JP6575931B2 - Epitaxial wafer manufacturing method - Google Patents

Description

  The present invention relates to an epitaxial wafer manufacturing method.

For example, there is a semiconductor element formed by patterning a part of an N-type semiconductor substrate and growing an epitaxial layer on the substrate so as to have the same resistivity as the bulk part of the substrate. Some epitaxial wafers that are the basis of such semiconductor elements have high resistivity in which the resistivity of the substrate and the epitaxial layer is, for example, 5 × 10 ¹⁴ atoms / cm ³ or less in terms of dopant concentration. At the outer periphery of the epitaxial wafer, the dopant concentration distribution from the wafer surface to the wafer depth direction (hereinafter referred to as “dopant concentration profile”) is as shown in the graph of FIG. There is. In FIG. 5, the dopant concentration profile is locally reduced near the interface between the substrate and the epitaxial layer (raised in a hump shape downward). This phenomenon is caused by a step of cleaning the substrate before growing the epitaxial layer on the substrate, and a transport destination in which the substrate cleaned in this step is housed and transported in a container as shown in Patent Document 1. This is caused by the fact that boron, which is a P-type dopant, adheres to the substrate (N-type) during the step of growing the substrate. That is, when the substrate is contaminated by a dopant having a conductivity type different from that of the substrate, the carrier of the substrate is canceled, the dopant concentration is lowered at and near the contaminated portion of the substrate, and the dopant concentration profile is disturbed. In an epitaxial wafer, the dopant concentration at the interface between the substrate and the epitaxial layer has a great influence on the characteristics of the semiconductor element, so that it is required to sufficiently control the dopant concentration profile in the vicinity of this interface.

  In this way, boron that disturbs the dopant concentration profile of the epitaxial wafer is generally brought in from an environment in which a semiconductor manufacturing line such as a semiconductor manufacturing apparatus is arranged. For example, the environment of a clean room provided with a semiconductor production line is contaminated with boron, and the boron in this environment contaminates the substrate through some process, so that the dopant concentration profile of the epitaxial wafer produced based on that substrate Is thought to be disturbed. In particular, the higher the resistivity of the N-type substrate and the epitaxial layer of the epitaxial wafer, in other words, the lower the dopant concentration, the more susceptible to the contamination by boron due to the presence of very slight boron in the environment. Therefore, even when a boron-less filter is installed in a clean room, contamination with boron may be a problem.

  As described above, contamination of the wafer by boron present in the environment in a slight amount can be highly sensitive and quantitatively evaluated by the methods disclosed in Patent Document 2 and Patent Document 3, for example.

  As a method for preventing contamination of the wafer with boron, for example, Patent Document 4 discloses a method in which the surface of the wafer is terminated with hydrogen by hydrofluoric acid treatment.

JP 2003-224103 A JP 2000-211942 A JP 2006-269962 A JP 2008-112892 A

  However, if the surface of the wafer is terminated with hydrogen, the number of particles increases extremely, causing a stacking fault during epitaxial growth. Therefore, a method for suppressing contamination of the wafer by boron without terminating the surface of the wafer with hydrogen is required.

  An object of the present invention is to provide an epitaxial wafer manufacturing method capable of suppressing boron contamination.

Means for Solving the Problems and Effects of the Invention

The method for producing an epitaxial wafer of the present invention includes:
Cleaning a high resistivity silicon single crystal substrate doped with an N-type dopant;
A step of growing an epitaxial layer on the silicon single crystal substrate after the cleaning step;
Storing and transporting the silicon single crystal substrate in a box from the cleaning process to the growing process;
With
When the number of times the box is transported by storing the silicon single crystal substrate in the process of growing from the cleaning process is defined as the number of times the box is used, the transporting process should use a box whose number of times of use is a predetermined number or less. Features.

