WO2006101458A1

WO2006101458A1 - Method for patterning ferrelectric/piezoelectric films

Info

Publication number: WO2006101458A1
Application number: PCT/SG2006/000068
Authority: WO
Inventors: Wenzhong Li; John Wang; Anthony Zhaohui Zhou; Junmin Xue; Jianmin Miao; Hong Zhu
Original assignee: National University Of Singapore; Nanyang Technological University
Priority date: 2005-03-22
Filing date: 2006-03-22
Publication date: 2006-09-28

Abstract

A method relates to an etching and patterning process suitable for microfabrication of ferroelectric/piezoelectric thin and thick films, using an acid- resistant polymer mask. The method of the present invention possesses several advantages, including patterns of well-defined features in the submicron regions, long withstand time in acid and base (over 30 minutes) environments, easy mask removal after etching (less than 3 minutes), low cost and the wide availability of polymer masks. The ferroelectric/piezoelectric films thus patterned exhibit sharply delineated etch, minimized contamination of etching residues and more importantly the improved ferroelectric properties.

Description

METHOD FOR PATTERNING FERROELECTRIC/PIEZOELECTRIC FILMS

FIELD OF INVENTION

The present invention relates to patterning of films, especially thermally annealed films of ferroelectric/piezoelectric materials. The patterned films have application in microfabrications, sensors, actuators, VLSI and ULSI fabrications, and other technologies.

BACKGROUND

Ferroelectric/piezoelectric thin and thick films are technologically important and useful for a number of device applications, owing to their unique ferroelectric and piezoelectric properties. Indeed, they have been widely employed in a wide variety of technologically demanding applications, such as in microelectromechanical systems (MEMs), sensors, actuators, dynamics random access memories, and non-volatile ferroelectric random access memories.

Etching is an important step for fabrication and microfabrication of film structures that are required in these devices. There exist two main groups of etching techniques for patterning and microfabrication of ferroelectric/piezoelectric films, namely dry etching and wet etching. Among the various dry etching and patterning techniques developed for ferroelectric/piezoelectric films, reactive ion etching (RIE) attracts great attention. However, RIE often degrades electrical properties of thin or thick films, due to chemical contamination and physical damage. Unwanted chemical reactions on the film surfaces adversely affect the electrical properties and surface roughness of the films (M. G. Kang, KT. Kim and C.I. Kim, Recovery of plasma- induced damage in PZT thin film with O₂ gas annealing, thin Solid Films 398- 399 (2001), p. 448.). The contamination can also result in a leakage path between electrodes due to their non-crystal structure and high conductivities. Physical damage can be caused by bombardment of high energetic ions on the film surface, which degrades the film structure and generates structural defects, such as stack faults and vacancies (WJ. Lee, CR. Cho, S. H. Kim, I. K. You, B.W. Kim, B. G. Yu, CH. Shin and H. C Lee, Etching behavior and damage recovery of SrBi₂Ta₂O₉ thin films, Jpn. J. Appl. Phys. 38 (1999), p. 1428.).

While various techniques have been attempted for recovering the ferroelectric/piezoelectric properties of films after patterning and microfabrication, almost all of them involve a thermal annealing step of the ferroelectric/piezoelectric films in oxygen after patterning. This can result in excess lead loss from the Pb-based ferroelectric/piezoelectric thin films, especially from the film boundaries and edges of micromachined patterns (fringe effect), hence degrading their electrical properties, increasing leakage current and even leading to complete device failure. Various wet etching processes have also been attempted for ferroelectric/piezoelectric thin and thick films, such as the process disclosed in relation to Pbi-χLa_x(Zr,Ti)O₃ (PLZT) family materials (Asselanis, Dino, Mancha, Sylvia D., US Patent No. 4759823, 1988). However, most of the known wet etching processes use a photoresist as the etching mask. These have several limitations. Firstly, the ferroelectric/piezoelectric films have to be etched before they are thermally annealed at elevated temperatures, as the annealed films need prolonged etching time, which can lead to the photoresist mask being dissolved by the etchants. Also, the subsequent thermal annealing of patterned films often results in occurrence of fringe effects at the boundaries and edges. As a result, the ferroelectric/piezoelectric performance of patterned films is degraded. In addition, due to the same fringe effects, the effective areas of patterned ferroelectric/piezoelectric films can be different from what are required for specific device applications.

