METHOD FOR CLEANING A SEMICONDUCTOR WAFER

Abstract

A method for cleaning a semiconductor wafer is provided that is capable of reducing adhering particles on the surface of the semiconductor wafer. The method of this disclosure comprises, while the semiconductor wafer is being rotated: a first cleaning process for cleaning the semiconductor wafer; a first drying process for drying the semiconductor wafer after the first cleaning process; a second cleaning process for cleaning the semiconductor wafer after the first drying process; and a second drying process for drying the semiconductor wafer after the second cleaning process, wherein the second cleaning process comprises, in the following sequence: a pure water supply process for supplying pure water to the surface of the semiconductor wafer after the first drying process; a second initial ozone cleaning process for supplying an ozone solution to the surface of the semiconductor wafer to perform a cleaning.and a second alternating cleaning process that alternately uses: a second hydrofluoric acid cleaning process to clean the surface of the semiconductor wafer with an aqueous solution of hydrofluoric acid; and a second ozone cleaning process to clean the surface with an ozone solution, following the second hydrofluoric acid cleaning process.

Description

TECHNICAL AREA

[0001] The present disclosure relates to a method for cleaning a semiconductor wafer. BACKGROUND

[0002] Traditionally, semiconductor wafers, such as silicon wafers, have been used as substrates for semiconductor devices. A semiconductor wafer is obtained by subjecting a single-crystal ingot, grown using the Czochralski (CZ) method or similar techniques, to wafer processing. During this processing, particles, such as polishing powder, adhere to the surface of the semiconductor wafer, and therefore a cleaning process is performed on the semiconductor wafer after processing to remove such particles.

[0003] It is known that in the cleaning process of a semiconductor wafer, particles adhering to the surface of the wafer can be efficiently cleaned and removed by cleaning the wafer surface using various cleaning solutions. For example, patent document 1 discloses a method in which ozone cleaning is carried out by supplying an ozone solution to the surface of the semiconductor wafer, followed by hydrofluoric acid cleaning by supplying hydrofluoric acid to the wafer surface, and then drying of the semiconductor wafer. CITATION LIST Patent literature

[0004] PTL 1: JP H8-181137 A Summary (Technical Problem)

[0005] However, in substrates cleaned by such a cleaning process, adhering particles, such as polishing powder, which could not be completely removed during the cleaning process, may remain on the surface of the dried substrate, resulting in insufficient cleaning. The present disclosure aims to provide a method for cleaning a semiconductor wafer that can further reduce the number of residual particles on the surface of the semiconductor wafer. (Solution to the problem)

[0006] To solve the aforementioned problem, the inventors of the present disclosure have conducted intensive studies. When a semiconductor wafer is cleaned using a conventional cleaning method, adhering particles remain on the surface of the substrate after drying. As a result, when the surface of the cleaned semiconductor wafer is inspected using a surface inspection device (e.g., Surfscan SP5 or later models manufactured by KLA Corporation), a large number of light spot defects (LPDs), which are presumed to be caused by adhering particles, are detected. Accordingly, the inventors have carried out a detailed investigation of various methods for cleaning semiconductor wafers and have examined the relationship between such methods and the number of LPDs detected on the surface of the cleaned semiconductor wafer.As a result, they found that to efficiently remove adhering particles from the semiconductor wafer, it is effective to temporarily pause the cleaning process during several cleaning treatments using cleaning solutions, perform a drying process on the semiconductor wafer, then add purified water, and then resume the cleaning process. This sequence was found to significantly reduce the number of LPDs caused by adhering particles. The core of the present disclosure, completed based on the foregoing results, is as follows.

