WO2019082450A1 - Epitaxial wafer manufacturing method - Google Patents

Abstract

After preparing a silicon semiconductor substrate whose back surface is polished and cleaning the prepared substrate, a plurality of wafers are put into the substrate storage unit 2 as one lot. The total concentration of NO ₂ and NO _{3 in} the atmosphere of the substrate storage unit 2 is controlled to be 140 ng / m ³ or less. The substrates stored in the substrate storage unit 2 are transported one by one to the reaction furnace 5 to grow a silicon epitaxial layer in a vapor phase. As a result, it is possible to provide a method which makes it possible to manufacture a high quality epitaxial wafer by suppressing the generation of the back surface halo depending on the passage of time after substrate cleaning.

Description

Method of manufacturing epitaxial wafer

The present invention relates to a method of forming a silicon epitaxial layer on a silicon semiconductor substrate to obtain an epitaxial wafer.

Conventionally, a CVD (Chemical Vapor Deposition) apparatus etc. are known as a substrate processing apparatus used for a manufacturing process of semiconductor substrates, such as a silicon semiconductor substrate. As an example of the epitaxial processing of a silicon semiconductor substrate, a method of vapor phase epitaxial growth of an epitaxial layer made of single crystal silicon on the surface of a silicon semiconductor substrate has been developed. As the manufacturing method, the substrate is horizontally disposed on the susceptor housed in the reactor for epitaxial growth, and then the substrate is heated at a high temperature by a heat source such as a halogen lamp while rotating the susceptor around a vertical rotation axis 1000 ° C. to 1200 ° C.) and flow silicon source gas. Thereby, silicon generated by thermal decomposition (and reduction) of the reaction gas is deposited on the substrate surface, and an epitaxial layer made of single crystal silicon is grown on the substrate surface.

Here, although the manufacture of epitaxial wafers is normally performed in a clean room maintained at high cleanliness, in regard to clean rooms, Patent Documents 1 and 2 introduce exhaust air from a clean work space such as a clean room to perform cleaning. It is described that various contaminants such as ammonia, nitrogen oxides (NOx), sulfur oxides (SOx), etc. are made to have a certain concentration or less as the cleaning in circulating supply to the cleaning work space after carrying out. . For example, when it comes to nitrogen oxide (NOx) as one of the pollutants, it is described that it is 1 ppb or less (Patent Document 1) and 0.1 ppb or less (Patent Document 2).

JP 2009-138977 JP, 2009-138978, A

By the way, when forming a silicon epitaxial layer on a silicon semiconductor substrate, when the back surface of the substrate is a polished surface of silicon, a trace amount of Poly-Si may be deposited also on the back surface due to penetration of silicon source gas to the back surface. is there. It is considered that when the generation of a slight amount of Poly-Si is uneven in the back surface of the substrate, a cloud called a halo and surface roughening occur. The generation of the back surface halo becomes remarkable as the time from the substrate cleaning to the epitaxial reaction becomes longer, and the halo pattern tends to be dark. The generation of the back surface halo leads to the deterioration of the yield of the silicon epitaxial process due to the appearance defect and is a problem. Even if epitaxial wafers are manufactured in the clean room proposed in Patent Documents 1 and 2, the above problems still exist, that is, the back surface halo becomes remarkable as the time from the substrate cleaning to the epitaxial reaction becomes longer. , Hello pattern also darkens.

The present disclosure has been made in view of the above problems, and it is an object of the present disclosure to provide a method capable of suppressing the generation of a back surface halo depending on the passage of time after substrate cleaning and manufacturing a high quality epitaxial wafer. I assume.

