JP4857738B2 - Semiconductor wafer cleaning method and manufacturing method - Google Patents

Description

  The present invention relates to a cleaning method performed in a process of manufacturing a semiconductor wafer such as silicon, and a semiconductor wafer manufacturing method using the cleaning method, and more particularly, a metal contaminant that adheres during a manufacturing process of a semiconductor substrate (wafer). It is related with the method of removing effectively.

  In the manufacture of semiconductor devices, the presence of metal or particulate contaminants on the wafer itself can adversely affect the performance characteristics of the device. A semiconductor substrate (wafer) used for a semiconductor device is manufactured by processing an ingot block grown mainly by a pulling method (Czochralski method, CZ method) into a mirror-like thin plate. The processing steps mainly include a slicing step of slicing an ingot block into a wafer shape, a chamfering step of chamfering the outer peripheral portion of the sliced wafer, and flattening the chamfered wafer using lapping or surface grinding. A polishing step, an etching step for removing the processing distortion of the flattened wafer, and a polishing step for polishing both or one side of the etched wafer. Furthermore, it has a heat treatment process, an inspection process, and various cleaning processes.

Conventionally, (1) NH ₄ OH + H ₂ O ₂ + H ₂ O mixed solution immersion treatment (for cleaning a semiconductor substrate, pre-cleaning in a thermal oxidation process, pre-cleaning in a CVD process, or cleaning a semiconductor wafer in phosphorus glass removal) 1: 1: 5, 80 ° C., 10 minutes), (2) pure water rinse, (3) HF + H ₂ O immersion treatment (containing 1% HF), (4) pure water rinse, (5) HCl + H ₂ O ₂ + H ₂ So-called RCA cleaning method (W. Kern et.al.:RCA) in which O mixture solution immersion treatment (1: 1: 6, 80 ° C., 10 minutes), (6) pure water rinsing, and (7) drying are continuously performed. Reveiw, 31, p.187,1970), the mixing ratio of each treatment liquid, immersion time, heating temperature, and the order of washing treatment with the washing liquids of (1), (2) and (3) above. A cleaning method that is appropriately selected and used in accordance with the process, such as replacement, is generally used.

Here, (1) NH ₄ OH + H ₂ O ₂ + H ₂ O mixed liquid is effective for removing foreign substances such as organic substances and heavy metals, and (3) HF + H ₂ O adheres to the substrate surface simultaneously with the removal of the oxide film. It is said that (5) HCl + H ₂ O ₂ + H ₂ O mixed solution is effective for removing heavy metals.

  Conventionally, the above-described cleaning has been performed on a mirror-polished wafer that is close to the subsequent process in the semiconductor device manufacturing process and the semiconductor substrate (wafer) manufacturing process (see, for example, Patent Document 1). This is because the RCA cleaning takes a long process, and it is only necessary that the finally mirror-polished wafer is clean, and it is considered that it is practically wasteful to apply it to a wafer being processed.

  However, in recent years, the influence of contaminants before polishing, particularly in the etching process, is becoming important. In the etching process, the surface is in an active state, and the etchant used contains a large amount of contaminants, so there is a concern that the contaminants may adhere to the wafer surface and diffuse inside.

  Generally, the influence of contaminants on the wafer during the wafer processing is reduced by subsequent polishing and cleaning. In addition, various types of gettering techniques for capturing contaminants have produced devices that do not affect the devices.

  However, when a processing step or polishing step with a large mechanical action such as surface grinding is performed after etching, contaminants diffuse into the wafer, and due to the problem of insufficient gettering capability due to low temperature of the device process, Therefore, it has become necessary to lower the contamination level of the wafer.

  Therefore, it is important that the etched wafer is free from contaminants. For this reason, it has become necessary to perform processing so as to prevent contamination as much as possible even before the final cleaning, particularly in the etching process. In particular, contamination of heavy metals such as Ni and Cu, which have a large diffusion coefficient and affect device characteristics, is a problem. Efficient treatment is required to avoid as much as possible these heavy metals from adhering to the wafer surface and diffusing into the wafer.

