A method for dry etching lithium niobate

Abstract

The present invention relates to a method for dry etching lithium niobate, and belongs to the field of semiconductor processing. The etching step of the method for dry etching lithium niobate includes: placing patterned lithium niobate into an etcher; introducing a mixed etching gas Cl2, H2 and an inert gas into the etching chamber of the etcher, igniting the etcher by radio frequency, and starting etching; after the etching time is reached, the etching is completed. The present invention adopts a method for dry etching of lithium niobate, and its gas uses Cl2 / H2 to etch lithium niobate, which is different from the traditional fluorine-based etching lithium niobate system. The present invention can use dielectric materials or photoresists as masks. After being applied to the production line, it can optimize the production process, greatly improve production capacity, and save costs. Dry etching of lithium niobate can use traditional photoresist masks or dielectric materials such as SiO, SiN, Si as hard masks, and obtain better selectivity and good morphology.

Description

Technical Field

[0001] The invention relates to a method for dry etching lithium niobate, belonging to the field of semiconductor processing. Background Art

[0002] Lithium niobate (LN) crystal is a ferroelectric with an oxygen octahedral structure. It combines piezoelectric, electro-optical, acousto-optical, nonlinear optical properties and photorefractive effects, and has a wide range of applications in optical modulation, optical amplification, optical switching, optical storage and optical waveguides. It is one of the artificial crystals with the most optical properties and the best comprehensive indicators discovered so far. With the development of integrated optics, the requirements for device performance and integration are constantly increasing, and more requirements are also put forward for the etching process of LN.

[0003] Dry etching is a process that uses plasma atoms and molecules to interact with the surface of materials to form volatile substances or directly bombard the surface of samples to etch them. It can achieve anisotropic etching, that is, the longitudinal etching rate is much greater than the lateral etching rate, thereby ensuring the fidelity of small patterns after transfer. Inductively coupled plasma (ICP) etching technology in dry etching is increasingly used in semiconductor device manufacturing due to its advantages such as high control accuracy, good etching uniformity over a large area, and less pollution.

[0004] However, LN is a very difficult material to etch. Traditionally, ICP is used to etch LN, and a combination of fluorine-based gases (such as CF4, CHF3, SF6) and inert gases (such as Ar) are generally used. For chlorine-based gases such as Cl2, which are commonly used in dry etching, there are few reports in literature and patents about their use for etching LN. The Nb element in LN reacts chemically with F ions to produce easily volatile NBF3, NBF4, and NBF5; Li in lithium niobate reacts with F ions to produce non-volatile LiF that is deposited on the etched surface, reducing the etching rate and increasing the roughness of the etched surface. Ion bombardment of Ar gas can remove LiF deposits, increase the physical action in the etching reaction, increase the etching rate, and improve the smoothness of the etched surface.

[0005] LN etching rate is slow. In order to obtain a deeper etching depth, the mask often uses a metal film layer that is resistant to etching under F-based gas, such as metal Cr, Cu, and Al. However, the production of metal thin film requires special equipment, the production process is cumbersome, the cost is high, and it is difficult to remove after etching; the metal may damage the LN crystal sheet during the process of forming the pattern through the lift-off process, causing dark cracks in the wafer and affecting the subsequent process; after the metal mask forms the pattern, there are often vertical stripes on the side wall, and dry etching will bring the stripes to the LN side wall after etching, resulting in insufficient smoothness of the LN side wall after etching. Summary of the invention

[0006] In view of the above-mentioned shortcomings, the present invention provides a method for dry etching lithium niobate.

[0007] The present invention adopts the following technical solution:

[0008] The method for dry etching lithium niobate of the present invention comprises the following steps:

[0009] Step 1: Place the patterned lithium niobate into an etcher;

[0010] Step 2: introducing mixed etching gas Cl2, H2 and inert gas, wherein the inert gas is Ar gas, He gas, etc., and the etcher is ignited by radio frequency to start etching;

[0011] Step 3: After the etching time is reached, the etching is completed.

[0012] In the method for dry etching lithium niobate of the present invention, the lithium niobate in step 1 may be a lithium niobate wafer, and its tangent direction is not limited, and the wafer is the material to be etched;

[0013] In the method for dry etching lithium niobate described in the present invention, the lithium niobate sample described in step one is a wafer made of a lithium niobate film grown on a substrate, and its tangent direction is not limited; the wafer containing the lithium niobate film is used as the material to be etched. The substrate is a silicon substrate or other substrate, and thin film materials such as silicon dioxide may exist on the substrate. In the method for dry etching lithium niobate described in the present invention, the lithium niobate sample described in step one can use a hard mask such as SiO film, SiN film or Si film as a mask material in dry etching, and the sample should have been patterned before etching;

[0014] In the method for dry etching lithium niobate described in the present invention, in the step 1, the sample can use photoresist as a mask material in dry etching, and the sample should have been patterned before etching; in the method for dry etching lithium niobate described in the present invention, in the step 2, the etching gas H2 accounts for 20%-80% of the total gas flow.

