A wafer grinding method and the ground wafer

Abstract

This invention discloses a wafer polishing method and a polished wafer. The polishing method sequentially includes a first polishing, a second polishing, a third polishing, a fourth polishing, and a fifth polishing. The first, second, third, and fourth polishing steps polish the metal film on the wafer surface. After the fourth polishing, all the metal film on the wafer surface is polished. The polished thickness satisfies the following conditions: T0 = 2 × T1 - T2 - 0.2; T1 = 0.7 × T0 - 0.2; T2 = 4 × T3 - 0.4; where T0 is the initial thickness of the metal film on the wafer surface, T1 is the remaining metal film thickness after the first polishing, T2 is the remaining metal film thickness after the second polishing, and T3 is the remaining metal film thickness after the third polishing. This invention employs a five-step polishing process, where the first four steps polish the metal film on the wafer surface to a specific thickness, ultimately improving polishing efficiency and simultaneously improving surface defects on the wafer.

Description

Technical Field

[0001] This invention relates to the field of wafer manufacturing, and more specifically to a wafer grinding method and the ground wafer. Background Technology

[0002] In integrated circuit manufacturing, ultra-thick metal (UTM) deposition is frequently encountered due to device design requirements. Typically, when forming copper interconnects, copper is deposited in trenches. After deposition, the thickness of the copper layer outside the trenches and on the dielectric layer can reach 4 micrometers or more. This portion of copper needs to be removed by chemical mechanical polishing (CMP). CMP for ultra-thick metals is problematic due to the large amount of metal removed, long polishing time, rapid temperature rise during polishing, and difficulty in completely removing byproducts. This leads to a decrease in polishing rate, changes in wafer surface morphology uniformity, and increased susceptibility to scratch defects, ultimately reducing product yield and reliability.

[0003] In existing technologies, a two-step polishing method is commonly used. Taking the removal of the copper layer and diffusion barrier layer outside the trench as an example, the first step of polishing removes part of the copper layer, and the second step removes the remaining copper layer, diffusion barrier layer, and part of the interlayer dielectric layer. In the first polishing step, the wafer undergoes high-pressure polishing on the first polishing pad P1, high-pressure polishing on the second polishing pad P2, and cleaning in a cleaning tank. In the second polishing step, the wafer undergoes high-pressure polishing on the first polishing pad P1, low-pressure polishing on the second polishing pad P2, polishing on the third polishing pad P3, and cleaning in a cleaning tank. Because the wafer needs to be placed in the first polishing pad, the second polishing pad, and the cleaning tank twice, the turnaround time between the polishing pads and the cleaning tank is increased, thereby reducing throughput and increasing costs. Later, some researchers improved this technology by integrating the first step into the first polishing pad. After rinsing the polishing pad with high-pressure water, the second step was performed on the first polishing pad. While this avoided secondary cleaning and shortened processing time, it resulted in excessively long processing time for the wafer on the first polishing pad, also impacting throughput. Furthermore, as the number of wafers processed increases, the difference in actual usage time between polishing pads one and two becomes increasingly significant, leading to material waste and higher costs. The existing ultra-thick metal polishing process flow is as follows: Existing ultra-thick metal chemical mechanical polishing methods suffer from drawbacks such as low machine throughput, poor wafer uniformity, and high costs. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is that the existing grinding methods have low production capacity, poor uniformity within the wafer, and high cost, thereby providing a wafer grinding method and a ground wafer.

[0005] Therefore, the present invention adopts the following technical solution:

[0006] The present invention provides a wafer polishing method, characterized in that it includes a first polishing, a second polishing, a third polishing, a fourth polishing and a fifth polishing in sequence, wherein the first polishing, the second polishing, the third polishing and the fourth polishing are for polishing the metal film on the wafer surface, and after the fourth polishing is completed, all the metal film on the wafer surface is polished.

[0007] The thickness of the ground material meets the following requirements:

[0008] T0 = ​​2 × T1 - T2 - 0.2;

[0009] T1 = 0.7 × T0 - 0.2;

[0010] T2 = 4 × T3 - 0.4

[0011] Where T0 is the initial thickness of the metal film on the wafer surface, T1 is the remaining thickness of the metal film after the first polishing, T2 is the remaining thickness of the metal film after the second polishing, and T3 is the remaining thickness of the metal film after the third polishing, which is generally between 0.2 and 0.5 μm.

[0012] The initial thickness of the metal film on the wafer surface is 3.5-5 μm.

