PZT piezoelectric film wet etching liquid with high selectivity and low lateral corrosion

Abstract

The invention belongs to the technical field of semiconductor processing and manufacturing, and provides a high-selectivity low-lateral-corrosion PZT piezoelectric film wet etching solution, which is prepared by the following steps: mixing a fluoboric acid solution, a hydrochloric acid solution, a nitric acid solution and water until the temperature is stable, thereby obtaining the PZT piezoelectric film wet etching solution. The etching solution obtained by the invention can realize complete residual-free PZT etching on the whole surface; the obtained etching liquid is low in lateral corrosion, high-precision etching can be achieved through different etching operations such as soaking-rinsing circulation and rotary spraying, the angle of the side wall after etching is a regular trapezoid close to 45 degrees, and the follow-up semiconductor processing technology can be conveniently carried out; the etching liquid has good selectivity for a bottom electrode Pt and photoresist of PZT, and can be practically applied to processing and manufacturing of semiconductor devices.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductor processing and manufacturing, and in particular to a PZT piezoelectric film wet etching solution with high selectivity and low lateral corrosion. Background Art

[0002] Piezoelectric materials can convert tiny mechanical deformations into electrical signals, thereby realizing the conversion between force signals and electrical signals. They have attracted attention in the fields of materials, equipment, and recently in micro-nano devices such as MEMS (microelectromechanical systems). Among these piezoelectric materials, PZT (lead zirconate titanate) has been increasingly widely used in various fields of MEMS devices, including transducers, actuators, energy harvesting devices, pyroelectrics, etc., due to its high piezoelectric properties and electromechanical coupling properties. In recent years, researchers have been constantly exploring methods to enhance the performance of PZT materials and manufacturing methods that are compatible with semiconductor manufacturing processes. Unlike traditional bulk PZT piezoelectric ceramics, PZT films in semiconductor processes are usually grown on the surface of Si or SOI substrates with lower electrodes by sol-gel spin coating, PVD magnetron RF sputtering, CVD chemical vapor deposition, PLD pulsed laser deposition, etc. Therefore, its physical and chemical properties have certain changes compared with traditional bulk PZT materials, such as high consistency of crystal phase orientation and uniformity of grains, which makes PZT thin film materials have fewer internal defects and more dense materials. In addition, in terms of processing, traditional bulk PZT materials are usually patterned by thinning, mechanical cutting, etc., but these processes cannot be applied to semiconductor processes, limiting the application of bulk PZT in semiconductors. Thin-film PZT can be patterned by wet or dry etching that is compatible with semiconductor processes, thereby gaining an increasingly large application market.

[0003] At present, the main methods for patterning PZT thin films are dry ICP etching and wet etching through etching liquid. However, all the current etching methods have certain problems. ICP dry etching has the advantages of good process controllability and good film edge quality, but it also has disadvantages, such as high equipment cost, low etching speed, poor etching selectivity, and easy damage to the bottom electrode layer. In addition, as a lead-containing material, PZT's waste gas treatment after etching and regular cleaning of the etching chamber will affect production. For wet etching liquid, although the etching speed is fast and the equipment required for etching is low, the optimal ratio and application method have not been fully demonstrated. In addition, there are problems such as PZT residue after incomplete etching, difficult to control lateral corrosion, low process precision, low selectivity for metals and photoresists, and dangerous use due to the presence of HF. Therefore, it is currently mainly used in laboratories and other environments, and there is still a lack of products on the market that can meet actual production requirements.

[0004] In view of the above-mentioned needs and problems, there is an urgent need for a low-cost PZT wet etching solution with controllable etching accuracy and high selectivity for photoresist and metal. Summary of the invention

[0005] The purpose of the present invention is to provide a PZT piezoelectric film wet etching solution with high selectivity and low lateral corrosion, which can perform low-cost and high-precision wet etching on the PZT film to overcome the defects existing in the prior art.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing a PZT piezoelectric thin film wet etching solution with high selectivity and low lateral corrosion, comprising the following steps:

[0008] The fluoroboric acid solution, hydrochloric acid solution, nitric acid solution and water are mixed until the temperature is stable to obtain the PZT piezoelectric film wet etching solution.