[0015] In the dry etching method for lithium niobate of the present invention, in step 2, the etching gas Cl2 accounts for 5%-60% of the total gas flow.

[0016] In the dry etching method for lithium niobate of the present invention, the upper radio frequency power of the etcher is 200w-1200w, and the lower radio frequency power is 30w-600w.

[0017] In the dry etching method for lithium niobate of the present invention, the chamber pressure of the etcher during etching is less than 20mT.

[0018] In the dry etching method for lithium niobate of the present invention, the temperature of the coolant of the etcher during etching is 0-80°C.

[0019] Beneficial Effects

[0020] The present invention adopts a dry etching method for lithium niobate, and the gas used is Cl2 / H2 for lithium niobate etching, which is different from the traditional fluorine-based etching lithium niobate system. The present invention can use dielectric materials or photoresists as masks. After being applied to the production line, the production process can be optimized, the production capacity can be greatly improved, and the cost can be saved.

[0021] Due to the dry etching method of lithium niobate adopted by the present invention, the dry etching of lithium niobate can use a traditional photoresist mask or a dielectric material such as SiO, SiN, Si, etc. as a hard mask, and obtain a better selectivity and a good morphology.

[0022] Since the dry etching method of lithium niobate adopted in the present invention has a high selectivity ratio of lithium niobate to the mask, the thickness of the dielectric mask or the photoresist mask can be made thinner, thereby simplifying the patterning process and removal process of the mask.

[0023] In traditional production lines, metal masks are often used to etch lithium niobate, such as Cr, Al, Cu, etc. There are many disadvantages to using metal masks to etch LN.

[0024] The metal mask manufacturing process used in the prior art is complicated and costly; metal mask deposition requires special equipment, and metal mask patterning requires photolithography first, and then a complex process is used to transfer the pattern to the metal film layer. The photoresist mask used in the dry etching method of lithium niobate used in the present invention forms a pattern through the photolithography process; the dielectric mask deposition cost is low, and it is easy to pattern, and the patterning can even be completed in the same etching chamber as the dry etching step.

[0025] The metal mask used in the prior art is difficult to remove after etching, and the removal cost is high. However, the dielectric and photoresist used in the dry etching method of lithium niobate used in the present invention are easy to remove after dry etching, the removal cost is low, and the method is mature; it can even realize the mask removal process without breaking the vacuum after etching.

[0026] For lithium niobate crystal sheets, during metal mask deposition and patterning, the relevant processes are prone to damage the lithium niobate crystal, causing dark cracks in the crystal. The dry etching method of lithium niobate adopted by the present invention uses a dielectric mask or a photoresist mask to avoid the occurrence of dark cracks.

[0027] The dry etching method of lithium niobate adopted by the present invention is an effective way to reduce costs and simplify the process for the process of lithium niobate devices; it has the potential to become a new process route in the production line, greatly saving production costs and improving production capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of etching result 1 of SiO mask LN crystal slice;

[0029] Figure 2 Schematic diagram of SiO mask LN crystal sheet etching result 2;

[0030] Figure 3 Schematic diagram of etching result 1 of LN crystal slice with PR mask;

[0031] Figure 4 Schematic diagram of PR mask LN crystal etching result 2. DETAILED DESCRIPTION

[0032] In order to make the purpose and technical solution of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings of the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] The basic principle of the dry etching method of lithium niobate described in the present invention is as follows:

[0034] In the process of dry etching of lithium niobate, it is very important that the generated products can exist in gaseous form under vacuum conditions and be pumped away by a pump; among them, Nb compounds generally have a low boiling point and are easy to exist and be pumped away in gaseous form under high vacuum conditions, and will not affect the etching process; but Li compounds generally have a high boiling point and are easy to form non-volatile deposits even under high vacuum conditions, which hinder the etching process, reduce the steepness of the side wall, and cause the side wall to be rough.

[0035] LiF generated by traditional fluorine-based gas etching of lithium niobate has a boiling point of 1717°C at room temperature. In the present invention, H2 and Cl2 react chemically with Li2NbO3, and the LI compounds include LiH and LiCl; LiH has a boiling point of 950°C at room temperature and pressure, and LiCl has a boiling point of 1383°C at room temperature and pressure. Compared with LiF, LiH and LiCl have lower boiling points and are more volatile, which reduces the side wall inclination and roughness caused by deposition, and is conducive to obtaining a steep etching morphology and a smooth surface after etching. The traditional fluorine-based etching LN system generally obtains a side wall steepness of about 60-75°; while this system can obtain a side wall steepness of more than 80° after etching LN.

[0036] The present invention can use a traditional PR mask or SiO, SiN, Si and other dielectrics as a hard mask to etch LN, and obtain a good selectivity and a good morphology. For the LN process, it is an effective way to reduce costs and simplify the process, and avoids the disadvantages of using a metal mask to etch LN, such as complicated manufacturing process, high cost, difficult removal, lift-off process easily damages LN crystals, and easily causes LN side wall roughness; at the same time, because SiO and PR masks are easy to make the side wall smooth, it is beneficial to obtain a smooth LN side wall after etching.

