Chemical etching solution and method for selectively etching titanium

Abstract

The invention relates to a chemical etching solution for chemically etching a titanium-based material, the solution comprising: - from 26 wt% to 39 wt% hydrogen peroxide; - from 1 wt% to 6 wt% tribasic potassium phosphate (K3PO4); - from 0.015 wt% to 0.2 wt% of a compound chosen from among diethylenetriamine penta(methylene phosphonic acid) (DTPMP), aminotris(methylenephosphonic acid) (ATMP) and mixtures thereof; - water, wherein the weight percentages are expressed relative to the weight of the chemical etching solution, the solution having a pH of 6.5 to 8.6. The invention also relates to a method for chemically etching a layer of a titanium-based material on a microelectronic device by means of the etching solution and to a method for preparing the etching solution.

Description

[0001] CHEMICAL ETCHING SOLUTION AND METHOD FOR ETCHING

[0002] SELECTIVELY TITANIUM

[0003] TECHNICAL FIELD OF THE INVENTION

[0004] A stable chemical etching solution for etching titanium-based materials, including titanium-based barrier layers formed on microelectronic devices, while being substantially selective with other materials potentially exposed thereto, such as copper, aluminum / copper, tin or its alloys, and / or dielectric materials.

[0005] The invention also relates to a method of etching titanium-based materials using said solution.

[0006] STATE OF THE ART

[0007] In the manufacture of new generation electrical contacts, for example copper pillars, a barrier layer is deposited before copper deposition to reduce diffusion in dielectric materials and improve adhesion performance.

[0008] Such a barrier layer can be deposited either by CVD (Chemical Vapor Deposition) or PVD (Physical Vapor Deposition) methods, and generally has a thickness less than or equal to 100 nm.

[0009] The metals of choice for such barrier layers are titanium, titanium nitride or titanium tungsten.

[0010] In the fabrication of copper pillars, the titanium-based barrier layer is deposited on a dielectric or polyimide surface already having contact holes with the underlying copper metal layers and possibly aluminum pads, and then a copper seed layer is deposited by PVD.

[0011] A thick layer of photoresist is applied and developed to form holes through which electrochemical copper can grow, and optionally a thin layer of tin or tin / silver alloy is deposited over the copper.

[0012] After removal of the photoresist and the remaining thin PVD-deposited copper seed layer, the titanium-based barrier must be selectively removed relative to other exposed metals to form isolated conductive pillars.

[0013] Copper removal is usually carried out in mixtures of dilute sulfuric acid or phosphoric acid and hydrogen peroxide. Some aluminum pads may be partially exposed due to, for example, lithographic misalignment.

[0014] It is then desirable to have a barrier layer removal solution that is selective with copper, aluminum / copper, tin or tin alloys, as well as with dielectric materials and polyimide.

[0015] Removal of the titanium-based barrier layer is generally carried out with a heated concentrated hydrogen peroxide solution (comprising 5 to 30% by weight of hydrogen peroxide), such as with the cleaning solution SCl (Standard Clean 1 for an ammonia solution mixed with hydrogen peroxide) or a similar mixture or with very dilute hydrogen fluoride-based solutions at room temperature used specifically for dissolving pure titanium.

[0016] Conventional solutions for removing the barrier layer of titanium-based material suffer from several weaknesses.

[0017] For example, hydrogen peroxide can hardly be recirculated due to its susceptibility to decomposition and the rapid change in etching rate occurring when contaminated with metals. In addition, when titanium nitride or titanium is used as a barrier layer, pure hydrogen peroxide can hardly remove the titanium oxide usually present on the surface and at the interface with the dielectric. The SC l solution corresponding to a mixture of hydrogen peroxide and ammonium hydroxide can improve the etching rate on titanium oxide but becomes very difficult to control with regard to the selectivity with aluminum. Indeed, the mixture of ammonium hydroxide and hydrogen peroxide at the point of use would require extremely specific equipment to allow the mixture to remain at a pH below 8 to ensure its selectivity with aluminum and control of copper oxidation.

[0018] Dilute hydrogen fluoride solutions, on the other hand, can readily dissolve titanium oxide but will not dissolve titanium nitride or titanium tungsten. Furthermore, dilute hydrogen fluoride solutions are incompatible with aluminum, tin or its alloys, and silicon oxide-based dielectrics.

[0019] Furthermore, it is quite difficult to control etch profiles with hydrogen fluoride-based etchants, due to the very high etch rates even at very low hydrogen fluoride concentrations because dissolution does not stop as soon as the rinsing step begins.

[0020] Complexing agents such as EDTA (Ethylenediamine tetraacetic acid) and CDTA (Trans-diamino-1,2-cyclohexane, N,N,N,N tetraacetic acid) can be added to the hydrogen peroxide mixture with an inorganic base to increase stability and allow recirculation, but this can cause problems in waste treatment plants because these molecules, which are very effective at capturing metals, are difficult to eliminate.

[0021] Patent application EP3436621 thus describes a solution for chemical etching of titanium-based materials comprising hydrogen peroxide, potassium hydroxide and a complexing agent which is preferably CDTA because the chemical etching solutions obtained are then the most stable.

[0022] STATEMENT OF THE INVENTION

[0023] From an industrial point of view, it is desirable to have a chemical etching solution that has the following advantages: it is stable for a sufficient time to be usable industrially, it can rapidly dissolve titanium-based barriers selectively to exposed materials (e.g. copper, copper aluminum, tin or tin alloys, dielectric materials and polyimide) and this, with easy control of the etching profile, it can be recirculated in the presence of metals and it meets environmental criteria in terms of toxicity.

