Method for cleaning a semiconductor wafer

Abstract

Method for cleaning a semiconductor wafer using a plurality of chemical tanks, wherein each of the chemical tanks of the plurality of chemical tanks contains a Standard Cleaning 2 (SC-2) solution, wherein In the first chemical tank used, out of the majority of chemical tanks used to clean a semiconductor wafer, the HCl concentration in the SC-2 solution contained in the first chemical tank used is 0.3 to 2 wt.%. In the final chemical tank of the majority of chemical tanks used to clean a semiconductor wafer, the HCl concentration in the SC-2 solution contained in the final chemical tank is 0.001 to 0.2 wt.%, and the final chemical tank has the lowest value of the HCl concentration in the SC-2 solution of the SC-2 solutions contained in the majority of chemical tanks used to clean a semiconductor wafer.

Description

TECHNICAL AREA

[0001] The present invention relates to a method for cleaning a semiconductor wafer. STATE OF THE ART

[0002] Previously, a cleaning process known as "RCA cleaning" using an SC-1 (Standard Cleaning 1) solution and an SC-2 (Standard Cleaning 2) solution was widely used to clean semiconductor wafers, such as silicon wafers. The SC-1 solution is an aqueous solution of ammonium hydroxide and hydrogen peroxide and is characterized by excellent performance in removing particles from the semiconductor wafer surface. The SC-2 solution is an aqueous solution of hydrochloric acid and hydrogen peroxide and is used to remove metal contaminants.

[0003] For example, patent literature 1 describes a method for cleaning a semiconductor wafer by using an SC-1 solution and an SC-2 solution to prevent anions from adhering to the semiconductor wafer surface when the SC-2 solution is used for cleaning (SC-2 cleaning). In this method, the SC-1 solution is used for cleaning (SC-1 cleaning) in such a way that a cationized metal remains on the surface of the semiconductor wafer. Furthermore, patent literature 2 discloses a method for cleaning semiconductor substrates in which two types of cleaning solutions, one of which is an acidic solution with a pH of about 2 or less (first cleaning solution) and the other an acidic solution with a pH of about 3 to 4 (second cleaning solution), are used successively to clean a semiconductor substrate.In a first cleaning step, the semiconductor substrate is cleaned with the first cleaning solution to convert metals on the surface of the semiconductor substrate into metal complex salts, and then in a second cleaning step, the semiconductor substrate is cleaned with the second cleaning solution to transfer the metal complex salts adsorbed on the surface of the semiconductor substrate into the second cleaning solution by osmotic pressure due to the pH difference between the first and second cleaning solutions. LIST OF CAPLETS PATENT LITERATURE Patent literature 1: JP 2005 - 64 276 A Patent Literature 2: US 5,472,513 A REVELATION OF THE INVENTION: A TASK SOLVED BY THE INVENTION

[0004] Since the SC-1 solution is alkaline, the wafer surface and the surfaces of various particles are both negatively charged at the time of SC-1 cleaning. Thus, the electrostatic repulsion between them prevents particle adhesion. However, since the SC-2 solution is acidic, the wafer surface and particle surfaces are not always charged with the same sign at the time of SC-2 cleaning. This leads to a greater likelihood of particle adhesion. Furthermore, the higher the concentration of HCl added to the SC-2 solution or the longer the SC-2 cleaning time, the more likely the particles are to adhere to the wafer surface. This deterioration of the particle level can be prevented by shortening the SC-2 cleaning time and reducing the HCl concentration in the SC-2 solution.In this case, however, the metal removal effect of the acid is reduced, so the level of metal contamination worsens.

[0005] The present invention was developed in response to the aforementioned problems. One object of the present invention is to provide a method for cleaning a semiconductor wafer which enables the improvement of the particle level during SC-2 cleaning of the semiconductor wafer without worsening the metal contamination level on the semiconductor wafer surface. MEANS OF SOLVING THE TASK

[0006] To achieve the preceding problem, the present invention provides a method for cleaning a semiconductor wafer using a plurality of chemical tanks, wherein each of the chemical tanks in the plurality of chemical tanks contains a Standard Cleaning 2 (SC-2) solution, wherein In the first chemical tank used, out of the majority of chemical tanks used to clean a semiconductor wafer, the HCl concentration in the SC-2 solution contained in the first chemical tank used is 0.3 to 2 wt.%. In the final chemical tank of the majority of chemical tanks used to clean a semiconductor wafer, the HCl concentration in the SC-2 solution contained in the final chemical tank is 0.001 to 0.2 wt.%, and the final chemical tank has the lowest value of the HCl concentration in the SC-2 solution of the SC-2 solutions contained in the majority of chemical tanks used to clean a semiconductor wafer.

