A plasma-based surface polishing method for non-oxide semiconductor wafers

Abstract

The invention relates to the technical fields of surface processing and atomic-level manufacturing, and discloses a surface polishing method for a non-oxide semiconductor wafer based on plasma. The method comprises the following steps: placing a non-oxide semiconductor wafer to be polished under an atmospheric plasma matrix tube, and continuously introducing a carrier gas into the atmospheric plasma matrix tube; starting plasma, and introducing a reaction gas into the atmospheric plasma matrix tube, performing plasma oxidation treatment on the non-oxide semiconductor wafer, and forming an oxide film on the surface of the non-oxide semiconductor wafer; after the thickness of the oxide film reaches a predetermined thickness, stopping introducing the reaction gas, adjusting the power of the plasma to 500-700 W, and performing plasma control treatment on the non-oxide semiconductor wafer; after controlling for 3-10 min, uniformly reducing the power of the plasma to a predetermined power at a first rate, immersing the non-oxide semiconductor wafer after the control treatment in an etching solution to remove the oxide film, and completing the surface polishing of the non-oxide semiconductor wafer.

Description

Technical Field

[0001] The invention relates to the technical field of surface processing and atomic-level manufacturing, and in particular to a plasma-based surface polishing method for a non-oxide semiconductor wafer. Background Art

[0002] With the development of the digital economy, many fields such as artificial intelligence, big data, and the Internet of Things are inseparable from the semiconductor industry represented by integrated circuits. Non-oxide semiconductor wafers are the basis for manufacturing integrated circuits. As Moore's Law approaches its limit, the surface quality requirements for non-oxide semiconductor wafers are becoming more and more stringent. At this stage, the most advanced chip manufacturing process has developed below 3 nm, which requires the surface of the semiconductor wafer to be atomically smooth, that is, under ideal conditions, all atoms on the surface of the non-oxide semiconductor wafer are on the same layer of the crystal plane, which is also considered to be the limit state of material surface roughness.

[0003] At present, the most widely used atomic-level polishing process is chemical mechanical polishing, which first softens the surface of the material and then removes the material by plastic deformation caused by the extrusion of abrasive particles. It has been widely used in the polishing of semiconductor wafers. In addition, researchers have proposed a variety of methods for polishing at the atomic scale in recent years. Yamamura et al. proposed plasma-assisted polishing, whose material removal mechanism is to modify the material surface by plasma and remove the modified layer by soft abrasive particles. At present, atomic-level smooth surfaces have been obtained on difficult-to-process semiconductor materials such as SiC and GaN. Hara et al. proposed catalyst-assisted etching polishing, which achieves preferential removal of rough peaks on the surface of the material through the action of metal catalysts, and obtains atomic-level smooth surfaces with a surface roughness of about 0.1 nm on various semiconductor materials such as Si, GaN, SiC, and ZnO. Deng et al. proposed a plasma atomic selective etching technology, which selectively etches atoms with different numbers of dangling bonds on the surface of the material through the etching gas (CF4) excited by plasma, thereby obtaining an atomic-level smooth surface with an extremely high material removal rate. It has been successfully applied to semiconductor materials such as Si, GaN, and SiC.

[0004] Although the above methods can obtain atomically smooth surfaces on semiconductor wafers, they all have certain disadvantages. Chemical mechanical polishing requires the use of a large amount of polishing liquid during the processing process. In order to improve the polishing efficiency, acidic or alkaline liquids are usually added to the polishing liquid to adjust the acidity and alkalinity. The abrasive particles in the polishing liquid are at the nanoscale and difficult to recycle, resulting in high pollution to the environment. Plasma-assisted polishing usually requires the processing equipment to be placed in a vacuum chamber in order to constrain the reaction gas to ensure the stability and uniformity of the plasma during high-speed rotation. This makes the processing equipment complex and has great restrictions on the wafer size. Catalyst-assisted etching polishing can be performed in an atmospheric environment, but its material removal rate is only tens of nanometers per hour, and efficient polishing cannot be achieved. Plasma atom selective etching polishing has an extremely high material removal rate (tens of microns per minute), but because it preferentially removes atoms with more dangling bonds, the material removal rate at the edge is greater, so the flatness of the processed wafer is poor.