[0024] Surprisingly, it has been found that a chemical etching solution comprising hydrogen peroxide, a complexing agent derived from phosphonic acid such as diethylenetriaminepentamethylenephosphonic acid (DTPMP) or aminotrimethylenephosphonic acid (ATMP), and potassium tribasic phosphate (K3PO4) has optimized properties in terms of stability over time, particularly in the presence of metallic contaminants, and allows to etch titanium-based barriers selectively to other exposed materials such as copper, aluminum / copper, tin and its alloys, or dielectric materials and polyimide, while maintaining good control of the etching profiles. In addition, such a solution is satisfactory in terms of environmental criteria.

[0025] Summary of the invention

[0026] The invention relates to a solution for chemical etching of a titanium-based material comprising: from 26% by weight to 39% by weight of hydrogen peroxide, from 1% by weight to 6% by weight of potassium tribasic phosphate (K3PO4), from 0.015% by weight to 0.2% by weight of a compound chosen from diethylenetriaminepentamethylenephosphonic acid (DTPMP), aminotrimethylenephosphonic acid (ATMP) and mixtures thereof, water, the percentages by weight being expressed relative to the weight of the chemical etching solution, said solution having a pH of 6.5 to 8.6.

[0027] The invention also relates to a method for chemically etching a layer of a titanium-based material on a microelectronic device, said method comprising bringing said layer into contact with the chemical etching solution as described above for a time sufficient to remove said layer, said titanium-based material being made of titanium, titanium nitride, titanium-tungsten or a mixture thereof, preferably titanium.

[0028] Advantageously, the chemical etching solution, after etching the microelectronic device, is reused to etch one or more other microelectronic devices.

[0029] Advantageously, the chemical etching solution is heated and brought into contact with the microelectronic device at a temperature of 20°C to 60°C, preferably 35°C to 50°C.

[0030] The invention also relates to a method for preparing a chemical etching solution as described above comprising the mixture: of a composition comprising: o potassium tribasic phosphate (K3PO4), o the compound chosen from diethylenetriaminepentamethylenephosphonic acid (DTPMP), aminotrimethylenephosphonic acid (ATMP) and mixtures thereof o water, and an aqueous solution of hydrogen peroxide at a mass concentration of hydrogen peroxide of 30% by weight to 40% by weight relative to the weight of the aqueous solution. to reach a pH of 6.5 to 8.6.

[0031] Advantageously, the chemical etching solution is prepared using a point-of-use mixing technique consisting of mixing just before dispensing the aqueous hydrogen peroxide solution and the composition comprising the potassium phosphate salt, the compound selected from diethylenetriaminepentamethylenephosphonic acid (DTPMP), aminotrimethylenephosphonic acid (ATMP) and mixtures thereof and water.

[0032] Other aspects of the invention are as described below and in the claims.

[0033] Definitions

[0034] In this text, the expression "the remainder being water" means that the percentage by weight of water corresponds to 100% less the sum of the percentages by weight of the other chemical substances present in the composition.

[0035] As used herein, the term "microelectronic device" means semiconductor substrates, flat panel displays, phase change memory devices, solar panels, and other products, including solar cell devices, photovoltaic systems, and microelectromechanical systems (MEMS), manufactured for use in microelectronics, integrated circuit, energy harvesting, or computer chip applications.

[0036] It is to be understood that the terms “microelectronic device”, “microelectronic substrate” and “microelectronic device material” are not intended to be limiting in any way and include any substrate or structure that will eventually become a microelectronic device or microelectronic assembly.

[0037] "Titanium-based material" means a material consisting of Titanium, Titanium Nitride or Titanium Tungsten or a mixture thereof. It is understood that the surface of the material may have a layer of titanium oxide due to the oxidation of titanium. Thus, a layer of titanium-based material may have a superficial layer of titanium oxide, on the surface and at the interface with the dielectric.

[0038] As used herein, the term "Titanium-based barrier layer" means any thin film with a thickness ranging from 5 nm to 500 nm, composed of Titanium, Titanium Nitride, Titanium Tungsten or a mixture thereof. As used herein, the term "approximately" is intended to correspond to ± 5% of the stated value.

[0039] As used herein, the term "room temperature" means a temperature ranging from 20°C to 25°C.

[0040] As defined herein, the term "complexing agent" includes compounds that are understood by a person skilled in the art to be complexing, chelating, sequestering agents, and combinations thereof. Complexing agents chemically combine or physically associate with the metal atom and / or metal ion to be removed. Complexing agents are used to capture contaminants, particularly metal contaminants, in the chemical etching solution, thereby improving the stability of the chemical etching solution and thus limiting attack or corrosion of potentially exposed materials other than titanium-based materials. The terms "complexing agents" and "anti-corrosion agents" are equivalent herein.

[0041] The terms "aqueous hydrogen peroxide solution" and "oxygenated water" are equivalent here.

[0042] The "percentages" of a compound, as indicated herein, are percentages by weight or mass of said compound relative to the weight of the composition comprising said compound. By "the etching solution consists of", it is understood that the etching solution does not include components other than those cited.

[0043] By "the etching solution consists essentially of" is meant that the etching solution contains other components than the mandatory components in the etching solution, provided that the essential characteristics of the etching solution, such as its stability, the etching rate of titanium-based materials and the selectivity of the etching with respect to the exposed materials are not affected by the presence of these components.

[0044] By "the etching solution is stable or has satisfactory stability" is meant an etching solution whose stability is evaluated in the stability test described in the examples (point 1.3) and for which the variation in pH (A[pH]) in absolute value ranges from 0 to 10% and the variation in hydrogen peroxide content (AfFLCL]) in absolute value ranges from 0 to 35%.