[0007] In this semiconductor wafer cleaning process, the HCl concentration in the SC-2 solution in the final chemical tank is reduced to the lowest value (0.001 to 0.2 wt.%) of the SC-2 solutions found in the majority of chemical tanks. This results in minimal particle adhesion to the semiconductor wafer surface after SC-2 cleaning. Furthermore, the HCl concentration in the tank(s) preceding the final chemical tank is higher than in the final tank. This ensures sufficient removal of metal contaminants. Additionally, using multiple chemical tanks for SC-2 cleaning allows the subsequent tank(s) to remove any metal contaminants not completely removed by the first chemical tank.In the following description, a chemical tank containing an SC-1 solution and a chemical tank containing an SC-2 solution will each be referred to as an SC-1 tank and an SC-2 tank, respectively.

[0008] Additionally, the HCl concentration in an SC-2 solution contained in a second chemical tank and a subsequent chemical tank is preferably lower than in the first chemical tank.

[0009] According to such a method for cleaning a semiconductor wafer, metal impurities can be reliably removed and the deterioration of the particle level on the semiconductor wafer surface can be prevented even more reliably.

[0010] Furthermore, the semiconductor wafer is preferably a silicon wafer.

[0011] The method for cleaning a semiconductor wafer according to the present invention can be particularly suitable for cleaning a silicon wafer. IMPACT OF THE INVENTION

[0012] The method for cleaning a semiconductor wafer according to the present invention enables the improvement of the particle level without deteriorating the metal impurity level. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 shows a flow diagram illustrating an example of a method for cleaning a semiconductor wafer of the present invention. Fig. Figure 2 shows a graph comparing the number of particles of 26 nm or larger per silicon wafer after SC-2 cleaning by relative values ​​between Example 3 and Comparison Example 1. Fig. Figure 3 shows a graph comparing the number of particles of 45 nm or larger per silicon wafer after SC-2 cleaning by relative values ​​between Example 3 and Comparison Example 1. Fig. Figure 4 shows a graph comparing the number of particles of 120 nm or larger per silicon wafer after SC-2 cleaning according to relative values ​​between Example 3 and Comparison Example 1. Fig. Figure 5 shows a graph illustrating the relationships between metal impurity concentrations on the silicon wafer surface after SC-2 cleaning and the number of cleaning batches for SC-2 cleaning in Example 3. Fig. Figure 6 shows a graph illustrating a relationship between the zeta potential (ψ) of particles and the pH. Fig. Figure 7 shows a SEM / EDX-generated image of SiO2, characterized by a dotted line in Fig. 6 is surrounded. Fig. Figure 8 shows a SEM / EDX-generated image of Si, characterized by a dotted line in Fig. 6 is surrounded. Fig. Figure 9 shows a graph illustrating a relationship between the zeta potential (ψs) on a silicon wafer surface and the pH. Fig. Figure 10 shows a flow diagram illustrating an example of a process for cleaning a semiconductor wafer by using two SC-2 tanks containing SC-2 solutions of the same composition. Fig. Figure 11 shows a graph illustrating a relationship between the HCl concentration and the increased number of particles due to SC-2 purification. Fig. Figure 12 shows a graph illustrating a relationship between the SC-2 cleaning time and the increased amount of particles due to the SC-2 cleaning. Fig. Figure 13 shows a flow diagram illustrating an example of a process for cleaning a semiconductor wafer using only one SC-2 tank. Fig. Figure 14 shows a graph illustrating a relationship between the number of SC-2 tanks and the number of particles of 26 nm or larger per silicon wafer after SC-2 cleaning, expressed as relative values. Fig. Figure 15 shows a graph illustrating a relationship between the number of SC-2 tanks and the number of particles of 45 nm or larger per silicon wafer after SC-2 cleaning, expressed as relative values. Fig. Figure 16 shows a graph illustrating a relationship between the number of SC-2 tanks and the number of particles of 120 nm or larger per silicon wafer after SC-2 cleaning, expressed as relative values. Fig. Figure 17 shows a graph for the relative comparison of the relationship of the Al concentration on the silicon wafer surface after SC-2 cleaning with cleaning batches for SC-2 cleaning between the case of using one SC-2 tank and the case of using two SC-2 tanks. BEST WAYS TO IMPLEMENT THE INVENTION

[0013] The present invention is described in detail below.