The present inventor estimates that the occurrence of the back surface halo is different depending on the exposure time of the substrate (the time from cleaning to epitaxial growth) and the difference in the halo generation tendency due to the difference in the exposure environment due to the influence of the exposure atmosphere of the substrate. did. Therefore, when the exposure atmosphere was evaluated, there is a correlation between the concentration of NO ₂ and NO _{3 in} the exposure atmosphere and the generation of the back surface halo, in particular, the exposure atmosphere having a total concentration of NO ₂ and NO ₃ of 140 ng / m ³ or less. It has been found that the generation of the back surface halo can be suppressed by using the back surface polished silicon substrate stored in the present invention, resulting in the present invention.

That is, in the method of manufacturing an epitaxial wafer according to one aspect of the present disclosure, after cleaning the back-polished silicon semiconductor substrate, the total concentration of NO ₂ and NO ₃ is stored in an environmental atmosphere of 140 ng / m ³ or less This is a manufacturing method of vapor-phase growing a silicon epitaxial layer on a semiconductor substrate.

According to one aspect of the present disclosure, it is possible to manufacture a high quality epitaxial wafer in which the occurrence of the back surface halo is suppressed.

Further, 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. According to this, when the silicon epitaxial layer is vapor-phase grown on the silicon semiconductor substrate, the haze level on the back surface of the substrate can be further suppressed, and the generation of the back surface halo can be further suppressed.

It is a schematic block diagram of a single wafer type epitaxial growth apparatus. It is the flowchart which showed the manufacturing procedure of the epitaxial wafer. It is the flowchart which showed the evaluation procedure in an Example and a comparative example. And NO ₂ concentration in the exposure atmosphere after the substrate cleaning is a diagram showing the relationship of DWN-HazePeak value of the back surface of the epitaxial wafer. And NO ₃ concentration in the exposure atmosphere after the substrate cleaning is a diagram showing the relationship of DWN-HazePeak value of the back surface of the epitaxial wafer.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present embodiment, an example in which the present invention is applied to the manufacture of an epitaxial wafer using a single wafer type epitaxial growth apparatus will be described. First, the configuration of a single wafer type epitaxial growth apparatus will be described with reference to FIG.

In the single wafer type epitaxial growth apparatus 1 of FIG. 1, a substrate storage unit 2 in which a plurality of cleaned silicon semiconductor substrates W (hereinafter, may be simply referred to as a substrate W) are stored as one lot and the substrates are stored. A transport path 3 provided adjacent to the portion 2, a transport robot 4 for transporting one of the substrates W provided in the transport path 3 and stored in the substrate storage portion 2 to a reaction furnace 5 described later, and transport A reaction furnace 5 provided adjacent to the passage 3 for performing a reaction of vapor-phase growing a silicon epitaxial layer on the surface of the substrate W transferred by the transfer robot 4 and provided in the reaction furnace 5 A susceptor 6 on which the substrate W is mounted so that the front and back surfaces of W are horizontal, and a lamp 7 provided around the reaction furnace 5 to heat the inside of the reaction furnace 5 are provided. The epitaxial growth apparatus 1 also includes a drive unit (not shown) for rotating the susceptor 6 during epitaxial growth.

The susceptor 6 is supported by a support shaft 8 so as to be formed in a disk shape and whose upper surface is horizontal. In the upper surface of the susceptor 6, a pocket portion 61 for mounting the substrate W is formed. The pocket portion 61 is formed in a circle having a diameter slightly larger than that of the substrate W. Further, the pocket portion 61 is formed in a stepped shape so as to contact only the back surface outer peripheral portion of the substrate W, for example, and to form a gap with the other substrate back surface portion. The pocket portion 61 may be formed to be in contact with the entire back 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 substrate W is blocked between the substrate storage unit 2 and the transport path 3 so as not to be accessible. When the gate valve is opened, the substrate W can be conducted between the substrate storage unit 2 and the transport path 3 so that the substrate W can enter and leave. Similarly, also between the transport path 3 and the reaction furnace 5, a gate valve (not shown) for switching between conduction and shut-off thereof is provided.