[0005] Therefore, the prior art still needs to be improved and developed. Summary of the invention

[0006] In view of the above-mentioned deficiencies in the prior art, the present invention provides a plasma-based surface polishing method for non-oxide semiconductor wafers to solve the problems of environmental pollution, large size limitations and low polishing efficiency in the existing atomic-level surface polishing methods for non-oxide semiconductor wafers.

[0007] The technical solution adopted by the present invention to solve the above technical problems is as follows:

[0008] A first aspect of the present invention provides a plasma-based surface polishing method for a non-oxide semiconductor wafer, the method comprising the following steps:

[0009] Placing the non-oxide semiconductor wafer to be polished under an atmospheric plasma torch, and continuously introducing a carrier gas into the atmospheric plasma torch;

[0010] Starting the plasma and introducing the reaction gas into the atmospheric plasma torch to perform plasma oxidation treatment on the non-oxide semiconductor wafer to form an oxide film on the surface of the non-oxide semiconductor wafer;

[0011] After the thickness of the oxide film reaches a predetermined thickness, the reaction gas is stopped from being introduced, and the power of the plasma is adjusted to 500-700 W to perform plasma control treatment on the non-oxide semiconductor wafer;

[0012] After regulating for 3-10 minutes, the power of the plasma is uniformly reduced to a predetermined power at a first rate, and the non-oxide semiconductor wafer after the regulation is immersed in an etching solution to remove the oxide film, thereby completing the surface polishing of the non-oxide semiconductor wafer.

[0013] Preferably, in the step of performing plasma oxidation treatment on the non-oxide semiconductor wafer, the specific parameters are: the plasma oxidation power is 400-700 W, and the oxidation time is 1-5 min.

[0014] Preferably, the predetermined thickness is greater than or equal to 100 nm.

[0015] Preferably, the predetermined power is 400 W.

[0016] Preferably, the first rate is 1-30 W / min.

[0017] Preferably, the reaction gas provides oxidation capability for the plasma.

[0018] Preferably, the reaction gas is a gas containing oxygen atoms or a gas containing hydroxyl groups.

[0019] Preferably, the non-oxide semiconductor wafer to be polished is placed in front of the atmospheric plasma torch, and the non-oxide semiconductor wafer is sequentially cleaned and dried.

[0020] Beneficial effects:

[0021] The present invention discloses a surface polishing method for non-oxide semiconductor wafers based on plasma. The processing equipment used in the surface polishing method provided by the present invention is simple and does not require the use of etching gas. Only by using different modes of plasma to first prepare an oxide film on the surface of the wafer, then regulating and controlling, and then removing the oxide film, finally obtaining an atomic-level smooth surface of the wafer. The method provided by the present invention is environmentally friendly, has high polishing efficiency and does not damage the flatness of the wafer, does not require the use of a vacuum chamber, and has the ability to process large-sized wafers. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A flow chart of a plasma-based non-oxide semiconductor wafer surface polishing method provided for a preferred embodiment of the present invention;

[0023] Figure 2 A schematic diagram of a large-size wafer processing path in an embodiment of the present invention;

[0024] Figure 3 A schematic diagram of a polishing method according to an embodiment of the present invention;

[0025] Figure 4 This is a comparison diagram of the surface morphology and roughness of the wafer before and after polishing in Example 1 of the present invention;

[0026] Figure 5 This is a graph showing the relationship between wafer surface temperature and plasma power during plasma processing in Examples 1-7 of the present invention;

[0027] Figure 6 This is a graph showing the relationship between wafer surface roughness and plasma power during plasma processing in Examples 1-7 of the present invention;

[0028] Figure 7 This is a graph showing the relationship between wafer surface roughness and plasma power reduction rate during plasma processing in Examples 1, 8-10 of the present invention. DETAILED DESCRIPTION

[0029] The present invention provides a plasma-based surface polishing method for non-oxide semiconductor wafers. In order to make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0030] An embodiment of the present invention provides a plasma-based surface polishing method for a non-oxide semiconductor wafer, the method comprising the following steps:

