Pretreatment method, silicon substrate recombination lifetime measurement method, and passivation treatment method

Abstract

To provide a pretreatment method that allows pretreatment in a water-soluble environment and enables reliable measurement of the recombination lifetime when the pretreatment is performed on the silicon substrate. [Solution] A pretreatment method performed before measuring the recombination lifetime of a silicon substrate, characterized in that the silicon substrate is subjected to passivation treatment on the surface of the silicon substrate by immersing it in a heavy aqueous solution in which HF is dissolved in D2O.

Description

Technical Field

[0001] The present invention relates to a pretreatment method performed before measuring the recombination lifetime of a silicon substrate, a method for measuring the recombination lifetime of a silicon substrate, and a passivation treatment method for a silicon substrate.

Background Art

[0002] When crystal defects exist in a silicon substrate (silicon wafer) or the silicon substrate is contaminated with metal impurities, the recombination lifetime (wafer lifetime: WLT) decreases, which adversely affects the characteristics of the product. Therefore, it is necessary to measure the recombination lifetime of the silicon substrate. The recombination lifetime is the time until the concentration of excess carriers decreases to, for example, 1 / e due to recombination when carriers such as electrons are injected into silicon. As a method for measuring such a recombination lifetime, there is a method of measuring the entire silicon substrate (bulk) by the μ-PCD method. This method irradiates the silicon substrate with microwaves, then samples the power of the microwaves reflected by the silicon substrate and captures it into a recording device, and measures the recombination lifetime from the power attenuation curve. In this case, if the silicon substrate is measured as it is, the recombination on the surface becomes rate-determining and the bulk information cannot be seen. Therefore, it is necessary to suppress the surface recombination by forming an oxide film on the surface or contacting a chemical with the surface.

[0003] In order to perform recombination lifetime measurement that realizes high-sensitivity measurement of several milliseconds, surface treatment (pretreatment) with a low interface state density (Dit < 10 10 / cm 2 ·eV) is required. For example, when forming an oxide film, it is known to perform thermal oxidation in a heating atmosphere of 950°C to 1050°C (Patent Document 1).

[0004] In addition, various other surface treatment methods have been investigated, and some representative methods include the following: Non-Patent Document 1 discloses a method using a solution of iodine dissolved in ethanol (iodine / ethanol solution), which is commonly used as one of the surface treatment methods. Furthermore, Patent Document 2 reports a surface treatment method using hydroquinones. Patent Document 3 describes performing chemical passivation by contacting an iodine alcohol solution with the surface of a silicon crystal substrate. Patent Document 4 describes performing passivation treatment on the surface of a silicon substrate by immersing it in an ascorbic acid solution. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2000-100884 [Patent Document 2] Japanese Patent Publication No. 2002-329692 [Patent Document 3] Japanese Patent Publication No. 2010-192809 [Patent Document 4] Japanese Patent Publication No. 2016-46468 [Non-patent literature]

[0006] [Non-Patent Document 1] TS Horanyi et al. Appl. Surf. Sci. 63 (1993) 306 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The above-mentioned surface treatment method, which forms an oxide film, requires a thermal history to the silicon substrate and consideration of contamination from the furnace used for heating. Therefore, it may not be suitable for evaluating defects caused by oxygen or metal impurities in the silicon substrate, for example. On the other hand, the above-mentioned surface treatment method using iodine or hydroquinones does not require a thermal history and does not require consideration of contamination from the furnace, making it a highly versatile method. However, since iodine and hydroquinones are either not water-soluble or are extremely insoluble in water, organic solvents must be used to dissolve them, which necessitates complicated chemical treatment after the surface treatment.

[0008] The present invention has been made to solve the above problems and aims to provide a pretreatment method that can be performed in a water-soluble environment and that can obtain highly reliable measurement values ​​when the recombination lifetime is measured on a silicon substrate after pretreatment, a recombination lifetime measurement method that can obtain highly reliable measurement values, and a passivation treatment method that can be performed in a water-soluble environment and that can obtain highly reliable measurement values ​​when the recombination lifetime is measured on a silicon substrate after treatment. [Means for solving the problem]

[0009] To solve the above problems, the present invention provides a pretreatment method performed before measuring the recombination lifetime of a silicon substrate, The present invention provides a pretreatment method characterized by performing a passivation treatment on the surface of the silicon substrate by immersing the silicon substrate in a heavy aqueous solution in which HF is dissolved in D2O.