[0045] FIGURES

[0046] [Fig. 1] illustrates the evolution of the thickness of the remaining titanium layer (expressed as a percentage of the initial thickness) according to the etching test described in paragraph 1.1. of the examples as a function of the immersion time for the different etching solutions of example 1 at 25°C (• solution 1 / ▲ solution 2 / ♦ solution 3).

[0047] [Fig. 2] illustrates the evolution of the thickness of the remaining titanium layer (expressed as a percentage of the initial thickness) according to the etching test described in paragraph 1.1. of the examples as a function of the immersion time and temperature for the etching solution of example 6.

[0048] [Fig. 3] illustrates the evolution of the etching speed in nm / min of the titanium layer according to the etching test described in paragraph 1.1. of the examples as a function of the temperature for the etching solution of example 6.

[0049] [Fig. 4] illustrates the effectiveness of cleaning the titanium layer of copper pillars according to example 6 by etching solutions aged at 50°C for different durations: top left (1): chemical etching solution aged for 5 min at 50°C top right (2): chemical etching solution aged for 1h30 at 50°C bottom left (3): chemical etching solution aged for 3h at 50°C bottom right (4): chemical etching solution aged for 6h at 50°C.

[0050] [Fig. 5] represents the foot of a copper pillar etched according to example 6 using the unaged chemical etching solution 1 (left photo - A) and this same etching solution aged for 2 hours at 50°C (right photo - B).

[0051] DETAILED DESCRIPTION OF THE INVENTION

[0052] The main difficulty in developing an effective chemical etching solution for a titanium-based barrier layer lies in the need to etch the titanium oxide surface or interface at an acceptable rate while remaining selective with respect to exposed metals, such as copper, aluminum / copper or tin.

[0053] The inventors know that titanium and tungsten materials can be dissolved in hydrogen peroxide at an appreciable rate.

[0054] The inventors also know that increasing the pH by adding ammonia or any base can improve not only the etching rate on bulk materials, but also the dissolution rate of titanium oxide, due to the increase in the concentration of HCh' which is considered to be the active species in the etching of titanium-based materials.

[0055] However, given the current limitations of most industrial equipment, it is difficult to maintain a point-of-use mixture with a stable pH. As a result, corrosion of exposed metals and decomposition of hydrogen peroxide are difficult to control.

[0056] In addition, complexing agents such as CDTA help to stabilize etching solutions, but their use poses environmental problems.

[0057] The inventors have developed a chemical etching solution that meets the needs expressed.

[0058] The inventors thus surprisingly discovered that the use of a complexing agent derived from phosphonic acid of the diethylenetriaminepentamethylenephosphonic acid (DTPMP) or aminotrimethylenephosphonic acid (ATMP) type and a potassium phosphate salt makes it possible to optimize the properties of etching solutions based on hydrogen peroxide.

[0059] Without wishing to be bound by any theory, potassium phosphate could allow the generation of HOO' ions for the attack of titanium while allowing the stabilization of the pH by exerting a buffer effect in the chemical etching solution.

[0060] A first subject of the invention thus relates to a solution for chemical etching of a titanium-based material comprising: from 26% by weight to 39% by weight of hydrogen peroxide, from 1% by weight to 6% by weight of potassium tribasic phosphate (K3PO4), from 0.015% by weight to 0.2% by weight of a compound chosen from diethylenetriaminepentamethylenephosphonic acid (DTPMP), aminotrimethylenephosphonic acid (ATMP) and mixtures thereof, water, the percentages by weight being expressed relative to the weight of the chemical etching solution, said solution having a pH of 6.5 to 8.6.

[0061] By the chemical etching solution comprising a potassium phosphate salt as described above, it is to be understood that the chemical etching solution can be prepared from said potassium phosphate salt.

[0062] Phosphate salt can also be generated once in solution by mixing phosphoric acid and potassium hydroxide.

[0063] Potassium tribasic phosphate is used according to the present invention because its aqueous solubility is higher than that of sodium tribasic phosphate, which allows more concentrated salt solutions to be obtained. This is particularly advantageous when the chemical etching solution is prepared by mixing an aqueous concentrate comprising the phosphate salt and a concentrated hydrogen peroxide solution.

[0064] Furthermore, surprisingly, etching solutions obtained from potassium tribasic phosphate exhibit better chemical selectivity towards exposed materials such as copper, aluminium or polyimide than etching solutions obtained from ammonium phosphate salts.

[0065] The percentage by weight of potassium tribasic phosphate in the chemical etching solution is 1% to 6%, preferably 1 to 4%, more preferably 1 to 2%.

[0066] When the weight percentage of potassium tribasic phosphate in the etching solution is less than 1%, the stability of the etching solution is reduced.

[0067] When the weight percentage of tribasic potassium phosphate in the chemical etching solution is greater than 6%, the pH of the resulting solution may be too high, which can lead to excessive attack of exposed materials such as aluminum or to an etching speed that is too fast, making the etching operation difficult to control.

[0068] The chemical etching solution according to the invention further comprises hydrogen peroxide.

[0069] The source of hydrogen peroxide may be commercially available hydrogen peroxide of any starting concentration equal to or greater than 30% by weight with or without phosphate / phosphonate / stanate stabilizers, but may also be prepared by diluting a more concentrated solution of hydrogen peroxide with pure water.

[0070] The weight percentage of hydrogen peroxide in the chemical etching solution is chosen to optimize the etching of titanium and the stability of the chemical etching solution.

[0071] It is 26 to 39%, preferably 26% to 35%, more preferably 27 to 30%. The percentage by weight of hydrogen peroxide entering into the chemical etching solution of the present invention is expressed as pure hydrogen peroxide relative to the total weight of the chemical etching solution.

