JP3579069B2 - Method for manufacturing semiconductor device - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a method for manufacturing a semiconductor device , and more particularly to an improvement in a method for manufacturing a semiconductor device related to removal of contaminants in a silicon substrate.
[0002]
[Prior art]
Contaminants, such as heavy metals such as iron and copper, which enter during the manufacturing process of a semiconductor device form a minority carrier generation and annihilation center, increase a pn junction leak current, and shorten the life of an excess carrier. And the electrical characteristics of the semiconductor device are degraded as a result.
[0003]
For example, in a MOS memory device, when a heavy metal is present in a charge storage cell, the stored charge is reduced. When the stored charge becomes less than the critical charge, the state of the memory cell is inverted from 1 to 0, and Information is lost.
[0004]
As described above, heavy metal contamination causes deterioration of the electrical characteristics of the device. Particularly in the production of VLSI, even a small amount of contamination deteriorates and fluctuates the device characteristics, which is a major cause of lowering the production yield.
[0005]
Conventionally, two countermeasures have been taken against such contamination.
One is to minimize contamination of the wafer by cleaning the production environment. As the contamination source, for example, dust in a clean room, dust and contamination from various manufacturing apparatuses, or contamination from pure water, gas, chemicals, and the like can be considered. The technology for reducing these dusts and pollution is being developed as an ultra-clean technology.
[0006]
However, achieving complete cleaning of these production environments has many difficulties due to various factors such as time and cost.
The other is to remove contaminants such as heavy metals from the active region of the device, that is, gettering.
[0007]
Gettering is roughly classified into intrinsic gettering (IG) and extrinsic gettering (EG).
In the IG, after a precipitation nucleus of oxygen is formed by low-temperature heat treatment at about 650 to 750 ° C., oxygen is precipitated by high-temperature heat treatment at about 1000 to 1100 ° C., and contaminants such as heavy metals are incorporated into the oxygen. Further, in order to prevent the generation of precipitates in the element active region near the substrate surface, a high-temperature heat treatment at about 1200 ° C. is often performed before the low-temperature heat treatment. Usually, the low-temperature heat treatment is performed in a wafer manufacturing process, while the high-temperature heat treatment is performed in an VLSI manufacturing process.
[0008]
However, in the case of IG, in order to create an optimal oxygen precipitation state, it is necessary to manage the thermal history of the wafer in all thermal processes from low to high temperatures, and high technology is required in view of the balance with the dislocation strength of the wafer.
[0009]
The IG effect can be expected in the CZ crystal, but the effect cannot be expected in the FZ crystal having a low oxygen concentration.
Recently, it has been reported that IG merely captures supersaturated metal impurities in a silicon substrate at each heat treatment temperature, and has no gettering effect on impurities below the solid solubility limit. For this reason, in the IG, there is a problem that impurities once captured at a low temperature are re-emitted by the next high-temperature heat treatment. Further, in general, the solid solubility limit of each metal impurity increases as the temperature increases, and the amount of supersaturated metal impurities decreases, so that the IG can hardly expect a gettering effect in a high temperature state.
[0010]
On the other hand, the EG includes ring gettering, wafer backside damage gettering, gettering due to misfit transition generated at the p / p ⁺ vapor phase epitaxial interface, and wafer backside polysilicon gettering.
[0011]
In the phosphorus gettering, phosphorus is diffused from the back surface of the wafer in the final step of the process, and the metal impurities are removed from the element active region by segregating the metal impurities into the phosphorus diffusion layer. However, in order to perform phosphorus gettering, it is necessary to use POCl ₃ or the like as a phosphorus source gas and to form a phosphorus diffusion layer having a high concentration of 10 ²¹ atoms / cm ³ or more. It is necessary to expose to an oxidizing atmosphere at a moderate temperature. Further, a heat treatment at a high temperature for a long time is required to form a sufficient phosphorus diffusion layer.
