JP2010109141A - Manufacturing method of semiconductor substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of an inexpensive semiconductor substrate having high productivity, a strong gettering property and a low metal impurity concentration. <P>SOLUTION: The manufacturing method of the semiconductor substrate has a process for preparing a silicon substrate, a process for implanting ions to the silicon substrate and a process for forming an epitaxial layer on a main surface of the silicon substrate to which the ions are implanted. In the ion implantation process, the ions are directly implanted to the silicon substrate without the acceleration of the implanted ions and post-acceleration after mass spectrometry. A cleaning process for etching and cleaning a surface of the silicon substrate is given after the ion implantation process and before the epitaxial layer forming process. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a semiconductor substrate having a strong gettering ability, and specifically, a proximity getter ability by a carbon ion implanted layer near the surface layer and a double getter of a bulk getter by an oxygen precipitate in the bulk. The present invention relates to a method for manufacturing a semiconductor substrate on which a high-quality epitaxial layer having getter capability and few defects is formed.

  As a semiconductor substrate for forming a semiconductor element, a silicon single crystal wafer grown by CZ (Czochralski) method or MCZ (Magnetic field CZ) method, and an epitaxial wafer in which an epitaxial layer is formed on the surface of these silicon single crystal wafers Conventionally, annealed wafers obtained by heat-treating silicon single crystal wafers have been used.

On the other hand, semiconductor elements are manufactured in an ultra clean room of class 100 or less, but contamination of silicon single crystal wafers by impurities from raw materials (gas, water, chemicals) and semiconductor manufacturing equipment is completely avoided. It is not possible. If these impurities are present in the element active region of the silicon single crystal wafer, the quality and characteristics of the semiconductor element are significantly deteriorated.
Therefore, intrinsic gettering (IG) and extrinsic gettering (EG) are conventionally performed in order to getter these impurities and remove them from the element active region. Further, an epitaxial layer may be formed on the surface of the wafer subjected to these treatments.

  In particular, from the viewpoint of manufacturing a semiconductor element, an epitaxial wafer can form an electrically active layer having a resistivity different from that of a substrate wafer, so that the degree of freedom in designing a semiconductor element is great. There are many advantages such as the ability to form a single crystal thin film (epitaxial layer) of high purity with a low concentration of oxygen and carbon that cause crystal defects to an arbitrary thickness, so high voltage semiconductor elements, integrated circuit elements, solid-state imaging elements (CCD <Charge-Coupled Device>, CIS <CMOS Image Sensor>) and the like are used in many cases and are put into practical use as products.

As a practical method for forming such an epitaxial layer, the CVD (Chemical Vapor Deposition method) is mainly used, and the following four main source gases are used.
For example, in the hydrogen reduction method, SiCl ₄ and SiHCl ₃ are used as the source gas.
SiCl ₄ + 2H ₂ → Si + 4HCl
SiHCl ₃ + H ₂ → Si + 3HCl
In the thermal decomposition method, SiH ₂ Cl ₂ and SiH ₄ are used as source gases.
SiH ₂ Cl ₂ → Si + 2HCl
SiH ₄ → Si + 2H ₂
Among these, SiHCl ₃ is mainly used for manufacturing a semiconductor substrate for a solid-state imaging device because it is inexpensive, has a high growth rate, and is suitable for epitaxial growth of a thick film.

  However, in an epitaxial wafer in which an epitaxial layer is formed using any source gas, many impurities, particularly metal impurities, are mixed during the formation of the epitaxial layer. Such metal impurities have caused white defect defects due to dark current to not be sufficiently reduced when the produced epitaxial wafer is applied to a solid-state imaging device, resulting in poor characteristics and yield.