[0013] During the first polishing process, the polishing disc applies a pressure of 2.2-2.6 psi to the wafer surface and injects a metal polishing slurry at a flow rate of 250-350 ml / min;

[0014] During the second polishing process, the polishing disc applies a pressure of 2.2-2.5 psi to the wafer surface and injects a metal polishing slurry at a flow rate of 250-350 ml / min;

[0015] During the third grinding process, the grinding disc applies a pressure of 2.2-2.5 psi to the wafer surface and injects a metal polishing slurry with a flow rate of 250-350 ml / min.

[0016] During the fourth polishing process, the polishing disc applies a pressure of 1.4-1.8 psi to the wafer surface and injects a metal polishing slurry with a flow rate of 250-350 ml / min. The metal polishing slurry is selected according to the material of the metal film, including U3061 polishing slurry produced by Anji Technology and CU3086 slurry from Versum.

[0017] The fifth polishing process involves removing the barrier layer on the wafer surface and polishing the dielectric material, wherein the thickness of the polished dielectric material is 1–1.5 μm.

[0018] During the fifth polishing process, the polishing disc applies a pressure of 1.2-1.8 psi to the wafer surface and injects a barrier polishing slurry at a flow rate of 250-350 ml / min. The barrier polishing slurry includes LK393C4 polishing slurry produced by Dow Chemical and H6S polishing slurry from Anji Technology.

[0019] The metal film can be copper, or it can be tungsten or aluminum.

[0020] The third and fourth grinding are performed on the same grinding disc, while the first, second, and fifth grinding are performed independently on different grinding discs.

[0021] During grinding, the grinding disc rotates at 83-103 rpm, and the grinding head rotates at 77-97 rpm.

[0022] The present invention also provides a wafer, which is ground by the above-described grinding method.

[0023] The technical solution of this invention has the following advantages:

[0024] (1) The present invention employs a five-step grinding process, wherein the first four steps grind the metal film on the wafer surface to a specific thickness, thereby improving the grinding efficiency and improving the surface defects of the wafer.

[0025] (2) This invention employs four independent grinding discs for grinding, removing excess conductive metal layers, barrier layers, and a small amount of dielectric layers outside the trenches. Wafer cleaning is performed after grinding, achieving dry-in, dry-out wafer processing. Specifically, the first, second, and third grinding discs are paired with hard polishing pads for metal grinding, while the fourth grinding disc is paired with a soft polishing pad for grinding the barrier layer and a small amount of dielectric material. Since the wafer passes sequentially through the first, second, and third grinding discs, the grinding is completed by the fourth grinding disc and cleaning device. This eliminates the need for repeated grinding between different grinding discs and cleaning devices, shortening the grinding time per disc, thus increasing productivity and reducing costs. Furthermore, the chemical mechanical polishing method of this invention uses high-pressure grinding on the first and second discs, combined with eddy current detection to measure the wafer's metal film thickness. In the third disc grinding, high-pressure grinding is first used with eddy current detection, followed by low-pressure grinding, finally stopping at the barrier layer using optical endpoint monitoring. Finally, the barrier layer and a portion of the dielectric material are removed on the soft polishing pad of the fourth grinding disc.

[0026] (3) The present invention yields wafers with good quality and excellent production capacity, making it suitable for large-scale production. Attached Figure Description

[0027] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of the structure of the wafer to be ground in Embodiment 1 of the present invention;

[0029] Figure 2 This is a schematic diagram of the morphological changes of the wafer surface during the grinding process in Embodiment 1 of the present invention;

[0030] Figure 3 This is a schematic diagram of the morphological changes of the wafer surface during the grinding process in Comparative Example 1 of the present invention.

[0031] Figure label:

[0032] 1-Metallic material; 2-Barrier layer; 3-Dielectric layer. Detailed Implementation

[0033] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0034] Where specific experimental steps or conditions are not specified in the embodiments, they can be performed according to the conventional experimental steps or conditions described in the literature in this field.

[0035] The following specific embodiments further illustrate the present invention. The examples given do not represent all embodiments of the present invention; only some embodiments are described as examples. Specific embodiments are as follows:

[0036] Example 1

[0037] This embodiment provides a wafer grinding method, such as... Figure 1 As shown, the thickness T0 of the metal film layer 1 of the wafer is 4.5 μm, the material is copper, the barrier layer 2 is tantalum nitride and tantalum, and the dielectric 3 is pure silicon dioxide. From T0 = 2 × T1 - T2 - 0.2; T1 = 0.7 × T0 - 0.2; T2 = 4 × T3 - 0.4, we can obtain T1 = 2.95 μm, T2 = 1.2 μm, and T3 = 0.4 μm.

