Etchant compositions and methods

Abstract

The present invention relates to compositions and methods for selectively etching titanium nitride, cobalt, or a combination thereof. The compositions and methods typically render molybdenum and other materials present unaffected by the process. The process may achieve high etch rates and may provide uniform recess top and bottom layers in the pattern.

Description

Technical Field

[0001] The present disclosure relates to the field of semiconductor manufacturing. In particular, the present disclosure relates to etchant compositions and methods for etching titanium nitride films.

[0002] priority

[0003] This disclosure claims priority to U.S. Provisional Patent No. 63 / 346,748, filed May 27, 2022. The priority document is incorporated herein by reference. Background Art

[0004] A photoresist mask may be used to pattern materials such as semiconductors or dielectrics. For example, a photoresist mask may be used in a dual damascene process to form interconnects in the back end metallization of a microelectronic device. The dual damascene process may involve forming a photoresist mask on a low-k dielectric layer overlying a metal conductor layer (such as a copper layer). The low-k dielectric layer may be etched according to the photoresist mask to form trenches that expose the metal conductor layer. The trenches, which are often referred to as dual damascene structures, are typically defined using two photolithography steps. The photoresist mask is then removed from the low-k dielectric layer, after which a conductive material is deposited in the trenches to form interconnects. Summary of the invention

[0005] In some embodiments, a metal mask is used to provide better profile control of the trench. The metal hard mask can be made of titanium or titanium nitride and is removed by a wet etching process after forming the trench of the dual metal damascene structure. In some embodiments, the wet etching process uses a removal chemistry that effectively removes the metal hard mask and / or photoresist etch residues without affecting the underlying metal conductor layer and low-k dielectric materials or other materials on the microelectronic device. Some embodiments of the etchant composition can be used in a wet etching process to selectively remove substances such as titanium nitride while reacting with metal conductive layers (e.g., molybdenum, AlO x 、SiO x or polysilicon).

[0006] In some embodiments, a composition comprises an oxidizer; an etchant; a first corrosion inhibitor; and a second corrosion inhibitor, wherein the second corrosion inhibitor comprises an N-heteroatom-containing aromatic compound.

[0007] In some embodiments of the composition, the first corrosion inhibitor inhibits a chemical reaction of a first material, wherein the first material includes Cr, Mo, W, or any combination thereof.

[0008] In some embodiments of the composition, the second corrosion inhibitor inhibits a chemical reaction of the second material.

[0009] In some embodiments of the composition, the first corrosion inhibitor comprises 5-methylbenzotriazole.

[0010] In some embodiments of the composition, the second corrosion inhibitor comprises polyvinylpyrrolidone.

[0011] In some embodiments of the composition, the first corrosion inhibitor comprises 4-(3-phenylpropyl)pyridine.

[0012] In some embodiments of the composition, the second corrosion inhibitor comprises polyvinylpyrrolidone.

[0013] In some embodiments, an etching method uses a composition described herein and the method comprises removing TiN at a TiN removal rate of at least 5.0 nm per minute. In some embodiments of the method, the TiN removal rate is at least 10 nm per minute.

[0014] In some embodiments, the method further comprises removing Co at a Co removal rate of at least 20 nm per minute. In some embodiments of the method, the Co removal rate is at least 25 nm per minute.

[0015] In some embodiments of the method, a removal rate of the first material is less than 1.8 nm per minute due to protection by the first corrosion inhibitor. In some embodiments of the method, the first material is Cr, Mo, W or any combination thereof.

[0016] In some embodiments of the method, a removal rate of the second material is less than 0.5 nm per minute due to protection via the second corrosion inhibitor. DETAILED DESCRIPTION

[0017] Among those benefits and improvements disclosed, other objects and advantages of the present disclosure will become apparent from the following description. Detailed embodiments of the present disclosure are disclosed herein; however, it should be understood that the disclosed embodiments are merely illustrative of the present disclosure that can be implemented in various forms. In addition, each of the examples given with respect to the various embodiments of the present disclosure is intended to be illustrative and not restrictive.

