JP4150200B2 - Fine particle formation method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fine particle forming method.
[0002]
[Prior art]
In recent years, a single-electron transistor, which is an example of an ultra-fine electronic device including nanometer-sized fine particles, and a method for creating a memory element including fine particles called nanodots or nanocrystals in a gate insulating film have been proposed.
[0003]
Conventionally, as a method for forming fine particles, there is a method disclosed in Japanese Patent Application Laid-Open No. 2000-22005. In the fine particle forming method disclosed in Japanese Patent Laid-Open No. 2000-22005, amorphous silicon is first deposited on a silicon thermal oxide film by an LPCVD (low pressure chemical vapor deposition) apparatus. Thereafter, the amorphous silicon is annealed to form silicon microcrystals on the silicon thermal oxide film. Further, a silicon oxide film is deposited on the silicon microcrystal by a CVD (chemical vapor deposition) method.
[0004]
As another fine particle forming method, a thin film is formed on a substrate by CVD (Chemical Vapor Deposition), vapor deposition, MBE (Molecular Beam Epitaxy), etc., and then the thin film is processed by a fine processing technique such as photolithography or etching. To form fine particles on the substrate. After the formation of the fine particles, an insulator layer is laminated on the fine particles in the same manner as in Japanese Patent Application Laid-Open No. 2000-22005.
[0005]
[Problems to be solved by the invention]
However, the fine particle forming method disclosed in Japanese Patent Application Laid-Open No. 2000-22005 has a problem that when the surface density of the fine particles is increased, the number of times of repeating the deposition process is increased, which requires a lot of labor and time.
[0006]
In addition, in the fine particle forming method using a fine processing technique such as photolithography or etching, there is a problem that it is extremely difficult to simultaneously reduce the size of the fine particles and the distance between the fine particles to the nanometer order.
[0007]
As a fine particle forming method capable of solving these problems, there is a method of forming metal fine particles by injecting metal ions into an insulating film by ion implantation and aggregating the metal ions by heat treatment. When a conductive element is introduced into an insulator using such an ion implantation method, it is possible to form isolated nanometer-sized fine particles in the insulator relatively easily.
[0008]
However, the insulator after ion implantation is gradually charged to a positive potential, and the potential of the insulator eventually rises to near the acceleration voltage of ions. In general, considering that the acceleration voltage of ions reaches at least several keV, if the film pressure of the insulator is about the same as the gate insulating film of a thin film transistor normally used, the insulator reaching the ion acceleration voltage is There is a problem that even if some charge neutralization mechanism is used, the insulator is likely to be defective.
[0009]
In addition, since the conductive element injected into the insulator is charged to a high positive potential, the conductive element is not injected at the injection depth expected from the injection energy due to the Coulomb repulsive force. There is a problem that variations occur.
[0010]
SUMMARY OF THE INVENTION An object of the present invention is to provide a method for forming fine particles that can prevent an insulator into which a metal element or a semiconductor element is implanted from being destroyed and can reduce variations in the implantation depth of a conductive element.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, the fine particle forming method of the present invention comprises:
Diffusing into an insulator formed on the substrate, after injection with negative ionization of the metal element or semiconductor element, by heat treating the ion-implanted metal element or semiconductor element to said insulator, the metal element or semiconductor element or are aggregated to form a conductive fine particles in the insulating body,
The heat treatment is performed at a temperature lower than the melting point of the metal element or semiconductor element and less than 6 hours,
The substrate is a silicon substrate and the insulator is silicon oxide or silicon nitride;
The thickness of the insulator is larger than the particle diameter of the conductive fine particles and is thinner than 5 nm.
[0012]
According to the fine particle formation method having the above structure, when the metal element or the semiconductor element (hereinafter referred to as “conductor element”) is negatively ionized and injected into the insulator, the negatively charged secondary electron is an insulator . The insulator is hardly charged. Therefore, it is possible to prevent the above-mentioned insulator is destroyed, it is possible to prevent the defects in the insulation.
[0013]
Further, since no the insulator is almost charged, irrespective large Coulomb force to the conductor element injected into an insulator, it can accurately control the injection depth of the conductor elements, variation in implantation depth of the conductive elements Can be reduced.