[0038] The specific steps are as follows:

[0039] (1) The wafer surface is subjected to a first grinding with a pressure of 2.4 psi, and copper polishing liquid is injected into the wafer surface at a flow rate of 300 ml / min to remove the metal film layer on the wafer barrier layer to a metal film layer thickness of 2.95 μm;

[0040] (2) The wafer surface obtained in step (1) is subjected to a second grinding with a pressure of 2.2 psi, and copper polishing liquid with a flow rate of 300 ml / min is injected into the wafer surface to remove the metal film layer on the wafer barrier layer until the thickness of the metal film layer is 1.2 μm.

[0041] (3) Apply a third grinding pressure of 2.2psi to the wafer surface obtained in step (2), and simultaneously inject copper polishing slurry at a flow rate of 300ml / min onto the wafer surface to remove the metal film layer on the wafer barrier layer until the thickness of the metal film layer is 0.4μm; then apply a fourth grinding pressure of 1.6psi to the wafer surface, and simultaneously inject copper polishing slurry at a flow rate of 300ml / min onto the wafer surface until all the metal film layer on the barrier layer is ground clean.

[0042] (4) The wafer surface obtained in step (3) is subjected to a fifth grinding with a pressure of 1.5 psi, accompanied by the injection of a barrier layer polishing slurry with a flow rate of 300 ml / min, to remove the barrier layer and grind the dielectric to the required thickness of 1 μm.

[0043] In this process, steps (1)-(4) are carried out independently in the grinding disc, and the grinding disc rotates at 93 rpm and the grinding head rotates at 87 rpm. In addition, the polishing liquid used in steps (1)-(3) is U3061 polishing liquid produced by Anji Technology, and the barrier layer polishing liquid used in step (4) is LK393C4 polishing liquid produced by Dow Chemical.

[0044] Tests showed that the wafer production capacity in this embodiment is 16 wafers per hour, which can effectively increase output and reduce costs.

[0045] Example 2

[0046] This embodiment provides a wafer polishing method. The thickness T0 of the metal film layer of the wafer is 4μm, the material is copper, the barrier layer is tantalum nitride and tantalum, and the dielectric is pure silicon dioxide. From T0 = 2×T1-T2-0.2; T1 = 0.7×T0-0.2; T2 = 4×T3-0.4, we can obtain T1 = 2.6μm, T2 = 1μm, and T3 = 0.35μm.

[0047] The specific steps are as follows:

[0048] (1) The wafer surface is subjected to a first grinding with a pressure of 2.5 psi, and copper polishing slurry with a flow rate of 280 ml / min is injected into the wafer surface to remove the metal film layer on the wafer barrier layer to a metal film layer thickness of 2.6 μm;

[0049] (2) The wafer surface obtained in step (1) is subjected to a second grinding with a pressure of 2.3 psi, and copper polishing liquid with a flow rate of 280 ml / min is injected into the wafer surface to remove the metal film layer on the wafer barrier layer until the thickness of the metal film layer is 1 μm.

[0050] (3) Apply a third grinding pressure of 2.3psi to the wafer surface obtained in step (2), and simultaneously inject copper polishing slurry at a flow rate of 280ml / min onto the wafer surface to remove the metal film layer on the wafer barrier layer until the thickness of the metal film layer is 0.35μm; then apply a fourth grinding pressure of 1.7psi to the wafer surface, and simultaneously inject copper polishing slurry at a flow rate of 280ml / min onto the wafer surface until all the metal film layer on the barrier layer is ground clean.

[0051] (4) The wafer surface obtained in step (3) is subjected to a fifth grinding with a pressure of 1.6 psi, accompanied by the injection of a barrier layer polishing slurry with a flow rate of 280 ml / min, to remove the barrier layer and grind the dielectric to the required thickness of 1 μm.

[0052] In this process, steps (1)-(4) are performed independently in the grinding disc, and the grinding disc rotates at 103 rpm and the grinding head rotates at 97 rpm. In addition, the polishing fluid used in steps (1)-(3) is Versum's CU3086 polishing fluid, and the barrier layer polishing fluid used in step (4) is Anji Technology's H6S polishing fluid.

[0053] Tests showed that the wafer production capacity in this embodiment is 17 wafers per hour, which can effectively increase output and reduce costs.

