Semiconductor wafer cleaning method, semiconductor wafer manufacturing method, and semiconductor wafer

Abstract

Provided is a method for cleaning a semiconductor wafer with which the generation of tadpole-shaped defects can be inhibited. The method for cleaning a semiconductor wafer includes a spin cleaning step in which a cleaning fluid is supplied to at least the front surface of the semiconductor wafer while the semiconductor wafer is being rotated. The method is characterized in that the spin cleaning step includes one or more sets of a combination of an ozonated-water cleaning step, in which the cleaning fluid is ozonated water, and an immediately subsequent hydrofluoric-acid cleaning step, in which the cleaning fluid is hydrofluoric acid, and is characterized by including, prior to the spin cleaning step, a pretreatment step in which an electroconductive liquid selected from the group consisting of hydrofluoric acid, carbonated water, and carbonated ozonated water is supplied only to the back surface of the semiconductor wafer while the semiconductor wafer is being rotated.

Description

[Technical Field]

[0001] The present invention relates to a semiconductor wafer cleaning method, a semiconductor wafer manufacturing method, and a semiconductor wafer, and more particularly to a semiconductor wafer cleaning method and a semiconductor wafer manufacturing method that include a step of performing single-wafer spin cleaning on the surface of the semiconductor wafer. [Background technology]

[0002] The manufacturing process of semiconductor wafers such as silicon wafers includes a cleaning process (hereinafter also referred to as "single wafer spin cleaning") in which a cleaning solution is supplied to the surfaces (front and back surfaces) of the wafer while the wafer is rotating, thereby removing particles adhering to the surfaces.

[0003] A typical example of such a single-wafer cleaning method for cleaning semiconductor wafers one by one is the SCROD (Single-Wafer Spin Cleaning with Repetitive Use of Ozonized Water and Dilute HF) method, which involves repeatedly performing spin cleaning with ozone water and spin cleaning with hydrofluoric acid, as described in Patent Document 1. In this method, an oxide film is formed on the wafer surface by spin cleaning with ozone water, and then particles and the like on the wafer surface are removed along with the oxide film by spin cleaning with hydrofluoric acid. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-220284 Summary of the Invention [Problem to be solved by the invention]

[0005] However, single-wafer cleaning has been found to produce so-called ladle-shaped defects, with a depression near the center and raised edges. Ladle-shaped defects have protrusions with heights of 5 to 20 nm and recesses with depths of 5 to 20 nm. Ladle-shaped defects have been causing problems by increasing the number of LPDs (Light Point Defects).

[0006] In view of the above problems, the present invention aims to provide a semiconductor wafer cleaning method and a semiconductor wafer manufacturing method that can suppress the occurrence of ladle-shaped defects during cleaning at the semiconductor wafer manufacturing stage before device formation. [Means for solving the problem]

[0007] As a result of extensive research aimed at solving the above-mentioned problems, the inventors discovered that ladle-shaped defects are caused by electrostatic breakdown occurring between the semiconductor wafer and the cleaning liquid. Furthermore, they discovered that in a semiconductor wafer cleaning process, supplying a conductive liquid to the backside of the semiconductor wafer prior to the spin cleaning process of the front side can eliminate static electricity charged to the semiconductor wafer via the conductive liquid. The conductive liquid is a liquid that ensures conductivity, specifically, any one selected from the group consisting of hydrofluoric acid, carbonated water, and carbonated ozone water. By eliminating static electricity from the semiconductor wafer in the above manner, the occurrence of ladle-shaped defects on the front side of the semiconductor wafer can be suppressed.

[0008] Although electrostatic breakdown also occurs in semiconductor wafers after device formation, this is mainly due to the fact that cleaning water, which is made of pure water, is sprayed onto the semiconductor wafer in an electrically charged state, and the problem is different from that of the present invention. Furthermore, in cleaning semiconductor wafers during semiconductor wafer manufacturing as in the present invention, hydrofluoric acid, ozone water, etc. are used for cleaning, so it can be said that this is a process that is completely different from cleaning semiconductor wafers after device formation in terms of the chemicals used, application, etc.

[0009] That is, the gist and configuration of the present invention are as follows.

