A method and system for measuring wafer surface damage depth

Abstract

An embodiment of the present invention discloses a method and system for measuring the damage depth of a wafer surface. The method comprises: placing a wafer to be tested in a nitrogen atmosphere for heat treatment; cracking the wafer to be tested that has completed the heat treatment and selecting a sample to be tested according to a set selection strategy; performing angle polishing on the sample to be tested and then etching the polished oblique section; and measuring the surface damage depth of the wafer sample based on the oblique section morphology after etching.

Description

Technical Field

[0001] The embodiments of the present invention relate to the field of wafer production technology, and in particular to a method and system for measuring the depth of damage on a wafer surface. Background Art

[0002] The manufacturing process of semiconductor silicon wafers generally includes: growth of silicon ingots, rolling (grinding), cutting (wire cutting), lapping, polishing and other processes. In order to remove the mechanical damage existing on the surface and edge areas of the wafer, an etching process will be performed after the above processing steps. For some silicon wafers used in semiconductors, the conventional method currently used to measure the depth of mechanical damage existing on the surface area of ​​the wafer is to follow the method proposed in the international standard (ASTM F95-88). Its essence is to use a polishing process to make a small angle bevel on the surface of the sample to expose the cracks in the damaged layer, and then use microscopic means to measure the crack depth on the wafer surface. In the above process, it is also necessary to etch the angle-polished bevel to make the damage more obvious, which is more conducive to subsequent microscopic observation.

[0003] In order to make the boundary between the angle-polished bevel and the surface of the test sample clear and facilitate the selection of the starting point for microscope measurement, the conventional solution usually also glues a companion piece to the test sample; this will cause the following problems: first, it is necessary to glue two samples smaller than 1*1cm, and the surfaces to be angle-polished need to be kept on the same plane, which increases the difficulty of operation; second, the thickness of the adhesive layer between the two samples is difficult to maintain consistency, and there is a risk of falling off during the polishing process, which increases the test error; third, the adhesive layer needs to be removed during subsequent etching, otherwise it will contaminate the etching solution and cannot be reused, increasing the complexity of the operation. In addition to the above problems, the current conventional solution cannot measure damage with a small depth or residual damage stress that still exists in the sample, and the impact of unmeasurable items on the subsequent process and the quality of the final wafer production is very important. Summary of the Invention

[0004] In view of this, an embodiment of the present invention hopes to provide a method and system for measuring the depth of damage on the wafer surface; it can reduce the difficulty of operation, measure the shallow depth of damage and the residual stress in the sample, so that damage that cannot be observed in conventional schemes can be measured, thereby improving measurement efficiency.

[0005] The technical solution of the embodiment of the present invention is achieved as follows:

[0006] In a first aspect, an embodiment of the present invention provides a method for measuring the depth of damage on a wafer surface, the method comprising:

[0007] placing the wafer to be tested in a nitrogen atmosphere for heat treatment;

[0008] The wafer to be tested that has completed the heat treatment is cracked and the sample to be tested is selected according to the set selection strategy;

[0009] After performing angle polishing on the sample to be tested, etching is performed on the polished oblique section;

[0010] The surface damage depth of the wafer sample is measured based on the oblique cross-section morphology after etching.

[0011] In a second aspect, an embodiment of the present invention provides a wafer surface damage depth measurement system, the system comprising: a heat treatment chamber capable of accommodating a wafer to be measured and having a heater, a nitrogen pump capable of supplying nitrogen into the heat treatment chamber, a wafer cutter, an angle polishing kit, an etching kit, and a measurement kit; wherein,

[0012] The nitrogen pump is used to supply nitrogen to the heat treatment chamber containing the wafer to be tested so that the wafer to be tested can be heat treated in a nitrogen atmosphere;

[0013] The wafer cutter is used to crack the wafer to be tested after the heat treatment and select the sample to be tested according to the set selection strategy;

[0014] The angle polishing kit is used to perform angle polishing on the sample to be tested;

[0015] The etching kit is used to etch the polished oblique section after angle polishing;

[0016] The measurement kit is used to measure the surface damage depth of the wafer sample according to the oblique cross-section morphology after etching.