[0014]
Further, the fine particle forming method is excellent in mass productivity because the implantation depth of the conductor element can be controlled with high accuracy.
[0015]
[0016]
[0017]
Further, when the conductor element ion-implanted into the insulator is heat-treated, the conductor element diffuses or aggregates, so that the size of the conductor fine particles can be set to a desired size, the density of the conductor fine particles can be changed, The distribution of the conductive fine particles can be changed. Therefore, the conductive fine particles can be formed in various forms.
[0018]
Further, from the heat-treating the ion implanted conductor element to said insulator, can be easily obtained, for example, nanometer-sized conductive fine particles.
Further, since the substrate is a silicon substrate and the insulator is silicon oxide or silicon nitride, the substrate can be used in an existing method for manufacturing a semiconductor device, and versatility can be greatly enhanced.
In addition, when the fine particle forming method is used in, for example, a method for manufacturing a semiconductor device, it is not necessary to make a major change to the method for manufacturing the semiconductor device. can do.
The fine particle forming method is practical because it can be used when a plurality of different semiconductor devices are manufactured using a silicon substrate.
Further, when the fine particle forming method is used in a method for manufacturing a semiconductor device, the reliability of the semiconductor device can be improved by a simple process.
In one embodiment, the metal element is a silver element, and the dose of the silver element is greater than 1 × 10 ¹⁴ ions / cm ^{2 and} less than 1 × 10 ¹⁷ ions / cm ² .
[0019]
In one embodiment of the method for forming fine particles, the implantation energy of the metal element is less than 30 keV.
[0020]
According to the microparticles forming method of the embodiment, by the implantation energy of the metal element to less than 30 keV, without metal elements are widely implanted insulator, metal particles are formed varies within the insulator Can be reliably suppressed.
[0021]
[0022]
[0023]
[0024]
[0025]
[0026]
[0027]
[0028]
[0029]
[0030]
[0031]
[0032]
[0033]
In the fine particle forming method of one embodiment, the heat treatment is performed in an inert atmosphere.
In the fine particle forming method of one embodiment, the heat treatment is performed at 300 ° C. or higher and 900 ° C. or lower .
[0034]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the fine particle forming method of the present invention will be described in detail with reference to the illustrated embodiments.
[0035]
(Embodiment 1)
In general, when ion implantation is performed, an element to be implanted is positively ionized, and then the positively ionized element is accelerated by voltage and introduced into a solid. In contrast, in the fine particle forming method of the present invention, an element to be implanted is negatively ionized, and then the positively ionized element is accelerated by voltage and introduced into a solid.
[0036]
Hereinafter, the fine particle forming method according to the first embodiment of the present invention will be described with reference to FIGS. In the following, for example, silver fine particles are prepared as the fine particles.
[0037]
First, as shown in FIG. 3A, a silicon oxide film 210 as an insulator is formed on the surface of a silicon substrate 200 as a substrate by a thermal oxidation process. Here, the thickness of the silicon oxide film 210 is, for example, about 50 nm.
[0038]
Next, as shown in FIG. 3B, the silver element 201 is negatively ionized and implanted into the silicon oxide film 210. At this time, if the implantation energy of the silver element 201 is too high, the implantation distribution of the silver element 201 is so wide that it is not suitable for ion implantation into the thin film, and the silicon oxide film 210 is damaged and defects are generated. Therefore, the implantation energy is preferably less than 100 keV, and more preferably less than 50 keV.
[0039]
If the dose of the silver element 201 is too large, the particle size of silver fine particles 202 (see FIG. 3C) formed in the silicon oxide film 210 later becomes too large, Damage will increase. On the contrary, if the dose of the silver element 201 is too small, the density of the silver fine particles 202 becomes too small. Therefore, the dose of the silver element 201 is preferably greater than 1 × 10 ¹³ ions / cm ^{2 and} less than 1 × 10 ²⁰ ions / cm ² . The dose of the silver element 201 is more preferably greater than 1 × 10 ¹⁴ ions / cm ^{2 and} less than 1 × 10 ¹⁷ ions / cm ² .
[0040]
In the first embodiment, Ag201 is introduced with an implantation energy of about 30 keV and a dose of about 1 × 10 ¹⁵ ions / cm ² .
