JP2010199036A - Generating method of gas cluster ion beam, and processing method of solid surface using its method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize enlargement of an ion beam current of gas cluster ion beams. <P>SOLUTION: In a method for generating gas cluster ion beams by ionizing a neutral gas cluster to positive by electron bombardment, in curves showing a relation between an ionizing electron current and an ion beam current, ionization is processed with the use of combination of an ionizing electron current larger than a crossing point with two curves each having a different ionizing electron voltage crossing with the other and an ionizing electron voltage further increasing the ion beam current in an ionizing electron current region greater than the crossing point. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for generating a gas cluster ion beam for processing a solid surface, and more particularly to a method for generating a high current gas cluster ion beam.

  In recent years, solid surface processing methods using a gas cluster ion beam, such as etching, planarization, film formation, and ion implantation, have attracted attention because they have different characteristics from processing using a monomer ion beam.

  A typical processing apparatus using a gas cluster ion beam is disclosed in Patent Document 1. In Patent Document 1, a high-pressure gas is ejected from a nozzle into a vacuum to generate a neutral cluster. Among the neutral clusters, neutral gas cluster beams that have passed through a skimmer are ionized by electron impact, A gas cluster ion beam is generated. And it accelerates from several kV to several tens kV with an acceleration electrode, and irradiates a workpiece.

  Since the energy per atom constituting the cluster ion is much smaller than that of the monomer ion having the same acceleration energy, the processing using the gas cluster ion beam can reduce the damage on the solid surface. Also, due to the interaction between the cluster and the solid surface, surface atoms are sputtered and the material that constitutes the surface moves laterally, so that the convex portions of the surface are cut and the concave portions are filled to flatten the surface. Can do.

  As described above, the gas cluster ion beam has a sputtering (etching) action, a surface flattening action, and the like, but these actions generally proceed faster as the ion beam current of the gas cluster ion beam increases.

  Factors for increasing the ion beam current of a gas cluster ion beam include increasing the dose of neutral clusters generated mainly from the nozzle, increasing the current by optimizing the ionization method, and loss of the ion beam current during transportation. There is a high vacuum to prevent it. Here, a conventional technique related to an increase in current by optimization of an ionization method will be described.

As described in Patent Document 1, the ionization method is performed by an electron impact method in which a neutral cluster beam is irradiated with thermoelectrons emitted from an incandescent filament (usually tungsten), and is a positively ionized cluster beam. Is generated. As described in Patent Document 2 and Patent Document 3, about 60 eV to several hundred eV is usually used as the energy of electrons. Further, the current value of the ionization electron current _Ie is generally about 300 mA or less. According to Non-Patent Document 1, when the ionization electron current _Ie is 10 mA, the ion beam current (integrated value of the size distribution) increases as the ionization electron voltage (acceleration voltage of ionization electrons) V _e increases to 50V, 100V, and 500V. ) I _i increases. In addition, when V _e is 300 V, when I _e increases to 10 mA, 100 mA, and 300 mA, the ion beam current I _i increases as I _e increases, although a slight saturation tendency is seen at 300 mA. Therefore, as a condition for increasing the ion beam current I _i , for example, a combination of V _e = 300 V and I _e = 300 mA is often used.

In the ionization of clusters, the cluster size distribution (to be exact, the cluster size, that is, the distribution of the number of atoms or molecules constituting the cluster N and the ratio of the valence q of the ions, N / q) changes. Under the ionization conditions of Non-Patent Document 1 in which the electron voltage V _e is 50 to 500 V and the ionization electron current I _e is 10 to 300 mA, the N / q distribution peak is about 2000 to 20000. It is known that not only monovalently charged cluster ions but also divalent or higher charged cluster ions are generated.

  On the other hand, the following is known about the ionization of the non-clustered monomer.

That is, the ion beam current I _i of the monomer is proportional to the pressure P of the monomer gas and the ionization electron current I _e and is expressed by the following relational expression.

I _i = S × I _e × P
Here, S is a coefficient indicating sensitivity. This principle is used in ionization gauges. The ionization efficiency varies depending on the ionization electron energy. For example, in the case of argon gas, it is known that the ionization efficiency becomes the highest when the ionization electron energy is about 70 eV. Therefore, the sensitivity S depends on the ionized electron energy. Therefore, when the ionization electron voltage V _e is used as a parameter, the ion beam current I _i and the ionization electron current (sometimes referred to as an emission current) I _e are represented by straight lines having different proportional coefficients for each ionization electron energy.

