JP3669384B2 - Method for forming a doping layer in a semiconductor substrate - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for forming a doping layer in a semiconductor substrate, and more particularly, to a method for forming a doping layer in a semiconductor substrate suitable for use in forming a relatively deep doping layer in a semiconductor substrate. .
[0002]
[Prior art]
In general, in a CMOS LSI or a sensitivity variable light receiving element which is a semiconductor device, it is necessary to form a well structure with a doping layer in order to electrically isolate the elements.
[0003]
Here, the well structure means a p-type region formed as a doping layer in an n-type semiconductor substrate and having a size of several tens of μm square, a depth of several μm, and a carrier concentration of about 10 ¹⁷ cm ⁻³ (this p-type region). Is referred to as a “p-well”) or an n-type region formed as a doping layer in a p-type semiconductor substrate and having a size of several tens of μm square, a depth of several μm, and a carrier concentration of about 10 ¹⁷ cm ⁻³ ( This n-type region is referred to as “n-well”). These p-well and n-well are selectively used according to the type of semiconductor device to be configured.
[0004]
Conventionally, as a method for forming a doping layer for forming a well structure as described above in a semiconductor substrate, the semiconductor substrate is placed in an impurity (donor) gas and heat treatment is performed to form the well structure by vapor phase doping. Alternatively, a thermal diffusion method in which impurities are applied to a semiconductor substrate and heat treatment is performed to form a well structure by solid-phase doping, or heat treatment such as electric furnace annealing is performed after the impurities are implanted into the semiconductor substrate by ion implantation. A method of forming a well structure has been performed.
[0005]
[Problems to be solved by the invention]
However, in any of the conventional methods for forming a doping layer in a semiconductor substrate described above, in order to limit the region of the well structure to several tens of μm square, a photolithography process is performed to form SiO 2. _It was necessary to mask the area other than the well structure on the semiconductor substrate by ₂ or the like.
[0006]
That is, the conventional method for forming a doping layer in a semiconductor substrate requires a step of masking a region other than the well structure region on the semiconductor substrate, which has a problem that the work process becomes complicated. .
[0007]
Further, in a conventional method for forming a doping layer in a semiconductor substrate, in order to obtain a deep doping layer having a depth of about several μm as a well structure, the semiconductor substrate is kept at a high temperature for a long time (for example, 16 hours to 17 hours). In addition to the problem that the heat treatment is required and the operation time is long, the semiconductor substrate is heat-treated at a high temperature for a long time, so that the semiconductor substrate is laterally diffused.
[0008]
The present invention has been made in view of such various problems of the prior art, and the object of the present invention is to form a semiconductor structure when a well structure is formed as a doping layer in a semiconductor substrate. A semiconductor substrate that eliminates the need to mask a predetermined area on the substrate, simplifies the work process, significantly shortens the work time, and does not cause lateral diffusion of the semiconductor substrate. An object of the present invention is to provide a method for forming a doping layer therein.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, a method for forming a doping layer in a semiconductor substrate according to the present invention includes: irradiating a semiconductor substrate with laser light in a pulsed manner; The semiconductor substrate was rapidly melted by utilizing the rapid melting phenomenon based on the temperature rise of the surface and the recrystallization phenomenon due to the temperature drop of the semiconductor substrate surface when the irradiation of the laser beam on the surface of the semiconductor substrate was stopped. Impurities are mixed into the semiconductor when the semiconductor substrate is recrystallized so that the impurities mixed into the semiconductor are confined in the semiconductor so that a deep doping layer (for example, a depth of several μm) is formed with respect to the semiconductor substrate. It is formed at high speed.
[0010]
At this time, in order to prevent the occurrence of surface irregularities in the laser beam irradiation area on the semiconductor substrate surface, immediately after irradiating the semiconductor substrate with a laser beam having a high irradiation intensity, a laser having a lower irradiation intensity with a predetermined delay time. In order to prevent the rapid cooling phenomenon and to prevent the rapid temperature rise of the semiconductor substrate by irradiating light, one set of irradiation with such laser light with high irradiation intensity and laser light with low irradiation intensity. The above-mentioned one set is repeated a predetermined number of times according to the required depth of the doping layer while lowering the temperature of the semiconductor substrate.