[0012]
In the backside damage gettering of the wafer, mechanical strain is intentionally formed on the backside of the wafer, and the mechanical strain is used as a nucleus to generate oxidation-induced stacking faults (OSF) in the first oxidation step, and to remove metal impurities there. Let it be trapped. The mechanical strain can be formed, for example, by spraying SiO ₂ fine powder on the back surface of the wafer. However, even in this gettering, a high-temperature heat treatment is required, and the trapping capacity of metal impurities has a correlation with the OSF density, and the capacity is limited and the capacity is small.
[0013]
In gettering by misfit transition of the p / p ⁺ epitaxial film, a silicon film is vapor-phase epitaxially grown at a high temperature on a substrate to which a high concentration of impurities such as boron is added, and misfit transition occurs at an interface. , Gettering metal impurities there. Since this is also gettering by transition similarly to the above gettering, its capacity is limited and its capacity is relatively small.
[0014]
In the backside polysilicon gettering of the wafer, a polysilicon film is deposited on the backside of the wafer, and metal impurities in the wafer are precipitated at grain boundaries in the polysilicon film or at the interface with the silicon substrate. Then, there is a problem that the gettering effect is small.
[0015]
In these EGs, since the gettering sites are mainly located on the back surface of the wafer, in addition to the above-mentioned problems, these gettering techniques have the following problems.
As the miniaturization progresses in the semiconductor industry in the future, the diameter of the wafer will inevitably increase due to the relationship between cost and yield, and as a result, the thickness of the wafer will increase due to the warpage and strength of the wafer. In addition, a shallow impurity diffusion layer is required for high integration. As a result, the heat treatment temperature is reduced, and the heat treatment time is shortened. Therefore, it is very difficult to diffuse metal impurities near the wafer surface to gettering sites on the back surface and to sufficiently remove contaminants from the element formation layer.
[0016]
Due to such a problem, it is necessary to form a gettering site on the surface of the wafer, and as a result, another raw wafer is stuck on a wafer having a gettering effect such as EG, and the raw wafer is polished from the surface and thinned. To form an EG layer of another wafer in the vicinity of the surface by implanting high-energy ions into the wafer surface to form a gettering site several microns deep from the element formation layer; A technique for gettering impurities into a misfit transition layer formed at the interface of / p ⁺ vapor phase epitaxial growth has been developed.
[0017]
However, gettering using a bonded wafer requires two wafers, and thus has a problem of high cost.
Also, gettering by high-energy ion implantation involves high-energy ion implantation, which causes a problem in that deep sites are contaminated by metal impurities in the chamber. Further, crystal defects may be generated in shallow element formation regions.
[0018]
In addition, gettering due to misfit transition has a problem that the capacity is relatively small because the misfit transition layer serves as a gettering site as described above.
[0019]
[Problems to be solved by the invention]
As described above, various types of gettering have been conventionally proposed, and a certain effect has been recognized, and it is regarded as promising. However, the drawback is also remarkable, and there is no one that is regarded as important for future miniaturization. .
[0020]
The present invention has been made in consideration of the above circumstances, and its purpose is to sufficiently remove contaminants in a silicon substrate even in a high-temperature, short-time or low-temperature heat treatment required for future miniaturization of elements. And a method of manufacturing the same.
[0021]
[Means for Solving the Problems]
In order to achieve the above object, in a method for manufacturing a semiconductor device according to the present invention, at least a part of a silicon substrate contains at least one of boron and phosphorus having a concentration distribution of 10 ²⁰ atoms / cm ³ or more. A step of forming an amorphous silicon film, a step of changing the amorphous silicon film into a single crystal silicon film by solid phase growth to form a gettering site, and a step performed following the step of forming the gettering site. And introducing a contaminant in the silicon substrate into the single crystal silicon film by heat treatment .
