PN junction dyeing method and PN junction characterization method

Abstract

The invention provides a PN junction dyeing method and a PN junction characterization method.The PN junction dyeing method comprises the steps that a to-be-dyed sample with a to-be-dyed PN junction exposed out of the cross section is provided; preparing a first solution; a second solution is added into the first solution to form a first staining solution, the first staining solution comprises a first component and a second component, and the second component is the same as the second solution; a first substance is added into the first staining solution to form a second staining solution, the second component and the first substance react at the reaction rate smaller than a preset threshold value to generate hydrofluoric acid, and the first substance and the second component react completely after a first duration; and within a second duration of adding the first substance into the first staining solution, immersing the cross section of the PN junction to be dyed exposed in the sample to be dyed into a second staining solution, and dyeing the PN junction to be dyed, the second duration being shorter than the first duration. According to the PN junction dyeing method, the controllability and safety in the operation process of the PN junction dyeing method can be improved.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor manufacturing, and in particular to a PN junction dyeing method and a PN junction characterization method. Background Art

[0002] Chemical staining is a widely used method for determining PN junction morphology in semiconductor production, offering advantages such as low cost, ease of use, and rapid experimentation. Common chemical staining methods include chromic acid solution staining, acetic acid solution staining, and copper sulfate solution staining. However, there are some differences between these methods, resulting in varying PN junction size and morphology. The appropriate method must be selected based on factors such as the PN junction size and doping concentration. However, all of these methods require the use of hydrofluoric acid to etch the silicon.

[0003] However, hydrofluoric acid has the following disadvantages during daily storage and use: 1. Hydrofluoric acid is highly corrosive, so special plastic or corrosion-resistant containers are required for storage and handling.

[0004] 2. Hydrofluoric acid is highly toxic. Even low-concentration hydrofluoric acid solutions may cause serious harm to the human body. In addition, it can enter the human body through skin contact, inhalation or accidental ingestion, and combine with calcium, magnesium and other ions to cause tissue necrosis and systemic poisoning.

[0005] 3. The emergency response requirements for hydrofluoric acid accidents are very high, and specific antidotes (such as defluorination) need to be used immediately to neutralize fluoride ions.

[0006] 4. Due to the high risk of hydrofluoric acid, its storage, transportation, and handling require special equipment and measures, increasing its cost. In addition, hydrofluoric acid accidents can lead to high medical and environmental remediation costs. Summary of the Invention

[0007] The present invention provides a PN junction dyeing method to improve the controllability and safety during the operation process using the PN junction dyeing method.

[0008] According to a first aspect of the present invention, a PN junction dyeing method is provided, comprising: Providing a sample to be dyed, wherein a cross section of the sample to be dyed exposes a PN junction to be dyed; preparing a first solution in a preparation container; adding a second solution to the first solution to form a first staining solution, wherein the first staining solution includes a first component and a second component, and the second component is the same as the second solution; adding a first substance to the first staining liquid to form a second staining liquid, wherein the second component reacts with the first substance at a reaction rate less than a preset threshold to generate hydrofluoric acid, and the first substance reacts completely with the second component in the first staining liquid after a first time period; Within a second time period after adding the first substance to the first staining liquid, the cross section of the sample to be stained where the PN junction to be stained is exposed is immersed in the second staining liquid to stain the PN junction to be stained, and the second time period is shorter than the first time period.

[0009] Optionally, the first solution includes a chromic acid solution, the second solution includes a hydrochloric acid solution, and the first component of the first dyeing solution formed by mixing the first solution and the second solution is dichromic acid, and the second component is hydrochloric acid.

[0010] Optionally, the first substance includes lithium fluoride crystals or lithium fluoride powder.

[0011] Optionally, the mass of the first substance added to the first dyeing solution is 1 gram to 2 grams.

[0012] Optionally, preparing the first solution in the preparation container includes: A second substance of a preset mass of 0.5 g to 1.5 g is placed in the preparation container, wherein the second substance is chromium trioxide crystals; 40 ml to 60 ml of water are added to the preparation container and stirred to form the first solution.

[0013] Optionally, the volume of the hydrochloric acid solution is 3 ml to 5 ml.

