JPH08293483A - Flattening method for solid surface with gas cluster ion beam - Google Patents

Abstract

PURPOSE: To prevent defects from being produced on the surface of a substrate by irradiating a solid surface with gas cluster ions being a massive group of atoms or molecules of a substance being gaseous at a normal temperature and pressure. CONSTITUTION: By using an oxide, a nitride, a carbide, a rear gas substance, and a mixed gaseous substance obtained by mixing them by a proper ratio, and so on, a cluster of gases of these substances are formed. A gas cluster ion beam obtained by ionization on irradiating this gas cluster with electrons under a condition of an accelerating voltage of 10kV irradiates solid surfaces, selecting a beam of specific size as occasion demands. Consequently, it becomes possible to flatten and cleanse the surfaces of boards under a lower temperature condition without damaging the surfaces.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for flattening a solid surface using a cluster ion beam.
More specifically, the present invention relates to a method for treating a solid surface using a cluster of a gas substance at room temperature, which is useful for flattening or cleaning the surface of a substrate such as a semiconductor or other electronic device.

[0002]

2. Description of the Related Art Conventionally, various gas phase reaction methods have been developed for the purpose of cleaning and flattening the surface of substrates such as electronic devices such as semiconductors. For example, sputtering, vacuum deposition, CVD, ion beam. Methods such as vapor deposition have been put to practical use. However, in the case of these conventional methods, it is difficult to avoid undesired effects such as damage and deterioration of the surface of the target substrate, which has been a major problem in manufacturing high-precision and high-quality electronic devices.

That is, for example, as a method of flattening the surface of a substrate, there is known a method of flattening by irradiating the surface of the substrate with a single atom or a molecular ion such as Ar (argon) gas at a low angle and sputtering. . However, in the case of this conventional method, the convex portions existing on the substrate surface are preferentially shaved and flattened to some extent, while ripples and undulations that did not exist before sputtering are newly added. Therefore, it is necessary to suppress the incident angle of the ions by setting it to a high angle to some extent.
However, such suppression of the incident angle, on the contrary, weakens the priority of the sputtering of the convex portion and makes the substrate surface remarkable due to the incident ions. Further, the incident energy needs to be about 100 eV or less in order to suppress the damage on the substrate surface, but in this case, the ion current becomes extremely small and a practical sputtering rate cannot be obtained. .

As a method for cleaning the substrate surface, A
Known methods include a dry method of irradiating the substrate surface with an ion beam of a rare gas substance such as r and a wet method of eroding the substrate surface with a chemical. However, in the method of irradiating with an ion beam, when the incident energy is 100 eV or less, the ion current becomes extremely small.
I had to use an ion beam that was raised to eV. Therefore, there are drawbacks such that defects are generated on the surface of the substrate, or Ar is injected into the surface to become impurity atoms, so that a clean surface cannot be obtained.

Therefore, as a substrate technology for advancing advanced electronics such as ULSI, it is possible to realize a new ion beam technology capable of flattening and cleaning the substrate surface without damage while using an ion beam. It was strongly desired. The present invention has been made in view of the circumstances as described above, eliminates the drawbacks of the conventional ion beam technology, and performs damage-free surface flattening without causing defects on the substrate surface, and further cleaning. It is an object of the present invention to provide a new ion beam surface treatment method that makes it possible.

[0006]

In order to solve the above-mentioned problems, the present invention irradiates a solid surface with ions of gas clusters, which are a group of aggregated atoms or molecules of a gaseous substance at room temperature and pressure. Provided is a method for flattening a solid surface by a gas cluster ion beam, which is characterized by flattening the surface.

Further, the present invention irradiates the surface of the substrate with ions of gas clusters, which are a group of massive atoms or a group of molecules of a reactive substance that is in a gaseous state at room temperature and atmospheric pressure, to cause a reaction.
A method is also provided for forming a thin film on a substrate surface and planarizing the substrate surface at the same time.

[0008]

In other words, according to the present invention, gaseous substances such as oxides and nitrides at room temperature and atmospheric pressure as described above are used.
Use of carbides, noble gas substances, and substances in the form of mixed gas in appropriate proportions of these substances to form gas clusters of these substances, and electron beam irradiation of these to generate gas clusters It is characterized by selecting and irradiating a beam of a specific size according to.

