Method for rapidly determining ion implantation dose

Abstract

The invention discloses a method for rapidly determining an ion implantation dose. The method comprises the following steps: firstly, carrying out ion implantation on a piezoelectric wafer; the injected wafer is heated to a set temperature and then is subjected to heat preservation; observing whether the surface roughness of the wafer changes and the occurrence time of the wafer in the heat preservation process, and accordingly judging whether the ion implantation dose is appropriate: if the heat preservation time is less than a hours, the change occurs, and the dose is too large; if the change occurs between a and b hours, the dosage is appropriate; if the dose is not changed within b hours, the dose is insufficient. According to the method, injected ions are promoted to gather to form bubbles through heat treatment, surface bubbling or stripping is caused, and therefore the corresponding relation between the heating time and the dosage is established, rapid and visual dosage judgment is achieved, the process debugging period is greatly shortened, and the development cost is reduced.

Description

Technical Field

[0001] This invention relates to the fields of semiconductor material processing and ion implantation technology, and specifically to a method for rapidly determining the ion implantation dose. Background Technology

[0002] Lithium niobate (LiNbO3) and lithium tantalate (LiTaO3) piezoelectric wafers combine electro-optical and acoustic physical properties, making them widely used in integrated optics, RF front-end filters, and other fields. Due to the anisotropy of crystals, wafers with different cut orientations have different application areas. For example, in the field of RF filters, there are mainly X-cut, 15°YX, 128°YX, and Z-cut lithium niobate piezoelectric wafers and 38°YX, 42°YX, 50°YX, and Z-cut lithium tantalate piezoelectric wafers. By using smart-cut technology to integrate substrate materials such as silicon, silicon carbide, diamond, and sapphire with lithium niobate or lithium tantalate piezoelectric wafers to prepare piezoelectric single-crystal composite thin film (POI) materials, the performance of devices such as operating frequency, bandwidth, loss, and temperature stability can be significantly improved.

[0003] In the Smart-Cut method for preparing piezoelectric single-crystal composite thin films, ion implantation is first performed on lithium niobate or lithium tantalate piezoelectric wafers to form a release layer (defect layer). Subsequently, heat treatment and bonding processes are used to achieve the release and transfer of the single-crystal thin film. The ion implantation dose is a critical process parameter that directly affects the crystal quality and structural integrity of the final piezoelectric single-crystal thin film. Insufficient implantation dose will prevent effective release; excessive implantation dose may lead to defects such as stress stripes on the surface of the released film wafer or excessive damage to the internal structure. With the continuous expansion of applications in optics, acoustics, and other fields, the demand for various cuts of lithium niobate and lithium tantalate piezoelectric wafers is increasing. Due to the anisotropic nature of their lattice structures, different wafers require matching ion implantation doses. Therefore, accurately determining the optimal ion implantation dose for various wafer types is crucial.

[0004] Currently, the implantation dose is mainly confirmed by observing the quality of the piezoelectric single crystal film after peeling through processes such as ion implantation, substrate preparation, CMP polishing, cleaning, bonding, and peeling. However, this method involves very complicated processes and requires a lot of manpower and resources. For example, the cleaning process alone involves multiple steps such as acid washing, brushing, RCA cleaning, QDR rinsing, ultrasonic cleaning, and spin drying. In order to reduce the impact of cleaning particles on bonding quality, some steps need to be repeated.

[0005] Clearly, existing methods for determining injection dosage suffer from problems such as long cycles, high costs, complex operations, and strong dependence on equipment. Summary of the Invention

[0006] In view of the above-mentioned shortcomings of the existing technology, the purpose of this invention is to provide a method for rapidly determining ion implantation dosage, thereby solving the problems of long cycle, high cost, complex operation and strong dependence on equipment in existing ion implantation dosage determination methods.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0008] A method for rapidly determining ion implantation dosage includes the following steps:

[0009] (1) Ion implantation treatment of piezoelectric wafers;

[0010] (2) Heat the implanted piezoelectric wafer to a set temperature, and then continue heating to maintain that temperature;

[0011] (3) During the continued heating process, observe whether the surface roughness of the piezoelectric wafer changes and the time of change, and determine whether the ion implantation dose is appropriate according to the following three scenarios:

[0012] If the surface changes before heating continues for less than a hours, the ion implantation dose is deemed too high.

