Method for removing plastic package and metal base of semiconductor device

Abstract

The invention provides a method for removing plastic package and stripping a metal base of a semiconductor device, which comprises the following steps of: firstly, mechanically polishing to remove a non-chip area and back base copper, then separating a device base on the back of the metal base by using aqua regia, and finally, putting the device without the base into a mixed solution of concentrated sulfuric acid and concentrated nitric acid for heating reaction, and after reaction, washing and cleaning. According to the method, innovative mechanical polishing, local aqua regia treatment and optimized chemical unsealing steps are comprehensively applied, so that a metal base of a device can be effectively removed while plastic package is removed, high-efficiency unsealing treatment is realized, the use amount of chemicals is greatly reduced, the use amount of chemical reagents is greatly reduced, and the production cost is reduced. Furthermore, little waste acid liquid is generated, so that not only is the environmental pollution reduced, but also the waste treatment cost is saved for enterprises.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor device cover opening, and relates to a method for removing plastic packaging from a semiconductor device and stripping off a metal base. Background Art

[0002] Opening the device cover is of great significance for understanding the internal structure and principle of the device. By opening the cover, possible sources of failure inside the device can be discovered and eliminated in a timely manner; by observing and analyzing the internal structure of the device, it can help optimize the design and manufacturing process of the device.

[0003] At present, the device opening process can be divided into four categories: chemical corrosion opening, mechanical opening, laser opening, and plasma opening. Although the mechanical opening method is simple and easy to operate, it is more likely to damage the device, and the plastic sealing material will have more residues on the chip, which is not conducive to the analysis of the device. The laser opening method and the plasma opening method have less damage to the device and no plastic sealing material residue, but they may damage the fine structure on the surface of the chip, and require corresponding instrument configuration, high cost and long opening time, and are not widely applicable. The chemical corrosion opening method can have a better plastic removal effect without damaging the device. The general chemical opening method requires heating at least 160°C. A single sample is opened with at least 10mL of concentrated sulfuric acid and fuming nitric acid mixed acid. The opening time is generally longer due to the large amount of plastic sealing material on the surface, and the operation is more dangerous. And after opening, if there is a metal layer on the surface of the device, the metal base of the device cannot be removed, and the observation and analysis of the bottom of the device cannot be realized. Summary of the invention

[0004] The purpose of the present invention is to provide a method for combining chemical corrosion and mechanical cover opening to simultaneously remove the plastic seal and metal base on the surface of the device, thereby solving the problems that the common chemical corrosion method uses mixed concentrated strong acid under high temperature heating conditions, has high operating risks, and cannot remove the metal base of the device.

[0005] The specific technical solutions of the present invention are as follows: A method for removing plastic packaging and stripping a metal base of a semiconductor device, firstly mechanically polishing to remove the non-chip area and the back base copper, then using aqua regia to separate the device base on the back of the metal base, finally putting the device without the base into a mixed solution of concentrated sulfuric acid and concentrated nitric acid for heating reaction, and then rinsing it after the reaction.

[0006] The specific steps are as follows: The first step is mechanical grinding. The sample to be opened is glued to the grinding fixture, and it is ground with coarse sandpaper on the automatic grinding machine in the order of the four sides, the front side, and the back side. Step 2: Dip a glass rod in aqua regia on the back of the metal base according to the size and position of the device. Gently grind the device and rinse with clean water. Repeat the operation until the device base is completely removed. Step 3: Take 2-5 mL of a mixture of concentrated sulfuric acid and fuming nitric acid, place the sample with the base removed into the mixed acid, heat to 110-150°C and react for 5-30 minutes, then rinse the surface of the silicon wafer.

[0007] In the first step, the polishing standard is: polish away obvious non-chip areas on all sides, polish the back side until there is no obvious copper color on the copper base of the device, and polish the front side until the device bonding is almost disconnected; In the third step, in the mixed solution, the volume ratio of concentrated sulfuric acid to fuming nitric acid is 1:1.

[0008] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: The present invention uses a combination of innovative mechanical polishing, local aqua regia treatment and optimized chemical unsealing steps, which not only achieves highly efficient unsealing treatment, but also greatly reduces the use of chemicals. The use of chemical reagents is greatly reduced, and the amount of waste acid liquid generated is also extremely small, which not only reduces environmental pollution, but also saves the cost of waste treatment for enterprises.

[0009] Compared with the traditional chemical corrosion opening method and mechanical opening method, the present invention can effectively remove the metal base of the device while removing the plastic package. This feature undoubtedly increases its practicality and application range. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a sample view before opening.

[0011] Figure 2 This is a view of the plastic sealing material not being completely removed during the conventional chemical opening process.

[0012] Figure 3 This is a view after the opening materials are completely removed after conventional chemical opening.

[0013] Figure 4 This is a view after the first step of mechanical polishing in the method of the present invention.

[0014] Figure 5 This is a rear view after the metal base is removed in the second step of the method of the present invention.

[0015] Figure 6 This is a view of completely removing the plastic packaging material and the metal base according to the method of the present invention.

[0016] Figure 7 Schematic diagram of the cross-sectional structure of a semiconductor device.

[0017] Figure 8 Flow chart of the method of the present invention. DETAILED DESCRIPTION

[0018] The specific contents of the present invention are further explained in detail below in conjunction with embodiments.

[0019] The present invention discloses a method for removing plastic packaging of a semiconductor device and stripping a metal base, which specifically comprises the following steps: The first step is mechanical polishing. Stick the sample to be opened on the grinding fixture, and polish it with coarse sandpaper on the automatic grinder in the order of the four sides, the front side, and the back side. Pick up the sample from time to time for observation. The judgment criteria are as follows: polish off 0.15-0.25mm width on the left and right sides, 0.5-0.7mm width on the front side, 0.1-0.15mm width on the back side of the non-chip area, polish off 0.1-0.2mm on the back, and polish off 0.05-0.1mm on the front side.

