Method for non-destructive measurement of wafer bonding strength

Abstract

The application discloses a kind of non-destructive measurement wafer bonding strength method and equipment, the method includes the following steps: step 1: the two wafers of completion bonding are placed on work platform, wherein, first wafer fixed on the surface of work platform is located below;Step 2: simultaneously exerting pressure and tension on the second wafer located above different areas thereof;Step 3: crack is generated between the second wafer and the first wafer under the pressing action of pressure and the action of tension;Step 4: after crack formation, water mist or other liquid is sprayed into the crack, and the water mist is infiltrated into the crack;Step 5: measure the size of the crack, and calculate the wafer bonding strength according to the formula.The application does not need to use blade, so as to avoid the destructive measurement caused by the insertion of blade, and avoid the cost problem caused by the scrap of wafer.The non-destructive measurement bonding strength method provided by the application can accurately measure the bonding strength without damaging the wafer, so it is very advantageous in accuracy and cost.

Description

TECHNICAL FIELD

[0001] The present application relates to wafer detection method technical field, and particularly to a method for non-destructive measurement of wafer bonding strength. BACKGROUND

[0002] Low-temperature wafer direct bonding technology is the most popular bonding method in recent years, and there is great difficulty. This is because it is the highest requirement for silicon wafer surface morphology and surface treatment process. Poor silicon wafer surface morphology or surface treatment will cause the bonded wafer pair to have irreparable defects. The process of wafer direct bonding has experienced from early high-temperature wafer bonding to the current popular low-temperature wafer bonding process, which is mainly to overcome the influence of high temperature on the device, so people begin to focus on the research of low-temperature wafer bonding. The current main research includes hydrophilic bonding and hydrophobic bonding. The essence of low-temperature direct bonding is to improve the surface energy of the silicon surface through surface treatment, and then to bridge two or more silicon wafers together through water molecules (hydrophilic bonding) or HF molecules (hydrophobic bonding) and intermolecular forces.

[0003] In the low-temperature wafer direct bonding technology, bonding strength is one of the most important determination characteristics, which is an important indicator related to the quality of the bonding. If the bonding strength is small, the two bonded wafers may crack during the processing, resulting in failure. Small changes in manufacturing process parameters (especially the surface pretreatment steps of the wafer and the bonding conditions) will directly affect the strength performance of the bonding interface, so the bonding strength is not enough to reflect that something is wrong in some links in the bonding process; if the bonding strength is large, it proves that the two wafers are in close contact, and the influence of cracks and cavities in the bonding interface is minimal, and the devices made by using the bonding technology are also less likely to be damaged by environmental factors such as temperature and humidity and fail.

[0004] The current commercial bonding strength measurement method is a destructive measurement method, including crack propagation diffusion method, straight pull method, micro wedge groove test method, static oil pressure test method and four-point bending test method, among which the crack propagation diffusion method is the most commonly used. For example, see the Chinese patent application No. 201811368336.8, which discloses a bonding strength measurement method and a bonded wafer using the measurement method. The technical solution is to use the crack propagation diffusion method, commonly known as the blade insertion method. This is the most traditional and most common method for measuring bonding strength. It separates the two wafers by inserting a thin blade into the bonding interface. The crack length obtained by the technical solution is a representation of the bonding strength. However, in this method, the thin blade will cause serious damage to the wafer, which is a destructive measurement method. The bonding energy is related to the crack length, blade thickness, wafer thickness and blade insertion speed. Moreover, the thin blade will cause serious damage to the wafer, resulting in wafer scrap, so it is very unfavorable in terms of accuracy and cost.

[0005] In summary, in the low-temperature wafer direct bonding technology, the bonding strength is one of the most important determination characteristics, which is an important indicator related to the quality of the bonding. However, the current commercial bonding strength measurement method is a destructive measurement method, resulting in a high wafer scrap rate. In view of the above, the present inventors have proposed the following technical solution in combination with the deficiencies of the prior art. SUMMARY

[0006] The technical problem to be solved by the present application is to overcome the deficiencies of the prior art and provide a non-destructive method for measuring wafer bonding strength.