[0007] (1) Method for cleaning a semiconductor wafer, comprising while the semiconductor wafer is being rotated: a first cleaning process to clean the semiconductor wafer; a first drying process to dry the semiconductor wafer after the first cleaning process; a second cleaning process to clean the semiconductor wafer after the first drying process; and a second drying process to dry the semiconductor wafer after the second cleaning process, the first cleaning process comprises the following sequence: an initial ozone cleaning process for supplying an ozone solution to a surface of the semiconductor wafer to perform cleaning; and a first alternating cleaning process that alternately uses: a first hydrofluoric acid cleaning process to clean the surface of the semiconductor wafer with an aqueous solution of hydrofluoric acid; and a first ozone cleaning process to clean the surface with an ozone solution, following the first hydrofluoric acid cleaning process, and the second cleaning process comprises the following sequence: a pure water supply process for supplying pure water to the surface of the semiconductor wafer after the first drying process; a second initial ozone cleaning process for supplying an ozone solution to the surface of the semiconductor wafer to perform cleaning; and a second alternating cleaning process that alternately uses: a second hydrofluoric acid cleaning process to clean the surface of the semiconductor wafer with an aqueous solution of hydrofluoric acid; and a second ozone cleaning process to clean the surface with an ozone solution, following the second hydrofluoric acid cleaning process.

[0008] (2) Method for cleaning a semiconductor wafer according to (1), wherein the number of additional passes of the alternating cleaning process in the first cleaning process is not less than one and not more than four.

[0009] (3) Method for cleaning a semiconductor wafer according to (1) or (2), wherein the number of additional passes of the alternating cleaning process in the first cleaning process is not less than one and not more than two.

[0010] (4) Method for cleaning a semiconductor wafer according to (1) or (3), wherein the number of additional passes of the alternating cleaning process in the second cleaning process is one.

[0011] (5) Method for cleaning a semiconductor wafer according to any of (1) to (4), wherein the rotational speed of the semiconductor wafer in the pure water supply process is not less than 25 rpm and not more than 100 rpm. (Beneficial effect)

[0012] According to the present disclosure, adhering particles on the surface of a semiconductor wafer can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The attached drawings show: Fig. 1. A flowchart illustrating essential steps in the process of cleaning a semiconductor wafer according to the present disclosure; and Fig. 2. A diagram showing the number of LPDs for an example and a comparison example. DETAILED DESCRIPTION (Method for cleaning a semiconductor wafer)

[0014] An embodiment of the present disclosure is described below with reference to Fig. 1 described. The method for cleaning a semiconductor wafer according to the present disclosure comprises, at least while the semiconductor wafer is being rotated: a first cleaning process for cleaning the semiconductor wafer; a first drying process for drying the semiconductor wafer after the first cleaning process; a second cleaning process for cleaning the semiconductor wafer after the first drying process; and a second drying process for drying the semiconductor wafer after the second cleaning process. In the first cleaning process, the initial ozone cleaning process is specifically referred to as the first “initial” ozone cleaning process and is distinct from a first hydrofluoric acid cleaning process and a first ozone cleaning process that are subsequently repeated.Similarly, in the second cleaning process, the initial ozone cleaning is specifically referred to as the second "initial" ozone cleaning process and differs from a second hydrofluoric acid cleaning process and a second ozone cleaning process, which are subsequently repeated. The details of each process are described below. < First cleaning process >

[0015] The first cleaning process comprises, in the following sequence: an initial ozone cleaning process to introduce an ozone solution to a surface of the semiconductor wafer to perform cleaning; and an initial alternating cleaning process that alternately uses: the initial hydrofluoric acid cleaning process to clean the surface of the semiconductor wafer with an aqueous solution of hydrofluoric acid; and the initial ozone cleaning process to clean the surface with an ozone solution, following the initial hydrofluoric acid cleaning process. Each of these processes is described below in sequence. <Erster anfänglicher Ozonreinigungsprozess>

[0016] In the initial ozone cleaning process, the semiconductor wafer is rotated while an ozone solution is applied to its surface to perform ozone cleaning. During this process, metals and organic substances adhering to the surface of the semiconductor wafer can be oxidized and removed, and an oxide film can be formed among other adhering particles remaining on the surface. It is also preferred that, prior to the initial ozone cleaning process, purified water is applied to the surface of the semiconductor wafer so that the surface is in a wet state. <Erster Fluorwasserstoffsäurereinigungsprozess und Erster Ozonreinigungsprozess>

