PN junction developing method

Abstract

The invention provides a PN junction developing method, which comprises the following steps of: cutting a PN junction sample for the first time by adopting gallium ions so as to expose a PN junction; cutting the PN junction for the second time by adopting gallium ions so as to remove a damaged layer caused by the first cutting; and carrying out third cutting on the PN junction by adopting ions of which the relative atomic mass is smaller than that of the gallium ions so as to remove a damaged layer caused by gallium ion cutting. According to the method, the PN junction is cut for the third time by adopting the ions with the relative atomic mass smaller than that of the gallium ions, a damaged layer caused by gallium ion cutting is removed, namely, the sample surface influenced by the gallium ions is removed, the influence of the gallium ions on PN junction ion concentration observation is reduced, and meanwhile, due to the fact that the ions with the relative atomic mass smaller than that of the gallium ions are adopted, the detection accuracy is improved. Compared with gallium ions, the action depth on the surface of a sample is greatly reduced, and the original PN junction of the sample can be kept unchanged, so that the observation sensitivity of the PN junction is improved, and the aim of accurately analyzing the PN junction with low doping concentration is fulfilled.

Description

Technical Field

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

[0002] Semiconductor chips conduct electricity through PN junctions, which are the basis of their operation. Therefore, the visible junction observation of PN junctions is crucial for monitoring diffusion and ion implantation processes and analyzing chip production capacity.

[0003] However, the current analysis of lightly doped PN junctions still presents challenges. This is mainly because the conventional preparation method for PN junction samples in the industry requires the use of a gallium (Ga) ion source in a FIB (focused ion beam micro-nanoprocessing instrument) to cut the sample and remove the amorphous layer on the surface. However, while removing the amorphous layer, gallium ions can also cause damage to the observation area (including physical damage and the effects of gallium ion implantation), thereby affecting the analysis results of the PN junction and even causing the PN junction to be unable to be visualized. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for displaying PN junctions, remove the damaged layer caused by gallium ion cutting, reduce the influence of gallium ions on the observation of PN junction ion concentration, make the PN junction clearly displayed, and thus enable accurate analysis of low-doping concentration PN junctions.

[0005] In order to solve the above technical problems, the present invention provides a method for forming a PN junction, comprising the following steps:

[0006] Gallium ions are used to perform the first cutting of the PN junction sample to expose the PN junction;

[0007] Performing a second cutting of the PN junction using gallium ions to remove the damaged layer caused by the first cutting; and

[0008] The PN junction is cut for the third time using ions with a relative atomic mass smaller than that of gallium ions to remove the damaged layer caused by gallium ion cutting.

[0009] Optionally, in the third cutting, the ions having a relative atomic mass smaller than that of gallium ions include argon ions.

[0010] Optionally, the argon ions include an argon ion beam or an argon plasma.

[0011] Optionally, the acceleration voltage of the argon ion beam is 0.2 kV to 1 kV, and the ion beam current is 1.3 nA to 1.5 nA.

[0012] Optionally, the forward power of the argon plasma is 750W to 850W, and the gas flow is 90 sccm to 110 sccm.

[0013] Optionally, the energy of the second cutting is less than the energy of the first cutting.

[0014] Optionally, the first cutting uses a gallium ion beam, and the acceleration voltage of the gallium ion beam in the first cutting is 25kV to 30kV, and the ion beam current is 0.5nA to 21nA.

[0015] Optionally, the second cutting uses a gallium ion beam, and the acceleration voltage of the gallium ion beam in the second cutting is 3kV to 5kV, and the ion beam current is 1pA to 80pA.

[0016] Optionally, after the third cutting, the method further includes: performing dyeing treatment on the cut surface.

[0017] Optionally, the dyeing treatment includes: soaking the cut surface in a chemical reagent.

[0018] In the method for revealing a PN junction provided by the present invention, gallium ions are first used to perform a first cut on a PN junction sample to expose the PN junction. Gallium ions are then used to perform a second cut on the PN junction to remove the damaged layer caused by the first cut. Subsequently, ions with a relative atomic mass less than that of gallium ions are used to perform a third cut on the PN junction to remove the damaged layer caused by the gallium ion cut. In the present invention, by performing a third cut on the PN junction using ions with a relative atomic mass less than that of gallium ions, the damaged layer caused by the gallium ion cut is removed, thereby removing the sample surface affected by the gallium ions and reducing the impact of gallium ions on the observation of ion concentration at the PN junction. Furthermore, because ions with a relative atomic mass less than that of gallium ions are used, their depth of action on the sample surface is significantly reduced compared to that of gallium ions, thereby maintaining the original PN junction of the sample unchanged and improving the observation sensitivity of the PN junction, thereby achieving the purpose of accurately analyzing low-doping concentration PN junctions. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a flow chart of a method for displaying a PN junction provided in one embodiment of the present invention.