[0014] As previously described, a method for cleaning a semiconductor wafer is desirable which enables the improvement of the particle level during SC-2 cleaning of the semiconductor wafer without worsening the metal contamination level on the semiconductor wafer surface.

[0015] The present inventors first investigated a relationship between the adhesion and the zeta potential of particles in a chemical tank containing an SC-2 solution. This relationship is subsequently described in relation to Fig. 6, Fig. 7, Fig. 8 to Fig. 9 described.

[0016] Fig. Figure 6 shows a graph illustrating the relationship between the zeta potential (ψ) of particles and pH. Fig. 6 include the particles Si, PSL (polystyrene latex), Si3N4 and SiO2. Furthermore, it shows Fig. 7 A photograph of SiO2 produced by SEM (Scanning Electro Microscopy) / EDX (Energy Dispersive X-ray Spectroscopy), which is defined by a dotted line in Fig. 6 is surrounded. Furthermore, it shows Fig. 8 A SEM / EDX-generated image of Si, characterized by a dotted line in Fig. 6 is surrounded. Furthermore, it shows Fig. 9 a graph to represent a relationship between the zeta potential (ψs) on a silicon wafer surface and the pH.

[0017] As in the dotted lines in Fig. The sections enclosed in 6 show the absolute values ​​of the zeta potentials of SiO2 and Si particles, etc., in an acidic environment (pH of approximately 2 to 4), i.e., in an SC-2 tank containing an acidic solution, which are smaller than those in an alkaline environment. Furthermore, as shown in a diagram enclosed by a dotted line in Fig. The section enclosed in Figure 9 shows the zeta potential on the silicon wafer surface, approximately 0, slightly higher on the positive side in an acidic environment. The theoretical formula for electrical repulsion (Vr) is as follows. Accordingly, it can be seen that the electrical repulsion between the silicon wafer surface and the particles in an SC-2 tank (acidic) is lower than in an SC-1 tank (alkaline). In particular, it is likely that SiO2 and Si particles, among others, whose absolute zeta potential values ​​are small in the acidic environment, adhere to the silicon wafer after SC-2 cleaning. Vr=εa4{(ψ2+ψs2)lnexp(2κx)−1exp(2κx)+2ψψslnexp(κx)+1exp(κx)−1} ψ: Particle surface potential (≈zeta potential) ψ s : Wafer surface potential (≈zeta potential) K: Debye constant (dependent on the ion concentration in the solution) α: Particle radius ε: Permittivity of the solution χ: Distance

[0018] Since the SC-1 solution is alkaline, the wafer surface and the surfaces of various particles are both negatively charged at the time of SC-1 cleaning. Thus, the electrostatic repulsion between them prevents the particles from adhering. However, since the SC-2 solution is acidic, the wafer surface and the particle surfaces are not always charged with the same sign at the time of SC-2 cleaning. This leads to the problem that particle adhesion is likely (see Fig. 6, Fig. 7, Fig. 8 to Fig. 9 and the preceding theoretical formula).

[0019] The inventors then investigated the increased number of particles resulting from cleaning when the conditions of the SC-2 tank were changed. The following are relationships between the SC-2 cleaning conditions and the increased number of particles with respect to... Fig. 10, Fig. 11 to Fig. 12 described. Fig. Figure 10 shows a flowchart illustrating an example of a process for cleaning a semiconductor wafer using two SC-2 tanks containing SC-2 solutions of the same composition. The reference conditions (REF) for the SC-2 cleaning were as follows: one SC-2 tank used first and one SC-2 tank used second were each set to a concentration (volume ratio) of HCl:H₂O₂:H₂O = 1:1:100, the temperature was set to 80 °C, and the time was set to 125 seconds. Furthermore, Figure 10 shows... Fig. 11 a graph to illustrate a relationship between the HCl concentration and the amount of particles increased by SC-2 purification. Fig. Figure 11 shows that the number of particles increased under REF conditions and when the HCl concentrations in the SC-2 solutions were doubled or halved, both in the first and second tanks used. Furthermore, it shows Fig. 12 a graph to show a relationship between the SC-2 cleaning time and the amount of particles increased by the SC-2 cleaning. Fig. Figure 12 shows the increased amount of particles under REF conditions and the increase achieved by doubling or halving the SC-2 cleaning time in both the first and second tanks used under REF conditions.