In such a case, the conventionally known NH ₄ OH + H ₂ O ₂ + H ₂ O mixed liquid (hereinafter referred to as SC-1 cleaning) or HCl + H ₂ O ₂ + H ₂ O mixed liquid (SC-2 cleaning) is used after etching. It is conceivable to wash it.

  Even if such a cleaning liquid is used, there is a certain effect, but a more efficient cleaning method is required in terms of the liquid life, ease of handling, the number of steps, and the cleaning ability.

JP-A-8-115894

  The present invention has been made in view of such problems, and provides a cleaning method and a manufacturing method of a semiconductor wafer that can effectively remove contaminants attached to the wafer after etching, particularly heavy metals. It is intended.

The present invention has been made to solve the above-described problems. At least, a wafer sliced into a thin plate is flattened by lapping and / or surface grinding, and the flattened wafer is alkali-etched, and then the alkali- Provided is a method for cleaning a semiconductor wafer, wherein the etched wafer is cleaned with an acidic solution containing citric acid / hydrogen peroxide solution .

As described above, by washing the alkali-etched wafer with an acidic solution containing citric acid / hydrogen peroxide solution, contaminants, particularly heavy metals, attached to the wafer after the alkali etching can be effectively removed. Citric acid ionizes the metal on the wafer surface by the effect of acid, and further, chelate complex of ionized metal is formed by the chelate effect of citric acid, and adhesion of the metal to the wafer can be prevented. In addition, hydrogen peroxide can prevent a redox reaction by raising the standard potential and prevent metal deposition on the wafer surface. In addition, oxides such as iron oxide and copper oxide are also generated by the effect of hydrogen peroxide, and the effect of further reducing the metal adhering to the wafer can be obtained. Furthermore, compared with ammonia (NH ₄ OH), hydrochloric acid (HCl), hydrofluoric acid (HF), etc., citric acid is easy to handle and can be safely handled in operation. Moreover, since this citric acid / hydrogen peroxide solution has almost no etching action on the silicon wafer, there is no fear that the surface roughness or thickness of the wafer is reduced.

In this case, the cleaning can be performed by immersing the semiconductor wafer in the acidic solution .

  As described above, if the cleaning is performed by immersing the semiconductor wafer in the acidic solution, the cleaning can be performed efficiently and easily because, for example, the cleaning can be continuously performed by an alkali etching apparatus following the alkali etching.

The acidic solution containing citric acid / hydrogen peroxide solution may have a citric acid concentration of 0.005% to 0.5% and a hydrogen peroxide concentration of 0.01% to 1.0%. Is preferred .

  Thus, even if the concentrations of citric acid and hydrogen peroxide are low, a sufficient cleaning effect can be obtained, so that the cost of the chemical solution can be reduced.

Moreover, it is preferable that the pH of the acidic solution is greater than 3 and 4 or less .

  Thus, when the pH of the acidic solution is set to be greater than 3 and 4 or less, the metal is stably ionized and the chelate effect of citric acid is sufficiently exhibited, so that a higher cleaning effect can be obtained.

Moreover, it is preferable to perform the said washing | cleaning as the liquid temperature of the said acidic solution being 20 degreeC or more and 60 degrees C or less, and washing | cleaning time 60 seconds or more .

  In this way, if the cleaning is performed at a liquid temperature of the acidic solution of 20 ° C. or more and 60 ° C. or less and a cleaning time of 60 seconds or more, contaminants attached to the wafer after alkali etching can be effectively removed. . Moreover, the life of a chemical | medical solution can be extended by setting it as 60 degrees C or less.