[0017] An embodiment of the present invention provides a method and system for measuring the depth of damage on a wafer surface. Before cracking and sampling, the wafer to be tested is heat-treated in a nitrogen atmosphere to form a thin silicon nitride film on the surface of the wafer to be tested, thereby making the interface between the silicon wafer surface and the subsequent angle-polished surface clearer. In addition, the mechanical damage stress of the wafer to be tested can be released through heat treatment, and silicon oxide or silicon nitride can be formed on the damaged surface under the action of nitrogen and air. The mechanical damage can be amplified and visualized through etching, so that damage that cannot be observed under a microscope in conventional schemes can be measured, thereby increasing the limit of damage detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the conventional method for measuring the depth of machining damage on the wafer surface;

[0019] Figure 2Schematic diagram of damage on the polished section after angle polishing using conventional method;

[0020] Figure 3 A schematic flow chart of a method for measuring wafer surface damage depth provided by an embodiment of the present invention;

[0021] Figure 4 A schematic diagram of interface comparison provided by an embodiment of the present invention;

[0022] Figure 5 A schematic diagram of the composition of a wafer surface damage depth measurement system provided by an embodiment of the present invention;

[0023] Figure 6 A schematic diagram of the composition of an angle polishing kit provided in an embodiment of the present invention;

[0024] Figure 7 A schematic diagram of the composition of a measurement kit provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention.

[0026] Currently, according to the method proposed in the international standard (ASTM F95-88), the conventional method for measuring the depth of machining damage existing in the surface area of ​​the wafer may specifically include the following: Figure 1 The steps shown are as follows: first, a wafer to be tested is selected; then, the wafer to be tested is cracked to obtain a sample wafer and a companion wafer; then, the sample wafer and the companion wafer are bonded together; then, the bonded sample wafer is bonded to a fixture; then, angle polishing is performed; then, the angle-polished sample surface is etched; finally, the subsurface damage after etching is observed under a microscope to measure the damage depth caused by machining.

[0027] In the process of angle polishing according to the above conventional scheme, in detail, Figure 2 As shown, the sample and companion piece are cut at an angle β to the machined surface, and the bevel is polished to remove any damage caused during the cutting process. The polished sample surface is then etched to expose subsurface cracks. Finally, the subsurface crack size L is observed and measured using a microscope. The depth of the subsurface damage, H, can be expressed as: H = L * sin β. As can be appreciated, the bonded companion piece provides a clear boundary with the sample, making it easier to select the starting point for measurement during microscopic observation.

[0028] As for the above conventional scheme, it is understandable that, first, two samples with a size smaller than 1*1cm and a companion sheet need to be bonded together, and the surfaces to be angle-polished need to be kept in the same plane, so the sample preparation method is complicated and the operation is difficult; secondly, the thickness of the adhesive layer between the sample and the companion sheet is difficult to ensure consistency, and there is a risk of falling off during the angle polishing process, which leads to large test errors; then, when etching, the adhesive layer between the sample and the companion sheet needs to be removed, otherwise the etching solution will be contaminated and cannot be reused, which will increase the test cost; finally, and most importantly, the conventional scheme cannot measure residual damage stress in samples with a small damage depth or existing damage, and these unmeasurable hidden dangers are very important for the subsequent processes of wafer production and the impact on silicon wafer quality.

[0029] In view of this, the embodiment of the present invention is expected to be able to pre-process the sample before angle polishing, which can reduce the difficulty of operation, make the boundary clear, and also be able to measure shallow damage and residual stress in the sample, providing strong data support for silicon wafer quality evaluation and subsequent process settings. Based on this, see Figure 3 , which shows a method for measuring wafer surface damage depth provided by an embodiment of the present invention, the method comprising:

[0030] S301: placing the wafer to be tested in a nitrogen atmosphere for heat treatment;

[0031] S302: Cracking the wafer to be tested that has completed the heat treatment and selecting a sample to be tested according to a set selection strategy;

[0032] S303: performing angle polishing on the sample to be tested and then etching the polished oblique section;

[0033] S304: measuring the surface damage depth of the wafer sample according to the oblique cross-section morphology after etching.

[0034] for Figure 3 In the technical solution shown, before cracking and sampling, the wafer to be tested is heat-treated in a nitrogen atmosphere, thereby forming a thin silicon nitride film on the surface of the wafer to be tested, so that the interface between the silicon wafer surface and the subsequent angle polished surface is clearer; in addition, the mechanical damage stress of the wafer to be tested can be released through heat treatment, and silicon oxide or silicon nitride is formed on the damaged surface under the action of nitrogen and air, which can be amplified and revealed through etching, so that damage that cannot be observed under a microscope in conventional schemes can be measured, increasing the limit of damage detection.

[0035] for Figure 3 In some examples of the technical solution shown, the step of placing the wafer to be tested in a nitrogen atmosphere for heat treatment includes:

[0036] Placing the wafer to be tested in a nitrogen atmosphere with a flow rate of 1 to 10 liters / minute LPM;

[0037] The wafer to be tested is subjected to a heat treatment in a nitrogen atmosphere at a temperature of 700 to 900° C. for 2 to 4 hours;

[0038] The wafer to be tested that has been placed in a nitrogen atmosphere and completed the primary heat treatment is subjected to a secondary heat treatment in an environment of 1000 to 1200° C. for 10 to 20 hours to obtain a wafer to be tested that has completed the heat treatment.