The present inventor has conducted investigations from various angles in order to identify the source of contamination by boron that causes the disturbance of the dopant concentration profile in the vicinity of the interface between the epitaxial layer and the N-type substrate of the epitaxial wafer and the N-type substrate. As a result, after the step of cleaning the substrate, in order to carry out the step of growing an epitaxial layer on the cleaned substrate, the inside of the box for storing and transporting the cleaned substrate is contaminated with boron. I found it. Then, it was determined that this contaminated box was the cause of disturbing the dopant concentration profile of the epitaxial wafer, and the boron concentration in the box increased with the number of times the box was used to transport the cleaned substrate. I found out. Therefore, by limiting the number of times the box is used for storing and transporting the silicon single crystal substrate, it is possible to suppress the contamination of boron that is generated inside the box. Therefore, an epitaxial wafer capable of suppressing contamination by boron can be manufactured. In the present specification, the “high resistivity silicon single crystal substrate” is a silicon single crystal substrate doped with, for example, phosphorus, arsenic, or antimony at 5 × 10 ¹⁴ atoms / cm ³ or less.

  In the embodiment of the present invention, the transporting step uses a box that is used 10 times or less.

  According to this, an epitaxial wafer in which contamination by boron is effectively suppressed can be manufactured.

  The embodiment of the present invention includes a step of cleaning the box before the transporting step.

  According to this, it is possible to prevent the contamination from spreading from the box to the silicon single crystal substrate by cleaning the box before transporting the silicon single crystal substrate.

  In an embodiment of the present invention, the step of cleaning the box replaces the atmosphere around the box with a vacuum atmosphere and heats the box.

  According to this, boron in the box can be effectively removed, and the spread of contamination from the box to the silicon single crystal substrate can be more effectively suppressed.

  In an embodiment of the present invention, the method includes a step of replacing a box that is used more than 10 times with a new box containing a silicon single crystal substrate.

  According to this, a box in which the number of times of use of the box is increased and the boron contamination in the box is deteriorated can be replaced with a new box, and it is possible to prevent the contamination from spreading from the box in which the boron contamination has deteriorated to the silicon single crystal substrate.

In the embodiment of the present invention, the cleaning step uses a silicon single crystal substrate doped with phosphorus, arsenic or antimony and having a dopant concentration of 5 × 10 ¹⁴ atoms / cm ³ or less as the N-type dopant.

  According to this, an epitaxial wafer in which contamination by boron is effectively suppressed can be manufactured.

The flowchart which shows an example of the manufacturing method of the epitaxial wafer in this invention. The graph which shows the relationship between the use frequency of a box, and the density | concentration (microgram / L) of the boron in a box. The graph which shows the relationship between the frequency | count of use of a box, and the height of the peak of the dopant density | concentration profile of the outer peripheral part of an epitaxial wafer (peak height shown by dopant density | concentration (atomics / cm < ³ >)). The graph of Example 1 and 2 which shows the relationship between the depth (micrometer) from the surface in an epitaxial wafer, and the dopant concentration (atomics / cm < ³ >) of the epitaxial wafer corresponding to the depth. The graph which shows the relationship between the depth (micrometer) from the surface in an epitaxial wafer, and the dopant concentration (atomics / cm < ³ >) of the epitaxial wafer corresponding to the depth.

  Hereinafter, as an example of a method for manufacturing an epitaxial wafer of the present invention, a method for manufacturing a silicon epitaxial wafer by growing a silicon epitaxial layer on a silicon single crystal substrate will be described. In the following description, a cleaning device for cleaning a substrate cut out from a silicon single crystal ingot and subjected to a predetermined process, a box used for transporting the substrate from the cleaning device, and a substrate transported using the box A method of manufacturing an epitaxial wafer using a vapor phase growth apparatus that performs vapor phase growth will be described.

