TW201923847A - Epitaxial wafer manufacturing method - Google Patents

Abstract

According to the present invention, silicon semiconductor substrates are prepared so as to have polished rear surfaces, and the substrates thus prepared are cleansed and then placed in a substrate storage part 2 in a batch consisting of more than one substrate. The atmosphere in the substrate storage part 2 is controlled so as to contain NO2 and NO3 in a total concentration of at most 140 ng/m3. The substrates stored in the substrate storage part 2 are conveyed, one by one, to a reactor 5, in which a silicon epitaxial layer is formed by vapor phase epitaxy. Accordingly, provided is a method that suppresses the generation of a rear surface halo dependent on time passage following the cleaning of substrates, and that enables manufacturing of high-grade epitaxial wafers.

Description

Epicrystalline wafer manufacturing method

The invention relates to a method for obtaining an epitaxial wafer by forming a silicon epitaxial layer on a silicon semiconductor substrate.

A CVD (Chemical Vapour Deposition) device has been known as a substrate processing device used for manufacturing steps of a semiconductor substrate such as a silicon semiconductor substrate. As an example of the epitaxial treatment of a silicon semiconductor substrate, a method for growing a vapor phase epitaxy of an epitaxial layer composed of single crystal silicon on the front surface of a silicon semiconductor substrate has been developed. As this manufacturing method, a substrate is horizontally placed on a base housed in a reaction furnace for epitaxial growth, and thereafter, the base is rotated around a vertical axis of rotation at the same time, and the substrate is heated at a high temperature by a heat source such as a halogen lamp. Heat (1000 ℃ ～ 1200 ℃), and circulate silicon source gas. Thereby, silicon generated by thermal decomposition (and reduction) of the reaction gas is precipitated on the front surface of the substrate, and an epitaxial layer composed of single crystal silicon is grown on the front surface of the substrate.

Here, the production of epitaxial wafers is generally performed in a clean room maintained at a high cleanliness. The clean room is described in Patent Documents 1 and 2 as follows: When the exhaust gas is taken in and purified and then circulated and supplied to the clean working space, various pollutants such as ammonia, nitrogen oxides (NO _x ), sulfur oxides (SO _x ), and the like are used for the purification to have a fixed concentration or less. For example, it is described that nitrogen oxides (NO _x ), which is one of the pollutants, are 1 ppb or less (Patent Document 1) and 0.1 ppb or less (Patent Document 2). Prior art literature patent literature

Patent Document 1: Japanese Patent Application Laid-Open No. 2009-138977 Patent Document 2: Japanese Patent Application Laid-Open No. 2009-138978

In addition, when a silicon epitaxial layer is formed on a silicon semiconductor substrate, when the silicon substrate has a polished silicon surface on the back surface, a small amount of poly-Si is also deposited on the back surface by transferring silicon source gas toward the back surface. . It is considered that the occurrence of unevenness in the trace polycrystalline silicon on the back surface of the substrate may cause haze and opaqueness and rough surface. The generation of the halo on the back surface tends to become prominent as the time from the substrate cleaning to the epitaxial reaction becomes longer, and the halo pattern also becomes thicker. The generation of the halo on the back causes deterioration in the yield rate of the silicon epitaxial step caused by poor appearance, which becomes a problem. That is, it is convenient to manufacture epitaxial wafers in a clean room as proposed in Patent Documents 1 and 2. The above problem still exists, that is, as the time from the substrate cleaning to the epitaxial reaction becomes longer, the back halo Becomes noticeable, and the halo pattern becomes thicker.

The present disclosure has been made in view of the above-mentioned problems, and an object thereof is to provide a method of manufacturing a high-quality epitaxial wafer capable of suppressing the occurrence of back halo depending on the elapsed time after the substrate is cleaned.

The inventor speculates that the generation of halo on the back surface varies according to the exposure time of the substrate (the time from the washing to the epitaxial growth), and the difference in the halo generation tendency due to the difference in the exposure environment is affected by the substrate. Expose the effects of the atmosphere. Therefore, it was found that when evaluating the exposure atmosphere, the concentrations of NO ₂ and NO ₃ in the exposure atmosphere are related to the occurrence of halo on the back, especially by using the total concentration of NO ₂ and NO ₃ stored at 140 ng / m ³ Polishing the silicon substrate on the back surface in the following exposure atmosphere can suppress the occurrence of back halo, thereby completing the present invention.