[0014] Optionally, the preparation processes of the first solution and the dyeing solution are both carried out at an ambient temperature between 20°C and 25°C.

[0015] Optionally, provide a sample to be stained including: providing a semiconductor device sample; A grinder is used to polish the cross section of the semiconductor device sample, and the grinder is stopped at a cross section where the PN junction to be dyed is exposed, so as to form the sample to be dyed.

[0016] Optionally, the time for dyeing the PN junction to be dyed is 5 seconds to 30 seconds.

[0017] According to a second aspect of the present invention, a method for characterizing a PN junction is provided, comprising: Providing a dyeing sample in which the exposed PN junction is dyed using the above-mentioned PN junction dyeing method, wherein the cross section of the dyeing sample exposes the dyed PN junction; Observe the cross section of the exposed PN junction using a scanning electron microscope or a focused ion beam electron microscope; The cross section where the dyed PN junction is exposed is photographed to obtain an image of the dyed PN junction.

[0018] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: In a PN junction dyeing method provided by the technical solution of the present invention, a first substance reacts with a second component in the first dyeing liquid in a second dyeing liquid at a reaction rate less than a preset threshold to produce hydrofluoric acid. In other words, the first substance reacts slowly with the second component in the first dyeing liquid (forming a small amount of hydrofluoric acid per unit time), requiring a first duration for complete reaction. Based on this, during the second duration after the first substance is added to the first dyeing liquid, the cross-section of the sample to be dyed where the PN junction to be dyed is exposed is immersed in the second dyeing liquid to dye the PN junction to be dyed, and the second duration is less than the first duration. Therefore, when the second dyeing liquid contains a small amount of hydrofluoric acid, the cross-section of the exposed PN junction to be dyed can be immersed in the second dyeing liquid. Thus, the small amount of hydrofluoric acid already in the second dyeing liquid participates in the dyeing reaction of the PN junction to be dyed, while the first substance continues to react with the first dyeing liquid to form a new small amount of hydrofluoric acid, which also continues to participate in the dyeing reaction of the PN junction to be dyed. Therefore, on the one hand, since the reaction rate of the first substance and the first dyeing liquid is relatively slow (i.e., the reaction rate of generating hydrofluoric acid is relatively slow), the dyeing reaction takes a longer time, thereby making the operation of dyeing the PN junction using the dyeing method more controllable. On the other hand, since the small amount of hydrofluoric acid present in the second dyeing liquid participates in the dyeing reaction while the first substance and the first dyeing liquid continue to react to form a new small amount of hydrofluoric acid, the consumption and production of hydrofluoric acid in the second dyeing liquid reach a dynamic balance, thereby ensuring the presence of a small amount of hydrofluoric acid in the second dyeing liquid throughout the dyeing process, thereby ensuring normal dyeing of the PN junction in an environment of a small amount of hydrofluoric acid, thereby making the operation of dyeing the PN junction using the dyeing method safer on the basis of avoiding the transportation risk of hydrofluoric acid, and reducing the emergency response requirements for hydrofluoric acid accidents. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a flow chart of a PN junction dyeing method provided by an embodiment of the present invention; Figure 2 This is a SEM image of a PN junction cross section provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0020] As described in the background art, in the process of dyeing the PN junction using a chemical dyeing method, directly using hydrofluoric acid to corrode silicon will increase the safety during the operation and the controllability requirements during the dyeing process. In addition, hydrofluoric acid has high requirements for storage containers, so directly using hydrofluoric acid will increase storage costs and transportation costs.

[0021] In view of this, the technical solution of the present invention creatively proposes a PN junction dyeing method, comprising: Providing a sample to be dyed, wherein a cross section of the sample to be dyed exposes a PN junction to be dyed; preparing a first solution in a preparation container; adding a second solution to the first solution to form a first staining solution, wherein the first staining solution includes a first component and a second component, and the second component is the same as the second solution; adding a first substance to the first staining liquid to form a second staining liquid, wherein the second component reacts with the first substance at a reaction rate less than a preset threshold to generate hydrofluoric acid, and the first substance reacts completely with the second component in the first staining liquid after a first time period; Within a second time period after adding the first substance to the first staining liquid, the cross section of the sample to be stained where the PN junction to be stained is exposed is immersed in the second staining liquid to stain the PN junction to be stained, and the second time period is shorter than the first time period.

