WO1998011276A1

WO1998011276A1 - Gas mixture and method of dry etching metals, in particular copper, at low temperatures

Info

Publication number: WO1998011276A1
Application number: PCT/DE1997/002073
Authority: WO
Inventors: Thomas Kruck; Michael Schober; Konrad Hieber; Günther Ruhl
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 1996-09-12
Filing date: 1997-09-12
Publication date: 1998-03-19
Also published as: DE19637194A1; DE19637194C2

Abstract

The invention concerns a method and a gas mixture for the dry etching of metals, in particular copper, wherein the metal is oxidized and a volatile metal compound which is stable under processing conditions is formed. The entire etching process can be reduced to a single step by using a special gas mixture. In particular, the process can be carried out at advantageously low temperatures and reduced pressure. The etching method displays high selectivity and a throughput which makes it suitable for production purposes.

Description

Gas mixture and method for dry etching metals, especially copper, at low temperatures

The invention relates to a gas mixture and a method for dry etching metals, in particular copper, at low temperatures.

The great need for ever more powerful microelectronic circuits requires constant improvement of the methods and materials for producing ever smaller structural elements in increasingly higher packing densities.

Due to its low specific resistance and its good resistance to electromigration, copper is a suitable material for conductor tracks of future integrated circuits.

Suitable processes for the production of layers and other prerequisites for the use of a new conductor track material in microelectronics to structure this layer. In addition to physical techniques, chemical deposition from the gas phase (CVD) is particularly suitable as a method for producing copper layers.

An anisotropic etching process, which removes the excess copper after applying a suitable mask, is necessary to produce a conductor track structure from a surface-covering layer. On the other hand, to produce copper nails for the electrical connection of different interconnect levels, a full-area copper layer is applied to the structured dielectric and then etched back isotropically.

Another method for producing conductor track structures is the so-called damascene or "inverse metal" technology. The merall is applied to the structured dielectric and isolated by subsequent full-surface polishing using CMP. When using this technique with copper, metal is smeared over the dielectric bars due to the low hardness of the copper, which leads to short circuits between the conductor tracks. In addition, by electrochemical

Operations require a redeposition of metal from the abrasive to occur. Both effects require the polished disks to be cleaned to remove the excess copper.

Copper layers are applied to process disks using CVD or PVD, among other things. An undesirable coating of reactor parts with copper occurs here. To avoid impairment of the process result by chipping The reactor must be cleaned of copper particles at regular intervals.

Previous solutions for dry etching of metals and especially copper can be divided into plasma etching processes, laser etching processes and purely chemical approaches.

The basis of the plasma and laser etching processes is a chlorination of the copper surface by different chlorine sources (eg Cl- ,, CC1 ₄ ), which leads to the formation of a thin layer of the composition CuCl _x (with x = 0-2). The copper layer is removed by desorption of the species Cu ₃ Cl ₃ and CuCl (see, for example, HF Winters, J. Vac.

Technol. 1985, A3, 786). However, their very low vapor pressure either causes very low etching rates, or else high temperatures are necessary which no longer allow the use of conventional photoresist masks or even damage structures that have already been applied to the substrate.

The RIE method (RIE = Reactive Ion Etching) for etching copper allows process temperatures from 200 ° C (see, for example, G.C. Schwartz, PM Schaible, J. Electroche. Soc. 1983, 130, 1777; US Patent 4,352,716 ). By applying a suitable AC voltage, the substrate is bombarded with cationic chlorine species, which facilitates the desorption of the CuCl _χ species.

Laser etching processes are also known which use the energy of the laser light to desorb the CuCl _x - Use species after prior chlorination of the copper surface (two-stage process) (US 4,490,210 and US 4,490,211).

A disadvantage of the processes using halogen-containing etching gases is, however, the deposition of the same in the downstream of the valve in valves and vacuum pumps, which is caused by the low vapor pressure of the etching products, which leads to increased wear of these parts.