[0072] The chemical etching solution according to the invention also comprises a complexing agent making it possible to improve the stability of the chemical etching solution and which is chosen from diethylenetriaminepentamethylenephosphonic acid (DTPMP), aminotrimethylenephosphonic acid (ATMP) and mixtures thereof.

[0073] Complexing agents typically used in etching solutions include EDTA (ethylenediamine tetraacetic acid) and CDTA (trans-1,2-diaminocyclohexane, N,N,N,N tetraacetic acid). Such complexing agents are difficult to remove during wastewater treatment in sewage treatment plants, which can cause environmental problems.

[0074] The use of less toxic complexing agents such as diethylenetriaminepentamethylenephosphonic acid (DTPMP), aminotrimethylenephosphonic acid (ATMP) and their mixtures in the chemical etching solution overcomes this difficulty.

[0075] The weight percentage of complexing agent in the chemical etching solution is 0.015% to 0.2%, preferably 0.015% to 0.1%, more preferably 0.015% to 0.04%.

[0076] When the mass percentage of DTPMP, ATPMP or their mixture in the chemical etching solution is less than 0.015%, the stabilizing effect of the complexing agent on the chemical etching solution is reduced.

[0077] When the mass percentage of DTPMP, ATPMP or their mixture in the chemical etching solution is greater than 0.2%, there is no increase in the stabilizing effect of the complexing agent with respect to the chemical etching solution.

[0078] Advantageously, the complexing agent is diethylenetriaminepentamethylenephosphonic acid (DTPMP) used alone.

[0079] The pH of the chemical etching solution according to the invention is from 6.5 to 8.6, preferably from 7 to 8, more preferably from 7.3 to 7.8.

[0080] When the pH of the chemical etching solution is higher than 8.5, it is difficult to control the temperature of the cleaning solution to avoid self-accelerating decomposition in case of accidental contamination, for example.

[0081] Advantageously, the chemical etching solution according to the invention consists of or consists essentially of: hydrogen peroxide, potassium tribasic phosphate (K3PO4), diethylenetriaminepentamethylenephosphonic acid (DTPMP), aminotrimethylenephosphonic acid (ATMP) or a mixture thereof, and water.

[0082] Advantageously, the chemical etching solution according to the invention consists of or consists essentially of: hydrogen peroxide, potassium tribasic phosphate (K3PO4), diethylenetriaminepentamethylenephosphonic acid (DTPMP), and water.

[0083] The chemical composition according to the invention may comprise other components provided that the essential characteristics of the etching solution, such as its stability, the etching speed of titanium-based materials and the selectivity of the etching with respect to the exposed materials are not affected by the presence of these components.

[0084] Advantageously, the chemical etching solution according to the invention does not comprise any other complexing agent or anti-corrosion agent than diethylenetriaminepentamethylenephosphonic acid (DTPMP), aminotrimethylenephosphonic acid (ATMP) and their mixture.

[0085] Advantageously, the chemical etching solution according to the invention does not comprise an organic acid capable of complexing metals such as citric acid. Being able to selectively remove titanium compared to other exposed metals without using any other corrosion inhibitor makes it possible to reduce the manufacturing costs of etching solutions, and therefore to reduce the costs of etching processes for microelectronic devices using such solutions.

[0086] An engraving method is proposed.

[0087] A second subject of the invention relates to a method for chemically etching a layer of a titanium-based material on a microelectronic device, said method comprising bringing said layer into contact with the chemical etching solution as described above for a time sufficient to remove said layer, said titanium-based material consisting of titanium, titanium nitride, titanium-tungsten or a mixture thereof, preferably titanium.

[0088] According to one embodiment, the chemical etching solution is heated and brought into contact with the microelectronic device at a temperature of 20°C to 60°C, preferably 35°C to 50°C.

[0089] According to the etching method of the invention, the chemical etching solution is brought into contact with the layer of titanium-based material for a period of about 45 seconds to about 10 minutes, preferably about 1 minute to about 5 minutes.

[0090] Such contact times are illustrative, and can be adapted depending on the temperature of the chemical etching solution and its composition.

[0091] Advantageously, the etching method makes it possible to efficiently remove the layer of titanium-based material from the surface of a microelectronic device without substantially removing other materials present on the microelectronic device such as copper, copper aluminum, tin or tin alloys or even dielectric materials or polyimide.

[0092] Due to its stability over time, the chemical etching solution is reusable and can be stored in a tank before further use.

[0093] Thus, advantageously, the chemical etching solution, after etching the microelectronic device, can be reused to etch one or more other microelectronic devices. A third subject of the invention relates to a method for preparing a chemical etching solution as described above comprising the mixture: of a composition comprising: o potassium tribasic phosphate (K3PO4), o the compound chosen from diethylenetriaminepentamethylenephosphonic acid (DTPMP), aminotrimethylenephosphonic acid (ATMP) and mixtures thereof o water, and an aqueous solution of hydrogen peroxide at a mass concentration of hydrogen peroxide of 30% by weight to 40% by weight relative to the weight of the aqueous solution. to reach a pH of 6.5 to 8.6.

[0094] The method of preparing the chemical etching solution thus comprises adding an aqueous concentrate of the potassium phosphate salt and the complexing agent to a concentrated solution of hydrogen peroxide.

[0095] When the aqueous hydrogen peroxide solution comprises more than 40% hydrogen peroxide, controlling the temperature of the cleaning solution becomes too difficult to avoid self-accelerating decomposition in the event of accidental contamination, for example.

[0096] The percentage of tribasic potassium phosphate in the concentrate is limited by the aqueous solubility of the salt. Advantageously, the concentrate according to the invention comprises a maximum of 46% by weight of tribasic potassium phosphate.