[0010] [1] A method for cleaning a semiconductor wafer, comprising a spin cleaning step of supplying a cleaning solution to at least a front surface of the semiconductor wafer while rotating the semiconductor wafer, the spin cleaning step includes one or more sets of a combination of an ozone water cleaning step in which the cleaning liquid is ozone water and a subsequent hydrofluoric acid cleaning step in which the cleaning liquid is hydrofluoric acid; A semiconductor wafer cleaning method characterized by including, prior to the spin cleaning step, a pretreatment step of supplying a conductive liquid selected from the group consisting of hydrofluoric acid, carbonated water, and carbonated ozone water only to the back surface of the semiconductor wafer while rotating the semiconductor wafer.

[0011] [2] The method for cleaning a semiconductor wafer according to [1], wherein the conductive liquid is hydrofluoric acid.

[0012] [3] The method for cleaning a semiconductor wafer according to [1], wherein the conductive liquid is carbonated water.

[0013] [4] The semiconductor wafer cleaning method according to [1], wherein the conductive liquid is carbonated ozone water.

[0014] [5] The method for cleaning a semiconductor wafer according to any one of [1] to [4], wherein in the pretreatment step, the rotation speed of the semiconductor wafer is 10 rpm or more and 100 rpm or less.

[0015] [6] The method for cleaning a semiconductor wafer according to [5], wherein the spin cleaning step comprises a first period during which the rotation speed of the semiconductor wafer is the same as the rotation speed of the semiconductor wafer in the pretreatment step, followed by a second period during which the rotation speed of the semiconductor wafer is greater than 100 rpm and equal to or less than 1000 rpm.

[0016] [7] The method for cleaning a semiconductor wafer according to any one of [1] to [6], wherein in the pretreatment step, the flow rate of the conductive liquid is 0.3 L / min or more and 1.5 L / min or less.

[0017] [8] The method for cleaning a semiconductor wafer according to any one of [1] to [7], wherein in the pretreatment step, the conductive liquid is supplied for a time period of 1.0 seconds or more and 5.0 seconds or less.

[0018] [9] The method for cleaning a semiconductor wafer according to any one of [1] to [8], wherein the conductive liquid is discharged from a nozzle via a piping line and supplied to the back surface of the semiconductor wafer, and the piping line and the nozzle are made of non-metal.

[0019]

[10] The method for cleaning a semiconductor wafer according to any one of [1] to [9], wherein the semiconductor wafer is a silicon wafer.

[0020]

[11] A method for manufacturing a semiconductor wafer, comprising the method for cleaning a semiconductor wafer according to any one of [1] to

[10] .

[0021]

[12] A semiconductor wafer before device formation, A semiconductor wafer characterized in that the number of defects occurring on the front surface of the semiconductor wafer is zero, the defects having a convex portion with a height of 5 nm or more and 20 nm or less and a concave portion with a depth of 5 nm or more and 20 nm or less adjacent to the convex portion. [Effects of the Invention]

[0022] According to the present invention, it is possible to provide a method for cleaning a semiconductor wafer and a method for manufacturing a semiconductor wafer that can suppress the occurrence of ladle-shaped defects. [Brief explanation of the drawings]

[0023] [Figure 1] (a) SEM image of a ladle-shaped defect, and (b) AFM observation results. [Figure 2] 1 is a flow diagram of a semiconductor wafer cleaning method according to an embodiment of the present invention. [Figure 3] 1A is a diagram showing the mechanism by which electrostatic breakdown occurs in a conventional cleaning method, and FIG. 1B is a diagram showing the mechanism by which static electricity is removed in the cleaning method according to the present invention. [Figure 4] 1 is a cross-sectional view showing the arrangement of a semiconductor wafer and a cleaning nozzle in a semiconductor wafer cleaning method according to an embodiment of the present invention. [Figure 5] 1A and 1B are typical SEM images of a ladle-shaped defect, a particle, and an SF defect, respectively, in an example of the present invention. [Figure 6] 10A is a graph showing the count results of the number of LPDs in an example of the present invention, and FIG. 10B is a graph showing the average number of defect types in LPDs. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, an embodiment of the semiconductor wafer cleaning method according to the present invention will be described. Note that the embodiment described below is an example of the present invention, and the configuration of the present invention is not limited to this specific example.