[0018] Throughout this specification and claims, unless the context clearly dictates otherwise, the following terms adopt the meanings explicitly associated herein. As used herein, the phrases "in one embodiment," "in an embodiment," and "in some embodiments" may not all refer to the same embodiment, but they may refer to the same embodiment. In addition, the phrases "in another embodiment" and "in some other embodiments" as used herein may not all refer to different embodiments, but they may refer to different embodiments. All embodiments of the present disclosure are intended to be combined without departing from the scope or spirit of the present disclosure.

[0019] As used herein, the term "microelectronic device" corresponds to semiconductor substrates, flat panel displays, phase change memory devices, solar panels, and other products manufactured for use in microelectronics, integrated circuits, energy harvesting, or computer chip applications, including solar cell devices, photovoltaic devices, and microelectromechanical systems (MEMS). It should be understood that the terms "microelectronic device," "microelectronic substrate," and "microelectronic device structure" are not intended to be limiting in any way and include any substrate or structure that will ultimately become a microelectronic device or microelectronic assembly. The microelectronic device may be patterned, covered, and may be a control and / or test device.

[0020] As used herein, the terms "titanium nitride" and "TiN x " corresponds to pure titanium nitride and impure titanium nitride (i.e., TiO x N y ).

[0021] As used herein, "about" is intended to correspond to +0.5% or -0.5% of the stated value.

[0022] As used herein, the term "low-k dielectric material" corresponds to any material used as a dielectric material in a layered microelectronic device, wherein the material has a dielectric constant of less than about 3.5. In certain embodiments, the low-k dielectric material includes low polarity materials such as silicon-containing organic polymers, silicon-containing hybrid organic / inorganic materials, organosilicate glass (OSG), TEOS, fluorinated silicate glass (FSG), silicon dioxide, aluminum oxide (AlO x )、ZrO x ) and carbon doped oxide (CDO) glass. It should also be understood that low-k dielectric materials can have different densities and different porosities.

[0023] As used herein, the term "metal conductor layer" includes copper, tungsten, cobalt, molybdenum, aluminum, ruthenium, alloys thereof, or combinations thereof.

[0024] As used herein, a "fluoride" species corresponds to a compound comprising ionic fluorine (F - ) or covalently bonded fluorine species. It should be understood that the fluoride species can be included or generated in situ in the form of a fluoride species.

[0025] As described more fully below, the compositions of the present invention may be implemented in a wide variety of specific formulations.

[0026] In all of these compositions, where specific components of the composition are discussed with reference to weight percent ranges (including a lower limit of zero), it is understood that these components may or may not be present in various specific embodiments of the composition, and where these components are present, they may be present in concentrations as low as 0.0001 weight percent, based on the total weight of the composition in which they are employed.

[0027] In some embodiments, the present disclosure relates to compositions and methods for creating recesses in microelectronic device structures, such as 3D NAND flash memory devices. Some embodiments of the methods may be characterized as processes that include dry or wet etching processes and selective etching of titanium nitride (TiN) layers, which typically leave some other materials present and any aluminum oxide, silicon dioxide, and polysilicon that may be present unaffected by the process. In some embodiments, the methods may have improved etch rates and may provide uniform recessed top and bottom layers in the pattern. In some embodiments, the compositions are very stable, such as having a bath life of more than 24 hours and a shelf life of more than 6 months.

[0028] According to some embodiments, exemplary materials include a TiN layer and a cobalt (Co) layer, wherein the TiN layer and the Co layer are to be selectively removed, typically leaving some other materials present unaffected by a chemical etching process using the exemplary composition.

[0029] Some examples of some other materials include, but are not necessarily limited to, the first material, the second material, a silicon-based material, etc. According to some embodiments, an example of the first material includes molybdenum (Mo) or a Mo-containing alloy. According to some embodiments, an example of the first material is or includes Cr, Mo, W, a Cr-containing alloy, a Mo-containing alloy, a W-containing alloy, or any combination thereof. According to some embodiments, an example of a silicon-based material includes silicon (Si), SiO x , silicon oxide, SiN x 、Silicon Nitride (Si x N y ), polysilicon or a combination thereof.

