JP3647507B2 - Method for forming gas clusters and gas cluster ions - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a gas cluster and a method for forming gas cluster ions. More particularly, the present invention relates to a method for forming a gas cluster ion beam by ionization of a cluster of gaseous substances at normal temperature and pressure, which is useful for flattening and cleaning a solid surface, or forming a thin film. is there.
[0002]
[Prior art and its problems]
Conventionally, various gas phase reaction methods have been developed for the purpose of cleaning and planarizing the surface of a substrate such as an electronic device such as a semiconductor, or forming a thin film. For example, sputtering, vacuum deposition, CVD, ion beam deposition, etc. The method has been put into practical use.
[0003]
However, in the case of these conventional methods, it is difficult to avoid unfavorable effects such as damage and deterioration of the target substrate surface, which has been a big problem for manufacturing high-precision and high-quality electronic devices.
That is, for example, as a method of flattening the substrate surface, a method of flattening by irradiating the substrate surface with a single atom or molecular ion such as Ar (argon) gas at a low angle and performing sputtering is known. However, in the case of this conventional method, the convex portions present on the substrate surface are preferentially shaved and flattened to a certain extent, while rippled undulations that did not exist before sputtering are newly added. For this reason, the incident angle of ions had to be suppressed to a certain degree by increasing the incident angle. However, such suppression of the incident angle conversely weakens the priority of sputtering of the convex portion and makes the substrate surface significantly damaged by incident ions. Furthermore, in order to suppress damage to the substrate surface, it is necessary to reduce the incident energy to about 100 eV or less. In this case, however, there is a disadvantage that the ion current becomes extremely small and a practical sputtering rate cannot be obtained. .
[0004]
Further, as a method for cleaning the substrate surface, a dry method in which an ion beam of a rare gas substance such as Ar is irradiated on the substrate surface, a wet method in which a chemical agent erodes the substrate surface, and the like are known. However, in the method of irradiating the ion beam, the ion current becomes extremely small when the incident energy is 100 eV or less. Therefore, it is necessary to use an ion beam whose incident energy is increased to several KeV. For this reason, there are defects such that defects are generated on the substrate surface or Ar becomes impurity atoms implanted into the surface, so that a clean surface cannot be obtained.
[0005]
In forming a thin film on the substrate surface, various elements and compounds are excited and ionized, and a method of forming a thin film with the generated ion beam includes ion sputtering, cluster ion beam evaporation, ion plating, It is known as a plasma CVD method or the like. However, these methods also have a problem that inconveniences such as damage to the substrate surface and deterioration of the thin film are unavoidable due to high energy ion particles accompanying ionization excitation.
[0006]
Therefore, the realization of a new ion beam technology that can flatten and clean the substrate surface without damage while using an ion beam as a substrate technology for the development of advanced electronics such as ULSI is strongly desired. It was.
Under such circumstances, the inventor of the present invention has proposed a new method for surface modification and thin film formation by an ion beam which has not been known so far.
[0007]
In this method, a gas cluster which is a massive atomic group or molecular group is generated from a gaseous substance at normal temperature and pressure, such as Ar (argon), CO _2, etc., and the gas cluster ion generated after ionizing the gas cluster. It is characterized by using. The extremely low energy gas cluster ions make it possible to flatten and clean the surface as a phenomenon that has never been known before, and to form a thin film.
[0008]
However, the technological development using such a gas cluster ion beam has only just opened the edge, leaving many unknown problems. One of these issues is that gaseous substances at normal temperature and pressure are generally difficult to produce clusters, and there are practical limits to using them as cluster ions. Met.
[0009]
Therefore, the present invention has been made in view of the circumstances as described above, and further develops the gas cluster ion beam technology, flattening and cleaning damage-free surfaces without causing defects on the substrate surface, The object is to provide a method for generating a new gas cluster and its ion beam, which enable the formation of a high-quality thin film practically.
[0010]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention is directed to the above-mentioned gas by ejecting a pressurized gas in which a gaseous substance and a rare gas are mixed at normal temperature and pressure in an expansion nozzle portion cooled to −30 ° C. or lower. There is provided a method for forming a gas cluster, characterized in that a gas cluster composed of a massive atomic group or a molecular group of a gaseous substance is generated.
[0011]
The present invention also provides a gas cluster ion forming method characterized by ionizing a gas cluster formed by the above method.
[0012]
[Action]
That is, in the present invention, gaseous substances at normal temperature and normal pressure as described above, such as oxides, nitrides, carbides, halides, and mixed gas substances at an appropriate ratio thereof are used. It is possible to form a gas cluster ion beam by ionizing this gas cluster.