[0031] Placing the non-oxide semiconductor wafer to be polished under an atmospheric plasma torch, and continuously introducing a carrier gas into the atmospheric plasma torch;

[0032] Starting the plasma and introducing the reaction gas into the atmospheric plasma torch to perform plasma oxidation treatment on the non-oxide semiconductor wafer to form an oxide film on the surface of the non-oxide semiconductor wafer;

[0033] After the thickness of the oxide film reaches a predetermined thickness, the reaction gas is stopped from being introduced, and the power of the plasma is adjusted to 500-700 W to perform plasma control treatment on the non-oxide semiconductor wafer;

[0034] After regulating for 3-10 minutes, the power of the plasma is uniformly reduced to a predetermined power at a first rate, and the non-oxide semiconductor wafer after the regulation is immersed in an etching solution to remove the oxide film, thereby completing the surface polishing of the non-oxide semiconductor wafer.

[0035] The polishing method provided by the embodiment of the present invention is as follows Figure 1As shown. Non-oxide semiconductor wafers often have more dangling bonds due to the presence of rough peaks and surface damage on the surface. In the atmospheric environment, a natural oxide film several nanometers thick will be formed. This process can occur at room temperature. In order to avoid the influence of the natural oxide film and protect the surface of the wafer material at the same time, the embodiment of the present invention first introduces the reaction gas into the plasma, and uses the oxidation ability of the plasma to prepare an oxide film with a thickness much greater than the natural oxide film on the surface of the semiconductor wafer, so as to isolate the oxygen in the atmospheric environment and avoid the wafer surface from reacting with the oxygen in the atmosphere due to its own high temperature after the regulation is completed, resulting in oxidation of the polished surface. This oxidation process will also construct an unsaturated oxide layer between the wafer and the oxide film. When the oxide film thickness is sufficient to isolate the atmosphere, the reaction gas is turned off, and the plasma regulation mode is switched to achieve regulation of the surface atoms of the wafer through the energy input of the plasma. Under the action of the plasma, the surface atoms of the wafer tend to the energy minimization state (1. The unsaturated oxide layer is transformed into a saturated oxide layer, 2. The surface of the wafer below the oxide layer is smooth at the atomic level). Since the maximum temperature of the wafer material surface can reach above 900°C during plasma processing, the embodiment of the present invention chooses to reduce the plasma power at a uniform speed to slowly reduce the surface temperature of the wafer material, so as to avoid the rapid cooling of the wafer material after the plasma is turned off, causing ripples on its surface and affecting the wafer flatness. Finally, the oxide film on the surface of the material is completely removed using an etching solution to obtain an atomically smooth surface.

[0036] Common non-oxide semiconductor wafers include silicon, silicon carbide, silicon nitride, aluminum nitride, etc.

[0037] In some embodiments, in the step of performing plasma oxidation treatment on the non-oxide semiconductor wafer, specific parameters are: the oxidation power of the plasma is 400-700 W, and the oxidation time is 1-5 min.

[0038] Within this power range, the plasma can meet the temperature required for oxidation without being too high to damage the wafer.

[0039] In some embodiments, the predetermined thickness is greater than or equal to 100 nm.

[0040] In some preferred embodiments, the predetermined thickness is 100-200 nm. For example, when the predetermined thickness is 150 nm, that is, when the thickness of the oxide film gradually increases to 150 nm, the introduction of the reaction gas is stopped.

[0041] The preparation of the oxide film is a necessary step in the embodiment of the present invention. Without this step, the wafer will still be in a high temperature state after polishing and will react with oxygen in the atmosphere, causing the wafer surface to be oxidized. At this time, even if the etching solution is used to remove the oxide film, an atomically smooth surface cannot be obtained. The preparation of the oxide film during the polishing process has a protective effect on the polished surface. In order to ensure that the polished wafer surface does not react with oxygen in the atmosphere at high temperature, the thickness of the prepared oxide film should be greater than 100 nm to isolate oxygen.

[0042] In some preferred embodiments, the power of the plasma is adjusted to 550-650W.

[0043] In some embodiments, the predetermined power is 400W.

