Method and device for producing bubble-free ultrapure water for cleaning semiconductor substrates

Abstract

The invention relates to a device and a method for removing microbubbles from ozonized deionized water (DI / O3), the device comprising: an inner chamber, an outer chamber, with the two chambers being connected via a permeable membrane, an inlet which is designed such that ozonized deionized water (DI / O3) can be forced into the inner chamber, an outlet which is designed such that ozonized deionized water (DI / O3) can escape from the outer chamber, and a ventilation line which is designed such that it can receive gases from the upper space of the outer chamber and conduct them away.

Description

[0001] Method and apparatus for producing bubble-free ultrapure water for cleaning semiconductor substrates

[0002] The invention relates to a method for producing bubble-free ultrapure water for cleaning semiconductor wafers, a method for cleaning semiconductor wafers and a group of semiconductor wafers.

[0003] In the vast majority of semiconductor wafer cleaning processes, ozonated ultrapure water is a crucial component of the cleaning chain. Its strong oxidizing effect removes organic contaminants from the surface and creates defined silicon dioxide (SiO2) layers on the silicon surface. These layers are essential for protecting the semiconductor wafer surface during subsequent processing steps.

[0004] Ozonated ultrapure water (DI / O3) is typically produced by dissolving gaseous ozone in ultrapure water. In an ozone generator, oxygen is enriched with ozone, and this mixture is dissolved in ultrapure water (DI) via a bubble column. This process creates water saturated with oxygen (O2) and ozone (O3). During the purification process, the gas-saturated water tends to degas and form small gas bubbles. In addition to the gas content, new oxygen (O2) is constantly being produced in ozonated water through the decomposition of ozone (O3). This decomposition can easily lead to supersaturated solutions, which can then form gas bubbles.

[0005] These gas bubbles are potentially harmful to the cleaning process because particles can accumulate at the gas / air interface, which can then be deposited on the surface of the semiconductor disk via the gas bubbles.

[0006] The prior art includes documents describing the production of ozonated water. These include, for example, the use of Venturi nozzles (e.g., in WO 2013094309 A1) or static mixers (e.g., in US 2006021634 A1), in which ozonated water can be produced at high concentrations. 2024P00019WG

[0007] 2

[0008] Despite efficient gas injection and mixing, the problem remains that gas bubbles form or excess gas must be removed.

[0009] The prior art mentions methods that utilize membrane degassing or remove gas bubbles from liquids via buoyancy. In particular, documents US 2014357734 A1 and JP 2000015006 A are cited in this context.

[0010] The prior art also includes documents describing the removal of microbubbles from the process medium (JP 2016156744 A and JP 2006334545 A).

[0011] Documents KR 101776020 B1 and JP-H0256201 A describe a specific gas bubble size distribution.

[0012] The purpose of the present patent is to provide suitable devices and methods that make it possible to remove bubbles from ozonated deionized water (DI / O3).

[0013] This problem is solved by the devices and methods described in the claims. Brief description of the figures

[0014] Fig. 1 shows an embodiment of the device according to the invention for removing microbubbles from ozonated deionized water (DI / O3). Ozonated deionized water (DI / O3) is forced through an inlet (102) into an inner chamber (101), which is connected to the outer chamber (100) by a membrane. The water then passes to the outlet (103). Gases that are produced are discharged from the system via the degassing line (104).

[0015] Fig. 2 shows a defect distribution according to the invention. A total of 1251 defects were found during the analysis. These defects are distributed across a total of 30 semiconductor wafers. The mean distance to the nearest neighbor, determined from the spatial coordinates, was 3.77 pm, while the theoretically determined mean distance is 3.70 pm.

[0016] Fig. 3 also shows a defect distribution according to the invention. A total of 4000 defects were found here. The mean distance to the nearest neighbor, calculated from the respective coordinates, is 2.07 pm, while the calculated mean distance is 2.10 pm.

[0017] Fig. 4 shows a defect distribution not according to the invention. 7195 defects were located. The mean distance to the nearest neighbor, calculated from the spatial coordinates, is 0.84 pm, while the theoretically determined mean distance should be 1.01 pm. This figure also visually reveals areas where the probability of defects occurring is apparently higher.

[0018] Fig. 5 shows two size distributions of air bubbles in ozonated deionized water (DI / O3). The solid columns represent the size distribution that can be measured after ozonated deionized water (DI / O3) flows through the device according to the invention, whereas the hatched columns represent the size distribution with the opposite flow. The abscissa describes the diameter D of the bubbles and the ordinate the relative number. Detailed description of embodiments of the invention

[0019] In testing a prior art method for cleaning semiconductor wafers using a semiconductor wafer cleaning device, the inventors found that defect patterns can occur on the wafer that are measurable with an LLS measurement.

[0020] These defect patterns can be visualized by light scattering (LLS) measurement, for example with a measuring device from KLA-Tencor using the Surfscan SP-X (e.g.: Surfscan SP7), and by simultaneously using additional evaluation methods.