As a generation source of such heavy metal impurities, a source derived from a SUS member in an epitaxial growth apparatus, a source gas piping, and the like can be considered. If the source gas contains chlorine, it is decomposed during epitaxial growth to produce HCl gas. It is considered that the HCl gas corrodes the SUS-based member in the bell jar and is taken into the source gas as a metal chloride, and this metal chloride is taken into the epitaxial layer.
In addition, HCl gas may be intentionally introduced to lightly etch off the surface of the silicon single crystal wafer before forming the epitaxial layer, which also contributes to corrosion.

  Therefore, when a solid-state imaging device is formed using an epitaxial wafer, carbon ions are implanted from the main surface of the silicon substrate as a gettering technique for gettering and removing the metal impurities. There is a method of manufacturing a carbon gettering epitaxial wafer in which a silicon epitaxial layer is formed on the surface (see Patent Document 1).

JP-A-6-338507

However, it is known that metal contamination is introduced into the substrate in the carbon ion implantation process when forming the carbon gettering layer, thereby deteriorating device characteristics. As a countermeasure, for example, in the technique described in Japanese Patent Application Laid-Open No. 2004-165225, after confirming that the metal contamination level of the ion implantation apparatus is equal to or lower than a predetermined level, a step of implanting carbon ions is performed. Yes.
However, with this method, only ion implanters with low metal contamination levels can be used. In addition, since it is necessary to strictly maintain and manage the metal contamination level of the ion implantation apparatus, much time and labor are required for that purpose. For this reason, productivity was not increased and costs were increased.

  The present invention has been made in view of the above problems, and is a method for manufacturing a semiconductor substrate capable of manufacturing a semiconductor substrate having high productivity, low cost, strong gettering capability, and low metal impurity concentration. It aims to provide a method.

  In order to solve the above problems, in the present invention, at least a step of preparing a silicon substrate, a step of implanting ions into the silicon substrate, and forming an epitaxial layer on the main surface of the silicon substrate subjected to the ion implantation And a step of performing ion implantation directly on the silicon substrate without performing post-stage acceleration after acceleration / mass analysis of the implanted ions, In addition, the semiconductor substrate manufacturing method includes a cleaning step of cleaning the surface of the silicon substrate after the ion implantation step and before the epitaxial layer forming step. .

Thus, during ion implantation, ion implantation is performed without performing acceleration after mass spectrometry. As a result, the implanted contaminants can remain in the vicinity of the wafer surface or in the surface protective film (oxide film or organic thin film). Then, by removing the surface layer of the substrate containing contaminants by a cleaning process that etches the surface of the silicon substrate, contaminants, particularly metal impurities implanted by the ion implantation process are removed from the silicon substrate. Can do.
According to this method, it is not necessary to select the ion implantation apparatus according to the contamination level, the apparatus can be freely selected, and it is not necessary to strictly control the contamination level. Therefore, productivity can be improved and a silicon substrate having a low metal impurity concentration can be obtained. By forming an epitaxial layer on the main surface of such a silicon substrate, a semiconductor substrate having a low metal impurity concentration and a strong gettering site near the surface can be manufactured.

The implanted ions are preferably carbon or carbon-containing ions (claim 2).
In this way, by using carbon or carbon-containing ions as the ions to be implanted, a gettering layer having a high gettering capability can be formed immediately below the epitaxial layer of the semiconductor substrate, and the precipitation of oxygen precipitates is promoted. Can be made.

The dose amount of the implanted ions is preferably 5 × 10 ^{13 to} 5 × 10 ¹⁵ / cm ² (Claim 3).
When the dose amount of implanted ions is 5 × 10 ¹³ / cm ² or more, a semiconductor substrate having sufficient gettering ability can be obtained even if the time required for ion implantation is short. Further, if the dose amount is 5 × 10 ¹⁵ / cm ² or less, the possibility of defects occurring in the epitaxial layer can be sufficiently reduced without performing annealing treatment for crystallinity recovery.

Furthermore, it is preferable that the cleaning step is a step of cleaning at least the silicon substrate with ammonia water.
By washing with ammonia perwater having a slow etching rate with respect to silicon as described above, the surface of the silicon substrate can be uniformly etched and particles on the surface of the substrate can be removed at the same time, which is very suitable.