[0020] Figure 2 Schematic diagram of the depth of action of gallium ions and argon ions on a sample according to one embodiment of the present invention.

[0021] Figure 3 This is a schematic diagram of a sample after the first cutting and the second cutting and dyeing using gallium ions provided by an embodiment of the present invention.

[0022] Figure 4 This is a schematic diagram of a sample after the first and second cuttings are performed using gallium ions, the third cutting is performed using argon ions, and dyeing is performed, provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0023] As described in the background technology, the gallium ion source in the FIB is first used to cut the sample to expose the PN junction, and then the gallium ion source is continued to be used to remove the amorphous damage layer caused by the gallium ion bombardment in the previous step. However, while using gallium ions to remove the amorphous damage layer, the gallium ions will also damage the PN junction, thereby affecting the analysis results of the PN junction. In severe cases, the PN junction cannot be displayed.

[0024] Table 1

[0025] ion Energy (keV) Sputtering rate (atoms / ion) Xe+ 30 39 Ga+ 30 27 Ar+ 30 18 Xe+ 5 16 Ar+ 0.5 3

[0026] The depth of ion impact on a sample is related to the energy and type of the ions. Table 1 shows the relationship between ion type, energy, and sputtering rate, where the ion incident angle and the stage tilt angle are fixed. As can be seen from Table 1, at the same energy (e.g., 30 keV), the sputtering rate of argon ions (Ar+) on a sample is lower than that of gallium ions (Ga+), while at the same energy (e.g., 30 keV), the sputtering rate of gallium ions on a sample is lower than that of xenon ions (Xe+). The relative atomic mass of argon ions is smaller than that of gallium ions, which in turn is smaller than that of xenon ions. The lower the relative atomic mass of the ion, the lower the sputtering rate. A lower sputtering rate indicates a lower depth of impact on the sample and less damage to the sample's intrinsic structure.

[0027] After using gallium ions to remove the amorphous damage layer caused by gallium ion bombardment, ions with a relative atomic mass smaller than that of gallium ions can be used to bombard the PN junction to remove the damage layer caused by gallium ions. Since ions with a relative atomic mass smaller than that of gallium ions are used, the depth of their action on the sample surface will be greatly reduced compared to gallium ions, thereby keeping the original PN junction of the sample unchanged.

[0028] After further research, the present invention provides a method for revealing a PN junction, comprising the following steps: performing a first cutting on a PN junction sample using gallium ions to expose the PN junction; performing a second cutting on the PN junction using gallium ions to remove a damaged layer caused by the first cutting; and performing a third cutting on the PN junction using ions with a relative atomic mass smaller than that of gallium ions to remove the damaged layer caused by the gallium ion cutting.

[0029] In the present invention, ions with a relative atomic mass smaller than that of gallium ions are used to perform a third cutting on the PN junction, thereby removing the damaged layer caused by the gallium ion cutting, that is, removing the sample surface affected by the gallium ions, thereby reducing the influence of the gallium ions on the ion concentration observation of the PN junction. At the same time, since ions with a relative atomic mass smaller than that of gallium ions are used, the depth of their action on the sample surface is greatly reduced compared with that of gallium ions, thereby maintaining the original PN junction of the sample unchanged, thereby improving the observation sensitivity of the PN junction, and achieving the purpose of accurately analyzing the low-doping concentration PN junction.

[0030] To make the objects, advantages, and features of the present invention more clearly apparent, the present invention is further described below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the drawings are all in a very simplified form and are not drawn to scale. They are only used to conveniently and clearly assist in illustrating the purposes of the embodiments of the present invention. In addition, the structures shown in the drawings are often part of the actual structure. In particular, different drawings may need to illustrate different focuses and sometimes use different scales.

[0031] As used in the present invention, the singular forms "a", "an" and "the" include plural objects, unless the content clearly indicates otherwise. As used in the present invention, the term "or" is generally used in a sense including "and / or", unless the content clearly indicates otherwise. As used in the present invention, the term "several" is generally used in a sense including "at least one", unless the content clearly indicates otherwise. As used in the present invention, the term "at least two" is generally used in a sense including "two or more", unless the content clearly indicates otherwise. In addition, the terms "first", "second" and "third" are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first", "second" and "third" may explicitly or implicitly include one or at least two of the features, unless the content clearly indicates otherwise.