[0013] If the surface changes after heating for a to b hours, the ion implantation dose is deemed appropriate.

[0014] If no change is observed on the surface after heating for b hours, the ion implantation dose is deemed insufficient; where a < b.

[0015] If the dose is appropriate, then determine that the dose is the applicable dose; if the dose is insufficient or excessive, adjust the ion implantation dose and repeat steps (1) to (3).

[0016] Furthermore, the set temperature is 195℃~205℃, and the heating time is 0.5~3 hours.

[0017] Furthermore, the ions used in the ion implantation are hydrogen ions, helium ions, or hydrogen-helium co-implanted ions.

[0018] Furthermore, the ion implantation energy is 50keV to 400keV, and the implantation dose is 1×10⁻⁶. 16 cm -2 ~1×10 17 cm -2 .

[0019] Furthermore, in step (2), the heating rate to the set temperature is 10℃ / min to 20℃ / min.

[0020] Furthermore, the piezoelectric wafer is a lithium niobate wafer or a lithium tantalate wafer.

[0021] Furthermore, when the piezoelectric wafer is a lithium niobate wafer, the implanted ions are helium ions, the implantation energy is 100keV to 300keV, and the implantation dose is 1×10⁻⁶. 16 cm -2 ~4×10 16 cm -2 When the piezoelectric wafer is a lithium tantalate wafer, the implanted ions are hydrogen ions, the implantation energy is 80keV~200keV, and the implantation dose is 5×10⁻⁶. 16 cm -2 ~1×10 17 cm -2 .

[0022] Furthermore, the surface roughness is determined by visual observation or by instrument detection.

[0023] Furthermore, the instrument includes a roughness tester or a microscope.

[0024] Furthermore, ion implantation was performed on multiple wafers using a dose gradient method, and the wafers were uniformly heated and observed to determine the optimal implantation dose.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. This invention provides a method for rapidly determining the ion implantation dose. This method involves heat-treating an ion-implanted piezoelectric wafer at a specific temperature. The phenomenon of ions in the implanted layer agglomerating to form microbubbles under heating conditions, causing an increase in internal pressure, induces blistering or localized delamination on the wafer surface, resulting in a significant change in surface roughness. By establishing a correlation between heating time and surface roughness change, the suitability of the ion implantation dose can be quickly and intuitively determined: a change occurring within 'a' hours indicates an excessive dose; a change occurring between 'a' and 'b' hours indicates a suitable dose; and no change occurring after 'b' hours indicates an insufficient dose. This method is simple to operate, provides intuitive results, and achieves rapid dose screening and optimization without relying on complex subsequent processes, significantly improving process debugging efficiency and reducing development costs.

[0027] 2. The method of this invention is applicable to lithium niobate or lithium tantalate wafers of any orientation and can be applied under different implantation conditions (such as energy, ion type, etc.). Furthermore, the equipment only requires an implanter and a common heating device, eliminating the need for multiple large and expensive pieces of equipment, thus significantly reducing manpower and material resources, and simplifying the operation process. Qualitative results of "insufficient dosage" and "insufficient dosage" can be clearly determined by visually observing the reflective state of the wafer surface, making it intuitive and easy to distinguish. In addition, the cycle from ion implantation to result determination can be shortened from more than 20 days to less than 2 days, greatly improving the efficiency of process feedback. Attached Figure Description

[0028] Figure 1 This is a flowchart of a method for rapidly determining ion implantation dosage according to the present invention;

[0029] Figure 2 This is a schematic diagram of the surface state of the piezoelectric wafer of the present invention;

[0030] Figure 3 This is a schematic cross-sectional view of the defect layer formed inside the piezoelectric wafer after ion implantation according to the present invention.

[0031] Figure 4 This is a schematic cross-sectional view illustrating the mechanism of the protrusions and pits on the surface of the piezoelectric wafer after heat treatment according to the present invention.

