An etching method capable of reducing the degree of lateral corrosion of a wafer

Abstract

The present invention aims at the problem that when a wafer is wet-etched in the prior art, the lateral corrosion of the wafer is large, which reduces the photosensitive area of ​​the wafer and reduces the responsiveness of the wafer. The present invention provides an etching method that can reduce the degree of lateral corrosion of the wafer. Specifically, the wafer is wet-etched by a method of multiple longitudinal etchings and multiple photoresist coatings, and the total longitudinal corrosion amount is divided into N times. After each etching, photoresist is coated on the etched surface to cover the etched part, and then the next etching is performed at the original position. By adopting this method, the depth of each etching is controlled, so that the lateral corrosion time is shorter and the degree of lateral corrosion is lower during each etching. Combined with the process of multiple coating, photolithography and etching, after the coating and photolithography are performed again, the photoresist forms a coating on the step, which prevents the etching liquid from further contacting the coated position, thereby significantly reducing the degree of lateral corrosion.

Description

Technical Field

[0001] The invention belongs to the field of semiconductor manufacturing, relates to a wafer etching method, and in particular to a novel semiconductor detection chip etching method. Background Art

[0002] In the manufacturing process of chips and other wafers, etching is indispensable. Etching is also called corrosion, which includes dry etching and wet etching. The anisotropic characteristics of dry etching are obvious. The verticality of the chip after etching is better and the lateral corrosion is smaller. However, due to the large energy of the etching particles in the etching, it will cause certain damage to the chip surface, and the surface material lattice will be damaged, which will reduce the chip yield and performance, such as reducing the detection performance of the wafer and increasing the dark current. Wet etching has basically no damage to the surface of the chip, but wet etching is isotropic corrosion. When the chip is corroded, the lateral corrosion is large, resulting in a reduction in the photosensitive surface of the chip and a larger side area, which will reduce the chip detection response and increase the dark current. Especially when a thicker chip needs to be etched, the lateral corrosion of the chip will increase greatly, which seriously reduces the performance of the chip in all aspects. Summary of the invention

[0003] The present invention aims at the disadvantage that when wet etching a wafer in the prior art, the lateral corrosion of the wafer is large, resulting in a small reduction in the photosensitive area of ​​the wafer and an increase in the side area, and provides an etching method that can reduce the degree of lateral corrosion of the wafer.

[0004] The technical solution adopted by the present invention to achieve the above-mentioned purpose is:

[0005] An etching method capable of reducing the lateral corrosion degree of a wafer, characterized in that the wafer is wet-etched by a method of multiple longitudinal etchings and multiple photoresist coatings, the total longitudinal etching amount is divided into N times, photoresist is coated on the etched surface after each etching to cover the etched part, and then the next etching is performed at the original position;

[0006] The depth of each longitudinal corrosion is different, and the depth of the longitudinal corrosion increases from small to large; the depth of each longitudinal corrosion is different, and the depth of the first few longitudinal corrosions increases from small to large, and the depth of the last few longitudinal corrosions is equal;

[0007] The depth of each longitudinal corrosion is equal;

[0008] Each longitudinal corrosion depth is 0.8 to 1.3 um;

[0009] The following steps are used for etching: 1. Dry the wafer first to remove moisture from the surface of the wafer, then perform photolithography, and then heat the wafer to solidify the photoresist; 2. Etch the wafer according to the set longitudinal etching depth, apply photoresist on the etched surface after each etching to cover the etched part, stop etching and clean it; 3. Remove the photoresist from the etched wafer; 4. Repeat steps 1, 2, and 3 according to the total longitudinal depth that the wafer needs to be etched, and perform photolithography at the same position each time until the required longitudinal depth of etching is reached.