That is, the manufacturing method of an epitaxial wafer according to one aspect of the present disclosure is a manufacturing method in which the total concentration of NO ₂ and NO ₃ after cleaning the silicon semiconductor substrate polished on the back surface is stored at 140 ng / m ^In the ambient atmosphere below ³ , a silicon epitaxial layer is vapor-grown on the silicon semiconductor substrate.

According to one aspect of the present disclosure, a high-quality epitaxial wafer capable of suppressing the occurrence of back halo can be manufactured.

In addition, it is more preferable to store the silicon semiconductor substrate in an environmental atmosphere in which the total concentration of NO ₂ and NO ₃ is 10 ng / m ³ or less. Therefore, when the silicon epitaxial layer is vapor-grown on a silicon semiconductor substrate, the haze level on the back surface of the substrate can be further suppressed, and the occurrence of halo on the back surface can be further suppressed.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this embodiment, an example in which the present invention is applied to the production of an epitaxial wafer using a monolithic epitaxial growth device will be described. First, the structure of a monolithic epitaxial growth device will be described with reference to FIG. 1.

The monolithic epitaxial growth device 1 shown in FIG. 1 includes a substrate storage unit 2 that stores the cleaned silicon semiconductor substrate W (hereinafter, sometimes simply referred to as the substrate W) in a plurality of pieces as a batch; The path 3 is provided adjacent to the substrate storage unit 2; the transfer robot 4 is installed in the transfer path 3 and transfers one substrate W stored in the substrate storage unit 2 to the reaction furnace 5 described below; The furnace 5 is provided adjacent to the conveying path 3 for performing a reaction for vapor-phase growth of a silicon epitaxial layer on the front surface of the substrate W carried by the conveying robot 4; the base 6 is provided for the reaction The substrate W is placed in the furnace 5 such that the front and back surfaces of the substrate W are horizontal; and a lamp 7 is provided around the reaction furnace 5 to heat the inside of the reaction furnace 5. The epitaxial growth device 1 also includes a driving unit (not shown) that rotates the base 6 during epitaxial growth.

The base 6 is formed in a disc shape, and is supported by a support shaft 8 such that the upper surface is horizontal. A groove portion 61 on which the substrate W is placed is formed on the upper surface of the base 6. The groove portion 61 is formed in a circular shape having a slightly larger diameter than the substrate W. In addition, the groove portion 61 is formed in a stepped shape, for example, so as to be in contact with only the outer peripheral portion of the back surface of the substrate W and to form a gap with other portions of the back surface of the substrate. The groove portion 61 may be formed so as to be in contact with the entire rear surface of the substrate W.

A gate valve (not shown) is provided between the substrate storage unit 2 and the transport path 3. When the gate valve is closed, the space between the substrate storage unit 2 and the transport path 3 is blocked, and the substrate W cannot be moved in and out. When the gate valve is opened, the substrate storage unit 2 and the conveyance path 3 are conducted to allow the substrate W to be moved in and out. Similarly, a gate valve (not shown) is provided between the conveyance path 3 and the reaction furnace 5 to switch the conduction and blocking between them.

The substrate storage unit 2, the transport path 3, and the reaction furnace 5 are blocked from the atmosphere. In addition, in order to prevent foreign substances (moisture, oxygen, metal, etc.) from being mixed into the substrate storage unit 2, the substrate storage unit 2 is provided with a structure to be replaced with an inert gas such as nitrogen. Specifically, a pump (not shown) that evacuates the substrate storage unit 2 or a gas pipe (not shown) that introduces an inert gas such as nitrogen into the substrate storage unit 2 is connected. This gas pipe is connected to a container (not shown) that stores an inert gas such as nitrogen (atmospheric gas of the substrate storage unit 2). Similarly, a gas pipe (not shown) for introducing an inert gas such as nitrogen is also connected to the transport path 3. Furthermore, in FIG. 1, a collector 10 in which a trapping liquid such as pure water is placed, and a part of the atmosphere in the substrate storage unit 2 is guided to a tube 11 in the collector 10 to evaluate the substrate storage. Atmosphere in Department 2.