Further, it is preferable that an annealing treatment is performed on the silicon substrate after the cleaning step and before the epitaxial layer forming step.
As described above, by performing an annealing process to recover crystallinity disturbed by ion implantation before forming the epitaxial layer, a semiconductor substrate with fewer defects in the epitaxial layer can be manufactured.

The semiconductor substrate is preferably used for manufacturing a solid-state imaging device.
As described above, since the semiconductor substrate manufactured by the manufacturing method of the present invention is a substrate having a low metal impurity concentration and a high gettering capability, it is suitable for a solid-state imaging device.

  As described above, according to the present invention, it is possible to eliminate the need to strictly control the metal impurity level of the ion implantation apparatus. Therefore, the cost and time required for management can be saved as compared with the conventional case. In addition, since it is not necessary to select and use an ion implantation apparatus, the apparatus can be freely selected, and the efficiency of the production line can be increased. From the above, improvement in productivity and cost reduction can be expected. In addition, since the ion-implanted layer is formed, a semiconductor substrate with high gettering capability can be manufactured.

Hereinafter, the present invention will be described more specifically.
As described above, development of a semiconductor substrate manufacturing method capable of manufacturing a semiconductor substrate having high productivity, low cost, strong gettering capability, and low metal impurity concentration has been awaited.

  Therefore, as a result of intensive studies on the ion implantation conditions for the underlying silicon substrate, the present inventors have performed ion implantation based on the following idea, and then also used for etching the surface of the silicon substrate. It was found that the above problems can be solved by performing subsequent cleaning and then forming an epitaxial layer, and the present invention has been completed.

The idea is briefly described below.
First, an ion implantation apparatus will be briefly described with reference to FIG. FIG. 4 is a diagram showing an example of an outline of an ion implantation apparatus.
In the ion implantation apparatus 30, ions are first generated by the ion source 31, and the generated ions are taken out by applying an electric field, and accelerated (previous stage acceleration) by the front stage acceleration mechanism 32. Thereafter, mass analysis by a magnetic field is performed using the mass analysis mechanism 33, and only ions having a predetermined mass are taken out. Thereafter, an electric field is further applied by the post-acceleration mechanism 34, and the second further acceleration (post-acceleration) is performed. . The ions accelerated in this way are implanted into the surface of the silicon substrate 35. The depth implanted into the silicon substrate 35 is deeper as the acceleration energy is larger and shallower as the acceleration energy is smaller.

Here, in the ion implantation apparatus, the ionized contaminant generated before the mass analysis is separated by the mass analyzer, and thus there is no influence on the silicon substrate. However, ionized contaminants generated after the mass spectrometer cannot be separated because no separation means is provided.
If post-acceleration is performed after mass spectrometry as usual, ionized contaminants are similarly accelerated and deeply implanted into the wafer. However, if there is no acceleration after mass spectrometry, the ionized contaminants have only low energy, so that they remain on the wafer surface or in a very shallow region.
By applying this principle, post-acceleration is not performed after mass spectrometry, so that contaminants remain on the wafer surface and in a very shallow region, and then cleaning is performed to etch the surface easily and reliably. The present invention was completed based on the idea that it can be removed.

  Hereinafter, the present invention will be described in detail with reference to the drawings, but the present invention is not limited thereto. FIG. 1 is a flowchart showing an example of steps of a method for manufacturing a semiconductor substrate according to the present invention.

Step (a)
First, a silicon substrate 11 to be a substrate is prepared.
The silicon substrate prepared at this time may be any generally used substrate, and for example, a silicon substrate sliced from a silicon single crystal rod grown by the CZ method may be used. Further, the electrical characteristic values such as the conductivity type and the specific resistivity, the crystal orientation, and the crystal diameter can be appropriately selected so as to be suitable for the semiconductor device to be designed (for example, a solid-state imaging device).