[0032] Figure 5 This is a schematic diagram of the surface macroscopic state of the piezoelectric wafer after ion implantation and heat treatment according to the present invention.

[0033] In the figure, 1-wafer, 11-wafer surface, 12-bump, 13-pit, 21-ion implantation, 22-defect layer, 23-bubble. Detailed Implementation

[0034] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0035] See Figure 1 This invention provides a method for rapidly determining ion implantation dosage, comprising the following steps:

[0036] S1. Ion implantation treatment is performed on the piezoelectric wafer;

[0037] In specific implementation, the material of the piezoelectric wafer 1 is an existing piezoelectric single crystal material, such as lithium niobate or lithium tantalate. Figure 2 As shown, the surface 11 of the piezoelectric wafer is smooth and exhibits a specular reflection. Optionally, the diameter of the piezoelectric wafer can be 4 inches, 6 inches, or 8 inches.

[0038] In practice, the surface roughness of the piezoelectric wafer is ≤0.5nm. This is because piezoelectric wafers are mainly used in the Smart-Cut process, and excessive roughness would prevent high-quality bonding.

[0039] like Figure 3 As shown, after ion implantation 21 on the piezoelectric wafer, an implantation defect layer 22 is formed at a specific depth within the piezoelectric wafer. However, its surface condition is the same as before implantation, and the surface roughness of the piezoelectric wafer does not change after implantation. Similarly, the surface of the piezoelectric wafer is smooth and exhibits a specular reflection phenomenon, which can be observed with the naked eye.

[0040] It should be noted that the implanted ions can damage the lattice structure of the implantation defect layer of the piezoelectric wafer. Specifically, during ion implantation, ions enter the interatomic spaces of the lattice and form nanoscale void-type defects within the implantation defect layer; despite this, the interface region still maintains high mechanical strength.

[0041] The height of the defect layer from the surface of the piezoelectric wafer is set according to the actual thin film structure to be prepared; typically, the height of the defect layer from the surface of the piezoelectric wafer is 50nm to 2000nm.

[0042] In specific implementation, the ion implantation is hydrogen ion implantation, helium ion implantation, or hydrogen-helium ion co-implantation.

[0043] In specific implementation, the ion implantation energy is 50 keV to 400 keV; the ion implantation dose is 1 × 10⁻⁶. 16 cm -2 ~1×10 17 cm -2 The energy of ion implantation directly affects the depth of the ion-implanted defect layer. During implantation, the ion implantation energy can be set according to the specific thickness of the desired piezoelectric single-crystal thin film. On the other hand, the ion implantation dose determines the defect density required for effective stripping. Since piezoelectric wafers of different materials differ in atomic arrangement and bond strength, the required ion implantation dose will also vary. Even for piezoelectric wafers of the same material, different crystal phases will result in different atomic arrangements, thus affecting the ion implantation dose. Close-packed atoms have stronger bonds and require a larger dose for implantation and stripping; while sparsely packed atoms have relatively weaker bonds and require a smaller dose for implantation and stripping. Therefore, the ion implantation dose must be precisely determined based on the characteristics of different materials and crystal phases.

[0044] In specific implementation, when the piezoelectric wafer is a lithium tantalate piezoelectric wafer, the implanted ions are hydrogen ions, the ion implantation energy is 80keV~200keV, and the implantation dose is 5×10⁻⁶. 16 cm -2 ~1×10 17 cm -2 When the piezoelectric wafer is a lithium niobate piezoelectric wafer, the implanted ions are helium ions, the ion implantation energy is 100keV to 300keV, and the implantation dose is 1×10⁻⁶. 16 cm -2 ~4×10 16 cm -2 .

[0045] S2. Heat the implanted piezoelectric wafer to a set temperature, and then continue heating to maintain that temperature;

[0046] In practice, the heating device used is a hot table, oven, or muffle furnace, with a heating rate of 10℃ / min to 20℃ / min. A heating rate that is too slow and takes too long not only reduces work efficiency but also increases the wafer's thermal budget during the prolonged heating process, thus affecting its blistering time. Conversely, a heating rate that is too fast can generate thermal stress that can easily lead to wafer cracking and other problems. Therefore, the heating rate should be kept neither too fast nor too slow to maintain a proper balance.