Further, the present invention provides a method for manufacturing a semiconductor wafer in which at least a wafer sliced into a thin plate is flattened by lapping and / or surface grinding, and the flattened wafer is alkali etched and then polished. Further, the present invention provides a method for producing a semiconductor wafer, characterized by washing with an acidic solution containing citric acid / hydrogen peroxide solution before polishing the wafer .

In this way, by cleaning the alkaline-etched wafer with an acidic solution containing citric acid / hydrogen peroxide before polishing, contaminants attached to the wafer after alkaline etching can be effectively removed. The possibility of contaminants diffusing into the wafer by the polishing process can be reduced. Therefore, a high-quality wafer with a high cleanliness can be produced. In the washing, citric acid ionizes the metal on the wafer surface by the effect of acid, and further, chelate complex of ionized metal is formed by the chelate effect of citric acid, preventing adhesion of metal to the wafer. it can. In addition, hydrogen peroxide can prevent a redox reaction by raising the standard potential and prevent metal deposition on the wafer surface. In addition, oxides such as iron oxide and copper oxide are also generated by the effect of hydrogen peroxide, and the effect of further reducing the metal adhering to the wafer can be obtained. Furthermore, compared with ammonia (NH ₄ OH), hydrochloric acid (HCl), hydrofluoric acid (HF), etc., citric acid is easy to handle and can be safely handled in operation. Moreover, since this citric acid / hydrogen peroxide solution has almost no etching action on the silicon wafer, there is no fear that the surface roughness or thickness of the wafer is reduced.

The cleaning is preferably performed by immersing the semiconductor wafer in the acidic solution .

  Thus, if the cleaning is performed by immersing the semiconductor wafer in the acidic solution, it is efficient because it can be continuously cleaned following alkali etching, for example, with an alkali etching apparatus, and can be easily performed. Compared with RCA cleaning, the wafer can be manufactured in a short time and at a low cost.

The acidic solution containing citric acid / hydrogen peroxide solution may have a citric acid concentration of 0.005% to 0.5% and a hydrogen peroxide concentration of 0.01% to 1.0%. Is preferred .

  Thus, even if the concentrations of citric acid and hydrogen peroxide are low, a sufficient cleaning effect can be obtained, so that the cost of the chemical solution can be reduced.

Moreover, it is preferable that the pH of the acidic solution is greater than 3 and 4 or less .

  Thus, when the pH of the acidic solution is set to be greater than 3 and 4 or less, the metal is stably ionized and the chelate effect of citric acid is sufficiently exhibited, so that a higher cleaning effect can be obtained.

Moreover, it is preferable to perform the said washing | cleaning as the liquid temperature of the said acidic solution being 20 degreeC or more and 60 degrees C or less, and washing | cleaning time 60 seconds or more .

  In this way, if the cleaning is performed at a liquid temperature of the acidic solution of 20 ° C. or more and 60 ° C. or less and a cleaning time of 60 seconds or more, contaminants attached to the wafer after alkali etching can be effectively removed. . Moreover, the life of a chemical | medical solution can be extended by setting it as 60 degrees C or less.

  As described above, according to the present invention, there are provided a semiconductor wafer cleaning method and manufacturing method for cleaning an alkali-etched wafer with an acidic solution containing citric acid / hydrogen peroxide solution. By performing such cleaning, it is possible to effectively remove contaminants, particularly heavy metals, attached to the wafer after alkaline etching, and the contaminants are transferred to the inside of the wafer through processing and polishing processes with large mechanical action. The possibility of spreading can be reduced. Therefore, a high-quality wafer with a high cleanliness can be produced. Further, with regard to the liquid life, ease of handling, the number of steps, cost, and cleaning ability, it has become possible to perform cleaning with a higher cleaning effect than before.