[0010] The method of the present invention overcomes the disadvantages of the conventional wet etching that the etched step is always in the etching solution, the etched step and the solution are not blocked, the wet etching has the characteristic of isotropy so that the lateral corrosion always exists, the longer the etching time, the greater the degree of lateral corrosion, and the various performances of the chip finally formed are reduced. The present invention uses multiple etching of the wafer, and controls the depth of each etching, so that the time for lateral corrosion is shorter and the degree of lateral corrosion is lower during each etching. Combined with the process of multiple coating, photolithography, and etching, after the coating and photolithography are performed again, the photoresist forms a coating on the step, preventing the etching solution from further contacting the coating position, so that the degree of lateral corrosion can be significantly reduced. The reduction of the degree of lateral corrosion is particularly beneficial to the growth of epitaxial materials on the substrate of the active detection chip. This process can effectively increase the photosensitive surface of the detection chip, reduce the side area of ​​the etching step surface, and greatly improve the various performances of the chip, which is of great significance in national defense and related fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 The shape of the developed photoresist and the wafer to be etched have three photoresists on the wafer.

[0012] Figure 2 A schematic diagram of the shape of a wafer after the first etching and cleaning in deionized water;

[0013] Figure 3 Schematic diagram of the shape of the wafer after the first etching and photoresist removal;

[0014] Figure 4 The schematic diagram of the wafer and photoresist shape after the first etching to remove the photoresist, then the photolithography and development. It can be seen in this figure that the photoresist forms a coating on the etched step, and a photoresist protection layer is formed on the etched step;

[0015] Figure 5 The shape of the wafer is the photoresist and etching during the secondary etching;

[0016] Figure 6 The shape of the wafer obtained after the photoresist is removed by the second etching;

[0017] Figure 7 The shape of the wafer after photoresist and etching during the third etching;

[0018] Figure 8 The shape of the final wafer;

[0019] Fig. 9 The schematic diagram of the wafer shape obtained when unequal etching is used;

[0020] Fig.10 , a schematic diagram for marking the longitudinal depth and lateral depth of the wafer;

[0021] Fig.11 Schematic diagram of the refraction of light on the chip.

[0022] Description of Reference Numerals

[0023] 1. Photoresist; 2. Wafer body; 3. Wafer separation; 4. Photoresist protective layer DETAILED DESCRIPTION

[0024] The method of the present invention is described in detail below with specific implementation modes.

[0025] like Figure 1-Figure 11 As shown, 1. Dry the wafer to remove moisture from the surface of the wafer. Generally, the baking method is adopted. There is no specific requirement for the baking temperature and time. As long as the wafer can be dried without damaging the wafer, it is fine. In practice, the baking temperature is often set to 80-120°C and the time is 5-10 minutes. Other drying methods can also be used. After drying, the wafer is coated with photoresist. Generally, a glue spreader is used for glue spread. The dried wafer is placed on the glue spreader for glue spread. In order to make the glue spread more evenly, the glue is spread slowly first, generally 800-2000 rmp / min, and then a high glue spread speed is used, and the high glue spread speed is 3000-6000 rmp / min. After that, the wafer is heated to solidify the photoresist. Generally, the wafer is placed on a hot plate and baked for 5-10 minutes at a baking temperature of 80-120°C.

[0026] 2. Wet-etch the wafer using multiple etching and multiple photoresist coating methods. Divide the total amount of etching into multiple times, and apply photoresist on the etched surface after each etching to cover the etched part. Of course, in order to obtain a good quality wafer, the smaller the depth of each etching, the better. However, considering the efficiency of photolithography and economic benefits, the etching is stopped when the vertical etching depth reaches 0.8-1.3um each time, and the etching is cleaned in deionized water after etching.

[0027] 3. Soak the etched wafer in acetone in a 50-80°C water bath for 5-15 minutes to remove the photoresist. This step provides the best temperature for removing the photoresist.

[0028] 4. Repeat steps 1, 2, and 3 according to the thickness of the wafer to be etched, performing photolithography at the same position each time until the required etching depth is reached.