JP-T-2003-521812 Special table 2008-518407 gazette JP 2007-317491 A

Ed. Yamada, edited by “Cluster Ion Beam Fundamentals and Applications”, Nikkan Kogyo Shimbun, October 31, 2006, P.50

In the gas cluster ion beam generated by the ionization method disclosed in Patent Documents 1 and 2, a wafer or the like for a semiconductor device is assumed as an object to be processed, and therefore surface damage needs to be extremely small. It was. For this purpose, it has been considered that cluster ions having a small valence q and a large cluster size N are effective in the process. This is because if the acceleration voltage is V _a (typically 20 kV), the acceleration energy is qV _{a in} the multivalently ionized cluster, and the energy is q times larger than that of the monovalent ionized cluster. Therefore, the surface damage is increased, and the surface flattening effect may not be maximized. Also, with respect to the cluster size N, it is considered that the larger N is, the smaller the energy per atom, the more advantageous for the process for the same reason. Thus, in the conventional ionization method, an ionization method in which the average N / q is large, that is, an ionization method in which the peak of the N / q distribution is about 2000 or more and the energy per atom is about 10 eV or less. Has been used.

Specific ionic conditions such that the average of the N / q increases, ionization electron energy is 60eV~ number 100 eV (the number 60 as the ionizing electrons voltage _{V e} 100 V), the ionization electron current _{I e} is in the range of 100mA~300mA In general, it has been used frequently.

  However, for workpieces that are not very sensitive to damage, such as semiconductor device wafers, the above ionization conditions are not necessarily optimal for the problem of high-speed planarization or etching. However, the optimum ionization conditions for performing flattening or etching on such a workpiece at high speed have not been clarified so far.

  In view of such circumstances, an object of the present invention is to provide a method for generating a gas cluster ion beam capable of increasing the ion beam current so that planarization and etching can be performed at a higher speed than before. is there.

  According to the first aspect of the present invention, in a method of generating a gas cluster ion beam by positively ionizing a neutral gas cluster by electron impact, an ionization electron voltage is expressed in a curve indicating a relationship between the ionization electron current and the ion beam current. Ionization is performed using a combination of an ionization electron current larger than an intersection at which two different curves intersect and an ionization electron voltage in which an ion beam current increases more greatly in an ionization electron current region larger than the intersection.

  According to the invention of claim 2, in the invention of claim 1, the ionization electron current is set to 360 mA or more.

  In the invention of claim 3, in the invention of claim 1, the ionization electron energy is set to 50 eV or more and less than 100 eV.

According to the invention of claim 4, a method for generating positively ionized by the gas cluster ion beam neutral gas cluster by electron impact, the average cluster size N _a gas cluster _ions, the average valence q _a In this case, gas cluster ions satisfying q _a > 0.008N _a +1 or q _a > 5 are generated by ionization.

  According to the method for generating a gas cluster ion beam according to the present invention, the ion beam current of the gas cluster ion beam can be increased as compared with the conventional method. Therefore, if the gas cluster ion beam generated by the present invention is used for processing of a solid surface, the processing speed of etching or planarization can be improved as compared with the prior art.

The schematic diagram of an ionization part. Graph showing the relationship of the ionization electron current I _e and the ion beam current I _i in the ionization of Ar cluster. The table | surface which shows the ionization conditions of an Ar cluster ion beam, and the etching rate of the silicon | silicone at that time. Graph showing the relationship between the ion beam current I _i and the etching rate of the Ar cluster ion beam in the table of FIG. Graph showing the relationship of the ionization electrons voltage V _e and the ion beam current I _i of Ar cluster ion beam at various ionization electron current value. Graph showing the relationship of the ionization electrons voltage V _e at the surface roughness Ra and ionization of Ar clusters of the sample after Ar cluster ion beam irradiation. Graph showing the relationship of the ionization electron current I _e and the ion beam current I _i in the ionization of the monomer. First graph illustrating a relationship between the average valence q _a and the average cluster size N _a. Second graph showing the relationship between the average valence q _a and the average cluster size N _a.

The conditions under which high ion beam current value of the gas cluster ion beam is obtained a result of extensive studies, a large area than a conventional condition ionizing electron current I _e with different ionization conditions from the conventional in the present invention, the ionization electron current I _e and ion It has been found that there is a characteristic relationship with the beam current I _i, and it has been found that the ion beam current can be increased by selecting conditions in this region.

  Hereinafter, embodiments of the present invention will be described by way of examples.

