Method for optimizing the thickness range of a wafer surface after wet etching

Abstract

The application provides a method for optimizing the thickness range of a wafer surface after wet etching, comprising the following steps: S1, performing a bonding process on an epitaxial wafer and a pure silicon wafer and a device wafer and a logic circuit wafer to form a wafer; S2, grinding the back surface of the epitaxial wafer or the logic wafer to a thickness of 13-15 μm by a mechanical grinding method, and the total thickness of the wafer is at least 2-3 μm; the grinding parameters are adjusted for the first time, and the non-contact measurement thickness compensation value in the grinding equipment is adjusted, so that the thickness of the wafer is in a state of being thin in the middle and thick on both sides; S3, the silicon wafer rotation speed, etching reaction time, etching liquid spraying position and flow parameters are adjusted for the second time, so that the etching reaction rate of the whole wafer is in a state of being slow in the middle and fast on the edge; the epitaxial wafer is etched to a P-type epitaxial layer by etching liquid; finally, the total thickness of the wafer is 0.05-0.1 μm, the thickness of the wafer of the back epitaxial wafer reaches a target value, and the thickness range of the wafer surface can be effectively controlled.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, and in particular to a method for optimizing the thickness range of a wafer surface after wet etching. Background Technology

[0002] With the development of semiconductor manufacturing processes, image sensor technology has evolved from front-illuminated to back-illuminated. Back-illuminated technology uses a bonding technique between two silicon wafers (device wafer and logic circuit wafer). Currently, the back silicon wafer thinning and subsequent processing in the fabrication of back-illuminated complementary metal-oxide-semiconductor image sensors not only require the average thickness to reach the target value, but also require control of the silicon wafer surface thickness deviation (wafer surface thickness deviation = maximum wafer surface thickness - minimum wafer surface thickness), which is quite difficult. Furthermore, the current processing steps are cumbersome, requiring thinning first through mechanical grinding, followed by a first wet etching, then smoothing through chemical mechanical polishing (CMP), and finally a second wet etching. The overall process is complex and wastes time and resources. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of existing technologies and propose a method to optimize the thickness range of the wafer surface after wet etching. This method solves the problem of poor image sensor imaging quality caused by uneven silicon surface in silicon thinning process through a two-step process of mechanical grinding and wet etching.

[0004] To achieve the above objectives, the present invention adopts the following specific technical solution:

[0005] The method for optimizing the thickness range of a wafer surface after wet etching provided by this invention includes the following steps:

[0006] S1. Bond the epitaxial wafer to the pure silicon wafer and the device wafer to the logic wafer to form a wafer;

[0007] S2. By using mechanical grinding, the back side of the epitaxial wafer or logic wafer is ground to between 13-15μm and the total thickness of the wafer is at least 2-3μm. By adjusting the grinding parameters for the first time and adjusting the non-contact measurement thickness compensation value inside the grinding equipment, the thickness of the wafer is made to be thin in the middle and thick on both sides.

[0008] S3. By adjusting the silicon wafer rotation speed, etching reaction time, and the position and flow rate of the etchant spray for the second time, the wafer etching reaction rate is made to be the slowest in the middle and the fastest at the edge. The etchant will etch the epitaxial wafer to the P-type epitaxial layer, and finally the total thickness of the wafer will be in the range of 0.05 to 0.1 μm.

[0009] Preferably, the first adjustment is to set the grinding speed to 2000–4000 rpm / min, the grinding disc speed to 100–500 rpm / min, the flow rate to 100–500 ml / min, and the non-contact thickness compensation value inside the grinding equipment to 0.8–1.2 μm. The second adjustment is to set the silicon wafer speed to 500–2000 rpm / min, the etching reaction time to 100–300 s, the flow rate to 600–1500 ml / min, and the position of the etching solution sprayed from the machine to 11–55 mm.

[0010] Preferably, the epitaxial wafer is an 8-inch epitaxial wafer.

