vacuum vessel is adjusted to 0.5 Pa, and the power density is 150 KW / m ² , and the film is formed for 1 min. Carried out.
As a result, a film formation rate of 250 nm / min and a film density of 1.98 g / cm ³ were obtained. The substrate thickness distribution was ± 10%.

(Example 2)
In the same structure as in Example 1, the same test as in Example 1 was performed with the gaps w1 and w2 between the magnetron plasma electrode 4 and the metal plate 5 set to 50 mm.
As a result, a film formation rate of 250 nm / min and a film density of 2.1 g / cm ³ were obtained. The substrate thickness distribution was ± 10%.

(Example 3)
In the same structure as in Example 2, two magnetron plasma electrodes 4 were arranged adjacent to each other in the metal plate 5, and the same test as in Example 1 was performed with the interval between the two magnetron plasma electrodes 4 being 5 mm.
As a result, a film formation rate of 290 nm / min and a film density of 2.1 g / cm ³ were obtained. The film thickness distribution of the substrate was ± 8%.

Example 4
In the same structure as in Example 3, the same test as in Example 1 was performed with the interval between two adjacent magnetron plasma electrodes 4 set to 50 mm.
As a result, a film formation rate of 310 nm / min and a film density of 2.1 g / cm ³ were obtained. The film thickness distribution of the substrate was ± 8%.

(Example 5)
In the same structure as in the fourth embodiment, a gas supply nozzle 9 is provided between the base material 2 and the magnetron plasma electrode 4, and O ₂ gas is introduced from the gas supply port 8 and HMDSO is introduced from the gas supply nozzle 9. The same test as 1 was performed.
As a result, there was no formation of solids due to the film-forming species at the gas supply port 8, and the plasma 7 was more stable than in Examples 1 to 4. In addition, since the HMDSO raw material is not decomposed in the plasma 7 generation section, it is possible to suppress the deposition loss of film formation species on the metal plate 5 and the plasma generation surface 13, and the film formation rate is 350 nm / min and the film density is 2.1 g / cm ^3. Obtained. The film thickness distribution of the substrate was ± 8%.

(Comparative Example 1)
Although the structure is substantially the same as that of the first embodiment, a magnetron plasma 7 is provided with a magnetron plasma electrode 4 and a base material 2 sandwiched between them as shown in FIG. 7, and a plurality of through holes are formed between the plasma 7 and the base material 2. A test similar to that in Example 1 was performed using a plasma processing apparatus including the formed shield plate 10.
As a result, a film formation rate of 180 nm / min and a film density of 1.8 g / cm ³ were obtained. The substrate thickness distribution was ± 10%.

(Comparative Example 2)
Although the structure is substantially the same as that of Comparative Example 1, a plasma processing apparatus in which a second metal plate 11 is provided between the plasma 7 and the base material 2 with a gap from the metal plate 5 as shown in FIG. The same test as in Example 1 was performed.
As a result, a film formation rate of 250 nm / min and a film density of 1.9 g / cm ³ were obtained. The substrate thickness distribution was ± 10%.

  The present invention can be applied to plasma surface modification, plasma CVD, plasma etching, and the like, but its application range is not limited thereto.

DESCRIPTION OF SYMBOLS 1 Vacuum container 2 Base material 3 Base material holding mechanism 4 Magnetron plasma electrode 5 Metal plate 6 Power supply 7 Plasma 8 Gas supply port 9 Gas supply nozzle 10 Shield plate 11 Second metal plate 12 Magnetron generation part 13 Magnetron generation surface 14 Gas exhaust Mechanism 15 Vacuum gauge 16 Mass flow controller 17 Cover plate 18 Cooling channel

Claims (6)

A vacuum vessel;
A substrate holding mechanism provided in the vacuum vessel;
A magnetron plasma electrode provided in the vacuum container so as to face the base material holding mechanism, and having a magnetron generation surface facing a direction opposite to the base material holding mechanism;
A plasma processing apparatus, comprising: a metal plate provided in the vacuum container at a distance from the magnetron plasma electrode, surrounding the magnetron plasma electrode so as to cover the magnetron generation surface, and provided with a gas supply port.   The plasma processing apparatus of Claim 1 whose space | interval of the said magnetron plasma electrode side surface and the said metal plate is 10 mm or more and 100 mm or less.   The plasma processing apparatus according to claim 1, wherein a plurality of the magnetron plasma electrodes are provided adjacent to each other and surrounded by the metal plate.   The plasma processing apparatus of Claim 3 whose distance between the said adjacent magnetron plasma electrodes is 10 mm or more and 100 mm or less.   The plasma processing apparatus according to claim 1, wherein a gas supply nozzle is provided between the magnetron plasma electrode in the vacuum vessel and the substrate holding mechanism.   Using the plasma processing apparatus according to claim 5, radicals are generated by decomposing a source gas that does not contain a film-forming species supplied from the gas supply port with plasma toward the magnetron generation surface surrounded by the metal plate. Then, the radical is used to radically decompose the source gas containing the film-forming species supplied from the gas supply nozzle provided between the magnetron electrode and the substrate holding mechanism, and the film formed by the decomposition A method for producing a substrate with a thin film, wherein seeds are deposited on the substrate.

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