Chemical etching processes presented so far either use the reverse of the CVD reaction of precursors of the type (/ 3-diketonate) CuL (L = neutral ligand, e.g. triethyl vinyl silane, bis (trimethyl silyl) acetylene)

Cu ° + Cu ^π (/ 3-diketonate) - + 2 L -> 2 (0-diketonate) CU'L

(see e.g. JAT Norman, BA Muratore, PN Dyer, DA Roberts, AK Hochberg, J. Phys. (Paris) 1991, IV (1) C2-271) or the generation of volatile Cu (I) - and Cu (II) - Compounds on previously oxidized or chlorinated copper surfaces (see, for example, F. Rousseau, A. Jain, TT Kodas, MJ Hampden-S ith, JD Farr, R. Muenchhausen, J. Mater Chem. 1992, 2,

893; J. Farkas, KM Chi, TT Kodas, MJ Hampden-Smith, Advanced Metallization for ULSI, AT&T Bell Laboratories, Murray Hill, NJ 445, 1992): CuO + 2 Hhfac -> Cu (hfac) ₂ + H ₂ 0

CUC1 + 2 PEt ₃ -> ClCu (PEt ₃ ) ₂

Hhfac = 1,1,1,5,5,5-hexafluoropentane-2,4-dione, hfac = anionic 1, 1, 1, 5, 5, 5-hexafluoropentane

2,4-dionato chelating ligand The disadvantages of the latter two methods are, on the one hand, that they are two-stage processes in which the actual etching step is preceded by a pretreatment of the surface at high temperatures or in plasma. This results in lower throughput compared to single-stage processes. On the other hand, in the case of etching via ClCu (PEt ₃ ) _: the use of triethylphosphine poses a risk of contamination for the semiconductor component by the doping element phosphorus.

The reversal of the CVD reaction of (/ 3-diketonate) CuL requires the evaporation of the solid Cu (-diketonate) _: which requires more equipment.

The object of the invention is to provide a gas mixture and a method which enable dry etching of metals and in particular copper at low temperatures with sufficiently high etching rates in a single process step.

As far as the gas mixture is concerned, this object is achieved by the characterizing features of claim 1 and, in terms of process engineering, by the characterizing features of claim 15. Advantageous refinements and developments of the invention result from the respective subclaims.

According to claim 1, the gas mixture according to the invention for dry-etching metals, in particular copper, contains at least oxygen and two further reactants L and HA. With this gas mixture in a single process step the oxidation of Metals and the formation of a volatile metal compound that is stable under process conditions.

When copper is etched, for example, a volatile copper (I) compound is formed. The reaction taking place is represented by the following general equation:

2 Cu + h O, + 2 HA + 2n L -> 2A-Cu-L _n + H-, 0 (n = l, 2)

The formation of the compound A-Cu-L _n advantageously takes place under much milder conditions than in conventional etching processes. Particularly in comparison to the known methods for dry etching, which are based on the formation of CuCl _x , the very good permits

Volatility of the reaction product A-Cl-L _n advantageously low substrate temperatures.

In addition to oxygen and at least one neutral ligand L, the gas mixture according to the invention contains at least one further substance HA of the general formula (I)

X'C (R ') CH ₂ C (R ² ) X ² , (I)

in which X ¹ and X ^{2 are} identical or different and are linear or branched alkyl having preferably 1 to 7 C atoms, a halogen-substituted linear or branched alkyl having preferably 1 to 7 C atoms, an organylsilyl or an aryl, for example a substituted or unsubstituted phenyl, and R ¹ and R ^{2 are the} same or different and R ^{1 is} oxygen or NX ³ and R ^{2 is} oxygen or NX ⁴ , where X ³ and X ^{4 are the} same or different and Hydrogen, a halogen, a linear or branched alkyl having preferably 1 to 7 C atoms, a halogen-substituted linear or branched alkyl having preferably 1 to 7 C atoms, an organosilyl or an aryl, for example a substituted or unsubstituted phenyl , are.

The substance HA according to the general formula (I) is preferably a / 3-diketone of the general formula (II)

X'C (0) CH ₂ C (0) X ² , (ii;

an unsubstituted or substituted _/ 3-keto-ketimin of the general formula (III)

X'C (0) CH ₂ C (NX ³ ) X ² , (III)

or an unsubstituted or substituted dike in the general formula (IV)

X'C (NX ³ ) CH ₂ C (NX ⁴ ) X ² , (IV)

where X ¹ , X ² , X ³ and X ^{4 have} the meaning given above.