It is especially difficult to use conventional photoresist masks for thick films, which often need prolonged etching time, regardless of whether they are thermally annealed or not before patterning. A prolonged etching time often lead to dissolution of the photoresist masks before completion of the etching process.

The second limitation of using a conventional photoresist mask is the strict requirement for etching solution and etching schedule. A slight change in solution composition can greatly change the etching rate of the photoresist mask, hence altering the etching time. If the etching time is too short, the ferroelectric/ferroelectric film will not be etched effectively. If the etching time is too long, this can cause the photoresist mask being dissolved before completion of the etching process, hence failure of the whole patterning process.

Prior attempts towards successful wet etching and patterning of ferroelectric/piezoelectric films led to little progress, as far as the realization of well defined features in micron and submicron regions is concerned, where the ferroelectric/piezoelectric properties have to be maintained.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided a method of patterning a film, in which an acid resist polymer layer is formed or coated over the film to be patterned, a patterned photoresist layer is then provided over the acid resist polymer layer and is used during the etching of the acid resist polymer layer and the underlying film. The etching may include reactive ion etching, preferably using an O₂ plasma, alone or in combination with etching using an etching solution. Any residue of the acid resist polymer layer and the photoresist layer may subsequently be removed. Additional steps of rinsing and drying may be carried out as required.

The use of an acid-resistant polymer mask enables an effective etching process for patterning films, including ferroelectric/piezoelectric thin and thick films, which can produce improved ferroelectric/piezoelectric properties suitable for device microfabrications, VLSI and ULSI fabrications. The improved ferroelectric/piezoelectric properties that can be achieved using the present invention widen the applications of these ferroelectric/piezoelectric films in microelectromechanical systems, sensors, actuators and microcircuit devices.

It is advantageous and preferable that the film is etched after thermal annealing. By doing so, there is no need to thermally anneal the film after etching with the disadvantages associated with this. It is possible to etch a thermally annealed film due to the use of the acid resist polymer mask.

The present invention provides a process which is more flexible than known methods as far as the requirement for etching solution is concerned. An acid- resist polymer provides well defined pattern features in micron and submicron scales, long withstand time in acid and base environments (over 30 minutes), and easy removal of mask and residues after etching (less than 3 minutes). Acid resist polymers are easily available and relatively inexpensive. The acid- resist polymer masks can be used not only in acid-based etching process, but also in base etching process for other applications, such as silicon and silicon dioxide etching.

The invention provides a much simplified requirement on the concentration and composition of etching solutions due to the strong resistance of polymer masks to both acids and bases. The invention therefore provides a great flexibility in choosing the concentration and composition of etching solutions, in order to cope with various requirements for different ferroelectric and piezoelectric films.

In other aspects, the present invention provides a method of improving the ferroelectric properties of patterned thin and thick films. Use of O₂ plasma in combination with an acid-resist polymer by RIE can effectively reduce the coercive voltage and increase the remnant polarization of the resulting ferroelectric/piezoelectric films, hence improving their functional performances.

Conventional etching of ferroelectric/piezoelectric films often results in residue contaminations on film surfaces, which are difficult to be removed without a further acid-based cleaning process. An acid-based cleaning process can cause undercutting of the film patterns. The use of the warm etching solution can effectively remove the residues. The temperature range that can be varied for the etching solution is 3O⁰C to 8O⁰C, although preferably at 65⁰C. This constitutes a separate embodiment of the present invention.

In a particularly preferred example of the present invention, the method comprises the steps of: (a) coating an acid-resistant polymer mask on a ferroelectric/piezoelectric film grown on Si or other substrates; (b) drying the polymer mask by heating to a temperature up to about 110 ⁰C for a sufficient period of time to drive off residual solvent from the acid-resistant polymer mask; (c) applying a photoresist on the polymer mask, and forming the designed pattern of photoresist by photolithography;

(d) etching the acid-resistant polymer mask covered by photoresist using reactive ion beam by oxygen plasma to develop the designed pattern;

(e) immersing the ferroelectric/piezoelectric films, covered with patterned acid-resistant polymer mask, in an etching solution for a sufficient time period to etch off portions of the ferroelectric/piezoelectric films that are not covered by the acid- resistant polymer;

