JP4092961B2 - Manufacturing method of semiconductor substrate - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a method for manufacturing a semiconductor substrate for forming a semiconductor device such as a solid-state imaging device.
[0002]
[Prior art]
As a semiconductor substrate for forming a semiconductor device, a CZ substrate grown by the CZ method, an MCZ substrate grown by the MCZ method, an epitaxial substrate having an epitaxial layer formed on the surface of these CZ substrate or MCZ substrate, etc. Is conventionally used.
[0003]
On the other hand, the process for forming a semiconductor device is currently performed in an ultra clean room of class 100 or less, but contamination of the semiconductor substrate due to impurities from gas, water, semiconductor manufacturing equipment, etc. cannot be completely avoided. Moreover, the amount of impurities introduced into the semiconductor substrate in the process of forming the epitaxial layer on the surface of the semiconductor substrate is much larger than the amount of impurities introduced in the process of forming the semiconductor device.
[0004]
If impurities or crystal defects exist in the element active region of the semiconductor substrate, the quality and characteristics of the semiconductor device are significantly deteriorated. Further, if impurities or crystal defects are present in the semiconductor substrate, the semiconductor substrate is easily damaged by radiation such as α rays, and the quality and characteristics of the semiconductor device are further deteriorated by this damage.
[0005]
Therefore, intrinsic gettering (IG) and extrinsic gettering (EG) are conventionally performed to remove these impurities and crystal defects from the element active region. 2 and 3 show the characteristics of a semiconductor device formed on an epitaxial substrate or the like subjected to these treatments.
[0006]
In order to obtain the results shown in FIGS. 2 and 3, first, epitaxial layers were simultaneously formed on a CZ substrate not subjected to gettering, a CZ substrate subjected to EG, and a CZ substrate subjected to IG. The EG in this case was performed by forming a polycrystalline Si film having a thickness of 1.5 μm on the back surface of the CZ substrate by a CVD method at a temperature of 620 ° C. In addition, IG sequentially adds a heat treatment at 1100 ° C. for 1.5 hours, a heat treatment at 650 ° C. for 10 hours, and a heat treatment at 1050 ° C. for 2 hours, and precipitates oxygen to cause crystal defects in the CZ substrate. It was done.
[0007]
Then, a MOS capacitor having a gate insulating film made of a SiO ₂ film having a thickness of 20 nm and a gate electrode made of an Al film and a CCD image pickup device were formed on these epitaxial substrates. FIG. 2 shows the generated lifetime obtained by the Ct method using this MOS capacitor as a value normalized with the measured value on the CZ substrate as 1. FIG. 3 shows the number of white defect of the CCD image pickup device as a value normalized with the measured value on the MCZ substrate being 1. The white defect corresponds to a dark current caused by impurities or the like.
[0008]
[Problems to be solved by the invention]
However, as is apparent from FIGS. 2 and 3, even if EG or IG is performed on the epitaxial substrate, the generation life is not much different from that of the CZ substrate, and the number of white scratch defects is as high as that of the MCZ substrate. It cannot be reduced. On the other hand, even in the CZ substrate and the MCZ substrate, defects exist not only in the substrate but also in the gate insulating film formed on the surface of the substrate, and due to the increase in current leakage and interface state due to the breakdown voltage degradation of the gate insulating film, A transfer defect or the like has occurred in the CCD imaging device.
[0009]
[Means for Solving the Problems]
The method of manufacturing a semiconductor substrate according to claim 1 includes a step of forming an oxide film on a surface of the semiconductor substrate, and carbon in the semiconductor substrate in a state where the oxide film covers the surface of 5 × 10 ^{13 to} 5 × 10 5. a step of ion-implanted at a dose of ¹⁵ cm ^-2, a step of pre-Symbol annealing the semiconductor substrate table surface after the ion implantation in a state where the oxide film covers the epitaxial layer on the surface after the annealing Forming the step. For this reason, a semiconductor substrate capable of strongly gettering impurities and crystal defects with carbon can be manufactured.
[0010]
In addition , channeling of carbon to be ion-implanted and sputtering of the surface of the semiconductor substrate at the time of ion implantation are prevented, the gettering capability by carbon is strong, and the surface of the semiconductor substrate before the epitaxial layer formation is not sputtered A substrate can be manufactured.