In order to manufacture a silicon epitaxial wafer using a vapor phase growth apparatus, first, a silicon single crystal substrate which is a growth substrate on which an epitaxial layer is grown is manufactured. For example, polycrystalline silicon and quartz silicon crucible and N-type dopant (phosphorus, arsenic, or antimony) to adjust the resistivity are immersed in a liquid surface of a molten liquid and pulled up to obtain a silicon single-piece. A crystal ingot is produced. At the time of producing the silicon single crystal ingot, phosphorus, arsenic, or antimony is added as a dopant at 5 × 10 ¹⁴ atoms / cm ³ or less (for example, phosphorus is added at 5 × 10 ¹⁴ atoms / cm ³ ). Then, after the silicon single crystal ingot thus produced is cut out to a predetermined thickness, the cut wafer is subjected to rough polishing, etching, polishing, etc. to produce a substrate W in a state where the surface is mirror-finished. The substrate W is adjusted to have an N conductivity type and a resistivity of, for example, 10 Ω · cm or more by a dopant added when a silicon single crystal ingot is manufactured.

  The produced substrate W is transported to a known cleaning device, and the dirt attached to the substrate W is cleaned in the steps so far (S1 in FIG. 1). A known cleaning apparatus includes a load port for mounting a box for storing and transporting a plurality of substrates W, and the plurality of cleaned substrates W are stored in a box mounted on the load port.

  The box placed on the load port of the cleaning apparatus includes a container-like main body having an opening and a lid for closing the opening. A sealed space is formed inside the box with the lid portion closing the opening of the main body portion. When the box arranged in the load port is opened so that the inside of the box is shielded from the outside air, and a predetermined number of substrates W are stored in the main body through the opened opening (S2). The opening of the main body is sealed by the lid. In a state where the substrate W is stored in the box thus sealed, the substrate W is automatically transferred from the cleaning apparatus to a known vapor phase growth apparatus together with the box (S3).

  A known vapor phase growth apparatus into which a box containing a substrate W is loaded includes, for example, a load port for placing the box and a transfer robot for taking out the substrate W from the box placed on the load port. When the box is placed on the load port of the vapor phase growth apparatus, the lid is opened so that the inside of the box is shielded from the outside air, and the substrate is taken out by the transfer robot from the opened opening. Epitaxial growth is performed on W. Specifically, the growth conditions are set so that an epitaxial layer having a dopant concentration equivalent to the dopant concentration of the substrate W is grown. For example, a 4 μm silicon epitaxial layer is grown on the substrate W, Manufacture (S4).

  The substrate W of the epitaxial wafer manufactured as described above has an N conductivity type, and the dopant concentration of the substrate W is low. Therefore, only a small amount of P-type boron exists in the environment for manufacturing such an epitaxial wafer, and the manufactured epitaxial wafer is affected by the contamination by boron. Such boron contamination is caused by, for example, P-type boron adhering to the N-type substrate W while the substrate W cleaned by the cleaning apparatus is stored in a box and transported to the vapor phase growth apparatus. This occurs when the carrier is canceled. When an epitaxial layer is grown on the substrate W in which carriers have been canceled in this way to manufacture an epitaxial wafer, the dopant concentration decreases at and near the location where the substrate W is contaminated in the depth direction of the manufactured wafer. As a result, the dopant concentration profile of the epitaxial wafer is disturbed.

  The present inventor has conducted research from various angles in order to identify the source of boron contamination that causes the dopant concentration profile to be disturbed in this way. An example of the results of the investigation is shown in FIG. 2. FIG. 2 shows the relationship between the number of times the box is used for transporting the substrate W from the cleaning apparatus to the vapor phase growth apparatus, and the boron concentration (μg / L) in the box. Is shown. As the number of times the box was used, the total number of times the box was transferred from the cleaning apparatus to the vapor phase growth apparatus after storing the substrate W was defined as the number of times the box was used. 2 shows a value obtained by measuring the boron concentration in the box by the ICP-MS method. Specifically, a small amount of dilute nitric acid was placed in a box that was used a predetermined number of times, the whole box was stirred, and the value obtained by measuring the solution in the box by the ICP-MS method was taken as the boron concentration. As shown in FIG. 2, the boron concentration in the box increases as the number of times the box is used, and the boron concentration tends to be saturated when the number of times the box is used is 20 times or more.

