JP3539738B2 - Impurity addition method - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to an impurity doping method for adding an electrically active impurity to a semiconductor wafer , and a semiconductor substrate obtainable by the method.
[0002]
Summary of the Invention
The present invention relates to a technique for adding an electrically active impurity in a usual semiconductor device fabrication, and by irradiating a high-brightness X-ray beam after ion implantation, a high-efficiency electrical activation in a short time at a low temperature. It is possible to achieve the conversion.
[0003]
[Prior art]
Usually, when electrically active impurities are added to a semiconductor wafer, ion implantation is performed. In this ion implantation, the high energy particles collide with the semiconductor crystal lattice, so that the crystal structure is destroyed. In this state, the implanted impurities are not electrically activated. Therefore, conventionally, after ion implantation, heat treatment has been performed to recover crystallinity and electrically activate impurities.
[0004]
As this heat treatment method, a method of annealing the semiconductor wafer in an electric furnace is most common. For example, an electric furnace anneal is performed on a silicon wafer into which boron (p-type) or phosphorus (n-type) ions are implanted at a temperature of 900 ° C. or more and about several tens of minutes.
[0005]
By the way, if electric furnace annealing is performed when impurities are implanted at a high concentration, the activation rate of the impurities is significantly reduced. Further, since the processing takes a long time, it is disadvantageous for cost reduction. Further, due to the long-time treatment by the electric furnace annealing, in a device having a three-dimensional laminated structure such as an SOI (Silicon on Insulator) or a device having a large number of times of annealing, the structure may be deteriorated by heat.
[0006]
On the other hand, a laser annealing method for instantaneously melting and solidifying the ion-implanted layer by irradiation with a pulsed laser beam has been proposed.
[0007]
This laser annealing method is capable of 1) processing only the surface layer, 2) spatially local processing, and 3) instantaneously (within several hundred nanoseconds). There is an advantage in that it cannot be achieved by electric furnace annealing, such as the fact that 4) impurities can be added in large amounts beyond the thermal equilibrium solid solubility limit.
[0008]
However, this laser annealing method is not suitable for materials that are easily decomposed at high temperatures, such as 1) deterioration of device structure, 2) contamination of impurities such as oxygen which adversely affects device performance, and 3) compound semiconductors. There is a drawback caused by the high temperature treatment close to the above.
[0009]
Further, there is a flash annealing method as a method having an intermediate characteristic between electric furnace annealing and laser annealing. In this method, a strong xenon or halogen lamp light is applied to the ion implantation layer for several seconds. At this time, the temperature of the semiconductor wafer reaches about 1000 to 1100 ° C., but the crystal does not melt. However, spatial local processing such as laser annealing is difficult.
[0010]
In short, the heat treatment performed on silicon or after the ion implantation that has been attempted has been performed at a high temperature of 900 ° C. or more, and thus thermally affects the device. The impurity concentration after annealing cannot exceed the peak concentration at the time of ion implantation, and the impurity concentration to be activated does not exceed the thermal equilibrium solid solubility limit.
[0011]
[Problems to be solved by the invention]
The present invention has been made in order to solve the above technical problems, and aims at being able to recover in a short time at a low temperature without melting a crystal surface layer of a semiconductor wafer destroyed by ion implantation, Another object of the present invention is to provide a method capable of adding an implantation impurity beyond a peak concentration of the implantation profile.
[0012]
[Means for Solving the Problems]
To achieve the above object, the doping method of the present invention, the addition of the electrically active impurity to the semiconductor wafer to a doping method of an n-type or p-type substrate, the semiconductor wafer Implanting impurities by ion implantation , and irradiating the crystal surface layer of the semiconductor wafer destroyed by the ion implantation with high-intensity X-rays by wiggler from synchrotron radiation to destroy the semiconductor wafer . Recovering crystallinity without melting the crystal surface layer, and simultaneously segregating implanted impurities in the crystal surface layer beyond the peak concentration of the injection profile . Here, when irradiating the high-brightness X-rays, thermal annealing may be additionally performed on the crystal surface layer of the semiconductor wafer. Further, the concentration of the implanted impurity segregated in the crystal surface layer can exceed the thermal equilibrium solid solubility limit.
