Low-angle profile ion beam etching method and application

Abstract

The application belongs to the technical field of semiconductor processing, and particularly relates to an ion beam etching method for low-angle morphology and application. A metal film to be etched is deposited on a wafer surface, then a photoresist mask is spin-coated and exposed and developed to complete patterning of the photoresist mask; then high-temperature hard mask treatment is performed, the photoresist mask is caused to produce thermal reflow by high temperature to reduce the angle of the photoresist mask; the angle of the sidewall of the hard-masked photoresist mask is obtained, the ion beam etching incidence angle is adjusted, the ion beam incidence angle and the sidewall angle of the photoresist mask are complementary, and etching is performed until completion. The method can control the steepness of the sidewall of the ion beam etching groove to be within 50°, and no sidewall deposition occurs, which greatly increases the reliability between metal layers in a multilayer wiring process.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of semiconductor processing, and particularly relates to an ion beam etching method for low-angle morphology and application. BACKGROUND

[0002] Ion beam etching technology is a dry etching process developed in the 1970s, which is widely used in the etching process of Au (gold), Pt (platinum), Ag (silver) thin film and other stable chemical properties of metal wires in the field of micro-nano device manufacturing due to high line width processing precision, adjustable etching morphology angle, and multiple etching material types.

[0003] In the conventional application of ion beam etching, it is desirable to obtain high anisotropy to ensure the processing line width precision. However, in the practical application of multi-layer metal wiring, too high steepness is not conducive to the conformal deposition of silicon oxide film, which will increase the risk of leakage between the metal wire layers. In addition, when the aspect ratio of the trench of the multi-layer metal wiring is large or the etching mask steepness is too large, because the sputtering particles have a certain angle, not all sputtering particles can fly out of the groove, and a part of the sputtering particles with large angles will hit the groove wall that has been etched, forming a re-deposition process, i.e. Fence (side wall), which will further deteriorate the insulation between the metal wire layers.

[0004] In order to avoid the above problems, without affecting the performance of the device, low-angle and smooth and gentle etching side wall becomes the preferred solution to improve the insulation between the metal wire layers.

[0005] At present, the most conventional method for low-angle and smooth and gentle ion beam etching side wall is double-angle etching (see Figure 1 ). That is, a lower ion incidence angle alpha (generally selected from 10° to 30°) is first selected as the main etching angle for quickly opening the etching trench, at this time the trench side wall is approximately vertical, and due to the re-deposition effect, a certain height of side wall will be formed on the trench side wall; the second step selects a large angle beta as the auxiliary etching (generally selected from 65° to 75°), the etching ion beam is difficult to enter the bottom of the trench, and more is to remove the side wall at the trench side wall, thereby forming a low-angle and smooth and gentle side wall. However, this method has certain limitations, the auxiliary etching has low efficiency in removing the side wall, and a long process time is required; in addition, the auxiliary etching will damage the main etching side wall morphology, which is easy to form double side wall angles, and the side wall angle reduction range is limited.

[0006] Therefore, it is a technical problem to be solved at present to provide a simple and efficient etching method with good etching effect for low-angle, smooth and gentle etching. SUMMARY

[0007] To solve the above technical problems, one of the purposes of the present application is to provide a low-angle profile ion beam etching method.

[0008] The technical solutions adopted by the present application are as follows:

[0009] A low-angle profile ion beam etching method, comprising the following steps:

[0010] S1. Depositing a metal thin film to be etched on the surface of a wafer, then spin-coating a photoresist mask with a set thickness, performing exposure and development processing, and completing the patterning of the photoresist mask;

[0011] S2. Performing high-temperature hardening treatment, generating thermal reflow of the photoresist mask through high temperature to reduce the photoresist mask angle, the photoresist mask angle being the included angle between the sidewall of the photoresist mask and the bottom edge of the photoresist mask, and the high-temperature hardening temperature being 130-150℃;

[0012] S3. Obtaining the sidewall angle of the hardening photoresist mask;

[0013] S4. Adjusting the ion beam etching incident angle, making the ion beam incident angle and the photoresist mask sidewall angle complementary, and performing etching until completion, so that the ion beam etching trench formed on the metal thin film has a low inclination angle and a smooth sidewall without sidewall deposition.