Hereinafter, although this invention is demonstrated in detail, this invention is not limited to these.
As described above, when a processing step with a large mechanical action such as surface grinding is performed after etching, contaminants diffuse into the wafer or due to the problem of insufficient gettering ability due to low temperature of the device process. Therefore, it has become necessary to lower the contamination level. In particular, it is desirable to easily remove metal contamination not only after polishing the wafer but also at an earlier stage. Accordingly, the present inventors have found that contaminants, particularly heavy metals such as Cu, can be effectively removed by cleaning the etched semiconductor wafer with an acidic solution containing citric acid / hydrogen peroxide solution, and completed the present invention. I let you.

  That is, in the semiconductor wafer cleaning method of the present invention, at least the wafer sliced into a thin plate is flattened by lapping and / or surface grinding, and the flattened wafer is alkali-etched, and then the alkali-etched wafer is removed. It is characterized by washing with an acidic solution containing citric acid / hydrogen peroxide solution.

  In addition, the method for manufacturing a semiconductor wafer according to the present invention includes a method for manufacturing a semiconductor wafer in which at least a wafer sliced into a thin plate is flattened by lapping and / or surface grinding, and the flattened wafer is polished after alkali etching. In the method, the wafer etched with alkali is washed with an acidic solution containing citric acid / hydrogen peroxide solution before polishing.

  Thus, by washing the wafer in an acid solution after alkali etching, the metal on the wafer surface is easily ionized. Citric acid is conventionally known to have a chelating effect, and a metal ionized with citric acid forms a chelate complex, masks the metal ion, and prevents the metal from adhering to the wafer. In addition, by mixing hydrogen peroxide water in the same solution, the standard potential can be raised by hydrogen peroxide to prevent the oxidation-reduction reaction and to prevent the deposition of metal on the wafer surface. In addition, oxides such as iron oxide and copper oxide are also generated by the effect of hydrogen peroxide, and the effect of further reducing the metal adhering to the wafer can be obtained.

By washing the semiconductor wafer with an acidic solution in which citric acid and hydrogen peroxide solution are mixed in the same chemical solution in this way, contaminants, particularly heavy metals, can be effectively removed from the wafer surface. In particular, in the previous stage of the wafer manufacturing process such as the alkali etching process, the metal level is relatively high, and it is insufficient to remove this by the chelate effect of citric acid alone, and it should be mixed with hydrogen peroxide. Can effectively prevent reattachment. When cleaning is performed immediately after alkali etching, for example, when metal removal cleaning is incorporated in an etching apparatus, ammonia (NH ₄ OH), hydrochloric acid (HCl), and hydrofluoric acid (HF) used in RCA cleaning are used. It is a safety issue, and there are many processes, and both time and cost are heavy. On the other hand, citric acid is easy to handle and can be safely processed.
Therefore, the cost can be kept low. In addition, the cleaning solution of the present invention, unlike HF + HNO ₃ + acetic acid, which is an acid etching solution conventionally used for etching silicon wafers, has almost no etching action on silicon, and therefore surface roughness may occur. The flatness is not deteriorated by reducing the thickness.

Here, FIG. 1 is a schematic view for explaining an example of a semiconductor wafer manufacturing method and cleaning method of the present invention.
First, a silicon single crystal ingot pulled up by the Czochralski method or the like is sliced and processed into a thin disk-shaped wafer (slicing step, FIG. 1A).

  Subsequently, the wafer is mechanically ground (lapped) in order to remove the work-affected layer induced in the wafer surface layer by the cutting process in the slicing process and to flatten the wafer (flattening process, FIG. 1B). . This flattening may be performed by surface grinding (including double-head grinding).

  Further, the wafer is subjected to alkali etching (alkali etching process, FIG. 1 (c)) in order to remove the processing distortion generated on the wafer surface layer in the above process.

  The process up to this point is not particularly different from the conventional method, and other processes such as chamfering, cleaning, and heat treatment may be added. In addition, some processes may be omitted, replaced, repeated, etc. Various processes can be employed.