  First, the structure of an ionization part for realizing the ionization method in the gas cluster ion beam generation method of the present invention will be described with reference to the schematic diagram of FIG.

By passing an electric current through the filament 11 made of a tungsten wire, the filament 11 is heated and thermoelectrons 12 are generated. In order to extract the thermoelectrons 12 and irradiate the neutral clusters 20, a voltage is applied to the anode 13. This voltage is referred to as the ionization electrons voltage V _e. The anode 13 is a mesh-like stainless steel, and the accelerated thermoelectrons 12 that have passed through the anode 13 are irradiated to the neutral cluster 20, and the neutral cluster 20 is ionized. In addition to being ionized monovalently, it may be ionized more than divalently. Among the thermoelectrons 12, the one that reaches the anode 13 is observed as a current. This current is called ionization electron current _Ie . I _e can be controlled by changing the current flowing through the filament 11.

The ion beam current I _i was measured using a Faraday cup having a diameter of 50 mm at a position 100 mm from the exit of the ionization section. Moreover, in order to investigate the etching rate by gas cluster ion beam irradiation, the sample 30 was installed in the position of 100 mm from the ionization part exit. Neutral clusters generated from Ar gas were ionized, accelerated at 20 kV, and irradiated onto the sample. The average etching depth in the φ50 mm region was measured.

When the ionization electron voltage V _e was 50 V and 200 V, the relationship between the ionization electron current I _e and the ion beam current I _i was examined. The results are shown in FIG.

I _e is at the _360mA, curve in the case of the curve and _V e = 200V in the case of V e = 50V crosses. The etching rate was investigated by irradiating silicon with an Ar cluster ion beam obtained under ionization conditions in a region where I _e is larger and smaller than I _e = 360 mA, which is an intersection. The results are shown in Table 1 in FIG. FIG. 4 shows the relationship between the ion beam current I _i and the etching rate.

The relationship between the ionization electron voltage V _e and the ion beam current I _i when the ionization electron current I _e was fixed was examined. FIG. 5 shows the relationship between V _e and I _i when I _e = 100, 200, 300, 350, 400, 450, 500, 600, 700, and 800 mA.

_Then, by irradiating the Ar cluster ion beam in the case of changing the _{V e} under the condition of I e = 700 mA in the sample was examined a relationship between _{V e} and the surface roughness. Beam dose are both set to ^{1 × 10 17 ions / cm 2} . The sample was SKD11 which is a material such as a stainless steel mold. The average surface roughness Ra before irradiation was 520 nm. The surface roughness after irradiation was measured at the center of the irradiation area. The results are shown in FIG.

Referring to Example 1, in the case of the ionization electron voltage V _e = 50 V and 200 V, both I _i tend to increase as I _e increases, but I I in the monomer ionization shown in FIG. It is not a monotonous proportional line like the relationship between _e and I _i . That is, in the following areas _{I e} is 360 _mA, but towards the case of V e = 200V is large ion beam current value than in the case of _V e = 50 _V, towards the case of _V e = 50 V the boundary of I e = 360 mA However, as the ion beam current value increases and the ionization electron current _Ie increases, the difference increases. That is, when the ionization electron current I _e is 360 mA, a characteristic phenomenon is seen in which the I _e -I _i curves of V _e = 50 V and V _e = 200 V intersect. This is considered to be a phenomenon peculiar to cluster ionization. With large ionization electron current I _e from the point where the curve intersects, by using an ion beam current I _i increase rate is higher ionizing electrons voltage (in FIG. 2 V _{e =} 50V), conventionally used conditions, Compared with the case of V _e = 200 V and I _e = 300 mA, the ion beam current I _i can be increased.

The relationship between I _e and I _i as shown in FIG. 2 can be considered as follows.
The ionization of the monomer low ionization efficiency, because the number of monomers ionized monovalent with increasing ionizing electron current I _e is gradually increased simply proportional to the ionizing electron current I _e as shown in FIG. 7 As a result, the ion beam current I _i increases. On the other hand, the ionization rate of about ionizing electron current I _{e =} 100 mA in ionization clusters reaches 80% or more, the ionization rate in more ionizing electron current I _e is saturated ( "Cluster Ion Beam Technology", p. 37). Also in FIG. 2, it is considered that the ionization rate is in the saturation region at about I _e = 100 mA. Actually, when V _e = 200 V and I _e = 100 mA, the ion beam current I _i is 75 μA, and when I _e = 300 mA, I _i = 120 μA. Even if I _e increases three times, I _i is 1. It has increased only 6 times. Even at V _e = 50 V, the increase rate of I _i in the range of I _e = 100 mA to 300 mA is substantially the same.