[0013]
[Action]
In the present invention, when high-brightness X-rays are irradiated on the surface layer of a semiconductor wafer which has been destroyed and made amorphous by ion implantation with a large dose, a large number of pores having a thermal equilibrium concentration or more are formed. In an amorphous semiconductor, atom diffusion occurs via a large number of vacancies. Due to this atomic diffusion, solid-phase epitaxial growth using a deep portion of the semiconductor wafer that has not been made amorphous as a seed is promoted at a low temperature, and the crystallinity of the surface layer of the amorphous portion is recovered in a short time.
[0014]
Further, in the present invention, the semiconductor wafer surface layer destroyed by ion implantation with a small dose is not necessarily amorphized, but is damaged by atom diffusion caused by vacancies formed by high-brightness X-ray irradiation. Crystal recovery proceeds.
[0015]
Furthermore, in the present invention, the diffusion of impurities is enhanced by high-brightness X-ray irradiation, so that segregation of impurities occurs at the same growth interface as in melt growth by pulsed laser annealing. The smaller the segregation coefficient K ^* is 1, the greater the deposition on the surface. Due to solid phase growth in which diffusion is enhanced by high-brightness X-ray irradiation, in the surface layer, the implanted impurity can exceed the peak concentration of the implantation profile and can exceed the thermal equilibrium solid solubility limit .
[0016]
Further, in the present invention, by utilizing the high transmittance of a high-brightness X-ray beam to a material, a multilayer ion implantation layer can be collectively processed in a three-dimensional stacked structure such as an SOI (Silicon on Insulator).
[0017]
【Example】
An embodiment of the present invention will be described below with reference to the drawings.
[0018]
FIG. 1 is an elevational sectional view showing each step of the impurity doping method of the present invention. In FIG. 1, reference numeral 1 denotes a semiconductor substrate wafer (hereinafter abbreviated as a substrate). As a material of the substrate 1, a compound semiconductor such as silicon or GaAs can be used. As shown in FIG. 1A, for example, boron (p-type) or phosphorus (n-type) impurity ions are added to the main surface of the substrate 1 by ion implantation (indicated by an arrow 2). An ion implantation layer 3 is formed as shown.
[0019]
Here, when the dose of impurities added to the main surface of the substrate 1 by ion implantation is large, the crystal structure of the ion-implanted layer 3 is broken, and the ion-implanted layer 3 becomes amorphous. On the other hand, when the dose is small, the ion-implanted layer 3 does not become amorphous but the crystal is damaged.
[0020]
Next, as shown in FIG. 1B, the ion implantation layer 3 is irradiated with high-luminance X-rays (indicated by arrows 4). Synchrotron radiation (SOR) can be suitably used for the X-rays 4.
[0021]
Here, the crystallinity of the ion-implanted layer 3 is recovered in a short time at a low temperature by irradiating the ion-implanted layer 3 with the X-rays 4. Hereinafter, the operation and effect of the present invention will be described in comparison with the operation and effect of conventional electric furnace annealing and flash annealing.
[0022]
When the dose of impurities into the ion-implanted layer 3 is large to some extent, the implanted layer 3, which is the surface layer on the main surface of the substrate 1, is generally destroyed by the ion implantation and becomes amorphous. Therefore, the crystallinity of the surface layer can be recovered by solid-phase epitaxial growth using a deep portion below the injection layer 3 that does not become amorphous as a seed. That is, solid phase growth from an amorphous phase is governed by atomic diffusion in the amorphous phase, but atomic diffusion in an amorphous semiconductor occurs through vacancies.
[0023]
By the way, in solid phase growth by a conventional thermal method such as an electric furnace or flash annealing, conditions such as an annealing time are determined by an atomic diffusion coefficient based on a hole having a thermal equilibrium concentration at an annealing temperature. On the other hand, when high-intensity X-rays are irradiated on the ion-implanted substrate, a large amount of holes having a thermal equilibrium concentration or more are formed in a short time, thereby promoting solid phase growth even at a low temperature.