[0030] In some embodiments, the exemplary composition includes an oxidant, an etchant, a first corrosion inhibitor, and a second corrosion inhibitor. The first corrosion inhibitor inhibits the chemical reaction of the oxidant and / or the etchant with the first material. According to some embodiments, the composition selectively etches TiN and Co and does not etch the first material (e.g., Mo) (i.e., does not chemically react with the first material (e.g., Mo)), and the chemical reaction does not produce or form an oxide of the first material (e.g., MoO xAccording to some embodiments, the composition selectively etches TiN and Co and does not etch the first material (e.g., Mo) due to the first corrosion inhibitor in the composition (i.e., does not chemically react with the first material (e.g., Mo)). Therefore, use of the composition does not generate or form an oxide of the first material (e.g., MoO x ).

[0031] In some embodiments, the first corrosion inhibitor includes 5-methylbenzotriazole, benzotriazole, or a combination thereof.

[0032] In some embodiments, the first corrosion inhibitor is 5-methylbenzotriazole.

[0033] In some embodiments, the first corrosion inhibitor is benzotriazole.

[0034] Some embodiments of the composition further include one or more pH adjusting agents and a solvent (or solvent solution). In some embodiments, the composition includes a solvent as a solvent miscible with water. Some embodiments of the composition include water (such as deionized water). In some embodiments, the composition includes a solvent miscible with water and water (such as deionized water). In some embodiments of the composition, the etchant is one or more TiN etchants. In some embodiments of the composition, the etchant is or includes a TiN etchant and a Co etchant. In some embodiments of the composition, the etchant is or includes one or more TiN etchants and a Co etchant.

[0035] Additionally, for example, according to some embodiments, the material includes a TiN layer disposed over a Co layer. The Co layer is disposed over a Mo layer (an example of a first material). The Mo layer is disposed over a Si layer. x N y Above the material.

[0036] For example, according to some embodiments, the material includes a TiN layer disposed over a Co layer. The Co layer is disposed over a Mo layer (an example of a first material). The Mo layer is disposed over a SiO x Above the material.

[0037] For example, according to some embodiments, the material includes a TiN layer disposed over a Co layer. The Co layer is disposed over a Mo layer (an example of a first material). The Mo layer is disposed over a Si material.

[0038] In some embodiments, the composition has a TiN etch rate (at 60° C.) of 5 nm per minute or more.

[0039] In some embodiments, the composition has a Co etch rate (at 60° C.) of 20 nm per minute or more.

[0040] In some embodiments, the composition has a TiN etch rate of 5 nm per minute or more and a Co etch rate of 20 nm per minute or more (at 60° C.).

[0041] Exemplary materials include titanium nitride (TiN) layers and cobalt (Co) layers, wherein the TiN and Co layers are to be selectively removed, typically leaving some other materials present unaffected by the chemical etching process using the exemplary compositions.

[0042] Some examples of some other materials include, but are not necessarily limited to, the first material, the second material, a silicon-based material, and the like.

[0043] In some embodiments, the second material includes one or more of a transition metal.

[0044] In some embodiments, the exemplary composition includes an oxidant, an etchant, a first corrosion inhibitor, and a second corrosion inhibitor. The first corrosion inhibitor inhibits the chemical reaction of the oxidant and / or the etchant with the first material. The second corrosion inhibitor includes an aromatic compound containing an N-heteroatom, which inhibits the chemical reaction of the oxidant and / or the etchant with the second material.

[0045] For example, according to some embodiments, the material includes a TiN layer disposed on a Co layer. The Co layer is disposed on a second material. The second material is disposed on a Si x N y Above the material.

[0046] For example, according to some embodiments, the material includes a TiN layer disposed on a Co layer. The Co layer is disposed on a second material. The second material is disposed on a SiO x Above the material.

[0047] For example, according to some embodiments, the material includes a TiN layer disposed over a Co layer. The Co layer is disposed over a second material. The second material is disposed over a Si material.

[0048] In some embodiments, the composition has a very high TiN etch selectivity at 60°C. In some embodiments, the composition has a TiN etch rate of 5 nm or more per minute, a Co etch rate of 20 nm or more per minute, and the composition has a high selectivity to TiN and Mo, Si. x N y and SiO x In some embodiments, the composition does not etch Mo, Si x N y and SiO x In some embodiments, the composition is Mo, Si x N y and SiO x No reactivity.