Step (b)
Next, ion implantation is performed on the prepared silicon substrate 11 to form the ion implantation layer 12. In FIG. 1, an example in which carbon is used as an implanted ion is described. However, the present invention is not limited to this, and ions such as Ge, Sn, and Pb can be implanted.
Here, in the present invention, in this ion implantation step, ions after mass analysis are directly implanted into the silicon substrate without performing re-acceleration (post-stage acceleration) after performing pre-acceleration and mass analysis of the implanted ions.
In the present invention, since the subsequent acceleration is not performed, in order to obtain the desired acceleration energy, it is desirable to obtain the desired acceleration energy at the stage of the previous acceleration.

Also, carbon or ions containing carbon can be implanted into the silicon substrate 11 as the implanted ions.
Thus, by implanting carbon or carbon-containing ions, oxygen precipitation can be promoted, so that the manufactured semiconductor substrate can have a higher IG capability. For this reason, a semiconductor substrate with higher gettering capability can be manufactured.

The dose amount of implanted ions can be set to 5 × 10 ^{13 to} 5 × 10 ¹⁵ / cm ² .
Thus, by implanting ions at a dose of 5 × 10 ^{13 to} 5 × 10 ¹⁵ / cm ² , it is possible to promote the precipitation of oxygen precipitates. Further, since the dose amount of ions to be implanted is small, the work time required for the ion implantation process itself can be shortened, and therefore, a high-quality semiconductor substrate can be manufactured at low cost. Furthermore, the disorder of the crystallinity of the silicon substrate can be reduced, and the occurrence of defects when the epitaxial layer is formed later can be suppressed.

Step (c)
Thereafter, a cleaning process that also serves as etching of the surface of the silicon substrate 11 after the ion implantation is performed.
By performing this cleaning process, the surface layer including the contaminants injected into the silicon substrate 11 by the previous ion implantation process is etched and removed together with the contaminants.

Here, as the cleaning process, any process that etches at least the surface of the silicon substrate 11 may be used. However, this cleaning process can be a process of cleaning with ammonia overwater.
Ammonia hydrogen peroxide etches the surface of the silicon substrate, but the etching rate at this time is slower than that of an alkaline solution such as KOH. By cleaning with such ammonia water, the surface of the silicon substrate can be uniformly etched, so that a semiconductor substrate having a flat surface can be obtained. Moreover, the particles adhering to the substrate surface can be removed at the same time by washing with ammonia overwater.

In addition, after the cleaning process and before the epitaxial layer forming process described later, the silicon substrate 11 can be annealed.
In this way, by performing an annealing process for crystal recovery before forming the epitaxial layer, the crystallinity of the silicon substrate surface disturbed by the ion implantation can be recovered, and defects are also introduced into the formed epitaxial layer. It can be suppressed more.

Step (d)
Thereafter, the epitaxial layer 13 is formed on the main surface of the cleaned silicon substrate 11, and the semiconductor substrate 10 is manufactured.
A general method can be used for forming the epitaxial layer. For example, in the case of forming by vapor phase growth, it may be performed under general conditions. For example, the semiconductor single crystal substrate described above is arranged on a susceptor by introducing a source gas such as SiHCl ₃ into the chamber using H ₂ as a carrier gas. Can be epitaxially grown at about 1050 to 1250 ° C. by the CVD method.

And the semiconductor substrate 10 obtained in this way can be used for solid-state image sensor formation.
As described above, according to the present invention, since a semiconductor substrate having a low concentration of contaminants, particularly metal impurities, and a high gettering capability can be obtained, a solid-state imaging device is manufactured using such a semiconductor substrate. If so, a solid-state imaging device having good characteristics can be manufactured with high yield.