[0024]
When the dose is small, the implanted layer 3 is not necessarily amorphized, but the recovery of the damaged crystal proceeds by atomic diffusion, so that the same effect as in the case of amorphization can be expected.
[0025]
Further, by irradiating the ion implantation layer 3 with the X-rays 4, impurities can be added at a high concentration. This high concentration addition will be described in comparison with the conventional method.
[0026]
In electric furnace annealing or flash annealing, during the solid phase growth of the ion-implanted layer, the implanted impurities are directly taken into the growth interface, and the impurity concentration in the depth direction after the growth is not different from that at the time of implantation. This is because the diffusion coefficient of impurities at these annealing temperatures is significantly smaller than the growth rate. If annealing is continued after the growth (these annealing methods usually have a longer annealing after the growth), redistribution occurs due to diffusion based on the concentration distribution in the grown crystal. Therefore, these conventional annealing methods cannot add impurities beyond the peak concentration of the injection profile as well as the thermal equilibrium solid solubility limit .
[0027]
On the other hand, in the method of the present invention, the diffusion of the impurity is enhanced by the irradiation of the X-ray 4, so that the impurity is segregated at the growth interface.
[0028]
2, when the melted from the crystal surface to a depth x _0, impurities having less than 1 segregation coefficient K ^* was solidified in one direction toward the surface uniformly added crystals at a concentration c ₀ 4 is a graph showing a calculated concentration distribution after solidification. In FIG. 2, V is the growth rate, and D is the diffusion coefficient of the impurity. As is clear from FIG. 2, the smaller the segregation coefficient K ^* , the greater the deposition on the surface. This is based on the fact that the diffusion coefficient of impurities in the melt is large. The effect of the melt growth shown in FIG. 2 also applies to solid-phase growth in which diffusion is enhanced by high-brightness X-ray irradiation. For example, in FIG. 2, the concentration c ₀ can be considered by replacing the concentration c ₀ with the impurity concentration in the implantation layer 3 achieved by ion implantation. That is, in the surface layer of the implanted layer 3 shown in FIG. 1 (b), it may be a concentration exceeding the implanted impurity concentration c _0.
[0029]
FIG. 3 is an elevational sectional view showing a multilayer SOI film to which the impurity doping method of the present invention can be suitably applied. In FIG. 3, reference numeral 5 denotes an insulating film made of SiO ₂ or the like, and 6 denotes a silicon crystal thin film. The insulating films 5 and the silicon crystal thin films 6 are alternately stacked. On the contact surface of each silicon crystal thin film 6 with the insulating film 5, an ion implantation part 7 is formed at a predetermined position.
[0030]
Next, such a laminated structure is irradiated with high-intensity X-rays (indicated by arrows 8). X-rays have material permeability to the insulating film 5 and the silicon crystal thin film 6. Therefore, by this X-ray irradiation, the respective ion implantation sections 7 can be processed collectively.
[0031]
In addition, the X-ray beam can be narrowed down or patterned by utilizing interference by a zone plate or a crystal, so that extremely fine and selective processing can be performed.
[0032]
In each of the above embodiments, when irradiating with high-brightness X-rays, thermal annealing can be performed on the ion-implanted layer 3 or the ion-implanted portion 7 during or after irradiation as necessary. When performing thermal annealing, X-ray irradiation is preferably performed. This is because when the amount of X-ray irradiation is small, thermal annealing is expected to contribute to enhancement of impurity diffusion. Examples of the annealing here include the above-described electric furnace annealing, laser annealing, flash annealing, and the like.
[0033]
Hereinafter, the present invention will be described in more detail with reference to specific examples.
