JP3865513B2 - Method of forming nitride or nitride surface by nitrogen compound gas cluster ion beam - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The invention of this application relates to a method of forming a nitride by a Christer ion beam. More specifically, the invention of this application relates to Si nitride deposition on a Si substrate or gate oxide film for suppressing impurity diffusion from a gate to a channel region in a fine MOS transistor, MBE growth of a group III nitride semiconductor, The present invention relates to a new method for forming a nitride or a nitrided surface using a cluster ion beam, which is useful in surface nitriding of various metals, increasing the strength and weather resistance of material surfaces, surface nitriding of low melting point metals, and the like.
[0002]
[Prior art]
Conventionally, various methods for forming a nitride or a nitrided surface have been adopted. For example, known methods include nitriding (thermal CVD method) by surface adsorption and thermal decomposition of ammonia gas, and film formation with the assistance of plasma obtained by discharge of rare gas such as Ar. There are so-called plasma or ion beam assist methods. These methods are generally employed because they are convenient for the treatment of a large area sample surface. However, these methods have a problem in that a high temperature of 500 to 1000 ° C. is required. The device means for maintaining such a high temperature condition is a special one, and the burden of production and maintenance is large, and the kind of the target sample is naturally restricted from the viewpoint of deterioration and alteration due to heat. Further, the ion beam assist method has a drawback that it is difficult to avoid damage to the substrate surface by high energy ions.
[0003]
Thus, among these conventional techniques, the plasma or ion beam assist method is capable of more precise film formation and surface nitriding, and is expected to be able to adopt a lower temperature. The actual situation is that there are still many problems in concrete development.
In recent years, there has been a demand for innovation in this nitride formation technology in terms of the use of nitrides in electronic devices. For example, Group III nitride semiconductors have a forbidden band from the violet to the ultraviolet wavelength region, and are attracting attention as light emitting devices (LEDs or LDs (laser diodes)) from the violet to the ultraviolet wavelength region. The crystal growth is performed at a high temperature of about 1000 ° C. by the CVD method, while the growth of group III nitride has been mainly the CVD method in the past, whereas the MBE (Molecular Beam Epitaxy) method is an RF discharge. Alternatively, chemically active nitrogen molecules called radical nitrogen obtained by ECR plasma, etc. are used, however, the actual situation is a mixture containing a large amount of atomic nitrogen, nitrogen ions, etc. It is not clear whether it contributes, and the crystallinity of the obtained thin film is inferior to that of the CVD method. Therefore, the formation of group III nitride by the MBE method is realistic. Not now. In addition there is a problem with the growth rate such as nitrogen molecular beam intensity is also not sufficient.
[0004]
The above plasma source is also used exclusively for nitrogen doping as an acceptor species for II and VI group compounds having a wide band gap. However, it is not clear which species contribute to the actual doping as described above. Furthermore, wide-forbidden band II-VI group compounds other than ZnSe cannot control p-type conduction.
As described above, the plasma or ion assist method and further the MBE method are expected as means for precise solid surface processing, modification, modification and film formation, and some of them are also practically used. However, the reality is that it still has many problems. In particular, in these conventional methods, nitride or nitridation is performed as a process such as selective processing, modification, modification, and film formation at a lower temperature without damaging the sample or the surface thereof. Forming the surface has been a major issue.
[0005]
[Means for Solving the Problems]
The invention of this application provides the following method as a solution to the problems of the prior art as described above. That is,
First, there is provided a nitride or nitride surface forming method characterized in that a nitride or nitride surface is formed by irradiating the surface of a GaAs substrate with an ion beam of a nitrogen compound gas cluster.
[0006]
And in connection with this method, secondly, the nitrogen compound is nitrogen, ammonia, nitric oxide, an organic nitrogen-containing compound, or ammonium or a metal complex of an organic nitrogen-containing compound, and thirdly, Provided is a method of irradiating a cluster ion beam of an inert gas or another kind of element compound together .
[0007]
According to a fourth aspect of the present invention , there is provided a method of forming a nitride or a nitrided surface characterized in that in any of the above methods, the solid surface is cleaned or planarized beforehand by irradiation with cluster ions of an inert gas . No. 5 is a method of forming a nitride or nitride surface by focusing or deflecting a gas cluster ion beam to selectively form a nitride or nitride surface, and sixth is a nitrogen compound gas cluster. There is also provided a method of forming a nitride or nitride surface, which is characterized by irradiating an elemental or elemental compound molecular beam with an ion beam .
[0008]
The invention of this application having the features as described above is a further development of the gas cluster ion beam technology which has been proposed by the inventors and is being developed as a specific technology.
The present invention is epoch-making in that a nitride or nitride surface can be formed as a gas cluster ion beam technique.
[0009]
The features of the present invention will be further outlined as follows.