[0014] Preferably, the metal thin film is any one of Pt, Au, and Ti, and the deposition thickness is 0.1-1 µm.

[0015] Preferably, the set thickness of the photoresist mask is 1-3 µm.

[0016] Preferably, in the exposure and development processing, the exposure dose is 100-300 mJ / cm 2 , and the focal length is ±0.5 μm.

[0017] Preferably, the high-temperature hardening is performed until the photoresist mask angle is between 40-60°.

[0018] Preferably, in the step S3, the photoresist mask is sliced and sampled by a focused ion beam, and then the sidewall angle of the photoresist mask is obtained using a scanning electron microscope.

[0019] Preferably, the ion beam etching energy is 50-700 eV, the screen grid current is 160-740 mA, the screen grid voltage is 200-700 V, and the acceleration voltage is 40-140 V.

[0020] Preferably, the working gas used in the ion beam etching is argon.

[0021] The second object of the present application is to provide an application of the ion beam etching method with low-angle topography in the preparation of a multi-metal wiring layer.

[0022] The third object of the present application is to provide a multi-layer metal wiring layer prepared by the ion beam etching method with low-angle topography.

[0023] The fourth object of the present application is to provide a chip comprising the multi-layer metal wiring layer.

[0024] The present application has the following advantages:

[0025] 1) The ion beam etching method provided by the present application can obtain smooth sidewalls with low inclination angle and no sidewall deposition by single-angle etching, avoiding technical problems such as great difficulty in processing low-angle topography, serious influence of etching rate on incident angle, and difficulty in removing sidewall Fence, which are caused by conventional double-angle etching.

[0026] 2) In the conventional application of photoresist, thermal reflow is a phenomenon that should be avoided. In order to ensure the line width accuracy, the photoresist needs to have high steepness, so a low hardening temperature (below 100 DEG C) is often set in the hardening process to avoid deformation of the photoresist caused by heat. However, the present application breaks the inherent thinking and uses high-temperature hardening (130-150 DEG C) process to make the photoresist produce thermal reflow and destroy the original topography of the photoresist. The mask angle of the photoresist after reflow is significantly reduced. The FIB (focused ion beam) is used to obtain the sidewall angle of the photoresist mask. According to the SEM test, the sidewall angle of the photoresist mask formed by controlling the hardening time (2-30 min) can be controlled below 60 DEG.

[0027] 3) The present application ingeniously connects the ion beam etching exit angle with the photoresist mask angle after thermal reflow. By setting a reasonable ion incident angle (90 DEG minus the photoresist mask angle), the re-deposition of the ion etching product on the photoresist sidewall can be greatly reduced at this angle, and the sidewall angle of the etching trench can be effectively reduced.

[0028] 4) By using the method of the present application, the steepness of the sidewall of the ion beam etching trench can be controlled within 50 DEG, and there is no sidewall deposition on the mask sidewall, which greatly increases the reliability between the metal layers in the multi-layer wiring process. The method can also save process time by single-angle etching, greatly improving the etching efficiency and improving the equipment capacity. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The figure is a schematic diagram of the double-angle etching in the prior art. In the figure, A is the main etching at a low ion incident angle, and B is the auxiliary etching at a high ion incident angle.

[0030] Figure 2Figure A is a schematic diagram of a photoresist mask patterning process, Figure B is a schematic diagram of a high-temperature hardened photoresist mask, Figure C is a schematic diagram of an ion beam incident angle, and Figure D is a schematic diagram of the final effect of the etching process.

[0031] Figure 3 Figure A is a schematic diagram of a photoresist mask patterning process, Figure B is a schematic diagram of a high-temperature hardened photoresist mask, Figure C is a schematic diagram of an ion beam incident angle, and Figure D is a schematic diagram of the final effect of the etching process.