(f) removing the patterned ferroelectric/piezoelectric films on the substrate from the said etching solution;

(g) immersing the said ferroelectric/piezoelectric films on substrate from step (f) into deionized or distilled water for a sufficient time period to remove residues remaining on the surface after step (f);

(h) immersing the said ferroelectric/piezoelectric films on the substrate from step (g) into a mask-removing solution for a sufficient time period, to remove the acid-resistant polymer mask;

(i) immersing the said ferroelectric/piezoelectric films on substrate from step (h) in deionized water for a sufficient time period, to remove residues remaining on the film surface; and,

(j) drying the said ferroelectric/piezoelectric films on substrate from step (i) by N₂ blowing or by heating up to 15O⁰C for a sufficient time period, to remove moisture from the film surfaces. According to a further aspect of the present invention, there is provided a patterned ferroelectric or piezoelectric film formed in accordance with the method of the present invention.

Other novel aspects, features and advantages of the present invention will become apparent to those of ordinary skill in the art upon review of the following descriptions of specific embodiments of the invention in conjunction with the accompanying figures.

DESCRIPTION OF THE DRAWINGS

The present invention will be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a side view of the film structure during a patterning process;

Figure 2 show examples of alignment patterns for polystyrene masks prepared by photolithography and RIE;

Figure 3 shows an example of microcantilever patterns for polystyrene mask prepared by photolithography and RIE; Figure 4 shows an example of alignment marks for PbZr_1-xTi_xθ₃ (PZT) film patterns, after wet etching for 1 minute in 20v% HCI (37wt%) + 20v% NH₄F (20wt%) using polystyrene mask;

Figure 5 show an example of microcantilever patterns for PZT film with electrode pad after wet etching for 1 minute in 20v% HCI (37wt%) + 20v% NH₄F (20wt%) using polystyrene mask;

Figure 6 shows the P-E hysteresis loop of as-prepared PZT film, before patterning;

Figure 7 shows the P-E hysteresis loop of PZT film at lever pad after wet etching for 1.0 minute;

Figure 8 shows the P-E hysteresis loop of PZT film, when polystyrene mask is removed by RIE;

Figure 9 shows the P-E hysteresis loop of PZT film at lever pad after wet etching for 5 minutes; and,

Figure 10 shows the P-E hysteresis loop of PZT film of microcantilever pattern after wet etching for 1 minute.

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a fast and effective wet etching process for patterning of ferroelectric/piezoelectric thin and thick films, such as PbZri-_xTi_xθ₃ (PZT), Pb(Mg₁₇₃Nb₂Z₃)O₃ (PMN), Pb(Mg₁₇₃Nb₂Z₃)O₃-PbTiO₃ (PMN-PT), Pb(Mg₁Z₃Nb₂Z₃)O₃-Pb(Zn₁₇₃Nb₂Z₃)O₃-PbTiO₃ (PMN-PZN-PT), Pb_1-xl_a_x(Zr,Ti)O₃ (PLZT), and Pb(Mg_1/3Ta₂z₃)O₃-PbTiO₃ (PMT-PT), using an acid-resistant polymer mask. The patterned films with features in the micron and submicron scales exhibit improved ferroelectric/piezoelectric properties, as compared to the unpatterned films.

In one example, a PZT film can be prepared by any suitable method known to a person skilled in the art and preferably by sol-gel or sputtering techniques. The etching process disclosed in the present invention is advantageously performed on thermally annealed ferroelectric/piezoelectric films, so that the fringe effect is effectively eliminated.

As shown in Figures 1.1 to 1.6, a top electrode can be formed using photolithography to expose a window in a photoresist layer into which a conducting electrode material can be deposited by sputtering or other techniques. The excess material around the electrode can then be removed with the remaining photoresist layer to create the electrode.

An acid-resist polymer solution, preferably 10w.t% polystyrene solution in toluene as the solvent, is deposited on the thermally annealed ferroelectric/piezoelectric films grown on Pt/SiOa/Si silicon substrates by spin coating. The resulting device is shown in Figure 1.7. The spin speed is about 2000 to 5000 rpm for a coating time period of about 30 seconds. Preferably, the spin coating speed is 2000 rpm for 30 seconds to get a thickness of about 14μm for the polystyrene mask. The mask is then heated to between about 50 and 200⁰C for an appropriate time period, for example for about 3 minutes at a temperature of about 110⁰C, to eliminate the solvent from the polystyrene mask.