A) In addition to the use of gas cluster ion beam, which focused on surface modification of the prior art, such as cleaning, flattening of the solid surface by sputtering effect, or selective etching with reactive gas cluster ion beam, the cluster It was applied to crystal growth using atoms or molecular species constituting ions as a component of the crystal. That is, by directly irradiating the nitrogen compound cluster ion beam, it is possible to form a high-quality nitride film that is denser and has higher adhesion, which cannot be formed by vapor deposition.
[0010]
B) As a material for forming a cluster ion beam for producing a nitride material, attention was paid to a cluster material other than nitrogen gas, which is usually low in reactivity, and this can be used.
C) By ionizing several hundred to several thousand molecular groups to be monovalent, the number of high-density molecules can be secured with a low current, and the state is close to that of neutral beam irradiation. Therefore, there is almost no problem of charge-up on the substrate surface as in the case of using an ion beam of a single molecule or the plasma assist method, and it can be applied to nitriding of an insulator.
[0011]
D) Since it is a much lower energy beam (about 1 to 10 eV per molecule) than an ion beam of atoms or molecules, there is almost no risk of damage to the substrate surface. On the other hand, if converted into thermal energy per molecule, it corresponds to an ultra-high temperature of 10,000 to 100,000 degrees C. Further, the nitrogen compound decomposes without increasing the temperature of the substrate due to the many-body effect at the time of substrate collision, Nitriding reaction is possible at low temperature.
[0012]
E) Since it is an ion beam, it can be converged to a very small area (several tens of μm) by using an electrostatic lens, and it is possible to deflect the beam by using a deflection electrode. By utilizing this property, it becomes possible to perform nitridation or nitrogen implantation of the microstructure of the sample. Furthermore, since the directivity of the beam is good, in the mask projection method, it is possible to perform nitridation or nitrogen implantation of a sample having a small beam wraparound from the mask edge, that is, a pattern faithful to the mask pattern.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Therefore, examples of the present invention will be shown below, and the embodiments will be described in more detail.
[0014]
【Example】
FIG. 1 illustrates a cluster ion beam apparatus for the method of the present invention. This cluster ion beam apparatus includes a cluster generation part (A), an ionization part (B), an acceleration part (C), and an action part (D). In the cluster generating part (A), a conical nozzle made of quartz glass is attached to a manipulator for position adjustment. A nitrogen compound gas introduced from a gas introduction pipe connected to the outside is ejected from a nozzle to form a cluster.
[0015]
The gas for generating the gas cluster may be various nitrogen compounds, such as N ₂ , NH ₃ , NO _x , an N-containing organic compound, or an N-containing metal complex. For these gases, for example, ammonia has only a saturated vapor pressure of about 10 bar at 300 K and 4.3 bar at 273 K (0 ° C.). On the other hand, it is necessary to supply at a pressure of 2 to 4 bar for cluster generation. This can cause reliquefaction in the supply piping system, particularly in a portion having a mechanism with gas expansion such as a cylinder pressure reducing valve, a mass flow meter (flow rate adjusting valve) and a nozzle portion. Also, the supply pressure may vary with changes in room temperature. Supply pressure fluctuations affect cluster size. Therefore, the nozzle is provided with a temperature adjusting mechanism for maintaining a constant temperature, and the piping system including the gas cylinder is provided with a heating mechanism.
[0016]
The formed cluster is incident on the ionization part (B) and the acceleration part (C) through the skimmer provided in the partition between the cluster generation part (A) and the ionization part (B). A cluster is ionized by the ionization part (B), for example by thermionic irradiation generated with the filament. After being drawn out by the drawing electrode, it is accelerated and converged by the acceleration part (C). The cluster size distribution in the obtained cluster ion beam can be measured, for example, by the blocking voltage method.
[0017]
A solid surface substrate for forming nitrides as particles or thin films, or forming a nitrided surface by film formation or ion implantation, for example, is attached to a substrate holder made by Molybdenden, and then fixed to a manipulator, for example, resistance heating from the back Is done. In addition, the apparatus is provided with a port for supplying raw materials other than the cluster ion beam, and in the case of a gas or solid, it is supplied as a molecular beam by resistance heating or the like.
[0018]
In the above apparatus, substrate surface treatment (planarization and cleaning) is performed with an argon cluster ion beam as necessary, and then nitridation is performed using a nitrogen compound cluster ion beam. Also, nitride thin film growth is performed by supplying various metal material molecular beams or organic metals in a gaseous state.
<1> Generation of Argon Cluster Ion Beam; FIG. 2 shows the inhibition voltage dependency of the argon cluster ion current value obtained by the inhibition voltage method. As the argon flow rate increases, the current value increases. FIG. 3 shows the cluster size distribution obtained from this result. In FIG. 3, the horizontal axis represents the number of argon atoms forming one cluster, and the vertical axis represents the number of classifiers. When the flow rate is small, the monomer (position of zero on the horizontal axis) occupies most. Large clusters are gradually formed as the flow rate increases. The number also increases. The maximum cluster size obtained in this example is about 800 atoms / cluster at a flow rate of 0.6 SLM.