[0011]
Here, when examining the effect on the semiconductor substrate by irradiating a set of laser beams of a laser beam having a high irradiation intensity and a laser beam having a low irradiation intensity, the surface of the semiconductor substrate is rapidly melted by the laser beam having a high irradiation intensity. Therefore, the surface roughness of the laser beam irradiation region on the surface of the semiconductor substrate caused by this rapid melting is melted without generating new surface roughness by irradiation of the laser beam with low irradiation intensity, and the surface of the semiconductor substrate surface is flattened. Can be achieved.
[0012]
In addition, the thermal strain generated in the process of rapid cooling / resolidification after irradiation with a laser beam having a high irradiation intensity is alleviated by irradiation with a laser beam having a low irradiation intensity, thereby improving crystallinity.
[0013]
When the semiconductor substrate is irradiated with laser light, the semiconductor substrate is heated to form a deep doping layer at a high speed.
[0014]
Further, it is desirable that the temperature of the semiconductor substrate be kept below the boiling point of the semiconductor even when the semiconductor substrate is irradiated with laser light.
[0015]
Furthermore, various lasers can be used as the laser for irradiating the semiconductor substrate. In general, when laser light having a short wavelength and a short pulse width is used, doping obtained by the one set of irradiation is performed. When the laser beam having a long wavelength and a long pulse width is used, the depth of the doping layer obtained by the one set of irradiation tends to be deep.
[0016]
Further, when the irradiation intensity of laser light is increased, the depth of the obtained doping layer becomes deeper.
[0017]
Embodiment
Hereinafter, embodiments of a method for forming a doping layer in a semiconductor substrate according to the present invention will be described with reference to the accompanying drawings.
[0018]
FIG. 1 shows a schematic configuration diagram of an apparatus for carrying out one embodiment of a method for forming a doping layer in a semiconductor substrate according to the present invention.
[0019]
In FIG. 1, reference numeral 10 denotes a sample which is a semiconductor substrate on which a doping layer is to be formed. As the sample 10, as an n-type dopant (donor), As was previously ion-implanted into a Si substrate at a dose of 1 × 10 ¹⁵ cm ⁻² and an acceleration voltage of 150 keV.
[0020]
Such a sample 10 is supported in a chamber 12 by a carbon susceptor 14.
[0021]
The chamber 12 includes valves 14 and 16. Various gases can be sucked through the valve 14 and introduced into the chamber 12, and the gas in the chamber 12 can be introduced through the valve 16. The chamber 12 can be evacuated. The upper surface of the chamber 12 is opened, and a quartz glass plate 20 is placed in the opening via a seal 18.
[0022]
Further, in the chamber 12, a halogen lamp 22 is provided for irradiating light to the bottom surface of the carbon susceptor 14 that supports the sample 10 and heating the sample 10 via the carbon susceptor 14. .
[0023]
In the apparatus shown in FIG. 1, as a laser source of laser light irradiated to the sample 10 in the chamber 12 through the quartz glass plate 20, a KrF excimer laser whose delay time is controlled by a pulse generator 24 is controlled. (KrF Excimer
Laser) 26 and 28 are used.
[0024]
One KrF excimer laser 26 is controlled to emit a laser beam having a pulse width of 34 ns and an irradiation intensity of 2.4 J / cm ² , and the other KrF excimer laser 28 has a pulse width of 23 ns and an irradiation intensity of 0.5 J. It is controlled to irradiate with / cm ² of laser light.
[0025]
The laser beams emitted from the KrF excimer lasers 26 and 28 are reflected by the total reflection mirrors 34 and 36 through the cylindrical lenses 30 and 32, and are collected by the lenses 38 and 40. The sample 10 in the chamber 12 is irradiated through.
[0026]
A shutter 42 is provided on the optical path of the laser light emitted from the KrF excimer lasers 26 and 28, and the laser light emitted from the KrF excimer laser 26 and the laser emitted from the KrF excimer laser 28 are provided. The sample 10 can be selectively irradiated with light.