[0032] Figure 1 This is a flow chart of a PN junction display method provided in one embodiment of the present invention. Figure 1 As shown, the PN junction display method provided by the embodiment of the present invention includes the following steps:

[0033] S1: Use gallium ions to perform the first cutting on the PN junction sample to expose the PN junction;

[0034] S2: performing a second cutting on the PN junction using gallium ions to remove the damaged layer caused by the first cutting; and

[0035] S3: using ions with a relative atomic mass smaller than that of gallium ions to perform a third cutting on the PN junction to remove the damaged layer caused by the gallium ion cutting.

[0036] In step S1 , gallium ions are used to perform a first cutting, ie, rough cutting, on the PN junction sample to expose the PN junction.

[0037] In this embodiment, gallium ions in a FIB are used for the first cutting, forming a groove in the PN junction sample to expose the PN junction. The gallium ions are, for example, a gallium ion beam. In one embodiment, the gallium ion beam has an accelerating voltage of 25 kV to 30 kV, and an ion beam current of 0.5 nA to 21 nA, but this is not limited to these. Exemplarily, the accelerating voltage is 25 kV, 27 kV, 29 kV, or 30 kV, preferably 30 kV, and the ion beam current is 0.5 nA, 5 nA, 10 nA, 15 nA, 20 nA, or 21 nA, preferably 15 nA.

[0038] When the PN junction is exposed during the first cutting, gallium ions damage the PN junction and form a damage layer, for example, an amorphous damage layer is formed on the surface of the PN junction.

[0039] In step S2, gallium ions are used to perform a second cutting on the PN junction to remove the damaged layer caused by the first cutting.

[0040] In this embodiment, gallium ions in the FIB are used to fine-tune the exposed PN junction to remove the damaged layer caused by the first cutting process. The energy of the second cutting is less than the energy of the first cutting, so as to cut slowly. The gallium ions are, for example, a gallium ion beam. In one embodiment, the acceleration voltage of the gallium ion beam is 3kV to 5kV, and the ion beam current is 1pA to 80pA, but of course it is not limited to this. Exemplarily, the acceleration voltage is 3kV, 3.5kV, 4kV, 4.5kV or 5kV, and the acceleration voltage is preferably 5kV. The ion beam current is 1pA, 20pA, 40pA, 60pA or 80pA, and the ion beam current is preferably 40pA.

[0041] The purpose of performing the second cutting in this embodiment is to remove the damaged layer caused by the first cutting. However, while removing the damaged layer caused by the first cutting, the second cutting will also cause damage to the PN junction. On the basis that the energy of the second cutting is less than the energy of the first cutting, the depth of the damaged layer will be reduced, but the damaged layer still exists, and due to the existence of the damaged layer, the analysis results of the PN junction will be affected. In severe cases, the PN junction may even be unable to be visualized.

[0042] To solve the above problem, step S3 is continued to be performed, in which ions with a relative atomic mass smaller than that of gallium ions are used to perform a third cutting on the PN junction to remove the damaged layer caused by the gallium ion cutting.

[0043] In this embodiment, the PN junction is subjected to a third cut, using ions with a relative atomic mass smaller than that of gallium ions. The third cut removes the damaged layer caused by the gallium ion cut, which may include the damage caused by both the first and second cuts. In one embodiment, the second cut removes the damaged layer caused by the first cut, and the third cut removes the damaged layer caused by the second cut. In another embodiment, if some of the damaged layer caused by the first cut remains after the second cut, it will also be removed during the third cut.

[0044] The third cutting can remove the damaged layer caused by gallium ion cutting. At the same time, since the relative atomic mass of the ions used is smaller than that of gallium ions, the depth of their effect on the sample surface will be greatly reduced compared with gallium ions, thereby keeping the original PN junction of the sample unchanged.

[0045] In the embodiment of the present invention, ions with a relative atomic mass smaller than that of gallium ions are used to perform a third cutting on the PN junction, thereby removing the damaged layer caused by the gallium ion cutting, that is, removing the sample surface affected by the gallium ions, thereby reducing the influence of the gallium ions on the ion concentration observation of the PN junction. At the same time, since ions with a relative atomic mass smaller than that of gallium ions are used, the depth of their action on the sample surface is greatly reduced compared with that of gallium ions, thereby maintaining the original PN junction of the sample unchanged, thereby improving the observation sensitivity of the PN junction, and achieving the purpose of accurately analyzing the low-doping concentration PN junction.