[0020] As in Fig. 10, Fig. 11 to Fig. As shown in Figure 12, the higher the concentration of HCl to be added to the SC-2 solution and the longer the SC-2 cleaning time, the more likely it is that the particles will adhere to the wafer surface.

[0021] Furthermore, the present inventors implemented SC-2 cleaning by reducing the number of SC-2 tanks from two to one. The following are related to Fig. 13, Fig. 14, Fig. 15, Fig. 16 to Fig. Seventeen relationships between particle level and metal impurity level after a silicon wafer was subjected to SC-2 cleaning using only one SC-2 tank are described. In this study, the cleaning conditions were the same as the REF conditions in Fig. 10; only the number of SC-2 tanks was reduced from two to one. Fig. Figure 13 shows a flowchart illustrating an example of the process for cleaning a semiconductor wafer using only one SC-2 tank. Furthermore, they show Fig. 14, Fig. 15 to Fig. 16 graphs illustrating a relationship between the number of SC-2 tanks and the number of particles per silicon wafer after SC-2 cleaning, expressed as relative values. Fig. Figure 14 shows the number of particles of 26 nm or larger, counted with a particle inspection system SP3 (manufactured by KLA-Tencor), Fig. Figure 15 shows the number of particles of 45 nm or larger, counted with a particle inspection system SP2 (manufactured by KLA-Tencor), and Fig. Figure 16 shows the number of particles 120 nm or larger, counted with SP2. Furthermore, it shows Fig. 17 a graph for the relative comparison of a relationship of the Al concentration on the silicon wafer surface after SC-2 cleaning with cleaning batches for SC-2 cleaning between the case of using one SC-2 tank and the case of using two SC-2 tanks.

[0022] As in Fig. 14, Fig. 15, Fig. 16 to Fig. Figure 17 shows that particle levels are improved by reducing the number of SC-2 tanks from two to one. However, in this case, increasing the number of cleaning batches raises the aluminum capture level and worsens the metal contamination level.

[0023] As in Fig. 10, Fig. 11, Fig. 12, Fig. 13, Fig. 14, Fig. 15, Fig. 16 to Fig. As shown in Figure 17, the deterioration of the particle level can be prevented by shortening the SC-2 cleaning time and reducing the HCl concentration in the SC-2 solution. However, in this case, the metal removal effect of the acid is reduced, so the metal contamination level deteriorates.

[0024] The present inventors then investigated the solution to the aforementioned problems. As a result, the inventors determined that the problems can be solved by a method for cleaning a semiconductor wafer using a chemical tank containing an SC-2 solution, characterized as follows. In the method, a plurality of chemical tanks are used, and the HCl concentration in one of the SC-2 solutions contained in the plurality of chemical tanks is reduced to the lowest value for final use in cleaning the semiconductor wafer. This finding led to the completion of the present invention.

[0025] The following are specific embodiments of the present invention. However, the present invention is not limited to these.

[0026] As previously described, in the semiconductor wafer cleaning process of the present invention, a plurality of SC-2 tanks are used for the SC-2 cleaning of a semiconductor wafer. The HCl concentration in the SC-2 solution contained in the plurality of SC-2 tanks is reduced to the lowest possible value (0.001 to 0.2 wt.%) for final use in cleaning a semiconductor wafer. In such a semiconductor wafer cleaning process, the HCl concentration in the SC-2 solution contained in the chemical tank is reduced to the lowest possible value (0.001 to 0.2 wt.%) of the SC-2 solutions contained in the plurality of chemical tanks. This results in minimal particle adhesion to the semiconductor wafer surface after SC-2 cleaning.Furthermore, metal contaminants can be sufficiently removed because the HCl concentration in the tank(s) preceding the final chemical tank is higher than in the final tank. Moreover, since the majority of chemical tanks used in SC-2 cleaning are used, even if metal contaminants are not completely removed by the first chemical tank, the subsequent tank(s) will remove them.