[0027]
Here, generally, the laser light emitted from the excimer laser is a laser beam having a short wavelength in the ultraviolet region and a short pulse, so the absorption coefficient to the substance is large and the heat action time is short. Application to the formation of a very shallow doping layer of 100 nm or less is expected. That is, since the doping layer required in the semiconductor device may be a very shallow doping layer of about 100 nm or less except for the well structure, the semiconductor device for forming a very shallow doping layer of about 100 nm or less excluding the well structure Excimer laser is expected to be used as a manufacturing technology.
[0028]
By the way, in order to form a deeper doping layer using an excimer laser in a semiconductor substrate, the laser beam irradiation intensity must be increased in order to increase the melting depth on the semiconductor substrate by laser beam irradiation. Don't be.
[0029]
However, when the irradiation intensity of the laser beam on the semiconductor substrate is increased, the surface temperature of the semiconductor substrate is excessively increased, and a large number of defects and surface roughness are generated. Therefore, a doping layer having a depth of about 500 nm at most. But it was only possible.
[0030]
Therefore, the applicant tried to smooth the temperature gradient of the surface temperature of the semiconductor substrate by heating the semiconductor substrate during laser light irradiation.
[0031]
For example, as shown in FIG. 2, when the surface temperature of the semiconductor substrate during laser light irradiation is room temperature (RT), the depth of the doping layer is at most about 350 nm. When the semiconductor substrate was heated during laser light irradiation, the doping layer depth could be increased.
[0032]
That is, as shown in FIG. 2, when the semiconductor substrate is heated to 500 ° C. during irradiation of the semiconductor substrate with a laser beam, a doping layer having a depth of about 650 nm can be formed. When the semiconductor substrate was heated to 700 ° C. during irradiation, a doping layer having a depth of 1 μm or more could be easily formed.
[0033]
As shown in FIG. 3A, the laser light irradiation conditions of the experiment that obtained the results shown in FIG. 2 were as follows: laser light irradiation intensity per pulse: 2.4 J / cm ² , number of pulses: 20 pulses, laser pulse The repetition frequency is 1 Hz. Accordingly, the processing time is 20 seconds, which is a very short time.
[0034]
Note that a method of irradiating laser light having the same pulse width and irradiation intensity in a predetermined cycle is referred to as “single pulse irradiation method” in this specification.
[0035]
Also, as the sample, as in the sample 10 shown in FIG. 1, As was used as an n-type dopant (donor) in which As was previously ion-implanted into the Si substrate at a dose of 1 × 10 ¹⁵ cm ⁻² and an acceleration voltage of 150 keV.
[0036]
Of course, a gas or a solid source can be used as a dopant source. When a gas is used as a dopant source, laser light is irradiated in a gas atmosphere, and a solid is used as a dopant source. In such a case, the laser beam may be irradiated onto a semiconductor substrate deposited or coated with a solid dopant source.
[0037]
As described above, by heating the semiconductor substrate during laser light irradiation, a deeper doping layer can be easily formed than when laser light is irradiated at room temperature, and crystallinity and surface state are greatly improved. Although the experimental result was obtained, some surface roughness still remains as can be seen from FIG. 4 showing the surface state when the semiconductor substrate is heated to obtain a deeper doping layer during laser light irradiation. It was.
[0038]
Further, the crystallinity of the case to obtain a deeper doping layer by heating the semiconductor substrate during laser irradiation also channeling Rutherford backscattering spectrometry (C-RBS) of Χ results about 6.55% as assessed by _min Yes, it was not enough for application to semiconductor devices.
[0039]
Therefore, the applicant has improved the single pulse irradiation method as described above, and using an apparatus as shown in FIG. 1, the semiconductor substrate is irradiated with a laser beam having a high irradiation intensity, and is weaker than that. Irradiate laser light of irradiation intensity, and set the irradiation of laser light with such high irradiation intensity and laser light with low irradiation intensity as a set, with a predetermined time interval to prevent the temperature rise of the semiconductor substrate. The present invention has developed a method for forming a doping layer in a semiconductor substrate according to the present invention, in which the above one set is repeated a predetermined number of times in accordance with the required depth of the doping layer while the temperature of the semiconductor substrate is lowered.