[0010] With this pretreatment method of the present invention, pretreatment can be performed simply by immersing HF in a heavy water solution diluted with D2O. Furthermore, with this pretreatment method of the present invention, stable surface passivation treatment is possible due to the effect of D, which has a higher electronegativity than H. As a result, according to the pretreatment method of the present invention, pretreatment can be performed in a water-soluble environment, and reliable measurement values ​​can be obtained when measuring the recombination lifetime of the silicon substrate after pretreatment.

[0011] Furthermore, it is preferable that the HF concentration in the heavy aqueous solution is 0.5% or more and 2% or less.

[0012] Such concentrations of heavy aqueous solutions are sufficient and economical to obtain reliable recombination lifetime measurements.

[0013] Furthermore, the present invention provides a method for measuring the recombination lifetime of a silicon substrate, The present invention provides a method for measuring the recombination lifetime of a silicon substrate, characterized by performing pretreatment on the silicon substrate using the above-described pretreatment method, and then measuring the recombination lifetime of the pretreated silicon substrate.

[0014] With the recombination lifetime measurement method of the present invention, stable surface passivation treatment can be performed in the pretreatment stage due to the effect of D, which has an electronegativity greater than H. As a result, highly reliable recombination lifetime measurement values ​​can be obtained using the recombination lifetime measurement method of the present invention.

[0015] Furthermore, the present invention provides a method for performing passivation treatment on the surface of a silicon substrate, The present invention provides a passivation treatment method for a silicon substrate, characterized by performing a passivation treatment on the surface of the silicon substrate by immersing the silicon substrate in a heavy aqueous solution in which HF is dissolved in D2O.

[0016] With such a passivation treatment method, due to the effect of D whose electronegativity is greater than that of H, it becomes possible to perform stable surface passivation treatment. As a result, according to the passivation treatment method of the present invention, it is possible to perform the treatment in a water-soluble environment, and when measuring the recombination lifetime of the silicon substrate after the treatment, a highly reliable measurement value can be obtained for the passivation treatment.

Advantages of the Invention

[0017] As described above, with the pretreatment method of the present invention, it is possible to perform the pretreatment in a water-soluble environment, and when measuring the recombination lifetime of the silicon substrate after the pretreatment, a highly reliable measurement value can be obtained for the pretreatment.

[0018] Also, with the recombination lifetime measurement method of the present invention, a highly reliable recombination lifetime measurement value can be obtained.

[0019] And, with the passivation treatment method of the present invention, it is possible to perform the treatment in a water-soluble environment, and when measuring the recombination lifetime of the silicon substrate after the treatment, a highly reliable measurement value can be obtained for the passivation treatment.

Brief Description of the Drawings

[0020] [Figure 1] It is a diagram showing the difference in the measured values of the recombination lifetime of the silicon substrate after pretreatment between the case of using a heavy water solution in which HF is dissolved in D2O (Example 1) and the case of using an aqueous solution in which HF is dissolved in H2O (Comparative Example 1). [Figure 2] It is a diagram showing the relationship between the HF concentration in the D2O solution and the HF concentration in the H2O solution and the measured value of the recombination lifetime of the silicon substrate after pretreatment.

Embodiments for Carrying Out the Invention

[0021] As described above, there was a need to develop a pretreatment method that could be performed in a water-soluble environment and that could provide highly reliable measurement values ​​when the recombination lifetime of the silicon substrate was measured after pretreatment.

[0022] As a result of diligent research into the above-mentioned problems, the inventors of the present invention have found that by using a heavy aqueous solution in which HF is dissolved in D2O, more reliable recombination lifetime measurements can be obtained than with the conventional pretreatment method of treatment with an aqueous solution in which HF is dissolved in H2O, and have completed the present invention.

[0023] In other words, the present invention is a pretreatment method performed before measuring the recombination lifetime of a silicon substrate, The pretreatment method is characterized by performing a passivation treatment on the surface of the silicon substrate by immersing the silicon substrate in a heavy aqueous solution in which HF is dissolved in D2O.

[0024] The present invention will be described in detail below, but the present invention is not limited thereto. All concentrations in this specification are expressed in mass percent.

[0025] [Processing method] First, the present invention provides a pretreatment method performed before measuring the recombination lifetime of a silicon substrate, The present invention provides a pretreatment method characterized by performing a passivation treatment on the surface of the silicon substrate by immersing the silicon substrate in a heavy aqueous solution in which HF is dissolved in D2O.