[0027] In this case, the HCl concentration in an SC-2 solution contained in a second chemical tank and a subsequent chemical tank is preferably lower than that in the first chemical tank. This ensures reliable removal of metal impurities and even more reliably prevents the deterioration of the particle level on the semiconductor wafer surface.

[0028] The semiconductor wafer cleaned according to the present invention is not particularly limited. Besides a silicon wafer, an elemental semiconductor such as germanium, a compound semiconductor such as GaAs or InP, or similar materials can also be used. In particular, the method for cleaning a semiconductor wafer according to the present invention can be used especially suitable for cleaning a silicon wafer.

[0029] The following is the method for cleaning a semiconductor wafer of the present invention with regard to Fig. 1. A case is described below in which two SC-2 tanks are used, and the SC-2 solutions contained in the second SC-2 tank have a lower HCl concentration than the solution in the first tank used for cleaning a semiconductor wafer. However, the present invention is not limited to this. For example, the present invention can also use three SC-2 tanks, such that the SC-2 solutions contained in the first and second SC-2 tanks have the same HCl concentration, while the SC-2 solution in the final SC-2 tank has a lower HCl concentration than the solution in the first and second tanks used for cleaning a semiconductor wafer.Alternatively, although three SC-2 tanks are used, a semiconductor wafer can also be cleaned with SC-2 solutions contained in these SC-2 tanks, provided that the HCl concentrations decrease in the following order: first tank used > second tank used > third tank used. The number of SC-2 tanks used in the present invention must be a plurality. For example, 2 to 5 tanks can be used.

[0030] First, a semiconductor wafer undergoes SC-1 cleaning ( Fig. 1(a)). For example, an SC-1 tank is filled with an aqueous solution of ammonium hydroxide and hydrogen peroxide (SC-1 solution), and the semiconductor wafer is immersed in the SC-1 solution to clean it. The material of the SC-1 tank is not particularly restricted. For example, an SC-1 tank made of silicate glass can be used.

[0031] The semiconductor wafer that has undergone SC-1 cleaning is then rinsed with pure water ( Fig. 1(b), (c)). Ultrapure water can be used in this process. In the method for cleaning a semiconductor wafer as in Fig. As shown in Figure 1, the ultrapure water rinsing process is carried out a total of four times; however, these ultrapure water rinsing conditions can be the same or different.

[0032] The semiconductor wafer, which has undergone ultrapure water rinsing, is then subjected to SC-2 cleaning ( Fig. 1(d)). For example, an SC-2 tank is filled with an aqueous solution of hydrochloric acid and hydrogen peroxide (SC-2 solution), and the semiconductor wafer is immersed in the SC-2 solution to clean it. The material of the SC-2 tank is not particularly restricted. For example, an SC-2 tank made of silicate glass can be used.

[0033] The composition of the SC-2 solution in the first SC-2 tank used is not particularly restricted. The SC-2 solution can be used with the same composition as a conventional SC-2 solution for cleaning according to a conventional procedure. However, the HCl concentration in the SC-2 solution of the first tank used must be higher than that in the second tank used, as described below. The HCl concentration in the SC-2 solution of the first tank used is 0.3 to 2 wt%. The SC-2 solution of the first tank used can have a pH of, for example, 1 to 4.

[0034] The H2O2 concentration in the SC-2 solution of the first tank used is not particularly limited and can, for example, be 0.01 to 2 wt.%.

[0035] The temperature of the SC-2 solution in the first tank used is not particularly limited and can, for example, range from 40 to 90 °C.

[0036] The time required for the first SC-2 cleaning is not particularly limited and can be shorter than when using only one SC-2 tank. This is because multiple SC-2 tanks are used in the present invention. The cleaning time can, for example, be 50 to 200 seconds.

[0037] The semiconductor wafer that has undergone the first SC-2 cleaning process is then subjected to a second SC-2 cleaning process ( Fig. 1(e)). In the method for cleaning a semiconductor wafer as in Fig. Figure 1 shows two SC-2 tanks prepared such that the HCl concentration in the SC-2 solution in the subsequent tank is lower than in the preceding tank. The amount of hydrochloric acid in the subsequent tank is very small; however, the pH is acidic. Thus, the HCl concentration in the SC-2 solution in the subsequent tank is lower than in the preceding tank, resulting in minimal particle adhesion. Even if the metal impurities are not completely removed by the preceding tank, removal and therefore cleaning are still possible because the SC-2 solution in the second tank is acidic. The HCl concentration in the SC-2 solution of the second tank is 0.001 to 0.2 wt%. The SC-2 solution in the second tank can have a pH of, for example, 2 to 6.