[0019]
<2> Generation of Ammonia Cluster Ion Beam; FIGS. 4 and 5 show the results when ammonia is used as the source gas. FIG. 4 shows the inhibition voltage dependency of the ammonia cluster ion current value obtained by the inhibition voltage method, and the same result as in the case of argon is obtained. FIG. 5 shows the cluster size distribution obtained from this result. As in the case of argon, large clusters are gradually formed as the flow rate increases. It should be noted that larger clusters are formed at the same flow rate as argon. Since ammonia has a higher intermolecular bond energy than argon, it is expected that larger clusters will be formed under the same conditions.
[0020]
<3> An example of nitriding when ammonia is used as the nitrogen compound gas is shown. An ammonia cluster ion beam having a predetermined energy is irradiated for a predetermined time under a predetermined substrate temperature. After irradiation, the sample was once taken out into the air and transferred to an XPS (X-ray Photo-clcctron Spectroscopy) apparatus. The presence or absence of nitriding was examined by measuring the XPS spectrum. The results are shown below. Irradiation conditions are 2 hours at a current value of about ² μA / cm ² . Only the irradiation temperature is different. Since the peak value of the cluster size is 1000 / cluster, the total dose amount is less than 10 ¹⁷ / cm ² .
[0021]
FIG. 6 shows the results for the Si substrate. The irradiation substrate temperature is room temperature. It is an XPS spectrum after etching the surface with an Ar ion beam for 30 seconds in consideration of carrying in the air after irradiation, and a nitrogen signal is observed. Incidentally, no nitrogen signal was observed in the sample that was not irradiated with cluster ions, and it is clear that this was not the result of the attachment of nitrogen in the air. Similar results were obtained for samples irradiated at several points from room temperature to 700 ° C., and it is clear that Si nitride was formed. In view of the fact that nitride is never formed at room temperature when a single ammonia gas is supplied, this is a very important effect.
[0022]
FIG. 7 shows the results for a GaAs substrate. The irradiation substrate temperature is 550 ° C., and a nitrogen signal is also observed. In GaAs, no nitrogen signal was observed at temperatures below about 450 ° C. or above 650 ° C. The nitridation of GaAs suggests that the degree of As desorption from the substrate and the supply ratio of nitrogen atoms are important factors. Considering that a high temperature of 900 to 1000 ° C. is required for nitriding in an ammonia gas atmosphere without using cluster ions, the usefulness of using gas cluster ions is obvious.
[0023]
Of course, the invention of this application is not limited by the above examples. The present invention is implemented in various embodiments.
[0024]
【The invention's effect】
As described above in detail, according to the invention of this application, it is possible to form a nitride using a gas cluster ion beam of a nitrogen compound and to nitride the sample surface. A wide range of nitrogen compounds such as nitrogen, ammonia, and ammonium metal complexes can be used as the gas cluster material, and the sample to be processed can be applied to various materials such as metals, semiconductors, and insulators. Compared with the CVD method, the treatment can be performed at a low temperature, and excellent effects such as less surface damage than the ion beam assist method can be obtained.
[Brief description of the drawings]
FIG. 1 is a configuration diagram illustrating a gas cluster ion beam apparatus of the present invention.
FIG. 2 is a diagram showing the relationship between the blocking voltage of an Ar gas cluster ion beam and the ion current.
FIG. 3 is a diagram showing a distribution of cluster sizes of an Ar gas cluster ion beam.
FIG. 4 is a diagram showing the relationship between the blocking voltage of an ammonia gas cluster ion beam and the ion current.
FIG. 5 is a diagram showing a cluster size distribution of an ammonia gas cluster ion beam.
FIG. 6 is an XPS spectrum diagram showing an example of nitriding of a Si substrate.
FIG. 7 is an XPS spectrum diagram showing an example of nitriding of a GaAs substrate.

Claims (6)

A method of forming a nitride or nitride surface, wherein a nitride or nitride surface is formed by irradiating the surface of a GaAs substrate with an ion beam of a nitrogen compound gas cluster.   The method according to claim 1, wherein the nitrogen compound is nitrogen, ammonia, nitric oxide, an organic nitrogen-containing compound, or ammonium or a metal complex of an organic nitrogen-containing compound.   The formation method of Claim 1 or 2 which irradiates together with the cluster ion beam of an inert gas or another kind of element compound. 4. The method according to claim 1, wherein the surface of the GaAs substrate is previously cleaned or flattened by irradiation with an inert gas cluster ion. 5. The forming method according to claim 1, wherein a nitride or a nitrided surface is formed in a position-selective manner by focusing or deflecting a gas cluster ion beam. 6. The forming method according to claim 1, wherein an element or an element compound molecular beam is irradiated together with a nitrogen compound gas cluster ion beam.

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