[0022] Since the reaction rate between the first substance and the second component in the first dyeing liquid is relatively slow (i.e., the reaction rate of generating hydrofluoric acid is relatively slow), the dyeing reaction takes a longer time, thereby making the operation of dyeing the PN junction using this dyeing method more controllable. On the other hand, since the small amount of hydrofluoric acid present in the second dyeing liquid participates in the dyeing reaction while the first substance continues to react with the first dyeing liquid to form a new small amount of hydrofluoric acid, the consumption and production of hydrofluoric acid in the second dyeing liquid reach a dynamic balance, thereby ensuring the presence of a small amount of hydrofluoric acid in the second dyeing liquid throughout the dyeing process, thereby ensuring normal dyeing of the PN junction in an environment with a small amount of hydrofluoric acid. Furthermore, while avoiding the transportation risk of hydrofluoric acid, the operation of dyeing the PN junction using this dyeing method is safer, thereby reducing the emergency response requirements for hydrofluoric acid accidents.

[0023] The following will provide a clear and complete description of the embodiments of the present invention, in conjunction with the accompanying drawings. Obviously, the described embodiments are only some of the embodiments of the present invention, and not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. The terms "first," "second," "third," and so on, in the specification and claims of the present invention, and in the accompanying drawings, are used to distinguish similar objects and are not necessarily used to describe a specific order or precedence. It should be understood that such terms are interchangeable where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than that illustrated or described herein. Furthermore, the terms "including," "having," and any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, product, or apparatus.

[0024] Please refer to Figure 1 , the steps of the PN junction dyeing method include: A sample to be dyed is provided, wherein a cross section of the sample to be dyed exposes a PN junction to be dyed.

[0025] In this embodiment, a method for providing a sample to be dyed includes: providing a semiconductor device sample; and using a grinder to polish a cross section of the semiconductor device sample, stopping at a cross section where a PN junction to be dyed is exposed, thereby forming the sample to be dyed. The size of the PN junction to be dyed is selected to be approximately 40 microns.

[0026] Specifically, before using a grinder to polish the cross-section of the semiconductor device sample, the method also includes the step of fixing the semiconductor device sample to the grinder, that is, fixing the semiconductor device sample to the base of the grinder, and installing the grinding base with the semiconductor device sample fixed on the power head of the grinder to fix the semiconductor device sample on the grinder.

[0027] Prepare a first solution in a preparation vessel.

[0028] In this embodiment, the method for preparing the first solution in the preparation container includes: taking a preset mass of the second substance and placing it in the preparation container; adding 40 ml to 60 ml of water to the preparation container and stirring uniformly to form the first solution.

[0029] The second substance is chromium trioxide crystals, with a preset mass of 0.5 g to 1.5 g. Therefore, the first solution is a chromic acid solution, and the chemical reaction equation for the chromium trioxide crystals dissolving in water to form the chromic acid solution is as follows: The second solution is added to the first solution and stirred to form a first dyeing solution, wherein the first dyeing solution includes a first component and a second component, and the second component is the same as the second solution.

[0030] In this embodiment, the second solution is a hydrochloric acid solution, and the volume of the second solution is 3 ml to 5 ml. In addition, those skilled in the art will appreciate that the second solution can also be a strong acid solution such as sulfuric acid that can ionize hydrogen ions.

[0031] In this embodiment, since a chromic acid solution undergoes a condensation reaction in an acidic environment to produce a dichromic acid solution, the first dyeing solution includes a first component (dichromic acid) and a second component (hydrochloric acid). The chemical reaction equation for the condensation reaction of a chromic acid solution in an acidic environment to produce a dichromic acid solution is as follows: A first substance is added to a first dyeing liquid and stirred, causing a second component in the first dyeing liquid to react with the first substance to form a second dyeing liquid. The second component of the first dyeing liquid reacts with the first substance at a reaction rate less than a predetermined threshold to produce hydrofluoric acid, and the first substance and the second component of the first dyeing liquid react completely after a first time period. Specifically, the first dyeing liquid includes a dichromic acid solution and a hydrochloric acid solution. After the first substance is added, the hydrochloric acid solution in the first dyeing liquid reacts with the first substance.