[0038] The temperature of the SC-2 solution in the second tank is not particularly restricted and can, for example, range from 40 to 90 °C. The temperature of the SC-2 solution in the first tank and the SC-2 solution in the second tank can be the same or different.

[0039] The duration of the second SC-2 cleaning cycle is not strictly limited and can, for example, range from 50 to 200 seconds. The duration of the first and second SC-2 cleaning cycles can be the same or different.

[0040] In the present invention, when semiconductor wafers are cleaned in a batch, the SC-2 solutions for each batch can be replaced with fresh solutions. To reduce costs, individual solutions can be used for a predetermined number of batches, for example, up to 80 batches. In such a case, the metal contamination level is also hardly affected, since the present invention uses a plurality of SC-2 tanks. The number of semiconductor wafers treated in a batch is not particularly limited. The number can, for example, be 5 to 25.

[0041] The semiconductor wafer that has undergone the second SC-2 cleaning process is then rinsed with pure water ( Fig. 1(f), (g)).

[0042] The semiconductor wafer, which has undergone the fourth pure water rinse, is then dried ( Fig. 1(h)). EXAMPLES

[0043] The present invention is described in more detail below with reference to examples and comparative examples. However, the present invention is not limited to the examples described below. (Example 1)

[0044] According to the in Fig. In the flow diagram shown in Figure 1, mirror-polished, boron-doped p-type single-crystal silicon wafers with a diameter of 300 mm were cleaned. In the examples and comparative examples described below, the cleaning was carried out by treating 25 silicon wafers in a single batch.

[0045] First, the silicon wafers underwent SC-1 cleaning using a silicate glass SC-1 tank ( Fig. 1(a)). Under SC-1 purification conditions, the concentration (volume ratio) was NH4OH:H2O2:H2O=1:1:20, the temperature was 70 °C and the time was 125 seconds.

[0046] Subsequently, the silicon wafers that had undergone SC-1 cleaning were subjected to a pure water rinse using ultrapure water twice ( Fig. 1(b), (c)).

[0047] First, the silicon wafers that had undergone pure water rinsing were subjected to SC-2 cleaning using a previously used SC-2 tank made of silicate glass ( Fig. 1(d)). For the first SC-2 cleaning conditions, the HCl concentration was 0.4 wt.%, the H2O2 concentration was 0.4 wt.%, the pH was 1, the temperature was 80 °C and the time was 125 seconds.

[0048] Subsequently, the silicon wafers that had undergone the first SC-2 cleaning were subjected to a second SC-2 cleaning using a second SC-2 tank made of silicate glass ( Fig. 1(e)). As the second SC-2 cleaning conditions, the HCl concentration was 0.2 wt.%, the H2O2 concentration was 0.4 wt.%, the pH was 1, the temperature was 80 °C and the time was 125 seconds.

[0049] Subsequently, the silicon wafers that had undergone the second SC-2 cleaning process were subjected to a pure water rinse using ultrapure water twice ( Fig. 1(f), (g)).

[0050] The silicon wafers that had undergone the fourth pure water rinse were then dried ( Fig. 1(h)). (Example 2)

[0051] Silicon wafers were purified according to the same procedure as in Example 1, except that the HCl concentration in the second SC-2 purification was changed to 0.04 wt.%. (Example 3)

[0052] Silicon wafers were purified according to the same procedure as in Example 1, except that the HCl concentration in the second SC-2 purification was changed to 0.01 wt.%. (Example 4)

[0053] Silicon wafers were purified according to the same procedure as in Example 1, except that the HCl concentration and the H2O2 purification in the second SC-2 purification were changed to 0.01 wt.% and 0.1 wt.% respectively. (Comparative example 1)

[0054] According to the in Fig. In the flow diagram shown in Figure 10, silicon wafers were cleaned as in Example 1. Specifically, the silicon wafers were cleaned according to the same procedure as in Example 1, except that the HCl concentration in the second SC-2 cleaning was changed to 0.4 wt.%. (The HCl concentration was 0.4 wt.% in both the first and second tanks used.) (Comparative example 2)

[0055] According to the in Fig. In the flow diagram shown in Figure 13, silicon wafers were cleaned as in Example 1. Specifically, the silicon wafers were cleaned according to the same procedure as in Example 1, except that the second SC-2 cleaning was omitted. (Only one SC-2 tank was used.)

