Method for cleaning semiconductor wafers

Abstract

The invention relates to a method for cleaning the front side and the back side of a semiconductor wafer, comprising, in the following order: cleaning the front side of the semiconductor wafer, comprising, in the following order: (1) a pre-cleaning step with water such that the front side is still wet when the next cleaning step begins, (2) a first cleaning step for cleaning with ozone water such that the front side is still wet when the next cleaning step begins, and (3) a second cleaning step for cleaning with ozone water; (3) a second cleaning step comprising a treatment step with ozone water, followed by a treatment step with a liquid containing HF, (4) a third cleaning step for cleaning with ozone water, followed by a flushing step with purified water, the invention relates to the co-cleaning of the front and back surfaces of a semiconductor wafer, comprising a fourth cleaning step comprising a treatment step with ozone water followed by a treatment step with a liquid containing HF, and a drying step in which both sides of the semiconductor wafer are dried.

Description

Technical Field

[0001] The invention provides a method for cleaning a semiconductor wafer. Background Art

[0002] Semiconductor wafers (typically silicon wafers) used as substrates, e.g. for the manufacture of microelectronic components, are cleaned by wet chemical methods after having been polished, coated (e.g. by epitaxial deposition) or subjected to heat treatment (annealing) steps and / or before high-temperature process steps.

[0003] The purpose of cleaning is to eliminate as far as possible any contamination of the semiconductor wafer by metallic or organic substances such as copper and particles adhering to the wafer surface, because, for example, during the subsequent manufacturing of the components, such contamination leads to problems such as uneven growth of gate oxide or uneven deposition of polysilicon gates.

[0004] The cleaning method adopted includes a single wafer method, in which the semiconductor wafer is set to rotate rapidly around its central axis and is first cleaned by one or more liquids, then rinsed and dried with deionized water. The liquid is applied to the rotating semiconductor wafer and accelerated toward the edge of the wafer by centrifugal force, causing the liquid to flow out externally and form a roughly blanket-like film on the wafer surface. When the semiconductor wafer is subsequently dried by further rotation, for example, by adding a vapor (e.g., isopropyl alcohol vapor) that reduces the surface tension of the liquid film, the liquid film completely flows out to the outside. This method is described, for example, in US 2004 / 0 103 915 A1 and EP 0 905 747 A1.

[0005] US 2014 / 048 100 A1 discloses a method for cleaning semiconductor wafers, wherein the following method steps are used:

[0006] (1) a first cleaning step for cleaning with ozone water, followed by a rinsing step with purified water,

[0007] (2) a second cleaning step comprising a treatment step using ozone water, followed by a treatment step using a liquid containing HF, wherein the second cleaning step may be repeated multiple times,

[0008] (3) a third cleaning step for cleaning with ozone water, followed by a rinsing step with purified water,

[0009] (4) A drying step in which the side surfaces of the semiconductor wafer are dried.

[0010] While testing this method, the inventors discovered that defect patterns that can be measured using LLS measurements can appear on the wafer. These defects appear to occur preferentially in the center of the substrate and can adversely affect the behavior of the affected semiconductor wafer during component manufacturing. If both one side and the other side of a semiconductor wafer are processed when using this process, additional defects can appear in the edge region of the respective opposite side of the semiconductor wafer. For example, if the back side (or reverse side) of a semiconductor wafer is cleaned using this method, particles can subsequently appear in the edge region of the front side and potentially disrupt the semiconductor component process. Summary of the Invention

[0011] It is therefore an object of the present invention to provide a method which does not lead to these drawbacks or at least minimizes the likelihood of their occurrence.

[0012] This object is achieved by the method described in the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] As a graphic illustration, Figure 1 The number of defects D, expressed in relative units, is shown as a function of the radius R of a semiconductor wafer with a nominal diameter of 300 mm. The solid circles represent the number of defects obtained during cleaning according to the prior art. In contrast, the hollow circles represent the number of defects obtained during cleaning according to the method of the present invention. Clearly, the method of the present invention is able to better avoid defects at the edge of the semiconductor wafer than the prior art method.

[0014] abbreviation

[0015] DIW deionized water.

[0016] O3W ozone water consists of 15 to 20 ppm of ozone (O3) dissolved in deionized water.

[0017] SC1 "Standard Clean 1", which contains 0.3% tetramethylammonium hydroxide (TMAH, [N(CH3)4]OH) and 0.7% hydrogen peroxide (H2O2) in deionized water.

[0018] 0.5%-1% hydrogen fluoride (HF) in HF deionized water solution.

[0019] DRY is a drying process performed in a 100% nitrogen atmosphere (N2).

[0020] D. Number of defects. DETAILED DESCRIPTION

[0021] Detailed description of a working example of the present invention

[0022] While testing a method from the prior art for cleaning a semiconductor wafer using an apparatus for cleaning a single wafer (single wafer cleaner), the inventors determined that defect patterns measurable with LLS measurements may occur on the wafer.