[0044] In some embodiments, the first rate is 1-30 W / min.

[0045] During the plasma regulation process, the wafer surface temperature can reach up to 900 ° C. If the plasma is turned off directly after the regulation is completed, the temperature difference between the wafer surface temperature and room temperature will reach more than 800 ° C. In this case, the wafer surface will be deformed due to rapid cooling, resulting in a decrease in flatness. In order to avoid this adverse effect, the embodiment of the present invention proposes to regulate the wafer surface temperature by uniformly reducing the plasma power, thereby achieving a slow decrease in the overall temperature of the wafer. When the temperature difference between the wafer surface temperature and room temperature is reduced to below 600 ° C, the flatness of the wafer surface will not be affected. Since an excessively fast power reduction rate will cause the overall temperature of the wafer to be unable to be fully reduced, it is necessary to control the rate of power reduction.

[0046] In some preferred embodiments, the first rate is 5-10 W / min.

[0047] In some embodiments, the carrier gas is an inert gas.

[0048] The carrier gas is the main excitation gas for plasma and needs to be continuously introduced during the processing. Its composition can be inert gases such as argon and helium.

[0049] In some embodiments, the reactant gas provides oxidizing power to the plasma.

[0050] In some embodiments, the reaction gas is a gas containing oxygen atoms or a gas containing hydroxyl groups.

[0051] The reaction gas provides the plasma with oxidation ability. Since both oxygen free radicals and hydroxyl free radicals have oxidation ability, the plasma can be made to have oxidation ability in the following two ways: 1. Directly introduce gases containing oxygen atoms such as O2, CO2, and NO2 into the plasma to excite oxygen free radicals; 2. Allow a portion of the carrier gas to pass through a gas washing bottle filled with pure water or hydrogen peroxide solution to carry a certain amount of water vapor or hydrogen peroxide molecules, and generate hydroxyl free radicals after plasma excitation. It should be noted that the reaction gas can be selectively turned off according to the different modes of the plasma, that is, the reaction gas is introduced in the oxidation treatment mode and turned off in the regulation treatment mode.

[0052] In some embodiments, before placing the non-oxide semiconductor wafer to be polished under the atmospheric plasma torch, the non-oxide semiconductor wafer is sequentially cleaned and dried.

[0053] In some embodiments, a plasma-based surface polishing method for a non-oxide semiconductor wafer is provided, the method comprising the following steps:

[0054] Cleaning the surface of the non-oxide semiconductor wafer to be polished with anhydrous ethanol and pure water in sequence, and then drying the surface of the non-oxide semiconductor wafer with nitrogen;

[0055] Place the non-oxide semiconductor wafer on the workbench under the atmospheric plasma torch. For small-sized wafers that can be covered by the plasma, place them in the center of the plasma. For large-sized wafers that cannot be completely covered by the plasma, select the appropriate scanning path length and width according to the plasma flame size, and place the wafer to be processed at the starting position of the path. Figure 2 ;

[0056] Introduce carrier gas into the plasma tube, start the plasma, and introduce reaction gas after the plasma is stable;

[0057] The plasma power is set to the oxidation power W1 (400 W≤W1≤700 W), the oxidation treatment time is t1 (1min≤t1≤5 min), and the oxide film thickness reaches 100 nm to meet the further polishing requirements;

[0058] After the oxidation treatment is completed, the reaction gas is turned off, and the plasma power is set to the control power W2 (500 W≤W2≤700 W) and the control time is t2 (3 min≤t2≤10 min);

[0059] After the regulation is completed, the plasma power is reduced at a fixed rate v (1 W / min≤v≤30 W / min) until the power is reduced to 400 W;

[0060] When the plasma power drops to 400 W, the plasma is turned off and the temperature of the non-oxide semiconductor wafer is allowed to drop to room temperature.

[0061] Immerse the non-oxide semiconductor wafer after the above steps in the etching solution, set the appropriate etching temperature and time according to the thickness of the oxide film, the etching time t3 (5 min≤t2≤20 min), the etching temperature T (50 ℃≤T≤100 ℃), until the oxide film is completely removed;

[0062] The etched non-oxide semiconductor wafer is cleaned with anhydrous ethanol and pure water, and the surface of the non-oxide semiconductor wafer is dried with nitrogen to complete polishing.