[0026] D2O is called heavy water in contrast to ordinary water, i.e., light water (H2O). The nuclear mass number of deuterium (D), which is composed of one proton and one neutron, is larger than that of hydrogen (H). For this reason, D is more electronegative than H. When HF is diluted in heavy water, the H undergoes an exchange reaction with the D in the heavy water to form DF.

[0027] In the pretreatment of the present invention, DF dissociates, allowing the dangling bonds on the silicon surface to be terminated with D. A surface terminated with D, which has high electronegativity, can exhibit excellent stability. When the recombination lifetime is measured on a silicon substrate after such treatment, the surface of the silicon substrate exhibits excellent stability, allowing for highly reliable measurement results.

[0028] Furthermore, according to the treatment method of the present invention, since a heavy aqueous solution is used, there is no need to use organic solvents, and pretreatment can be performed in a water-soluble environment.

[0029] In other words, the pretreatment method according to the present invention allows for pretreatment in a water-soluble environment, and enables the acquisition of highly reliable measurement values ​​when measuring the recombination lifetime of the silicon substrate after pretreatment.

[0030] To confirm the effect of high electronegativity, p-type silicon substrates (typical resistors) were immersed in solutions of light water (H2O) and heavy water (D2O), each containing 1% HF, and the change in recombination lifetime over time was obtained. The results are shown in Figure 1. From the results shown in Figure 1, it was confirmed that the time to stabilize the lifetime was shorter when using the heavy water solution in which HF was dissolved in D2O compared to when using the solution in which HF was dissolved in H2O.

[0031] Furthermore, the concentration of HF in the heavy aqueous solution used in the pretreatment of the present invention is preferably 0.5% to 2%. This preferred concentration was determined by the concentration dependence of the recombination lifetime value when the concentration of HF was changed, as shown in the experiment described below. The heavy aqueous solution used in the pretreatment of the present invention may also contain light water (H2O). If light water (H2O) is included, the proportion of H2O to the mass of the heavy aqueous solution is preferably 10% or less.

[0032] (experiment) First, several P-type silicon substrates were prepared. Multiple types of heavy water solutions were also prepared by dissolving HF at varying concentrations in D2O. Each silicon substrate was then subjected to passivation treatment using each heavy water solution. Subsequently, the recombination lifetime values ​​were measured and plotted to determine the relationship (concentration dependence) between HF concentration and the measured recombination lifetime. The graph is shown in Figure 2. As shown in Figure 2, the recombination lifetime values ​​become more stable at concentrations of 0.5% or higher, suggesting that this is a sufficient treatment concentration. Furthermore, since no improvement in recombination lifetime values ​​was observed at concentrations higher than 0.5%, it is preferable to set the upper limit of the concentration at 2%, considering economic factors. While it is estimated that higher concentrations may also be effective, the HF concentration increases, making it preferable to keep it below 2% from a cost perspective. Also, as shown in Figure 2, an improvement in lifetime values ​​can be achieved even at HF ​​concentrations lower than 0.5%.

[0033] The specific pretreatment procedure involves immersing the silicon substrate in a heavy water solution prepared by diluting (dissolving) HF in D2O, and the specific immersion method is, of course, not limited.

[0034] The immersion time of the silicon substrate in the heavy aqueous solution is not particularly limited, but can be, for example, 30 seconds or more and 300 seconds or less, preferably 60 seconds or more and 180 seconds or less, and more preferably 90 seconds or more and 120 seconds or less.

[0035] As described above, the pretreatment method of the present invention allows pretreatment to be carried out in a water-soluble environment, making it easy to dispose of the chemical solution after pretreatment. Furthermore, when the recombination lifetime is measured on the silicon substrate after pretreatment, more reliable measurement values ​​can be obtained than when conventional pretreatment methods are used. In addition, because a heavy aqueous solution is used, it is less harmful to the human body compared to methods using organic solvents, making it easy to handle, and therefore the pretreatment method of the present invention is also superior in terms of safety.

[0036] [Method for measuring the recombination lifetime of silicon substrates] The present invention provides a method for measuring the recombination lifetime of a silicon substrate, and is a method for measuring the recombination lifetime of a silicon substrate. The present invention is characterized by performing a pretreatment on the silicon substrate using the pretreatment method described above, and then measuring the recombination lifetime of the pretreated silicon substrate.