[0011]
The method of manufacturing a semiconductor substrate according to claim 2 removes the oxide film after the annealing and before the formation of the epitaxial layer. For this reason, the oxide film does not hinder the formation of the epitaxial layer.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, first and second embodiments of the present invention will be described with reference to FIGS. FIG. 1 shows a first embodiment. In the first embodiment, as shown in FIG. 1A, a CZ substrate 11 which is a Si substrate grown by a CZ method is prepared. In this CZ substrate 11, the <100> plane is the mirror surface 12, the resistivity is 1 to 10 Ωcm, and the oxygen concentration is 1.5 × 10 ¹⁸ atoms cm ⁻³ . The CZ substrate 11 is first washed with an NH ₄ OH / H ₂ O ₂ aqueous solution and further washed with an HCl / H ₂ O ₂ aqueous solution.
[0013]
Next, dry oxidation is performed at a temperature of 1000 ° C. to form an SiO ₂ film 13 having a thickness of about 20 nm on the mirror surface 12 as shown in FIG. Then, carbon 14 is ion-implanted from the mirror surface 12 through the SiO ₂ film 13 into the CZ substrate 11 with an acceleration energy of 800 keV and a dose of 1 × 10 ¹⁴ cm ⁻² . At this time, the projected range distance of the carbon 14 is about 1.3 μm, and the peak concentration is about 1 × 10 ¹⁸ atoms cm ⁻³ .
[0014]
Next, annealing is performed at 1000 ° C. for 10 minutes in an N ₂ atmosphere. As a result, as shown in FIG. 1C, a carbon implantation region 15 having a peak concentration is formed at a position deeper than the mirror surface 12 of the CZ substrate 11. The peak concentration of carbon 14 in the carbon implantation region 15 may be 1 × 10 ¹⁶ atoms cm ⁻³ or more.
[0015]
Thereafter, the SiO ₂ film 13 is removed with an HF / NH ₄ F aqueous solution. Then, an Si epitaxial layer 16 having a resistivity of about 20 to 30 Ωcm is grown on the mirror surface 12 to a thickness of about 10 μm at a temperature of about 1150 ° C. using SiHCl ₃ gas to complete the epitaxial substrate 17. Let
[0016]
In addition, the position of the peak concentration of carbon 14 in the carbon implantation region 15 is made deeper than the mirror surface 12 when the position of the peak concentration is the mirror surface 12, the crystallinity of the mirror surface 12 is deteriorated, This is because the crystallinity of the Si epitaxial layer 16 grown on the mirror surface 12 is also deteriorated. Also, annealing in the N ₂ atmosphere after the ion implantation of carbon 14 causes the Si epitaxial layer 16 to grow on the mirror surface 12 later, so that it is in the vicinity of the mirror surface 12 that has become amorphous by ion implantation. This is for recovering crystallinity.
[0017]
Further, the SiO ₂ film 13 is formed on the mirror surface 12 in order to prevent channeling from occurring when the carbon 14 is ion-implanted and to prevent the mirror surface 12 from being sputtered. However, the SiO ₂ film 13 and the annealing in the N ₂ atmosphere are not necessarily required depending on the acceleration energy and the dose amount when the carbon 14 is ion-implanted.
[0018]
2 and 3 also show values measured using the epitaxial substrate 17 of the first embodiment. The CZ substrate for forming the conventional epitaxial substrate shown in FIGS. 2 and 3 and the CZ substrate 11 for forming the epitaxial substrate 17 of the first embodiment have the same specifications. As apparent from FIGS. 2 and 3, the generation lifetime is improved to about 1.4 times that of the CZ substrate, and the number of white scratch defects is improved to about 1/2 of that of the MCZ substrate. That is, in the epitaxial substrate 17, the gettering capability functions effectively even after the semiconductor device is formed.
[0019]
In the first embodiment described above, carbon 14 is ion-implanted into the CZ substrate 11 with an acceleration energy of 800 keV and a dose of 1 × 10 ¹⁴ cm ⁻² . FIG. The relationship between the dose of carbon 14 obtained by variously changing only the dose and the number of white defects of the CCD imaging device formed on the epitaxial substrate 17 is shown.