[0041]
As shown in FIG. 1, the negative ions of the silver element 201 are emitted from the negative ion source 100 and sequentially pass through the mass separation electromagnet 120, the acceleration tube, and the scanning deflection unit 140, and then the implantation chamber that houses the silicon substrate 200. 150.
[0042]
As shown in FIG. 2, xenon gas for maintaining and sputtering is introduced into the plasma generation chamber 101 serving as the negative ion source 100, and a high frequency of 13.56 MHz is applied to the coil in the plasma generation chamber 101. Inductively coupled discharge has occurred. At this time, the sputtering target 102 attached to the plasma generation chamber 101 applies a target voltage V _{tar of} about −600 V to the plasma generation chamber 101. The target material constituting the sputtering target 102 is sputtered by positive ions in the plasma generated in the plasma generation chamber 101 to generate negative ions of the silver element 201.
[0043]
Therefore, the target material is a material containing an element to be implanted into the silicon oxide film 210, and is a silver thin plate in the first embodiment. Moreover, the work function is lowered by blowing cesium vapor onto the surface of the target material, thereby increasing the negative ion generation efficiency. Negative ions generated on the surface of the target material are reversely accelerated by the target voltage, pass through the plasma, and travel toward the ion emission hole 103.
[0044]
A magnetic field is applied in the vicinity of the ion emission hole 103 in order to remove secondary electrons and electrons in plasma. The negative ions that have passed through the ion emission hole 103 are accelerated by the extraction voltage V _ext of the extraction electrode 109, converged by the Einzel lens 110, and transported to the mass separation electromagnet 120. Thereafter, the negative ions pass through the accelerating tube 130 and the scanning deflecting unit 140 in order, and enter the implantation chamber 150 in substantially the same manner as in a normal ion implantation apparatus.
[0045]
In the negative ion implantation apparatus used in the first embodiment, only a desired amount of negative ions is extracted by the mass separation electromagnet 120, and the negative ions are accelerated to a desired implantation energy by the acceleration voltage _Vacc of the acceleration tube 130. At the entrance of the accelerating tube 130, an electron removing suppressor is installed to suppress generation of X-rays due to acceleration of stray electrons. Then, on the output side of the accelerating tube 130, the negative ion beam is converged by an electrostatic quadrupole lens as a subsequent lens. The scanning deflection unit 140 has scanning / deflection electrodes for negative ion implantation into a large area substrate. In the scanning deflection unit 140, the beam central axis is deflected by about 7 degrees to remove neutral particles generated by collision of negative ions and residual gas during acceleration. Thereafter, the negative ions are implanted into the silicon oxide film 210 on the silicon substrate 200 accommodated in the implantation chamber 150.
[0046]
As can be seen from the above, since the negative ion implantation apparatus has a reverse ion polarity to that of the normal ion implantation apparatus, the applied voltage and the like of the negative ion implantation apparatus are as shown in FIG. The applied voltage must be reversed.
[0047]
When positive ions are implanted into the silicon oxide film 210 using a normal ion implantation apparatus, the surface potential of the silicon oxide film 210 rises to near the acceleration voltage of the positive ions, but the negative ion implantation apparatus having the above-described configuration is used. Thus, when negative ions are implanted into the silicon oxide film 210, the surface potential of the silicon oxide film 210 does not rise to near the accelerating voltage of the negative ions, and falls within a very low value of about several volts. That is, in the positive ion implantation, positively charged ions are incident on the surface of the silicon oxide film 210 and secondary electrons of negative charges are emitted from the surface of the silicon oxide film 210. Is positively charged, and the surface potential of the silicon oxide film 210 eventually rises to the acceleration voltage of positive ions. However, in negative ion implantation, negatively charged ions are incident on the surface of the silicon oxide film 210. As a result, negatively charged secondary electrons are emitted from the surface of the silicon oxide film 210, so that the surface potential of the silicon oxide film 210 is about ± several volts. As a result, since the silicon oxide film 210 is hardly charged, it is possible to prevent the silicon oxide film 210 from being broken or the silicon oxide film 210 from being defective.