[0007] To solve the above technical problems, the present application adopts the following technical solution: the non-destructive method for measuring wafer bonding strength comprises the following steps: step 1: placing two bonded wafers on a work platform, wherein the first wafer on the lower side is fixed on the surface of the work platform; step 2: applying pressure and tension to the second wafer on the upper side at different regions; step 3: forming a crack between the second wafer and the first wafer under the pressure and tension; step 4: after the crack is formed, spraying water mist or other liquid into the crack to allow the water mist to penetrate into the crack; step 5: measuring the size of the crack and calculating the wafer bonding strength according to the following formula: γ = 3Et 3 y 2 / 32L 4 .

[0008] Further, in the above technical solution, the first wafer is fixed on the surface of the work platform by vacuum adsorption, that is, there are air holes on the surface of the work platform, and the first wafer is adsorbed on the surface of the work platform by forming a vacuum or negative pressure at the air holes.

[0009] Further, in the above technical solution, the first wafer is fixed on the surface of the work platform by mechanical clamping, i.e. a positioning groove is formed on the surface of the work platform, and the first wafer is clamped in the positioning groove.

[0010] Further, in the above technical solution, the pulling force acting on the second wafer is near the edge, the pressing force acting on the second wafer is away from the pulling force, and the distance between the two is greater than the length L of the crack.

[0011] Further, in the above technical solution, in step 5, the size of the crack is measured by infrared detection or ultrasonic detection.

[0012] Further, in the above technical solution, another technical problem to be solved by the present application is to provide a device for non-destructive measurement of wafer bonding strength according to the above technical solution, which comprises: a work platform for placing two wafers after bonding, and the work platform has a vacuum suction or mechanical positioning device to fix the first wafer below the surface of the work platform; a pressure mechanism on the work platform, which forms a downward pressure on the two wafers of the work platform; a tension mechanism on the work platform, which acts on the second wafer above to form an upward tension; a spraying mechanism on the side of the work platform; a detection device which is an infrared detector or an ultrasonic detector.

[0013] After adopting the above technical solution, the present application has the following beneficial effects compared with the prior art:

[0014] Firstly, the present application refers to the existing blade insertion method, but does not need to use the blade, thereby avoiding the destructive measurement caused by the insertion of the blade and avoiding the cost problem caused by the scrap of the wafer.

[0015] Secondly, after adopting the measurement method of the present application, the measurement error caused by the inconsistent factors such as the speed and angle of the inserted blade in the existing blade insertion method can be avoided.

[0016] In summary, the method for non-destructive measurement of bonding strength provided by the present application can accurately measure the bonding strength without damaging the wafer, so it is very advantageous in accuracy and cost. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a working principle diagram of the present application;

[0018] Figure 2 is a schematic diagram of the first device embodiment in the present application;

[0019] Figure 3 This is a schematic diagram of the second embodiment of the device in this invention. Detailed implementation method:

[0020] The present invention will be further described below with reference to specific embodiments and accompanying drawings.

[0021] See Figure 1 The diagram shown illustrates the working principle of the non-destructive method for measuring wafer bond strength used in this invention. The method includes the following steps:

[0022] Step 1: Place the bonded wafer 2 onto the work platform 1, with the lower first wafer 21 fixed to the surface of the work platform 1. In this step 1, the first wafer 21 can be fixed to the work platform 1 by vacuum adsorption. This method will not damage the first wafer 21 and ensures its integrity to the greatest extent possible.

[0023] Step 2: Apply pressure and tension to different areas of the second wafer 22 located above. Applying pressure creates a compressive force, forming a compressive fulcrum with relative tension, thus pressing the second wafer 22 onto the first wafer 21, preventing the bonded wafer 2 from detaching directly from the work platform under tension. The applied pressure should not cause damage to the wafer; it should simply hold it in place.