[0017] In this process, the surface of the semiconductor wafer is cleaned alternately by the first hydrofluoric acid cleaning process, which uses an aqueous solution of hydrofluoric acid, and the first ozone cleaning process, which uses an ozone solution to clean the surface. In the first hydrofluoric acid cleaning process and the first ozone cleaning process, the semiconductor wafer, which has undergone the initial ozone cleaning process, is first subjected to the first hydrofluoric acid cleaning process. In this process, the semiconductor wafer is rotated while an aqueous solution of hydrofluoric acid (HF) is applied to the surface to perform hydrofluoric acid cleaning.Then, in the subsequent first ozone cleaning process, the hydrofluoric acid-cleaned semiconductor wafer is rotated while an ozone solution is applied to the surface to perform the ozone cleaning process. In the first hydrofluoric acid cleaning process and the first ozone cleaning process, the oxide film formed in the initial ozone cleaning process can be removed, and in the course of this removal, metals and particles adhering to the surface of the semiconductor wafer can also be removed.

[0018] In the alternating cleaning process, which alternately uses the first hydrofluoric acid cleaning process and the first ozone cleaning process, it is preferred to additionally perform a predetermined number of cycles of the first hydrofluoric acid cleaning process and the first ozone cleaning process alternately. It is preferred that the number of additional cycles of the alternating cleaning process within the first cleaning process be set within a range of not less than one and not more than four, and more preferably within a range of not less than one and not more than two. It should be noted that in this specification, "additionally performed" refers to the number of cycles performed in addition to the one mandatory cycle.That is, the total number of cycles of the alternating cleaning process in the first cleaning process is preferably within a range of not less than two and not more than five, and more preferably within a range of not less than two and not more than three. <<Erster Trocknungsprozess>

[0019] In the first drying process, after the initial ozone cleaning, the semiconductor wafer is rotated at high speed to perform centrifugal drying while continuing to rotate. In this first drying process, the rotational speed of the semiconductor wafer must be, for example, no less than 1000 rpm and no more than 2000 rpm. This first drying process reduces the adhesive force between the particles and the semiconductor wafer, thus reducing the adhesion force that could not be removed in the first cleaning process and thus reducing the adhesion force between the particles and the semiconductor wafer. <Zweiter Reinigungsprozess>

[0020] The second cleaning process comprises, in the following sequence: a purified water supply process to introduce purified water to the surface of the semiconductor wafer after the first drying process; a second initial ozone cleaning process to introduce an ozone solution to the surface of the semiconductor wafer to perform cleaning; and a second alternating cleaning process that alternately uses: a second hydrofluoric acid cleaning process to clean the surface of the semiconductor wafer with an aqueous solution of hydrofluoric acid; and a second ozone cleaning process to clean the surface with an ozone solution, following the second hydrofluoric acid cleaning process. Each of these processes is described below in sequence. <<Reinwasserzuführungsprozess>

[0021] First, at the beginning of the second cleaning process, a pure water supply process is performed. In this process, pure water is preferably supplied at a low flow rate using a vertical nozzle while the semiconductor wafer rotates at a low speed. This pure water supply process preferentially delivers pure water to the central portion of the wafer's surface as it rotates. This central delivery allows the pure water to spread evenly across the entire wafer from the center to the periphery due to centrifugal force, thus forming a film of pure water on the wafer's surface.

[0022] By forming a film of pure water on the surface of the semiconductor wafer when switching from pure water to a cleaning solution, the cleaning solution is diluted by the pure water present on the wafer surface. This reduces its reactivity and suppresses turbulence caused by the high concentration of the cleaning solution during the initial phase of its supply. As a result, the cleaning solution can spread evenly across the entire surface of the semiconductor wafer at a uniform concentration, ensuring a consistent cleaning of the wafer surface.

[0023] It is preferred that the supply of purified water be continued at least until a film of purified water is formed over the entire surface of the semiconductor wafer. In the present disclosure, it is also preferred to continue the supply of purified water to the surface of the semiconductor wafer until the subsequent second initial ozone cleaning, in which the supply is switched to an ozone solution.