[0054] Example 3

[0055] This embodiment provides a wafer polishing method. The thickness T0 of the metal film layer of the wafer is 3.5 μm, the material is copper, the barrier layer is tantalum nitride and tantalum, and the dielectric is pure silicon dioxide. From T0 = 2 × T1 - T2 - 0.2; T1 = 0.7 × T0 - 0.2; T2 = 4 × T3 - 0.4, we can obtain T1 = 2.25 μm, T2 = 0.8 μm, and T3 = 0.3 μm.

[0056] The specific steps are as follows:

[0057] (1) The wafer surface is subjected to a first grinding with a pressure of 2.5 psi, and copper polishing liquid is injected into the wafer surface at a flow rate of 250 ml / min to remove the metal film layer on the wafer barrier layer to a metal film layer thickness of 2.25 μm;

[0058] (2) The wafer surface obtained in step (1) is subjected to a second grinding with a pressure of 2.4 psi, and copper polishing liquid with a flow rate of 250 ml / min is injected into the wafer surface to remove the metal film layer on the wafer barrier layer until the thickness of the metal film layer is 0.8 μm.

[0059] (3) Apply a third grinding pressure of 2.3psi to the wafer surface obtained in step (2), and simultaneously inject copper polishing slurry at a flow rate of 250ml / min onto the wafer surface to remove the metal film layer on the wafer barrier layer until the thickness of the metal film layer is 0.3μm; then apply a fourth grinding pressure of 1.5psi to the wafer surface, and simultaneously inject copper polishing slurry at a flow rate of 250ml / min onto the wafer surface until all the metal film layer on the barrier layer is ground clean.

[0060] (4) The wafer surface obtained in step (3) is subjected to a fifth grinding with a pressure of 1.5 psi, accompanied by the injection of a barrier layer polishing slurry with a flow rate of 300 ml / min, to remove the barrier layer and grind the dielectric to the required thickness of 0.8 μm.

[0061] In this process, steps (1)-(4) are carried out independently in the grinding disc, and the grinding disc rotates at 93 rpm and the grinding head rotates at 87 rpm. In addition, the polishing liquid used in steps (1)-(3) is Versum's CU3086 polishing liquid, and the barrier layer polishing liquid used in step (4) is Dow Chemical's LK393C4 polishing liquid.

[0062] Tests showed that the wafer production capacity in this embodiment is 20 wafers per hour, which can effectively increase output and reduce costs.

[0063] Comparative Example 1

[0064] This comparative example provides a wafer polishing method. The wafer to be polished is exactly the same as that in Example 1, but only three polishing pads are used. The specific steps are as follows:

[0065] (1) The wafer surface is subjected to a first grinding with a pressure of 2.4 psi, and copper polishing liquid with a flow rate of 300 ml / min is injected into the wafer surface to remove the copper body on the wafer barrier layer until the thickness of the resulting wafer is 3 μm.

[0066] (2) The wafer surface obtained in step (1) is subjected to a second grinding with a pressure of 2.2 psi, and copper polishing liquid with a flow rate of 300 ml / min is injected into the wafer surface to remove the copper body on the wafer barrier layer until the thickness of the obtained wafer is 1.7 μm.

[0067] (3) Place the wafer obtained in step (2) into the cleaning device for cleaning.

[0068] (4) The wafer surface obtained in step (3) is subjected to a third grinding with a pressure of 2.2 psi, and copper polishing liquid with a flow rate of 300 ml / min is injected into the wafer surface to remove the copper body on the wafer barrier layer until the thickness of the obtained wafer is 0.3 μm.

[0069] (5) Apply a pressure of 1.6 psi to the wafer surface for the fourth grinding, and inject copper polishing slurry at a flow rate of 300 ml / min onto the wafer surface until all the copper on the barrier layer is ground off.

[0070] (6) The wafer surface obtained in step (5) is subjected to a fifth polishing with a pressure of 1.5 psi, accompanied by the injection of a barrier layer polishing slurry with a flow rate of 300 ml / min, to remove the barrier layer and polish the dielectric to the required thickness.

[0071] Steps (1) and (4) are performed on the first grinding table, steps (2) and (5) are performed on the second grinding table, and step (6) is performed on the third grinding table. The grinding disc rotates at 93 rpm and the grinding head rotates at 87 rpm. In addition, the polishing liquid used in steps (1) and (5) is U3061 polishing liquid produced by Anji Technology, and the barrier layer polishing liquid used in step (6) is LK393C4 polishing liquid produced by Dow Chemical.

[0072] Calculations show that the wafer production capacity in this comparative example is 11 wafers per hour.

