Preparation method of quantum dot single photon source micro-column cavity and single photon source sample sheet

Abstract

The application discloses a preparation method of a quantum dot single photon source micro-column cavity and a single photon source sample. The method comprises the following steps: generating a first mask layer on an epitaxial layer of a sample sheet to be etched, and generating a second mask layer in an inverted mesa type on the first mask layer; etching the first mask layer by taking the second mask layer as a mask, so that the first mask layer is formed into a cylindrical structure; etching the epitaxial layer of the sample sheet by taking the first mask layer in the cylindrical structure as a mask, so as to form a micro-column, wherein different etching parameters are adopted for etching the epitaxial layer at different depths of the epitaxial layer. The application solves the technical problem that it is difficult to prepare a micro-column cavity with good perpendicularity.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of semiconductor, in particular, to a preparation method of quantum dot single photon source micro-column cavity and single photon source sample. BACKGROUND

[0002] Quantum communication and quantum computation are two important directions of quantum information technology. Quantum secure communication uses quantum key transmission or quantum state transmission, and quantum computation uses entanglement and coherence characteristics of quantum states to process information, both of which need to rely on high-quality single photon or entangled photon source core quantum devices. Among various schemes of material systems and quantum structures for realizing quantum light sources, a semiconductor self-organized quantum dot is a typical "atomic-like" structure, which has the advantages of narrow linewidth, long coherence time, excellent homogeneity, and easy integration, etc., and is a front and hot spot of the current international high-quality single photon light-emitting device research direction.

[0003] There are three common ways to realize high-quality and high-brightness single photon source of quantum dots in microcavities, namely, planar cavity, micro-column cavity and target eye cavity, among which the micro-column cavity is most widely studied. Generally, the preparation method of single photon source quantum dot micro-column cavity is to directly etch a micro-column through dry etching after preparing a mask through exposure and etching and other steps. However, the perpendicularity of the micro-column and the smoothness of the micro-column sidewall seriously affect the quality factor of the micro-column cavity. Therefore, it is particularly important to obtain In(Ga)As micro-columns with good perpendicularity and smooth sidewall. In addition, the removal of the hard mask layer and by-products after dry etching of the micro-column is also a process difficulty.

[0004] At present, no effective solution has been proposed for the above problems. SUMMARY

[0005] The embodiments of the present application provide a preparation method of quantum dot single photon source micro-column cavity and a single photon source sample, to at least solve the technical problem that it is difficult to prepare a micro-column cavity with good perpendicularity.

[0006] According to an aspect of the embodiments of the present application, a preparation method of quantum dot single photon source micro-column cavity is provided, including: generating a first mask layer on an epitaxial layer of a sample to be etched, and generating a second mask layer in an inverted mesa type on the first mask layer; etching the first mask layer with the second mask layer as a mask, so that the first mask layer is formed into a cylindrical structure; etching the epitaxial layer of the sample with the first mask layer in a cylindrical structure as a mask, to form a micro-column, wherein different etching parameters are used for etching the epitaxial layer at different depths of the epitaxial layer.

[0007] According to another aspect of the embodiments of the present application, a preparation method of a micro-column enhanced quantum dot single photon source is further provided, which comprises using the above method to prepare the micro-column cavity of the single photon source.

[0008] According to still another aspect of the embodiments of the present application, a quantum dot single photon source sample sheet relying on optical pumping is further provided, which comprises a plurality of micro-column cavities prepared by using the above method, wherein the micro-column cavities are arranged periodically.

[0009] In the embodiments of the present application, different etching parameters are used to etch the epitaxial layer for different depths of the epitaxial layer when etching the epitaxial layer, thereby solving the technical problem that it is difficult to prepare a micro-column cavity with good verticality. BRIEF DESCRIPTION OF DRAWINGS

[0010] The accompanying drawings, which are included to provide a further understanding of the present application, form a part of the present application and illustrate the illustrative embodiments of the present application and the explanation of the present application, and do not constitute improper limitations on the present application. In the drawings:

[0011] Figure 1 is a flow chart of a preparation method of a quantum dot single photon source according to an embodiment of the present application;

[0012] Figure 2 is a flow chart of another preparation method of a micro-column cavity of a quantum dot single photon source according to an embodiment of the present application;

[0013] Figure 3 is a schematic diagram of a growth structure of a sample sheet according to an embodiment of the present application;

[0014] Figure 4 is a column shaped like an inverted table according to the morphology of the negative photoresist after exposure according to an embodiment of the present application;

[0015] Figure 5 is a schematic diagram of the angle between the side wall of the inverted table and the horizontal plane according to an embodiment of the present application;

[0016] Figure 6 is a schematic diagram of the morphology of the first mask layer etched according to an embodiment of the present application;

[0017] Figure 7 is a schematic diagram of the epitaxial layer etched to form a cylindrical array structure with good verticality according to an embodiment of the present application;

[0018] Figure 8 is a schematic diagram of using a polyimide high-temperature adhesive tape to cover the single crystal silicon area outside the sample sheet according to an embodiment of the present application;

[0019] Figure 9 is a schematic diagram of the structure of the removed residual first mask layer according to an embodiment of the present application;

[0020] Figure 10 is a flow chart of a preparation method of an In(Ga)As quantum dot single photon source micro-column cavity according to an embodiment of the present application;

[0021] Figure 11 is a structural diagram of a nearly vertical micro-column cavity prepared by a processing technology according to an embodiment of the present application. DETAILED DESCRIPTION

[0022] In order to make the personnel in the technical field better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without making creative labor should belong to the scope of protection of the present application.