As described above, in the method for manufacturing a semiconductor substrate according to the present invention, in the ion implantation step, ion implantation is performed without performing acceleration after mass spectrometry (post-stage acceleration). Further, after the ion implantation, before the epitaxial layer is formed, cleaning is performed to etch the silicon substrate surface.
Thereby, in the ion implantation apparatus, it is possible to suppress the contaminants mixed after the mass analysis from being deeply implanted into the silicon substrate, and it is possible to keep the contamination in the vicinity of the surface. Then, the contamination in the ion implantation process can be prevented by removing the surface of the silicon substrate containing contaminants by cleaning that etches the surface of the silicon substrate.
According to such a manufacturing method, it is not necessary to select the ion implantation apparatus according to the contamination level, the apparatus can be freely selected, and it is not necessary to strictly control the contamination level. Therefore, productivity can be improved and cost can be reduced. Further, since impurities derived from the ion implantation process can be removed, the impurity concentration in the semiconductor substrate, particularly the metal impurity concentration can be lowered. For this reason, it is very suitable when used for a solid-state imaging device or the like in which the metal impurity concentration is strictly limited.

EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated more concretely, this invention is not limited to these.
(Example)
A semiconductor substrate was manufactured according to the process shown in FIG.
First, as a silicon substrate 11, a silicon substrate grown by the Czochralski method (CZ method) and having a plane orientation (100), a resistivity of 10 to ²⁰ Ω · cm, and an oxygen concentration of 1.12 × 10 ¹⁸ atoms / cm ³ . Was prepared (step (a)).

Next, this substrate was washed with an NH ₄ OH / H ₂ O ₂ aqueous solution and an HCl / H ₂ O ₂ aqueous solution. Next, carbon was ion-implanted from the main surface of the silicon substrate 11 at an acceleration energy of 70 keV and a dose of 1 × 10 ¹⁵ / cm ² to form an ion-implanted layer 12 (step (b)).
The acceleration energy at this time was performed only by the previous stage acceleration. At this time, the projected range of carbon was about 0.2 μm from the surface of the silicon substrate, and its peak concentration was about 5 × 10 ¹⁹ atoms / cm ³ .

Thereafter, the silicon substrate 11 was washed with an NH ₄ OH / H ₂ O ₂ aqueous solution having an etching effect and an HCl / H ₂ O ₂ aqueous solution for removing metal contamination on the outermost surface (step (c)).

Thereafter, recovery annealing for ion implantation damage was performed. Specifically, after the wafer was put into the chamber, annealing was performed at 1130 ° C. for 60 seconds in a hydrogen atmosphere.
Then, after introducing into an epitaxial growth furnace, SiHCl ₃ gas was introduced to grow an epitaxial layer 13 having a thickness of 6 μm and a resistivity of 30 Ω · cm, and a semiconductor substrate 10 was manufactured (step (d)).

(Comparative example)
A semiconductor substrate was manufactured according to the process shown in FIG.
First, as a silicon substrate 21, a silicon substrate grown by the Czochralski method (CZ method) having a plane orientation (100), a resistivity of 10 to ²⁰ Ω · cm, and an oxygen concentration of 1.12 × 10 ¹⁸ atoms / cm ³ . Was prepared (step (a ′)).

Next, this substrate was washed with an NH ₄ OH / H ₂ O ₂ aqueous solution and an HCl / H ₂ O ₂ aqueous solution. Next, carbon was ion-implanted from the main surface of the silicon substrate 21 at an acceleration energy of 70 keV and a dose of 1 × 10 ¹⁵ / cm ² to form an ion-implanted layer 22 (step (b ′)).
At this time, the acceleration energy of ions before mass analysis was 35 keV, and the acceleration energy after mass analysis was 35 keV. At this time, the projected range of carbon was about 0.2 μm from the surface of the silicon substrate.

Thereafter, the silicon substrate 21 was washed with an NH ₄ OH / H ₂ O ₂ aqueous solution having an etching effect and an HCl / H ₂ O ₂ aqueous solution for removing metal contamination on the outermost surface (step (c ′)). .