[0025] In the present invention, the "front surface" of a semiconductor wafer refers to the surface on which semiconductor devices are fabricated or on which a dissimilar substrate is attached, and the "back surface" of a semiconductor wafer refers to the flat surface opposite the front surface. An identifier (laser mark) recording product information is engraved on either the front surface or the back surface of a semiconductor wafer. Therefore, the front surface and the back surface of a semiconductor wafer are clearly distinguishable.

[0026] In the present invention, a "ladle-shaped defect" is a defect having a protrusion with a height of about 5 to 20 nm and a depression with a depth of about 5 to 20 nm. Figure 1 shows (a) the results of SEM observation of a ladle-shaped defect and (b) the results of AFM observation of the ladle-shaped defect. The ladle-shaped defect has a depression near the center and a raised periphery.

[0027] [Semiconductor wafer cleaning method] The semiconductor wafer cleaning method of the present invention includes a spin cleaning step of supplying a cleaning liquid to at least the front surface of the semiconductor wafer while rotating the semiconductor wafer. The spin cleaning step includes one or more combinations of an ozone water cleaning step in which the cleaning liquid is ozone water, followed by a hydrofluoric acid cleaning step in which the cleaning liquid is hydrofluoric acid. The semiconductor wafer cleaning method of the present invention further includes a pretreatment step of supplying a conductive liquid selected from the group consisting of hydrofluoric acid, carbonated water, and carbonated ozone water to only the back surface of the semiconductor wafer while rotating the semiconductor wafer, prior to the spin cleaning step.

[0028] FIG. 2 shows a flow diagram of a semiconductor wafer cleaning method according to one embodiment of the present invention. In FIG. 2, the spin cleaning process includes a plurality of cycles of an ozone water cleaning process, a hydrofluoric acid cleaning process, and a pure water cleaning process in this order. Prior to the spin cleaning process, a pretreatment process is performed in which the backside of the semiconductor wafer is cleaned with a conductive liquid. The conductive liquid is selected from the group consisting of hydrofluoric acid, carbonated water, and carbonated ozone water. Thus, the spin cleaning process may include a pure water cleaning process in which the cleaning water is pure water, in addition to the ozone water cleaning process and the hydrofluoric acid cleaning process. The pure water cleaning process in the spin cleaning process may be performed after any step, and is preferably performed after the hydrofluoric acid cleaning process. That is, the hydrofluoric acid cleaning process may be followed by the pure water cleaning process, followed by the ozone water cleaning process, or the hydrofluoric acid cleaning process may be followed by the ozone water cleaning process. Furthermore, as shown in FIG. 2, it is preferable to perform the ozone water cleaning process, the hydrofluoric acid cleaning process, and the pure water cleaning process multiple times in this order, followed by the ozone water cleaning process, to complete the spin cleaning process. The spin cleaning process may be completed after a pure water cleaning process.

[0029] In the spin cleaning process, an oxide film is formed on the surface of the semiconductor wafer in the ozone water cleaning process, and particles and the like on the surface of the semiconductor wafer are removed together with the oxide film in the hydrofluoric acid cleaning process performed subsequent to the ozone water cleaning process. A combination of the ozone water cleaning process and the hydrofluoric acid cleaning process is considered as one set, and one or more sets are performed in the spin cleaning process. The number of combinations of the ozone water cleaning process and the hydrofluoric acid cleaning process in the spin cleaning process is preferably three or more sets, and more preferably five or more sets. Meanwhile, the number of such combinations in the spin cleaning process is preferably seven or less sets.

[0030] In the ozone water cleaning step in the spin cleaning process, the ozone concentration is not particularly limited as long as an oxide film is formed on the semiconductor wafer surface, but can be 15 to 30 mass ppm. The flow rate of the ozone water is not particularly limited as long as an oxide film is formed on the semiconductor wafer surface, but can be 0.5 to 1.5 L / min. The processing time per ozone water cleaning step is also not particularly limited as long as an oxide film is formed on the semiconductor wafer surface, but can be 10 to 45 seconds.