[0034]
As shown in FIG. 1A, impurity phosphorus (P) is ion-implanted into a silicon substrate surface layer at a liquid nitrogen temperature at a high concentration of about 3.7 × 10 ²⁰ / cm ³ to obtain a surface layer. Was made amorphous. Next, as shown in FIG. 1B, this surface layer was irradiated with high-intensity X-rays to be recrystallized. As the X-rays, high-brightness X-rays by wiggler from synchrotron radiation were used (Radiation Experiment Facility, Institute for High Energy Physics). Irradiation conditions were a radiation photoelectron storage ring current of about 300 mA, an irradiation time of about 1 second, and a sample temperature during irradiation of about 800 ° C.
[0035]
FIG. 4 is a graph showing the concentration distribution in the depth direction of phosphorus in the silicon substrate surface layer after phosphorus ion implantation and recrystallization by high-brightness X-ray irradiation , measured by SIMS (secondary ion analysis). In FIG. 4, a broken line indicates a phosphorus concentration distribution in the surface depth direction immediately after phosphorus (P) ions are implanted into the silicon surface layer, and a solid line indicates phosphorus in the surface layer depth direction immediately after high-intensity X-ray irradiation after ion implantation. 3 shows a concentration distribution.
[0036]
In FIG. 4, the concentration after high-intensity X-ray irradiation and recrystallization is higher than the concentration after implantation in a shallow region immediately below the surface, and vice versa in the deeper region. This indicates that P segregates from the deep portion during the growth process by high-brightness X-ray irradiation, deposits occur on the surface, and the concentration distribution as shown in FIG. 2 has been realized. Further, the concentration of the shallow region after the high-brightness X-ray irradiation and recrystallization exceeds the thermal equilibrium solid solubility limit of about 1000 ° C.
[0037]
【The invention's effect】
As described above, according to the impurity doping method of the present invention, spatial local processing can be performed by irradiating a high-brightness X-ray beam, and deep or SOI In addition to the advantage of being able to perform batch processing with multi-layered films, it is possible to recover the crystal surface layer of a semiconductor wafer destroyed by ion implantation of impurities at a lower temperature and in a shorter time than conventional heat treatment methods. In addition, implantation impurities can be added beyond the peak concentration of the implantation profile, and even beyond the thermal equilibrium solid solubility limit .
[Brief description of the drawings]
FIG. 1 is an elevational sectional view showing each step of an impurity doping method of the present invention.
FIG. 2 shows a crystal melted from a crystal surface to a depth x ₀ and uniformly doped with an impurity having a segregation coefficient K ^* smaller than 1 at a concentration c ₀ in one direction toward the surface. 7 is a graph showing a calculated concentration distribution after solidification in a case.
FIG. 3 is an elevational sectional view showing a multilayer SOI film to which the impurity doping method of the present invention can be suitably applied.
FIG. 4 is a graph showing the concentration distribution in the depth direction of phosphorus in a silicon substrate surface layer after phosphorus ion implantation and X-ray recrystallization, measured by SIMS.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 semiconductor substrate wafer 2 impurity ion implantation 3 ion implantation layer 4 high-brightness X-ray irradiation 5 insulating film 6 semiconductor crystal thin film 7 ion implantation section 8 X-ray irradiation

Claims (3)

An impurity doping method in which an electrically active impurity is added to a semiconductor wafer to form an n-type or p-type substrate,
Implanting impurities into the semiconductor wafer by ion implantation, and irradiating the crystal surface layer destroyed by the ion implantation of the semiconductor wafer with high-intensity X-rays by wiggler from synchrotron radiation to destroy the semiconductor wafer. Recovering the crystallinity without melting the crystal surface layer, and simultaneously segregating the impurity implanted in the crystal surface layer beyond the peak concentration of the injection profile ,
An impurity doping method comprising: 2. The impurity doping method according to claim 1, wherein, when irradiating the high-brightness X-ray, thermal annealing is performed on the crystal surface layer of the semiconductor wafer in an auxiliary manner. 3. The method according to claim 1, wherein the concentration of the impurities segregated in the crystal surface layer exceeds a thermal equilibrium solid solubility limit.

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