Next, the manufacturing sequence of the epitaxial wafer according to this embodiment will be described. FIG. 2 is a flowchart showing the sequence. First, a silicon semiconductor substrate W (S1) is prepared. The diameter, crystal orientation, conductivity, and resistivity of the prepared substrate W are not particularly limited. As the prepared substrate W, a polished wafer subjected to mirror polishing processing on both the front and back surfaces is prepared.

A general manufacturing method of a polished wafer is described, and a single crystal ingot having a specific crystal orientation is manufactured using a Czochralski (CZ) method (single crystal growth step). The manufactured single crystal ingot is ground to adjust the outer diameter of the side surface, and a notch indicating the crystal orientation is formed on the outer periphery of the single crystal ingot (cylinder grinding step). The single crystal ingot is sliced into a thin circular plate-shaped wafer along a specific crystal orientation (slicing step), and the outer periphery of the sliced wafer is chamfered (chamfering step) in order to prevent cracking and defect of the sliced wafer. Thereafter, both sides of the chamfered wafer are simultaneously ground and flattened (double-head grinding step), and the processing distortion remaining on the chamfered and ground wafer is etched and removed (etching) step). Furthermore, the front and back surfaces of the wafer are polished to be mirror-finished (polishing step). Through these steps, a polished wafer is obtained.

Then, the prepared substrate W (polished wafer) is cleaned by RCA cleaning including SC-1 cleaning and SC-2 cleaning, etc., and abrasives or foreign materials are removed from the substrate W (S2).

Next, the washed substrates W are placed in a substrate storage unit 2 in a plurality of pieces, and the substrate W is waited in the substrate storage unit 2 until an epitaxial reaction is performed (S3). At this time, the atmosphere is managed so that the total concentration of NO ₂ and NO ₃ in the atmosphere in the substrate storage unit 2 is 140 ng / m ³ or less. For example, if the management is performed so that the respective concentrations of NO ₂ and NO ₃ become 70 ng / m ³ or less, the total concentration of NO ₂ and NO ₃ becomes 140 ng / m ³ or less. In addition, as long as the total concentration of NO ₂ and NO ₃ becomes 140 ng / m ³ or less, the concentration of one of NO ₂ and NO ₃ may exceed 70 ng / m ³ . Furthermore, it is more preferable that the total concentration of NO ₂ and NO ₃ in the atmosphere in the substrate storage unit 2 is 10 ng / m ³ or less. The reason is that, as shown in the following examples, by setting the total concentration to 10 ng / m ³ or less, the haze level of the back surface of the obtained epitaxial wafer can be further suppressed.

In addition, whether or not the total concentration is 140 ng / m ³ or less can be confirmed by the following method, for example. That is, a part of the atmosphere in the substrate storage unit 2 is dissolved in the trapped liquid by passing a pump (not shown) or the like through a tube 11 to a trapped liquid such as pure water in the collector 10. Ion concentration and NO ₃ ^{- -} ion concentration in the collected liquid by NO ₂ in the measurement method using an ion chromatographic analysis. The obtained NO ₂ ^- ion concentration and the NO ₃ ^- ion concentrations respectively became represent NO ₂ concentration atmosphere substrate storage section 2 of the and the NO ₃ concentration by way conversion, confirmed ₂ concentration after the conversion of NO and NO ₃ The total concentration is 140 ng / m ³ or less.

Regarding the reduction of the NO ₂ and NO ₃ concentrations, for example, after the inside of the substrate storage unit 2 is evacuated by a pump, a high-purity inert gas such as nitrogen is introduced into the substrate storage unit 2. Further, also considered trapped, removed the chemical filter circulation substrate storage portion 2 in the atmosphere of NO _x in the gas introduction pipe is provided, to improve the purity of the circulating atmosphere.