[0046] In one embodiment of the present invention, the ions having a relative atomic mass smaller than that of gallium ions include argon ions, that is, argon ions are used to perform a third cutting on the PN junction to remove the damaged layer caused by gallium ion cutting. Of course, this is not limited to this, and other suitable ions having a relative atomic mass smaller than that of gallium ions can also be selected for the third cutting.

[0047] In one embodiment of the present invention, the argon ions include an argon ion beam or an argon plasma. Thus, the third cutting may be performed using an argon ion beam or an argon plasma. For example, the third cutting may be performed using a reactive ion etch (RIE) apparatus or an ion milling apparatus containing argon plasma or an argon ion beam, but the present invention is not limited thereto.

[0048] In one embodiment, an argon ion beam is used for the third cutting. The argon ion beam has an accelerating voltage of 0.2 kV to 1 kV, and an ion beam current of 1.3 nA to 1.5 nA, but is not limited thereto. Exemplary acceleration voltages include 0.2 kV, 0.4 kV, 0.6 kV, 0.8 kV, or 1 kV, preferably 1 kV, and an ion beam current of 1.3 nA, 1.4 nA, or 1.5 nA, preferably 1.4 nA.

[0049] In another embodiment, the third cutting is performed using argon plasma. The forward power of the argon plasma is 750W to 850W, and the gas flow is 90 sccm to 110 sccm. Exemplarily, the forward power is 750W, 800W, or 850W, preferably 800W, and the gas flow is 90 sccm, 100 sccm, or 110 sccm, preferably 100 sccm.

[0050] Figure 2 Schematic diagram of the depth of action of gallium ions and argon ions on a sample according to an embodiment of the present invention, wherein Figure 2 The depth of action of argon ions on the sample is the depth of cutting the sample using argon plasma. Figure 2 As shown in the figure, after removing the damaged layer in the previous step, the depth of action of gallium ions is much greater than the depth of action of argon ions. Therefore, using argon ions for the third cutting can not only remove the damaged layer caused by gallium ion cutting in the previous step, that is, remove the sample surface affected by gallium ions, reduce the influence of gallium ions on the observation of PN junction ion concentration, but also the depth of action on the sample will not be too large. It can be understood that while using argon ions to remove the damaged layer caused by gallium ion cutting in the previous step, argon ions also form a new action area at the same time. Therefore, after the third cutting with argon ions, there will also be the following on the sample surface. Figure 2 However, compared with the cutting with gallium ions, the depth of the active area is greatly reduced, so the impact on the sample can be ignored, so that the original PN junction of the sample can be kept unchanged, and the observation sensitivity of the PN junction is improved, thereby achieving the purpose of accurate analysis of low-doping concentration PN junctions.

[0051] In the low doping concentration region of the nanometer scale (e.g. less than 10 15 atom / cm 2 For samples with high requirements for the visible junction (surface concentration), the introduction of ions with a relative atomic mass smaller than that of gallium ions (such as argon ions) to bombard (i.e., perform the third cutting) can remove the sample surface originally affected by gallium ions, and the depth of action of argon ions is greatly reduced, thereby maintaining the original PN structure of the sample. When the affected surface is removed and the depth of action on the surface is greatly reduced, the observation sensitivity of the PN junction can be increased from 1015 atom / cm 2 Surface concentration increased to 10 12 atom / cm 2 Surface concentration.

[0052] After the third cutting, the method further includes: performing a dyeing treatment on the cut surface, that is, performing a dyeing treatment on the PN junction.

[0053] In one embodiment, the cut surface is immersed in a chemical reagent for dyeing. The cut PN junction sample is immersed in a prepared chemical reagent for dyeing. The dyeing process can be an electrochemical etching process. Due to the electrochemical potential difference between the P region and the N region of the PN junction, the two regions exhibit different reaction rates, resulting in the PN junction morphology. After dyeing is completed, the sample is removed, and the dyed grooves are rinsed with deionized water and finally dried.

[0054] Finally, the PN junction sample is imaged under a focused ion beam microscope, and the characterized PN junction morphology is analyzed. For example, the depth and width of the PN junction can be characterized. PN junction morphology analysis is crucial for chip failure analysis, process monitoring, process improvement, and reverse engineering.