[0032] In this embodiment, the first substance includes lithium fluoride crystals or lithium fluoride powder, and the mass of the first substance is 1 gram to 2 grams.

[0033] In this embodiment, lithium fluoride crystals or lithium fluoride powder can slowly react with the hydrochloric acid solution in the first dyeing solution to generate hydrofluoric acid and lithium chloride. The corresponding chemical reaction equation is as follows: In this embodiment, the first duration is approximately 1 minute, and the reaction rate of the preset threshold is approximately 0.1 mol / (L·s). Specifically, when the reaction rate of generating hydrofluoric acid is much greater than the reaction rate of the preset threshold, a large amount of hydrofluoric acid will be rapidly generated in the preparation container. Since hydrofluoric acid is highly corrosive and toxic, the probability of an accident increases. When the reaction rate of generating hydrofluoric acid is much less than the reaction rate of the preset threshold, the dyeing time of the PN junction is longer, thereby reducing the dyeing efficiency of the PN junction. In addition, when the concentration of the second component of the first dyeing liquid is constant, the first duration is positively correlated with the mass of the first substance and the volume of the second component of the first dyeing liquid, and when the mass of the first substance and the volume of the second component of the first dyeing liquid are constant, the first duration is negatively correlated with the concentration of the second component of the first dyeing liquid.

[0034] Among them, after the first period of time, the hydrochloric acid solution and the lithium fluoride crystals or lithium fluoride powder no longer react, that is, the remaining hydrochloric acid solution and the remaining lithium fluoride crystals or lithium fluoride powder are insufficient to react to generate hydrofluoric acid and lithium chloride, or, there is no remaining hydrochloric acid solution, or there is no remaining lithium fluoride crystals or lithium fluoride powder.

[0035] Since highly corrosive hydrofluoric acid will be generated in the preparation container, the preparation container is a polytetrafluoroethylene beaker, which has high corrosion resistance.

[0036] During the second time period after adding the first substance to the first staining liquid, the cross section of the sample to be stained where the PN junction to be stained is exposed is immersed in the second staining liquid to stain the PN junction to be stained. The second time period is shorter than the first time period.

[0037] In the present embodiment, the second duration is about 5 seconds.Specifically, in the second duration of adding the first substance in the first staining liquid, a small amount of hydrofluoric acid can be generated in the second staining liquid. If the second duration is much greater than 5 seconds, a large amount of hydrofluoric acid can be generated in the second staining liquid. Because hydrofluoric acid has higher corrosivity and toxicity, the probability of an accident is increased. Of course, those skilled in the art will appreciate that the setting of the second duration can be set according to actual conditions such as hydrofluoric acid generation rate, and the present invention does not limit this.

[0038] In this embodiment, because the second duration is shorter than the first duration, the second dyeing liquid includes dichromic acid, hydrochloric acid, lithium fluoride, a small amount of hydrofluoric acid, and a small amount of lithium chloride during the second duration of adding the first substance to the first dyeing liquid. After the cross-section of the sample to be dyed, where the exposed PN junction is to be dyed, is immersed in the second dyeing liquid, the PN junction to be dyed directly reacts with the dichromic acid and the small amount of hydrofluoric acid in the second dyeing liquid. Simultaneously, the lithium fluoride in the second dyeing liquid can continue to react with the hydrochloric acid to form a new small amount of hydrofluoric acid, which continues to participate in the dyeing reaction of the PN junction to be dyed. Therefore, on the one hand, due to the slow reaction rate of lithium fluoride and hydrochloric acid (i.e., the slow reaction rate of generating hydrofluoric acid), the dyeing reaction takes longer, thus making the dyeing method for PN junction dyeing more controllable. On the other hand, because the small amount of hydrofluoric acid present in the second dyeing solution participates in the dyeing reaction, the lithium fluoride and hydrochloric acid continue to react to form a new small amount of hydrofluoric acid, which allows the consumption and production of hydrofluoric acid in the second dyeing solution to reach a dynamic equilibrium. As a result, a small amount of hydrofluoric acid is always present in the second dyeing solution during the dyeing process, ensuring normal dyeing of the PN junction in the presence of a small amount of hydrofluoric acid, thereby reducing the risks involved in the PN junction dyeing process. Furthermore, because hydrochloric acid solution and lithium fluoride crystals or lithium fluoride powder are both common chemicals, they are easy to obtain and store. This makes the dyeing method for PN junction dyeing safer while avoiding the transportation risks of hydrofluoric acid, thereby reducing the emergency response requirements for hydrofluoric acid accidents.