[0023] These defect patterns can be visualized by scattered light measurement (eg with an instrument from KLA-Tencor using the Surfscan SP 1MX) and are therefore also referred to as local light scattering load. WO 2005 101 483 A1 discloses a method for scattered light measurement of epitaxially coated semiconductor wafers.

[0024] like Figure 1 As shown in Figure 1, these defects preferentially appear at the edges of semiconductor wafers and can negatively impact the behavior of the affected semiconductor wafers during the component manufacturing process.

[0025] If the back side of a semiconductor wafer is cleaned using methods known from the prior art, the semiconductor wafer has an increased defect density in the edge region of the front side. The inventors have been able to demonstrate these defects using the described measurement technique.

[0026] After cleaning, defects cannot be tolerated on either the front or back side of the semiconductor wafer and must therefore be minimized.

[0027] In attempting to eliminate these defects, the inventors discovered that it was necessary to first clean the front side of the semiconductor wafer, and then to clean both sides collectively (ie, front side and back side).

[0028] According to the invention, the front side of the semiconductor wafer is first subjected to a pre-cleaning step in which the liquid consists essentially of water. The inventors have determined that it is essential that the front side is still wet before the subsequent first cleaning step with ozone water, which is followed by a subsequent rinsing step with pure water, begins.

[0029] According to the invention, a second cleaning step is then performed and comprises a treatment step with ozone water followed by a treatment step with a liquid containing HF.

[0030] After the second cleaning step, according to the present invention, a third cleaning step is performed for cleaning with ozone water, followed by a rinsing step with pure water.

[0031] Thereafter, according to the present invention, joint cleaning of the front and back sides of the semiconductor wafer is performed, including a fourth cleaning step comprising a treatment step using ozone water, followed by a treatment step using a liquid containing HF, and a drying step of drying both sides of the semiconductor wafer.

[0032] Preferably, during the pre-cleaning step, the fraction of ozone water increases from 0% at the beginning of the pre-cleaning step to 100% at the end of the pre-cleaning step, wherein the duration of the fraction less than 5% is less than 10 seconds and greater than 1 second. This continuous increase in the fraction of ozone water between the pre-cleaning step and the first cleaning step obviously has the effect of further reducing the number of defects found.

[0033] More preferably, the pre-cleaning step lasts at least 1 s and no longer than 15 s.

[0034] More preferably, the front side of the semiconductor wafer is aligned horizontally and rotated at a speed greater than 500 rpm and less than 1000 rpm during the pre-cleaning step.

[0035] More preferably, in the pre-cleaning step, water is applied using a nozzle and the nozzle flow velocity here is between 0.5 m / s (meters / second) and 2 m / s, with an associated flow rate between 0.5 L / min (liters / minute) and 1.5 L / min.

[0036] More preferably, the nozzles used are aligned such that the direction of the nozzle stream forms an angle α of less than 70° and greater than 30° with the surface of the semiconductor wafer.

[0037] More preferably, the pre-cleaning step lasts at least 1 s and no more than 15 s; very preferably, this step lasts at least 3 s and no more than 8 s.

[0038] For this method, it is preferred that the side of the semiconductor wafer to be cleaned is aligned horizontally and rotated at a speed greater than 500 rpm and less than 1000 rpm during the pre-cleaning step.

[0039] More preferably, in the pre-cleaning step, water is applied using a nozzle. The nozzle flow rate here is more preferably between 0.5 m / s and 2 m / s, and the associated flow rate is preferably between 0.5 L / min and 1.5 L / min.

[0040] Also preferably, the nozzle is aligned such that the direction of the nozzle stream forms an angle α of less than 70° and greater than 30° with the surface of the semiconductor wafer.

[0041] A particularly preferred embodiment of the method according to the invention for cleaning a front side is shown in Table 1.

[0042]

[0043] Table 1.

Claims

1. A method for cleaning the front and back sides of a semiconductor wafer comprising, in the order given: Cleaning the front side of the semiconductor wafer comprises, in the given order: (1) a pre-cleaning step with water so that the front side is still wet when the next cleaning step begins, (2) a first cleaning step for cleaning with ozone water, followed by a rinsing step with pure water, (3) a second cleaning step comprising a treatment step using ozone water, followed by a treatment step using a liquid containing HF, (4) a third cleaning step for cleaning with ozone water, followed by a rinsing step with pure water, The combined cleaning of the front and back sides of the semiconductor wafer comprises: The fourth cleaning step comprises a treatment step using ozone water, followed by a treatment step using a liquid containing HF, and a drying step, wherein both sides of the semiconductor wafer are dried.

2. The method according to claim 1, wherein The second cleaning step is repeated multiple times.

3. The method according to claim 1, wherein The third cleaning step is followed by a drying step in which the front side of the semiconductor wafer is dried.

4. The method according to claim 1, wherein The fourth cleaning step is repeated multiple times.

5. The method according to claim 1, wherein The fourth cleaning step was repeated more than three times.

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