In this case, since the cluster is usually composed of several hundreds of atoms or molecules, even if the acceleration voltage is 10 kV, each atom or molecule is
Since the irradiation is performed as an ultra-slow ion beam of several tens of eV or less, the solid surface can be treated with extremely low damage.
When a solid surface is irradiated with this gas cluster ion beam, the molecules or atomic species that make up the cluster ions collide with each other and with the atoms on the solid surface in multiple stages, resulting in a lateral motion component. This results in the selective sputtering of substrate surface protrusions, which results in the generation of reflective molecules or atoms. By utilizing this effect, the surface can be flattened. This flattening phenomenon can also be obtained from the effect of preferentially sputtering the atoms present in the convex portion of the surface, which has a weak bonding force, by the energy concentrated on the surface. Furthermore, due to the selective sputtering effect from this surface, it is possible to remove impurities on the solid surface and clean it at the same time as planarization.

Further, in the present invention, when ions of gas clusters, which are agglomerated atomic groups or molecular groups of a reaction product that are gaseous at room temperature and atmospheric pressure, are irradiated to the surface of the substrate to react with each other, a thin film is formed on the surface of the substrate. At the same time, the surface is flattened, the thin film formed on the surface at the same time as the flattening is irradiated with non-reactive gas cluster ions such as Ar, or removed by a wet method to expose the flat substrate material surface. It is also possible to let.

The gas clusters themselves can be generated by ejecting a gas under pressure into a vacuum device through an expansion nozzle, as already proposed by the inventor of the present invention. is there. The gas cluster thus generated can be ionized by irradiation with electrons. It should be noted that examples of typical substances that are gaseous at room temperature include CO ₂ , CO, N ₂ O,
_Examples thereof include oxides such as NO _x and C _x H _y O _z , O ₂ , N ₂ and various other substances, and rare gases such as Ar and He.

As the reactive gas cluster ions for forming the thin film simultaneously with the flattening, those which are generated by the reaction with the surface of the solid are selected depending on the kind of the solid to be flattened. For example, when forming an oxide film, cluster ions composed of oxygen-containing atoms and molecular groups are used. These surface thin films are removed by non-reactive gas cluster ions such as Ar (argon). Also,
It may be removed by a wet method using a hydrofluoric acid solution or the like. This exposes the flattened surface.

The method for flattening the solid surface by the gas cluster ion beam of the present invention will be described in more detail below with reference to examples.

[0014]

Example 1 FIG. 1 of the accompanying drawings shows that CO ₂ monomer ions and CO ₂ cluster ions having a cluster size of 250 or more were produced using the gas cluster ion beam of the present invention.
It shows the result of measuring the average roughness of the Pt thin film surface when irradiated under the condition of an acceleration voltage of 10 kV.

The average roughness is flattened to 27 Å or more when irradiated with monomer ions, whereas it is 48 Å before irradiation when gas cluster ions are irradiated at 2 × 10 ¹⁶ ions / cm ^2. To 8Å, and the surface could be greatly flattened. This result is an example in which the Pt surface of the CO ₂ cluster is flattened.
The semiconductor can also be planarized. Example 2 CO ₂ monomer ions, CO ₂ cluster ions having a cluster size of 250 or more, and 5 × 10 ¹⁵ ions / cm
^The Pt thin film surface was irradiated under the condition ² and the acceleration voltage was changed to measure the flatness of the thin film surface. FIG. 2 shows the result.

CO₂Acceleration in the case of cluster ions
The higher the voltage, the more effective the acceleration voltage is 5 kV.
The energy per constituent atom is 20 eV or less
Confirmed that flattening effect is achieved even at extremely low energy below
Was done. On the other hand, CO₂For monomer ions, the acceleration voltage
Even if it was increased, the flattening effect was not significant. Example 3 Accelerating voltage 10kV, 5 × 10^Fifteenions / cm²Conditions
And CO₂The cluster size of gas cluster ions
The flatness of the Pt thin film surface when the Pt thin film was changed was measured. So
FIG. 3 shows the results of the above.

In the case of Pt thin film, cluster size 250
It was confirmed that the degree of flattening effect by cluster ions was the highest. Example 4 The relationship between the sputtering amount and the surface flatness of the Pt thin film surface after irradiation with CO ₂ monomer ions and CO ₂ cluster ions was examined.