[0032] Figure 4 Figure A is a schematic diagram of a photoresist mask patterning process, Figure B is a schematic diagram of a high-temperature hardened photoresist mask, Figure C is a schematic diagram of an ion beam incident angle, and Figure D is a schematic diagram of the final effect of the etching process. DETAILED DESCRIPTION

[0033] Unless otherwise defined, all terms used herein have meanings commonly understood by those skilled in the art.

[0034] The technical solutions of the present application will be described in more detail below with reference to the embodiments:

[0035] Embodiment 1

[0036] Reference Figure 2 A low-angle profile ion beam etching method, comprising the following steps:

[0037] S1. Au / Ti composite film of 3000 Å / 300 Å is deposited on the wafer surface, then 1.0 μm of photoresist is spin-coated, and after the photoresist mask is exposed and developed, the photoresist mask is patterned.

[0038] S2. The patterned wafer is placed in a high-temperature oven or hot plate for high-temperature hardening treatment, the oven or hot plate hardening temperature is 150°C, the hardening time is 2 min, and the photoresist mask is heated to produce thermal reflow, thereby reducing the angle of the photoresist mask.

[0039] S3. The steepness of the photoresist mask is measured using FIB, and the bottom edge of the photoresist is taken as the reference point. According to the measurement, the mask angle after hardening in this embodiment 1 is 5 .

[0040] S4. The wafer after hardening is placed in an ion beam etching machine, the ion beam etching incident angle is adjusted so that the ion beam incident angle and the sidewall angle of the photoresist mask are complementary, i.e. 35°, and then a single-angle etching process is used for etching until the process is completed.

[0041] In this embodiment, the energy used for etching is 500 eV, the screen grid current BMI is 540 mA, the screen grid voltage BMV is 500 V, the acceleration voltage ACV is 120 V, and the rotation speed is 10 rpm. In actual use, ion beam etching can be achieved by using conventional techniques, and various parameters of etching can be adjusted adaptively according to specific conditions, which are not specially limited in this application.

[0042] In ion beam etching, optical etching endpoint monitoring is used, and etching is stopped when the etching reaches a predetermined film layer.

[0043] Embodiment 2

[0044] A low-angle profile ion beam etching method, comprising the following steps:

[0045] S1. A Pt / Ti composite film with a thickness of 6000 Å / 300 Å is deposited on the wafer surface, and then 2 µm of photoresist is spin-coated. After the photoresist mask is subjected to exposure and development treatment, the patterning of the photoresist mask is completed.

[0046] S2. The patterned wafer is placed in a high-temperature oven or hot plate for high-temperature hardening treatment, and the hardening temperature of the oven or hot plate is 120 °C, and the hardening time is 5 min.

[0047] S3. The steepness of the photoresist mask is measured using FIB, and the bottom edge of the photoresist is taken as the reference. According to the measurement, the mask angle after hardening in this embodiment 2 is 52 °.

[0048] S4. The wafer after hardening is placed in an ion beam etching machine, the incident angle of the ion beam etching is adjusted to be complementary to the sidewall angle of the photoresist mask, i.e. 38 °, and then single-angle etching process is used for etching until the process is completed.

[0049] In this embodiment, the etching parameters are the same as those in embodiment 1.

[0050] Comparative Example

[0051] A low-angle profile ion beam etching method using double-angle etching, comprising the following steps:

[0052] S1. A Au / Ti composite film with a thickness of 3000 Å / 300 Å is deposited on the wafer surface, and then 1.0 µm of photoresist is spin-coated. After the photoresist mask is subjected to exposure and development treatment, the patterning of the photoresist mask is completed.

[0053] S2. The patterned wafer is placed in a high-temperature oven or hot plate for high-temperature hardening treatment, and the hardening temperature of the oven or hot plate is 120 °C, and the hardening time is 2 min. Under this condition, the angle of the photoresist changes only slightly: the steepness of the photoresist mask is measured using FIB, and the bottom edge of the photoresist is taken as the reference. Referring to, measured, after hard mask, the mask angle is 82°.