As shown in Figure 1.8, a photoresist layer is then deposited on the polymer mask. Figures 1.9 and 1.10 show the use of photolithography to produce a pattern with the photoresist, which serves as a mask for patterning of the underneath polymer mask by RIE. As shown in Figure 1.11 , in the RIE process, O₂ plasma etches off the polymer mask and photoresist mask at similar rates. As a result, the required thickness for the polymer mask can be determined by the etching rate ratio between the polymer mask and the photoresist. The use of O₂ plasma to etch the polymer mask can advantageously reduces the coercive voltage and increase the remnant polarization of patterned ferroelectric/piezoelectric films, hence improving the performance of these films.

As shown in Figure 1.12, the thermally annealed ferroelectric/piezoelectric films covered by patterned polystyrene mask are immersed in a warm etching solution, containing hydrochloric acid and ammonia fluoride with a concentration of about 0.1 to 99.9v% hydrochloric acid (37wt%), and about 0.1 to 50v% of a fluorine ion donor (20wt%), at a temperature in the range of 3O⁰C to 8O⁰C, for a time period of between about 10 and 300 seconds. This process thoroughly removes all the exposed portions of the ferroelectric/piezoelectric films and preserves the designed film pattern without significant undercutting. In comparison, in the conventional wet etching process, where a photoresist mask is used, the etching time is limited to about 2 to 15 seconds, which is not sufficient for etching the thermally annealed ferroelectric/piezoelectric thin or thick films.

At temperatures in the range of 3O⁰C to 8O⁰C, the etching solution removes the etch residues from the film surfaces and substrates. It is therefore not necessary to perform an additional cleaning step to remove etch residues as needed in conventional wet etching process, where nitric acid is typically used as the cleaning solution. This is advantageous as the nitric acid can cause damage to the patterned ferroelectric/piezoelectric films.

The patterned ferroelectric/piezoelectric films are taken out from the etching solution and rinsed with deionized water. Finally, the remaining polystyrene mask is then easily dissolved by toluene as shown in Figure 1.13, leaving only patterned ferroelectric/piezoelectric film with feature sizes down to submicrons.

The fluorine ion donor is selected from the group comprising hydrofluoric acid, ammonium fluoride, and mixtures thereof. Ammonium fluoride is preferably used as the fluoride ion donor, in view of the potential health hazards of hydrofluoric acid and its mixtures. Owing to the ability of long withstand time in both base and acid environments, the acid-resistant polymer is not sensitive to the concentration and composition of etching solution. The invention therefore provides flexible choices on the concentration and composition of etching solution, to cope with the etching requirements for various ferroelectric and piezoelectric films. The etching solution is preferably an aqueous solution comprising 0.1 to 99.9v% hydrochloric acid (37wt%) and 0.1 to 50v% of fluorine ion donor (20wt%). The flexibility in choosing the concentration and composition of etching solution make the present invention suitable for patterning many types of ferroelectric/piezoelectric films with several advantages, including a well controlled etching rate, sharply delineated etch and minimization of residue contamination.

The required etching time for a given ferroelectric/piezoelectric film varies with the type and concentration of etching solution, as well as the film thickness and configurations. An aqueous solution consisting of 20v% hydrochloric acid (37wt%) and 20v% fluorine ion donor (20wt%) is chosen advantageously for effective etching of PZT-based ferroelectric/piezoelectric films with minimized undercutting, where the etching time is controlled at about 60 seconds.

After removal from the etching solution, patterned ferroelectric/piezoelectric films are rinsed with deionized water to remove the remaining etching solution so that further undercutting is prevented. Contamination by etching residues on film and substrate surfaces is a common problem in the conventional etching process performed at room temperature. These residues are difficult to remove and can significantly affect the performance of patterned ferroelectric/piezoelectric films. A cleaning step has to be adopted in the conventional wet etching process to remove the etching residues. The commonly used nitric acid and hydrogen peroxide, however, can result in severe undercutting. In the present invention, thermally annealed ferroelectric/piezoelectric films are etched in an aqueous etching solution. Warming the aqueous solution can effectively remove the etch residues. The present invention thus bypasses the cleaning step that is commonly practiced in the conventional wet etching process. The temperature of the aqueous etching solution is controlled in the range of 3O⁰C to 8O⁰C, although preferably at 65⁰C.