[0023] It should be noted that the terms "first", "second", and the like in the specification and claims of the present application and the above-described drawings are used to distinguish similar objects, and do not necessarily have to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device including a series of steps or units does not have to be limited to the clearly listed steps or units, but can include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0024] Embodiment 1

[0025] According to an embodiment of the present application, a preparation method of a quantum dot single photon source is provided, as shown in Figure 1 The method comprises:

[0026] Step S102, generating a first mask layer on an epitaxial layer of a sample to be etched, and generating an inverted table type second mask layer on the first mask layer.

[0027] For example, spin-coating a negative glue capable of being exposed and developed on the surface of the first mask layer; performing laser direct writing exposure, development and fixing on the negative glue, so that the negative glue morphology after exposure is an inverted table type cylinder, to constitute the inverted table type second mask layer; wherein the inverted table type is the shape of the frustum left after cutting the top of the cone, and the surface area of the frustum far away from the top surface of the first mask layer is greater than the surface area of the bottom surface close to the first mask layer. Wherein, the included angle between the sidewall of the frustum and the plane where the first mask layer is located is about 80° to 85°.

[0028] Step S104, etching the first mask layer with the second mask layer as a mask, so that the first mask layer is formed into a cylindrical structure.

[0029] For example, the following mask etching parameters are set first: the sample stage temperature is set to 0-10℃, the helium purge pressure of the sample back is set to 5-15 Torr, the etching gas is set to argon and trifluoromethane, the flow rate ratio of argon and trifluoromethane is set to 1:5-1:1, the process pressure is set to 5-10 mTorr, the upper electrode power is set to 800-1000 W, and the lower electrode power is set to 30-50 W; then, the first mask layer is etched with the second mask layer as a mask based on the set mask etching parameters, so that the first mask layer is formed into a cylindrical structure close to a cylinder, and it should be noted that the cylindrical structure here is a structure similar to a cylinder, for example, it can be a columnar structure with a small upper end cross-sectional area and a large lower end cross-sectional area.

[0030] After etching the first mask layer of the sample, the residual second mask layer is removed completely.

[0031] Step S106, etching the epitaxial layer of the sample with the first mask layer in a cylindrical structure as a mask to form a microcolumn, wherein different etching parameters are used for etching the epitaxial layer at different depths of the epitaxial layer.

[0032] First, the etching parameters are set before etching. For example, the sample stage temperature is set to 20-40℃, the helium purge pressure of the sample back is set to 5-15 Torr, the etching gas is set to chlorine, boron trichloride and argon, the process pressure is set to 1-5 mTorr, the upper electrode power is set to 300-500 W, and the lower electrode power is set to 30-60 W.

[0033] Next, the sample is adhered to a single crystal silicon wafer using a heat-conducting material, and the single crystal silicon area on the single crystal silicon wafer other than the sample is covered with a cover.

[0034] Finally, the epitaxial layer of the sample is etched in stages.

[0035] In the first stage, i.e., the cylindrical top etching stage of the epitaxial layer, the epitaxial layer is etched with a preset flow rate of chlorine, boron trichloride and argon, for example, 6-8 sccm of chlorine, 10-12 sccm of boron trichloride and 6-15 sccm of argon, for 1-2 minutes, wherein the flow rate of chlorine should be less than that of boron trichloride.

[0036] In the second stage, i.e. the stage of etching the middle part of the cylinder of the epitaxial layer, the flow rate of chlorine gas is increased or the flow rate of boron trichloride is decreased to change the flow rate ratio of chlorine gas, boron trichloride and argon gas for etching. For example, the flow rate of chlorine gas is increased to 1.5 to 2 times of the flow rate of chlorine gas in the first stage, or the flow rate of boron trichloride is decreased to 1 / 3 to 1 / 2 of the flow rate of boron trichloride in the first stage, and the middle part of the cylinder of the epitaxial layer is etched for 3 to 5 minutes with chlorine gas, boron trichloride and argon gas in the changed flow rate ratio.

[0037] In the third stage, i.e. the stage of etching the bottom part of the cylinder of the epitaxial layer, the flow rate of chlorine gas is restored to the flow rate of chlorine gas in the first stage, the flow rate of boron trichloride is changed to be lower than the flow rate of boron trichloride in the first stage and higher than the flow rate of boron trichloride in the second stage, and the bottom part of the cylinder of the epitaxial layer is etched with chlorine gas, boron trichloride and argon gas in the changed flow rate ratio. For example, the flow rate of chlorine gas is restored to the flow rate of chlorine gas in the first stage, and the flow rate of boron trichloride is decreased to 5 / 6 to 1 times of the flow rate of boron trichloride in the first stage, and the bottom part of the cylinder of the epitaxial layer is etched for 2 to 3 minutes with chlorine gas, boron trichloride and argon gas in the changed flow rate ratio.