[0031] In the hydrofluoric acid cleaning step in the spin cleaning process, the concentration of hydrofluoric acid can be appropriately set depending on the contamination level of the wafer, and is not particularly limited, but can be 0.50 to 3.00 mass %. The flow rate of hydrofluoric acid can be appropriately set depending on the contamination level of the wafer, and is not particularly limited, but can be 0.5 to 1.5 L / min. The processing time for each hydrofluoric acid cleaning step can also be appropriately set depending on the contamination level of the wafer, and is not particularly limited, but can be 3 to 20 seconds.

[0032] After the spin cleaning step is completed, it is preferable to perform spin drying in which the semiconductor wafer continues to rotate without supplying the cleaning liquid, thereby removing the cleaning liquid from the semiconductor wafer surface and drying the semiconductor wafer surface. The rotation speed of the semiconductor wafer in spin drying is not particularly limited, but can be 1000 to 1500 rpm.

[0033] In the present invention, prior to the spin cleaning step, a pretreatment step is performed in which a conductive liquid selected from the group consisting of hydrofluoric acid, carbonated water, and carbonated ozone water is supplied only to the back surface of the semiconductor wafer while the semiconductor wafer is being rotated. By performing the pretreatment step prior to the spin cleaning step, the semiconductor wafer can be neutralized and the occurrence of ladle-shaped defects can be suppressed.

[0034] FIG. 3(a) shows the mechanism of electrostatic breakdown in a conventional cleaning method and (b) the method of charge removal in a cleaning method according to the present invention. During the manufacturing process, semiconductor wafers become charged due to transport and other factors. In the conventional cleaning method shown in FIG. 3(a), the cleaning solution is supplied to the front surface of the semiconductor wafer before the back surface. Therefore, electrostatic breakdown occurs when the cleaning solution 20 supplied from the front surface cleaning nozzle 10 comes into contact with the semiconductor wafer 100, resulting in the formation of ladle-shaped defects on the front surface. In contrast, in the present invention shown in FIG. 3(b), a pretreatment step is performed prior to the spin cleaning step. This allows the conductive liquid 40 supplied from the back surface cleaning nozzle 30 to first come into contact with the back surface of the semiconductor wafer 100, thereby preventing the formation of ladle-shaped defects on the front surface. The mechanism by which ladle-shaped defects do not occur on the front surface is thought to be that the conductive liquid 40 supplied to the back surface serves as an earth, thereby neutralizing the charge on the semiconductor wafer 100, or that electrostatic breakdown occurs when the conductive liquid 40 is supplied to the back surface, thereby discharging the semiconductor wafer 100. Note that the back surface of the semiconductor wafer 100 is not required to be as smooth as the front surface, and therefore, even if there are irregularities due to ladle-shaped defects, this does not pose a practical problem.

[0035] The conductive liquid supplied in the pretreatment step is any one selected from the group consisting of hydrofluoric acid, carbonated water, and carbonated ozone water. Note that "carbonated ozone water" in the present invention refers to ozone water containing carbon dioxide. When the conductive liquid is hydrofluoric acid, the concentration of hydrofluoric acid is preferably 0.5 to 3.0 mass%. Similarly, when the conductive liquid is carbonated water, the concentration of carbon dioxide is preferably 5 to 20 mass ppm. Similarly, when the conductive liquid is carbonated ozone water, the concentration of carbon dioxide is preferably 5 to 20 mass ppm and the concentration of ozone is preferably 15 to 30 mass ppm.

[0036] In the pretreatment step, when the discharge flow rate of the conductive liquid is 0.3 L / min or more, the semiconductor wafer can be suitably de-electrified. Therefore, the discharge flow rate of the conductive liquid is preferably 0.3 L / min or more, and more preferably 0.8 L / min or more. On the other hand, when the discharge flow rate of the conductive liquid is 1.5 L / min or less, the risk of the liquid being leaked around or splashing can be suitably reduced. Furthermore, since a 4 mm diameter pipe is often used for the conductive liquid, it may be difficult to achieve a discharge flow rate exceeding 1.5 L / min due to the structure of the device. Therefore, the discharge flow rate of the conductive liquid is preferably 1.5 L / min or less.