[0047] It should be noted that, as Figure 4-5 As shown, when the injection dose is appropriate, the defect layer easily traps hydrogen or helium atoms to form bubbles during heating. As the temperature rises or the holding time increases, the bubbles 23 inside the material merge and grow, continuously increasing the internal pressure. This is equivalent to applying a vertical force to the surface of the piezoelectric wafer, causing the surface to bulge 12. When the internal pressure exceeds a threshold, some of the bulges will rupture or even detach, releasing the internal gas and leaving a pit 13. At this point, due to diffuse reflection, the surface of the piezoelectric wafer no longer appears smooth and mirror-like to the naked eye. If the injection dose is too small, there are not enough hydrogen or helium atoms to provide pressure inside the bubbles during heating, so no bulges or pits will appear, and the surface of the piezoelectric wafer will remain the same as its initial state, exhibiting a smooth and mirror-like appearance. If the injection dose is too large, excessive hydrogen or helium atoms will provide excessive pressure inside the bubbles during heating, causing bulges and pits to appear on the wafer surface prematurely.

[0048] S3. During the continued heating process, observe whether the surface roughness of the piezoelectric wafer changes and the time it takes for the change to occur. Determine whether the ion implantation dose is appropriate based on the following three scenarios:

[0049] If the surface changes before heating continues for less than a hours, the ion implantation dose is deemed too high.

[0050] If the surface changes after heating for a to b hours, the ion implantation dose is deemed appropriate.

[0051] If no change is observed on the surface after heating for b hours, the ion implantation dose is deemed insufficient; where a < b.

[0052] If the dose is appropriate, then determine that the dose is the applicable dose; if the dose is insufficient or excessive, then adjust the ion implantation dose and repeat steps S1 to S3.

[0053] In practice, the set temperature is 195–205°C, and the heating duration is 0.5–3 hours. During actual heating, if the heating duration is less than 0.5 hours, the wafer surface roughness will change. This indicates that the ion implantation dose is too high. Even if the heating duration is less than 0.5 hours, heating can be stopped, and ion implantation can be restarted to determine the appropriate dose, saving time and costs.

[0054] It should be noted that the present invention sets the temperature within the range of 195–205°C based on the following considerations:

[0055] At excessively low temperatures, ions cannot quickly acquire enough energy to form the internal pressure of the bubbles required for effective stripping; at excessively high temperatures, bubbles expand too rapidly, reducing the ability to distinguish between different dosages. This temperature range was determined experimentally, taking into account both process tolerances and ensuring the consistency of the judgment logic. The inventors experimentally verified that, under heating conditions of 200±5℃, the nucleation and growth behaviors of bubbles are essentially consistent, and using 0.5h as the lower limit of time is reliable.

[0056] In practice, the appropriateness of the implantation dose can be determined by visually observing the change in surface roughness of the piezoelectric wafer after heat treatment. Alternatively, a roughness tester or microscope can be used to observe the surface roughness instead of the naked eye. The diameter of the protrusions and pits observed under a roughness tester or microscope is usually in the nanometer or submicrometer range, and the roughness test results after heat treatment are 1 nm to 10 nm.

[0057] In practice, if the injected dose is insufficient, the dose is increased and steps S1-S3 are repeated; if the injected dose is too large, the dose is reduced and steps S1-S3 are repeated until the dose is appropriate.

[0058] In practice, multiple (two or more) piezoelectric wafers in specific orientations can be used for implantation using a dose gradient, followed by uniform heating and observation.