[0011] Preferably, the etching solution is a mixture of hydrofluoric acid, nitric acid and acetic acid, with a concentration ratio of 1:3:4 and a temperature of 20℃~30℃.

[0012] The present invention can achieve the following technical effects: by making the overall thickness of the wafer into a specified shape, the thickness of the back epitaxial wafer or logic wafer can reach the target value, and most importantly, the wafer surface thickness can be effectively controlled within the range of 0.05 to 0.1 μm. Attached Figure Description

[0013] Figure 1 This is a flowchart of a method for optimizing the thickness range of a wafer surface after wet etching, provided by an embodiment of the present invention.

[0014] Figure 2 This is a diagram showing the overall thickness range of a mechanically ground wafer according to an embodiment of the present invention.

[0015] Figure 3 This is a diagram showing the overall thickness range of a wafer etched by an etching solution according to an embodiment of the present invention. Detailed Implementation

[0016] In the following description, embodiments of the invention will be described with reference to the accompanying drawings. In the description below, the same modules are denoted by the same reference numerals. Where the same reference numerals are used, their names and functions are also the same. Therefore, their detailed description will not be repeated.

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0018] Figure 1 The flowchart of the method for optimizing the thickness range of the wafer surface after wet etching provided by an embodiment of the present invention is shown.

[0019] like Figure 1As shown, this embodiment of the invention provides a method for optimizing the thickness range of a wafer surface after wet etching, comprising the following steps:

[0020] Step S1: Perform bonding processes on the epitaxial wafer and the pure silicon wafer, as well as on the device wafer and the logic wafer;

[0021] Step S2: By using mechanical grinding, the average thickness of the epitaxial wafer is ground to between 13-15 μm and the total thickness of the surface wafer is at least 2-3 μm. The thickness of the wafer is made into a "V" shape by adjusting the grinding speed and flow rate parameters for the first time.

[0022] The first adjustment is to set the grinding speed to 2000-4000 rpm / min, the grinding disc speed to 100-500 rpm / min, the flow rate to 100-500 ml / min, and the non-contact thickness compensation value inside the grinding equipment to 0.8-1.2 μm.

[0023] The final remaining thickness after mechanical polishing is calculated based on the final target value of the wafer. The final remaining thickness after mechanical polishing = the final thickness of the wafer + (10um ± 1um). For example, if the final thickness of the wafer is 4um, the final remaining thickness after mechanical polishing = 4 + (10um ± 1um). Mechanical polishing is used to polish the back side of the epitaxial wafer or logic wafer to between 13-15μm.

[0024] Step S3: By adjusting the silicon wafer rotation speed, etching reaction time, and the position and flow rate of the etchant spray for the second time, the etchant will etch the silicon wafer in the epitaxial wafer to the P-type epitaxial layer. The etchant will eventually etch an epitaxial layer of 1-2 μm, and finally the total wafer thickness range will reach the optimal state (total wafer thickness range of 0.05-0.1 μm).

[0025] The etching rate at wafer edges is generally too fast, resulting in thinner edges and a larger total thickness range (TTV) on the wafer surface. To achieve the optimal TTV, a "V" shape is achieved through a first mechanical grinding process, resulting in a thinner center and thicker edges, followed by a second etching process with a faster etching rate. ^ The "-" type allows the final thickness to reach an ideal, uniform, and flat horizontal state. The final wafer surface thickness can reach a range of 0.05 to 0.1 μm.

[0026] The second adjustment involves setting the silicon wafer rotation speed to 500–2000 rpm, the flow rate to 600–1500 ml / min, the etching reaction time to 100–300 s, and the position of the etching solution sprayed onto the machine to 11–55 mm. The epitaxial wafer or logic wafer size is 8 inches, with no limit on epitaxial layer thickness. The etching solution is a mixture of hydrofluoric acid, nitric acid, and acetic acid in a 1:3:4 ratio, at a temperature of 25±5℃. If the temperature of the mixture is outside this range, the etching rate will be unstable, leading to uncontrolled etching reaction time and preventing the wafer surface thickness from reaching the range of 0.05–0.1 μm.