[0038] After the epitaxial layer of the sample is etched, the temperature of the sample stage can also be set to be higher than the preset temperature, and at the preset temperature, the first mask layer remaining on the micro-pillar is removed, and the by-products deposited on the sidewall of the micro-pillar are removed.

[0039] Specifically, the first mask layer is removed first. For example, the following mask removal parameters are set: the temperature of the sample stage is set to be between 60 to 80℃, the pressure of helium blowing on the back of the sample is set to be between 5 to 15 Torr, the process pressure is set to be between 15 to 25 mTorr, the flow rate ratio of trifluoromethane and oxygen is set to be between 1:5 to 1:3, the upper electrode power is set to be between 800 to 1000 W, and the lower electrode power is set to be 0 W; and then, the first mask layer remaining on the micro-pillar is removed based on the set mask removal parameters.

[0040] Then, the by-products deposited on the sidewall of the micro-pillar are removed. For example, the following by-product removal parameters are set first: the temperature of the sample stage is set to be between 60 to 80℃, the pressure of helium blowing on the back of the sample is set to be between 5 to 15 Torr, the process pressure is set to be between 15 to 25 mTorr, the flow rate of trifluoromethane is set to be 0 sccm, the flow rate of oxygen is set to be the sum of the flow rates of trifluoromethane and oxygen when the first mask layer remaining on the micro-pillar is removed, the upper electrode power is set to be between 800 to 1000 W, and the lower electrode power is set to be 0 W; and then, the by-products deposited on the sidewall of the micro-pillar are removed based on the set by-product removal parameters.

[0041] After etching the epitaxial layer of the sample, the sample can be sequentially subjected to ultrasonic cleaning in an acetone, isopropanol and ultrapure water bath container at a preset temperature.

[0042] According to the micro-column cavity preparation method, the micro-column cavity with a verticality close to 90° can be prepared, the hard mask layer on the top of the micro-column cavity after etching can be easily removed, and the by-products deposited on the sidewall of the micro-column can also be removed. In this way, the performance of the single photon source can be improved.

[0043] Embodiment 2

[0044] According to the embodiment of the present application, another preparation method of a quantum dot single photon source micro-column cavity is also provided, as shown in Figure 2 The method comprises the following steps:

[0045] In step S201, the substrate is cleaned with an organic solvent and dried with nitrogen.

[0046] In step S201, the substrate is cleaned with an organic solvent and dried with nitrogen. Figure 3 As shown in

[0047] In step S202, a first mask layer is formed on the epitaxial layer.

[0048] In step S202, a first mask layer is formed on the epitaxial layer.

[0049] In step S203, a second mask layer is formed on the first mask layer, the second mask layer is exposed, and the second mask layer with a "inverted table type" structure is formed.

[0050] In step S203, a second mask layer is formed on the first mask layer, the second mask layer is exposed, and the second mask layer with a "inverted table type" structure is formed. Figure 4 As shown in Figure 5 The "inverted table type" column has a truncated cone top and the area of the top surface away from the epitaxial layer is larger than the area of the bottom surface close to the epitaxial layer. The angle between the inverted table sidewall and the horizontal plane is α, and the range is 80°-85°, as shown in

[0051] In the embodiment, the second mask layer is kept in an "inverted mesa" shape by using a negative photoresist, so that the problem of widening caused by etching of the first mask layer can be solved, and a more vertical shape can be provided. Specifically, it is difficult to form a 90° vertical shape by exposure process. If a "mesa" shape is formed by exposure, the etched SiO2 shape will be more inclined than the photoresist shape because the photoresist cannot mask the ion bombardment in the vertical direction (downward etching direction) during etching of SiO2. If an "inverted mesa" shape is formed by exposure, the top of the inverted mesa will block the downward ion bombardment, so that the etched SiO2 shape is more vertical.

[0052] In step S204, the first mask layer is etched by using the second mask layer as a mask to form a circular truncated cone-shaped cylinder.

[0053] In the embodiment, the sample to be etched is adhered to a single crystal silicon wafer by using heat-conducting silicone oil for etching, and the etching process parameters are set as follows: the sample table is set to a temperature of 0-10°C, the pressure of helium (He) gas blowing at the back of the sample is 5-15 Torr, argon (Ar) and trifluoromethane (CHF B ) are used as etching gases, the flow ratio of Ar and CHF3 is set to be in the range of 1:5-1:1, the process pressure is set to be in the range of 5-10 mTorr, the upper electrode (ICP) power is set to be in the range of 800-1000 W, and the lower electrode (Bias) power is set to be in the range of 30-50 W.