FIG. 4 shows the result. It was confirmed that the surface was roughened by the sputtering of 25 Å or more by the irradiation of the monomer ions, while it was further flattened by the irradiation of the cluster ions and was saturated by the sputtering of 100 Å or more. The flatness of Ra 24 Å or less, which cannot be obtained by the irradiation of the monomer ions, was realized by the irradiation of the cluster ions. Example 5 FIG. 5 shows that Ni was forced to be 6 × 10 ¹² atoms / cm ^2.
Before and after irradiation of the attached Si substrate with CO ₂ cluster ions having 250 or more constituent atoms and CO ₂ monomer ions under the conditions of an acceleration voltage of 10 kV and a dose amount of 2 × 10 ¹⁵ ions / cm ^2. Surface of Ni
It is the result of measuring the concentration by the total reflection fluorescent X-ray analysis method. Thereby, the impurity concentration on the pole surface up to a depth of about 15 nm is measured.

Ni impurity concentration is
Gas cluster Io
In the case of ion irradiation, it decreases rapidly with the increase in dose.
2x10 dose^Fifteenions / cm²Cluster lighting
Ni impurity concentration after spraying is 1.3 × 10¹²atoms / c
m²And can be reduced to 1/5 of that before irradiation
It Further decrease the impurity concentration by increasing the dose amount
Can be reduced. Example 6 CO₂Monomer ion and CO₂With cluster ions,
Accelerating voltage 10kV, 5 × 10^Fifteenions / cm²Irradiation of
While changing the cluster size under the condition of quantity
The surface of the Cu thin film was irradiated.

FIG. 6 shows the cluster size and Cu in this case.
It shows the relationship with the flatness of the thin film surface. As is clear from FIG. 6, in the case of the Cu thin film, size 15
It was confirmed that the flattening effect by the cluster ion of about 0 was the highest. Example 7 An Ar (argon) monomer ion and an Ar cluster ion were used to irradiate an Si substrate surface having Cu adhered on the surface thereof at an accelerating voltage of 20 kV in the same manner as in Example 5, and the Cu on the surface before and after irradiation was irradiated. The concentration was measured.

FIG. 7 shows the result. The small clusters in the figure have a cluster size of about 1000, and the large clusters have a cluster size of 30.
Those of about 00 are shown. Cu can hardly be removed by Ar monomer ion irradiation, but 1 × 10 ¹⁵ io
1/6 by irradiation of large cluster of ns / cm ²
~ 1/10 can be removed, smal
It was confirmed that the removal effect can be obtained even when l cluster ions coexist with monomer ions. This is
It is shown that even if the monomer and the cluster are not completely separated, the effect of removing impurities can be obtained even in the state where both are coexisting. Example 8 Table 1 shows the results of measuring the surface average roughness before and after irradiation of various substrates with a CO ₂ cluster of size 250 or more under the condition of an acceleration voltage of 10 kV. In this way, in the case of cluster ion irradiation, a beam with a large current is equivalently obtained, so that charge-up of the substrate can be suppressed and the substrate surface can be flattened.

As described above, according to the method of the present invention, a flat and clean surface having no defects can be formed on the surface of the substrate even at a low temperature, so that single crystal growth using this clean surface is possible. It can be applied to the monolithicization of electronic devices using these materials, and its effect is great.

[0023]

[Table 1]

Example 9 Table 2 shows that CO ₂ cluster ions were accelerated at an acceleration voltage of 10 kV.
The film thickness of the SiO ₂ film formed on the surface of the polycrystalline silicon film irradiated under the condition of a dose amount of 5 × 10 ¹⁵ ions / cm ² and the average surface roughness before and after the hydrofluoric acid solution treatment are shown. . This hydrofluoric acid treatment is carried out for a time period during which the SiO ₂ film can be completely removed. For comparison, the values of the polycrystalline silicon thin film not irradiated with cluster ions are also shown.

Samples not irradiated with cluster ions
The average surface roughness is 37Å, and this value is
Does not change. Clusters of size 250 and 500
The surface roughness of the polycrystalline silicon film was reduced by the ion irradiation.
It decreased to 7Å and 18Å respectively. At the same time
In addition, the surface of the polycrystalline silicon film has SiO of 8 to 6 nm. ₂
A thin film is formed, and at the same time as planarization, SiO₂Thin film
Has been obtained. The flatness of the surface is hardly changed by removing hydrofluoric acid.
Flatness is maintained.

The oxide film formed by CO ₂ cluster ion irradiation can be removed by Ar cluster irradiation. In this case, the effect of removing the oxide film can be obtained simply by switching the type of the supply gas in the same irradiation device. As described above, if the effect of thin film formation is not required and only the effect of flattening is desired, the thin film can be removed after irradiation of cluster ions.