[0009] Preferably, the volume ratio of the fluoroboric acid solution, the hydrochloric acid solution, the nitric acid solution and water is 8-12:3-8:8-12:80-120.

[0010] Preferably, the volume fraction concentration of the fluoroboric acid solution is 15-25%;

[0011] The volume fraction concentration of the hydrochloric acid solution is 30-40%;

[0012] The volume fraction concentration of the nitric acid solution is 65-75%.

[0013] The invention provides a PZT piezoelectric film wet etching solution with high selectivity and low lateral corrosion.

[0014] The invention provides an application of a PZT piezoelectric film wet etching solution with high selectivity and low lateral corrosion in semiconductor device processing.

[0015] The present invention also provides a method for etching a PZT piezoelectric thin film wet etching solution with high selectivity and low lateral corrosion, comprising the following steps:

[0016] (1) Pour the PZT piezoelectric film wet etching solution into the wet etching acid tank;

[0017] (2) immersing the PZT sample into the wet etching liquid acid tank in step (1), taking it out after stirring and immersing, and rinsing the surface of the PZT sample with running water;

[0018] (3) Repeat the soaking-rinsing operation in step (2) until the etching of the PZT sample is completed.

[0019] Preferably, the stirring and soaking time in step (2) is 4 to 6 seconds;

[0020] The rinsing time in step (2) is 4 to 6 seconds.

[0021] The present invention also provides a method for etching a PZT piezoelectric thin film wet etching solution with high selectivity and low lateral corrosion, comprising the following steps:

[0022] (1) Pour the PZT piezoelectric film wet etching solution into the liquid storage tank of the spin coating equipment;

[0023] (2) Fixing the PZT sample on the vacuum rotating adsorption table of the spin coating equipment in step (1), and turning on the vacuum to adsorb the PZT sample;

[0024] (3) Activate the spin coating equipment and use the etching liquid to spray the etching liquid back and forth on the surface of the rotating PZT sample until the etching of the PZT sample is completed.

[0025] Preferably, the pressure of the vacuum adsorption in step (2) is 50-150 Torr, and the rotation rate of the vacuum rotation is 500-1500 rpm.

[0026] The present invention has the following beneficial effects:

[0027] (1) The etching solution obtained by the present invention can achieve PZT etching without any residue on the entire surface;

[0028] (2) The etching solution obtained by the present invention has low lateral corrosion, and high-precision etching can be achieved through different etching operations such as soak-rinse cycle and rotary spray, and the side wall angle after etching is a positive trapezoid close to 45°, which is convenient for subsequent semiconductor processing;

[0029] (3) The etching solution of the present invention has good selectivity for the bottom electrode Pt of PZT and the photoresist, and can be actually applied in the processing and manufacturing of semiconductor devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the etching method of different types of PZT samples using the PZT piezoelectric film wet etching solution of Example 1;

[0031] Figure 2 This is a SEM image of the PZT sample after being etched by the PZT piezoelectric film wet etching solution of Example 1. DETAILED DESCRIPTION

[0032] The present invention provides a method for preparing a PZT piezoelectric thin film wet etching solution with high selectivity and low lateral corrosion, comprising the following steps:

[0033] The fluoroboric acid solution, hydrochloric acid solution, nitric acid solution and water are mixed until the temperature is stable to obtain the PZT piezoelectric film wet etching solution.

[0034] In the present invention, the fluoroboric acid solution and water are first mixed, hydrochloric acid and nitric acid are added under stirring, and then the mixture is allowed to stand until the temperature is stable.

[0035] In the present invention, the volume ratio of the fluoroboric acid solution, the hydrochloric acid solution, the nitric acid solution and water is preferably 8-12:3-8:8-12:80-120, more preferably 8.5-11.5:3.5-7.5:8.5-11.5:85-115, and more preferably 9-11:4-7:9-11:90-110.

[0036] In the present invention, the volume fraction concentration of the fluoroboric acid solution is preferably 15 to 25%, more preferably 17 to 23%, and even more preferably 19 to 21%.