[0039] Specifically, a PN junction consists of a P-type doped region and an N-type doped region in close contact. The dyeing process for the PN junction is an electrochemical corrosion process. Due to the chemical potential difference between the P-type and N-type doped regions of the PN junction, and the fact that a higher impurity doping level in the doped region results in a faster reaction rate, the two regions exhibit a different reaction rate difference, thereby revealing the junction morphology. The greater the difference in dyeing reaction rates between the P-type and N-type doped regions, the clearer the junction morphology. The dyeing reaction rate is positively correlated with the concentration of the reactants and the doping level of the doped regions. In the P-type doped region of the PN junction, since the PN junction is made of silicon, silicon reacts with water in the second dyeing solution to form silicon dioxide. The resulting silicon dioxide then reacts with hydrofluoric acid to form a hexafluorosilicic acid complex, which detaches from the silicon surface and enters the second dyeing solution, thereby allowing the dyeing reaction in the P-type doped region to continue. The dichromic acid in the N-type doped region of the PN junction is reduced by hydrogen ions. Therefore, the overall chemical equation for dyeing the PN junction to be dyed is as follows: In this embodiment, the dyeing time for the PN junction to be dyed is 5 to 30 seconds. When the dyeing time is short (less than 5 seconds), the morphology of the PN junction to be dyed is not fully revealed, making it difficult to fully observe the morphology of the PN junction to be dyed. When the dyeing time is long (greater than 30 seconds), the extent of the dyeing reaction on the PN junction to be dyed is large, resulting in poorly observed morphology of the PN junction to be dyed. Therefore, when the concentration of the reactants participating in the reaction (for example, the concentration of dichromic acid or hydrofluoric acid in the second dyeing solution) is high, the dyeing time can be correspondingly shortened. When the concentration of the reactants participating in the reaction (for example, the concentration of dichromic acid or hydrofluoric acid in the second dyeing solution) is low, the dyeing time can be correspondingly extended.

[0040] In this embodiment, the preparation process of the first solution and the dyeing solution is carried out at an ambient temperature of 20° C. to 25° C. If the ambient temperature is too high, the acid is easily volatile, that is, the hydrochloric acid in the first dyeing solution and the hydrofluoric acid in the second dyeing solution are easily volatile, thereby affecting the dyeing process of the PN junction to be dyed.

[0041] In summary, in a PN junction dyeing method provided by an embodiment of the present invention, in a second dyeing liquid, a first substance reacts with a second component in the first dyeing liquid at a reaction rate less than a preset threshold to produce hydrofluoric acid. In other words, the first substance reacts slowly with the second component in the first dyeing liquid (forming a small amount of hydrofluoric acid per unit time), requiring a first duration for complete reaction. Furthermore, during the second duration after the first substance is added to the first dyeing liquid, the cross-section of the sample to be dyed where the PN junction to be dyed is exposed is immersed in the second dyeing liquid to dye the PN junction to be dyed, and the second duration is less than the first duration. Therefore, when the second dyeing liquid contains a small amount of hydrofluoric acid, the cross-section of the exposed PN junction to be dyed can be immersed in the second dyeing liquid. Thus, the small amount of hydrofluoric acid already in the second dyeing liquid participates in the dyeing reaction of the PN junction to be dyed, while the first substance continues to react with the first dyeing liquid to form a new small amount of hydrofluoric acid, which also continues to participate in the dyeing reaction of the PN junction to be dyed. Therefore, on the one hand, since the reaction rate of the first substance and the first dyeing liquid is relatively slow (i.e., the reaction rate of generating hydrofluoric acid is relatively slow), the dyeing reaction takes a longer time, thereby making the operation of dyeing the PN junction using the dyeing method more controllable. On the other hand, since the small amount of hydrofluoric acid present in the second dyeing liquid participates in the dyeing reaction while the first substance and the first dyeing liquid continue to react to form a new small amount of hydrofluoric acid, the consumption and production of hydrofluoric acid in the second dyeing liquid reach a dynamic balance, thereby ensuring the presence of a small amount of hydrofluoric acid in the second dyeing liquid throughout the dyeing process, thereby ensuring normal dyeing of the PN junction in an environment of a small amount of hydrofluoric acid, thereby making the operation of dyeing the PN junction using the dyeing method safer on the basis of avoiding the transportation risk of hydrofluoric acid, and reducing the emergency response requirements for hydrofluoric acid accidents.