[0073] Comparative Example 2

[0074] This comparative example provides a wafer polishing method. The wafer to be polished is exactly the same as in Example 1, except that the polishing thickness is different: T1 is 3.5 μm, T2 is 0.9 μm, and T3 is 0.3 μm. Although the first polishing time in Comparative Example 2 is 80 s, the second polishing time is 120 s, and the sum of the third and fourth polishing times is 60 s, while the sum of the first, second, third, and fourth polishing times in Example 1 is 90 s, the total polishing time in Comparative Example 2 is slightly less than that in Example 1. However, because it does not use a specific polishing thickness, the polishing time difference between multiple polishing pads is too large, which is not conducive to improving the machine's capacity. The final capacity is only 13 wafers per hour, which is significantly lower than the capacity in Example 1.

[0075] Test case

[0076] The same wafers were ground using the methods of Example 1 and Comparative Example 1. During the grinding process, the eddy current sensor on the machine was used to detect the change in the thickness and morphology of the metal film on the wafer surface over time. The wafer was scanned once as it passed through the monitoring device, and the results were displayed in real time on the monitoring software. Figure 2 and Figure 3 As shown, the vertical axis represents the thickness of the metal film, with units of... The horizontal axis represents the wafer diameter, used to indicate different positions on the wafer, from -150 to 150 mm, where 0 represents the center of the wafer. Using the polishing method in Example 1, the thickness difference between the highest and lowest Cu points within the wafer can be controlled to approximately 0.2 μm. Using the method in Comparative Example 1, the Cu thickness range within the wafer is approximately 0.3 μm. This is because as the polishing time increases, the temperature between the wafer and the polishing pad rises. The increased temperature leads to a higher polishing rate and a decreased ability to control the wafer surface morphology. Therefore, the uniformity within the wafer in Example 1 of this application is ultimately improved by approximately 33% compared to Comparative Example 1.

[0077] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for grinding a wafer, characterized in that, The process includes a first grinding, a second grinding, a third grinding, a fourth grinding, and a fifth grinding, wherein the first grinding, the second grinding, the third grinding, and the fourth grinding are for grinding the metal film on the surface of the wafer, and after the fourth grinding is completed, all the metal film on the surface of the wafer is ground. The thickness of the ground material meets the following requirements: T0 = ​​2 × T1 - T2 - 0.2; T1 = 0.7 × T0 - 0.2; T2 = 4 × T3 - 0.4; Where T0 is the initial thickness of the metal film on the wafer surface, T1 is the remaining thickness of the metal film after the first grinding, T2 is the remaining thickness of the metal film after the second grinding, and T3 is the remaining thickness of the metal film after the third grinding. The initial thickness of the metal film on the wafer surface is 3.5 μm-5 μm; During the first grinding process, the grinding disc applies a pressure of 2.2psi-2.6psi to the wafer surface and injects a metal polishing slurry at a flow rate of 250mL / min-350mL / min; During the second polishing process, the polishing disc applies a pressure of 2.2 psi to 2.5 psi to the wafer surface and injects a metal polishing slurry at a flow rate of 250 mL / min to 350 mL / min. During the third grinding process, the grinding disc applies a pressure of 2.2psi-2.5psi to the wafer surface and injects a metal polishing slurry at a flow rate of 250mL / min-350mL / min. During the fourth grinding process, the grinding disc applies a pressure of 1.4 psi to 1.8 psi to the wafer surface and injects a metal polishing slurry at a flow rate of 250 mL / min to 350 mL / min. In the fifth polishing process, the fifth polishing involves removing the barrier layer on the wafer surface and polishing the dielectric material, wherein the polishing thickness of the dielectric material is 1μm-1.5μm. After the fifth grinding process is completed, wafer cleaning is performed to achieve dry wafer in and dry out. The third and fourth grinding are performed on the same grinding disc, while the first, second, and fifth grinding are performed independently on different grinding discs.

2. The wafer grinding method according to claim 1, characterized in that, During the fifth polishing process, the polishing disc applies a pressure of 1.2 psi to 1.8 psi to the wafer surface and injects a barrier polishing slurry at a flow rate of 250 mL / min to 350 mL / min.

3. The wafer grinding method according to claim 1, characterized in that, The metal film is copper.

4. The wafer grinding method according to claim 1 or 2, characterized in that, During grinding, the grinding disc rotates at 83 rpm to 103 rpm, and the grinding head rotates at 77 rpm to 97 rpm.

5. A wafer, characterized in that, The wafer is ground using the grinding method described in any one of claims 1-4.

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