[0063] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments, and are only for illustrating the present invention but not limiting the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention.

[0064] Example 1

[0065] A plasma-based surface polishing method for non-oxide semiconductor wafers, such as Figure 3 As shown, the process includes the following steps: polishing a small-sized silicon wafer that can be completely covered by plasma, placing the silicon wafer to be polished under an atmospheric plasma torch, and continuously introducing argon gas into the plasma torch, starting the plasma, and introducing oxygen into the plasma torch, wherein the oxidation power of the plasma is W1 = 500 W, and the oxidation time is t1 = 2 min. After the oxidation is completed, the introduction of oxygen is stopped, and the power of the plasma is adjusted to the control power W2 = 620 W, and the control time is t2 = 5 min. After the control treatment is completed, the power of the plasma is reduced to 400 W at a rate of v = 10 W / min, and the silicon wafer after the control treatment is removed from the surface oxide film using a BOE buffered oxide etchant (the BOE buffered oxide etchant is composed of HF and NH4F, and NH4F is used as a buffer component to maintain the stability of the etching rate), and the etching temperature is 70 ° C, and the etching time is 10 min. The etched silicon wafer is cleaned with anhydrous ethanol and pure water, and dried with nitrogen. Finally, the surface roughness was detected by atomic force microscopy (AFM). The surface morphology and roughness of the wafer before and after polishing were as follows: Figure 4As shown in the figure, there are a lot of rough peaks on the initial wafer surface before polishing, and the surface roughness Sa = 0.36 nm. After polishing, the rough peaks on the wafer surface are completely removed, and the surface roughness Sa = 0.08 nm, reaching atomic-level smoothness.

[0066] Example 2

[0067] A plasma-based surface polishing method for a non-oxide semiconductor wafer. The method in this embodiment is substantially the same as that in Embodiment 1, except that the regulated power of the plasma is W2 = 400 W.

[0068] Example 3

[0069] A plasma-based surface polishing method for non-oxide semiconductor wafers. The method in this embodiment is basically the same as that in Embodiment 1, except that the regulated power of the plasma is W2 = 450 W.

[0070] Example 4

[0071] A surface polishing method for a non-oxide semiconductor wafer based on plasma. The method in this embodiment is substantially the same as that in embodiment 1, except that the regulated power of the plasma is W2 = 500 W.

[0072] Example 5

[0073] A surface polishing method for a non-oxide semiconductor wafer based on plasma. The method of this embodiment is basically the same as that of Embodiment 1, except that the regulated power of the plasma is W2 = 550 W.

[0074] Example 6

[0075] A surface polishing method for a non-oxide semiconductor wafer based on plasma. The method in this embodiment is substantially the same as that in embodiment 1, except that the regulated power of the plasma is W2 = 600 W.

[0076] Example 7

[0077] A surface polishing method for a non-oxide semiconductor wafer based on plasma. The method of this embodiment is basically the same as that of Embodiment 1, except that the regulated power of the plasma is W2 = 650 W.

[0078] Example 8

[0079] A plasma-based surface polishing method for non-oxide semiconductor wafers. The method in this embodiment is basically the same as that in Embodiment 1, except that the regulated power of the plasma is W2 = 700 W.

[0080] Since the regulation of the surface of the semiconductor wafer by plasma mainly depends on the input of energy, temperature is a key factor affecting the polishing effect. The temperature of the wafer surface during the plasma processing of Examples 2-8 was measured using an infrared thermal imager. The temperature changes with plasma power are shown in Figure 2. Figure 5 As shown in the figure, it can be seen that the wafer surface temperature increases approximately linearly with the increase of plasma power, and the wafer surface temperature can be regulated by changing the plasma power. When the wafer surface temperature is less than 750 °C, the wafer surface morphology hardly changes, and it can be considered that the plasma has no regulating effect on the wafer surface at this time; when the temperature is greater than 1000 °C, the edge of the wafer will reach the melting point first and melt, resulting in wafer damage. Therefore, according to the corresponding relationship between plasma power and temperature in the figure, it can be concluded that the plasma power range applicable to the polishing method proposed in the present invention is 500-700 W.