On the other hand, the situation is different in the range where _Ie is 300 mA or more, that is, in the region where the ionization electron current value has not been conventionally used. When V _e = 200 V, the increase in I _i continues to be smaller than the increase in I _e , but when V _e = 50 V, the increase in I _i is greater than the increase in I _e . That _is, as a large difference in the slope of _I e -I _i curve occurs in the case of V e = 50 V and 200V. Due to the difference in inclination, the two curves intersect at I _e = 360 mA. Despite entering the saturation region in ionization rate, the I _i is increases significantly with increasing I _e in the case of V _{e =} 50 V as compared with the case of V e ₌ 200V is left without being ionized This is probably because the ionized state of the cluster has changed, not because the neutral cluster was ionized.

Factors that ion beam current value of the cluster ion beam increases, clusters are decomposed in the course of ionization, the average cluster size N _a is reduced, the number of cluster ions is increased, or / addition average valence of clusters Two cases are possible in which q _a increases. That is, by mean of N / q is smaller, the ion beam current I _i of cluster ions is considered increased.

In FIG. 2, the reason why the ion beam current value increases after the intersection of the curves at V _e = 50 V compared to V _e = 200 V is that N / q is reduced under this ionization condition. It is thought that. In particular, it is presumed that multivalent cluster ions that have not been actively used to increase damage are generated.

  By the way, mass separation of cluster ions by the Time-Of-Flight method or the like makes it possible to examine N / q, which is the ratio of the cluster ion mass (that is, cluster size N) to the valence q. Many of the results examined as cluster size distributions were obtained by measuring the N / q distribution, and it was difficult to know N and q independently. Recently, a method for measuring N and q separately has been developed, and the relationship between N and q has been experimentally obtained in the following documents 1 and 2.

Reference 1: Subsequent Evaluation Subcommittee on “Next-Generation Quantum Beam Utilization Nanofabrication Process Technology”
(http://www.nedo.go.jp/iinkai/kenkyuu/bunkakai/19h/jigo/8/1/index.html)
Reference 2: DRSwenson, Nucl. Instr. Meth. B 222 (2004) 61

The horizontal axis of FIG. 8 is the average cluster size N _a, the vertical axis represents the average valence q _a. According to FIG. 8, q _a increases as N _a increases, and their relationship can be represented by a substantially linear line. More N _a is large, high stability of the clusters has been speculated that it would be able to maintain the condition of higher valency.

FIG. 9 is a graph that reproduces the result of FIG. 8 (Document 1) and also shows the relationship between N _a and q _a reported in Document 2.

The experimental results of Document 2 are plotted on a linear line different from Document 1. This is thought to be due to the different cluster generation conditions. For example, if the ionization electron voltage V _e and the ionization electron current I _e are both reduced, a cluster having a large average N / q is generated (“Cluster Ion Beam Fundamentals and Applications” p. 50). The proportionality coefficient of the second straight line is very small. According to Literature 2, _a cluster ion beam having an average valence qa larger than 5 has not been observed. Ionization conditions also cluster ion beam generated by the document 1 is not explicitly, N a ₌ since q _{a =} 5 is observed in 5000, in some conventional ionisation conditions most average N / q This is considered to be a condition for reducing.

That is, the relationship between N _a and q _a of cluster ions generated under conventional ionization conditions lies in the shaded area in FIG. 9, and cluster ions outside this area could not be generated. The increase in the ion beam current I _i when compared with the conventional ionization conditions found in the present invention is that cluster ions are generated in the region above the shaded region in FIG. It is thought that this occurred because q became smaller. This region _can be defined as an area that satisfies q _a> 0.008N a +1 or _q a> 5.

As described above, in the case of cluster ionization, the dependence of the ion beam current I _{i on} the ionization electron current I _e does not become a monotonous straight line due to a phenomenon peculiar to the cluster in which the average N / q of the cluster changes depending on the ionization conditions. It is considered a thing. In the I _e -I _i curve when the ionization electron voltage V _e is low, the ion beam current I _e is larger than the point where the ionization electron voltage V _e intersects the high I _e -I _i curve. _i can be increased.

As described above, in the ionization of clusters, the phenomenon that the ion beam current I _i greatly increases with the ionization electron current I _e under ionization conditions different from the conventional ones is found, which is a cluster ion having a small average N / q, that is, This is probably because a cluster ion having N _a and q _a in _a region satisfying q _a > 0.008N _a +1 or q _a > 5 was generated.