[0055] Figure 3 This is a schematic diagram of a sample after the first and second cutting and dyeing using gallium ions according to an embodiment of the present invention. Figure 3 As shown, the PN junction sample is first cut using gallium ions in the FIB to expose the PN junction, and then the PN junction is cut a second time using gallium ions in the FIB to remove the damaged layer caused by the first cutting, and then the junction is dyed, and the PN junction is not shown. Figure 4 This is a schematic diagram of a sample after the first and second cuttings using gallium ions, the third cutting using argon ions and dyeing according to an embodiment of the present invention. Figure 4 As shown, the PN junction sample is first cut using gallium ions in the FIB to expose the PN junction, and then the PN junction is cut a second time using gallium ions in the FIB to remove the damage layer caused by the first cutting. Then, the PN junction is cut a third time using argon ions to remove the damage layer caused by the gallium ion cutting. After that, the junction is dyed and the PN junction is clearly displayed.

[0056] contrast Figure 3 and Figure 4 It can be seen that the third cutting of the PN junction using argon ions can remove the damaged layer caused by gallium ion cutting, reduce the influence of gallium ions on the observation of PN junction ion concentration, make the PN junction clearly displayed, and thus enable accurate analysis of low-doping concentration PN junctions.

[0057] In summary, in the method for revealing a PN junction provided by the present invention, gallium ions are first used to perform a first cut on the PN junction sample to expose the PN junction, then gallium ions are used to perform a second cut on the PN junction to remove the damaged layer caused by the first cut, and then ions with a relative atomic mass less than that of gallium ions are used to perform a third cut on the PN junction to remove the damaged layer caused by the gallium ion cutting. In the present invention, by performing a third cut on the PN junction using ions with a relative atomic mass less than that of gallium ions, the damaged layer caused by the gallium ion cutting is removed, that is, the sample surface affected by the gallium ions is removed, thereby reducing the impact of gallium ions on the observation of ion concentration at the PN junction. At the same time, because ions with a relative atomic mass less than that of gallium ions are used, their depth of action on the sample surface is significantly reduced compared to that of gallium ions, thereby maintaining the original PN junction of the sample unchanged and improving the observation sensitivity of the PN junction, thereby achieving the purpose of accurately analyzing low-doping concentration PN junctions.

[0058] The above description is only a description of the preferred embodiments of the present invention and does not limit the scope of the present invention. Any changes and modifications made by ordinary technicians in the field of the present invention based on the above disclosure shall fall within the scope of protection of the claims.

Claims

1. A method for forming a PN junction, characterized in that: The following steps are involved: Gallium ions are used to perform the first cutting of the PN junction sample to expose the PN junction; Performing a second cutting of the PN junction using gallium ions to remove the damaged layer caused by the first cutting; as well as The PN junction is cut for the third time using ions with a relative atomic mass smaller than that of gallium ions to remove the damaged layer caused by gallium ion cutting.

2. The method for forming a PN junction according to claim 1, wherein: In the third cutting, the ions having a relative atomic mass smaller than that of gallium ions include argon ions.

3. The method for forming a PN junction according to claim 2, wherein: Argon ions include argon ion beams or argon plasma.

4. The method for forming a PN junction according to claim 3, wherein: The acceleration voltage of the argon ion beam is 0.2 kV to 1 kV, and the ion beam current is 1.3 nA to 1.5 nA.

5. The method for forming a PN junction according to claim 3, wherein: The forward power of the argon plasma is 750W to 850W, and the gas flow is 90 sccm to 110 sccm.

6. The method for forming a PN junction according to claim 1, wherein: The energy of the second cutting is less than the energy of the first cutting.

7. The method for forming a PN junction according to claim 6, wherein: The first cutting adopts a gallium ion beam, and the acceleration voltage of the gallium ion beam in the first cutting is 25kV to 30kV, and the ion beam current is 0.5nA to 21nA.

8. The method for forming a PN junction according to claim 6, wherein: The second cutting adopts a gallium ion beam, and the acceleration voltage of the gallium ion beam in the second cutting is 3kV to 5kV, and the ion beam current is 1pA to 80pA.

9. The method for displaying a PN junction according to any one of claims 1 to 8, characterized in that: After the third cutting, the method further includes: performing dyeing treatment on the cut surface.

10. The PN junction display method according to claim 9, characterized in that: The dyeing and knotting treatment includes: soaking the cut surface in a chemical reagent.

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