[0048]
Further, in the negative ion implantation method, the charging of the silicon oxide film 210 is suppressed, and a large Coulomb force is not applied to the silver element 201 implanted into the silicon oxide film 210. Therefore, the silver element 201 is aimed at the silicon oxide film 210 as intended. Therefore, it is possible to suppress the variation in the implantation depth of the silver element 201. In addition, since the effective acceleration voltage variation is smaller in the negative ion implantation than in the positive ion implantation, the implantation depth of the negatively ionized silver element 201 can be controlled with higher accuracy, and the variation in the implantation depth of the silver element 201 can be controlled. Can be reduced.
[0049]
After the negative ion implantation by the negative ion implantation apparatus, when the silicon oxide film 210 is subjected to a heat treatment, as shown in FIG. 3C, the negative ion implanted silver element 201 aggregates and is made of ultrafine particles. Nanometer-sized silver fine particles 220 having a particle size of about 3 nm were formed in the silicon oxide film 210. At this time, the silver fine particles 202 were accurately formed so as to be distributed at a depth expected from the acceleration energy of silver ions.
[0050]
As described above, by performing the heat treatment, the silver element 201 which is an implanted element can be aggregated or diffused to form silver fine particles 202 having a desired particle shape. Further, by performing the above heat treatment, defects generated in the silicon oxide film 210 at the time of negative ion implantation can be repaired.
[0051]
If the temperature of the heat treatment is too low, there is no effect, and if it is too high, the silver element 201 cannot diffuse and melt to form the silver fine particles 202. Therefore, the temperature of the heat treatment is preferably higher than 200 ° C. and lower than the melting point of the implanted element. Further, even if the heat treatment temperature is the same, if the heat treatment time is lengthened, the effect at that temperature increases. However, if the heat treatment time is too long, the particle size of the silver fine particles becomes too large, or the silver element 201 Diffusion outside the region where the fine particles are to be formed, the heat treatment time is preferably shorter than 6 hours. For example, in the case of a normal heat treatment furnace, it is more preferable to perform heat treatment at about 300 ° C. to 900 ° C. in an inert atmosphere such as argon or nitrogen. In the first embodiment, about 500 ° C. in an argon atmosphere. Heat treatment was performed for 1 hour.
[0052]
FIG. 4 shows a TEM (transmission electron microscope) image of the silicon oxide film 210 containing the silver fine particles 202. 4 indicates the silicon / silicon oxide interface. The white dots in the silicon oxide film 210 are silver fine particles 202.
[0053]
From the TEM image in FIG. 4, it can be confirmed that the silver fine particles 202 are moderately scattered in the silicon oxide film 210. As described above, the nanometer-sized silver fine particles 202 dispersed moderately in the silicon oxide film 210 can be formed by performing the negative ion implantation process and the heat treatment only once, so that the fine particle formation disclosed in Japanese Patent Laid-Open No. 2000-22005 is performed. There is no need to repeat the same steps as many times as in the method or use a nano-scale fine processing technique, the formation of the silver fine particles 202 is simple, and the productivity of the silver fine particles 202 is good.
[0054]
In the first embodiment, the silver fine particles 202 are formed. However, for example, metal fine particles such as gold and copper, or semiconductor fine particles such as silicon and germanium may be formed. That is, the fine particle forming method of the present invention can form conductive fine particles having conductivity.
[0055]
Instead of the silicon substrate 200, a semiconductor substrate other than silicon, an insulator substrate such as a glass substrate, a sapphire substrate, or the like may be used.
[0056]
Further, instead of the silicon substrate 200, an SOI (silicon on insulator) substrate, an SOS (silicon on sapphire) substrate, or the like may be used. In this case, conductor fine particles may be formed in a conductor formed in an electrically insulated state on the SOI substrate or SOS substrate. As described above, in the fine particle forming method of the present invention, conductive fine particles having conductivity may be formed in a conductive material formed in an insulated state on a substrate.
[0057]
(Embodiment 2)
In the second embodiment, nanometer-sized conductive fine particles are formed in the silicon oxide film on the silicon substrate by the same fine particle forming method as in the first preferred embodiment, and the silicon oxide containing the conductive fine particles is further formed. An electrode is formed on the film by a commonly used method. The electrode formed on the silicon oxide film may be any conductive material. In the second embodiment, for example, an aluminum electrode is used.