Referring to Example 1, the etching rate in the region where I _e = 360 mA or more, where I _e -I _i curves at different ionization electron voltages V _e intersect, increases with increasing ion beam current I _i. You can see that That is, by using an ionization condition of a combination of an ionization electron current at an intersection or higher (I _e > 360 mA) and an ionization electron voltage (V _e = 50 V) at which the increase rate of the ion beam current I _i is higher after the intersection, It turns out that it can etch at high speed.

Referring to FIG. 5 of Example 2, in any region where V _e is 100 to 500 V, the change of I _i with respect to the change of V _e is relatively small in any I _e , and when V _e = 50 V or less, V _e I _i it was found that there is a tendency to decrease with the decrease. On the other hand, it was found that in the region where V _e is 50 V or more and about 100 V or less, there is a case where a relationship in which the ion beam current I _i increases with a decrease in V _e is obtained, or there is a case where the relationship is flat or shows a decreasing tendency. Its boundary is at I _e = 350 mA, which roughly matches the intersection value in FIG. I _e> In the region of the ionization electron current _350mA, V e = the 50 to 100 degree and _{V e} is compared with the ion beam current _{I i} of greater than about 100 _V, the ion beam current in the order of V e = 50 to 100 I _i increases as I _e increases, which is consistent with the results of FIG.

Referring also to the surface roughness of the results (FIG. 6), V _e is less than 100 V, it can be seen that surface roughness 50V or more areas are smaller. I _e coincides with the region _{where I i} with decreasing _{V e} is greater than 350mA is increasing. The increase in I _i in this region is considered to be due to the generation of cluster ions having a small average N / q, but these cluster ions having a small average N / q are considered to have contributed to the surface flattening effect. In particular, when the surface is irradiated with cluster ions in a state where N _a is not so small and q _a is large, for example, multivalent cluster ions having q _a of 10 or more, etching proceeds at a high speed because of high energy. It is considered that the effect and the flattening effect peculiar to the cluster (lateral sputtering effect) can be used efficiently, and the surface roughness is reduced.

As described above, in the curve showing the relationship of the ionization electron current I _e and the ion beam current I _i, greater ionization electron current I _e from the intersection ionizing electrons voltage V _e is two curves different intersect, greater ionization than the intersection By performing ionization using a combination of the ionization electron voltage V _e in which the ion beam current I _i increases more greatly in the electron current region, a higher ion beam current can be obtained. This is considered to be due to the fact that cluster ions having an average N / q smaller than those generated by the conventional ionization method were generated, and q _a > 0.008N _a +1 or q _a > 5. It is considered to be a cluster ion consisting of N _a and q _{a in the} region to be filled.

  The gas cluster ion beam is generated not only from Ar gas but also from oxygen gas, nitrogen gas, carbon dioxide gas, halogen-based gas, etc., and the basic ionization mechanism by electron impact is the same. Therefore, this principle is considered to be valid not only in the Ar cluster shown in the above-described embodiment but also in the ionization of other neutral clusters. The same applies not only to the electron impact caused by thermionic electrons generated by heating the filament shown in the above embodiment, but also to the case where ionization is performed by generating electrons from another electron source such as an RF ion source.

Claims (5)

In a method of generating a gas cluster ion beam by positively ionizing neutral gas clusters by electron impact,
An ionization electron current larger than an intersection where two curves having different ionization electron voltages intersect in a curve indicating a relationship between an ionization electron current and an ion beam current, and an ionization in which an ion beam current increases more greatly in an ionization electron current region larger than the intersection. A method for generating a gas cluster ion beam, wherein ionization is performed using a combination of electron voltages. The method of generating a gas cluster ion beam according to claim 1,
A method for generating a gas cluster ion beam, wherein an ionization electron current is set to 360 mA or more. The method of generating a gas cluster ion beam according to claim 1,
A method for generating a gas cluster ion beam, wherein ionized electron energy is set to 50 eV or more and less than 100 eV. In a method of generating a gas cluster ion beam by positively ionizing neutral gas clusters by electron impact,
Gas cluster ions satisfying q _a > 0.008N _a +1 or q _a > 5 are generated by ionization when the average cluster size of gas cluster ions is N _a and the average valence is q _a Generation method of gas cluster ion beam.   A solid surface processing method, wherein the solid surface is processed by irradiation with a gas cluster ion beam generated by the gas cluster ion beam generation method according to claim 1.

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