[0023]
[Action]
According to the study of the present invention and the like, a peak concentration of 10 ²⁰ atoms / cm ³ is obtained as a gettering site on the surface of a silicon substrate. It was found that when a single crystal silicon film containing boron or phosphorus having the above concentration distribution and having no element formed thereon was used, a good gettering effect was obtained irrespective of the heat treatment temperature (about 600 to 1200 ° C.). . Further, since the single-crystal silicon film can be formed on the surface of the silicon substrate, the removal of contaminants is smaller than when a gettering site is formed deep from the surface of the silicon substrate (for example, the back surface of the silicon substrate). Heat treatment time can be shortened. Therefore, according to the method for manufacturing a semiconductor device of the present invention based on the above findings, it is possible to sufficiently remove contaminants in the silicon substrate even by a high-temperature, short-time or low-temperature heat treatment.
[0024]
【Example】
Hereinafter, embodiments will be described with reference to the drawings.
FIG. 1 is a process sectional view for explaining a gettering method according to a first embodiment of the present invention.
[0025]
First, as shown in FIG. 1A, for example, a film thickness of 300 nm is formed on a (100) plane of an n-type silicon substrate 1 by an LPCVD method using a Si ₂ H ₆ gas or a B ₂ H ₆ gas. The amorphous silicon film 2 having a boron concentration of about 10 ²⁰ atoms / cm ³ or more is deposited.
[0026]
Next, as shown in FIG. 1B, the amorphous silicon film 2 is changed to a single crystal silicon film 3 as a gettering site by solid phase epitaxial growth by a low-temperature heat treatment at about 600 ° C.
[0027]
Here, the single crystal silicon film 3 is used alone as a gettering site, and is electrically connected to an external electrode like a single crystal silicon film used for a buried epitaxial layer of a bipolar transistor. Therefore, an element having any structure can be formed on the single crystal silicon film 3.
[0028]
Thereafter, a heat treatment at about 1000 ° C. is performed for 30 minutes to segregate contaminants such as heavy metals in the silicon substrate 1 into the single crystal silicon film 3 to remove contaminants in a region serving as an element active region.
[0029]
FIG. 3 is a concentration profile of the impurity (Fe) showing the gettering effect.
This is because, after forming a single crystal silicon film as a gettering site with a boron concentration of 10 ²⁰ atoms / cm ³ and a film thickness of about 300 nm on the front side of the silicon substrate, Fe is forcibly contaminated on the back side of the silicon substrate ( This was obtained by performing SIMS analysis from the surface side where a single crystal silicon film was formed on a heat-treated one at 1000 ° C. for 30 minutes, which was heat-treated at 1000 ° C. for 30 minutes.
[0030]
FIG. 3 shows that Fe is uniformly captured in the single crystal silicon film which is a gettering site.
That is, it can be seen that Fe contaminated on the back side of the silicon substrate diffuses in the silicon substrate by the heat treatment and is captured by the single crystal silicon film.
[0031]
Further, since Fe is not gettered in the boron layer diffused in the silicon substrate, the boron-doped single crystal is formed by solid phase epitaxial growth rather than the high concentration boron diffusion layer in the silicon substrate. It can be seen that the silicon film has a higher gettering effect.
[0032]
For comparison, the gettering effect of a boron-doped polysilicon film formed on a silicon substrate was examined by the same method (SIMS analysis) as described above.
[0033]
As a result, it was found that Fe was uniformly gettered in the boron-added polysilicon film as well as in the boron-added single crystal silicon film.
In other words, the gettering site of polysilicon gettering is generally considered to be a crystal grain boundary of polysilicon or an interface between the polysilicon film and the silicon substrate. The field is not necessarily required as a gettering site, and point defects in polysilicon grains or solid-phase epitaxial growth layers or point defects generated by adding high-concentration impurities work as gettering sites. It is considered.
[0034]
In this embodiment, since the gettering site is not a polysilicon film but a single crystal silicon film, a semiconductor thin film can be easily formed thereon by epitaxial growth. Therefore, unlike the case of the polysilicon gettering described above, the buried gettering site can be easily formed without attaching another semiconductor substrate.