[0039] For the above example, it should be noted that after the two heat treatments in the above example, a layer with a thickness of about 3000 to 6000 angstroms will grow on the surface of the wafer to be tested. The thin silicon nitride film; Due to the presence of the silicon nitride film, the interface between the wafer surface and the subsequent angle polishing surface can be made more obvious and clear than the interface without heat treatment in the conventional solution, such as Figure 4 The comparison shown, Figure 4 The left side of the figure is a schematic diagram of the interface of a sample that has not been heat-treated according to the conventional scheme, and the right side is a schematic diagram of the interface after two heat treatments in a nitrogen atmosphere according to the above example. It can be seen that the interface on the right intersects more clearly with the left side. In addition, through the two heat treatments in the above example, the mechanical damage stress inside the wafer can be completely released, and silicon oxide or silicon nitride will be formed on the damaged surface under the action of nitrogen and air. In this way, after subsequent etching treatment, the mechanical damage can be further magnified and visible, so that damage that cannot be observed under a microscope can be measured, increasing the detection limit; still as Figure 4 As shown, the sample without heat treatment showed no damage, while the sample after heat treatment showed mechanical damage, with a damage length of approximately 36.50 μm.

[0040] For the above example, in the preferred implementation process of the embodiment of the present invention, the nitrogen flow rate is selected to be 8 LPM, followed by heat treatment at 900° C. for 2 hours (h); and then heat treatment at 1000° C. for 15 hours.

[0041] for Figure 3 In some examples of the technical solution shown, the process of cracking the wafer to be tested that has completed the heat treatment and selecting the sample to be tested according to the set selection strategy includes:

[0042] The wafer to be tested that has completed the heat treatment is cracked into pieces of 10 mm×10 mm in size to obtain a plurality of wafer samples;

[0043] A wafer sample located at the center of the wafer to be tested, a wafer sample located at R / 2 of the wafer to be tested, and a wafer sample located at the edge of the wafer to be tested are selected as the samples to be tested; wherein R represents the radius of the wafer to be tested.

[0044] For the above example, in detail, the wafer to be tested that has completed heat treatment can be cut into multiple samples with a size of 10mm×10mm. Subsequently, one sample is selected from the center of the wafer to be tested, R / 2 of the wafer to be tested, and the edge of the wafer to be tested as the sample to be tested.

[0045] for Figure 3 In some examples of the technical solution shown, the process of cracking the wafer to be tested that has completed the heat treatment and selecting the sample to be tested according to the set selection strategy includes:

[0046] The test samples with a size of 10 mm×10 mm are cut at the center of the test wafer, at the R / 2 position of the test wafer, and at the edge of the test wafer.

[0047] for Figure 3 In some examples of the technical solution shown, the step of performing angle polishing on the sample to be tested and then etching the polished oblique cross section includes:

[0048] The sample to be tested is pasted under the angle gauge using heated resin glue;

[0049] Placing the angle gauge with the sample to be tested attached thereto on an angle polishing machine for angle polishing, so as to expose the damaged layer of the wafer to be tested to the oblique cross section obtained by polishing;

[0050] After the angle polishing is completed, the sample to be measured is removed from the angle gauge and subjected to Wright etching.

[0051] For the above example, in combination with the aforementioned preferred implementation process, resin glue (such as epoxy glue) can be used to stick the sample to be tested at an angle of 11.32° on a fixture such as an angle gauge. Specifically, the sample to be tested can be stuck on a heating plate with resin glue, and then heated and cured at 140-180°C to firmly stick the sample to be tested; then, the fixture with the sample to be tested is adhered to an angle polishing machine for angle polishing for about 10 minutes (min); after polishing is completed, the sample to be tested can be removed from the angle gauge and Wright etching is performed, and the etching time is about 20s to 60s. After etching is completed, the etched sample to be tested is rinsed clean and dried for use.

[0052] for Figure 3 In some examples of the technical solution shown, measuring the surface damage depth of the wafer sample based on the oblique cross-sectional morphology after etching includes:

[0053] Place the etched sample to be tested on the inclined surface so that the inclined section is parallel to the test table;

[0054] Observe the etching morphology of the oblique cross section on the test table after etching through a microscope;

[0055] The thickness of the damaged layer on the surface of the wafer sample is measured according to the etching profile.