[0049] In some embodiments, at 60° C., the composition has a TiN etch rate of 5 nm or more per minute, a Co etch rate of 20 nm or more per minute, and ... TiN etch rate of 20 nm or more per minute, and the composition has a TiN etch rate of 5 x N y and SiO x Or any combination thereof. In some embodiments, the composition does not etch Mo, Si x N y and SiO x Or any combination thereof. In some embodiments, the composition is Mo, Si x N y and SiO x or any combination thereof is non-reactive.

[0050] In some embodiments, a portion of the material includes one exemplary material and another exemplary material, wherein each of the materials includes a titanium nitride (TiN) layer and a cobalt (Co) layer. The TiN layer and the Co layer are selectively removed, and some other materials present are generally left unaffected by the chemical etching process using the exemplary composition.

[0051] Some examples of some other materials include, but are not necessarily limited to, the first material, the second material, a silicon-based material, and the like.

[0052] According to some embodiments, examples of the first material include molybdenum (Mo) or alloys containing Mo. According to some embodiments, examples of the first material are or include Cr, Mo, W, alloys containing Cr, alloys containing Mo, alloys containing W, or any combination thereof.

[0053] Examples of silicon-based materials according to some embodiments include silicon (Si), SiO x , silicon oxide, SiN x 、Silicon Nitride (Si x N y ), polysilicon or a combination thereof.

[0054] In some embodiments, an exemplary composition includes an oxidant, an etchant, a first corrosion inhibitor, and a second corrosion inhibitor. The first corrosion inhibitor inhibits a chemical reaction of the oxidant and / or the etchant with the first material.

[0055] In some embodiments, the exemplary composition includes an oxidant, an etchant, a first corrosion inhibitor, and a second corrosion inhibitor. The first corrosion inhibitor inhibits the chemical reaction of the oxidant and / or the etchant with the first material. The second corrosion inhibitor includes an aromatic compound containing an N-heteroatom, which inhibits the chemical reaction of the oxidant and / or the etchant with the second material. The composition is compatible with silicon-based materials or non-reactive with silicon-based materials. That is, according to some embodiments, the composition is reacted with TiN and Co at a much faster rate than the reaction of silicon-based materials, thereby removing TiN and Co at a much faster rate than removing silicon-based materials, or the composition reacts with TiN and Co but does not react substantially with silicon-based materials, and therefore, when TiN and Co are removed, silicon-based materials are not substantially removed, or the composition reacts with TiN and Co but does not react with silicon-based materials, and therefore, when TiN and Co are removed, silicon-based materials are not removed.

[0056] In some embodiments, the composition is a TiN and Co etchant composition comprising an oxidant, an etchant, a first corrosion inhibitor, and a second corrosion inhibitor, wherein the first corrosion inhibitor comprises 5-methylbenzotriazole and 4-(3-phenylpropyl)pyridine, and the second corrosion inhibitor comprises polyvinylpyrrolidone. In some embodiments, the composition further comprises a pH adjuster and deionized water.

[0057] In some embodiments of the composition, the chemical reaction does not produce or form MoO x .

[0058] According to some embodiments, the etchants considered include, but are not limited to, fluoride sources such as HF; ammonium fluoride; tetrafluoroboric acid; hexafluorosilicic acid; other compounds containing B--F bonds or Si--F bonds; tetrabutylammonium tetrafluoroborate (TBA-BF4); tetraalkylammonium fluoride (NR1R2R3R4F); a strong base such as tetraalkylammonium hydroxide (NR1R2R3R4OH), wherein R1, R2, R3, R4 may be the same or different from each other and are selected from hydrogen, straight or branched C1 to C6 alkyl (e.g., methyl, ethyl, propyl, butyl, pentyl, hexyl), C1 to C6 alkoxy (e.g., hydroxyethyl, hydroxypropyl), substituted or unsubstituted aryl (e.g., benzyl); a weak base or a combination thereof. In one embodiment, the fluoride source comprises HF, tetrafluoroboric acid, hexafluorosilicic acid, H2ZrF6, H2TiF6, HPF6, ammonium fluoride, tetramethylammonium fluoride, tetramethylammonium hydroxide, ammonium hexafluorosilicate, ammonium hexafluorotitanate, or a combination of ammonium fluoride and tetramethylammonium fluoride. In another embodiment, the etchant comprises HF, hexafluorosilicic acid, or tetrafluoroboric acid. In yet another embodiment, the etchant is HF.