[0027]

[Table 2]

[0028]Example 10 By changing the accelerating voltage, an Ar class with an average size of 3000
Star ion dose 3 × 10¹⁴ions / cm²of
Cu was attached to the surface under the same conditions as in Example 5.
Measure the Cu concentration on the surface before and after irradiating the Si substrate surface
Decided FIG. 8 shows the result. 5kV
Even at low accelerating voltage, the same as when irradiating at 20 kV
It can be seen that the cleaning effect can be obtained. In this case,
The average energy per atom is 2 eV or less.
Therefore, cleaning of the substrate surface with low damage is realized.Example 11 Table 3 shows Ar clusters with an average size of 3000 on various substrates.
-Accelerating voltage 20kV, dose 1.3x10^Fifteenion
s / cm²Surface before and after irradiation under the conditions
The result of measuring the roughness is shown. For comparison
The same accelerating voltage and ion dose
The results of irradiation are also shown. CO ₂cluster
As in the case of irradiation, the surfaces of various substrates are flattened. C
In the case of u thin film, the convex part due to the crystal grains observed before irradiation
Is removed by Ar cluster irradiation, CO₂cluster
A stronger flattening effect is obtained than in the case of irradiation. This
In the case of, the average energy per atom constituting the Ar cluster is
Energy is about 7 eV, which is a very low energy. This
Because of the gas cluster ion irradiation, the substrate is less damaged
The surface is flattened.

[0029]

[Table 3]

[0030]

As described in detail above, according to the present invention, by irradiating an ultra-slow gas cluster ion beam, it is possible to flatten and clean the substrate surface under lower temperature conditions without causing surface damage. Become. Also,
Thin film formation is possible by irradiation with reactive gas cluster ion beam at the same time as flattening. It is possible to remove this thin film by non-reactive gas cluster ion beam or by wet method to expose the flattened surface. Is also possible.

[Brief description of drawings]

FIG. 1 is a diagram showing the flatness of the surface of a Pt thin film after irradiation with CO ₂ gas cluster ions according to the present invention and a monomer ion for comparison.

FIG. 2 is a diagram showing the acceleration voltage dependence of the flatness of the Pt thin film surface after irradiation with CO ₂ gas cluster ions according to the present invention and, as a comparison, with monomer ions.

FIG. 3 is a diagram showing the cluster size dependence of the flatness of the surface of a Pt thin film after irradiation of CO ₂ gas cluster ions and monomer ions according to the present invention.

FIG. 4 is a diagram showing a relationship between a gas cluster ion of CO ₂ according to the present invention and a sputtering amount and surface flatness of a Pt thin film surface after irradiation of a monomer ion.

FIG. 5: Ni on the surface after irradiation of CO ₂ gas cluster ions according to the present invention and monomer ions for comparison
It is the figure which showed the impurity concentration.

FIG. 6 is a diagram showing the cluster size dependence of the flatness of the surface of a Cu thin film after irradiation of CO ₂ gas cluster ions and monomer ions according to the present invention.

FIG. 7: Cu on the surface after irradiation with Ar gas cluster ions according to the invention and monomer ions for comparison.
It is the figure which showed the impurity concentration.

FIG. 8: Reduction amount (removal rate) of Cu impurity concentration on the surface after Ar gas cluster ion irradiation according to the present invention
It is a figure showing the acceleration voltage dependence of.

 ─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Atsushi Doi 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. -9

Claims (7)

[Claims] 1. A solid surface by a gas cluster ion beam, characterized by irradiating a solid surface with gas cluster ions, which are a group of aggregated atoms or a group of molecules of a gaseous substance, at room temperature and pressure to flatten the surface. Flattening method. 2. The method of claim 1, wherein surface impurities are removed. 3. A substance which is gaseous at room temperature and pressure is oxygen or a compound thereof, nitrogen or a compound thereof, a rare gas substance,
Alternatively, the method according to claim 1, which comprises a mixed substance thereof. 4. The method according to claim 1, which comprises irradiating a cluster ion having a selected number of constituent molecules. 5. A substrate surface is irradiated with gas cluster ions, which are agglomerated atomic groups or molecular groups of reactive substances that are gaseous at room temperature and atmospheric pressure, to react with each other to form a thin film on the substrate surface, and at the same time A method for planarizing a solid surface by a gas cluster ion beam, which is characterized by planarization. 6. The method according to claim 5, wherein the thin film formed on the surface simultaneously with the planarization is removed by irradiation with non-reactive gas cluster ions or by a wet method to expose the flat substrate material surface. 7. The method according to claim 2, wherein impurities on the surface are removed at an acceleration voltage of 5 kV or less.