[0056] The specific steps for measuring the damage depth through a microscope are consistent with the current conventional scheme, that is, the sub-surface crack size L is observed and measured under a microscope, the polishing angle is β, and the depth H of the sub-surface damage is calculated using the formula H=L*sinβ.

[0057] Based on the same inventive concept as the above technical solution, see Figure 5 , which shows a wafer surface damage depth measurement system 5 provided by an embodiment of the present invention, the system 5 may include: a heat treatment chamber 51 capable of accommodating a wafer to be measured W and having a heater 511, a nitrogen pump 52 capable of providing nitrogen into the heat treatment chamber 51, a wafer cutter 53, an angle polishing kit 54, an etching kit 55 and a measurement kit 56; wherein,

[0058] The nitrogen pump 52 is used to supply nitrogen to the heat treatment chamber 51 containing the wafer W to be tested so that the wafer to be tested can be heat treated in a nitrogen atmosphere;

[0059] The wafer cutter 53 is used to crack the wafer to be tested after the heat treatment and select the sample to be tested according to the set selection strategy;

[0060] The angle polishing kit 54 is used to perform angle polishing on the sample to be tested;

[0061] The etching kit 55 is used to etch the polished oblique section after angle polishing;

[0062] The measurement kit 56 is used to measure the damage depth on the surface of the wafer sample according to the oblique cross-section morphology after etching.

[0063] It is understandable that in the wafer surface damage depth measurement system 5, not all components are connected to each other, but the components have a sequence of use in the process of executing the aforementioned wafer surface damage depth measurement method. Therefore, Figure 5 The dotted arrows in the figure indicate the sequence of components in executing the method flow.

[0064] In some examples, the nitrogen pump 52 provides nitrogen to the thermal processing chamber 51 at a flow rate of 1 to 10 liters per minute (LPM), so that the wafer W to be tested is placed in a nitrogen atmosphere.

[0065] The heater 511 of the heat treatment chamber 51 is used to heat the heat treatment chamber 51 with a nitrogen atmosphere and the wafer W to be tested to a temperature of 700 to 900° C. for 2 to 4 hours to complete a heat treatment; and

[0066] After the first heat treatment is completed, the heat treatment chamber 51 with a nitrogen atmosphere and the wafer W to be tested is heated to 1000-1200° C. for 10-20 hours to complete the second heat treatment, thereby obtaining a wafer to be tested that has completed the heat treatment.

[0067] In some examples, the wafer cutter 53 is used to split the wafer to be tested that has completed heat treatment into 10mm×10mm sizes to obtain multiple wafer samples; and, select a wafer sample at the center of the wafer to be tested, a wafer sample at R / 2 of the wafer to be tested, and a wafer sample at the edge of the wafer to be tested as the samples to be tested; wherein R represents the radius of the wafer to be tested.

[0068] In some examples, the wafer cutter 53 is used to cut the sample to be tested with a size of 10 mm×10 mm at the center of the wafer to be tested, at the R / 2 position of the wafer to be tested, and at the edge of the wafer to be tested.

[0069] In some examples, such as Figure 6 As shown, the angle polishing kit 54 includes an angle gauge 541 and an angle polishing machine 542; wherein,

[0070] The angle gauge 541 is used to adhere the sample to be tested using heated resin glue;

[0071] The angle polisher 542 is used to perform angle polishing on the angle gauge to which the sample to be tested is attached, so as to expose the damaged layer of the wafer to be tested to the oblique cross section obtained by polishing.

[0072] In some examples, such as Figure 7 As shown, the measurement kit 56 includes a test table 561, a microscope 562 and a calculation part 563; wherein,

[0073] The test table 561 is used to place the sample to be tested after etching; specifically, the sample to be tested after etching can be placed on the inclined surface so that the inclined section is parallel to the test table;

[0074] The microscope 562 is used to observe the etching morphology of the oblique cross section on the test table after etching;

[0075] The calculation part 563 is used to measure the thickness of the damaged layer on the surface of the wafer sample according to the etching morphology.

[0076] It is understandable that the exemplary technical solution of the wafer surface damage depth measurement system 5 and the technical solution of the wafer surface damage depth measurement method described above are based on the same concept. Therefore, for details not described in detail in the technical solution of the wafer surface damage depth measurement system 5, reference can be made to the description of the technical solution of the wafer surface damage depth measurement method described above. This embodiment of the present invention will not be elaborated on in detail.

[0077] It should be noted that the technical solutions described in the embodiments of the present invention can be arbitrarily combined without conflict.