[0035]
FIG. 4 is a characteristic diagram showing the relationship between the recombination lifetime of minority carriers in a silicon substrate contaminated with Fe and the heat treatment temperature. For comparison, the backside polysilicon gettering (Comparative Example 1) and the two-step IG (Comparative Example 2) having the same thickness as the single-crystal silicon film of this example were also examined.
[0036]
From FIG. 4, the gettered silicon substrate of the present example has a shorter recombination lifetime than the gettered silicon substrates of Comparative Examples 1 and 2 in all temperature ranges (about 600 to 1200 ° C.). It can be seen that can be lengthened.
[0037]
That is, in the gettering of the present embodiment, the gettering effect increases as the temperature decreases, but even if the heat treatment temperature is high, a gettering effect sufficiently higher than that of the conventional gettering can be obtained.
[0038]
FIG. 5 is a diagram showing a relationship between a junction leakage current and a heat treatment time in a pn junction formed on the surface of the silicon substrate 1 when the single crystal silicon film 3 to which phosphorus is added is used. For comparison, a case of a wafer with backside polysilicon, which is one of the conventional backside EGs, was also examined.
[0039]
From FIG. 5, it can be seen that the gettering (front side gettering) of this embodiment has a smaller leak current even at a low temperature for a short time and a higher gettering effect than the gettering (backside gettering) of the conventional example.
[0040]
Further, since the gettering site is formed on the front surface side of the element formation region, it takes less time than when it is formed on the back surface side. Therefore, even if the thickness of the wafer increases with the expected diameter of the wafer in the future, it is not necessary to perform a high-temperature heat treatment for a long time, and the diffusion of the diffusion layer formed on the silicon substrate can be prevented.
[0041]
Therefore, according to the gettering of the present embodiment, contaminants in the silicon substrate can be sufficiently removed even by a high-temperature, short-time or low-temperature heat treatment required for miniaturization of elements in the future.
[0042]
Also, if a semiconductor integrated circuit is manufactured using the silicon substrate of the present embodiment in which a gettering site is provided on the substrate surface in the element formation region, an effective gettering process can be performed from the first stage of the manufacturing process. Can be performed.
[0043]
Here, the gettering of this embodiment is as follows when compared with various getterings of the related art.
First, the gettering of this embodiment is completely different from the method of gettering a metal impurity to a misfit transition formed on the p / p ⁺ substrate side by high-temperature vapor phase epitaxial growth.
[0044]
That is, in the gettering of this embodiment, the single crystal silicon film grown by solid phase epitaxial growth to which a high concentration of impurities (boron, phosphorus, etc.) is added acts as a gettering site. Ring site is different.
[0045]
In the gettering due to the misfit transition, only the supersaturated impurities can be gettered in the silicon substrate as in the case of the IG. However, the gettering in the present embodiment, as shown in FIG. Metal contaminants such as Fe dissolved therein can be effectively gettered.
[0046]
In comparison with gettering by high-energy ion implantation, which is front side gettering, since defects by ion implantation function as gettering sites in gettering by high-energy ion implantation, once high-temperature heat treatment is performed. Some of the defects are recovered, and the gettering effect is reduced.
[0047]
On the other hand, in the gettering of this embodiment, the gettering site is formed by deposition of an amorphous silicon film by LPCVD or the like and heat treatment for solid-phase growth, so that the gettering site is far more than the gettering site formed by high-energy ion implantation. A gettering site having a large capacity can be formed without damaging the silicon substrate such as a defect. In addition, the gettering effect does not decrease effectively no matter how many times the heat treatment is performed.
[0048]
Compared with phosphorus gettering, the phosphorus concentration is determined by the heat treatment temperature and diffusion time of phosphorus diffusion, and a high-temperature heat treatment of at least 850 ° C. or more must be performed for several hours to form a high-concentration phosphorus impurity layer. According to this embodiment, an impurity layer (single-crystal silicon film 3) containing phosphorus or boron at a low temperature of about 600 ° C. and a high concentration of 10 ²⁰ atoms / cm ³ or more is formed by a deposition method such as LPCVD. It can be easily formed.