[0021] Document WO 2005101 483 A1, for example, discloses a method for measuring scattered light in epitaxially coated semiconductor wafers. The additional evaluation methods are described below.

[0022] As shown in Fig. 4, these defect patterns can occur at different locations on the surface of the semiconductor wafer. Although these defect patterns are very difficult to detect, they nevertheless negatively affect the behavior of the semiconductor wafers during the component manufacturing process, potentially leading to yield losses and performance problems in the manufactured components.

[0023] The inventors therefore sought to find a solution to the aforementioned problem. They succeeded by employing a method using an inventive device that drastically reduces the number of microbubbles formed when ozone dissolves in water.

[0024] The device according to the invention for removing microbubbles from ozonated deionized water (DI / O3) comprises an inner chamber (100) and an outer chamber (101). Both chambers are connected by a permeable membrane. Preferably, the membrane contains pores with a size of less than 100 nm. The inlet (102) is designed such that ozonated deionized water (DI / O3) can be forced into the inner chamber (101). An outlet (103) is designed according to the invention such that the ozonated deionized water (DI / O3) can escape from the outer chamber (100) after it has been forced through the membrane.

[0025] The inventors recognized that a vent line (104) is necessary to collect and remove gases from the upper space of the outer chamber (100). It is particularly important to ensure that the vent line (104) is routed in such a way that no column of water can form.

[0026] The inner chamber (101) is most preferably located inside the outer chamber (100).

[0027] According to the invention, ozonized deionized water (DI / O3) is forced through an inlet (102) into the inner chamber (101) and passes through the membrane to the outer chamber (100) into the outlet (103), wherein the pressure p in the inner chamber (101) is greater than in the outer chamber (100).

[0028] According to the invention, ozonated deionized water (DI / O3) flows through the vent line (104), the volume flow being less than 10% of the volume flow that flows into the inner chamber (100).

[0029] The inventors conducted experiments to quantify both the number of bubbles formed and their size distribution. They found that the number of bubbles in the ozonated ultrapure water is significantly reduced when the water flows as described in the inventive process. A comparative experiment with the opposite flow direction yields a considerably higher number of bubbles. Figure 5 clearly illustrates this relationship.

[0030] The inventors have recognized that this inventive method is suitable for cleaning a group of semiconductor wafers and simultaneously imprinting them with unique properties that characterize them as a whole. A group of semiconductor wafers, wherein each of the semiconductor wafers contained therein has an orientation feature and a front surface with an area S, and all semiconductor wafers have the same diameter, is subjected to a full-surface measurement for particles on the front surface, whereby particles with a size greater than or equal to 15 nm LSE (latex sphere equivalent) are detected.

[0031] The measurement is performed using optical laser light scattering with a wavelength of less than 300 nm, whereby the laser power is chosen so that the scattering intensity is sufficient for the detection of 15 nm large latex spheres.

[0032] The result is a number n of defects for all semiconductor disks in the group, along with their two-dimensional spatial coordinates.

[0033] For the correct storage of spatial coordinates, it is crucial that the coordinate system used is aligned with the orientation feature of the respective semiconductor wafer. For example, an orientation feature might consist of a notch, and this notch defines the origin of the coordinate system to be used. To achieve this, the semiconductor wafers in question are aligned with the orientation feature before the measurement begins.

[0034] For the sake of simplicity, a Cartesian coordinate system can be used.

[0035] First, the distance of each defect to its nearest neighbor is calculated, and then all calculated distance values ​​are arithmetically averaged to calculate an average distance d to the nearest neighbor.

[0036] If the detected defects are evenly distributed across the surface of the semiconductor wafer, the mean distance d can be determined. eq The nearest neighbor can also be determined analytically:

[0037]

[0038] where S represents the surface area of ​​a front face of a semiconductor disk and n represents the number of all defects.

[0039] When examining a group of semiconductor wafers that have a region on their surface where the probability of a defect is higher or lower than on the rest of the surface, this region directly influences the calculated mean distance of the defects to their nearest neighbors. That is, the determined mean distance of the defects to their nearest neighbor deviates from the value that would be obtained if the defects were ideally randomly distributed.

[0040] The inventors assume that the defects are uniformly distributed on the surface of the group of semiconductor wafers under investigation if the determined mean distance to the nearest neighbor d lies within a numerical band between 90% ■ d eq and 110% ■ d eq is located.

[0041] For statistical reasons, the number of defects found must exceed a certain minimum to be meaningful. The inventors have determined that a meaningful conclusion can be drawn once the number of defects exceeds 1000. This directly impacts the number of semiconductor wafers to be measured in the group.

[0042] For example, if measurements are performed that reveal an average of 50 defects on the front face of each semiconductor wafer, then at least 20 semiconductor wafers are needed for the group to reach the minimum required number of 1000 defects. To obtain even better statistics, the number of semiconductor wafers in the group is preferably greater than 25.