[0037] In the pretreatment step, when the supply time of the conductive liquid is 1.0 second or longer, the semiconductor wafer can be suitably de-electrified. Therefore, the supply time of the conductive liquid is preferably 1.0 second or longer. On the other hand, when the supply time of the conductive liquid is 5.0 seconds or shorter, the liquid can be suitably prevented from completely reaching the outer periphery of the back surface, and deterioration of LPD due to leakage to the front surface side can be suitably suppressed. Therefore, the supply time of the conductive liquid is preferably 5.0 seconds or shorter, and more preferably 3.0 seconds or shorter.

[0038] When the rotation speed of the semiconductor wafer in the pretreatment step is 10 rpm or more, the conductive liquid can be suitably supplied to the back surface of the semiconductor wafer. Therefore, the rotation speed of the semiconductor wafer in the pretreatment step is preferably 10 rpm or more, and more preferably 30 rpm or more. On the other hand, by setting the rotation speed of the semiconductor wafer in the pretreatment step to a low value of 100 rpm or less, the conductive liquid can be suitably prevented from flowing onto the front surface of the semiconductor wafer. Therefore, the rotation speed of the semiconductor wafer in the pretreatment step is preferably 100 rpm or less, and more preferably 50 rpm or less.

[0039] FIG. 4 is a cross-sectional view showing the arrangement of a semiconductor wafer and cleaning nozzles in a semiconductor wafer cleaning method according to one embodiment of the present invention. A front surface cleaning nozzle (for hydrofluoric acid) 12 supplies hydrofluoric acid 22 to the front surface of the semiconductor wafer 100, and a front surface cleaning nozzle (for ozone water) 14 supplies ozone water 24 to the rear surface of the semiconductor wafer 100. A rear surface cleaning nozzle (for hydrofluoric acid) 32 supplies hydrofluoric acid 42 to the rear surface of the semiconductor wafer 100, and a rear surface cleaning nozzle (for ozone water) 34 supplies ozone water 44 to the rear surface of the semiconductor wafer 100. Each nozzle is installed so as to supply a cleaning solution or the like toward the center of the front surface or rear surface of the semiconductor wafer 100. Although not shown in FIG. 4, nozzles that supply pure water to the front surface and rear surface of the semiconductor wafer 100, respectively, are also positioned at different circumferential positions at the same angle.

[0040] 4, the angle of the front surface cleaning nozzle (for hydrofluoric acid) 12 and the front surface cleaning nozzle (for ozone water) 14 is shown as 4°, and the angle of the back surface cleaning nozzle (for hydrofluoric acid) 32 and the back surface cleaning nozzle (for ozone water) 34 is shown as 70°. Here, the "nozzle angle" refers to the angle between the axis of the nozzle and the perpendicular line to the surface of the semiconductor wafer.

[0041] As shown in Figure 4, in general, when cleaning a semiconductor wafer, the nozzle angle on the front surface is lower than the nozzle angle on the back surface. Therefore, if the rotation speed of the semiconductor wafer is high when supplying cleaning liquid to both the front and back surfaces, the cleaning liquid supplied to the back surface may reach the edge of the semiconductor wafer before the cleaning liquid supplied to the front surface, potentially resulting in the cleaning liquid being wrapped around the front surface. Therefore, in a typical semiconductor wafer cleaning method, the supply of cleaning liquid to the front surface is started several seconds earlier than the back surface, and the supply of cleaning liquid is adjusted so that the cleaning liquid supplied to the front and back surfaces reaches the edge of the semiconductor wafer simultaneously. In the present invention, since a conductive liquid is already supplied to the back surface of the semiconductor wafer during the pretreatment process, it is impossible to adjust the supply start time as described above. Therefore, in the present invention, the spin cleaning process preferably comprises a first period in which the rotation speed of the semiconductor wafer is the same as the rotation speed of the semiconductor wafer in the pretreatment process, followed by a second period in which the rotation speed of the semiconductor wafer is greater than 100 rpm and less than or equal to 1000 rpm. At the start of the spin cleaning process, there is a first period during which the rotation speed of the semiconductor wafer is the same as the rotation speed of the semiconductor wafer in the pre-processing process, i.e., a period during which the rotation speed of the semiconductor wafer is low, which effectively prevents the cleaning liquid supplied to the back surface from flowing over to the front surface.