[0037] In the present invention, the volume fraction concentration of the hydrochloric acid solution is preferably 30 to 40%, more preferably 32 to 38%, and even more preferably 34 to 36%.

[0038] In the present invention, the volume fraction concentration of the nitric acid solution is preferably 65 to 75%, more preferably 67 to 73%, and even more preferably 68 to 72%.

[0039] In the present invention, the temperature is stabilized to room temperature.

[0040] The invention provides a PZT piezoelectric film wet etching solution with high selectivity and low lateral corrosion.

[0041] The invention provides an application of a PZT piezoelectric film wet etching solution with high selectivity and low lateral corrosion in semiconductor device processing.

[0042] The present invention also provides a method for etching a PZT piezoelectric thin film wet etching solution with high selectivity and low lateral corrosion, comprising the following steps:

[0043] (1) Pour the PZT piezoelectric film wet etching solution into the wet etching acid tank;

[0044] (2) immersing the PZT sample into the wet etching liquid acid tank in step (1), taking it out after stirring and immersing, and rinsing the surface of the PZT sample with running water;

[0045] (3) Repeat the soaking-rinsing operation in step (2) until the etching of the PZT sample is completed.

[0046] In the present invention, the PZT sample needs to be subjected to conventional photolithography and development operations, the pattern to be protected is covered with photoresist, the part to be etched is exposed, and then immersed in a wet etching liquid acid tank.

[0047] In the present invention, the stirring and immersion time in step (2) is preferably 4 to 6 seconds, more preferably 4.5 to 5.5 seconds, and even more preferably 5 seconds.

[0048] In the present invention, the rinsing time in step (2) is preferably 4 to 6 seconds, more preferably 4.5 to 5.5 seconds, and even more preferably 5 seconds.

[0049] The present invention also provides a method for etching a PZT piezoelectric thin film wet etching solution with high selectivity and low lateral corrosion, comprising the following steps:

[0050] (1) Pour the PZT piezoelectric film wet etching solution into the liquid storage tank of the spin coating equipment;

[0051] (2) Fixing the PZT sample on the vacuum rotating adsorption table of the spin coating equipment in step (1), and turning on the vacuum to adsorb the PZT sample;

[0052] (3) Activate the spin coating equipment and use the etching liquid to spray the etching liquid back and forth on the surface of the rotating PZT sample until the etching of the PZT sample is completed.

[0053] In the present invention, the PZT sample needs to be subjected to conventional photolithography and development operations, the pattern to be protected is covered with photoresist, the part to be etched is exposed, and then immersed in a wet etching liquid acid tank.

[0054] In the present invention, the pressure of the vacuum adsorption in step (2) is preferably 50 to 150 Torr, more preferably 60 to 140 Torr, and even more preferably 70 to 130 Torr.

[0055] In the present invention, the rotation rate of the vacuum rotation is preferably 500 to 1500 rpm, more preferably 600 to 1400 rpm, and even more preferably 700 to 1300 rpm.

[0056] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0057] Example 1

[0058] Mix 20% by volume fluoroboric acid and water, add 35% by volume hydrochloric acid solution and 69% by volume nitric acid solution under stirring (the volume ratio of fluoroboric acid solution, hydrochloric acid solution, nitric acid solution and water is 10:5:10:100), and then let stand until the temperature stabilizes to 25°C to obtain the PZT piezoelectric film wet etching solution.

[0059] Example 2

[0060] Immersion etching of PZT piezoelectric film:

[0061] Pour the PZT piezoelectric thin film wet etching solution of Example 1 into a wet etching acid tank;

[0062] The PZT sample to be etched is subjected to conventional photolithography and development operations, the pattern to be protected is covered with photoresist, the part to be etched is exposed, the PZT sample is immersed in a wet etching liquid acid tank, the PZT piezoelectric film wet etching liquid completely covers the sample, and the sample is stirred and immersed until the etching of the PZT sample is completed.