  Next, it wash | cleans with the acidic solution containing a citric acid and hydrogen peroxide solution (FIG.1 (d)). Since the surface of the wafer after alkali etching is in an active state and the etchant used contains a large amount of contaminants, the contaminants are likely to adhere to the wafer surface, and the removal thereof is important. By washing with an acidic solution containing citric acid / hydrogen peroxide solution as in the present invention, contaminants, particularly heavy metals such as Cu, can be efficiently removed from the alkali-etched wafer.

Although the cleaning method is not particularly limited, for example, the semiconductor wafer can be immersed in an acidic solution containing citric acid / hydrogen peroxide solution.
In addition, since the cleaning method of the present invention is performed after the alkali etching as described above, it is efficient to integrate it with an alkali etching apparatus. By doing in this way, it can wash | clean continuously following alkali etching. Although it is dangerous to use strong acid such as hydrochloric acid in the alkaline tank due to the problem of heat generation, etc., the production method and cleaning method of the present invention using the weak acid citric acid and hydrogen peroxide water as the cleaning solution are safe. is there.

  The concentration of the acidic solution containing citric acid / hydrogen peroxide solution is not particularly limited, but the citric acid concentration is 0.005% to 0.5%, and the hydrogen peroxide concentration is 0.01% to 1. It is preferably 0% or less. Since a sufficient cleaning effect can be obtained even at such a very low concentration, the cost of the chemical solution can be reduced.

Further, the pH of the acidic solution containing citric acid / hydrogen peroxide solution is not particularly limited, but the pH is preferably more than 3 and 4 or less. The stock solution of the citric acid aqueous solution has a pH of about 1.9, and the stock solution of hydrogen peroxide solution has a pH of about 4.2. For example, the pH at which Cu metal is stably converted to Cu ions is 4 or less. Further, when the chelating effect of citric acid alone is confirmed, the chelating effect is weak on the strong acid side, and it becomes larger as it becomes the weak acid or alkali side. FIG. 2 is a graph showing the relationship between the chelate effect of citric acid alone and pH. As can be seen from FIG. 2, when the pH is lowered, the chelating effect is lowered, but when the pH is higher than 3, a sufficient chelating effect can be obtained. Therefore, if the pH of an acidic solution containing citric acid / hydrogen peroxide solution is washed to be greater than 3 and less than or equal to 4, the metal is stably ionized and the effect of preventing contamination due to the chelate effect is great. Can be obtained.

  In addition, it is preferable to perform the cleaning by setting the temperature of the acidic solution containing citric acid / hydrogen peroxide solution to 20 to 60 ° C. and the cleaning time to 60 seconds or more. If the liquid temperature of the acidic solution is 60 ° C. or lower, hydrogen peroxide is difficult to decompose and a sufficient cleaning effect can be obtained. In order to extend the life of the chemical solution, it is preferable to perform the treatment at a low temperature in order to suppress the decomposition of hydrogen peroxide as much as possible. In consideration of the cleaning effect, it is more preferable to perform the treatment within the range of room temperature in the range of about 20 ° C to 30 ° C.

  The cleaning time may be set as appropriate depending on the process status (contamination status), the chemical concentration, and the processing temperature. However, when the cleaning time is used as described above, a sufficient effect can be obtained by processing for 60 seconds or more. . Furthermore, if the treatment time is extended to about 180 seconds, a more stable cleaning effect can be obtained. However, even if it is too long, the effect will not increase any more, so it is better to set it to 10 minutes or less.

  Subsequent steps are not particularly different from the conventional method, and various conventional steps such as omission / replacement / repetition of some steps may be employed in the present invention.

  After washing with the acidic solution containing the citric acid / hydrogen peroxide solution, a polishing step for polishing the wafer is performed (FIG. 1E). The polishing method is not particularly limited, and a generally used method can be applied. For example, a wafer having a large diameter can be mirror-polished by holding a wafer on a polishing head and slidingly contacting a polishing surface plate to which a polishing cloth is attached while supplying the polishing liquid in a single wafer mode.