[0097] When the mass percentage of tribasic potassium phosphate in the concentrate is low, the amount of water added to the hydrogen peroxide to reach the target pH reduces the effectiveness of the final solution. Advantageously, the concentrate according to the invention comprises at least 5% by weight of tribasic potassium phosphate.

[0098] Adjusting the pH of the solution as described above to a value of 6.5 to 8.6 allows titanium-based materials to be etched efficiently while avoiding corrosion of potentially exposed metals other than titanium, such as copper or aluminum. The chemical etching solution as described above can be a ready-to-use solution or can be prepared before use by implementing the preparation method detailed above.

[0099] Advantageously, the chemical etching solution is prepared using a point-of-use mixing technique consisting of mixing just before dispensing the aqueous hydrogen peroxide solution and the composition comprising tribasic potassium phosphate, the compound selected from diethylenetriaminepentamethylenephosphonic acid (DTPMP), aminotrimethylenephosphonic acid (ATMP) and mixtures thereof and water.

[0100] Manufacturing the composition at the point of use means that the aqueous hydrogen peroxide solution and the composition comprising tribasic potassium phosphate, the compound selected from diethylenetriaminepentamethylenephosphonic acid (DTPMP), aminotrimethylenephosphonic acid (ATMP) and mixtures thereof and water, are mixed just before contacting the resulting composition with the substrate to be cleaned.

[0101] According to one embodiment, the aqueous solution of hydrogen peroxide and the composition comprising tribasic potassium phosphate, the compound selected from diethylenetriaminepentamethylenephosphonic acid (DTPMP), aminotrimethylenephosphonic acid (ATMP) and mixtures thereof and water, are mixed and heated in a tank.

[0102] Other point-of-use mixing techniques (e.g., in-line mixing of constituents just prior to dispensing) may be used.

[0103] Then the substrate is immersed in the chemical etching solution inside the tank.

[0104] Other techniques for bringing the substrate and the chemical etching solution into contact can be used without departing from the scope of the invention, such as, for example, spraying the substrate with the composition.

[0105] Preferably, the chemical etching solution is used at a temperature of 35°C to 50°C, in order to reduce the cleaning time. A lower temperature is however possible, the cleaning time then being extended.

[0106] The features and benefits of the solution are further illustrated by the examples discussed below. EXAMPLES

[0107] 1. Tests performed

[0108] 1.1 Titanium Etching Test

[0109] A volume of 50ml of chemical etching solution is previously activated by two 6 cm silicon coupons 2 with a 500 nm thick titanium layer.

[0110] The etching test consists of immersing a full-plate coupon comprising a 100 nm layer of Titanium deposited by PVD on silicon oxide in the activated chemical etching solution.

[0111] The solution is then heated to operating temperature, with moderate stirring (200 rpm, rpm meaning "revolution per minute"). The remaining thickness of the titanium, measured at regular intervals, is assessed by measuring the electrical resistance using a four-point probe.

[0112] From the remaining titanium thickness, it is also possible to calculate an etching rate expressed for example in nm / min. The evolution of the remaining thickness is not necessarily linear over time so it can be difficult to determine an etching rate. The etching rate can be reduced at the beginning and end of etching. This can be attributed to the presence of a thin oxide layer at the interface with the air and at the interface with the silicon oxide layer. The etching rate value as defined below corresponds to the thickness of titanium removed for a given time.

[0113] Coupons comprising structures comprising copper pillars were also used (see example 6). The resin was removed by a TechniStrip®P1331 solution at 60°C for 5 minutes, then the removal of the copper primer layer was carried out with a TechniEtch Cu Select solution at 20°C for 1 minute 30 seconds without agitation. The same process as previously described was used to remove the titanium barrier during the time required to clean the coupon. Then the coupons were observed under a scanning electron microscope to determine the presence or absence of titanium residues and the over-etching or not of the exposed layers.

[0114] 1.2 Chemical selectivity test

[0115] The chemical selectivity test for metallic elements consists of evaluating the attack speed of layers of said metallic elements in the presence of the chemical etching solution.

[0116] Thus, wafer coupons of 500 nm aluminum (AlCu) deposited by PVD on silicon oxide, or 40 nm copper deposited by PVD on silicon oxide are used.

[0117] A volume of 50ml of chemical etching solution is heated to 50°C and previously activated by two 6 cm silicon coupons 2 with a 500 nm thick titanium layer.

[0118] The copper and aluminum coupons are immersed for one hour with stirring at 200 rpm. The remaining film thickness on the coupons is assessed over time by measuring the electrical resistance using a four-point probe.

[0119] An attack speed can also be calculated.

[0120] The higher the etch rate value, the less selective the chemical etching solution is with the metal element.

[0121] 1.3 Stability testing of etching solutions

[0122] The stability test of etching solutions includes the following steps:

[0123] • heating the chemical etching solution of initial hydrogen peroxide concentration (CMC initial) with stirring at 65°C

[0124] • measurement of the pH of the solution (initial pH)

[0125] • activation of 50ml of the solution with 2 silicon coupons of 6 cm 2 with a 500 nm thick titanium layer

[0126] • aging for 6 hours at 65°C with stirring

[0127] • titration of the remaining hydrogen peroxide (cmtufinai) by titration with potassium permanganate

[0128] • pH measurement (final pH)

[0129] The variation of pH (A[pH] = (pHfmai - pHinitiai) / pHinitiai * 100) and the variation of hydrogen peroxide content (AfLLCh] = ((cmtufinaie - CH202initiaie) / CH202initiaie * 100) allow to characterize the stability of the chemical etching solution.