The substrate storage unit 2, the transport path 3 and the reactor 5 are shielded from the atmosphere. Further, in order to prevent foreign matter (water, oxygen, metal, etc.) from mixing into the substrate storage unit 2, the substrate storage unit 2 is provided with a configuration for substituting with an inert gas such as nitrogen. Specifically, a pump (not shown) for evacuating the substrate storage unit 2 and a gas pipe (not shown) for introducing an inert gas such as nitrogen into the substrate storage unit 2 are connected. The gas pipe is connected to a container (not shown) for storing an inert gas (atmospheric gas of the substrate storage unit 2) such as nitrogen. Similarly, a gas pipe (not shown) for introducing an inert gas such as nitrogen is also connected to the transport path 3. In FIG. 1, in order to evaluate the atmosphere in the substrate storage unit 2, an impinger 10 containing a collection liquid such as pure water and a part of the atmosphere in the substrate storage 2 are arranged in the impinger 10. And a tube 11 leading to the

Next, the manufacturing procedure of the epitaxial wafer of the present embodiment will be described. FIG. 2 is a flowchart showing the procedure. First, a silicon semiconductor substrate W is prepared (S1). The diameter, crystal orientation, conductivity type, resistivity, etc. of the substrate W to be prepared are not particularly limited. As a substrate W to be prepared, a polished wafer is prepared which has been mirror-polished on both the front and back surfaces.

A general manufacturing method of a polished wafer will be described. A single crystal ingot having a specific crystal orientation is manufactured using a Czochralski (CZ) method or the like (single crystal growth step). The side surface of the manufactured single crystal ingot is ground to adjust the outer diameter, and one notch indicating the crystal orientation is formed on the outer periphery of the single crystal ingot (cylindrical grinding process). The single crystal ingot is sliced into thin disk-like wafers along a specific crystal orientation (slicing step), and its outer peripheral portion is chamfered (chamfering step) in order to prevent cracking and chipping of the sliced wafer. Thereafter, both surfaces of the chamfered wafer are ground and planarized at the same time (double-head grinding process), and processing distortion remaining on the chamfered and ground wafer is etched and removed (etching process). Further, the front and back surfaces of the wafer are polished to mirror finish (polishing step). A polished wafer is obtained through these steps.

Next, the prepared substrate W (polished wafer) is subjected to cleaning such as RCA cleaning including SC-1 cleaning, SC-2 cleaning, etc. to remove the polishing agent and foreign substances from the substrate W (see FIG. S2).

Next, a plurality of substrates W after cleaning are set as one lot in the substrate storage unit 2, and the substrate storage unit 2 is caused to stand by until an epitaxial reaction is performed (S3). At this time, the atmosphere is controlled such 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, the concentration of _NO 2, NO ₃ is be managed such that the 70 ng / ^{m 3} or less, the total concentration of NO ₂ and NO ₃ becomes 140 ng / ^{m 3} or less. _{Incidentally,} if the total concentration of NO 2, NO ₃ is in the 140 ng / ^{m 3} or _less, one of the concentrations of NO 2, NO ₃ may be exceeded 70 ng / ^{m 3.} The total concentration of NO ₂ and NO ₃ in the atmosphere in the substrate storage unit 2 is more preferably 10 ng / m ³ or less. By setting the total concentration to 10 ng / m ³ or less, as shown in Examples described later, the haze level on the back surface of the obtained epitaxial wafer can be further suppressed.

In addition, it can be confirmed as follows, for example whether the said total density | concentration is 140 ng / m < ³ > or less. That is, a part of the atmosphere in the substrate storage unit 2 is vented to a collection liquid such as pure water in the impinger 10 through the pipe 11 by a pump (not shown) or the like, and dissolved in the collection liquid. Ion concentration and NO ₃ ^{- -} NO ₂ in the collected liquid in ion concentration measured by a technique such as ion chromatographic analysis. The resulting NO ₂ ^- ion concentration and NO ₃ ^- ion concentration is converted to respective concentrations as an indication NO ₂ concentration and NO ₃ concentration in the atmosphere of substrate storage section 2, after conversion NO ₂ concentration and NO ₃ Make sure that the total concentration is 140 ng / m ³ or less.