A semiconductor wafer can be obtained by the above manufacturing method and cleaning method.
In the present invention, contaminants, particularly metal contaminants, can be effectively removed by washing the wafer with an acidic solution containing citric acid / hydrogen peroxide solution after alkaline etching. Thus, since it grind | polishes after removing heavy metal contamination, a clean and high-quality wafer can be obtained easily, without diffusing a metal impurity in a wafer.

Examples of the present invention will be described below, but the present invention is not limited thereto.
Example 1
First, a silicon single crystal ingot pulled up by the Czochralski method was sliced and processed into a thin disk-like wafer (diameter 300 mm, P-type, orientation <100>) (slicing step, FIG. 1A).

  After chamfering the periphery of the wafer, the wafer was then mechanically ground (lapped) to remove the work-affected layer induced on the wafer surface by cutting in the slicing process and to flatten the wafer (flattening process) FIG. 1 (b)).

  Furthermore, in order to remove the processing distortion generated in the wafer surface layer in the above process, the wafer was subjected to alkali etching (alkali etching process, FIG. 1C). An aqueous NaOH solution having a concentration of 52% was used as the etchant, and the liquid temperature was 80 ° C.

Next, using a batch type cleaning machine, the wafer after alkaline etching was cleaned with an acidic solution containing citric acid / hydrogen peroxide solution (FIG. 1 (d)). A mixed solution of citric acid, hydrogen peroxide, and pure water was used as a cleaning solution (hereinafter, this solution may be abbreviated as citric acid / perwater). The concentration was adjusted to 0.5% (volume%) citric acid aqueous solution and 1.0% (volume%) hydrogen peroxide (H ₂ O ₂ ). After the adjustment, the temperature of the chemical solution was adjusted to 25 ° C. and washing was performed for 180 seconds. After washing, it was rinsed in pure water rinse and rotated by spin drying to dry.
Thereafter, a polishing step for polishing the wafer was performed (FIG. 1E).

(Comparative Example 1)
As a comparative example, the slicing step, flattening step, alkaline etching step, rinsing, and drying under the same conditions as in Example 1 except that the wafer after alkaline etching was not washed with an acidic solution containing citric acid / hydrogen peroxide solution -A polishing process was performed.

  For the silicon wafers obtained in Example 1 and Comparative Example 1, the impurity concentrations of Fe, Ni, and Cu were measured. As a measuring method, the surface of the wafer was etched by about 0.1 μm with hydrofluoric acid, and the liquid was analyzed by atomic absorption. The obtained results are shown in FIG.

  As is clear from FIG. 3, it was confirmed that a silicon wafer in which Fe and Cu are significantly reduced after polishing can be obtained by cleaning with an acidic solution containing citric acid / hydrogen peroxide solution.

(Example 2)
A slicing step and a flattening step were performed under the same conditions as in Example 1. Thereafter, in the alkaline etching step, a wafer that was processed in the initial stage of use of the etchant and a wafer that was processed in the final stage of use of the etchant that processed many silicon wafers were obtained (approximately 500 sheets to be cleaned: alkaline etching step). FIG. 1 (c)). An aqueous NaOH solution having a concentration of 52% was used as the etchant, and the liquid temperature was 80 ° C.

Next, using a batch-type cleaning machine, the wafer etched with alkali at the initial stage and the end stage of use of the etchant was cleaned with an acidic solution containing citric acid and hydrogen peroxide (FIG. 1 (d)). A mixed solution of citric acid, hydrogen peroxide, and pure water was used as the cleaning solution. The concentration was adjusted to 0.20% (volume%) citric acid and 0.21% (volume%) hydrogen peroxide (H ₂ O ₂ ). After the adjustment, the chemical temperature was adjusted to 30 ° C., and cleaning was performed for 180 seconds. After washing, it was rinsed in pure water rinse and rotated by spin drying to dry.