[0063] Example 3

[0064] Soak-rinse combined etching of PZT piezoelectric film:

[0065] Pour the PZT piezoelectric thin film wet etching solution of Example 1 into a wet etching acid tank;

[0066] The PZT sample to be etched is subjected to conventional photolithography and development operations, the pattern to be protected is covered with photoresist, and the part to be etched is exposed. The PZT sample is immersed in a wet etching liquid acid tank, and the PZT piezoelectric film wet etching liquid completely covers the sample. After stirring and soaking for 5 seconds, take it out and rinse the surface of the PZT sample with running water for 5 seconds;

[0067] Repeat the soaking-rinsing operation in the above steps until the etching of the PZT sample is completed.

[0068] Example 4

[0069] Spin jet etching of PZT piezoelectric thin films

[0070] Pour the PZT piezoelectric thin film wet etching solution of Example 1 into the liquid storage tank of the spin coating equipment;

[0071] The PZT sample to be etched is subjected to conventional photolithography and development operations, the pattern to be protected is covered with photoresist, and the part to be etched is exposed, the PZT sample is fixed on the vacuum rotating adsorption table of the spin coating equipment, and the vacuum is turned on to adsorb the PZT sample (wherein the rotation rate of the vacuum rotation is 1000rpm, and the pressure of the vacuum adsorption is 100Torr);

[0072] The spin coating equipment is activated, and the etching liquid is sprayed back and forth on the surface of the rotating PZT sample with the etching liquid until the etching of the PZT sample is completed.

[0073] The etching methods of Examples 2 to 4 were used to etch different PZT pressed films. The results are as follows: Figure 1 shown.

[0074] (1) The surface of a 2 μm thick PZT sample was subjected to glue coating, photolithography, development, and baking operations, and a 1.1 μm thick photoresist was patterned on the sample, i.e., the patterning step of the etching mask of the semiconductor process standard;

[0075] (2) Etching the entire surface of a 2 μm thick PZT sample without photoresist protection to test whether residue-free etching can be achieved for the entire surface of the PZT sample;

[0076] (3) Only the surface of the PZT sample is coated and baked without photolithography development, so that the 1.1 μm thick photoresist completely covers the 2 μm thick PZT sample, which is used to test the etching selectivity of the etching solution to the photoresist;

[0077] (4) After growing a 100 nm thick Pt bottom electrode, no PZT is grown on the sample to test the etching selectivity of the etching solution to Pt metal.

[0078] Prepare 3 groups of each sample for experiments, and take the average value of the results of each group of experiments. The test data are as follows:

[0079] For the experimental group (1), i.e., the sample with patterned photoresist on the surface of the PZT sample, the etching rates of the etching methods of Examples 2 to 4 were 66.6 nm / s, 90.9 nm / s, and 108.1 nm / s, respectively, and the lateral corrosion was 2.75 nm, 1.97 nm, and 1.85 nm, respectively. After etching, the sidewall of the PZT sample had a 45° regular trapezoidal structure, proving that the PZT piezoelectric thin film wet etching solution of Example 1 has high etching accuracy and semiconductor process compatibility;

[0080] For the experimental group (2), i.e., the entire surface of the PZT sample, the etching methods of Examples 2 to 4 can all be used to complete the etching without residue on the entire surface, and the time until the complete etching is clean is 38 seconds, 25 seconds, and 19 seconds, respectively. The PZT piezoelectric thin film wet etching solution obtained in Example 1 can achieve the etching of the PZT sample thin film without residue;

[0081] For the experimental group (3), i.e., the photoresist etching selectivity experiment, after 10 minutes of etching using the etching methods of Examples 2 to 4, no obvious etching marks appeared on the photoresist, i.e., the PZT piezoelectric thin film wet etching solution obtained in Example 1 had an extremely high etching selectivity for the PZT sample and the photoresist;

[0082] For the experimental group (4), i.e., the Pt bottom electrode etching selectivity experiment, the etching methods of Examples 2 to 4 all showed that the bottom electrode was completely etched in about 5 minutes, i.e., the etching rate for the bottom electrode Pt was 0.33 nm / s. The selectivity of the PZT piezoelectric thin film wet etching solution obtained in Example 1 for PZT and Pt was 202, 275, and 327, respectively, under the etching methods of Examples 2 to 4, which has an extremely high etching selectivity.