For reducing the concentration of NO ₂ and NO ₃ , for example, it is conceivable to introduce a high purity inert gas such as nitrogen into the substrate storage unit 2 after evacuating the inside of the substrate storage unit 2 with a pump. It is also conceivable to improve the purity of the circulation atmosphere by providing a chemical filter for collecting and removing NOx in the circulation atmosphere of the substrate storage unit 2 in the gas introduction pipe.

Next, one of the substrates W stored in the substrate storage unit 2 is selected, and the selected substrate W is transported to the reaction furnace 5 (S4). Specifically, the substrate W stored in the substrate storage unit 2 by the transfer robot 4 by opening the gate valve between the substrate storage unit 2 and the transfer passage 3 and the gate valve between the transfer passage 3 and the reaction furnace 5 respectively. The substrate W is transferred to the reaction furnace 5, and the transferred substrate W is placed on the pocket portion 61 of the susceptor 6. Then close each gate valve. In the example of FIG. 1, the substrate storage unit 2 is provided with a cassette (not shown) for storing the substrate W in the vertical direction, and an example is shown in which reactions are sequentially performed from the substrate W stored under this cassette. ing. In addition, the atmosphere in the conveyance path 3 is substituted by inert gas, such as nitrogen, for example.

Next, in the reaction furnace 5, a silicon single crystal film is formed on the surface of the substrate W by vapor phase growth (S5). Specifically, the substrate W is heated to a heat treatment temperature (for example, 1050 ° C. to 1200 ° C.) by the lamp 7 while rotating the susceptor 6. Next, hydrogen gas is introduced into the reaction furnace 5 to perform vapor phase etching for removing the natural oxide film formed on the surface of the substrate W. Note that this vapor phase etching is performed until just before vapor phase growth which is the next step. Next, the substrate W is cooled to a vapor phase growth temperature (for example, 1050 ° C. to 1180 ° C.), and a vapor phase growth gas, ie, source gas (for example, trichlorosilane), carrier gas (for example, hydrogen) and necessary Accordingly, a dopant gas (for example, PH ₃ ) is supplied substantially horizontally, respectively, to vapor-phase grow a silicon single crystal film of a predetermined film thickness on the surface of the substrate W, thereby forming a silicon epitaxial wafer.

Thereafter, the reactor 5 is taken out and cooled to a temperature (for example, 650 ° C.), and then the gate valve is opened, and the silicon epitaxial wafer is unloaded from the reactor 5 by the transfer robot 4 (S6). Then, the carried-out silicon epitaxial wafer is transported to a cooling chamber chamber (not shown), cooled in the cooling chamber chamber, and then carried out of the epitaxial growth apparatus 1.

The steps S4 to S6 are carried out one by one on the substrate W for one lot stored in the substrate storage unit 2.

The above is the manufacturing procedure of the epitaxial wafer of this embodiment. Here, conventionally, the back surface halo is not generated in the initial stage substrate of the lot, but the back surface halo tends to be generated in the second half of the lot (as the storage time in the substrate storage section becomes longer). On the other hand, in the present embodiment, since the substrate stored in the substrate storage unit 2 in which the total concentration of NO ₂ and NO _{3 in} the atmosphere is 140 ng / m ³ or less is used, as shown in the following example, Even if the storage time in the storage unit 2 is long, it is possible to obtain a high quality epitaxial wafer in which the occurrence of the back surface halo (haze level) is suppressed.