After patterning of the ferroelectric/piezoelectric films, the polymer mask is removed by immersion into toluene, acetone or mixtures of thereof, which effectively dissolves the polymer mask in about 1 minute. After thoroughly rinsing with deionized water, the patterned ferroelectric/piezoelectric film is then dried by nitrogen gas spin drying.

The following examples with reference to the accompanying drawing illustrate the present invention but are not limiting as to the nature of the invention.

EXAMPLE 1 Step 1 A PbZr_1-xTi_xO₃ (PZT) thin film, e.g., PbZr₀.₅₂Tio.₄₈θ₃₎ was formed by following the steps as follows:

• 50 ml of 0.4 M precursor solution of PbZro.₅₂Tio.₄eO₃ was prepared by dissolving an appropriate amount of Pb(CH₃COO)₂-SH₂O (7.963g, calculated from the concentration and volume of final solution mixture as well as the stoichiometry of organic solvent and the composition of PbZr₀.₅₂Tio.₄₈θ₃) into 10 ml of solvent, which was a mixture of ethylene glycol monomethyl ether (C₃H₈O₂) and acetic acid at a volume ratio of 5/1.3 at room temperature.

• Appropriate amounts of Zr[OCH(CH₃)₂]₄ and Ti[OCH(CH₃)₂]4 (4.867g and 2.785g) were dissolved, respectively, in two 5 ml of the same solvent.

• The above three solutions were mixed together, with the total volume of the mixed solution being brought up to 50 ml by adding the solvent.

• The mixed solution was stirred for 2 hours.

Step 2 The precursor solution of PbZr₀.₅₂Ti₀.₄₈θ₃ was spin-coated on silicon substrates at 2000 rpm for 30 seconds. The substrate surfaces are pre- coated with a thin layer of SiO₂ (100nm in thickness), a thin Ti layer

(50nm in thickness) and a thin Pt layer (100nm in thickness). The first PZT precursor layer was then dried at 35O⁰C for 5 minutes and subsequently baked at 500⁰C for 5 minutes. Step 3 The process described in the step 2 was repeated, until 12 precursor film layers (total thickness ~500nm) were formed.

Step 4 The precursor film was then thermally annealed at 65O⁰C for 1.0 hour. The resulting PZT film exhibited a well-defined hysteresis loop, as shown in Figure 6. It possessed a remnant polarization (2P_r) of 51.6 μ/cm² and a coercive field (2£_c) of 117.8kV/cm, which are comparable to those known polycrystalline PZT films.

Step 5 A top electrode was formed by photolithography (exposure time 3.8s), sputtering (5mins) and the lift off process.

Step 6 A polystyrene solution (10wt% in toluene) was prepared with toluene as the solvent and stirred for 30 minutes. Step 7 The polystyrene solution was spin-coated onto the thermally annealed

PZT film at a speed of 2000 rpm for 30 seconds. Step 8 The film was then heated to 110⁰C for 3 minutes to eliminate the residual solvent from the polystyrene mask. Step 9 For photolithography, a photoresist is spin coated on top of the polystyrene mask, and patterned by photolithography, where the spin coating speed was controlled at 2000 rpm and spin time 30 seconds. Step 10 The polystyrene mask was then etched by reactive ion etching (RIE) at an operation power of 300 W and chamber pressure of 120 mTorr for 30 minutes. Examples of etched polystyrene masks are shown in Figure 2 and Figure 3, where well defined patterns are shown.

Step 11 Thereafter, the PZT thin film covered with patterned polystyrene mask was etched using 20v% HCI (37wt%)+20v% NH₄F (20wt%) for 1 minute at 65⁰C. Step 12 The etched PZT film pattern with polystyrene mask was rinsed in deionized water for 5 minutes. Step 13 The patterned PZT film on substrate was immersed in toluene to remove the polystyrene mask. Step 14 The patterned PZT film was rinsed in deionized water for 5 minutes, followed by drying using spinning nitrogen blowing.