[0054] The sample after exposure is etched by using an inductively coupled plasma etching machine, and the etched SiO2 shape is more vertical, as shown in FIG. 3B, which is beneficial to improve the verticality of the micro-pillar formed by etching the epitaxial layer in the next step. Figure 6

[0055] In step S205, the second mask layer is removed.

[0056] The sample after etching of the first mask layer is processed, and the residual second mask layer is removed completely by using a plasma stripper and organic solvent.

[0057] In the prior art, the residual second mask layer is not removed and is directly etched, so that the ionized plasma also etches the photoresist to form polymer deposition on the sidewall of the micro-pillar, thereby intensifying the deposition of by-products on the sidewall of the micro-pillar. In the embodiment, the residual second mask layer is removed, so that the sidewall of the micro-pillar is not easy to deposit by-products, and the micro-pillar is more vertical.

[0058] In step S206, the epitaxial layer is etched by using the circular truncated cone-shaped cylinder-shaped first mask layer. ​

[0059] An inductively coupled plasma etching machine is used to etch the In(Ga)As epitaxial layer with the first mask layer as a mask until the target depth, to form a cylindrical array structure with good verticality, as shown in FIG. 1B. The specific process steps are as follows: Figure 7

[0060] 1) A polyimide high-temperature adhesive tape is used to cover the single crystal silicon area outside the sample piece.

[0061] The sample piece to be etched is adhered to a single crystal silicon wafer with heat-conducting silicone oil, and the single crystal silicon area outside the sample piece is covered with a polyimide high-temperature adhesive tape, as shown in FIG. 1A. It is placed in the etching machine cavity for etching. Figure 8

[0062] In the prior art, the single crystal silicon wafer carrying the sample piece is not covered with polyimide, which leads to the fact that, during the microcolumn etching, Cl2 will not only react with the sample piece, but also react with the bare single crystal silicon, forming gaseous SiCl4.

[0063] Si + 2Cl2→ SiCl4↑

[0064] The formed SiCl4 will be ionized again, increasing the concentration of Cl active radicals, thereby enhancing the chemical reaction, making the microcolumn etching uncontrollable in the lateral direction, and finally making it difficult to ensure the vertical morphology of the microcolumn etching.

[0065] In this embodiment, the single crystal silicon area outside the sample piece is covered with a polyimide high-temperature adhesive tape, making it easier to ensure the vertical morphology of the microcolumn etching.

[0066] 2) Set the etching process parameters.

[0067] In this embodiment, the etching process parameters are set as follows: the sample stage temperature is set to 20-40℃, the pressure of He gas blowing on the back of the sample piece is 5-15Torr, the etching gas is Cl2, BCl3 and Ar, the process pressure is set to 1-5mTorr, the upper electrode (ICP) power is set to 300-500W, and the lower electrode (Bias) power is set to 40-60W.

[0068] In this embodiment, the sample stage temperature is increased to the preset temperature range, that is, the temperature of the sample piece during etching is increased, thereby reducing the deposition of by-products generated during etching on the sidewall of the microcolumn. However, it should be noted that the temperature should not be too high, otherwise the microcolumn quantum dot cavity will be laterally etched, resulting in damage to the quantum dot cavity. In this embodiment, the sample stage temperature is preferably set to 20-40℃, so that the temperature range is moderate, thereby making the etched microcolumn more vertical.

[0069] ​​In addition, in the embodiment, a very low pressure is adopted, so that the density of active groups generated by ionization in the etching cavity is reduced, the rate of chemical reaction is lowered, and lateral etching is weakened. Moreover, the very low pressure reduces the collision probability of active groups, especially ions, in the plasma, increases the mean free path, and thus enhances the physical bombardment in the vertical direction, which is beneficial to improving the verticality of etching.

[0070] 3) Set the flow rate of etching gas.

[0071] In the embodiment, the setting of the flow rate of etching gas is as follows: in the initial stage of etching, i.e. when etching the top of the micro-pillar, the flow rates of Cl2, BCl3 and Ar are respectively set in the range of 6-8 Sccm, 10-12 Sccm and 6-15 Sccm, and the etching time in this stage is 1-2 minutes (min); in the middle stage of etching, i.e. when etching the middle part of the micro-pillar, the flow rate of Cl2 is increased to 1.5-2 times that in the initial stage, or the flow rate of BCl3 is reduced to 1 / 3-1 / 2 of that in the initial stage, and the etching time in this stage is 3-5 min; in the final stage of etching, i.e. when etching the bottom of the micro-pillar, the flow rate of Cl2 is restored to the value in the initial stage, and the flow rate of BCl3 is reduced to 5 / 6-1 of that in the initial stage, and the etching time in this stage is 2-3 min.