[0042] By setting the first period of the spin cleaning process to 1.0 second or more, it is possible to ensure a sufficient time for the cleaning solution on the front surface to reach the edge of the semiconductor wafer. Therefore, the first period of the spin cleaning process is preferably set to 1.0 second or more, and more preferably 3.0 seconds or more. On the other hand, from the viewpoint of the chemical solution flowing around to the front surface of the wafer, the first period of the spin cleaning process is preferably set to 5.0 seconds or less. Furthermore, after the cleaning solution on the front surface reaches the edge of the semiconductor wafer, the rotation speed of the semiconductor wafer can be increased to perform normal spin cleaning. The rotation speed of the semiconductor wafer during the second period is preferably more than 100 rpm and less than or equal to 1000 rpm. The duration of the second period can be set to 3.0 seconds or more and 15.0 seconds or less.

[0043] The nozzle that supplies the cleaning liquid in the spin cleaning process can also supply the same type of conductive liquid as the cleaning liquid in the pretreatment process. When supplying carbonated water or carbonated ozone water in the pretreatment process, carbonated water or carbonated ozone water is supplied from the pure water nozzle or ozone water nozzle on the backside, respectively. In this case, carbonated water is produced using a functional water device, and carbonated ozone water is produced by adding carbon dioxide to ozone water in an ozone production device.

[0044] When the angle of the nozzle supplying the cleaning liquid or conductive liquid to the back surface of the semiconductor wafer is 60° or more, the impact when the cleaning liquid comes into contact with the back surface can be suitably alleviated. Therefore, it is preferable that the angle of the nozzle supplying the cleaning liquid or conductive liquid to the back surface is 60° or more. On the other hand, when the angle of the nozzle supplying the cleaning liquid or conductive liquid to the back surface is 80° or less, the cleaning liquid can be suitably supplied to the back surface. Therefore, it is preferable that the angle of the nozzle supplying the back surface cleaning liquid is 80° or less.

[0045] On the other hand, if the angle of the nozzle supplying the cleaning liquid to the front surface of the semiconductor wafer is 4° or more, it is possible to suitably supply the cleaning liquid uniformly. Therefore, it is preferable that the angle of the nozzle supplying the cleaning liquid to the front surface is 4° or more. On the other hand, if the angle of the nozzle supplying the cleaning liquid to the front surface is 15° or less, a liquid film is suitably obtained. Therefore, it is preferable that the angle of the nozzle supplying the cleaning liquid to the front surface is 15° or less.

[0046] In the pretreatment process, if the diameter of the nozzle supplying the conductive liquid is 3.0 mm or more, the supplied cleaning liquid will effectively form a water column, thereby effectively eliminating static electricity from the semiconductor wafer. Therefore, the diameter of the nozzle supplying the conductive liquid is preferably 3.0 mm or more, and more preferably 4.0 mm or more. On the other hand, if the diameter of the nozzle supplying the conductive liquid is 6.0 mm or less, the same diameter as the nozzle on the front surface, the risk of the chemical liquid getting around to the front surface or splashing off the cup can be effectively reduced. Therefore, the diameter of the nozzle supplying the conductive liquid is preferably 6.0 mm or less.

[0047] When the conductive liquid in the pretreatment process is discharged from a nozzle through a piping line and supplied to the backside of the semiconductor wafer, the piping line and the nozzle are preferably made of a non-metallic material. By making the piping line and the nozzle non-metallic, metal contamination can be effectively prevented. Furthermore, the piping line and the nozzle are preferably made of a resin such as PFA (perfluoroalkoxy fluororesin) or PTFE (polytetrafluoroethylene). Conventionally, metal piping lines have been used to neutralize cleaning water, or earthing has been installed in the piping. However, there has been a concern that the cleaning liquid and the semiconductor wafer may be contaminated by metal due to contact of the cleaning liquid with metal. In the present invention, by adjusting the nozzle diameter and the like as described above and supplying the cleaning liquid as a water column, the semiconductor wafer can be sufficiently neutralized without contacting the cleaning liquid with metal, and therefore the piping line and the nozzle do not need to contain metal.