Note that the reduction of NO _2, NO ₃ present in the atmosphere of a substrate storage section 2 when estimating the mechanism of the back surface halo can be suppressed, that is NO _2, NO ₃ present in the atmosphere of a substrate storage section 2, of the substrate The front surface and the back surface are exposed to the oxidizing atmosphere and oxidation progresses gradually to form an oxide film on the front surface and the back surface. It is expected that depending on how the atmosphere gas flows to and from the substrate, the oxide film can be formed in places where the oxide film is thick and thin in the plane. This oxide film can not be completely removed by heat treatment before epitaxial growth, and due to unevenness in the amount of adhesion of Poly-Si on the back surface of the substrate between the removed portion and the remaining portion, halo occurs. Therefore, by controlling the atmosphere of the substrate storage unit 2 so that the total concentration of NO ₂ and NO ₃ is 140 ng / m ³ or less, the substrate storage unit 2 is prevented from becoming an oxidizing atmosphere, and halo generation occurs. It is thought that it can control.

Hereinafter, the present invention will be more specifically described by way of examples and comparative examples, but these are not intended to limit the present invention.

(Example, comparative example)
In the single wafer type epitaxial growth apparatus having the same configuration as that of FIG. 1, film formation was performed using a P-type silicon single crystal substrate with a diameter of 300 mm and a plane orientation of (100) on the main surface. The silicon single crystal substrate prepared the back-polished substrate. Thereafter, as an example, the substrate storage unit of two examples in which the atmosphere was controlled so that the total concentration of NO ₂ and NO ₃ is 140 ng / m ³ or less, and the total concentration of NO ₂ and NO ₃ as a comparative example 140 ng / m ³ The prepared substrates were exposed to the substrate storage parts in two cases of atmospheres exceeding 6 hours for 6 hours after cleaning, and epitaxial growth was performed in the same apparatus. At that time, the measurement of the NO ₂ concentration and the NO ₃ concentration in the substrate storage part was performed by ion chromatography analysis. Specifically, the atmosphere of the substrate storage unit is pumped up, aerated into pure water in the impinger and dissolved, and the NO ₂ ^- ion concentration and the NO ₃ ^- ion concentration in the pure water are measured by ion chromatography did. The NO ₂ ^- ion concentration and the NO ₃ ^- ion concentration in the obtained pure water were converted so as to indicate the NO ₂ concentration and the NO ₃ concentration in the atmosphere of the substrate storage unit, respectively. In addition, the said six hours assume the atmosphere exposure time in the board | substrate of the latter half of 1 lot.

In the epitaxial layer film formation, the source gas was TCS (trichlorosilane), the flow rate of TCS was 10 L / min, the flow rate of hydrogen as a carrier gas was 50 L / min, and a reaction of a non-doped layer with a film thickness of 10 μm was performed. Then, the back surface appearance evaluation of the reacted epitaxial wafer and the haze level were evaluated. In addition, haze is a minute unevenness generated on the surface and the back surface of the epitaxial wafer, and when the surface and the back surface of the epitaxial wafer are observed using a condensing lamp or the like in a dark room, light is irregularly reflected and appears white cloudy It is a thing. The haze level is an index correlating to the occurrence of the back surface halo, and when the haze level is large, the back surface halo is likely to occur.

Back surface appearance evaluation was performed in a dark room, under the focusing lamp (200,000 lux), and was subjected to back surface observation and evaluation. The haze level was evaluated by the DWN-HazePeak value obtained in the DW (Darkfield Wide) mode in particle counter SP1 of KLATencor.

In addition, as a reference example, an epitaxial wafer having an epitaxial reaction within 10 minutes after substrate cleaning was also prepared and subjected to the same evaluation. In the reference example, an epitaxial reaction was performed within 10 minutes after substrate cleaning with respect to the exposure atmosphere of each of the NO ₂ concentration and the NO ₃ concentration of the two examples of the example and the two examples of the comparative example.

The above evaluation procedure is shown in FIG. In FIG. 3, the process of S31 in the embodiment is the same as the process of S3 of FIG. 2, that is, the total of the NO ₂ concentration and the NO ₃ concentration in the atmosphere of the substrate storage unit is 140 ng / m ³ or less I managed to. On the other hand, in the step of S31 in the comparative example, the total of the NO ₂ concentration and the NO ₃ concentration in the atmosphere of the substrate storage unit was controlled to exceed 140 ng / m ³ . Moreover, in FIG. 3, the process (the said back surface external appearance evaluation and haze level evaluation) of S7 is added after the process of S6. Other than that, it is the same as the procedure of FIG.