[0024] The purity of the purified water supplied to the surface of the semiconductor wafer is not particularly limited, as long as it has a purity level sufficient to achieve the required product quality. The purity of the purified water can be at a so-called pure water level (for example, a resistivity of not less than 0.1 MΩ·cm and not more than 15 MΩ·cm) or at an ultra-pure water level (for example, a resistivity of more than 15 MΩ·cm).

[0025] It is preferred that the purified water be supplied during the purified water supply process while the semiconductor wafer is rotated at a speed of not less than 25 rpm and not more than 100 rpm. This prevents turbulence of the purified water caused by water splashing and also prevents turbulence of the hydrofluoric acid cleaning solution in the subsequent second cleaning process, even when the hydrofluoric acid cleaning solution is supplied, thus enabling a more uniform cleaning of the semiconductor wafer surface. <Zweiter anfänglicher Ozonreinigungsprozess>

[0026] In the second initial ozone cleaning process, the semiconductor wafer, supplied with purified water, is rotated while an ozone solution is applied to the surface of the semiconductor wafer to perform ozone cleaning. Similar to the first initial ozone cleaning process, this process allows metals and organic substances adhering to the surface of the semiconductor wafer to be oxidized and removed, and enables the formation of an oxide film beneath other adhering particles. <Zweiter Fluorwasserstoffsäurereinigungsprozess und Zweiter Ozonreinigungsprozess>

[0027] In this process, the surface of the semiconductor wafer is alternately cleaned by a second hydrofluoric acid cleaning process using an aqueous solution of hydrofluoric acid; and a second ozone cleaning process using an ozone solution, which follows the second hydrofluoric acid cleaning process. In both the second hydrofluoric acid and second ozone cleaning processes, after the initial second ozone cleaning process (which follows the purified water supply process), the semiconductor wafer is first rotated while an aqueous solution of hydrofluoric acid is applied to the surface of the semiconductor wafer to perform the hydrofluoric acid cleaning.Then, in the subsequent second ozone cleaning process, the hydrofluoric acid-cleaned semiconductor wafer is rotated while an ozone solution is supplied to the surface of the semiconductor wafer to perform ozone cleaning.

[0028] If the rotational speed of the semiconductor wafer is set higher than the rotational speed in the purified water supply process after the second initial ozone cleaning process, the rotational speed of the semiconductor wafer is preferably increased after the purified water on the surface of the wafer has been completely replaced by the ozone solution following the switch from the purified water supply to the ozone solution supply.

[0029] Most of the particles on the surface of the semiconductor wafer are removed by the first cleaning process, but some particles remain as adhering particles. These adhering particles are not strongly fixed to the surface of the semiconductor wafer but are considered more easily detached due to the initial drying process following the first cleaning process. Therefore, by performing the second cleaning process on the surface of the semiconductor wafer after the first drying process, the cleaning solution can penetrate further beneath the remaining adhering particles on the wafer surface, allowing these particles to be removed.

[0030] The alternating cleaning process, which alternately uses the second hydrofluoric acid cleaning process and the second ozone cleaning process, can be configured to repeat the second hydrofluoric acid cleaning process and the second ozone cleaning process alternately for a predetermined number of passes. It is preferred that the rotational speed of the semiconductor wafer during the supply of the aqueous hydrofluoric acid solution be not less than 50 rpm and not more than 800 rpm, and preferably not less than 300 rpm and not more than 500 rpm. It is also preferred that the aqueous hydrofluoric acid solution be supplied at a flow rate of not less than 0.5 L / min and not more than 1.5 L / min, and that its concentration be not less than 0.5 wt% and not more than 3.0 wt%.It is also preferred that the rotational speed of the semiconductor wafer during the supply of the ozone solution be not less than 50 rpm and not more than 800 rpm, and preferably not less than 300 rpm and not more than 500 rpm. The ozone solution is preferably supplied at a flow rate of not less than 0.5 L / min and not more than 2.0 L / min, and more preferably at a flow rate of not less than 1.0 L / min and not more than 2.0 L / min. It is also preferred that the ozone concentration be not less than 20 mg / l and not more than 30 mg / l. By adjusting these parameters within the above ranges, the surface of the semiconductor wafer can be cleaned uniformly.