[0027] Adjust the machine settings to spray the etching solution position. Based on the thickness measurement value of the first mechanical polishing, set the machine settings to spray the etching solution position. First, find the X-axis coordinate corresponding to the lowest point of the wafer mechanical polishing thickness (the Y-axis coordinate is set to 0 for thickness measurement). Calculate the actual wafer spray position = X-axis coordinate corresponding to the lowest thickness + (30mm ± 20mm). Since there is a difference between the machine settings and the actual wafer position, the machine settings need to be calculated based on the actual wafer position. The machine settings for spraying the etching solution position = actual wafer spray position * 1.1. For example, if the X-axis coordinate of the lowest polishing thickness is 0, the actual wafer spray position is 10mm to 50mm, and the machine settings for spraying the etching solution position are 11mm to 55mm.

[0028] Figure 2 The overall thickness range of mechanically ground wafers provided in embodiments of the present invention is shown.

[0029] like Figure 2 As shown, the X-axis is used as the measurement basis. When X = 0, it is the center of the wafer. When X = ±100, it is the edge of the wafer. By adjusting the grinding speed and flow rate parameters for the first time, the thickness of the wafer is made to be "V" shaped, so that the wafer after grinding reaches a state where the edge thickness is high and the center thickness is low.

[0030] Figure 3 The overall thickness range of the wafer etched by the etching solution provided in the embodiments of the present invention is shown.

[0031] like Figure 3 As shown, by adjusting the silicon wafer rotation speed, the position and flow rate of the etchant spray, the etching speed at the center of the wafer is slowed down and the etching speed at the edge of the wafer is fastened. Finally, by setting the above parameters, the optimal range of wafer thickness can be obtained.

[0032] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0033] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

[0034] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method of optimizing the range of thicknesses of a wafer surface after wet etching, characterized in that, It comprises the following steps: S1, bonding process is carried out between the epitaxial wafer and the pure silicon wafer to form a wafer; S2, the back surface of the epitaxial wafer is ground to 13-15 μm by mechanical grinding, and the total thickness of the wafer is at least 2-3 μm, the thickness of the wafer is in the state of being thin in the middle and thick on both sides by adjusting the grinding parameters and the non-contact measurement thickness compensation value in the grinding equipment for the first time; S3, the position of the spray etching liquid is calculated according to the first mechanical grinding thickness measurement value, the X-axis coordinate corresponding to the lowest point of the wafer mechanical grinding thickness is found first, the Y-axis coordinate is set to 0, the actual position of the wafer spray is calculated = the X-axis coordinate corresponding to the lowest point of the thickness + (30 mm ± 20 mm), the position of the spray etching liquid is set by the machine = the actual position of the wafer spray * 1.1, the etching reaction rate of the wafer is in the state of being slow in the middle and fast on the edge by adjusting the silicon wafer speed, etching reaction time, spray etching liquid position and flow parameters for the second time, the epitaxial wafer is etched to the P-type epitaxial layer by the etching liquid, and the total thickness of the wafer is finally in the range of 0.05-0.1 μm, the etching liquid is a mixture of hydrofluoric acid, nitric acid and acetic acid, and the mixing ratio is 1:3:4, and the temperature is 20-30℃; The first adjustment of the grinding speed is 2000-4000 rpm / min, the grinding disc speed is 100-500 rpm / min, the flow parameter is adjusted to 100-500 ml / min, and the non-contact measurement thickness compensation value in the grinding equipment is adjusted to 0.8-1.2 μm, the second adjustment of the silicon wafer speed is 500-2000 rmp / min, the etching reaction time is 100-300 s, the flow parameter is adjusted to 600-1500 ml / min, and the position of the machine spray etching liquid is adjusted to 11-55 mm, and the epitaxial wafer is an 8-inch epitaxial wafer.

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