[0040]
In the following, this method for forming a doping layer in a semiconductor substrate according to the present invention is referred to as a “double pulse irradiation method” in this specification, and a laser beam having a high irradiation intensity is referred to as a “first pulse”. The laser beam having a low irradiation intensity is referred to as “second pulse”.
[0041]
That is, in order to perform the double pulse irradiation method using the apparatus of FIG. 1, specifically, a laser beam (first pulse) having a pulse width of 34 ns and an irradiation intensity of 2.4 J / cm ² emitted from the KrF excimer laser 26. Is applied to the sample 10 and a signal is given by the pulse generator 24. After a delay time of 30 ns to 640 ns, a laser beam having a pulse width of 23 ns and an irradiation intensity of 0.5 J / cm ² emitted from the KrF excimer laser 28 is irradiated. Is applied to the sample 10. This process is set as one set and repeated 20 times (20 sets) at a repetition period of 1 Hz (see FIG. 3B).
[0042]
As a result of these experiments, the surface state of the sample 10 was greatly improved as shown in FIG. Note that the surface state of the semiconductor substrate is not affected by the delay time from the irradiation of the first pulse to the irradiation of the second pulse in the one set, and is almost equal in any delay time of 30 ns to 640 ns. A similar shape was obtained.
[0043]
In addition, regarding the depth of the doping layer, in this double pulse irradiation method, a laser beam having a pulse width of 34 ns and an irradiation intensity of 2.4 J / cm ² is substantially the same as in the single pulse irradiation method described above. Since 20 pulses are irradiated at a repetition period of 1 Hz to 10, a depth of 1 μm or more can be achieved according to the temperature of the sample 10 heated by the halogen lamp 22 as shown in FIG.
[0044]
Further, in FIG. 6, the delay time dependency of the chi _min which is an index of crystallinity is shown. In this way, the continuous irradiation of the first pulse and the second pulse with a delay time of 30 ns to 640 ns improves the 、 _min . In particular, a large improvement is obtained at the delay time of 150 ns, and 4.60% The almost satisfactory value was obtained.
[0045]
As described above, by the double pulse irradiation method, a deep doping layer having a surface morphology and crystallinity of 1 μm or more can be formed at high speed in a short time.
[0046]
As a laser for irradiating a semiconductor substrate, various lasers can be used in addition to a KrF excimer laser, but in any case, laser light is used, so that light condensing is excellent and only the irradiated region is used as a doping layer. Since it can be formed, the doping layer can be formed in a desired pattern without masking the surface of the semiconductor substrate by a photolithography process.
[0047]
In addition, when a short wavelength and short pulse width laser such as an excimer laser is used, it is easy to form a shallow doping layer on a semiconductor substrate. When an excimer laser is used, a deep doping layer and a shallow doping layer can be formed in the same substrate by an integrated process, and a semiconductor device such as a CMOS LSI or a variable sensitivity light receiving element can be manufactured.
[0048]
In the double-pulse irradiation method, the irradiation intensity of the first pulse is increased and the irradiation intensity of the second pulse is decreased, but the irradiation intensity of the second pulse is about a fraction of the irradiation intensity of the first pulse. desirable.
[0049]
In addition, when the temperature of the semiconductor substrate exceeds the boiling point when the laser beam is irradiated, the surface of the substrate is removed. Therefore, the temperature of the semiconductor substrate may be prevented from exceeding the boiling point by irradiation with the first pulse and the second pulse. desirable.
[0050]
Further, the repetition cycle of one set is not limited to 1 Hz, but a time interval is set such that the temperature of the semiconductor substrate raised by irradiation of the first pulse and the second pulse in the set returns to the original temperature. It is desirable.
[0051]
Further, although the semiconductor substrate is heated also in the double pulse irradiation method, it is needless to say that heating is not necessary.
