A method for measuring the height of bumps on a wafer surface having a repassivation layer

Abstract

The present invention discloses a method for measuring the height of a bump having a repassivation layer on the surface of a wafer, comprising: sputtering a layer of titanium on a wafer having completed bump manufacturing to form a titanium shielding layer, the titanium shielding layer being formed on the surface of the bump and the repassivation layer; then, measuring the highest signal on the top of the titanium shielding layer on the bump to obtain the top signal height, measuring the signal height of the titanium shielding layer on the repassivation layer corresponding to the bump to obtain the bottom signal height, and directly obtaining the bump height by subtracting the top signal height from the bottom signal height; finally, removing the titanium shielding layer. The measuring method provided by the present invention sputters a titanium shielding layer on a wafer having completed bump manufacturing, the titanium shielding layer covers the surface of the repassivation layer and the top of the bump, so that the light source cannot penetrate the titanium shielding layer, accurately grasps the reference surface, and measures the highest signal height and the bottom signal height. The height obtained by this method is the real height of the bump, so as to correctly evaluate the process capability and judge the product quality.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor packaging, and more particularly to a method for measuring the height of a bump having a repassivation layer on a wafer surface. Background Art

[0002] A wafer is a round silicon chip with many independent circuits built on it. A single independent circuit is called a die, and the electroplated bumps on the die are called bumps. After the wafer has completed the bumping process, all the bumps on the wafer are measured using 3D measurement equipment.

[0003] When using 3D measurement equipment for measurement, the light source of the 3D measurement equipment will penetrate the re-passivation layer on the chip surface, resulting in inaccurate measurement, such as Figure 1 As shown in the figure, the 3D measurement equipment measures the highest point on the bump to obtain the highest signal height A, and the re-passivation that penetrates the chip surface measures the bottom signal height B. It can only get the difference between the bottom signal height B and the highest signal height A. Since the bottom signal position B is lower than the re-passivation surface, the bump height is eventually too high. In this way, it is impossible to accurately measure the bump height, evaluate the process capability, and judge the product quality. Therefore, it is very important to be able to accurately measure the bump height.

[0004] The existing measurement method is to uniformly subtract a fixed value from the data after measuring it in the above manner to make it close to the true value. This method assumes that the thickness of the Re-passivation is also the fixed value, but the actual thickness of the Re-passivation will vary in distribution within the wafer, so this method has limitations. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a method for measuring the bump height of a wafer with a re-passivation layer on the surface. The light source of the 3D measuring equipment cannot penetrate the re-passivation layer, and can accurately capture the measured reference surface to obtain an accurate bump height value, thereby providing real data for subsequent processes.

[0006] According to one aspect of the present invention, a method for measuring the height of a bump having a repassivation layer on a wafer surface is provided, comprising:

[0007] S1: Complete bump manufacturing:

[0008] S1a, coating the surface of the incoming wafer with photoresist as a repassivation layer, and leaving an opening above the pad after exposure and development;

[0009] S1b, performing a sputtering process in the opening of the repassivation layer to form a sputtered layer;

[0010] S1c, coating a photoresist on the repassivation layer, and exposing and developing the sputtered layer at the opening of the repassivation layer;

[0011] S1d, making bumps through electroplating, photoresist removal, etching, and reflow processes;

[0012] S2: Sputtered Titanium Shielding:

[0013] The wafer obtained in S1 is subjected to sputtering of a layer of titanium to form a titanium shielding layer, wherein the titanium shielding layer is formed on the surface of the bump and the repassivation layer;

[0014] S3: Automatically measure the height of all bumps on the wafer using 3D measurement equipment:

[0015] The highest signal on the top of the titanium shielding layer on the bump is measured to obtain the top signal height, and the signal height of the titanium shielding layer on the passivation layer next to the bump is measured to obtain the bottom signal height. The height of the bump is directly obtained by subtracting the top signal height from the bottom signal height.

[0016] S4: Stripping of sputtered titanium shielding layer:

[0017] The titanium shielding layer is removed by chemical etching using titanium etching solution.

[0018] In some embodiments, the uniformity of the sputtered titanium shielding layer in S2 is

[0019] In some embodiments, the thickness of the sputtered titanium shielding layer in S2 is 0.05 μm.

[0020] In some embodiments, a titanium shielding layer is formed on the top surface of the bump in S2, and there is no titanium shielding layer on the side surface of the bump.

[0021] In some embodiments, the temperature for chemical etching in S4 is 35±2° C., and the time for chemical etching is 100±20 s.

[0022] In some embodiments, when chemical etching is performed in S4, a leakage current test is performed to confirm whether there is leakage current between the bump and the repassivation layer. If the leakage current is ≤2nA, the chemical etching is completed. If the leakage current test result does not reach ≤2nA, chemical etching is performed again until it meets the standard.