[0020]
FIG. 4 also shows the values normalized with the number of white scratch defects of the CCD image pickup device formed on the MCZ substrate as 1, similarly to FIG. However, FIG. 3 is a logarithmic graph, whereas FIG. 4 is a linear graph. From FIG. 4, the number of white scratch defects is smaller than that of the MCZ substrate as long as carbon 14 is ion-implanted, but the number of white scratch defects is particularly small when the dose amount is 5 × 10 ¹³ cm ⁻² or more. Thus, it can be seen that the gettering effect by the ion implantation of carbon 14 is large.
[0021]
However, if the dose of carbon 14 exceeds 5 × 10 ¹⁵ cm ⁻² , the crystallinity of the mirror surface 12 of the CZ substrate 11 deteriorates, and the crystallinity of the Si epitaxial layer 16 grown on the mirror surface 12 also increases. to degrade. Therefore, the dose of carbon 14 is preferably in the range of 5 × 10 ^{13 to} 5 × 10 ¹⁵ cm ⁻² .
[0022]
In the first embodiment described above, carbon 14 is ion-implanted with an acceleration energy of 800 keV. Even if the acceleration energy is 400 keV, the gettering effect by the ion implantation of carbon 14 is the same as in the case of 800 keV. Yes, even with 200 keV, the gettering effect is still considered to be the same as with 800 keV.
[0023]
Therefore, if carbon 14 is ion-implanted with low energy, a generally used high-current ion implanter can be used, and a current about 10 times that of C ²⁺ can be obtained. Since C ⁺ can be used, the throughput can be improved about 10 times.
[0024]
The projected range distances of carbon 14 when acceleration energy is 400 keV and 200 keV are about 0.75 μm and 0.40 μm, respectively, and in either case, as in the case of 800 keV, the CZ substrate 11 A carbon implantation region 15 having a peak concentration at a position deeper than the mirror surface 12 can be formed.
[0025]
In the first embodiment described above, the Si epitaxial layer 16 is temporarily grown on the mirror surface 12 of the CZ substrate 11, but once the Si epitaxial layer 16 is grown to a predetermined film thickness at the epitaxial growth temperature, The Si epitaxial layer 16 having a desired film thickness may be formed by repeating a series of steps of cooling to a temperature of ½ or less of the epitaxial growth temperature twice or more.
[0026]
In this way, two or more thermal histories are applied during the formation of the Si epitaxial layer 16, so that crystal defects formed in the CZ substrate 11 due to ion implantation of carbon 14 further grow, and the gettering capability of the epitaxial substrate 17 is increased. Is even higher.
[0027]
In the first embodiment described above, only the ion implantation of carbon 14 is performed in order to increase the gettering ability of the epitaxial substrate 17, but a polycrystalline Si film or a phosphorus glass film is formed on the back surface of the CZ substrate 11. If the EG performed by doing so is used together, the gettering ability can be further enhanced.
[0028]
Further, in the first embodiment described above, only carbon 14 is ion-implanted into the CZ substrate 11 that is a Si substrate, but group IV elements Ge, Sn, Pb, etc. are ion-implanted instead of carbon 14. Alternatively, elements other than group IV may be ion-implanted simultaneously with group IV elements such as carbon-14. In the first embodiment, the CZ substrate 11 which is a Si substrate is used. However, an MCZ substrate may be used, or a substrate other than the Si substrate may be used. When a substrate other than the Si substrate is used, at least an ion which is different from the element forming the substrate but is in the same family and electrically neutral is ion-implanted.
[0029]
In the first embodiment described above, the Si epitaxial layer 16 is grown using SiHCl _3. However, SiCl ₄ , SiH ₂ Cl ₂ , SiH ₃ Cl, or SiH ₄ may be used instead of SiHCl _3. In particular, it has been found that the use of SiH ₄ improves the characteristics of the semiconductor device.
[0030]
Next, a second embodiment will be described. In this second embodiment, the growth rate of the Si crystal by the MCZ method is set to 0.5 mm min− ¹ , the oxygen concentration is 1 × 10 ¹⁸ atoms cm ⁻³ , the <100> plane is the mirror surface, A Si substrate having a resistivity of about 20 Ωcm was prepared. A MOS capacitor having a gate insulating film made of a SiO ₂ film having a thickness of 20 nm and a gate electrode made of an Al film and a CCD image pickup device were formed on the Si substrate.