Further, FIG. 3 shows an example of the investigation result investigated by the present inventor as in FIG. FIG. 3 shows the number of times the same box is used as in FIG. 2 and the peak height at which the dopant concentration profile on the outer periphery of the epitaxial wafer on which the epitaxial layer is grown on the substrate W transported in that box is locally reduced. It is. The height of this peak is obtained by calculating the height of the peak portion from the dopant concentration (atomics / cm ³ ) obtained by measuring the dopant concentration profile at the outer peripheral portion of the epitaxial wafer by the spreading resistance measurement method. Is indicated by the dopant concentration (atomics / cm ³ ). Specifically, the peak height at which the dopant concentration locally decreases at the interface between the substrate W and the epitaxial layer and in the vicinity thereof was obtained. In FIG. 3, it can be seen that the height of the peak formed in the dopant concentration profile increases as the number of times the box is used, and the peak height tends to be saturated when the number of times of use is 20 times or more.

  As can be seen from FIGS. 2 and 3, it is preferable to use a box that is used less frequently when the substrate W is transferred from the cleaning apparatus to the vapor phase growth apparatus. Specifically, when a box that is used 10 times or less is used, the substrate W can be transferred from the cleaning apparatus to the vapor phase growth apparatus by the box in which the boron concentration is suppressed.

  In the embodiment of the present invention, as shown in S11 of FIG. 1, when the number of times of use of the box exceeds a predetermined number (for example, 10 times) (S11: No), it is replaced with a box in which the contamination with boron has deteriorated. A new box (the number of times of use is 10 times or less) is used (S12). On the other hand, when the number of times the box is used is equal to or less than a predetermined number (for example, 10 times) (S11: Yes), the box is transported to, for example, a well-known vacuum replacement device to clean the box (S13). As this vacuum replacement device, for example, a replacement furnace that can store a box and can replace the atmosphere around the box with a vacuum atmosphere is provided. When the box is cleaned by this vacuum replacement device, the box is stored in the replacement furnace (for example, with the opening of the main body of the box being opened), and a vacuum is drawn in the replacement furnace. The pressure in the furnace is reduced to 33 torr. The atmosphere around the box (atmosphere in the furnace) is made a vacuum atmosphere. Here, the vacuum atmosphere means an atmosphere whose pressure is lower than the normal atmospheric pressure, and is an atmosphere whose pressure is, for example, 1.33 torr or less. Then, the box is heated in a vacuum atmosphere at, for example, 80 ° C. for 20 minutes. This facilitates the removal of boron from the box. When the cleaning of the box is completed, the substrate W after the cleaning by the cleaning apparatus (S1) is stored in the box where the cleaning is completed (S14), and the box is transferred to the vapor phase growth apparatus together with the substrate W (S15). . Then, an epitaxial layer is grown on the substrate W. In the embodiment of the present invention, it is possible to limit the number of times the box is used and to clean the box, thereby suppressing the contamination of boron in the box. As a result, an epitaxial wafer that can suppress contamination by boron can be manufactured.

  In order to confirm the effect of the present invention, the following experiment was conducted. EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated concretely, these do not limit this invention.

(Example)
In Example 1, the following boxes were prepared. Specifically, an inner carrier capable of accommodating 25 wafers having a diameter of 200 mm, a lid having a holding portion for fixing the wafer, and a main body (which has an opening closed by the lid, and accommodates the inner carrier ( A box with an outer box was prepared. And the prepared box was decomposed | disassembled into said three parts (an inner carrier, a cover part, and an outer box), and each part was wash | cleaned. At the time of cleaning, a first cleaning tank containing a 25 ° C. cleaning liquid adjusted so that the concentration of the ether-based surfactant was 3 to 5% and a second cleaning tank containing pure water were prepared. Next, each part was passed through a shower with pure water to perform rough cleaning of each part, and then each part was immersed in the first cleaning tank. Then, each part was taken out from the 1st washing tank, immersed in the 2nd washing tank, and rinsed. Then, after removing each part from the second washing tank, air-dry until the moisture is removed from the surface of each part, reassemble the parts after air-drying, and prepare a box with an internal boron concentration of 0.01 μg / L or less did. And using this box, the substrate was transferred 10 times from the cleaning apparatus to the vapor phase growth apparatus, and the number of times the box was used (the number of times the box was transferred from the cleaning apparatus to the vapor phase growth apparatus together with the substrate) was 10 times. . In addition, a high resistivity N-type silicon single crystal substrate (diameter: 200 mm) prepared so that phosphorus becomes 4.4 × 10 ¹⁴ atoms / cm ³ as a dopant was prepared, and the prepared substrate was cleaned with a cleaning apparatus. It was stored in a box that was used 10 times later. Then, after the box containing the substrate was transported to the vapor phase growth apparatus, a silicon epitaxial layer having a thickness of 4 μm was grown on the substrate taken out from the box under the condition that the dopant concentration was adjusted to be equal to that of the substrate. . Thereafter, the dopant concentration profile at a point located 5 mm from the outer periphery to the center of the produced epitaxial wafer was spread and calculated by a resistance measurement method.