[0081] Figure 6 The corresponding relationship between the wafer surface roughness and the plasma power during the plasma processing of Example 1-8, the original surface roughness of the wafer used is Sa = 0.36 nm, and it can be seen from the figure that when the power is between 560-640 W, the surface roughness of the wafer is reduced compared with the original surface, and when the power is greater than 660 W, the surface roughness increases. Therefore, in order to obtain good surface roughness, the preferred plasma power range should be 550-650 W.

[0082] Example 9

[0083] A plasma-based surface polishing method for non-oxide semiconductor wafers. The method of this embodiment is basically the same as that of Example 1, except that after the control treatment is completed, the power of the plasma is reduced to 400 W at a rate of v = 1 W / min.

[0084] Example 10

[0085] A plasma-based surface polishing method for non-oxide semiconductor wafers. The method of this embodiment is basically the same as that of Example 1, except that after the control treatment is completed, the power of the plasma is reduced to 400 W at a rate of v = 5 W / min.

[0086] Embodiment 11

[0087] A plasma-based surface polishing method for non-oxide semiconductor wafers. The method of this embodiment is basically the same as that of Example 1, except that after the control treatment is completed, the power of the plasma is reduced to 400 W at a rate of v = 30 W / min.

[0088] Figure 7The relationship between the wafer surface roughness and the plasma power reduction rate during the plasma processing of Examples 1, 9-11 is shown in the figure. It can be seen from the figure that when the power reduction rate is less than 30 W / min, the surface roughness of the crystal surface is low, and when the power reduction rate reaches 30 W / min, the surface roughness will increase due to the deterioration of the surface flatness. Therefore, in order to ensure the acquisition of an atomically smooth surface, the appropriate plasma power reduction rate range is 1-30 W / min.

[0089] It should be understood that the application of the present invention is not limited to the above examples. For ordinary technicians in this field, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A plasma-based surface polishing method for a non-oxide semiconductor wafer, characterized in that: The method comprises the following steps: Placing the non-oxide semiconductor wafer to be polished under an atmospheric plasma torch, and continuously introducing a carrier gas into the atmospheric plasma torch; Starting the plasma and introducing the reaction gas into the atmospheric plasma torch to perform plasma oxidation treatment on the non-oxide semiconductor wafer to form an oxide film on the surface of the non-oxide semiconductor wafer; After the thickness of the oxide film reaches a predetermined thickness, the reaction gas is stopped from being introduced, and the power of the plasma is adjusted to 500-700W to perform plasma control treatment on the non-oxide semiconductor wafer; After regulating for 3-10 minutes, the power of the plasma is uniformly reduced to a predetermined power at a first rate, and then the non-oxide semiconductor wafer after the regulation is immersed in an etching solution to remove the oxide film, thereby completing the surface polishing of the non-oxide semiconductor wafer; The predetermined thickness is greater than or equal to 100 nm; The first rate is 1-30 W / min.

2. The plasma-based surface polishing method for non-oxide semiconductor wafers according to claim 1, characterized in that: In the step of plasma oxidation treatment of the non-oxide semiconductor wafer, the specific parameters are: the plasma oxidation power is 400-700 W, and the oxidation time is 1-5 min.

3. The plasma-based surface polishing method for non-oxide semiconductor wafers according to claim 1, characterized in that: The predetermined power is 400W.

4. The plasma-based surface polishing method for non-oxide semiconductor wafers according to claim 1, characterized in that: The reactive gas provides oxidizing power to the plasma.

5. The plasma-based surface polishing method for non-oxide semiconductor wafers according to claim 4, characterized in that: The reaction gas is a gas containing oxygen atoms or a gas containing hydroxyl groups.

6. The plasma-based surface polishing method for non-oxide semiconductor wafers according to claim 1, characterized in that: The non-oxide semiconductor wafer to be polished is placed in front of the atmospheric plasma torch, and the non-oxide semiconductor wafer is cleaned and dried in sequence.

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