The side view of film profile during the above described patterning process is shown in Figure 1.

One example of the film patterns after etching is shown in Figure 4, where a well defined film pattern in micron scale is demonstrated. The present patterning method leads to ferroelectric/piezoelectric film with sharply delineated etch and minimum residue contamination.

As shown in Figure 7, patterned PZT film on lever pad exhibits well defined ferroelectric properties, with a respective remnant polarization (2P_r) of 56.1 μC/cm² and coercive field (2E_C) of 72.1 kV/cm, when measured at an applied electric field of 500 kV/cm at room temperature, which are comparable with those of the PZT film prior to etching.

EXAMPLE 2

A PZT film of 0.04cm² in top electrode area covered by polystyrene mask, patterned by RIE, was formed using a similar procedure as in Example 1 , except that steps 11 and 12 were omitted. After patterning of the polystyrene mask by RIE at an operation power of 300W, chamber pressure of 120 mTorr and etching time of 30 minutes, the exposed PZT film exhibits further improved ferroelectric properties, as shown in Figure 8, when compared to those shown in Figure 6 for the as-prepared PZT film. O₂ plasma employed for etching of polystyrene mask by RIE can significantly reduce the coercive field (2E_C from 117.8kV/cm to 78.5kV/m at an applied electric field of 500kV/cm at room temperature) and increase the remnant polarization of the PZT film (although the variation of P_r is not as apparent as the coercive voltage due to saturation of the hysteresis loop at an applied field of 500 kV/cm).

O₂ plasma employed for RIE in the present invention improves the ferroelectric/piezoelectric properties of patterned PZT films.

EXAMPLE 3

PZT film was patterned by following a similar procedure as detailed in Example 1 , except that in step 10, the etching time was extended to 5 minutes, and the etching solution was changed to 10v% HCI (37wt%)+10v% NH₄F (20wt%).

The resulting microcantilever pattern of PZT films, showed in Figure 5, exhibits well defined ferroelectric properties, as shown in Figure 9. The present invention provides flexible choices in the concentration of etching solution and etching time. EXAMPLE 4

A patterned PZT film of 50x10 μm² in top electrode area was prepared by following the same procedure as detailed in Example 1.

As shown in Figure 10, the PZT film of microcantilever pattern exhibits ferroelectric properties comparable to those of the PZT film prior to patterning, shown in Figure 6. The present invention thus provides a feasible etching process for ferroelectric/piezoelectric film patterns that are commonly needed for MEM microfabrications, VLSI and ULSI fabrications.

Other features, benefits and advantages of the present invention not expressly mentioned above can be understood form this description and the accompanying drawings by those skilled in the art.

The successful patterning of PZT films by employing polystyrene mask and the process for patterning them described herein are all exemplary embodiments of one or more aspects of the invention. As can be understood by a person skilled in the art, many modifications to these exemplary embodiments are possible. The invention, rather, is intended to encompass all such modifications within its scope, as defined by the claim.

All documents referred to herein are fully incorporated by references.

Claims

1. A method of patterning a film, the method comprising: forming an acid resist polymer layer over the thermally annealed film; providing a patterned photoresist layer over the acid resist polymer layer; etching the acid resist polymer layer and the underlying film; and, removing any residue of the acid resist polymer layer and the photoresist layer.

2. The method of Claim 1 , in which the film to be patterned is a thermally annealed film.

3. The method of Claim 1 or Claim 2, in which the acid resist polymer layer comprises a polystyrene or polystyrene-based layer.

4. The method of any one of the preceding claims, in which the acid resist polymer layer is deposited on the thermally annealed film as a solution, and in which the solvent is subsequently removed to form a mask layer.

5. The method of Claim 4, in which the solvent is removed from the acid resist polymer layer by heating the solution.

6. The method of Claim 4 or Claim 5, in which the acid resist polymer solution comprises polystyrene in a toluene solvent.

7. The method of any one of the preceding claims, in which the acid resist polymer layer has a thickness of around 14μm.

8. The method of any one of the preceding claims, in which the etching of the acid resist polymer layer comprises reactive ion etching.