[0037] The measurement of the recombination lifetime after the pretreatment of the present invention described above can be performed by a known method, for example, by the μ-PCD method.

[0038] With the recombination lifetime measurement method of the present invention, stable surface passivation treatment can be performed in the pretreatment stage due to the effect of D, which has an electronegativity greater than H. As a result, highly reliable recombination lifetime measurement values ​​can be obtained using the recombination lifetime measurement method of the present invention.

[0039] [Passive treatment method] The passivation treatment method of the present invention is a method for performing a passivation treatment on the surface of a silicon substrate, This is a method for passivating a silicon substrate, characterized by immersing the silicon substrate in a heavy aqueous solution in which HF is dissolved in D2O, thereby performing a passivation treatment on the surface of the silicon substrate.

[0040] This embodiment implements the pretreatment method of the present invention described above as a passivation treatment method.

[0041] Therefore, the passivation treatment method of the present invention can be performed in a water-soluble environment, and when the recombination lifetime is measured on the silicon substrate after treatment, a highly reliable measurement value can be obtained. [Examples]

[0042] The present invention will be specifically described below using examples and comparative examples, but the present invention is not limited to these.

[0043] [Example 1] In Example 1, first, 300 mm diameter silicon wafers with boron-doped (P-type) and phosphorus-doped (N-type) resistivity of 10 Ω·cm were prepared as materials. Next, a 49% HF aqueous solution was dissolved in 1 L of D2O solvent to prepare a 1% HF D2O solution (heavy water aqueous solution). The wafers were immersed in this heavy water aqueous solution for 90 seconds to perform a passivation treatment (pretreatment). After this passivation treatment, the recombination lifetime (WLT) of the silicon wafers was measured by the μ-PCD method. The WLT was measured by varying the time between the passivation treatment and the WLT measurement from 1 minute to 80 minutes. The solid line in Figure 1 shows the measurement results for Example 1.

[0044] [Comparative Example 1] In Comparative Example 1, first, boron-doped (P-type) and phosphorus-doped (N-type) silicon wafers with a diameter of 300 mm and a resistivity of 10 Ω·cm were prepared as materials, in exactly the same manner as in Example 1. Next, a 49% HF aqueous solution was dissolved in 1 L of water (H2O) to prepare a 1% HF H2O solution. The wafers were immersed in this aqueous solution for 90 seconds to perform a passivation treatment (pretreatment). After this passivation treatment, the recombination lifetime (WLT) of the silicon wafers was measured by the μ-PCD method. The WLT was measured by varying the time between the passivation treatment and the WLT measurement from 1 minute to 80 minutes. The dashed line in Figure 1 shows the measurement results for Comparative Example 1.

[0045] As shown in Figure 1, since D has a higher electronegativity than H, it was confirmed that Example 1, which used a heavy aqueous solution in which HF was dissolved in D2O, had a shorter lifetime stabilization time than Comparative Example 1, which used an aqueous solution in which HF was dissolved in H2O.

[0046] From the above, it has become clear that the pretreatment method of the present invention allows pretreatment to be performed in a water-soluble environment without using organic solvents, and that highly reliable measurement values ​​can be obtained when measuring the recombination lifetime of the silicon substrate after pretreatment.

[0047] It should be noted that the present invention is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of the present invention and achieves similar effects is included within the technical scope of the present invention.

Claims

1. A pretreatment method performed before measuring the recombination lifetime of a silicon substrate, The aforementioned silicon substrate is configured with HF as D ２ A pretreatment method characterized by performing a passivation treatment on the surface of a silicon substrate by immersing it in a heavy aqueous solution in which oxygen is dissolved.

2. The pretreatment method according to claim 1, characterized in that the HF concentration in the heavy aqueous solution is 0.5% or more and 2% or less.

3. A method for measuring the recombination lifetime of a silicon substrate, A method for measuring the recombination lifetime of a silicon substrate, characterized by performing a pretreatment on the silicon substrate according to the pretreatment method described in claim 1 or claim 2, and then measuring the recombination lifetime of the pretreated silicon substrate.

4. A method for performing passivation treatment on the surface of a silicon substrate, The aforementioned silicon substrate is configured with HF as D ２ A method for passivating a silicon substrate, characterized by performing a passivation treatment on the surface of the silicon substrate by immersing it in a heavy aqueous solution in which oxygen is dissolved.

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