Thereafter, recovery annealing for ion implantation damage was performed. Specifically, after the wafer was put into the chamber, annealing was performed at 1130 ° C. for 60 seconds in a hydrogen atmosphere.
Then, after introducing into an epitaxial growth furnace, SiHCl ₃ gas was introduced to grow an epitaxial layer 23 having a thickness of 6 μm and a resistivity of 30 Ω · cm, and a semiconductor substrate 20 was manufactured (step (d ′)).

In the examples and comparative examples, the impurity concentration on the substrate surface after cleaning when the etching amount on the substrate surface was changed by changing the cleaning time in the NH ₄ OH / H ₂ O ₂ aqueous solution after carbon ion implantation ( As a representative example, Mo) is measured, a Mo impurity concentration profile in the depth direction is created, and the result is shown in FIG. The horizontal axis of the graph indicates the etching amount when washed with the NH ₄ OH / H ₂ O ₂ aqueous solution, that is, the thickness in the depth direction. However, data with an etching depth of 0 represents data without cleaning, that is, data immediately after ion implantation.

As can be seen from the data on the Mo depth distribution of the semiconductor substrate of the example of FIG. 2, various contaminants are detected on the wafer surface immediately after the ion implantation, but the NH ₄ OH / H ₂ O ₂ aqueous solution. It was found that all of the depths where etching was removed by 10 nm or more were lower detection limits, and almost no contaminants were injected despite ion implantation at a high concentration of 10 ¹⁹ / cm ³ .
On the other hand, as can be seen from the data on the depth distribution of Mo in the semiconductor substrate of the comparative example of FIG. 2, when post-stage acceleration is performed, the contaminants during ion implantation are distributed with a peak in a deep region from the surface. It was found that it was difficult to remove by washing.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

It is a flowchart which shows an example of the process of the manufacturing method of the semiconductor substrate of this invention. It is the graph which showed Mo concentration distribution of the depth direction of the semiconductor substrate manufactured with the manufacturing method of the Example and comparative example of this invention. It is a flowchart which shows the process of the manufacturing method of the semiconductor substrate of a comparative example. It is the figure which showed an example of the outline of an ion implantation apparatus.

Explanation of symbols

10, 20 ... Semiconductor substrate, 11, 21 ... Silicon substrate, 12, 22 ... Ion implantation layer, 13, 23 ... Epitaxial layer,
DESCRIPTION OF SYMBOLS 30 ... Ion implantation apparatus, 31 ... Ion source, 32 ... Pre-stage acceleration mechanism, 33 ... Mass spectrometry mechanism, 34 ... Post-stage acceleration mechanism, 35 ... Silicon substrate.

Claims (6)

A method for manufacturing a semiconductor substrate, comprising: a step of preparing a silicon substrate; a step of implanting ions into the silicon substrate; and a step of forming an epitaxial layer on a main surface of the silicon substrate subjected to the ion implantation. Because
The ion implantation step is a step of performing ion implantation directly into the silicon substrate without performing post-stage acceleration after acceleration / mass analysis of implanted ions,
And the manufacturing method of the semiconductor substrate characterized by having the washing | cleaning process which performs the washing | cleaning which etches the surface of the said silicon substrate after the said ion implantation process and before the said epitaxial layer formation process.   2. The method of manufacturing a semiconductor substrate according to claim 1, wherein the implanted ions are carbon or ions containing carbon. 3. The method of manufacturing a semiconductor substrate according to claim 1, wherein a dose amount of the implanted ions is set to 5 × 10 ^{13 to} 5 × 10 ¹⁵ / cm ² .   4. The method of manufacturing a semiconductor substrate according to claim 1, wherein the cleaning step is a step of cleaning at least the silicon substrate with ammonia hydrogen peroxide. 5.   5. The method of manufacturing a semiconductor substrate according to claim 1, wherein the silicon substrate is annealed after the cleaning step and before the epitaxial layer forming step. 6. .   6. The method for manufacturing a semiconductor substrate according to claim 1, wherein the semiconductor substrate is used for manufacturing a solid-state imaging device.

Images