[0020] The first step of mechanical polishing can quickly and effectively remove most of the plastic packaging materials on the surface of the device, and at the same time remove most of the metal base. However, because it is not completely polished, it can save corrosion time while ensuring that the device is not mechanically damaged, thus preparing for the next step of precise corrosion.

[0021] Step 2: Depending on the size and position of the device, use a glass rod to dip into aqua regia on the back of the metal base, gently grind the device location, and then rinse with clean water. Repeat the operation until the device base is completely removed.

[0022] In the second step, the front of the device is protected by the plastic packaging material, so the front of the device can be protected from being damaged by acid when the metal base is corroded with acid. Aqua regia is used to corrode the metal base because its corrosion rate is higher than that of dilute nitric acid, dilute sulfuric acid, and hydrochloric acid alone. Using a glass rod dipped in aqua regia to corrode the device base can better control the corrosion area and effectively control the reaction degree of the base, avoiding excessive aqua regia from washing the metal base and damaging the metal on the chip surface.

[0023] Step 3: Take 2-5 mL of a 1:1 volume ratio of concentrated sulfuric acid and fuming nitric acid mixture in a 25 mL PFA beaker, place the sample with the base removed into the mixed acid, heat to 110-150°C for 5-30 minutes, and then rinse the surface of the silicon wafer.

[0024] In the third step, because there is less plastic packaging material on the surface of the device, only a small amount of concentrated sulfuric acid + fuming nitric acid mixed acid is needed to heat and soak the device, which can quickly destroy the plastic packaging material and completely remove it from the device package. In addition, the reaction temperature is significantly reduced, reducing some operating risks.

[0025] Comparative Example Conventional chemical opening effects such as Figure 1-3 As shown, the specific steps are as follows: Take 15mL of concentrated sulfuric acid + fuming nitric acid (volume ratio 1:1) mixed solution in a 25mL PFA beaker and heat to 170~180℃ for 50~70min. Example

[0026] Step 1: Mechanical grinding: Take the unsealed sample, stick it on the grinding fixture, and grind it with coarse sandpaper on the automatic grinder. First grind the surrounding surface of the device to remove the obvious non-semiconductor device area, change the grinding position to the front side and grind until the device bond is almost disconnected, change the grinding position to the back side of the device, and stop grinding when the copper on the back of the device is almost gone. For the grinding effect, refer to Figure 4 .

[0027] Step 2: Dip a glass rod in aqua regia on the back of the metal base according to the size and position of the device. Gently grind the device and rinse with water. Repeat about 5 times until the metal at the bottom of the device is completely removed. The effect is as follows: Figure 5 .

[0028] Step 3: Take 5 mL of concentrated sulfuric acid + fuming nitric acid (volume ratio 1:1) in a 25 mL PFA beaker, put the sample without the base into the mixed acid, heat to 130°C for 10 minutes, and then rinse the surface of the silicon wafer. The effect is as follows: Figure 6 .

[0029] There are significant differences between the embodiment and the comparative example in the unsealing process of semiconductor devices. The embodiment not only improves the processing efficiency, but also significantly reduces the use of chemicals by comprehensively using the three steps of mechanical polishing, local aqua regia treatment and chemical unsealing, reflecting a stronger environmental awareness and cost control. At the same time, this multi-step processing method makes the operation more refined, and can first remove the non-critical parts, and then accurately treat the specific parts, which helps to protect the key parts of the sample from excessive chemical corrosion during the chemical unsealing process. In addition, since the chemical treatment temperature and time in the embodiment are relatively low, the risk of thermal damage and chemical damage is also effectively reduced. Therefore, compared with the single chemical unsealing method in the comparative example, the embodiment shows a more efficient, more environmentally friendly and more sophisticated processing method, which significantly improves the overall effect of the unsealing process.

[0030] The content of the present invention is not limited to the embodiments listed, and any equivalent changes made to the technical solution of the present invention by ordinary technicians in this field after reading the description of the present invention are covered by the claims of the present invention.

Claims

1. A method for removing plastic packaging and stripping metal base of a semiconductor device, characterized in that: First, mechanical polishing is used to remove the non-chip area and the copper on the back base. Then, aqua regia is used to separate the device base on the back of the metal base. Finally, the device with the base removed is placed in a mixture of concentrated sulfuric acid and concentrated nitric acid for heating reaction. After the reaction, rinse it clean.

2. A method for removing plastic packaging and stripping metal base of a semiconductor device according to claim 1, characterized in that: The specific steps are as follows: The first step is mechanical grinding. The sample to be opened is glued to the grinding fixture, and it is ground with coarse sandpaper on the automatic grinding machine in the order of the four sides, the front side, and the back side. Step 2: Dip a glass rod in aqua regia on the back of the metal base according to the size and position of the device. Gently grind the device and rinse with clean water. Repeat the operation until the device base is completely removed. Step 3: Take 2-5 mL of a mixture of concentrated sulfuric acid and fuming nitric acid, place the sample with the base removed into the mixed acid, heat to 110-150°C and react for 5-30 minutes, then rinse the surface of the silicon wafer.

3. A method for removing plastic packaging and stripping metal base of a semiconductor device according to claim 2, characterized in that: In the first step, the polishing standard is: polish away obvious non-chip areas on all sides, polish the back side until there is no obvious copper color on the copper base on the back of the device, and polish the front side until the device bonding is almost disconnected.

4. A method for removing plastic packaging and stripping metal base of a semiconductor device according to claim 3, characterized in that: In the third step, in the mixed solution, the volume ratio of concentrated sulfuric acid to fuming nitric acid is 1:1.

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