[0049]
Further, in the phosphorus gettering, it is difficult to widely form a high-concentration phosphorus impurity layer as a gettering site. However, according to the present embodiment, a single-crystal silicon film as a gettering site can be formed thick, so that Gettering site having a large value can be easily provided. That is, since a gettering site having a large capacity can be easily formed as compared with the conventional gettering, the gettering effect is also excellent in the sustainability.
[0050]
FIG. 2 is a sectional view showing the structure of the gettering site according to the second embodiment of the present invention.
This embodiment is different from the previous embodiment in that the single crystal silicon film 3 as a gettering site is formed on a part of the surface of the silicon substrate 1. Such a structure can be formed as follows. For example, after partially etching the surface of the silicon substrate 1 to form a groove or a hole, the single crystal silicon film 3 is formed on the entire surface in the same manner as in the first embodiment. Thereafter, the film is flattened by a film having the same etching rate as the single crystal silicon film 3, and finally completed by etching back.
[0051]
FIG. 6 is a sectional view showing the structure of the gettering site according to the third embodiment of the present invention.
A single-crystal silicon film 3 to which an impurity (boron or phosphorus) is added is formed on the entire surface of the silicon substrate 1 by solid phase epitaxial growth, and a silicon thin film 4 is formed on the single-crystal silicon film 3. The silicon thin film 4 is formed by, for example, vapor phase epitaxial growth or solid phase epitaxial growth.
[0052]
When a gettering site having a buried structure is formed as in this embodiment, removal of contaminants by gettering such as heavy metals mixed into the silicon thin film 4 serving as an element formation layer is performed by heat treatment during the element formation step. .
[0053]
FIG. 9 is a distribution diagram in the depth direction of Fe which is a contaminant by SIMS analysis showing the effect of the gettering.
From FIG. 9, it can be seen that Fe is uniformly captured in the single crystal silicon film which is a gettering site.
[0054]
Note that the impurity added to the single crystal silicon film may be either boron or phosphorus alone or both boron and phosphorus. Further, the concentration of boron or phosphorus to be added is set to 10 ²⁰ atoms / cm ³ or more, preferably 10 ²¹ atoms / cm ³ or more.
[0055]
In the case of the present embodiment, the concentration of the dopant added to the inside of the silicon thin film 4 may be lower than the concentration of the impurity (boron or phosphorus) added to the single crystal silicon film 3.
[0056]
Alternatively, another silicon substrate may be attached instead of the silicon thin film using a commonly used wafer attachment technique. That is, the semiconductor film, the semiconductor substrate, and the like formed over the single crystal silicon film can be formed by any method.
[0057]
FIG. 7 is a sectional view showing the structure of the gettering site according to the fourth embodiment of the present invention.
This embodiment is different from the third embodiment in that the single crystal silicon film 3 serving as a gettering site is partially formed on the surface of the silicon substrate 1. In such a structure, for example, after partially etching the surface of the silicon substrate 1 to form a groove or a hole, a single-crystal silicon film 3 is formed on the entire surface in the same manner as in the second embodiment. After flattening the silicon film 3 with a film having the same etching rate as that of the silicon film 3, the single crystal silicon film 3 is buried by etch-back, and then the silicon thin film 4 is deposited on the entire surface.
[0058]
A similar structure can be obtained by forming a single crystal silicon film 3 on the entire surface of the silicon substrate 1, partially removing the single crystal silicon film 3 by etching, and then depositing a silicon thin film 4 on the entire surface.
[0059]
Furthermore, it can be obtained by changing an amorphous silicon layer to which a high concentration impurity is partially added into a single crystal silicon film by epitaxial growth.
FIG. 8 is a sectional view showing the structure of the gettering site according to the fifth embodiment of the present invention.
[0060]
This embodiment is different from the third embodiment in that a single-crystal silicon film 3a as a gettering site is also formed on the back surface of the silicon substrate 1.