[0023] In some embodiments, the position of the titanium shielding layer on the re-passivation layer measured in S3 is within 120% of the corresponding bump diameter.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention provides a method for measuring the height of a bump having a repassivation layer on a wafer surface, which has low process difficulty and is easy to operate. A titanium shielding layer with a thickness of 0.05 μm and made of high-purity titanium is sputtered on a wafer on which bump manufacturing is completed, and the titanium shielding layer covers the surface of the repassivation layer and the top of the bump. During measurement, the light source of a 3D measuring device cannot penetrate the titanium shielding layer, and the bottom surface of the repassivation layer is not used as a reference surface for the bottom signal. The 3D measuring device can accurately grasp the titanium shielding layer as a reference surface, measure the highest signal height and the bottom signal height, and the difference between the two can accurately obtain the height value of the bump. The height obtained by this method is the true height of the bump, so as to correctly evaluate the process capability and judge the product quality. The bump height measurement method is applicable to various structural products such as PI+Pillar / Solder, (PI+)RDL+PI+Pillar / Solder, PI+UBM+Solder ball, (PI+)RDL+PI+UBM+Solderball, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the method of measuring the height of a bump in the prior art;

[0026] Figure 2 It is a measurement schematic diagram of the bump height measurement method provided by the present invention;

[0027] Figure 3 It is a schematic diagram of the measurement range of the bottom signal height on the titanium shielding layer. DETAILED DESCRIPTION

[0028] The present invention will be further described below in conjunction with specific implementation modes.

[0029] like Figure 2 As shown, a method for measuring the bump height of a wafer surface having a repassivation layer according to one embodiment of the present invention, the bump height refers to the actual height of the bump protruding outward relative to the upper surface of the repassivation layer, and the bump height measurement method comprises the following steps:

[0030] The first step: completing the manufacturing of the bump 6, specifically including the following steps:

[0031] a. The incoming wafer includes a silicon layer 1, a mounted chip 2, a passivation layer 3 on the surface, and a pad 4 on the chip. A photoresist is coated on the surface of the incoming wafer as a re-passivation layer 5, and after exposure and development processes, an opening 51 is left above the pad.

[0032] b. Perform a sputtering process in the opening 51 of the re-passivation layer 5 to form a sputtered layer 41 . The sputtered layer 41 is mainly used to improve the bonding force between the bump 6 and the pad 4 .

[0033] c. Coat photoresist (not shown) on the repassivation layer 5 , and expose the sputtered layer 41 at the opening of the repassivation layer 5 through exposure and development.

[0034] d. Through electroplating, photoresist removal, etching, and reflow processes, the bump 6 is manufactured. The bump 6 is generally made of three materials: Cu+Sn, Cu+SnAg, or Cu+Ni+SnAg.

[0035] Step 2: sputtering the metal titanium shielding layer 7, the specific operations include:

[0036] The wafer with the bump 6 obtained in the first step is sputtered with a layer of titanium to form a titanium shielding layer 7. The thickness of the sputtered titanium shielding layer 7 is 0.05 μm, and the uniformity of the sputtered titanium shielding layer 7 is The titanium shielding layer 7 covers the surfaces of the bumps 6 and the repassivation layer 5. The titanium shielding layer 7 is made of high-purity titanium.

[0037] It should be noted that before sputtering to form the titanium shielding layer 7, there is no need to perform conventional RF (plasma) etching. The function of conventional RF etching is to remove the oxide layer on the surface of the pad. The purpose of not performing RF etching here is to avoid affecting the completed bump 6 and prevent damage to the bump 6.

[0038] When performing this step, the titanium shielding layer 7 only needs to cover the top surface of the bump 6, and the side surface of the bump 6 does not need to be covered with the titanium shielding layer 7, because the side surface of the bump 6 will not be taken as the reference surface during measurement. In this way, the waste of process when sputtering the titanium shielding layer 7 can be avoided, and time and cost can be saved for subsequent stripping of the titanium shielding layer 7.

[0039] Step 3: Use 3D measurement equipment to automatically measure the height of all bumps 6 on the wafer. The specific operation method is as follows:

[0040] The 3D measuring device is placed directly above the object to be measured, and the highest signal on the top of the titanium shielding layer 7 on the bump 6 is measured to obtain the top signal height H1. The signal height of the titanium shielding layer 7 on the passivation layer 5 next to the bump 6 is measured to obtain the bottom signal height H2. The top signal height H1 is subtracted from the bottom signal height H2 to directly obtain the bump height. When selecting the reference point of the bottom signal height H2, the corresponding bump 6 is used as the center and expanded outward by 120% of the bump diameter ( Figure 3 As shown), the position of the titanium shielding layer 7 on the repassivation layer 5 within this range is detected.