[0130] 1.4 Metal element loading test of etching solutions - influence of metal contaminants on etching speed

[0131] The chemical etching solution is heated to 50°C and loaded with metallic contaminant by immersing the equivalent of 10 wafers of diameter 300 mm with or without pattern per liter for a time sufficient to remove the 100 nm layer of titanium present on the surface of the coupons. When the coupons are patterned, the exposed parts can be made of copper or polyimide.

[0132] The solution is then aged at 50°C and the etching rate of titanium in the aged solution is measured.

[0133] In all of the examples, the percentages of the constituents of the compositions are mass percentages expressed relative to the mass of said compositions, the remaining mass percentage corresponding to water.

[0134] 2. Examples

[0135] Example 1:

[0136] The following chemical etching solutions are used:

[0137] SCl (Standard Clean 1) solution obtained by mixing one volume of hydrogen peroxide solution, one volume of 30% aqueous ammonia solution by weight, and 20 volumes of water. The pH of the solution is 10.8. This solution is referred to as solution 1.

[0138] Aqueous solution of 30% by mass of hydrogen peroxide (denoted solution 2). The pH of solution 2 is 3.7.

[0139] Solution according to the invention obtained by mixing 94% by mass of an aqueous solution with 30% by mass of hydrogen peroxide and 6% by mass of an aqueous solution comprising 25% by mass of potassium tribasic phosphate (K3PO4) and 0.4% by mass of diethylenetriaminepentamethylenephosphonic acid (DTPMP). The pH of the chemical etching solution is 7.6. This solution is noted as solution

[0140] 3.

[0141] • titanium etching test

[0142] Figure 1 shows the change in thickness of the titanium layer, as a function of immersion time in the different solutions at 25°C.

[0143] The data in Figure 1 show that the chemical etching solution according to the invention is more effective for etching titanium than prior art solutions.

[0144] • selectivity of etching solutions with respect to copper and aluminum / copper

[0145] The selectivity towards copper and aluminum / copper of the 3 etching solutions above

[0146] RECTIFIED SHEET (RULE 91) ISA / EP above as well as an aqueous solution (denoted solution 4) based on hydrogen peroxide, potassium hydroxide and CDTA (trans- 1,2-diaminocy cl ohexane- N,N,N',N'-tetraacetic acid) as described in patent application EP 3436621 was evaluated.

[0147] Solution 4 has the following composition: 28.2% H2O2 / 0.35% KOH / 0.012% CDTA, the percentages being percentages by weight relative to the weight of the solution.

[0148] The etch rate of copper (Cu) and aluminum / copper (AlCu) is shown in Table 1. For copper, the value shown is the average value measured during the first 2 minutes of the test. For aluminum / copper, the value shown is the average value measured during the first 10 minutes of the test (except for solution 1 where the value shown is the value measured during the first minute of the test).

[0149] [Table 1]

[0150] The low attack speed of Cu and T Aluminium copper with solution 3 according to the invention shows that this solution is compatible with these metallic elements.

[0151] The results obtained with solution 3 according to the invention are comparable to those obtained with solution 4 of the prior art.

[0152] Example 2: Effect of the nature of the counterion of the tribasic phosphate salt

[0153] The following 3 chemical etching solutions are tested: solution 1 of composition: 28.2% hydrogen peroxide; 1.5% potassium tribasic phosphate; 0.024% diethylenetriaminepentamethylenephosphonic acid (DTPMP)

[0154] Solution 2 of composition: 28.2% hydrogen peroxide; 1.1% sodium tribasic phosphate; 0.024% diethylenetriaminepentamethylenephosphonic acid (DTPMP) Solution 3 of composition: 28.2% hydrogen peroxide; 1.1% ammonium tribasic phosphate; 0.024% diethylenetriaminepentamethylenephosphonic acid (DTPMP)

[0155] The percentages are mass percentages expressed relative to the mass of the chemical etching solution, the remaining percentage being water.

[0156] The 3 solutions are equimolar in tribasic phosphate salt.

[0157] • solubility of phosphate salts depending on the nature of the counter-ion of the phosphate salt:

[0158] The solubility of potassium tribasic phosphate in water at 25°C is 900g / l.

[0159] The solubility of sodium tribasic phosphate in water at 25°C is 110g / l.

[0160] The solubility in water at 25°C of tribasic ammonium phosphate is 580 g / l.

[0161] The potassium salt is preferred over the sodium salt due to its greater aqueous solubility. From an industrial point of view, the chemical etching solution is prepared from a concentrate of the phosphate salt in water. High aqueous solubility is therefore preferred.

[0162] • etching speed of titanium depending on the nature of the counter-ion of the phosphate salt:

[0163] The etching rate was evaluated at 50°C with stirring in the different prepared solutions.

[0164] It is respectively equal to 82 nm / min, 81 nm / min and 85 nm / min for the potassium salt, the sodium salt and the ammonium salt.

[0165] The etching rate of titanium is therefore independent of the nature of the counterion of the phosphate salt.

[0166] • evaluation of the stability of etching solutions 1 and 3

[0167] The hydrogen peroxide content is reduced by 31% whether the counterion of the phosphate salt is the potassium ion or the ammonium ion.

[0168] • evaluation of the selectivity of etching solutions 1 and 3 with respect to copper and aluminum

[0169] The etch rate for copper and aluminum is shown in Table 2. For copper, the value shown is the average value measured during the first 2 minutes of the test. For copper aluminum, the value shown is the average value measured during the first 10 minutes of the test.

[0170] [Table 2]

[0171] The attack rates of copper and aluminum are lower (3.3 times and 2.4 times respectively) when the counterion of the phosphate salt is a potassium ion (case of solution 1) rather than an ammonium ion (case of solution 3).