In this embodiment as well, the same effects as those of the previous embodiment can be obtained, and the diffusion of contaminants such as heavy metals mixed from the back surface of the silicon substrate 1 into the element formation region can be prevented.
[0061]
FIG. 10 is a sectional view showing the structure of the gettering site according to the sixth embodiment of the present invention.
A plurality of single-crystal silicon films 3 containing at least one of boron and phosphorus are formed on the surface of the silicon substrate 1 by solid phase epitaxial growth.
[0062]
Such a structure is formed by, for example, partially forming a plurality of single-crystal silicon films 3 by solid phase epitaxial growth, or forming the single-crystal silicon film 3 over the entire surface, and then separating the single-crystal silicon film 3 by etching. Or can be realized.
[0063]
FIG. 11 is a process chart showing a method for forming a gettering site according to the seventh embodiment of the present invention.
First, as shown in FIG. 11A, a plurality of grooves are formed on the surface of the silicon substrate 1. Next, after an amorphous silicon film (not shown) to which at least one of boron and phosphorus is added is formed on the entire surface, an etch back is performed to leave the amorphous silicon film only in the groove.
[0064]
Next, as shown in FIG. 11B, the amorphous silicon film is changed to a single crystal silicon film 3 by solid phase epitaxial growth.
According to such a method, a gettering site having a structure in which a plurality of single-crystal silicon films 3 are embedded in the surface is obtained.
[0065]
Note that the present invention is not limited to the above-described embodiment. For example, in the first embodiment, the single-crystal silicon film 3 serving as a gettering site is formed on the surface of the silicon substrate 1 which is to be an element formation region, but is formed on the entire back surface of the silicon substrate 1 as shown in FIG. Or may be formed partially on the back surface.
[0066]
Further, in the above embodiment, the effect when the contaminant is Fe has been described, but the present invention is also effective for other contaminants, for example, metal impurities such as Cu, Ni, and Cr.
In addition, various modifications can be made without departing from the scope of the present invention.
[0067]
【The invention's effect】
As described above in detail, according to the present invention, contaminants in a silicon substrate can be sufficiently removed even by a high-temperature, short-time or low-temperature heat treatment required for miniaturization of an element in the future.
[Brief description of the drawings]
FIG. 1 is a process sectional view for explaining a gettering method according to a first embodiment of the present invention.
FIG. 2 is a sectional view showing the structure of a gettering site according to a second embodiment of the present invention.
FIG. 3 is a profile of an impurity concentration showing a gettering effect of the present invention.
FIG. 4 is a characteristic diagram relating to a heat treatment temperature and a recombination lifetime showing a gettering effect of the present invention.
FIG. 5 is a characteristic diagram relating to a heat treatment time and a leak current showing a gettering effect of the present invention.
FIG. 6 is a sectional view showing the structure of a gettering site according to a third embodiment of the present invention.
FIG. 7 is a sectional view showing a structure of a gettering site according to a fourth embodiment of the present invention.
FIG. 8 is a sectional view showing the structure of a gettering site according to a fifth embodiment of the present invention.
FIG. 9 is an impurity concentration profile showing a gettering effect of the present invention. FIG. 10 is a cross-sectional view showing a structure of a gettering site according to a sixth embodiment of the present invention.
FIG. 11 is a process chart showing a method for forming a gettering site according to a seventh embodiment of the present invention.
FIG. 12 is a diagram showing a modification of the first embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Silicon substrate 2 ... Amorphous silicon film 3, 3a ... Single crystal silicon film 4 ... Silicon thin film

Claims (1)

Forming, on at least a portion of the silicon substrate, an amorphous silicon film containing at least one of boron and phosphorus having a peak concentration of 10 ²⁰ atoms / cm ³ or more;
Converting the amorphous silicon film into a single crystal silicon film by solid phase growth, and forming a gettering site;
Manufacturing the semiconductor device, comprising: a step performed after the step of forming the gettering site, wherein the step of introducing contaminants in the silicon substrate into the single crystal silicon film by heat treatment. Method.

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