[0048] [Semiconductor wafer manufacturing method] A method for manufacturing a semiconductor wafer according to one embodiment of the present invention includes the above-described semiconductor wafer cleaning method. This makes it possible to reliably manufacture semiconductor wafers in which the occurrence of ladle-shaped defects is suppressed. The method for manufacturing a semiconductor wafer according to this embodiment includes, for example: - obtaining a single crystal ingot by the Czochralski method; - slicing the single crystal ingot to obtain a plurality of semiconductor wafers; a planarization process in which the semiconductor wafer is subjected to lapping and grinding; a polishing step in which semiconductor wafers are subjected to double-side polishing followed by single-side finish polishing; an epitaxial growth step of forming an epitaxial layer on a semiconductor wafer; - A pre-cleaning process in which semiconductor wafers are cleaned using a combination of SC1 cleaning tanks, HF tanks, ozone tanks, etc., and then rinsed with pure water and dried. -Then there is an optional inspection process; a method for cleaning a semiconductor wafer according to an embodiment of the present invention, including a pretreatment step and a spin cleaning step; a final inspection step including measuring the number of LPDs on the front surface of the semiconductor wafer; The semiconductor wafer after manufacturing, i.e., the semiconductor wafer after the final inspection step, is subjected to device formation processing on the front surface. That is, the present invention is directed to a semiconductor wafer before device formation.

[0049] [Semiconductor wafers] The semiconductor wafer in the present invention is preferably a silicon wafer, more preferably a single crystal silicon wafer, and further preferably a polished wafer or an epitaxial wafer.

[0050] By cleaning a semiconductor wafer using the above cleaning method, a semiconductor wafer can be obtained in which the occurrence of ladle-shaped defects is suppressed. In the semiconductor wafer before device formation in the present invention, the number of defects with convex shapes having a height of 5 nm to 20 nm and concave shapes having a depth of 5 nm to 20 nm occurring on the front surface of the semiconductor wafer is zero. Note that LPD defects other than ladle-shaped defects, such as particles (foreign matter) and SF defects (stacking faults), may also be present. [Example]

[0051] A silicon single crystal wafer (300 mm in diameter) after epitaxial growth processing was prepared and placed in a single-wafer cleaning apparatus. The placed silicon single crystal wafer was subjected to static elimination for 2 seconds using a bar-type ionizer installed in a cleaning tank. The silicon single crystal wafer after processing with the ionizer was then cleaned. Table 1 shows the cleaning conditions. In Inventive Example 1, the conductive liquid in Step 1 was hydrofluoric acid with a concentration of 1.00 mass%, and in Inventive Example 2, the conductive liquid in Step 1 was carbonated ozone water with a carbonic acid concentration of 15 mass ppm and an ozone concentration of 25 mass ppm. In the Comparative Example, cleaning was performed without performing Step 1. In Inventive Examples 1 and 2 and the Comparative Example, after Steps 1 and 2, Steps 3 to 5 were repeated three times, and then Steps 6 and 7 were performed. This series of cleaning steps 1 to 7 was repeated four times. The nozzle that supplies the cleaning liquid to the front surface of the silicon single crystal wafer has a diameter of φ6 mm and a nozzle angle of 4°, and the nozzle that supplies the cleaning liquid and conductive liquid to the back surface of the semiconductor wafer has a diameter of φ4 mm and a nozzle angle of 70°.

[0052] [Table 1]

[0053] Twenty-five cleaned silicon single crystal wafers were prepared for each example, and the front surfaces of the silicon single crystal wafers were measured for LPDs (light point defects) of 14 nm or larger using a KLA Surfscan SP5. Five wafers were randomly selected from each example, and the LPDs detected by the SP5 were observed using a scanning electron microscope (SEM). The defects were classified into particle, SF defect, and ladle-shaped defect based on the observation results. Figure 5 shows representative SEM images of (a) ladle-shaped defects, (b) particles, and (c) SF defects in an example of the present invention. Ladle-shaped defects are observed as defects with depressions and protrusions, and a tail-like shape. Particles are observed as spherical foreign objects. SF defects are observed as defects with line or square edges. Figure 6 shows (a) the counted results of LPDs and (b) a graph of the number of LPD defects by type. In addition, Figure 6(a) plots data from 25 images.