[0031] In the alternating cleaning process, which alternately uses the second hydrofluoric acid cleaning process and the second ozone cleaning process, it is preferred to additionally perform a predetermined number of cycles of the second hydrofluoric acid cleaning process and the second ozone cleaning process alternately. It is preferred that the number of additional cycles of the alternating cleaning process performed in the second cleaning process is one. That is, it is preferred that the alternating cleaning process is performed a total of two times in the second cleaning process. <<Zweiter Trocknungsprozess>

[0032] Finally, the semiconductor wafer, which has undergone the alternating cleaning process (alternating between the second hydrofluoric acid cleaning process and the second ozone cleaning process), is rotated at high speed to undergo centrifugal drying. Although the drying conditions in the second drying process are not particularly restricted, it is preferred that the rotational speed of the semiconductor wafer be no less than 1000 rpm and no more than 2000 rpm, and that the drying time be no less than 25 seconds and no more than 40 seconds. It is also permissible to perform a rinsing process prior to the second drying process by supplying pure water to the surface of the rotating semiconductor wafer.

[0033] Thus, by using the semiconductor wafer cleaning method according to the present embodiment, adhering particles on the surface of the semiconductor wafer can be reduced. The semiconductor wafer to be cleaned by the present disclosure can be any type of semiconductor wafer, such as a silicon wafer, a germanium wafer, or a gallium arsenide wafer. Among these, the present disclosure is particularly suitable for cleaning silicon wafers. The semiconductor wafer can be a single-crystal wafer or a polycrystalline wafer. Furthermore, the semiconductor wafer can be an epitaxial wafer or a annealed wafer. There are no particular restrictions regarding the diameter, conductivity type, or resistivity of the semiconductor wafer. EXAMPLES

[0034] Examples of the present revelation are described below; however, the present revelation is not limited to these examples. (Comparative example 1)

[0035] In comparative example 1, eight silicon wafers with a diameter of 300 mm were fabricated, and each silicon wafer underwent a cleaning process using a centrifugal cleaning device. Specifically, each silicon wafer was first rotated while an ozone solution was applied to its surface to perform an ozone cleaning process. Next, an aqueous solution of hydrofluoric acid was applied to the surface of the silicon wafer to perform a hydrofluoric acid cleaning process, followed again by an ozone cleaning process. This alternating cleaning process was repeated a total of three times (i.e., the number of additional repetitions was two).The conditions for each ozone cleaning process (wafer rotation speed, ozone concentration, flow rate, and duration) were kept identical, as were the conditions for each hydrofluoric acid cleaning process (wafer rotation speed, HF concentration, flow rate, and duration). After the final ozone cleaning process, the wafer was dried by high-speed centrifugation. The silicon wafers of comparison example 1 were obtained in this manner. (Comparative example 2)

[0036] In Comparative Example 2, eight silicon wafers with a diameter of 300 mm were produced, and each silicon wafer was subjected to a cleaning process using a centrifugal cleaning device. Except that the alternating cleaning process of hydrofluoric acid followed by ozone cleaning was performed a total of five times (i.e., the number of additional repetitions was four), all other process conditions were the same as those in Comparative Example 1. The silicon wafers of Comparative Example 2 were obtained in this manner. (Example)

[0037] In this example, eight silicon wafers with a diameter of 300 mm were produced, and each wafer underwent a cleaning process using a centrifugal cleaning device. Specifically, each wafer was first rotated while an ozone solution was applied to its surface to perform an ozone cleaning process. Next, an aqueous solution of hydrofluoric acid was applied to the surface of the ozone-cleaned wafer to perform a hydrofluoric acid cleaning process, followed by another ozone cleaning process. This alternating cleaning process was repeated a total of three times (i.e., the number of additional repetitions was two). Finally, after the last ozone cleaning process, the wafer was dried by high-speed centrifugal drying.Then, while the dried silicon wafer was slowly rotated at 50 rpm, purified water was applied to the surface of the silicon wafer to perform a rinsing process. Following this, an ozone cleaning process was carried out by applying an ozone solution to the surface of the silicon wafer, which was then subjected to the purified water application process. Next, an aqueous solution of hydrofluoric acid was applied to perform a hydrofluoric acid cleaning process, followed again by an ozone cleaning process. This alternating cleaning process was performed a total of two times (i.e., the number of additional repetitions was one).