[0024] The pressure and tension are applied to different regions of the second wafer 22. To facilitate crack formation, the tension application point F1 on the second wafer 22 should be close to the edge of the second wafer 22. At the same time, the pressure application point F2 on the second wafer 22 should be far away from the tension application point F1. Typically, the pressure application point F2 and the tension application point F1 can be located on opposite sides of the second wafer.

[0025] Step 3: As the tension increases, the pressure application point F2 at one end of the second wafer 22 is suppressed by the pressure, while the tension application point F1 at the other end deforms under the tension. Within the elastic deformation range, a crack 20 is generated between the second wafer 22 and the first wafer 21. The distance between the pressure application point F2 and the tension application point F1 is greater than the crack length L, meaning the crack 20 cannot overlap with the pressure application point F2; otherwise, it will affect the crack length and cause the measurement results to fail. If the crack overlaps with the pressure application point F2, this can be improved by reducing the tension increase height or adjusting the pressure application point F2.

[0026] Step 4: After the crack 20 is formed, water mist or other liquid is sprayed into the crack 20, so that the water mist can penetrate into the crack 20. The water mist or other liquid is sprayed into the crack for the purpose of facilitating the subsequent measurement of the size of the crack. Because the subsequent measurement of the length of the crack is performed by using an infrared light camera or an ultrasonic microscope, different substances have different reflection and penetration behaviors under infrared light or ultrasonic waves, so that the length of the crack can be observed in the image.

[0027] Step 5: The size of the crack 20 is measured by using infrared detection or ultrasonic detection, and the wafer bonding strength is calculated according to the following formula:

[0028] γ = 3Et 3 y 2 / 32L 4 wherein,

[0029] γ is the wafer bonding strength;

[0030] E is the Young's modulus of the single wafer;

[0031] t is the thickness of the single wafer;

[0032] y is the height of the second wafer being stretched;

[0033] L is the length of the crack;

[0034] wherein the length L of the crack is the distance from the center of the force F1 to the deepest part of the crack, and the height y of the second wafer being stretched is the lifting height at the center of the force F1.

[0035] The present application refers to the existing blade insertion method, but does not need to use the blade, so as to avoid the destructive measurement caused by the insertion of the blade and the cost problem caused by the wafer scrap. At the same time, after the measurement method of the present application is used, the measurement error caused by the inconsistent factors such as the speed and angle of the inserted blade in the existing blade insertion method can be avoided.

[0036] After the wafer 2 is measured for the bonding strength by using the present application, the wafer 2 can be reused after the debonding process and the surface cleaning process, so as to avoid waste.

[0037] According to the measurement method of the present application, a corresponding measurement device can be designed, as shown in Figure 2 The device includes a workbench 1, a pressure mechanism 3, a tension mechanism 4, a spraying mechanism 5 and a detection device 6.

[0038] The workbench 1 is used to place the two wafers 2 after bonding, and the workbench 1 has a vacuum suction device to fix the first wafer 21 located below on the surface of the workbench 1. In combination with Figure 2As shown, the vacuum suction device is achieved by setting the air holes 11 distributed on the surface of the work platform 1, the air holes 11 are connected with the external vacuum pump, the first wafer is adsorbed on the surface of the work platform by forming vacuum or negative pressure at the air holes 11.

[0039] The vacuum suction mode does not damage or destroy the wafer. Of course, other mechanical methods can also be used, for example, see the attached Figure 3 As shown, it is the schematic diagram of the second embodiment of the present application. In the second embodiment, the first wafer is fixed on the surface of the work platform 1 by mechanical clamping, that is, the positioning groove 12 is formed on the surface of the work platform 1, and the second wafer 21 is clamped in the positioning groove 12. Of course, the first wafer can also be fixed by mechanical clamping. The present application prefers the vacuum suction fixing mode.

[0040] The pressure mechanism is located on the work platform 1, which can adopt air cylinder or hydraulic cylinder, or connecting rod mechanism, and is installed above the work platform, and the wafer 2 on the work platform 1 is pressed by the pressure mechanism 3.