[0029] The above method is used to wet etch the wafer in the same position and shape for multiple times, and each time the photoresist is applied to the etched part, and then the prescribed depth is etched in the same position and shape until the prescribed etching depth is reached. After the photoresist is coated on the etched shape, the photoresist prevents the contact between the etching liquid and the wafer, thereby reducing the degree of lateral corrosion of the wafer.

[0030] When performing multiple etchings, the amount of each etching can be equal or unequal. Generally speaking, the smaller the amount of each etching, the smaller the total length of lateral corrosion. However, in order to take into account both production efficiency and economy, the amount of each etching should be around 1um. In order to more effectively reduce the total length of lateral corrosion, it is best to adopt a scheme in which the amount of each etching is unequal. For example, in the first few etchings, the etching amount is increased, and the subsequent etching amounts are equal. With this scheme, the amount of the first etching can be a relatively small amount, so that the area of ​​the upper surface of the chip is as large as possible. In this way, compared with the scheme of the same etching amount each time, a large chip surface area can be obtained while improving the etching efficiency. The principle is as follows: From the law of refraction, it can be seen that since the refractive index of the chip is greater than that of air, light will be refracted when it enters the chip from the air. The angle of refraction is smaller than the angle of incidence of the light, so Fig.11 It can be seen that the larger the surface area of ​​the chip, the more light enters the chip, the stronger the detection signal of the detection chip, and the greater the responsiveness. Therefore, when starting to etch, a smaller longitudinal etching depth is used to maximize the area of ​​the upper surface of the etched chip, thereby increasing the intensity of the detection signal of the detector and, as far as possible, improving the response capability of the detector.

[0031] In Example 1, the etching depth of the wafer is 8 mm.

[0032] 1. Take the wafer to be coated and place it on a hot plate. Heat it at 120°C for 5 min to dry the wafer. Take the baked wafer and place it on the coating machine. Start with a speed of 1000 rpm and maintain for 10 seconds. Then accelerate to 5000 rpm after 4 seconds and maintain for 60 seconds to coat at a high speed. After coating, take out the wafer and place it on a hot plate to dry at 120°C for 5 minutes. After drying, select the photoresist of the required mask shape and perform photolithography on it in the photolithography machine. After photolithography, develop it in the developer and finally clean it with deionized water. The shape of the developed photoresist and wafer should be as shown below. Figure 1 shown.

[0033] 2. Clean the wafer with photoresist and put it into the etching solution to etch the depth of 0.3um. After etching, clean it in deionized water. Figure 2 In this embodiment, the etching solution is prepared as follows: citric acid and water are mixed in a mass ratio of 1:1 to form a citric acid solution, and then phosphoric acid: hydrogen peroxide: water: citric acid solution = 8:20:500:20 to form an etching solution. The etching solution is placed in a water bath at a temperature of 40°C, and after the temperature is stabilized for 10 minutes, the wafer is corroded.

[0034] 3. After cleaning the wafer, soak it in acetone at 80℃ water bath for 10min to remove the photoresist, then soak it in isopropanol at room temperature for 5min to remove the residual acetone. After removing the photoresist, the shape of the wafer is as follows: Figure 3 shown.

[0035] 4. Apply photoresist on the wafer after photolithography, repeat step 1, and the photoresist will cover the etched steps after coating. After coating, photolithography and development, the photoresist and wafer are shaped like Figure 4 shown.

[0036] 5. Repeat step 2 and use the same photomask to etch the photoresist again at the same position. At this time, the photoresist and the etched wafer are shaped like Figure 4 In this step, since the photoresist covers the etched step to form a photoresist protection layer on the surface of the etched step, further contact between the etching liquid and the step at the covered position is prevented, thus significantly reducing the degree of lateral corrosion.

[0037] 6. Repeat the conditions in step 3. Now the shape of the wafer is Figure 8 shown.

[0038] 7. Repeat steps 1, 2, and 3 for a total of 8 times to end the corrosion.