[0056] The metal contamination levels and particle levels in examples and comparison examples were evaluated as follows. First, before SC-2 cleaning (for example, in the cleaning process in Fig. 1, after Fig. 1(c), but before Fig. 1(d)) Particles were pre-measured using the SP3 particle inspection system (manufactured by KLA-Tencor). After SC-2 cleaning (for example, in the cleaning process in Fig. 1, after Fig. In the first instance (1(h)), the particles were measured again under the specified conditions. When comparing the results before and after washing to determine whether particles had re-adhered, these particles were counted as elevated points. In these examples and comparison examples, deteriorated particle quantities were investigated based on the elevated points. Furthermore, in the metal contamination analysis after SC-2 cleaning, the surface contamination concentrations of the silicon wafers were evaluated by ICP-MS (inductively coupled plasma mass spectroscopy) analysis.

[0057] Table 1 shows the results for metal contamination levels and particle levels. Table 1 shows the average result for each pair of silicon wafers cleaned in batch 80. [Table 1]

[0058] As shown in Table 1, Comparative Example 1 involved two SC-2 tanks containing SC-2 solutions with sufficient chemical concentrations. (The HCl concentrations in the first and second tanks used were 0.4 wt%.) Thus, the metal impurity levels were favorable, but the particle growth rate was large. Since the number of tanks in Comparative Example 2 was reduced from 1 to 2, the particle growth rate was small; however, a large amount of Al was detected. This indicates a deterioration in metal removal capability. In Examples 1 through 4, however, the HCl concentration in the second tank used was set lower than in the first tank used. Thus, the particle growth rate was small, and the amount of Al detected was also at or below the lower limit of detection, which was favorable.

[0059] Furthermore, as in Fig. 2, Fig. 3 to Fig. 4. As shown in Example 3, where SC-2 cleaning was carried out in the downstream tank under a low concentration condition, the particle number in all particle diameter types was reduced compared to Example 1, where SC-2 cleaning was carried out in the upstream and downstream tanks under the same concentration condition. Furthermore, as in Fig. 5 shown under the conditions in Example 3, the metal impurity levels did not deteriorate even when the number of cleaning batches was increased.

[0060] Fig. 2, Fig. 3 to Fig. Figure 4 shows graphs comparing the number of particles per silicon wafer after SC-2 cleaning according to relative values ​​between Example 3 and Comparison Example 1. Fig. 2, Fig. 3 to Fig. Figure 4 shows each average result of 25 silicon wafers cleaned in the 80th batch. Fig. Figure 2 shows the number of particles of 26 nm or larger, measured with SP3. Fig. Figure 3 shows the number of particles of 45 nm or larger, measured with SP2, and Fig. Figure 4 shows the number of particles 120 nm or larger, measured with SP2. Furthermore, it shows Fig. 5 a graph to illustrate the relationships between metal impurity concentrations on the silicon wafer surface after SC-2 cleaning and the number of cleaning batches for SC-2 cleaning in Example 3.

Claims

[1] Method for cleaning a semiconductor wafer using a plurality of chemical tanks, wherein each of the chemical tanks of the plurality of chemical tanks contains a Standard Cleaning 2 (SC-2) solution, wherein In the first chemical tank used, out of the majority of chemical tanks used to clean a semiconductor wafer, the HCl concentration in the SC-2 solution contained in the first chemical tank used is 0.3 to 2 wt.%. In the final chemical tank of the majority of chemical tanks used to clean a semiconductor wafer, the HCl concentration in the SC-2 solution contained in the final chemical tank is 0.001 to 0.2 wt.%, and the final chemical tank has the lowest value of the HCl concentration in the SC-2 solution of the SC-2 solutions contained in the majority of chemical tanks used to clean a semiconductor wafer. [2] Method for cleaning a semiconductor wafer according to claim 1, wherein the HCl concentration in a chemical tank subsequently used and an SC-2 solution contained as a second chemical tank is lower than in the chemical tank used first. [3] Method for cleaning a semiconductor wafer according to claim 1 or 2, wherein the semiconductor wafer is a silicon wafer.

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