[0058]
According to the second embodiment, a voltage is applied between the silicon substrate and the aluminum electrode, and the capacitance C (F) -voltage Vg (V) measurement is performed. As a result, the hysteresis characteristic as shown in FIG. 5 is exhibited. As a result. As can be seen from this result, the silicon oxide film containing the conductive fine particles functions as a memory function body, and performs binary discrimination from the magnitude of the capacitance when the same potential is applied to the silicon substrate and the aluminum electrode. Can do.
[0059]
Further, since the silicon oxide film functioning as the memory function body is manufactured by using the negative ion implantation method, the silicon oxide film maintains the same quality as the single thermal oxide film and is manufactured with high reliability. Therefore, the processing time is shorter than that of the CVD method, and the productivity is excellent.
[0060]
In addition, since the conductive fine particles can be prevented from being formed in the thickness direction in the silicon oxide film, the silicon oxide film can be made thinner and finer. Furthermore, even if the same potential is applied to the silicon substrate and the aluminum electrode, the effective electric field applied to the silicon oxide film becomes strong, so that the voltage can be lowered and the silicon oxide film is excellent in low power consumption. .
[0061]
In addition, if such a silicon oxide film functioning as a memory function body is used for a capacitor of a conventional DRAM (dynamic random access memory), a low power consumption DRAM that can eliminate the need for refreshing or can significantly reduce the number of refreshes. It becomes feasible. In this case, it is not necessary to use a special material such as a ferroelectric material of FeRAM (ferroelectric memory). Therefore, a low power consumption DRAM can be formed by a simple process and has excellent productivity.
[0062]
If the size of the conductive fine particles is too large, the silicon thin film cannot be miniaturized. However, if the size of the conductive fine particles is too small, the memory function of the silicon oxide film is lowered. Therefore, the size of the conductive fine particles is preferably larger than 0.1 nm and smaller than 4.0 nm. It is preferable that a large number of such conductive fine particles are formed in the silicon oxide film.
[0063]
Although the silicon substrate is used in the second embodiment, a semiconductor substrate other than silicon, an insulator substrate such as a glass substrate, a sapphire substrate, an SOI substrate, an SOS substrate, or the like may be used.
[0064]
In addition, nanometer-sized conductor fine particles are formed in the silicon oxide film by the same fine particle forming method as in the first embodiment. However, in the insulating film other than the silicon oxide film, the first embodiment is used. Nanometer-sized conductor fine particles may be formed by the same fine particle forming method.
[0065]
The electrode formed on the silicon oxide film may be composed of a metal electrode other than aluminum, polysilicon or the like.
[0066]
(Embodiment 3)
In Embodiment 3, a transistor as a memory element is manufactured as shown in FIG. This transistor includes a silicon substrate 300 and a silicon oxide film 310 as a gate insulating film formed on the silicon substrate 300. In the silicon oxide film 310, nanometer-sized conductor fine particles 302 formed by the same fine particle forming method as in the first embodiment are formed. On the silicon oxide film 310, an aluminum electrode 330 is formed as a gate electrode. A source region 340 and a drain region 350 are formed on the surface portion of the silicon substrate 300 so as to sandwich a region below the silicon oxide film 302.
[0067]
In such a transistor, after the aluminum electrode 330 is formed on the silicon oxide film 310, the silicon oxide film 210 is formed by performing photolithography and etching. Then, using a normal method, a source region 340 and a drain region 350 are formed on the surface portion of the silicon substrate 300, and a process for forming wiring is performed.
[0068]
In the transistor of the third embodiment, the magnitude of the threshold was observed corresponding to the magnitude of the capacitance of the second embodiment. When writing and erasing in the transistor, a sufficiently large positive or negative voltage is applied to the aluminum electrode 330 as a gate electrode, as in the floating gate type memory. In reading, the current flowing between the source region 340 and the drain region 350 may be detected. In the transistor, a difference of about 2 V was generated as a threshold immediately after +15 V was applied to the aluminum electrode 330 and immediately after −15 V was applied. Therefore, the transistor can perform a memory operation similar to that of a flash memory or the like.
[0069]
The transistor can be thinned because variation in the film thickness direction of the conductor fine particles 302 is suppressed in the silicon oxide film 310. As a result, the transistor can be miniaturized and the voltage can be reduced. For example, the transistor can be driven at less than 10V.