Examples of suitable substances HA are 1,1,1, 5,5, 5-hexafluoropentane-2, 4-dione, 1,1, 1-trifluoropentane-2,4-dione or 1, 1, 1, 5, 5, 5-hexafluoro-4- (N-isopropylketimino) pentan-2-one

The neutral ligand L represents linear or branched alkylisonitrile with preferably 1 to 10 C atoms, halogen-substituted linear or branched alkylisonitrile with preferably 1 to 10 C atoms, Arylisonitrile, substituted and unsubstituted 1, 5-cyclooctadiene, cyclooctatetraene (COT), bistrimethylsilylacetylene, alkynes (R'CCR ² , with R ¹ and R ^{2 the} same or different linear or branched alkyl with preferably 1 to 5 C atoms or unsubstituted or substituted phenyl), triorganylphosphine (PR ³ RR ⁵ , identical or different linear or branched alkyl having 1 to 5 carbon atoms or substituted or unsubstituted phenyl with R ³ , R ⁴ and R ⁵ ), triorganyl phosphite (P (OR ⁶ ) ₃ , with R ⁶ linear or branched alkyl having preferably 1 to 5 carbon atoms or substituted or unsubstituted phenyl) or trimethylvinylsilane (TMVS).

As the neural rally L, for example,

Butylisonitrile, tri ethyl phosphine or bis (tri ethyl silyl) acetylene or mixtures thereof in question.

When dry etching copper, for example, the neutral ligand L contained in the gas mixture has the task of coordinatively saturating the Cu (I) center and thus stabilizing the onomeric etching product. The oxidation of Cu ° to Cu ^lτ (Cu _: 0), which takes place at low temperatures, is sufficient to form a volatile reaction product. In conventional processes using volatile Cu (II) compounds, much tougher conditions (high temperature, plasma) are necessary for the oxidation of Cu ° to Cu ²⁺ .

HA is preferably 1, 1, 1, 5, 5, 5, -hexafluoropentane-2,4-dione and L is tert-butylisonitrile (CNtBu). The reaction of the etching process is then described by the following equation: 2 Cu + h 0-, + 2 Hhfac + 2 n CNtBu ->

2 (hfac) Cu (CNtBu) _n + H ₂ 0 (n = l, 2)

The compounds tert-butylisonitrile (1,1,1,5,5, 5-hexafluoropentane-2, 4-dionato) copper (I) and bis (tert-butylisonitrile) (1, 1, 1, 5, 5,5, -hexafluoropentane-2, -dionato) copper (I).

An advantage of the gas mixture according to the invention is the fact that the reaction products have a high volatility compared to, for example, copper chlorides. Deposits in the reactor system can therefore be largely avoided. In addition, no corrosive etching chemicals are required, which increases the life of the system.

Good meterability of liquid or gaseous etching chemicals and thus good controllability of the etching process results from the additional use of a carrier gas for the reactive components of the gas mixture. The reactive components can be introduced into the reaction chamber in defined amounts using this carrier gas. Suitable inert carrier gases are, for example, N ₂ or an inert gas. Oxygen can also be used as a carrier gas.

In the method for dry etching of metals according to the invention, the gas mixture according to one of claims 1 to 12 leads to a reactor pressure adapted to the desired etching isotropy and advantageously low substrate temperatures of to to 60 ° C in a single process step for an oxidation of the metal and the formation of a volatile metal compound stable under process conditions. The process is particularly suitable for the dry etching of copper. However, the etching of other metals, for example silver, is also conceivable.

The one-step etching process according to the invention allows a high throughput. Furthermore, even with very low substrate temperatures of 60 ° C, etching rates suitable for production are still obtained. Preferred substrate temperatures are 70 ° C and above. The etching rate can be increased with increasing substrate temperature.

The extremely low process temperatures allow the use of conventional paint masks to structure the copper surface. Furthermore, the inventive method has a high selectivity compared to conventional antireflection layers made of titanium or titanium nitride, so that these are also suitable for use as etching asks.

The reactor pressure should be between 10 ² and 10 ⁵ Pa, ideally approximately 5-10 ⁴ Pa, in order to achieve an isotropic etching attack for, for example, copper removal over the entire surface.

An anisotropic etching behavior is achieved by using oxygen and / or noble gas ions, preferably argon ions, which are generated in an ECR plasma and extracted and directed towards the substrate. The anisotropy effect is due to an increased oxidation rate parallel to the substrate surface or a supporting sputter removal. The reactor pressure should be anisotropic Etching attack between 10 ~ * and 10 ² Pa, preferably about 10 " ¹ Pa.