[0072] In the embodiment, the etching is set to three stages by adjusting the flow rate ratio of Cl2 to BCl3, so that the proportions of sidewall etching and deposition in the three stages can be mainly controlled. Specifically, Cl active radicals are generated after the ionization of Cl2, which has a fast chemical isotropic etching effect; BCl3 ions are generated after the ionization of BCl3, which has a physical anisotropic etching effect; and the radicals and groups generated by the ionization of BCl3 form polymers, which deposit to form a protective layer and block the sidewall from being subjected to lateral etching. Therefore, by adjusting the flow rate ratio of Cl2 to BCl3, the sidewall can be protected to different degrees, so as to achieve the effect of vertical etching. x The radicals and groups generated by the ionization of BCl3 form polymers, which deposit to form a protective layer and block the sidewall from being subjected to lateral etching. Therefore, by adjusting the flow rate ratio of Cl2 to BCl3, the sidewall can be protected to different degrees, so as to achieve the effect of vertical etching.

[0073] Step S207: remove the first mask layer.

[0074] The remaining first mask layer is removed by using an inductively coupled plasma etching machine, as shown in FIG. 6. The specific process steps are as follows: Figure 9

[0075] The sample to be etched is adhered to a sapphire wafer with heat-conducting silicone oil for etching. The etching process parameters are set, for example, the sample stage temperature is set to 60-80°C, the pressure of He gas blowing on the back of the sample is 5-15 Torr, and the etching gas is CHF3 and O2. In the embodiment, the sample stage is set to a higher temperature, so as to intensify the volatilization of by-products formed in the process, reduce the deposition of by-products on the sidewall of the micro-pillar, and thus improve the smoothness of the sidewall of the micro-pillar.

[0076] ​Specifically, the etching can be performed in two steps:

[0077] 1) The process pressure is set to 15-25 mTorr, the flow ratio of CHF3 and O2 is between 1 / 5 and 1 / 3, the upper electrode (ICP) power is set to 800-1000 W, and the lower electrode (Bias) power is set to 35-50 W. This step is mainly to remove the residual first mask layer.

[0078] 2) The process pressure is set to be consistent with step 1), the CHF3 flow is set to 0 sccm, the O2 flow is set to the sum of the CHF3 and O2 flows in step 1), the upper electrode (ICP) power is set to 800-1000 W, and the lower electrode (Bias) power is set to 35-50 W. This step is mainly to further remove the by-products deposited on the sidewall.

[0079] Step S208, wet cleaning.

[0080] After etching, the sample is placed in a water bath at about 30°C and sequentially cleaned with acetone, isopropanol and ultrapure water under ultrasonic cleaning to ensure the cleanliness of the microcolumn sample.

[0081] Through the above process, the diameter of the etched microcolumn is 0.5-5 um.

[0082] The related microcolumn cavity preparation methods in the prior art are difficult to prepare a microcolumn cavity with a verticality close to 90°; the hard mask layer (SiO2) on the top of the microcolumn cavity after etching is difficult to remove; by-products are deposited on the sidewall of the microcolumn, which causes the sidewall smoothness to be poor, which all leads to the decrease of the quality factor of the microcolumn cavity; in addition, the hard mask layer (SiO2) on the top of the microcolumn cavity after etching is also not removed, which all leads to the decrease of the performance of the single photon source.

[0083] The above processing process makes the microcolumn have good verticality; the hard mask layer (SiO2) on the top of the microcolumn cavity is easy to remove; the sidewall of the microcolumn has good smoothness; and the single photon source has good performance.

[0084] Embodiment 3

[0085] According to the embodiments of the present application, an In(Ga)As quantum dot single photon source microcolumn cavity preparation method is also provided, as shown in Figure 10 The method comprises the following steps:

[0086] Step S1001, pretreatment.

[0087] The epitaxially grown sample is sequentially cleaned with acetone, isopropanol and alcohol for 5 minutes, and then dried with a nitrogen gun.

[0088] Step S1002, forming a first mask layer.

[0089] A plasma chemical vapor deposition system (PD-220NL) was used to deposit a first mask layer of SiO2on the cleaned and dried sample at a thickness of about 350 nm.

[0090] The specific steps of forming the first mask layer can be:

[0091] 1) The temperature of the upper electrode and the lower electrode were set to 150 °C and 350 °C, respectively. The upper electrode is the gas inlet electrode plate for deposition reaction gas, and the lower electrode is the electrode for sample placement and the radio frequency electrode. After the temperature reached the set temperature, the prepared sample was placed on a SiC tray, and the SiC tray was transferred into the lower electrode plate of the growth reaction chamber.

[0092] 2) N2O was introduced into the reaction chamber at a flow rate of 460 sccm, the process pressure was controlled at 80 Pa, the radio frequency power was set to 0 W, and the time was 5 min.

[0093] 3) SiH4diluted by Ar (5% SiH4and 95% Ar) and N2O were introduced, with flow rates of 100 sccm and 460 sccm, respectively, the process pressure was set to 80 Pa, the radio frequency power was set to 50 W, and the growth time was 7 min.

[0094] Step S1003, forming a second mask layer.

[0095] The second mask layer was formed by performing spin coating, exposure, and development on the surface of the sample on which the first mask layer (SiO2) was grown.

[0096] In some examples, the specific steps of forming the second mask layer can be as follows:

[0097] The sample surface on which SiO2was grown was spin-coated with a negative UV photoresist AR-N4340, with spin-coating parameters of 4000 rpm (revolutions per minute) for 60 seconds (sec). Then, baking was performed on a hot plate at a temperature of about 100 °C for about 60 sec.