[0037] The main etching gases used in the process of the present invention are Cl2 and H2, supplemented by an appropriate amount of inert gas; the ME (main etch) step with stable parameters is used in the etching process: the upper RF power is 200-1200w, the lower RF power is 30-600w, the proportion of H2 in the total gas flow is 20%-80%, the proportion of Cl2 in the total gas flow is 5%-60%, the chamber pressure is less than 20mT, and the coolant temperature during the process is 0-80°C. The etching material is crystalline LN or thin film LN, and the pattern is not limited. Under appropriate parameters, the etching process can obtain an ideal morphology, a more ideal etching rate and a higher selectivity to the mask.

[0038] Example 1

[0039] like Figure 1 , Figure 2 In the embodiment shown, the etching process uses an inductively coupled plasma etcher (ICP), model HAASRODE-E200. The sample used is a LN crystal sheet, size 1cm*1cm, film structure: 2.1μmSiO / 500um Z-cut LN Sub, SiO hard mask has completed the patterning process. The pattern is CD about 3μm lines.

[0040] Transfer the sample into the chamber of the etcher. Set appropriate etching parameters, such as upper RF power 600w, lower RF power 100w, chamber pressure 5mT, process temperature 20℃, and process ME time 10min; introduce the mixed Cl2, H2 and Ar, ignite the RF, and start etching.

[0041] Transfer the sample into the chamber of the etcher. Set appropriate etching parameters, such as upper RF power 600w, lower RF power 100w, chamber pressure 5mT, process temperature 20℃, and process ME time 10min; introduce mixed Cl2, H2 and Ar, ignite the RF, and start etching. After etching, take out the sample and use SEM to take a cross-section to check the etching morphology.

[0042] Combination Figure 1 , Figure 2According to the experimental results after etching: ER = 46.7nm / min, LN / SiO selectivity is 1.57, the steepness is about 81°, the side wall is smooth, and the bottom is rough due to the value before etching. It can be seen that the traditional fluorine-based etching LN system generally obtains a side wall steepness of about 60-75°; while this system can obtain a side wall steepness of more than 80° after etching LN.

[0043] Example 2

[0044] like Figure 3 , Figure 4 As shown: In this embodiment, the etching process uses an inductively coupled plasma etcher (ICP), model HAASRODE-E200. The sample used is a LN crystal sheet, size 1cm*1cm, film structure: 1.8μmPR / 500um Z-cut LN Sub, the pattern is a CD groove of about 2μm.

[0045] Transfer the sample into the chamber of the etcher. Set appropriate etching parameters, such as upper RF power 600w, lower RF power 80w, chamber pressure 5mT, process temperature 20℃, and process ME time 10min; introduce mixed Cl2, H2 and Ar, ignite the RF, and start etching. After etching, take out the sample and use SEM to take a cross-section to check the sample etching morphology.

[0046] ER=53.7nm / min, LN / PR selectivity is 1.34, steepness is about 71°, and the sidewall and bottom are smooth. According to the experimental results of the above two embodiments, the selectivity of lithium niobate to dielectric material or photoresist in etching is about 1:1. The traditional fluorine-based etching lithium niobate system generally obtains a sidewall steepness of about 60-75°; while this system can obtain a sidewall steepness of more than 80° after etching lithium niobate; at the same time, because SiO and PR masks are easy to make the sidewall smooth, and the products in the etching are easier to volatilize than the traditional process, the sidewall deposition is less, which is conducive to obtaining a smooth sidewall after etching.

[0047] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for dry etching lithium niobate, characterized in that: The etching steps are as follows: Step 1, placing the patterned lithium niobate into an etcher; the lithium niobate is a lithium niobate wafer, and the lithium niobate wafer is used as the material to be etched; the lithium niobate is a wafer made of a lithium niobate film grown on a substrate, and the wafer containing the lithium niobate film is used as the material to be etched; The lithium niobate wafer and the wafer containing the lithium niobate film use a SiO film, a SiN film or a Si film as a mask material in dry etching, and the mask material has been patterned; the SiO film, the SiN film or the Si film is a hard mask; Step 2: introducing the mixed etching gas Cl2, H2 and inert gas into the etching chamber of the etcher, igniting the etcher by radio frequency, and starting etching; The proportion of etching gas H2 in the total gas flow is between 20% and 80%; The proportion of etching gas Cl2 in the total gas flow is 5%-60%; Step 3: After the etching time is reached, etching is completed; The upper RF power of the etcher is: 200w-1200w, and the lower RF power is: 30w-600w; the coolant temperature of the etcher during etching is 0-80℃.

2. The method for dry etching lithium niobate according to claim 1, characterized in that: The lithium niobate wafer and the wafer containing the lithium niobate film use photoresist as a mask material in dry etching, and the mask material has been patterned.

3. The method for dry etching lithium niobate according to claim 1, characterized in that: The chamber pressure of the etcher during etching is less than 20mT.

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