[0052]
Furthermore, in the double pulse irradiation method, it is of course possible to use a gas or a solid source as the dopant source. When a gas is used as the dopant source, the semiconductor substrate is subjected to double pulse irradiation in a gas atmosphere. When a solid is used as a dopant source, a double pulse irradiation method may be performed on a semiconductor substrate deposited or coated on a semiconductor substrate. An appropriate method can be used to introduce the impurities.
[0053]
Furthermore, in the apparatus shown in FIG. 1, lasers for generating the first pulse and the second pulse are provided, but the present invention is not limited to this. Of course, the pulse and the second pulse may be generated.
[0054]
【The invention's effect】
Since the present invention is configured as described above, it is not necessary to mask a predetermined region on the semiconductor substrate when a well structure is formed as a doping layer in the semiconductor substrate. In addition, the working time can be remarkably shortened, and further, there is an excellent effect that the lateral diffusion of the semiconductor substrate does not occur.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an apparatus for carrying out an embodiment of a method for forming a doping layer in a semiconductor substrate according to the present invention.
FIG. 2 is a graph showing the semiconductor substrate temperature dependence of the depth of a doping layer by a single pulse irradiation method.
FIGS. 3A and 3B are explanatory diagrams showing a repetition period of laser light irradiation, where FIG. 3A shows the case of a single pulse irradiation method, and FIG. 3B shows the case of a double pulse irradiation method.
FIG. 4 is an enlarged view showing the state of the surface of the semiconductor substrate when a single pulse irradiation method is performed.
FIG. 5 is an enlarged view showing the state of the surface of the semiconductor substrate when the double pulse irradiation method is performed.
6 is a graph showing the delay time dependency of the crystallinity of an indicator chi _min in the case of performing double pulse irradiation.
[Explanation of symbols]
10 Sample 12 Chamber 14, 16 Valve 18 Seal 20 Quartz glass plate 22 Halogen lamp 24 Pulse generator 26, 28 KrF excimer laser 30, 32 Cylindrical lens 34, 36 Total reflection mirror 38, 40 Lens 42 Shutter

Claims (3)

By irradiating the semiconductor substrate with laser light in a pulsed manner, a rapid melting phenomenon based on a temperature rise of the surface of the semiconductor substrate when the laser light is irradiated on the semiconductor substrate, and the laser light on the surface of the semiconductor substrate When the semiconductor substrate is rapidly melted, impurities are mixed into the semiconductor using the recrystallization phenomenon due to the temperature drop of the surface of the semiconductor substrate when irradiation of the semiconductor is stopped, and the semiconductor substrate is recrystallized. In the method for forming a doping layer in a semiconductor substrate, the impurity mixed when being formed is confined in the semiconductor, and a doping layer is formed on the semiconductor substrate.
Immediately after irradiating a semiconductor substrate with a laser beam having a high irradiation intensity, a laser beam having a lower irradiation intensity is irradiated with a predetermined delay time, and the laser beam having a higher irradiation intensity and the laser beam having a lower irradiation intensity are irradiated. The method of forming a doping layer in a semiconductor substrate is characterized in that the one set is repeated a predetermined number of times according to the required depth of the doping layer at a predetermined time interval with one irradiation as a set. In the formation method of the doping layer in the semiconductor substrate of Claim 1,
In the set of laser beams, the surface of the semiconductor substrate is rapidly melted by the laser beam having a high irradiation intensity, and the surface area of the laser beam irradiation region on the semiconductor substrate surface generated by the rapid melting is determined by the irradiation intensity. A method for forming a doping layer in a semiconductor substrate, wherein the surface of the semiconductor substrate is melted without generating new surface roughness by irradiation with a weak laser beam, and the surface of the semiconductor substrate is planarized and crystallinity is improved . In the formation method of the doping layer in the semiconductor substrate of any one of Claim 1 or 2,
A method for forming a doping layer in a semiconductor substrate, wherein the semiconductor substrate is heated to a predetermined temperature when the one set of laser beams is irradiated.

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