  In Example 2, as in Example 1, a box that was used 10 times was prepared, and the prepared box was carried into a replacement furnace in a known vacuum replacement device. Next, the inside of the replacement furnace containing the box was depressurized to 1.33 Torr, and the box was heated to 80 ° C. for 20 minutes under a vacuum atmosphere. And after taking out a box from a vacuum substitution apparatus, the board | substrate was accommodated in a box like Example 1, and it conveyed to the vapor phase growth apparatus, produced an epitaxial wafer, and computed the dopant concentration profile of the produced wafer. .

(Comparative example)
In the comparative example, an epitaxial wafer was produced in the same manner as in Example 1 except that a box with a usage count of 20 was used, and the dopant concentration profile of the produced wafer was calculated.

FIG. 4 shows dopant concentration profiles in Examples 1 and 2 and the comparative example. In Examples 1 and 2, the peak height of the dopant concentration at which the dopant concentration profile locally decreased near the interface between the substrate and the epitaxial layer could be suppressed to 1.0 × 10 ¹⁴ atoms / cm ³ or less. . Moreover, in Example 2, the peak height was able to be suppressed more effectively than Example 1. On the other hand, in the comparative example, the peak height of the dopant concentration was 1.0 × 10 ¹⁴ atoms / cm ³ or more. If a semiconductor element is produced based on an epitaxial wafer having such a peak, it is considered that the characteristics of the produced semiconductor element are adversely affected.

  As described above, in Examples 1 and 2, the degree of local decrease in the dopant concentration profile at the interface between the substrate and the epitaxial layer and in the vicinity thereof can be suppressed without preparing the clean room environment on a large scale. It was. As a result, an epitaxial wafer having a dopant concentration profile required for a semiconductor element could be manufactured.

  The embodiments of the present invention have been described above. However, the present invention is not limited to the specific description, and the illustrated configurations and the like can be appropriately combined within a technically consistent range. In addition, certain elements and processes may be replaced with known forms.

  W substrate

Claims (4)

Cleaning a high resistivity silicon single crystal substrate doped with an N-type dopant;
A step of growing an epitaxial layer on the silicon single crystal substrate after the cleaning step;
Storing and transporting the silicon single crystal substrate in a box from the cleaning step to the growing step;
Before the transporting step, the atmosphere around the box is replaced with a vacuum atmosphere, and the box is heated;
With
In the case where the number of times the box is transported by storing the silicon single crystal substrate from the cleaning step to the growing step is the number of times the box is used, the transporting step is performed when the number of times of use is equal to or less than a predetermined number. An epitaxial wafer manufacturing method using the certain box.   The method of manufacturing an epitaxial wafer according to claim 1, wherein the transporting step uses the box that is used 10 times or less. The manufacturing method of the epitaxial wafer of Claim 1 or 2 provided with the process of replacing | exchanging the said box in which the said use frequency exceeds 10 with the new box which accommodates the said silicon single crystal substrate. Wherein the step of washing, as the N-type dopant, phosphorus, epitaxial wafer according to claim 1, arsenic or antimony is doped with a dopant concentration of 5 × 10 ¹⁴ atоms / cm ³ or less is used the silicon single crystal substrate Manufacturing method.

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