[0172] • copper loading test of etching solutions 1 and 3

[0173] Chemical etching solution 1 is heated to 50°C and is loaded with copper by immersing the equivalent of 10 patterned copper wafers of diameter 300 mm per liter, or 44 coupons of 3 cm 2 in 20mL, for a time sufficient to remove the 100nm layer of titanium present on the surface of the coupons.

[0174] The etching speed of titanium is evaluated at tO (after loading with copper), then after aging at 50°C of the chemical etching solution loaded with copper.

[0175] The results are shown in Table 3.

[0176] Chemical etching solution 3 shows a loading capacity of only 3 wafers / liter before running away and degrading (high gassing) after 0.58 h. [Table 3]

[0177] As shown in the previous point, chemical etching solution 3 leads to a higher copper attack speed. Chemical etching solution 3 will therefore load more copper faster and therefore destabilize more quickly.

[0178] • conclusion

[0179] Tribasic phosphate salt (K3PO4) is preferred to ammonium salt because its use allows for more selective etching of titanium with respect to other exposed materials.

[0180] Example 3: Effect of the concentration of potassium tribasic phosphate Several etching solutions are prepared from: a 30% by mass aqueous solution of hydrogen peroxide and an aqueous solution: o comprising 25% by mass of potassium tribasic phosphate (K3PO4) and 0.4% by mass of diethylenetriaminepentamethylenephosphonic acid (DTPMP) o or comprising 46% by mass of potassium tribasic phosphate (K3PO4) and 0.74% by mass of diethylenetriaminepentamethylenephosphonic acid (DTPMP).

[0181] The mass proportion, in the chemical etching solution, of the aqueous solution comprising K3PO4 and DTPMP is 1.5%, 3%, 6% and 12%.

[0182] The stability of the obtained chemical etching solution is evaluated by measuring the variation of hydrogen peroxide content and the variation of pH according to the stability test described above. The results are listed in Table 4.

[0183] [Table 4]

[0184] CORRECTED SHEET (RULE 91) ISA / EP

[0185] Example 4: effect of the nature of the complexing agent and its concentration

[0186] • on the stability of etching solutions

[0187] The 7 chemical etching solutions of the following composition (28.2% by mass of hydrogen peroxide; 1.5% tribasic potassium phosphate; 0.024% of complexing agent, the remainder being water) are evaluated.

[0188] The etching solutions differ in the nature of the complexing agent: solution 1: glycine solution 2: histidine solution 3: ammonium citrate solution 4: 2,6 pyridine dicarboxylic acid (PDA) solution 5: N-(2-acetamino)-iminodiacetic acid (ADA) solution 6: diethylenetriamine-pentamethylenephosphonic acid (DTPMP), solution 7: aminotrimethylenephosphonic acid (ATMP)

[0189] The stability of the different etching solutions is evaluated according to the stability test detailed above.

[0190] Solution 1 and solution 2 are stable for 1 hour and then destabilize (uncontrolled degradation of the peroxide).

[0191] Solution 3 and solution 4 are stable for 4 hours.

[0192] Solution 5 is stable for 5.5 hours.

[0193] Solutions 6 and 7 are stable throughout the test (6 hours).

[0194] The stability of the etching solutions was also evaluated by multiplying the concentration of complexing agent in each of the solutions by 4 and by 8, while the concentration of the other components remained unchanged.

[0195] Solution 1 and solution 2 are then stable for 3 hours.

[0196] The stability of solutions 3 to 5 remains unchanged.

[0197] Solutions 6 and 7 remain stable throughout the test (6 hours).

[0198] RECTIFIED SHEET (RULE 91) ISA / EP case of DTPMP: influence of DTPMP concentration on the etching speed of titanium

[0199] The effect of DTPMP concentration on the etching rate of titanium was evaluated for solutions of the following composition: 28.2% by mass of hydrogen peroxide; 1.5% tribasic potassium phosphate; 0.024 / 0.048 / 0.096 / 0.192% of DTPMP, the remainder being water.

[0200] The etching speed is 8 nm / min, 84 nm / min; 86 nm / min and 93 nm / min for DTPMP concentrations of 0.024 / 0.048 / 0.096 / 0.192% respectively.

[0201] Example 5: Stability of etching solutions - effect of adding an organic acid The addition of an organic acid as a complexing agent, such as citric acid, is described as allowing the stabilization of etching solutions and increasing compatibility with copper - cf US9845538 (WACO).

[0202] The stability of the following 2 chemical etching solutions is evaluated according to the stability test described above: solution 1 of composition: 28.2% hydrogen peroxide; 1.5% potassium tribasic phosphate; 0.024% diethylenetriaminepentamethylenephosphonic acid (DTPMP)

[0203] Solution 2 of composition: 28.2% hydrogen peroxide; 1.5% potassium tribasic phosphate; 0.024% diethylenetriaminepentamethylenephosphonic acid (DTPMP); 2.36% citric acid; 1.63% KOH

[0204] The mass loss of hydrogen peroxide is 31% for solution 1 and 40% for solution 2.

[0205] Adding citric acid results in a decrease in the stability of the chemical etching solution.

[0206] After loading the chemical etching solution with 10 patterned copper coupons of diameter 300 mm per liter for a time sufficient to remove the 100 nm layer of titanium present on the surface of the coupons, and aging at 50°C for 1 hour, chemical etching solution 2 runs away and degrades (strong gas release). As illustrated by the data in Table 3, the etching rate of titanium remains unchanged with solution 1 for an aging time of 2 hours. Example 6: effect of temperature on titanium etching

[0207] The tested chemical etching solution has the following composition; 28.2% hydrogen peroxide; 1.5% potassium tribasic phosphate; 0.024% complexing agent, the remainder being water.