[0059] According to some embodiments, an oxidizing agent is included to etch or oxidize TiN x Ti in the film3+ The oxidants considered herein include, but are not limited to, hydrogen peroxide (H2O2), FeCl3, FeF3, Fe(NO3)3, Sr(NO3)2, CoF3, MnF3, (2KHSO5·KHSO4·K2SO4-CAS No. 70693-62-8), periodic acid, iodic acid, tert-butyl hydroperoxide, vanadium (V) oxide, vanadium (IV, V) oxide, ammonium vanadate, polyatomic ammonium salts (such as ammonium peroxymonosulfate, ammonium chlorite (NH4ClO2), ammonium chlorate (NH4ClO3), ammonium iodate (NH4IO3), ammonium nitrate (NH4NO3), ammonium perborate (NH4BO3), ammonium perchlorate (NH4ClO4), ammonium periodate (NH4IO4), ammonium persulfate ((NH4)2S2O8), ammonium hypochlorite (NH4ClO)), ammonium tungstate ((NH4) 10 H2(W2O7)), polyatomic sodium salts (e.g., sodium persulfate (Na2S2O8), sodium hypochlorite (NaClO), sodium perborate), polyatomic potassium salts (e.g., potassium iodate (KIO3), potassium permanganate (KMnO4), potassium persulfate, nitric acid (HNO3), potassium persulfate (K2S2O8), potassium hypochlorite (KClO)), polyatomic tetramethylammonium salts (e.g., tetramethylammonium chlorite ((N(CH3)4)ClO2), tetramethylammonium chlorate ((N(CH3)4)ClO3), tetramethylammonium iodate ((N(CH3)4)IO3), tetramethylammonium perborate Methylammonium ((N(CH3)4)BO3), tetramethylammonium perchlorate ((N(CH3)4)ClO4), tetramethylammonium periodate ((N(CH3)4)IO4), tetramethylammonium persulfate ((N(CH3)4)S2O8)), polyatomic tetrabutylammonium salts (e.g., tetrabutylammonium peroxymonosulfate), peroxymonosulfuric acid, ferric nitrate (Fe(NO3)3), urea peroxide ((CO(NH2)2)H2O2), peracetic acid (CH3(CO)OOH), 1,4-benzoquinone, toluenequinone, dimethyl-1,4-benzoquinone, tetrachloro-p-benzoquinone, alloxan, or a combination thereof. When the oxidant is a salt, it may be hydrated or anhydrous. The oxidant may be introduced into the composition at the manufacturer prior to introducing the composition into the device wafer, or alternatively introduced at the device wafer (i.e., in situ). In one embodiment, the oxidant comprises periodic acid.

[0060] Any suitable compound capable of adjusting the pH of the composition can be used to adjust the pH of the composition. The pH adjusting agent is preferably water-soluble and compatible with the other components of the composition. Typically, the composition has a pH of about -1 to 5, or 0 to 4, or 2 to 4 at the point of use. Non-limiting examples of pH adjusting agents include inorganic acids and organic acids, including methanesulfonic acid, ethanesulfonic acid, phosphoric acid, sulfuric acid, hydrogen chloride, etc.

[0061] In some embodiments, the solvent may include water, at least one water-miscible organic solvent, or a combination thereof, wherein the at least one water-miscible organic solvent is selected from the group consisting of: 1 R 2 R 3 C(OH) compounds, wherein R 1 , R 2 and R 3 are independent of each other and are selected from the group consisting of: hydrogen, C2 to C 30 Alkyl, C2 to C 30 Olefins, cycloalkyls, C2 to C 30 Alkoxy and combinations thereof. For example, the at least one solvent may include at least one species selected from the group consisting of water, methanol, ethanol, isopropanol, butanol and higher alcohols, tetrahydrofurfuryl alcohol (THFA), 3-chloro-1,2-propanediol, 3-chloro-1-propanethiol, 1-chloro-2-propanol, 2-chloro-1-propanol, 3-chloro-1-propanol, 3-bromo-1,2-propanediol, 1-bromo-2-propanol, 3-bromo-1-propanol, 3-iodo-1-propanol, 4-chloro-1-butanol, 2-chloroethanol), dichloromethane, chloroform, acetic acid, propionic acid, trifluoroacetic acid, tetrahydrofuran (THF), N-methylpyrrolidone (NMP), cyclohexylpyrrolidone, N-octylpyrrolidone, N-phenylpyrrolidone, methyldiethanolamine, methyl formate, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), tetramethylene sulfone (cyclopentane), ethyl ether, phenoxy-2-propanol (PPh), propiophenone, ethyl lactate, ethyl acetate, ethyl benzoate, acetonitrile, acetone, ethylene glycol, propylene glycol (PG), 1,3-propylene glycol, 1,4-propylene glycol, dioxane, butyryl lactone, butylene carbonate, ethylene carbonate, propylene carbonate, dipropylene glycol, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether (butyl In one embodiment, at least one solvent comprises water, for example, deionized water. In one embodiment, the solvent miscible with water is selected from ethylene glycol and propylene glycol.