[0098] The sample after baking and cooling was exposed using a laser direct writing system, such as a model DWL66+ system. The exposure parameters were set as follows: focus point about -20%, laser intensity about 80%, laser energy about 80 mW, and filter about 15%.

[0099] The sample after exposure was post-baked at a temperature of about 100 °C for about 120 sec. Then, the baked sample was developed and fixed. Development was performed in ZX238 developer for about 40 sec, and then fixing was performed in deionized water (DI Water) for about 5 min.

[0100] Finally, the fixed sample is baked at approximately 80°C for about 5 minutes.

[0101] Step S1004: Etch the first mask layer.

[0102] The exposed sample was etched using an inductively coupled plasma etching machine (e.g., Plasma Pro 100 Cobra).

[0103] The sample to be etched is adhered to a single-crystal silicon wafer using thermally conductive silicone oil. Then, it is placed in the pre-vacuum chamber of the etching machine, and after the vacuum reaches the preset value, it is transferred to the etching chamber.

[0104] In some examples, the parameters for etching the first mask layer can be set as follows:

[0105] The sample stage temperature is set to approximately 10℃, the He gas purging pressure on the back of the sample is approximately 10 Torr, the etching gases are CHF3 and Ar, and their flow rates are set to approximately 20 sccm and 10 sccm, respectively; the process pressure is set to approximately 5 mTorr, the upper electrode (ICP) power is set to approximately 1000W, and the lower electrode (Bias) power is set to approximately 35W.

[0106] Step S1005: Remove the second mask layer.

[0107] The residual photoresist on the SiO2 etched sample is removed, that is, the second mask layer is completely removed.

[0108] For example, a plasma degumming machine can be used, with the O2 flow rate set to approximately 50 sccm, the RF power set to approximately 100 W, and the processing time to approximately 5 minutes.

[0109] Use organic solvents such as acetone or NMP to further remove residual photoresist. Soak the sample in a water bath at 80°C for about 10 minutes, sonicate for about 5 minutes, then soak in isopropanol for about 5 minutes, sonicate for about 2 minutes, and finally dry the sample with N2.

[0110] Step S1006: Etch the epitaxial layer.

[0111] The sample after the second mask layer was removed was etched using an inductively coupled plasma etching machine (e.g., Plasma Pro 100 Cobra).

[0112] For example, the sample to be etched is adhered to a monocrystalline silicon wafer using thermally conductive silicone oil, and the monocrystalline silicon area outside the sample is covered with polyimide high-temperature tape. It is then placed in the pre-vacuum chamber of the etching machine, and after the vacuum reaches the preset value, it is transferred to the etching chamber.

[0113] In some examples, the etching process and parameters for etching the epitaxial layer can be as follows:

[0114] The sample stage temperature is set to 20-40°C, the He gas blowing pressure on the back of the sample is about 10 Torr, the upper electrode (ICP) power is about 400 W, the lower electrode (Bias) power is about 50 W, the etching gas is a mixture of chlorine (Cl2), boron trichloride (BCl3) and argon (Ar), and the process pressure is about 2 mTorr.

[0115] The etching process adopts a three-step method. In the first step, the flow rates of the etching gases Cl2 / BCl3 / Ar are 8 sccm / 12 sccm / 6 sccm, and the process time is about 1 min. In the second step, the flow rates of Cl2 / BCl3 / Ar are 8 sccm / 4 sccm / 6 sccm, and the time is about 5 min. In the third step, the flow rates of Cl2 / BCl3 / Ar are 8 sccm / 10 sccm / 6 sccm, and the time is about 2 min.

[0116] Step S1007, removing the first mask layer.

[0117] The remaining first mask layer is removed using an inductively coupled plasma etching machine. In some examples, the specific process steps can be as follows:

[0118] The sample to be etched is adhered to a sapphire wafer with heat-conducting silicone oil for etching. The etching process parameters are set as follows: the sample stage temperature is set to about 60°C, the He gas blowing pressure on the back of the sample is about 10 Torr, and the etching gas is CHF3 and O2, which is performed in two steps.

[0119] Step 1), the process pressure is set to about 20 mTorr, the flow rates of CHF3 and O2 are 20 sccm and 80 sccm respectively, the upper electrode (ICP) power is set to 1000 W, and the lower electrode (Bias) power is set to 35 W.

[0120] Step 2), the process pressure is set to remain consistent with step 1), the flow rate of CHF3 is set to about 0 sccm, the flow rate of O2 is set to about 10 sccm, the upper electrode (ICP) power is set to about 1000 W, and the lower electrode (Bias) power is set to about 35 W.

[0121] Step S1008, cleaning the sample.

[0122] The sample is placed in a water bath at 30°C, and is sequentially cleaned with acetone, isopropyl alcohol and ultrapure water through ultrasonic cleaning to ensure the cleanliness of the microcolumn sample.