[0041] The tension mechanism 4 is also located on the work platform 1, which can adopt air cylinder or hydraulic cylinder mechanism, and the tension mechanism 4 acts on the second wafer above to form upward tension. The connection between the tension mechanism 4 and the second wafer can also adopt the vacuum suction mode, that is, the vacuum suction head is arranged at the end of the tension mechanism 4, and the second wafer is pulled by the vacuum suction mode. Of course, the connection between the tension mechanism 4 and the second wafer 22 can also be achieved by using adhesive.

[0042] The spraying mechanism 5 is located on the side of the work platform 1, which is used for spraying water mist or other liquid to the crack.

[0043] The detection device 6 is infrared detector or ultrasonic detector. It can be directly arranged above the workbench, and moved by mechanical arm, or can be arranged separately from the workbench as an independent component. When detecting, the wafer is taken out from the work platform 1 and put into the detection device 6 for detection.

[0044] Of course, the above-mentioned is only a specific embodiment of the present application, and is not limited to the scope of the present application. Any equivalent changes or modifications made according to the structure, features and principles of the present application are included in the scope of the present application.

Claims

1. A method of non-destructively measuring wafer bonding strength, characterized by: The method comprises the following steps: Step 1: placing the completed bonded wafer on a work platform, wherein the first wafer located below is fixed on the surface of the work platform; Step 2: simultaneously applying pressure and tension to the second wafer located above at different regions thereof, forming a pressing force by applying the pressure, forming a pressing fulcrum of the opposite tension, and pressing the second wafer on the first wafer without directly separating the bonded wafer from the work platform under the action of the tension, wherein the pressure and the tension are applied at different regions of the second wafer, the tension acting position F1 on the second wafer is close to the edge of the second wafer, and the pressure acting position F2 on the second wafer is away from the tension acting position F1; Step 3: as the tension rises, the pressure acting position F2 at one end of the second wafer is pressed by the pressure, the tension acting position F1 at the other end is deformed under the action of the tension, and within the elastic deformation range, a crack is generated between the second wafer and the first wafer, and the distance between the pressure acting position F2 and the tension acting position F1 is greater than the length L of the crack; Step 4: after the crack is formed, spraying water mist into the crack, and allowing the water mist to penetrate into the crack, and measuring the size of the crack by spraying the water mist into the crack; Step 5: measuring the size of the crack by an infrared light camera or an ultrasonic microscope, and calculating the wafer bonding strength according to the following formula: γ = 3Et 3 y 2 / 32L 4 wherein, γ is the wafer bonding strength; E is the Young's modulus of the single wafer; t is the thickness of the single wafer; y is the height of the second wafer being stretched; L is the length of the crack; wherein the length L of the crack is the distance from the center of the tension acting position to the deepest part of the crack, and the height y of the second wafer being stretched is the lifting height of the center of the tension acting position; The device for realizing the method comprises: a work platform for placing the two bonded wafers, and the work platform is provided with a vacuum suction or mechanical positioning device to fix the first wafer located below on the surface of the work platform; a pressure mechanism on the work platform, which forms a downward pressure on the two wafers on the work platform; a tension mechanism on the work platform, which acts on the second wafer located above to form an upward tension thereon; a spraying mechanism located on the side of the work platform; a detection device which is an infrared detector or an ultrasonic detector.

2. The method of non-destructively measuring wafer bond strength of claim 1, wherein: The first wafer is fixed on the surface of the work platform by a vacuum suction method, that is, there are air holes on the surface of the work platform, and the first wafer is suctioned on the surface of the work platform by forming a vacuum at the air holes.

3. The method of non-destructively measuring wafer bond strength of claim 1, wherein: The first wafer is fixed on the surface of the work platform by a mechanical clamping method, that is, a positioning groove is formed on the surface of the work platform, and the first wafer is clamped in the positioning groove.

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