[0038] The silicon wafers of the example were obtained in this way. The conditions for each ozone cleaning process (wafer rotation speed, ozone concentration, flow rate, and duration) were the same as those in comparison examples 1 and 2, and the conditions for the hydrofluoric acid cleaning process (wafer rotation speed, hydrofluoric acid concentration, flow rate, and duration) were also the same as those in comparison examples 1 and 2.

[0039] For comparison examples 1 and 2, and the example, the surfaces of each of the eight cleaned silicon wafers were inspected using a surface inspection device (Surfscan SP7, manufactured by KLA Corporation). Oblique incident light (incident at an angle of 70 degrees relative to the normal direction of the wafer surface) was used as the incident light source, and the DCO channel was used as the detection channel. LPDs (light spot defects) with a size of 15 nm or larger were detected. The results are presented in Fig. 2 is given.

[0040] In comparison example 1, the number of LPDs per silicon wafer was 3.9. In comparison example 2, despite increasing the number of repeated cleaning cycles compared to comparison example 1, the number of LPDs per silicon wafer was 3.8, almost the same as in comparison example 1, and no improvement was observed. In contrast, in comparison example 2, the number of LPDs per silicon wafer was reduced to 1.5. That is, it was found that temporarily stopping the repeated cleaning process on the semiconductor wafer, performing a drying process, then adding purified water, and subsequently resuming the repeated cleaning process resulted in a significant reduction of LPDs caused by adhering particles. Commercial applicability

[0041] According to the present disclosure, adhering particles on the surface of a semiconductor wafer can be reduced, and thus the disclosure is useful in the semiconductor wafer manufacturing industry. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP H8-181137 A

[0004]

Claims

A method for cleaning a semiconductor wafer, comprising, while the semiconductor wafer is being rotated: a first cleaning process for cleaning the semiconductor wafer; a first drying process for drying the semiconductor wafer after the first cleaning process; a second cleaning process for cleaning the semiconductor wafer after the first drying process; and a second drying process for drying the semiconductor wafer after the second cleaning process, wherein the first cleaning process comprises, in the following sequence: a first initial ozone cleaning process for supplying an ozone solution to a surface of the semiconductor wafer to perform a cleaning; and a first alternating cleaning process, which alternately uses: a first hydrofluoric acid cleaning process for cleaning the surface of the semiconductor wafer with an aqueous solution of hydrofluoric acid;and a first ozone cleaning process for cleaning the surface with an ozone solution, following the first hydrofluoric acid cleaning process, wherein the second cleaning process comprises, in the following sequence: a purified water supply process for supplying purified water to the surface of the semiconductor wafer after the first drying process; a second initial ozone cleaning process for supplying an ozone solution to the surface of the semiconductor wafer to perform a cleaning; and a second alternating cleaning process, which alternately uses: a second hydrofluoric acid cleaning process for cleaning the surface of the semiconductor wafer with an aqueous solution of hydrofluoric acid; and a second ozone cleaning process for cleaning the surface with an ozone solution, following the second hydrofluoric acid cleaning process. Method for cleaning a semiconductor wafer according to claim 1, wherein the number of passes of the alternating cleaning process additionally performed in the first cleaning process is not less than one and not more than four. Method for cleaning a semiconductor wafer according to claim 1 or 2, wherein the number of passes in which the alternating cleaning process is additionally carried out in the first cleaning process is not less than one and not more than two. Method for cleaning a semiconductor wafer according to claim 1 or 3, wherein the number of passes the alternating cleaning process is additionally performed in the second cleaning process is one. Method for cleaning a semiconductor wafer according to any one of claims 1 to 4, wherein the rotational speed of the semiconductor wafer in the pure water supply process is not less than 25 rpm and not more than 100 rpm.

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