[0013]
As to the generation of this gas cluster, as described above, a pressurized gas in which a gaseous substance and a rare gas are mixed at room temperature and normal pressure is generated by being ejected from the expansion type nozzle section, and further, the nozzle is cooled. Are provided in this invention. As the nozzle portion in this case, for example, an expansion type having the shape illustrated in FIG. 1 is used, and representative indexes thereof include lengths l ₁ and l ₂ before and after the reduction portion,
l ₁ = 10-50mm
l ₂ = 5-50mm
And about its diameter,
d ₀ = 0.02 to 0.2 mm
d ₁ = 5 to 20 mm
d ₂ = 1 to 10 mm
The thing of a grade is illustrated.
[0014]
Of course, it is not limited to these dimensions. However, since l ₂ and d ₀ affect the cluster generation amount and cluster size distribution, the smaller the d _{0 and the} longer l ₂ , the more generally the cluster generation amount and its size. It is desirable to determine these sizes from the viewpoint of increasing.
About this nozzle, what was cooled with the refrigerant | coolant etc. is used more suitably.
[0015]
Various substances are considered as gaseous substances at room temperature and normal pressure. For example, as examples, oxides such as CO, CO ₂ , N _x O _y , C _x H _y O _z , N ₂ , Nitrides such as NH ₃ , halides such as SF ₆ , phosphorus compounds, boron compounds, hydrides and the like are shown. These can be used alone or in combination.
As the rare gas mixed with these gaseous substances, He, Ne, Ar, or the like is considered. In general, the mixing ratio is preferably at least 10% by volume or more.
[0016]
The mixture of the gaseous substance and the rare gas can appropriately set the mixing ratio, pressure, and cooling temperature when cooling the nozzle depending on the type.
As the rare gas, it is particularly preferable to use He. This is because He itself hardly forms a cluster. Of course, you may make it actively use Ar etc. which are easy to comprise a cluster.
[0017]
Taking this He as an example, the mixing ratio to the gaseous substance is preferably in the range of, for example, 10 to 50% in the case of N ₂ and 20 to 80% in the case of O _2. In the case of cooling, it is generally preferable that the temperature is −30 ° C. or lower, more preferably about −50 ° C. (203 K) or lower.
The synergistic effect due to the cooling of the nozzle and the mixing of the rare gas is extremely remarkable, and the generation of gas clusters is performed effectively.
[0018]
The gas clusters generated by the above method are then ionized to generate gas cluster ions. This ionization is possible by electron beam irradiation or the like.
The gas cluster is usually composed of tens to thousands of atoms or molecular groups. Therefore, even if the acceleration voltage is 10 KeV, each atom or molecule becomes an ultra-slow ion beam of several tens eV or less. Therefore, the solid surface can be treated with this ion beam with extremely low damage. When this gas cluster ion beam is irradiated onto a solid surface, the molecules or atomic species that make up the cluster ions, and reflected molecules with lateral motion components due to multi-stage collisions with atoms on the solid surface. Or, since atoms are generated, the substrate surface can be planarized or cleaned.
[0019]
Then, it is possible to activate a reaction on the substrate surface to form a thin film on the substrate surface.
The distribution of the size of the gas cluster can be controlled by the shape and size of the nozzle as described above, the mixing ratio of the rare gas, and the nozzle temperature. As for the nozzle, the smaller the diameter of the reduced portion, the larger the size, and by increasing the mixing ratio of the rare gas, the size becomes larger, and the size becomes larger by lowering the nozzle temperature. Is possible.
[0020]
Hereinafter, the method for planarizing a solid surface by a gas cluster ion beam of the present invention will be described in more detail with reference to examples.
[0021]
【Example】
Test example Using the expansion type nozzle (l ₁ = 30 mm, l ₂ = 32 mm, d ₀ = 0.1 mm, d ₁ = 12 mm, d ₂ = 8 mm) illustrated in FIG. A gas cluster of gaseous material was generated.
[0022]
FIG. 2 shows the supply pressure dependence of the cluster beam intensity of various gases at room temperature without mixing noble gases. The beam intensity was measured using an ion gauge provided in the irradiation chamber after passing through the skimmer of the system illustrated in FIG. The vertical axis represents a value obtained by subtracting the background vacuum degree from the indicated vacuum degree when the beam is directly introduced into the ion gauge. The sensitivity of the ion gauge for each gas was corrected. The beam intensity of N ₂ gas and SF ₆ is 1/6 or less of Ar gas. Further, the supply pressure at which clusters start to be generated is 4 atm or more, and there is a problem that large-sized clusters cannot be obtained.