[0062] Non-limiting exemplary compositions are described below:

[0063] Exemplary compositions

[0064] Methanesulfonic acid (MSA) 1 to 10 wt% Periodic acid (PIA) 0.5% 1 to 4 wt% HF 0.49% 2 to 20 wt% 4-(3-Phenyl)propylpyridine (PPP) 0.01 to 10 wt% Polyvinylpyrrolidone (PVP) 0.1% 0.01 to 10 wt% 1,2,3-Benzotriazole 0.01 to 1 wt% DIW (Deionized Water) margin

[0065] When using the above exemplary compositions (etched at 60°C), TiN etch rates of over 10 nm / min were obtained. The same exemplary compositions were also used to produce Co etch rates of 28.9 nm / min or higher. In addition, Mo etch rates of less than 1.8 nm / min were achieved. In some cases, Mo etch rates of less than 1.5 nm / min were achieved. In some cases, Mo etch rates of less than 0.7 nm were achieved. SiN etch rates of less than 0.1 nm / min were also achieved. x Etching rate.

Claims

1. A composition comprising: Oxidants; Etching agent; a first corrosion inhibitor; and Second corrosion inhibitor, The second corrosion inhibitor comprises an aromatic compound containing an N-heteroatom.

2. The composition of claim 1, wherein the first corrosion inhibitor inhibits a chemical reaction of a first material, wherein the first material comprises Cr, Mo, W, or any combination thereof.

3. The composition of any one of claims 1-2, wherein the second corrosion inhibitor inhibits a chemical reaction of the second material.

4. The composition of claim 1, wherein the first corrosion inhibitor comprises 5-methylbenzotriazole.

5. The composition of claim 4, wherein the second corrosion inhibitor comprises polyvinyl pyrrolidone.

6. The composition of claim 4, wherein the first corrosion inhibitor comprises 4-(3-phenylpropyl)pyridine.

7. The composition of claim 6, wherein the second corrosion inhibitor comprises polyvinyl pyrrolidone.

8. The composition of claim 1, wherein the first corrosion inhibitor comprises 4-(3-phenylpropyl)pyridine.

9. The composition of claim 8, wherein the second corrosion inhibitor comprises polyvinyl pyrrolidone.

10. The composition of claim 1, wherein the second corrosion inhibitor comprises polyvinyl pyrrolidone.

11. A method for etching using the composition according to any one of claims 1 to 8, the method comprising: The TiN is removed at a TiN removal rate of at least 5.0 nm per minute.

12. The method according to claim 11, further comprising: The Co is removed at a Co removal rate of at least 20 nm per minute.

13. The method of claim 12, wherein the TiN removal rate is at least 10 nm per minute. The method of claim 13 , wherein the Co removal rate is at least 25 nm per minute.

15. The method of claim 14, wherein a removal rate of the first material due to protection by the first corrosion inhibitor is less than 1.8 nm per minute. The method of claim 15 , wherein the first material is Cr, Mo, W, or any combination thereof.

17. The method of claim 16, wherein a removal rate of the second material due to protection by the second corrosion inhibitor is less than 0.5 nm per minute.

18. The method of claim 17, wherein the second material is any one or more of the Group 9 transition metals.

19. The method of claim 14, wherein a removal rate of the second material due to protection by the second corrosion inhibitor is less than 0.5 nm per minute.

20. The method of claim 19, wherein the second material is any one or more of the Group 9 transition metals.