[0123] Figure 11The micro-column cavity is prepared by the processing technology of the embodiment. Figure 11 It can be seen that the micro-column cavity is almost vertical, and the side wall can clearly see the upper / lower Bragg reflection layer structure (DBR) and the middle quantum dot GaAs cavity part.

[0124] It should be noted that for the foregoing method embodiments, in order to simply describe, they are all expressed as a series of action combinations, but those skilled in the art should know that the present application is not limited by the action sequence described, because according to the present application, certain steps can be performed in other sequences or simultaneously. Secondly, those skilled in the art should know that the embodiments described in the specification are all preferred embodiments, and the actions and modules involved are not necessarily necessary for the present application.

[0125] From the above description of the embodiments, those skilled in the art can clearly understand that the method according to the above embodiments can be realized by means of software and the necessary general hardware platform, of course, it can also be realized by hardware, but in many cases the former is a better embodiment. Based on such understanding, the technical solutions of the present application can be embodied in the form of a software product, which is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk) and includes a plurality of instructions for causing a terminal device (which can be a mobile phone, computer, server, or network device, etc.) to execute the method described in each embodiment of the present application.

[0126] Embodiment 4

[0127] According to the embodiments of the present application, a preparation method of a micro-column enhanced quantum dot single photon source is also provided, which includes a plurality of micro-column cavities prepared by the method of embodiments 1 to 3, wherein the micro-column cavities are arranged periodically.

[0128] Alternatively, specific examples in the present embodiment can refer to examples described in embodiments 1 to 3 described above, which will not be repeated here.

[0129] Embodiment 5

[0130] According to the embodiments of the present application, a quantum dot single photon source sample relying on optical pumping is also provided, which includes a micro-column cavity prepared by the method of embodiments 1 to 3.

[0131] Alternatively, specific examples in the present embodiment can refer to examples described in embodiments 1 to 3 described above, which will not be repeated here.

[0132] The integrated units in the above embodiments, if implemented in the form of software function units and sold or used as independent products, can be stored in the above computer-readable storage medium. Based on such understanding, the technical solutions of the present application essentially or the part that contributes to the prior art or the whole or part of the technical solutions can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes a number of instructions to make one or more computer devices (which can be personal computers, servers or network devices, etc.) execute all or part of the steps of the methods described in the various embodiments of the present application.

[0133] In the above embodiments of the present application, the description of each embodiment has its own focus, and the parts not described in detail in a certain embodiment can be referred to the relevant description of other embodiments.

[0134] In the several embodiments provided by the present application, it should be understood that the disclosed client can be implemented in other ways. Of course, the above device embodiment is only illustrative, and the division of the units is only a logical function division, and there can be another division manner in actual implementation, for example, a plurality of units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the coupling or direct coupling or communication connection between the units or modules shown or discussed can be indirect coupling or communication connection through some interface, unit or module, and can be electrical or other forms.

[0135] The units described as separate components can or can not be physically separate, and the components shown as units can or can not be physical units, i.e., they can be located in one place or distributed on multiple network units. Part or all of the units can be selected to achieve the purpose of the embodiment according to actual needs.

[0136] In addition, each functional unit in each embodiment of the present application can be integrated in one processing unit, or each unit can exist physically, or two or more units can be integrated in one unit. The integrated unit can be realized in the form of hardware or in the form of a software function unit.

[0137] The above is only the preferred embodiment of the present application, and it should be pointed out that for those skilled in the art, without departing from the principle of the present application, a number of improvements and refinements can be made, which should be considered as the protection scope of the present application.

Claims

1. A method for fabricating a quantum dot single photon source micro-pillar cavity, characterized in that, The method comprises: generating a first mask layer on an epitaxial layer of a sample to be etched, and generating a second mask layer in an inverted mesa type on the first mask layer; using the second mask layer as a mask to etch the first mask layer, so that the first mask layer is formed into a cylindrical structure; using the first mask layer in a cylindrical structure as a mask to etch the epitaxial layer of the sample to form a microcolumn, wherein different etching parameters are used to etch the epitaxial layer at different depths of the epitaxial layer; wherein, after etching the epitaxial layer of the sample, the method further comprises: setting the temperature of a sample stage to be higher than a preset temperature; and removing the first mask layer remaining on the microcolumn and removing by-products deposited on the sidewall of the microcolumn at the preset temperature; removing the first mask layer remaining on the microcolumn comprises: setting the following mask removal parameters: the temperature of the sample stage is set to be between 60 and 80 DEG C, the pressure of helium blowing on the back of the sample is set to be between 5 and 15 Torr, the process pressure is set to be between 15 and 25 mTorr, the flow ratio of trifluoromethane to oxygen is set to be between 1:5 and 1:3, the upper electrode power is set to be between 800 and 1000 W, and the lower electrode power is set to 0 W; and removing the first mask layer remaining on the microcolumn based on the set mask removal parameters; removing the by-products deposited on the sidewall of the microcolumn comprises: setting the following by-product removal parameters: the temperature of the sample stage is set to be between 60 and 80 DEG C, the pressure of helium blowing on the back of the sample is set to be between 5 and 15 Torr, the process pressure is set to be between 15 and 25 mTorr, the flow of trifluoromethane is set to 0 sccm, the flow of oxygen is set to be the sum of the flow of trifluoromethane and oxygen when removing the first mask layer remaining on the microcolumn, the upper electrode power is set to be between 800 and 1000 W, and the lower electrode power is set to 0 W; and removing the by-products deposited on the sidewall of the microcolumn based on the set by-product removal parameters.