[0078] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for measuring the depth of damage on a wafer surface, characterized in that: The method comprises: Placing the wafer to be tested in a nitrogen atmosphere for heat treatment so that a silicon nitride film is formed on the surface of the wafer to be tested; Cracking the wafer to be tested after the heat treatment and selecting the sample to be tested; After performing angle polishing on the sample to be tested, etching is performed on the polished oblique section; The surface damage depth of the sample to be tested is measured according to the oblique cross-section morphology after etching.

2. The method according to claim 1, characterized in that Placing the wafer to be tested in a nitrogen atmosphere for heat treatment includes: Placing the wafer to be tested in a nitrogen atmosphere with a flow rate of 1 to 10 liters / minute LPM; The wafer to be tested is subjected to a heat treatment in a nitrogen atmosphere at a temperature of 700 to 900° C. for 2 to 4 hours; The wafer to be tested that has been placed in a nitrogen atmosphere and completed the primary heat treatment is subjected to a secondary heat treatment in an environment of 1000 to 1200° C. for 10 to 20 hours to obtain a wafer to be tested that has completed the heat treatment.

3. The method according to claim 1, characterized in that The method of cracking the wafer to be tested after the heat treatment and selecting the sample to be tested includes: The wafer to be tested that has completed the heat treatment is cracked into pieces of 10 mm×10 mm in size to obtain a plurality of wafer samples; A wafer sample located at the center of the wafer to be tested, a wafer sample located at R / 2 of the wafer to be tested, and a wafer sample located at the edge of the wafer to be tested are selected as the samples to be tested; wherein R represents the radius of the wafer to be tested.

4. The method according to claim 1, wherein The method of cracking the wafer to be tested after the heat treatment and selecting the sample to be tested includes: The test samples with a size of 10 mm×10 mm are cut at the center of the test wafer, at the R / 2 position of the test wafer, and at the edge of the test wafer.

5. The method according to claim 1, wherein The step of performing angle polishing on the sample to be tested and then etching the polished oblique cross section comprises: The sample to be tested is pasted under the angle gauge using heated resin glue; Placing the angle gauge with the sample to be tested attached thereto on an angle polishing machine for angle polishing, so as to expose the damaged layer of the wafer to be tested to the oblique cross section obtained by polishing; After the angle polishing is completed, the sample to be measured is removed from the angle gauge and subjected to Wright etching.

6. The method according to claim 1, characterized in that The measuring of the surface damage depth of the sample to be tested according to the oblique cross-sectional morphology after etching includes: Place the etched sample to be tested on the inclined surface so that the inclined section is parallel to the test table; Observe the etching morphology of the oblique cross section on the test table after etching through a microscope; The thickness of the damaged layer on the surface of the sample to be tested is measured according to the etching morphology.

7. A wafer surface damage depth measurement system, characterized in that: The system includes: a heat treatment chamber capable of accommodating a wafer to be tested and having a heater, a nitrogen pump capable of supplying nitrogen into the heat treatment chamber, a wafer cutter, an angle polishing kit, an etching kit, and a measurement kit; wherein, The nitrogen pump is used to supply nitrogen to the heat treatment chamber containing the wafer to be tested so that the wafer to be tested can be heat treated in a nitrogen atmosphere, so that a silicon nitride film is formed on the surface of the wafer to be tested; The wafer cutter is used to crack the wafer to be tested after the heat treatment and select the sample to be tested; The angle polishing kit is used to perform angle polishing on the sample to be tested; The etching kit is used to etch the polished oblique section after angle polishing; The measurement kit is used to measure the surface damage depth of the sample to be tested based on the oblique cross-section morphology after etching.

8. The system according to claim 7, characterized in that The nitrogen pump provides nitrogen to the thermal treatment chamber at a flow rate of 1 to 10 liters per minute (LPM) so that the wafer to be tested is placed in a nitrogen atmosphere; The heater of the heat treatment chamber is used to heat the heat treatment chamber with a nitrogen atmosphere and a wafer to be tested to a temperature of 700 to 900° C. for 2 to 4 hours to complete a heat treatment; and After the first heat treatment is completed, the heat treatment chamber with a nitrogen atmosphere and the wafer to be tested is heated to 1000 to 1200° C. for 10 to 20 hours to complete the second heat treatment, thereby obtaining the wafer to be tested that has completed the heat treatment.

9. The system according to claim 7, wherein: The angle polishing kit includes an angle gauge and an angle polishing machine; wherein, The angle gauge is used to adhere the sample to be tested using heated resin glue; The angle polishing machine is used to perform angle polishing on the angle gauge to which the sample to be tested is attached, so as to expose the damaged layer of the wafer to be tested to the oblique cross section obtained by polishing.

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