(Comparative Example 2)
As a comparative example, a slicing step, a flattening step, and the like under the same conditions as in Example 2 except that the wafer etched with alkali at the initial use stage and the final use stage of the etchant was not washed with an acidic solution containing citric acid / hydrogen peroxide solution. An alkali etching process, rinsing and drying were performed.

(Comparative Example 3)
In addition, as a comparative example, a slicing step and a flattening step are performed under the same conditions as in Example 2 except that an alkali-etched wafer is washed with 0.20% (volume%) citric acid at the beginning and end of use of the etchant. -Alkali etching process, rinse, and drying were performed.

  For the silicon wafers obtained in Example 2 and Comparative Examples 2 and 3, the impurity concentration of Cu was measured. As a measuring method, the wafer surface was etched by about 0.1 μm with hydrofluoric acid, and the liquid was analyzed by atomic absorption. The obtained results are shown in FIG.

  As is clear from FIG. 4, when cleaning was performed using citric acid / overwater, the Cu level was below the lower limit of detection regardless of whether the etchant in alkaline etching was in the initial stage of use or at the end of use. In addition, when washed with citric acid / perwater, the impurity level is lower than when washed with citric acid alone, indicating the effect of mixing citric acid and hydrogen peroxide. The Cu level was high when no cleaning was performed after alkali etching. Therefore, it was confirmed that a silicon wafer with reduced Cu was obtained before polishing by washing with an acidic solution containing citric acid / hydrogen peroxide solution.

(Example 3)
Under the same conditions as in Example 1, a slicing step, a flattening step, and an alkali etching step were performed.
Next, using a batch type cleaning machine, the wafer after alkaline etching was cleaned with an acidic solution containing citric acid / hydrogen peroxide solution. A mixed solution of citric acid, hydrogen peroxide, and pure water was used as the cleaning solution. The concentration was adjusted to 0.20% (volume%) citric acid and 0.21% (volume%) hydrogen peroxide (H ₂ O ₂ ). After the adjustment, the chemical temperature was adjusted to 30 ° C., and cleaning was performed for 180 seconds. After washing, it was rinsed in pure water rinse and rotated by spin drying to dry.

(Comparative Example 4)
As a comparative example, a slicing step, a flattening step, an alkaline etching step, rinsing and drying were performed under the same conditions as in Example 3 except that the wafer after alkaline etching was SC-1 washed. The concentration of the SC-1 cleaning solution was adjusted to 3% ammonia (volume%) and 3% hydrogen peroxide water (volume%).

  For the silicon wafers obtained in Example 3 and Comparative Example 4, the impurity concentration of Cu was measured. As a measuring method, the wafer surface was etched by about 0.1 μm with hydrofluoric acid, and the liquid was analyzed by atomic absorption. The obtained results are shown in FIG.

  As is clear from FIG. 5, it was confirmed that a silicon wafer having a Cu content reduced as compared with SC-1 cleaning can be obtained by cleaning with an acidic solution containing citric acid / hydrogen peroxide solution.

Example 4
Under the same conditions as in Example 1, a slicing step, a flattening step, and an alkali etching step were performed.
Next, using a batch type cleaning machine, the wafer after alkaline etching was cleaned with an acidic solution containing citric acid / hydrogen peroxide solution. A mixed solution of citric acid, hydrogen peroxide, and pure water was used as the cleaning solution. Concentration and pH were adjusted as follows.

(1) Citric acid 0.005%: Overwater 0.01% ··· pH 3.7
(2) Citric acid 0.01%: 0.01% overwater ... pH 3.5
(3) Citric acid 0.01%: Overwater 0.3% ··· pH 3.5
(4) Citric acid 0.04%: Overwater 0.3% ··· pH 3.3
(5) Citric acid 0.07%: Overwater 0.3% ··· pH 3.1
(6) Citric acid 0.07%: Overwater 0.5% ··· pH 3.2

  After the adjustment, the chemical temperature was adjusted to 30 ° C., and cleaning was performed for 180 seconds. After washing, it was rinsed in pure water rinse and rotated by spin drying to dry.