[0042] Please refer to Figure 2 An embodiment of the present invention also provides a PN junction characterization method, comprising: providing a dyeing sample for dyeing an exposed PN junction using the above-mentioned PN junction dyeing method, wherein the cross section of the dyeing sample exposes the dyed PN junction; observing the cross section of the exposed dyed PN junction using a scanning electron microscope or a focused ion beam electron microscope; and photographing the cross section of the exposed dyed PN junction to obtain an image of the dyed PN junction.

[0043] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the scope defined by the claims.

Claims

1. A PN junction dyeing method, characterized in that: include: Providing a sample to be dyed, wherein a cross section of the sample to be dyed exposes a PN junction to be dyed; preparing a first solution in a preparation container; adding a second solution to the first solution to form a first staining solution, wherein the first staining solution includes a first component and a second component, and the second component is the same as the second solution; adding a first substance to the first staining liquid to form a second staining liquid, wherein the second component reacts with the first substance at a reaction rate less than a preset threshold to generate hydrofluoric acid, and the first substance reacts completely with the second component in the first staining liquid after a first time period; Within a second time period after adding the first substance to the first staining liquid, the cross section of the sample to be stained where the PN junction to be stained is exposed is immersed in the second staining liquid to stain the PN junction to be stained, and the second time period is shorter than the first time period.

2. The PN junction dyeing method according to claim 1, characterized in that: The first solution includes a chromic acid solution, the second solution includes a hydrochloric acid solution, and the first component of the first dyeing solution formed by mixing the first solution and the second solution is dichromic acid, and the second component is hydrochloric acid.

3. The PN junction dyeing method according to claim 2, characterized in that: The first substance includes lithium fluoride crystals or lithium fluoride powder.

4. The PN junction dyeing method according to claim 3, characterized in that: The mass of the first substance added to the first dyeing solution is 1 gram to 2 grams.

5. The PN junction dyeing method according to claim 4, characterized in that: Preparing a first solution in a preparation container comprises: A second substance of a preset mass of 0.5 g to 1.5 g is placed in the preparation container, wherein the second substance is chromium trioxide crystals; 40 ml to 60 ml of water are added to the preparation container and stirred to form the first solution.

6. The PN junction dyeing method according to claim 2, characterized in that: The volume of the hydrochloric acid solution is 3 ml to 5 ml.

7. The PN junction dyeing method according to claim 1, characterized in that: The preparation processes of the first solution and the dyeing solution are both carried out at an ambient temperature between 20°C and 25°C.

8. The PN junction dyeing method according to claim 1, characterized in that: A sample to be stained includes: providing a semiconductor device sample; A grinder is used to polish the cross section of the semiconductor device sample, and the grinder is stopped at a cross section where the PN junction to be dyed is exposed, so as to form the sample to be dyed.

9. The PN junction dyeing method according to claim 1, characterized in that: The time for dyeing the PN junction to be dyed is 5 seconds to 30 seconds.

10. A method for characterizing a PN junction, characterized in that: include: Providing a dyed sample in which an exposed PN junction is dyed using the PN junction dyeing method according to any one of claims 1 to 9, wherein a cross section of the dyed sample exposes the dyed PN junction; Observe the cross section of the exposed PN junction using a scanning electron microscope or a focused ion beam electron microscope; The cross section where the dyed PN junction is exposed is photographed to obtain an image of the dyed PN junction.

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