2. The method of claim 1, wherein, etching the epitaxial layer of the sample comprises: in a first stage, etching the top part of the cylinder of the epitaxial layer with a preset flow of chlorine, boron trichloride and argon, wherein the flow of chlorine is less than the flow of boron trichloride; in a second stage, increasing the flow of chlorine or reducing the flow of boron trichloride to change the flow ratio of the chlorine, boron trichloride and argon for etching the middle part of the cylinder of the epitaxial layer; in a third stage, restoring the flow of chlorine to the flow of chlorine in the first stage, changing the flow of boron trichloride to be lower than the flow of boron trichloride in the first stage and higher than the flow of boron trichloride in the second stage, and etching the bottom part of the cylinder of the epitaxial layer with the chlorine, boron trichloride and argon with the changed flow ratio.

3. The method of claim 2, wherein In the first stage, the top 1-2 minutes of the cylindrical part of the epitaxial layer is etched with a preset flow rate of 6-8 sccm of chlorine, 10-12 sccm of boron trichloride, and 6-15 sccm of argon, wherein the flow rate of the chlorine is less than that of the boron trichloride; In the second stage, the flow rate of the chlorine is increased to 1.5-2 times that in the first stage, or the flow rate of the boron trichloride is reduced to 1 / 3-1 / 2 times that in the first stage, and the middle 3-5 minutes of the cylindrical part of the epitaxial layer is etched with the chlorine, the boron trichloride, and the argon at the changed flow rate ratio; In the third stage, the flow rate of the chlorine is restored to that in the first stage, and the flow rate of the boron trichloride is reduced to 5 / 6-1 times that in the first stage, and the bottom 2-3 minutes of the cylindrical part of the epitaxial layer is etched with the chlorine, the boron trichloride, and the argon at the changed flow rate ratio.

4. The method according to claim 2 or 3, characterized in that, Before etching the epitaxial layer of the sample, the method further comprises setting the etching parameters, wherein setting the etching parameters comprises setting the sample stage temperature to be between 20-40°C, setting the pressure of the helium purge on the back of the sample to be between 5-15 Torr, setting the etching gas to be the chlorine, the boron trichloride, and the argon, setting the process pressure to be between 1-5 mTorr, setting the upper electrode power to be between 300-500 W, and setting the lower electrode power to be between 30-60 W.

5. The method according to claim 2 or 3, characterized in that, Before etching the epitaxial layer of the sample, the method further comprises adhering the sample to a single crystal silicon wafer using a heat-conducting material, and covering the single crystal silicon area on the single crystal silicon wafer other than the sample with a cover.

6. The method of claim 1, wherein, Generating a second mask layer in the shape of an inverted table on the first mask layer comprises: spinning a negative photoresist capable of being exposed and developed on the surface of the first mask layer; laser direct writing exposure, development, and fixation of the negative photoresist, so that the topography of the exposed negative photoresist is in the shape of an inverted table cylinder, to form the second mask layer in the shape of an inverted table; wherein the inverted table is in the shape of a truncated cone, and the surface area of the truncated cone away from the top surface of the first mask layer is greater than that close to the bottom surface of the first mask layer.

7. The method of claim 6, wherein, The angle between the side wall of the truncated cone and the plane on which the first mask layer is located is about 80-85°.

8. The method of claim 1, wherein, After etching the first mask layer of the sample, the residual second mask layer is completely removed.

9. The method of claim 1, wherein, Etching the first mask layer using the second mask layer as a mask comprises: setting the following mask etching parameters: the sample stage temperature is set to be between 0-10°C, the pressure of the helium purge on the back of the sample is set to be between 5-15 Torr, the etching gas is set to be argon and trifluoromethane, the flow rate ratio of argon and trifluoromethane is set to be between 1:5 and 1:1, the process pressure is set to be between 5-10 mTorr, the upper electrode power is set to be between 800-1000 W, and the lower electrode power is set to be between 30-50 W; Etching the first mask layer with the second mask layer as a mask based on the set mask etching parameters.

10. The method of claim 1, wherein, After etching the epitaxial layer of the sample piece, the method further comprises: The sample piece is sequentially subjected to ultrasonic cleaning in an acetone, isopropanol and ultrapure water in a water bath container at a preset temperature.

11. A method for preparing a microcolumn-enhanced quantum dot single-photon source, characterized in that, The method comprises preparing a micro-column cavity by using the method of any one of claims 1 to 10.

12. A quantum dot single photon source sample relying on optical pumping, characterized in that, The method comprises a plurality of micro-column cavities prepared by using the method of any one of claims 1 to 10, wherein the micro-column cavities are arranged periodically.

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