[0059] In this embodiment, five lithium tantalate piezoelectric wafers with a 42°Y orientation were selected. Hydrogen ion implantation was performed on the wafers, with the ion implantation energy controlled at 200 keV. The ion implantation dose for the five wafers was 6 × 10⁻⁶. 16 cm -2 7×10 16 cm -2 8×10 16 cm -2 9×10 16 cm -2 1×10 17 cm -2After ion implantation, five lithium tantalate piezoelectric wafers were placed on a 200°C heating stage for heating. The changes in surface roughness of the five lithium tantalate piezoelectric wafers during the heating process were observed, and the changes are shown in Table 1.

[0060] Table 1. Surface roughness variation of five lithium tantalate piezoelectric wafers along the 42°Y direction.

[0061]

[0062]

[0063] As shown in Table 1, the ion implantation dose of the lithium tantalate piezoelectric wafer in the 42°Y direction is 8 × 10⁻⁶. 16 cm -2 ~9×10 16 cm -2 That would be more appropriate.

[0064] In another embodiment of the present invention, three lithium niobate piezoelectric wafers with x-sections are selected, and helium ion implantation is performed on the wafers. The energy of the helium ion implantation is 300 keV, and the ion implantation doses are 1.5 × 10⁻⁶. 16 cm -2 2.5×10 16 cm -2 3.5×10 16 cm -2 Three lithium niobate piezoelectric wafers after ion implantation were simultaneously placed on a 200℃ hot stage for heating. The changes in surface roughness of the three lithium niobate piezoelectric wafers during the heating process were observed, and the changes are shown in Table 2.

[0065] Table 2. Surface roughness variation of three lithium niobate piezoelectric wafers in the x-section direction.

[0066]

[0067] As shown in Table 2, the ion implantation dose of the lithium niobate piezoelectric wafer in the x-section direction is 2.5 × 10⁻⁶. 16 cm -2 That's quite suitable.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A method of rapidly determining ion implantation dose, characterized by, The method comprises the following steps: (1) ion implantation treatment is performed on a piezoelectric wafer; (2) the piezoelectric wafer after the ion implantation is heated to a set temperature, and then continues to be heated to maintain the temperature; (3) during the continuous heating process, whether the surface roughness of the piezoelectric wafer changes and the time when the change occurs are observed, and whether the ion implantation dose is appropriate is determined according to the following three cases: if the surface has changed when the continuous heating time is less than a hours, it is determined that the ion implantation dose is too large; if the surface changes when the continuous heating time is between a and b hours, it is determined that the ion implantation dose is appropriate; if the surface still does not change when the continuous heating time reaches b hours, it is determined that the ion implantation dose is insufficient; wherein a < b; if the dose is appropriate, the dose is determined as the applicable dose; if the dose is insufficient or too large, the ion implantation dose is adjusted, and steps (1) to (3) are repeated.

2. The method of claim 1, wherein, In step (2), the set temperature is 195-205℃, and the continuous heating time is 0.5-3 hours.

3. The method of claim 1, wherein, The ion used in the ion implantation is hydrogen ion, helium ion or hydrogen-helium co-implantation ion.

4. The method of claim 1, wherein, The ion implantation energy is 50 keV to 400 keV, and the implantation dose is 1 x 10 16 cm -2 to 1 x 10 17 cm -2 .

5. The method of claim 1, wherein, In step (2), the heating rate to the set temperature is 10-20℃ / min.

6. The method of claim 1, wherein, The piezoelectric wafer is lithium niobate wafer or lithium tantalate wafer.

7. The method of claim 6, wherein, When the piezoelectric wafer is a lithium niobate wafer, the implanted ions are helium ions, the implantation energy is 100keV-300keV, and the implantation dose is 1x10 16 cm -2 -4x10 16 cm -2 ; when the piezoelectric wafer is a lithium tantalate wafer, the implanted ions are hydrogen ions, the implantation energy is 80keV-200keV, and the implantation dose is 5x10 16 cm -2 -1x10 17 cm -2 .

8. The method of claim 1, wherein, The surface roughness is determined by naked eye observation or instrument detection.

9. The method of claim 8, wherein, The instrument includes a roughness tester or a microscope.

10. The method of claim 1, wherein, Multiple wafers are implanted with dose gradient, and heating treatment and observation are uniformly performed to determine the optimal implantation dose.

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