Then, one piece is selected from the substrates W stored in the substrate storage unit 2, and the selected substrates W are transferred to the reaction furnace 5 (S4). Specifically, the gate valve between the substrate storage section 2 and the transfer path 3 and the gate valve between the transfer path 3 and the reaction furnace 5 are opened, so that the transfer robot 4 transfers one substrate W stored in the substrate storage section 2 to In the reaction furnace 5, the transferred substrate W is placed in the groove portion 61 of the susceptor 6. Thereafter, the gate valves are closed. In the example of FIG. 1, there is shown an example in which a cassette (not shown) that accommodates a substrate W in a vertical direction is provided in the substrate storage unit 2, and reactions are sequentially performed from the substrate W stored in the lower side of the cassette. The atmosphere in the transport path 3 is replaced with an inert gas such as nitrogen.

Then, a silicon single crystal film is formed on the front surface of the substrate W by vapor phase growth in the reaction furnace 5 (S5). Specifically, while the base 6 is rotated, the substrate W is heated to a heat treatment temperature (for example, 1050 ° C. to 1200 ° C.) by the lamp 7. Then, hydrogen gas is introduced into the reaction furnace 5 to perform gas-phase etching for removing a natural oxide film formed on the front surface of the substrate W. Furthermore, the vapor phase etching is performed until immediately before the next step, that is, vapor phase growth. Next, the substrate W is cooled down to the vapor phase growth temperature (for example, 1050 ° C to 1180 ° C), and in the reaction furnace 5, the vapor phase growth gas, ie, a raw material gas (for example, trichlorosilane) and a carrier gas (for example, trichlorosilane) are supplied approximately horizontally. For example, hydrogen) and an optional doping gas (for example, PH ₃ ), a silicon single crystal film with a predetermined film thickness is vapor-grown on the front surface of the substrate W to form a silicon epitaxial wafer.

After that, after the reaction furnace 5 is cooled down to the take-out temperature (for example, 650 ° C.), the gate valve is opened, and the silicon epitaxial wafer is carried out of the reaction furnace 5 by the transfer robot 4 (S6). Next, the silicon epitaxial wafer is transferred to a cooling chamber (not shown), and after cooling in the cooling chamber, the silicon epitaxial wafer is transferred out of the epitaxial growth apparatus 1.

The steps S4 to S6 described above are sequentially performed on the substrates W in one batch in the substrate storage unit 2 one by one.

The above is the manufacturing sequence of the epitaxial wafer in this embodiment. Here, it is known that the back halo does not occur in the substrate in the initial stage of the batch, but it tends to occur in the second half of the batch (as the storage time in the substrate storage section becomes longer). On the other hand, in this embodiment, the substrate of the substrate storage unit 2 whose total concentration of NO ₂ and NO ₃ stored in the atmosphere is controlled to be 140 ng / m ³ or less is used as shown in the following examples. That is, the storage time in the substrate storage unit 2 is facilitated, and a high-quality epitaxial wafer in which generation of halo on the back surface (haze level) is suppressed can be obtained.

In addition, if the mechanism of suppressing the halo on the back surface by reducing the presence of NO ₂ and NO _{3 in} the atmosphere of the substrate storage unit 2 is speculated, because the presence of NO ₂ and NO _{3 in} the atmosphere of the substrate storage unit ₂ , The front and back surfaces of the substrate are gradually oxidized by exposure to an oxidizing atmosphere, and an oxide film is formed on the front and back surfaces. Regarding the method of attaching the oxide film, it is predicted that a thicker part and a thinner part of the oxide film will appear in the plane according to the flow method of the atmospheric gas to the substrate and the contact method with the substrate. The oxide film will not be completely removed during the heat treatment before epitaxial growth, and unevenness in the adhesion amount of polycrystalline silicon on the back surface of the substrate occurs in the removed portion and the portion where the oxide film remains, thereby generating halo. Therefore, it is considered that by managing the atmosphere of the substrate storage unit 2 such that the total concentration of NO ₂ and NO ₃ becomes 140 ng / m ³ or less, the substrate storage unit 2 can be prevented from becoming an oxidizing atmosphere and the occurrence of halo can be suppressed. Examples

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but these do not limit the present invention.