[0041] Step 4: stripping the sputtered titanium shielding layer 7, the specific operation is as follows:

[0042] Use titanium etching solution and chemical etching method to remove the titanium shielding layer 7. Specifically, the components of the titanium etching solution are hydrogen peroxide with a concentration of 10-40%, potassium hydroxide with a concentration of 10-40%, and the rest are additives. The ratio of hydrogen peroxide to potassium hydroxide is 2:1, and the components of the additives include Al protective agent, Cu protective agent, SnAg protective agent, and Ni protective agent. The temperature for chemical etching is 35±2°C, and the time for chemical etching is 100±20s. When performing chemical etching, a leakage current test is performed to confirm whether there is leakage current between the bump and the repassivation layer. If the leakage current is ≤2nA, the chemical etching is completed; if the leakage current test result does not reach ≤2nA, chemical etching is performed again until the test meets the standard.

[0043] The method for measuring the bump height of a wafer surface with a repassivation layer provided by the present invention has a low process difficulty and is easy to operate, and can be realized on the basis of the prior art. By sputtering a 0.05 μm titanium shielding layer 7 on the wafer on which the bump 6 is manufactured, the titanium shielding layer 7 covers the surface of the repassivation layer 5 and the top of the bump 6. During measurement, the light source of the 3D measuring device cannot penetrate the titanium shielding layer 7, and the bottom surface of the repassivation layer 5 will not be used as the reference surface of the bottom signal. The 3D measuring device can accurately grasp the titanium shielding layer 7 as the reference surface, measure the top signal height H1 and the bottom signal height H2, and the difference between the two can accurately obtain the height value of the bump 6. The height obtained by this method is the real height of the bump 6, so as to correctly evaluate the process capability and judge the product quality. The bump height measurement method is applicable to various structural products such as PI+Pillar / Solder, (PI+)RDL+PI+Pillar / Solder, PI+UBM+Solder ball, (PI+)RDL+PI+UBM+Solder ball, etc., and has a wide range of applications.

[0044] The above are only some embodiments of the present invention. It should be pointed out that for ordinary technicians in this field, other modifications and improvements can be made without departing from the creative concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A method for measuring the height of a bump on a wafer surface having a repassivation layer, characterized in that: Includes steps: S1: Complete bump manufacturing: S1a, coating the surface of the incoming wafer with photoresist as a repassivation layer, and leaving an opening above the pad after exposure and development; S1b, performing a sputtering process in the opening of the repassivation layer to form a sputtered layer; S1c, coating a photoresist on the repassivation layer, and exposing and developing the sputtered layer at the opening of the repassivation layer; S1d, making bumps through electroplating, photoresist removal, etching, and reflow processes; S2: Sputtered Titanium Shielding: The wafer obtained in S1 is subjected to sputtering of a layer of titanium to form a titanium shielding layer, wherein the titanium shielding layer is formed on the surface of the bump and the repassivation layer; S3: Automatically measure the height of all bumps on the wafer using 3D measurement equipment: The highest signal on the top of the titanium shielding layer on the bump is measured to obtain the top signal height, and the signal height of the titanium shielding layer on the passivation layer next to the bump is measured to obtain the bottom signal height. The bump height is directly obtained by subtracting the top signal height from the bottom signal height. S4: Stripping of sputtered titanium shielding layer: The titanium shielding layer is removed by chemical etching using titanium etching solution.

2. The method for measuring the bump height of a wafer having a repassivation layer on the surface according to claim 1, characterized in that: The uniformity of the sputtered titanium shielding layer in S2 is 3. The method for measuring the bump height of a wafer having a repassivation layer on the surface according to claim 2, characterized in that: The thickness of the sputtered titanium shielding layer in S2 is 0.05 μm.

4. The method for measuring the bump height of a wafer having a repassivation layer on the surface according to claim 3, characterized in that: In the S2, a titanium shielding layer is formed on the top surface of the protrusion, and no titanium shielding layer is formed on the side surface of the protrusion.

5. The method for measuring the height of a bump having a repassivation layer on a wafer surface according to claim 1 or 4, wherein the temperature for chemical etching in S4 is 35±2°C, and the time for chemical etching is 100±20s.

6. According to the method for measuring the height of a bump having a repassivation layer on a wafer surface as claimed in claim 5, when chemical etching is performed in S4, a leakage current test is performed to confirm whether there is leakage current between the bump and the repassivation layer. If the leakage current is ≤2nA, the chemical etching is completed. If the leakage current test result does not reach ≤2nA, chemical etching is performed again until it meets the standard.

7. The method for measuring the bump height of a wafer having a repassivation layer on the surface according to claim 1, characterized in that: The position range of the titanium shielding layer on the repassivation layer to be measured in S3 is within 120% of the corresponding bump diameter.

Images