9. The method of Claim 8, in which the reactive ion etching is carried out using an O₂ plasma.

10. The method of Claim 8 or Claim 9, in which the reactive ion etching etches both the acid resist polymer layer and the underlying film to be patterned.

11. The method of Claim 8 or Claim 9, in which the reactive ion etching etches the acid resist polymer layer, and in which the underlying film to be patterned is etched in a subsequent etching step.

12. The method of Claim 11 , in which the subsequent etching step comprises wet etching using an etching solution.

13. The method of Claim 12, in which the etching solution includes a fluorine ion donor.

14. The method of Claim 13, in which the flourine ion donor comprises hydrofluoric acid and/or ammonium fluoride.

15. The method of Claim 13, in which the etching solution comprises a solution of hydrochloric acid and ammonia fluoride.

16. The method of Claim 15, in which the etching solution has a concentration of 0.1 to 99.9v% hydrochloric acid (37wt%) and 0.1 to 50v% of a fluorine ion donor (20wt%), and 0.1 to 99.0v% water.

17. The method of any one of Claims 12 to 16, in which the wet etching is carried out at a temperature of between 30 and 80⁰C, preferably around 35⁰C.

18. The method according to any one of Claims 12 to 17, in which the underlying thermally annealed film is etched by immersion in the etching solution for between about 30 and 300 seconds.

19. The method of any one of the preceding claims, further including the step of rinsing using deionised or distilled water after etching the acid resist polymer layer.

20. The method of Claim 19, in which the rinsing step comprises immersing in deionised or distilled water for between about 3 and 5 minutes.

21. The method of any one of the preceding claims, in which any residue of the acid resist polymer layer and the photoresist layer is removed by rinsing with a solvent.

22. The method of Claim 21 , in which the solvent comprises toluene and/or acetone.

23. The method of any one of the preceding claims, further including the step of rinsing using deionised or distilled water after the step of removing any residue of the acid resist polymer layer and the photoresist layer.

24. The method of Claim 23, in which the rinsing step comprises immersing in deionised or distilled water for between about 3 and 5 minutes.

25. The method of any one of the preceding claims, further comprising the step of drying the patterned thermally annealed film by heating or blowing.

26. The method of any one of the preceding claims, in which the film to be patterned is a thick or thin film of a ferroelectric or piezoelectric material.

27. The method of Claim 26, in which the film to be patterned comprises a film of PZT, PMN, PMN-PT, PMN-PZN-PT, PLZT or PMT-PT.

28. A method of etching a film using an etching solution, in which the etching is carried out at a temperature of between about 30 and 8O⁰C, and preferably at a temperature of around 35⁰C.

29. A method for etching and patterning of the thermally annealed ferroelectric/piezoelectric thin and thick films comprising steps of: a. coating an acid-resistant polymer mask on a ferroelectric/piezoelectric films deposited on a Si or other substrate; b. drying the polymer mask by heating to a temperature up to about 110 ⁰C for a sufficient period of time to drive off residual solvent from the acid-resistant polymer mask; c. applying a photoresist on the polymer mask, and forming the designed pattern of photoresist by photolithography; d. etching the acid-resistant polymer mask covered by photoresist using reactive ion beam by oxygen plasma to develop the designed pattern; e. immersing the ferroelectric/piezoelectric films, covered with patterned acid-resistant polymer mask in an etching solution for a sufficient time period to etch off portions of the ferroelectric/piezoelectric films that are not covered by the acid- resistant polymer; f. removing the patterned ferroelectric/piezoelectric films on substrate from the said etching solution; g. immersing the said ferroelectric/piezoelectric films on the substrate from step (f) into deionized or distilled water for a sufficient time period to remove residues remaining on the surface after step (f); h. immersing the said ferroelectric/piezoelectric films on the substrate from step (g) into a mask-removing solution for a sufficient time period, to remove the acid-resistant polymer mask; i. immersing the said ferroelectric/piezoelectric films on the substrate from step (h) in deionized water for a sufficient time period, to remove residues remaining on the film surface; and, j. drying the said ferroelectric/piezoelectric films on substrate from step (i) by N₂ blowing or by heating up to 15O⁰C for a sufficient time period, to remove moisture from the film surfaces.

30. A patterned ferroelectric or piezoelectric film formed in accordance with the method of any one of the preceding claims.