(Examples and Comparative Examples) In a monolithic epitaxial growth device having the same structure as that of FIG. 1, a P-type silicon single crystal substrate having a diameter of 300 mm and a main surface plane orientation (100) was used to form a film. Regarding a silicon single crystal substrate, a substrate polished on the back is prepared. Thereafter, the separately prepared substrates were cleaned, and the substrate storage unit of the two examples for managing the atmosphere so that the total concentration of NO ₂ and NO ₃ became 140 ng / m ³ or less as an example, and NO as a comparative example. The substrate storage section of two cases in an atmosphere with a total concentration of ₂ and NO ₃ exceeding 140 ng / m ³ was exposed for 6 hours, and epitaxial growth was performed in the same device. At this time, the NO ₂ concentration and the NO ₃ concentration of the substrate storage section were measured by ion chromatography analysis. Specifically, using a pump portion of the substrate to enhance the storage atmosphere, it is vented to the water and dissolved within the collector wherein the pure water was measured by ion chromatography of NO ₂ ^- ion concentration and the NO ₃ ^- ion concentration. The water obtained in the NO ₂ ^- concentration and the NO ₃ ^- ion concentration to the concentration of NO ₂ represent, respectively, become part of the atmosphere of the storage substrate and NO ₃ concentration by way conversion. In addition, it is assumed that the above-mentioned 6 hours is the atmospheric exposure time of the substrate in the latter half of one batch.

In the epitaxial layer film formation, the source gas was set to TCS (trichlorosilane), the flow rate of TCS was set to 10 L / min, and the flow rate of hydrogen gas as a carrier gas was set to 50 L / min, and the film thickness was 10 Reaction of μm undoped layer. Next, the back surface appearance evaluation and haze level evaluation of the epitaxial wafer after the reaction were performed. Moreover, the so-called haze is caused by the small unevenness on the front and back of the epitaxial wafer. If the front and back of the epitaxial wafer are observed using a spotlight or the like in a dark room, the light diffusely reflects and white haze appears. The haze level is an index related to the generation of halo on the back. If the haze level is larger, the possibility of halo on the back is higher.

The appearance of the back was evaluated by observing and evaluating the back in a dark room under a spotlight (200,000 lux). The haze level is evaluated by using the peak DWN-haze obtained by the DW (Darkfield Wide) mode of the particle counter SP1 of KLATencor.

As a reference example, an epitaxial wafer having undergone an epitaxial reaction within 10 minutes after the substrate was cleaned was prepared, and the same evaluation was performed. In the reference example, the epitaxial reaction was performed within 10 minutes after the substrate was cleaned in the exposure atmosphere of each of the NO ₂ concentration and the NO ₃ concentration in the 2 examples of the example and the 2 examples of the comparative example.

The evaluation order is shown in FIG. 3. In FIG. 3, the steps of S31 in the embodiment are the same as the steps of S3 in FIG. 2, that is, the management is performed so that the total of the NO ₂ concentration and the NO ₃ concentration in the atmosphere of the substrate storage section becomes 140 ng / m ³ or less. . On the other hand, in the step S31 of the comparative example, the total of the NO ₂ concentration and the NO ₃ concentration in the atmosphere of the substrate storage unit was managed so as to exceed 140 ng / m ³ . Moreover, in FIG. 3, the process of S7 is added after the process of S6 (the said external appearance evaluation and haze level evaluation). Otherwise, the procedure is the same as that of FIG. 2.

(Reference example) In the reference example, at any of the NO ₂ concentration and the NO ₃ concentration, no haze was recognized as hazy on the back of the wafer, and the peak DWN-haze was about 10 ppm.