[0054] As shown in Figure 6(a), it is clear that the average number of detected LPDs is lower in Example 1 than in the comparative example, and it is also slightly lower in Example 2 than in the comparative example. Furthermore, as shown in Figure 6(b), a ladle-shaped defect was confirmed in the comparative example, but no ladle-shaped defect was confirmed in Examples 1 and 2. [Industrial Applicability]

[0055] According to the present invention, it is possible to provide a method for cleaning a semiconductor wafer and a method for manufacturing a semiconductor wafer that can suppress the occurrence of ladle-shaped defects. [Explanation of symbols]

[0056] 100 semiconductor wafers 10 Front cleaning nozzle 12 Front cleaning nozzle (for hydrofluoric acid) 14 Front cleaning nozzle (for ozone water) 20 Surface cleaning solution 22 Surface cleaning solution (hydrofluoric acid) 24 Surface cleaning solution (ozone water) 30 Backside cleaning nozzle 32 Backside cleaning nozzle (for hydrofluoric acid) 34 Backside cleaning nozzle (for ozone water) 40 Conductive liquid 42 Backside cleaning solution (hydrofluoric acid) 44 Backside cleaning solution (ozone water)

Claims

1. A semiconductor wafer cleaning method including a spin cleaning step of supplying a cleaning solution to at least a front surface of a semiconductor wafer while rotating the semiconductor wafer, the spin cleaning step includes one or more sets of a combination of an ozone water cleaning step in which the cleaning liquid is ozone water and a subsequent hydrofluoric acid cleaning step in which the cleaning liquid is hydrofluoric acid; A semiconductor wafer cleaning method characterized by including, prior to the spin cleaning step, a pretreatment step of supplying a conductive liquid selected from the group consisting of hydrofluoric acid, carbonated water, and carbonated ozone water only to the back surface of the semiconductor wafer while rotating the semiconductor wafer.

2. 2. The method for cleaning a semiconductor wafer according to claim 1, wherein the conductive liquid is hydrofluoric acid.

3. 2. The method for cleaning a semiconductor wafer according to claim 1, wherein the conductive liquid is carbonated water.

4. 2. The method for cleaning a semiconductor wafer according to claim 1, wherein the conductive liquid is carbonated ozone water.

5. 5. The semiconductor wafer cleaning method according to claim 1, wherein the rotation speed of the semiconductor wafer is 10 rpm or more and 100 rpm or less in the pretreatment step.

6. 6. The semiconductor wafer cleaning method according to claim 5, wherein the spin cleaning step comprises a first period during which the rotation speed of the semiconductor wafer is the same as the rotation speed of the semiconductor wafer in the pretreatment step, followed by a second period during which the rotation speed of the semiconductor wafer is greater than 100 rpm and equal to or less than 1000 rpm.

7. 5. The semiconductor wafer cleaning method according to claim 1, wherein the flow rate of the conductive liquid in the pretreatment step is 0.3 L / min or more and 1.5 L / min or less.

8. 5. The semiconductor wafer cleaning method according to claim 1, wherein in the pretreatment step, the conductive liquid is supplied for a period of time ranging from 1.0 seconds to 5.0 seconds.

9. 5. The semiconductor wafer cleaning method according to claim 1, wherein the conductive liquid is discharged from a nozzle through a piping line and supplied to the back surface of the semiconductor wafer, and the piping line and the nozzle are made of non-metal.

10. The method for cleaning a semiconductor wafer according to any one of claims 1 to 4, wherein the semiconductor wafer is a silicon wafer.

11. A method for manufacturing a semiconductor wafer, comprising the method for cleaning a semiconductor wafer according to any one of claims 1 to 4.

12. A semiconductor wafer before device formation, A semiconductor wafer cleaned by the semiconductor wafer cleaning method according to any one of claims 1 to 4, A semiconductor wafer characterized in that the number of defects occurring on the front surface of the semiconductor wafer is zero, the defects having a convex portion having a height of 5 nm or more and 20 nm or less and a concave portion having a depth of 5 nm or more and 20 nm or less adjacent to the convex portion.

Images