[0070]
In addition, the transistor does not require a complicated manufacturing process like a flash memory and does not use a special material like FeRAM, and thus has excellent productivity.
[0071]
In the third embodiment, the thickness of the silicon oxide film 310 is about 50 nm, for example, but the silicon oxynitride film 310 can be further thinned. The film thickness of the silicon oxide film 310 is preferably set so as not to be thinner than the size of the conductive fine particles 302, for example, preferably less than 5 nm.
[0072]
In this way, devices such as memories using the fine particle formation method of the present invention are incorporated in all electronic devices and systems using integrated circuits such as mobile phones because of their ease of production and compatibility with conventional silicon processes. These electronic devices and systems can be reduced in size and power consumption.
[0073]
Although the silicon substrate 300 is used in Embodiment 3, a semiconductor substrate other than silicon, an insulator substrate such as a glass substrate, a sapphire substrate, an SOI substrate, an SOS substrate, or the like may be used.
[0074]
The conductive fine particles 302 may be fine particles having conductivity, and may be metal fine particles, semiconductor fine particles, or the like.
[0075]
【The invention's effect】
As is clear from the above, since the fine particle forming method of the present invention negatively ionizes a metal element or semiconductor element and injects it into the insulator, the insulator is hardly charged and prevents the insulator from being destroyed. be able to.
[0076]
Further, since the insulator is hardly charged, the implantation depth of the metal element or the semiconductor element can be controlled with high accuracy, and variation in the implantation depth of the conductive element can be reduced.
[0077]
In addition, since the metal element or semiconductor element ion-implanted into the insulator is subjected to heat treatment, the metal element or semiconductor element is diffused or aggregated to form conductor fine particles. Can be in a state.
Substrate on which the insulator is formed on the surface is a silicon substrate, because the insulator is silicon oxide or silicon nitride, can be used in the production method of the conventional semiconductor device, to increase the versatility very it can.
[0078]
Microparticle formation method of an embodiment, since the implantation energy of the metal element is less than 30 keV, without metal elements are widely implanted in the insulator, that the conductive fine particles is formed varies within the insulator It can be surely suppressed.
[0079]
[0080]
[0081]
[0082]
[Brief description of the drawings]
FIG. 1 is a block diagram of a negative ion implantation apparatus used in a fine particle formation method according to a first embodiment of the present invention.
FIG. 2 is a view for explaining negative ion implantation by the fine particle forming method.
FIGS. 3A to 3C are process diagrams of the fine particle forming method.
FIG. 4 is a view showing a TEM image of a silicon oxide film according to a second embodiment of the present invention.
FIG. 5 is a diagram showing electrical characteristics of the silicon oxide film of the second embodiment.
FIG. 6 is a schematic cross-sectional view of a transistor according to Embodiment 3 of the present invention.
[Explanation of symbols]
200, 300 Silicon substrate 201 Silver element 202 Silver fine particles 210, 310 Silicon oxide film 302 Conductor fine particles

Claims (5)

Diffusing into an insulator formed on the substrate, after injection with negative ionization of the metal element or semiconductor element, by heat treating the ion-implanted metal element or semiconductor element to said insulator, the metal element or semiconductor element or are aggregated to form a conductive fine particles in the insulating body,
The heat treatment is performed at a temperature lower than the melting point of the metal element or semiconductor element and less than 6 hours,
The substrate is a silicon substrate and the insulator is silicon oxide or silicon nitride;
The method for forming fine particles, wherein the insulator has a thickness larger than a particle size of the conductive fine particles and smaller than 5 nm. In the fine particle formation method according to claim 1,
A fine particle forming method, wherein the metal element is a silver element, and a dose amount of the silver element is more than 1 × 10 ¹⁴ ions / cm ^{2 and} less than 1 × 10 ¹⁷ ions / cm ² . In the fine particle formation method according to claim 2,
Microparticle formation wherein the implantation energy of the metal elemental of less than 30 keV. In the fine particle formation method according to claim 1,
A method for forming fine particles, wherein the heat treatment is performed in an inert atmosphere. In the fine particle formation method according to claim 4,
The method for forming fine particles, wherein the heat treatment is performed at 300 ° C. or higher and 900 ° C. or lower.

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