Good controllability of the etching process can be achieved by the additional use of a carrier gas for the reactive components of the gas mixture.

The figure shows a schematic representation of a device for performing the inventive

Process for dry etching metals, especially copper.

The reactor shown in the figure has a microwave generator 1, magnet coils 2, an ECR plasma source 3 and an RF generator 7. The reactor has a gas inlet 4 for oxygen, a further gas inlet 5 for the other reactive gases and a gas outlet 8 to the vacuum pump. The disc holder 6 can be tempered. Microwave generator 1 and high-frequency generator 7 are only operated for anisotropic etching.

The gas mixture according to the invention permits, for example, subsequent cleaning of dielectric webs on, for example, conductor tracks structured with the Damascene technique from excess copper which leads to component failure. An isotropic etching process is preferably used. With the gas mixture according to the invention, in-situ cleaning of the reactor shown for the deposition of, for example, copper (CVD, PVD) is also possible. An isotropic etching process allows the deposition reactor to be cleaned in the operating state, ie it is not necessary to switch off and open the deposition reactor. Through the The low temperature required for the etching process can also advantageously be carried out with little effort for heating the deposition reactor parts to be cleaned, or the reactor wall heating which is usually already present can be used.

Process parameters and gas compositions for the isotropic and anisotropic dry etching of copper are given below as examples:

Isotropic etching process:

1,1,1,5,5, 5-Hexafluorpentan-2, 4-dione (Hhfac) in carrier gas: 1 - 100 sccm tertiary butylisonitrile (CNtBu) in carrier gas: 1 - 100 sccm

Carrier gas (nitrogen, helium, argon):

10 - 300 sccm oxygen: 5 - 300 sccm process temperature: 60 - 450 ° C

Reactor pressure: 10 ³ - 5-10 ⁴ Pa

Substrate: Cu layer deposited over the entire surface. Etching rate: 100 - 500 nm / min

Anisotropic etching process

1,1,1,5,5,5-hexafluoropentane-2,4-dione (Hhfac) in carrier gas: 1-50 sccm tertiary butylisonitrile (CNtBu) in carrier gas: 1-50 sccm

Carrier gas (nitrogen, helium, argon):

5-100 sccm

Oxygen (ECR plasma): 5 - 100 sccm Argon (ECR plasma): 0 - 100 sccm ECR plasma power: <300 W.

RF power: 0 - 100 W.

Process temperature: 60 - 250 ° C

Reactor pressure: 10 ^'2 - 10 Pa

Substrate: Cu layer deposited over the entire surface

Photoresist / Ti mask

Etching rate: 50 - 200 n / min

Further examples

Under the same process conditions as in the two previous examples, the following etching gases in combination with oxygen are also suitable for carrying out the isotropic or anisotropic etching process according to the invention:

a) 1, 1, 1-trifluoropentane-2,4-dione + tri ethylphosphine

b) 1,1,1,5,5,5-hexafluoro-4- (N-isopropylketimino) pentan-2-one + triethylphosphine

c) Hhfac + bis (trimethylsilyl) acetylene

Claims

claims

1. Gas mixture for dry etching of metals, in particular copper, containing oxygen, at least one neutral ligand L and at least one further substance

HA of the general formula (I)

X ¹ C (R ¹ ) CHC (R ² ) X ² , (I)

in which X ¹ and X ^{2 are the} same or different and are a linear or branched alkyl, a halogen-substituted linear or branched alkyl, an aryl or organylsilyl and R ¹ and R ^{2 are the} same or different and R ^{1 is} oxygen or NX ³ and R ^{2 is} oxygen or

NX ⁴ is where X ³ and X ^{4 are the} same or different and are hydrogen, a halogen, a linear or branched alkyl, a halogen-substituted linear or branched alkyl, an aryl or

Organylsilyl are.

2. Gas mixture for dry etching of metals, in particular copper, according to claim 1, characterized in that the linear or branched, substituted or unsubstituted alkyl has X ¹ , X ² , X ³ , X ⁴ 1 to 7 carbon atoms.

3. Gas mixture for dry etching of metals, in particular copper, according to claim 1 or 2, characterized in that the substance HA of the general formula (I) is a -diketone of the general formula (II)

X'C (0) CH, C (0) X ² (II)

is, where X ¹ and X ^{2 have} the meaning given in claim 1 or 2.