[0054] S3. The wafer after hard mask is placed in the ion beam etching machine, the main etching incident angle of the ion beam is set to 10°, and the film layer is etched completely; then 65° is used as the auxiliary etching incident angle to modify the Fence on the photoresist sidewall until the process is completed.

[0055] In this embodiment, the etching parameters are the same as those in Embodiment 1.

[0056] Results

[0057] In Embodiments 1 and 2, the materials to be etched are both stable noble metal composite film layers, and the thicknesses thereof are 3000 Å and 6000 Å respectively. Due to the limitation of etching selectivity, the thicknesses of the photoresist masks used are 1 μm and 2 μm respectively. In Embodiment 1, 150℃ and 2 min are used as the hardening conditions of the photoresist mask thermal reflow, and in Embodiment 2, 120℃ and 5 min are used as the hardening conditions of the photoresist mask thermal reflow. After hardening, the photoresist mask angles of the two are close (55° and 52° respectively). According to the photoresist mask angle, the ion beam etching incident angle is slightly adjusted, and other etching conditions remain unchanged. After etching, the etching groove sidewall has a low steepness (maintained at about 45°), and the mask sidewall has no obvious Fence deposition.

[0058] Figure 3 The etching effect diagram of the comparative example is shown in FIG. 2, Figure 4 The ion beam etching method effect diagram in Embodiment 1 is shown in FIG. 1, and the steepness is 44.6°. It can be seen that the sidewall steepness after the ion beam etching of the present application is low, the sidewall is flat, and the sidewall Fence deposition is obviously improved.

[0059] The above is only a preferred embodiment of the present application, and does not limit the present application; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any modification, equivalent replacement and improvement within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. An ion beam etching method for low-angle morphology, characterized in that, Includes the following steps: S1. Deposit a thin metal film to be etched on the wafer surface, then spin-coat a photoresist mask of a set thickness, and perform exposure and development to complete the patterning of the photoresist mask; S2. Perform high-temperature hardening treatment, which causes thermal reflow of the photoresist mask through high temperature, thereby reducing the photoresist mask angle. The photoresist mask angle is the angle between the sidewall of the photoresist mask and the bottom edge of the photoresist. The high-temperature hardening temperature is 130~150℃. S3. Obtain the sidewall angle of the photoresist mask after hardening; S4. With the wafer surface perpendicular as Referring to the reference, the incident angle of the ion beam etching is adjusted so that the incident angle of the ion beam is complementary to the sidewall angle of the photoresist mask after hardening, and etching is performed until completion, so that the ion beam etched trenches formed on the metal thin film have smooth sidewalls with low tilt angle and no sidewall deposition.

2. The ion beam etching method for low-angle morphology as described in claim 1, characterized in that, The metal thin film is any one of Pt, Au, and Ti, and the deposition thickness is 0.1~1 µm.

3. The ion beam etching method for low-angle morphology as described in claim 1, characterized in that, The set thickness of the photoresist mask is 1~3 µm.

4. The ion beam etching method for low-angle morphology as described in claim 1, characterized in that, During the exposure and development process, the exposure dose is 100~300 mJ / cm2, and the focal length is ±0.5 μm.

5. The ion beam etching method for low-angle morphology as described in claim 1, characterized in that, The high-temperature hardening film is hardened until the angle of the photoresist mask is between 40 and 60°.

6. The ion beam etching method for low-angle morphology as described in claim 1, characterized in that, In step S3, the photoresist mask is sliced ​​and sampled using a focused ion beam, and then the sidewall angle of the photoresist mask is obtained using a scanning electron microscope.

7. The ion beam etching method for low-angle morphology as described in claim 1, characterized in that, The ion beam etching energy is 50~700 eV, the grid current is 160~740 mA, the grid voltage is 200~700 V, the accelerating voltage is 40~140 V, and the working gas is argon.

8. The application of the low-angle morphology ion beam etching method as described in claim 1 in the fabrication of multi-metal wiring layers.

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