[0039] After the etching process is completed, the etched wafer is Figure 6 shown.

[0040] In Example 2, the method of etching with equal amount each time is adopted, and the etching amount each time is 1 um, and the rest is the same as in Example 1.

[0041] In Example 3, the method of etching with equal amount each time is adopted, and the etching amount each time is 2 um, and the rest is the same as in Example 1.

[0042] In Example 4, unequal etching is adopted. The etching is first performed in an increasing etching amount method. The first etching amount is 0.3um, the second and third etching amounts are 0.5um and 0.7um respectively, and then each etching amount is 1um until the specified total etching depth is reached.

[0043] Comparative Example: Traditional wet etching. One etching was performed, and the etching solution and other parameters were the same as those in Example 1. The total lateral etching length of the wafers finally obtained by the methods of each embodiment and comparative example is shown in Table 1.

[0044] It can be seen that the present invention adopts the method of multiple photolithography, multiple wet etching, and multiple etchings. The existing step surface is covered with photoresist each time etching, which can greatly reduce the lateral corrosion degree of the wafer, thereby increasing the photosensitive surface of the chip, reducing the area of ​​the side surface, improving the chip's responsiveness, and reducing the chip's dark current. The method of first etching with a small depth and then etching with a relatively large depth, compared with equal amount of etching, when the first etching amount is the same, the total lateral corrosion length of the wafer finally obtained is equivalent to the total lateral corrosion length of the wafer obtained by equal amount of etching, but because the subsequent corrosion depth is much higher than the depth of equal amount of etching, a good surface area can be obtained, and the efficiency is significantly improved.

[0045] In the method of the present invention, although different total lengths of lateral etching are obtained by using different etching solutions and different etching temperatures under the same other conditions, the trends are consistent and will not be listed one by one.

[0046] The method of the present invention is used to perform photoresist multiple times. Since each time etching is performed, the etched step is coated with photoresist to form a photoresist protection layer, the photoresist protection layer prevents the etching solution from further contacting the step at the coated position, thereby significantly reducing the degree of lateral corrosion.

[0047] Table 1: Comparison of total lateral etching length and total longitudinal etching depth of wafers obtained by conventional wet etching and the etching method of the present invention

[0048]

[0049] Note: The total longitudinal corrosion depth and Fig.10 Corresponding to B in the figure, the total length of lateral corrosion is Fig.10 The length of 2A.

Claims

1. An etching method capable of reducing the degree of lateral corrosion of a wafer, characterized in that: The wafer is wet-etched by multiple longitudinal etchings and multiple photoresist coatings. The total longitudinal etching amount is divided into N times. After each etching, the photoresist is first removed, and then photoresist is coated on the surface after photoetching to cover the etched part. Then the next etching is performed in the same shape at the original position until the specified etching depth is reached. The depth of the first few longitudinal etchings increases from small to large, and the depth of the next few longitudinal etchings is equal. The depth of the last few longitudinal etchings is equal to the last etching depth after the first few etchings increase from small to large.

2. An etching method capable of reducing the degree of lateral corrosion of a wafer as claimed in claim 1, characterized in that: The depth of each longitudinal corrosion is 0.8~1.3um.

3. An etching method capable of reducing the degree of lateral corrosion of a wafer as claimed in any one of claims 1 to 2, characterized in that: The etching is performed in the following steps:

1. First dry the wafer to remove moisture from the wafer surface, then spread the photoresist, and then heat the wafer to solidify the photoresist; 2. Etch the wafer according to the set longitudinal corrosion depth. After each etching, apply photoresist on the etched surface to cover the etched part. Stop the etching and clean it.

3. Remove the photoresist from the etched wafer; 4. Repeat steps 1, 2, and 3 according to the total longitudinal depth of the wafer that needs to be etched, performing photolithography at the same position each time until the required longitudinal depth of etching is reached.

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