[0083] The PZT piezoelectric thin film wet etching solution obtained in Example 1 was used to etch the PZT sample using the method of Example 3. The etched PZT was examined by scanning electron microscopy. The results are as follows: Figure 2 shown.

[0084] Figure 2 This is the cross-sectional SEM image of the PZT after etching (the PZT surface is covered with a protective layer during cutting). Figure 2 It can be seen that the 45° morphology of the PZT edge is close to a positive trapezoid, which is convenient for subsequent semiconductor processing such as electrode layer growth.

[0085] As can be seen from the above embodiments, the present invention provides a PZT piezoelectric film wet etching solution with high selectivity and low lateral corrosion, comprising the following steps: mixing fluoroboric acid solution, hydrochloric acid solution, nitric acid solution and water until the temperature is stable, to obtain the PZT piezoelectric film wet etching solution. The etching solution obtained by the present invention can achieve PZT etching without residue on the entire surface; the etching solution obtained by the present invention has low lateral corrosion, and through different etching operations such as soaking-rinsing cycle and rotary spraying, high-precision etching can be achieved, and the side wall angle after etching is a regular trapezoid close to 45°, which is convenient for subsequent semiconductor processing technology; the etching solution in the present invention has good selectivity for the bottom electrode Pt and photoresist of PZT, and can be actually applied in the processing and manufacturing of semiconductor devices.

[0086] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a PZT piezoelectric thin film wet etching solution with high selectivity and low lateral corrosion, characterized in that: It includes the following steps: The fluoroboric acid solution, hydrochloric acid solution, nitric acid solution and water are mixed until the temperature is stable to obtain the PZT piezoelectric film wet etching solution.

2. The preparation method according to claim 1, characterized in that: The volume ratio of the fluoroboric acid solution, the hydrochloric acid solution, the nitric acid solution and water is 8-12:3-8:8-12:80-120.

3. The preparation method according to claim 1, characterized in that: The volume fraction concentration of the fluoroboric acid solution is 15-25%; The volume fraction concentration of the hydrochloric acid solution is 30-40%; The volume fraction concentration of the nitric acid solution is 65-75%.

4. A PZT piezoelectric thin film wet etching solution with high selectivity and low lateral corrosion obtained by the preparation method described in claim 1.

5. Application of the PZT piezoelectric thin film wet etching solution with high selectivity and low lateral corrosion as described in claim 4 in semiconductor device processing.

6. The etching method of the PZT piezoelectric thin film wet etching solution with high selectivity and low lateral corrosion as claimed in claim 4, characterized in that: It includes the following steps: (1) Pour the PZT piezoelectric film wet etching solution into the wet etching acid tank; (2) immersing the PZT sample into the wet etching liquid acid tank in step (1), taking it out after stirring and immersing, and rinsing the surface of the PZT sample with running water; (3) Repeat the soaking-rinsing operation in step (2) until the etching of the PZT sample is completed.

7. The etching method according to claim 6, characterized in that: The stirring and soaking time in step (2) is 4 to 6 seconds; The rinsing time in step (2) is 4 to 6 seconds.

8. The etching method of a PZT piezoelectric thin film wet etching solution with high selectivity and low lateral corrosion as claimed in claim 4, characterized in that: It includes the following steps: (1) Pour the PZT piezoelectric film wet etching solution into the liquid storage tank of the spin coating equipment; (2) Fixing the PZT sample on the vacuum rotating adsorption table of the spin coating equipment in step (1), and turning on the vacuum to adsorb the PZT sample; (3) Activate the spin coating equipment and use the etching liquid to spray the etching liquid back and forth on the surface of the rotating PZT sample until the etching of the PZT sample is completed.

9. The etching method according to claim 8, characterized in that: The pressure of the vacuum adsorption in the step (2) is 50-150 Torr, and the rotation speed of the vacuum rotation is 500-1500 rpm.

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