(Reference example)
In the reference example, no cloudiness which is considered to be a halo was observed on the back surface of the wafer at any of the NO ₂ concentration and the NO ₃ concentration, and the DWN-HazePeak value was about 10 ppm.

(Example)
_NO 2 / NO ₃ concentration obtained by ion chromatography analysis in Example (i.e., pure water was dissolve atmosphere _NO ² - / NO ₃ ^- ion concentration, _NO in the atmosphere of the substrate storage section 2 / It is 1.2 / 1.5 (ng / m ³ ) in the first case, 54.1 / 63.2 (ng / m ³ ) in the second case, and converted to show the concentration of NO ₃ there were. In the back surface appearance evaluation, no cloudiness which is considered to be a halo was confirmed in any of the wafers, and the DWN-HazePeak value was 10 ppm or less, which was the same quality as the reference example. In particular, the first case showed a lower value (8 ppm or less), which was a better result.

(Comparative example)
_NO 2 / NO ₃ concentration obtained by ion chromatography analysis of the comparative example (i.e., pure water was dissolve atmosphere _NO ² - / NO ₃ ^- ion concentration, _NO in the atmosphere of the substrate storage section 2 / NO ₃ which was converted to be a indicates the concentration) 161.0 / 122.7 at first case (ng ^{/ m} 3), in the second case at ^{451.2 / 223.8 (ng / m 3} ) there were. In the back surface appearance evaluation, any wafer was considered to be a halo, and the DWN-HazePeak value was 33.5 ppm in the first case and 59.8 ppm in the second case, which was worse than in the reference example.

The relationship between the NOx ion concentration and the DWN-HazePeak value in the example and the comparative example is shown in FIG. 4 and FIG. FIG. 4 shows the relationship between the NO ₂ concentration and the DWN-HazePeak value, and FIG. 5 shows the relationship between the NO ₃ concentration and the DWN-HazePeak value. 4. From FIG. 4 and FIG. 5, the DWN-HazePeak value decreases as NO ₂ and NO ₃ decrease, and there is no change in the DWN-HazePeak value similar to the reference example at around 70 ng / m ³ or less I understand.

Thus, by applying the present invention, it has been shown that back surface halo reduction is possible even for an epitaxial wafer having a long storage time (atmosphere exposure time) in the substrate storage unit, and in particular, the substrate storage unit the total concentration of NO ₂ and NO ₃ in the atmosphere 140 ng / ^{m 3} or less (more preferably 10 ng / ^{m 3} or less) by the can effectively implement the back surface halo suppression.

The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and has substantially the same configuration as the technical idea described in the claims of the present invention, and the same effects can be obtained by any embodiments. It is included in the technical scope of the invention. For example, the substrate size is not limited to 300 mm, and can be applied to a substrate of 200 mm or less or a substrate larger than 300 mm. Moreover, if it is a vapor phase growth apparatus which forms a film into silicon, you may apply not only to a single wafer type epitaxial growth furnace but to a batch type etc.

Reference Signs List 1 single wafer type epitaxial growth apparatus 2 substrate storage unit 3 transfer path 4 transfer robot 5 reactor 6 susceptor 61 susceptor pocket portion 7 ramp 8 support shaft 10 impinger

Claims (2)

After cleaning the back-polished silicon semiconductor substrate, it is stored in an environmental atmosphere having a total concentration of NO ₂ and NO ₃ of 140 ng / m ³ or less, and a silicon epitaxial layer is vapor-phase grown on the silicon semiconductor substrate. Method of manufacturing an epitaxial wafer. The said total is 10 ng / m < ³ > or less, The manufacturing method of the epitaxial wafer of Claim 1 characterized by the above-mentioned.

Images