(Example) Examples of the embodiment by ion chromatographic analysis to obtain concentration of NO _{3 2} / NO (i.e., the water has dissolved in an atmosphere of NO ₂ ^- / NO ₃ ^- ion concentration in the substrate storage portion becomes expressed The conversion of the NO ₂ / NO ₃ concentration in the atmosphere) is 1.2 / 1.5 (ng / m ³ ) in the first case, and 54.1 / 63.2 (ng / m ³ ) in the second case. In the evaluation of the appearance of the back surface, no haze was recognized as hazy for any of the wafers, and the peak value of DWN-haze was also 10 ppm or less, which was equivalent in quality to the reference example. In particular, the first case showed a lower value (below 8 ppm) and the result was better.

(Comparative Example) of Comparative Examples obtained by ion chromatographic analysis of the NO ₃ concentration of ₂ / NO (i.e., the water has dissolved in an atmosphere of NO ₂ ^- / NO ₃ ^- ion concentration in the substrate storage portion becomes expressed ₂ / NO ₃ concentrations on the manner of an atmosphere of NO is scaled earner) is in the first embodiment, ^{161.0 / 122.7 (ng / m 3} ), in the second embodiment of ^{451.2 / 223.8 (ng / m 3} ). In the evaluation of the appearance of the back surface, it was confirmed that the haze was not clear for any of the wafers. The peak DWN-haze was 33.5 ppm in the first case and 59.8 ppm in the second case, which was worse than the reference example. .

The relationship between the NO _x ion concentration and the DWN-haze peak in the examples and comparative examples is shown in FIGS. 4 and 5. Fig. 4 shows the relationship between NO ₂ concentration and the peak of DWN-haze, and Fig. 5 shows the relationship between the concentration of NO ₃ and the peak of DWN-haze. As can be seen from FIG. 4 and FIG. 5, with the decrease of NO ₂ and NO ₃ , the peak value of DWN- haze decreases, and the vicinity of 70 ng / m ³ or less is the same as the reference example, and there is no change in the peak value of DWN- haze.

In this way, it is shown that by using the present invention, even an epitaxial wafer with a long storage time (atmosphere exposure time) in the substrate storage section can reduce the halo on the back surface, especially by making the The total concentration of NO ₂ and NO ₃ is 140 ng / m ³ or less (more preferably 10 ng / m ³ or less), and back halo suppression can be effectively performed.

The present invention is not limited to the embodiments described above. The above-mentioned embodiment is an example, and those having substantially the same structure and technical effects described in the scope of patent application of the present invention and exhibiting the same effect are included in the technical scope of the present invention in any case. For example, the size of the substrate is not limited to 300 mm. It can also be applied to substrates below 200 mm or substrates larger than 300 mm. In addition, as long as it is a vapor-phase growth device for forming silicon, it is not limited to a monolithic epitaxial growth furnace, and can be applied to a batch type or the like.

1‧‧‧ Monolithic epitaxial growth device

2‧‧‧Substrate storage department

3‧‧‧ transport road

4‧‧‧ transfer robot

5‧‧‧Reactor

6‧‧‧ base

61‧‧‧Slot section of base

7‧‧‧ lights

8‧‧‧ support

10‧‧‧ Collector

11‧‧‧ tube

W‧‧‧ silicon semiconductor substrate

FIG. 1 is a schematic configuration diagram of a monolithic epitaxial growth device. FIG. 2 is a flowchart showing the manufacturing sequence of an epitaxial wafer. FIG. 3 is a flowchart showing an evaluation procedure of Examples and Comparative Examples. FIG. 4 is a graph showing the relationship between the concentration of NO ₂ in the exposed atmosphere after the substrate is cleaned and the peak DWN-haze of the epitaxial wafer. FIG. 5 is a graph showing the relationship between the NO ₃ concentration in the exposed atmosphere after the substrate was cleaned and the peak DWN-haze of the epitaxial wafer.

Claims (2)

An epitaxial wafer manufacturing method, which cleans a silicon semiconductor substrate polished on the backside and stores it in an ambient atmosphere with a total concentration of NO ₂ and NO ₃ of 140 ng / m ³ or less, and places the silicon semiconductor substrate on the silicon semiconductor substrate. The silicon epitaxial layer is vapor-grown. The method for manufacturing an epitaxial wafer according to claim 1, wherein the total amount is 10 ng / m ³ or less.