[0043] According to the invention, a group of semiconductor wafers, wherein each of the semiconductor wafers contained therein has an orientation feature and a front surface with an area S and all semiconductor wafers have the same diameter, and a full-surface measurement for particles of the front surface of all contained semiconductor wafers, which is carried out by means of optical laser light scattering with a wavelength of less than 300 nm, is a number n of defects together with 2024P00019WQ

[0044] whose two-dimensional spatial coordinates are obtained, wherein the coordinate system used is aligned with the orientation feature of the respective semiconductor disk, characterized in that the mean distance d - the nearest neighbor of a defect is greater than 0.9 ■ and less than 1.1 ■ - ■ and the approach-

[0045]

[0046] 2

[0047]

[0048] The number n of defects is greater than 1000.

[0049] The inventors also propose a method for cleaning semiconductor wafers, which includes the following steps in the given order:

[0050] (1) a first cleaning step to clean with ozonated deionized water and a subsequent rinsing step with purified water,

[0051] (2) a second cleaning step comprising a treatment step with ozonated deionized water, followed by a treatment step with a liquid containing HF, wherein the second cleaning step can be repeated multiple times,

[0052] (3) a third cleaning step for cleaning with ozonated deionized water and a subsequent rinsing step with purified water,

[0053] (4) a drying step in which the side of the semiconductor wafer is dried,

[0054] and that a pre-cleaning step with purified water takes place directly before the first cleaning step, so that one side of the semiconductor wafer is still wet when the first cleaning step begins,

[0055] Essential to this process is that microbubbles are removed from the ozonated deionized water (DI / O3) used by forcing it through an inlet (102) into the inner chamber (101) and through the membrane to the outer chamber (100) and into the outlet (103), where the pressure p in the inner chamber (101) is greater than in the outer chamber (100).

Claims

2024P00019WG 9 Patent claims 1. Device for removing microbubbles from ozonated deionized water (DI / O3), comprising: an inner chamber (100), an outer chamber (101) wherein both chambers are connected by a permeable membrane, and an inlet (102) designed to allow ozonated deionized water (DI / O3) to be forced into the inner chamber (101), and an outlet (103) designed to allow ozonated deionized water (DI / O3) to escape from the outer chamber (100), and a vent line (104) designed to receive and convey gases from the upper space of the outer chamber (100).

2. Device according to claim 1, wherein the membrane contains pores whose size is less than 100 nm.

3. Device according to claim 1, wherein the vent line (104) is guided in such a way that no water column can form.

4. Device according to claim 1, wherein the inner chamber (101) is located within the outer chamber (100).

5. Method for removing microbubbles from ozonated deionized water (DI / O3) using the device of claim 1, wherein ozonated deionized water (DI / O3) is forced through the inlet (102) into the inner chamber (101) and passes through the membrane to the outer chamber (100) and into the outlet (103), where the pressure p in the inner chamber (101) is greater than in the outer chamber (100).

6. The method of claim 5, wherein ozonated deionized water (DI / O3) flows through the vent line (104), the volume flow being less than 10% of the volume flow entering the inner chamber (100).

7. A method for cleaning semiconductor wafers comprising, in a given order: (1) a first cleaning step to clean with ozonated deionized water and a subsequent rinsing step with purified water, (2) a second cleaning step comprising a treatment step with ozonated deionized water, followed by a treatment step with a liquid containing HF, wherein the second cleaning step can be repeated multiple times, (3) a third cleaning step for cleaning with ozonated deionized water and a subsequent rinsing step with purified water, (4) a drying step in which the side of the semiconductor wafer is dried, and that a pre-cleaning step with purified water takes place directly before the first cleaning step, so that one side of the semiconductor wafer is still wet when the first cleaning step begins, characterized in that microbubbles were removed from the ozonized deionized water (DI / O3) according to the method of one of claims 5 or 6.

8. A group of semiconductor wafers, wherein each of the semiconductor disks contained therein has an orientation feature and a front face with an area S and all semiconductor disks have the same diameter, and a full-surface measurement for particles of the front side of all contained semiconductor disks, which is carried out using optical laser light scattering with a wavelength of less than 300 nm, yields a number n of defects together with their two-dimensional spatial coordinates, wherein the coordinate system used is aligned with the orientation feature of the respective semiconductor disk, characterized by the fact that the mean distance d of the nearest neighbor of a defect is greater than 2024P00019WG 11 90% ■- 2 ■ A| S and is smaller than and the number n of defects is greater than 1000.

9. A group of semiconductor wafers according to claim 7, characterized by the fact that the number n is greater than 3000.

10. A group of semiconductor wafers according to claim 7, characterized by the fact that the number n is greater than 10000.

11. A group of semiconductor wafers according to any one of claims 7 to 9, comprising 25 semiconductor wafers.

12. A group of semiconductor wafers according to any one of claims 7 to 9, comprising 100 semiconductor wafers.

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