4. Gas mixture for dry etching of metals, in particular copper, according to claim 1 or 2, characterized in that the substance HA of the general formula (I) is an unsubstituted or substituted β-keto-ketimine of the general formula (III)

X'C (0) CH ₂ C (NX ³ ) X ² (III)

is, wherein X ¹ , X ² and X ^{3 have} the meaning given in claim 1 or 2.

5. Gas mixture for dry etching of metals, in particular copper, according to claim 1 or 2, characterized in that the substance HA of the general formula (I) is an unsubstituted or substituted 3-dikimine of the general formula (IV)

X'C (NX ³ ) CH ₂ C (NX ⁴ ) X ² (IV)

is, wherein X ¹ , X ² , X ³ and X ^{4 have} the meaning given in claim 1 or 2.

6. Gas mixture for dry etching of metals, in particular copper, according to claim 1, characterized in that the substance HA of the general formula (I) 1, 1, 1.5, 5, 5-hexafluoropentane-2, 4-dione, 1st , 1,1-trifluoropentan-2, 4-dione or 1, 1, 1, 5, 5, 5-hexafluoro-4- (N-isopropylketimino) pentan-2-one.

7. Gas mixture for dry etching of metals, in particular copper, according to one of claims 1 to 6, characterized in that the neutral ligand L is a linear or branched alkylisonitrile, a linear or branched alkylisonitrile substituted by halogen, an arylisonitrile Substituted or unsubstituted 1, 5-cyclooctadiene, a cyclooctatetraene (COT), a bistrimethylsilyl acetylene, an alkyne of the general formula R'CCR ² , a triorganylphosphine of the general formula PR ³ R ⁴ R ⁵ , a triorganyl phosphite of the general formula P (0R ⁶ ) or a tri ethyl vinyl silane (TMVΞ), where R ^! , R ² , R ³ , R ⁴ , R ⁵ and R ^{6 are the} same or different, linear or branched alkyls or substituted or unsubstituted phenyls.

8. Gas mixture for dry etching of metals, in particular copper, according to claim 7, characterized in that the linear or branched, substituted or unsubstituted alkylisonitrile has 1 to 10 carbon atoms.

9. Gas mixture for dry etching of metals, in particular copper, according to claim 7 or 8, characterized in that the linear or branched alkyls R ¹ , R ² , R ³ , R ⁴ , R ⁵ and R ^{6 have} 1 to 5 carbon atoms exhibit.

10. gas mixture for dry etching of metals, in particular copper, according to one of claims 1 to 7, characterized in that the neutral ligand L tert-butylisonitrile,

Trimethylphosphine or bis (trimethylsilyl) a ethylene or a mixture thereof.

11. Gas mixture for dry etching of metals, in particular copper, according to one of claims 1 to 10, characterized in that the gas mixture additionally contains a carrier gas.

12. Gas mixture for dry etching of metals, in particular copper, according to claim 11, characterized in that the carrier gas is oxygen, nitrogen or a noble gas.

13. Use of a gas mixture according to one of claims 1 to 12 for in-situ cleaning of separator reactors.

14. Use of a gas mixture according to one of the

Claims 1 to 12 for the cleaning of structured conductor tracks.

15. A method for dry etching of metals, in particular copper, in which with the aid of a gas mixture according to at least one of claims 1 to 12, one correlated with the etching isotropy

Reactor pressure and at process temperatures above 60 ° C the metal is oxidized and a volatile metal compound stable under process conditions is formed.

16. A method for dry etching of metals, in particular copper, according to claim 15, characterized in that a reactor pressure between 10 ² and 10 ⁵ Pa is set to achieve an isotropic etching attack.

17. A method for dry etching of metals, in particular copper, according to claim 15, characterized in that to achieve an anisotropic etching attack, a reactor pressure between 10 ² and 10 " ⁵ Pa is set and the etching process is supported by a plasma discharge.

18. A method for dry etching of metals, in particular copper, according to claim 17, characterized in that oxygen and / or noble gas ions are directed onto the substrate during the plasma discharge.

19. A method for dry etching of metals, in particular copper, according to one of claims 15 to 18, characterized in that a carrier gas is added to the gas mixture.

20. A method for dry etching of metals, in particular copper, according to one of claims 15 to 19, characterized in that the process temperatures are above 70 ° C.