(Comparative Example 5)
As a comparative example, the slicing step, flattening step, alkaline etching step, rinsing and drying were performed under the same conditions as in Example 4 except that the wafer after alkali etching was washed with citric acid having a concentration of 0.20% (volume%). went.

  For the silicon wafers obtained in Example 4 and Comparative Example 5, the impurity concentration of Cu was measured. As a measuring method, the wafer surface was etched by about 0.1 μm with hydrofluoric acid, and the liquid was analyzed by atomic absorption. The obtained result is shown in FIG.

  As is clear from FIG. 6, in the examples where the cleaning was performed with an acidic solution containing citric acid / hydrogen peroxide solution, the Cu levels were all lower than the detection limit, which was significantly higher than the comparative example cleaned with citric acid alone. It was confirmed that a silicon wafer with reduced Cu was obtained.

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

  For example, it goes without saying that the cleaning method and the manufacturing method of the present invention can be applied not only to silicon wafers but also to various semiconductor wafers such as compound semiconductors.

It is the schematic explaining an example of the washing | cleaning method and manufacturing method of the semiconductor wafer of this invention. It is a graph which shows the relationship between the pH of a citric acid, and a chelate effect. It is a graph which shows the result of having measured the metal concentration of the surface about the wafer of Example 1 and Comparative Example 1 (a vertical axis is a relative value). It is a graph which shows the result of having measured the Cu density | concentration of the surface about the wafer of Example 2 and Comparative Examples 2 and 3 (a vertical axis is a relative value). It is a graph which shows the result of having measured the surface Cu density | concentration about the wafer of Example 3 and the comparative example 4 (a vertical axis | shaft is a relative value). It is a graph which shows the result of having measured the surface Cu density | concentration about the wafer of Example 4 and the comparative example 5 (a vertical axis | shaft is a relative value).

Claims (8)

The sliced wafers into a thin plate is flattened by lapping and / or surface grinding, the flattened wafer after alkali etching, there the alkali etched wafer with an acid solution containing citric acid-hydrogen peroxide And cleaning with an acid solution having a citric acid concentration of 0.005% to 0.5% and a hydrogen peroxide concentration of 0.01% to 1.0% .   2. The method for cleaning a semiconductor wafer according to claim 1, wherein the cleaning is performed by immersing the semiconductor wafer in the acidic solution. The method for cleaning a semiconductor wafer according to claim 1 or claim 2, characterized in that pH 4 or less larger than 3 of the acidic solution. The washing, the acid solution at a liquid temperature of 20 ° C. to 60 ° C. or less, cleaning the semiconductor wafer according to any one of claims 1 to 3, characterized in that for cleaning time as 60 seconds or more Method. In a method of manufacturing a semiconductor wafer in which a wafer sliced into a thin plate is flattened by lapping and / or surface grinding, and the flattened wafer is polished after alkali etching, and then the wafer subjected to alkali etching is polished before polishing. An acidic solution containing an acid / hydrogen peroxide solution, which is washed with an acidic solution having a citric acid concentration of 0.005% to 0.5% and a hydrogen peroxide concentration of 0.01% to 1.0%. A method for manufacturing a semiconductor wafer. 6. The method of manufacturing a semiconductor wafer according to claim 5 , wherein the cleaning is performed by immersing the semiconductor wafer in the acidic solution. The method of manufacturing a semiconductor wafer according to claim 5 or claim 6, characterized in that 4 or less greater than 3 the pH of the acidic solution. The semiconductor wafer production according to any one of claims 5 to 7 , wherein the cleaning is performed at a liquid temperature of the acidic solution of 20 ° C or higher and 60 ° C or lower and a cleaning time of 60 seconds or longer. Method.

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