[0208] The evolution of the thickness of the remaining titanium layer as a function of the etching time is illustrated in Figure 2 for temperatures between 25°C and 65°C.

[0209] The evolution of the etching rate as a function of the temperature of the chemical etching solution is illustrated in Figure 3.

[0210] The higher the temperature of the chemical etching solution, the faster the titanium etches.

[0211] High etching solution temperature can lead to evaporation of a fraction of the water from the etching solution and an increase in hydrogen peroxide concentration resulting in an acceleration of the etching rate.

[0212] The chemical etching solution can be kept in a closed container to limit these phenomena with suitable ventilation.

[0213] Example 7: Effect of metallic contamination on the etching rate of titanium Contamination of the chemical etching solution by titanium:

[0214] The tested chemical etching solution has the following composition; 28.2% hydrogen peroxide; 1.5% potassium tribasic phosphate; 0.024% complexing agent, the remainder being water.

[0215] The chemical etching solution is loaded with titanium by immersing the equivalent of 10 full wafers of 300 mm diameter per liter for a time sufficient to remove the 100 nm layer of titanium present on the surface of the coupons.

[0216] The etching rate of titanium is evaluated at tO (before and after titanium loading), then after different aging times at 50°C of the chemical etching solution loaded with titanium.

[0217] The etching speed is between 80 and 90nm / min up to 6 hours of aging of the chemical etching solution.

[0218] The chemical etching solution is therefore stable for at least 6 hours at 50°C.

[0219] Figure 4 illustrates the cleaning efficiency of the titanium layer of Cu pillars by etching solutions aged at 50°C for different durations: top left: use of a chemical etching solution aged for 5 min at 50°C top right: use of a chemical etching solution aged for 1h30 at 50°C bottom left: use of a chemical etching solution aged for 3h at 50°C bottom right: use of a chemical etching solution aged for 6h at 50°C

[0220] In each photo, the upper left portion corresponds to a copper pad, while the rest of the photo represents an area in which the titanium layer has been removed. The surface of the copper pads is not modified and no titanium residue is visible. Contamination of the chemical etching solution with titanium and other components:

[0221] Two etching solutions are tested: solution 1 with the following composition: 28.2% hydrogen peroxide; 1.5% potassium tribasic phosphate; 0.024% DTPMP, the remainder being water. solution 2 with the following composition: 28.2% hydrogen peroxide; 0.35% potassium hydroxide; 0.012% CDTA, the remainder being water.

[0222] According to this test, the chemical etching solution is loaded with metallic elements by immersing the equivalent of 10 wafers of patterned plates exposing the following materials (copper, polyimide) of diameter 300 mm per liter for a time sufficient to remove the 100 nm layer of titanium present on the surface of the coupons.

[0223] The etching speed of titanium is evaluated at tO (after wafer loading) then after different aging times at 50°C of the aged chemical etching solution.

[0224] The test results are shown in Table 5. [Table 5]

[0225] Solutions 1 and 2 are stable for at least 2 h at 50°C. However, there is a significant decrease in the etching rate (-30%) with solution 2 compared to solution 1 (-11%).

[0226] The cleaning efficiency of the titanium layer of Cu pillars by chemical etching solution 1 aged at 50°C for up to 2 hours was evaluated. The surface of the copper pads is not modified and no titanium residue is visible.

[0227] Figure 5 shows the base of a copper pillar etched using the etching solution loaded with wafers (left photo) and the same etching solution aged for 2 hours at 50°C (right photo). The etching profile is identical.

Claims

Tl CLAIMS 1. Solution for chemical etching of a titanium-based material comprising: - from 26% by weight to 39% by weight of hydrogen peroxide, - from 1% by weight to 6% by weight of potassium tribasic phosphate (K3PO4), - from 0.015% by weight to 0.2% by weight of a compound chosen from diethylenetriaminepentamethylenephosphonic acid (DTPMP), aminotrimethylenephosphonic acid (ATMP) and mixtures thereof - water, the weight percentages being expressed relative to the weight of the chemical etching solution, said solution having a pH of 6.5 to 8.

6.

2. A method of chemically etching a layer of a titanium-based material on a microelectronic device, said method comprising contacting said layer with the chemical etching solution according to claim 1 for a time sufficient to remove said layer, said titanium-based material consisting of titanium, titanium nitride, titanium-tungsten or a mixture thereof, preferably titanium.

3. Method according to claim 2, in which the chemical etching solution, after etching the microelectronic device, is reused to etch one or more other microelectronic devices.

4. A method according to claim 2 or claim 3, wherein the chemical etching solution is heated and contacted with the microelectronic device at a temperature of 20°C to 60°C, preferably 35°C to 50°C.

5. Method for preparing a chemical etching solution according to claim 1 comprising mixing: a composition comprising: o potassium tribasic phosphate (K3PO4), o the compound chosen from diethylenetriaminepentamethylenephosphonic acid (DTPMP), aminotrimethylenephosphonic acid (ATMP) and mixtures thereof o water, and an aqueous solution of hydrogen peroxide at a mass concentration of hydrogen peroxide of 30% by weight to 40% by weight relative to the weight of the aqueous solution. to reach a pH of 6.5 to 8.

6.

6. The method of claim 5, wherein the solution is prepared using a point-of-use mixing technique of mixing just before dispensing the aqueous hydrogen peroxide solution and the composition comprising the potassium phosphate salt, the compound selected from diethylenetriaminepentamethylenephosphonic acid (DTPMP), aminotrimethylenephosphonic acid (ATMP) and mixtures thereof and water.

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