Example 1
Therefore, He was mixed with N ₂ gas and ejected from an expansion type nozzle similar to the test example at a pressure of 5 atm and 6 atm to generate a gas cluster.
[0023]
FIG. 4 shows the He mixture ratio dependence of the N ₂ cluster beam intensity of the N ₂ / He mixed gas when the nozzle temperature is 300K. By mixing the He gas, a two-fold increase in beam intensity is observed compared to the case without mixing.
Example 2
FIG. 5 shows the mixing rate dependence of the beam intensity of the SF ₆ gas cluster in the case of the SF ₆ / He mixed gas when the nozzle temperature is 300K. The beam intensity became 11 × 10 ⁻⁴ Torr by mixing about 85% He gas. This value is 70 times that when He is not mixed, and the strength is remarkably increased.
Example 3
FIG. 6 shows the mixing rate dependence of the N ₂ cluster beam intensity of the N ₂ / He mixed gas when the nozzle temperature is lowered. A beam intensity increase of 3 times or more is observed by mixing He gas and cooling the nozzle.
Example 4
FIG. 7 shows the dependence of the CO ₂ gas cluster beam intensity on the mixing ratio in the case of a CO ₂ / He mixed gas at a nozzle temperature of 300K.
[0024]
It can be seen that an increase in beam intensity can be obtained by mixing about 15% of He. This CO ₂ gas cluster became cluster ions by ionization by electron beam irradiation.
Example 5
FIG. 8 shows the decelerated electric field spectrum of the cluster ion beam obtained by ionizing the SF ₆ gas cluster beam obtained in Example 2 by electron beam irradiation.
[0025]
The supply pressure was 4000 Torr, and the mixing ratio of He gas was 5% by volume.
Even in a positive deceleration electric field, an ion current is observed, and it can be seen that a cluster ion beam of SF ₆ is generated.
FIG. 9 shows the size distribution of SF ₆ gas cluster ions obtained by differentiating the deceleration electric field spectrum shown in FIG. It can be seen that a cluster ion beam having a wide distribution with a maximum size of 1,500 and a maximum size of 5,500 is obtained.
[0026]
The size of the cluster ions was controlled by changing the diameter of the reduced portion of the nozzle (d _{0 in} FIG. 1). That is, in order to obtain a larger size cluster, control was performed by reducing the diameter of the nozzle reduction portion, and in order to obtain a small size cluster, the diameter of the nozzle reduction portion was increased.
Thus, the SF ₆ gas cluster ion beam obtained by mixing the He gas was not observed when the He gas was not mixed.
[0027]
Further, by lowering the nozzle temperature to −30 ° C., a cluster ion beam intensity more than twice that at room temperature was obtained.
[0028]
【The invention's effect】
As described above in detail, the present invention enables efficient generation of gas clusters of gaseous substances at various normal temperatures and pressures, which has been difficult until now, and the practical use of gas cluster ion beams by their ionization is possible. It will be a thing.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating an expansion type nozzle.
FIG. 2 is a diagram showing the correlation between the pressure of various gases and the beam intensity of cluster generation when no rare gas is mixed.
FIG. 3 is a system configuration diagram illustrating a gas cluster and its ionization system.
FIG. 4 is a diagram showing the mixing ratio dependence of the beam intensity of an N ₂ gas cluster in an N ₂ / He mixed gas at a nozzle temperature of 300K.
FIG. 5 is a diagram showing the mixing ratio dependence of the beam intensity of SF ₆ gas clusters in an SF ₆ / He mixed gas at a nozzle temperature of 300K.
6 is a view similar to FIG. 4 at a nozzle temperature of 120K. FIG.
FIG. 7 is a diagram showing the mixing ratio dependence of the beam intensity of CO ₂ gas clusters in a CO ₂ / He mixed gas at a nozzle temperature of 300K.
FIG. 8 is a decelerated electric field spectrum diagram of an SF ₆ cluster ion beam.
FIG. 9 is a diagram showing the size distribution of SF ₆ gas cluster ions.

Claims (5)

In an expansion nozzle section cooled to −30 ° C. or less, a pressurized gas in which a gaseous substance and a rare gas are mixed at normal temperature and normal pressure is ejected to form a gas cluster composed of a massive atomic group or molecular group of the gaseous substance A method for forming a gas cluster, wherein The method of claim 1 , wherein the noble gas is He. The method according to claim 1 or 2 , wherein the gaseous substances are two or more kinds, and a gas cluster of these plural kinds of substances is generated. A method for forming gas cluster ions, comprising ionizing a gas cluster generated by the method according to claim 1 . The method according to claim 4 , wherein ionization is performed by electron beam irradiation.

Images