[0031]
When the Si substrate manufactured in the second embodiment is compared with the Si substrate manufactured in the conventional example, the non-defective product rate of the SiO ₂ film withstand voltage of the MOS capacitor is improved by about 4 times. Is also improved to 1/5 or less. In the second embodiment, the Si crystal is grown by the MCZ method, but the same effect can be expected by the CZ method.
[0032]
FIG. 5 shows the relationship between the oxygen concentration of the Si substrate obtained by further changing the oxygen concentration of the Si substrate in the second embodiment and the number of white defects of the CCD imaging device formed on the Si substrate. Show. From FIG. 5, it can be seen that the number of white scratch defects is stable at a low level when the oxygen concentration is 8 × 10 ¹⁷ atoms cm ⁻³ or more. This is presumably because impurities and crystal defects have been gettered by the IG effect that is naturally introduced in the process of forming the CCD imaging device.
[0033]
FIG. 6 shows the Si crystal growth rate obtained by variously changing the Si crystal growth rate with the oxygen concentration of the Si substrate fixed at 9 × 10 ¹⁷ atoms cm ⁻³ , and the Si substrate formed on the Si substrate. The relationship between the non-defective rate of the SiO ₂ film breakdown voltage of the MOS capacitor and the number of white scratch defects of the CCD image pickup device is shown. From FIG. 6, it can be seen that if the growth rate is 1 mm min- ¹ or less, the non-defective rate of the SiO ₂ film withstand voltage and the number of white defects are good. It is presumed that this is because the growth rate is slow and there are few point defects or clusters thereof introduced during crystal growth.
[0034]
Therefore, when the CCD image pickup device is formed on this Si substrate, not only are there few white defects, but there are also few transfer failures due to the breakdown voltage degradation of the gate insulating film. As the growth rate of the Si crystal, conventionally, about 1.5 mm min− ¹ has been generally adopted from the viewpoint of productivity.
[0035]
【The invention's effect】
According to the method for manufacturing a semiconductor substrate of claim 1, a semiconductor substrate capable of strongly gettering impurities and crystal defects with carbon can be manufactured, so that a semiconductor capable of forming a semiconductor device with excellent quality and characteristics can be formed. A substrate can be manufactured.
[0036]
In addition , a semiconductor substrate having a high carbon gettering ability and a surface of the semiconductor substrate on which the epitaxial layer is not sputtered can be manufactured, so that a semiconductor device having excellent quality and characteristics can be formed. Can be manufactured.
[0037]
In a second aspect of the method for manufacturing a semiconductor substrate, oxide film so does not become an obstacle to the formation of the epitaxial layer, it is possible to manufacture a semiconductor substrate can be formed of the quality and characteristics of good semiconductor devices.
[Brief description of the drawings]
FIG. 1 is a side sectional view showing a first embodiment of the present invention in the order of steps.
FIG. 2 is a graph showing the relationship between the type of semiconductor substrate and the generation lifetime.
FIG. 3 is a graph showing the relationship between the type of semiconductor substrate and the number of white defects.
FIG. 4 is a graph showing the relationship between the carbon dose and the number of white defects.
FIG. 5 is a graph showing the relationship between the oxygen concentration of the Si substrate and the number of white defects.
FIG. 6 is a graph showing the relationship between the growth rate of Si crystals, the yield rate of SiO ₂ film withstand voltage, and the number of white scratch defects.
[Explanation of symbols]
11 ... CZ substrate, 12 ... mirror surface, 14 ... carbon, 16 ... Si epitaxial layer, 17 ... epitaxial substrate

Claims (2)

Forming an oxide film on the surface of the semiconductor substrate;
A step of ion-implanting carbon into the semiconductor substrate at a dose of 5 × 10 ^{13 to} 5 × 10 ¹⁵ cm ^{−2 in} a state where the oxide film covers the surface ;
And annealing the semiconductor substrate after the ion implantation in a state where the pre-Symbol table surface the oxide film covers,
And a step of forming an epitaxial layer on the surface after the annealing. The method of manufacturing a semiconductor substrate according to claim 1, characterized in that removing the oxide film before the formation of and the epitaxial layer after said annealing.

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