US20040166692A1 - Method for producing hydrogenated silicon oxycarbide films - Google Patents

Abstract

A method for producing hydrogenated silicon oxycarbide (H:SiOC) films having low dielectric constant. The method comprises using plasma-assisted polymerization to react a cyclic silane compound containing at least one strained silicon bond to produce the films. The resulting films are useful in the formation of semiconductor devices.

Description

FIELD OF THE INVENTION
• This invention is a method for producing hydrogenated silicon oxycarbide (H:SiOC) films having low dielectric constant. The method comprises using plasma-assisted polymerization to react a cyclic silane compound containing at least one strained silicon bond to produce the films. The resulting films are useful in the formation of semiconductor devices.[0001]
BACKGROUND OF THE INVENTION
• The use of chemical vapor deposition (CVD) to produce SiO[0002]₂, SiNC:H or SiC:H or SiC:O:H thin films on semiconductor devices from silicon-containing materials such as silane (SiH₄), tetraethyl orthosilicate (TEOS), and methyl-containing silanes such as trimethylsilane has been disclosed in the art. Chemical vapor deposition processes typically comprise introducing the gaseous silicon-containing material and a non-Si containing reactive gas into a reaction chamber containing the semiconductor substrate. An energy source such as thermal or plasma induces the reaction between the silicon-containing material and reactive gas thereby resulting in the deposition of the thin film of SiO₂, SiNC:H or SiC:H or SiC:O:H on the semiconductor device. Plasma enhanced chemical vapor deposition (PECVD) is typically carried out at low temperatures (<500° C.) thereby making PECVD a suitable means for producing dielectric and passivation films on semiconductor devices.
• With the industry requirement to minimize the electrical resistance-capacitance (RC) delay associated with the circuit interconnections, new low permittivity dielectrics are required for use as isolation materials between adjacent conductors. While many candidate film materials exist with relative dielectric constant k, in the range 2.5<k<3.5, few have lower permittivity. Among the materials with k<2.5 are amorphous carbon alloys, fluorinated amorphous carbon alloys, and forms of porous silicon oxide.[0003]
• The typical amorphous carbon alloy films have been shown to have inadequate thermal stability, often decomposing at temperatures above 200° C. It has also been shown that it is difficult to obtain good adhesion between carbon alloys and the metal films used to form the circuit interconnections. It is proposed that this problem can be overcome by the use of a reactive gas comprising a silane compound having a strained silicon bond environment. The approach is to create a carbon based film with some minimal Si content. The presence of the Si allows the formation of a native Si—O siloxane or silicon oxide on the film surface, which improves adhesion compared to an all carbon surface as is found in a-C:H, and a-C:F:H and Teflon based films.[0004]
• U.S. Pat. No. 6,440,876 to Wang et al. discloses the use of a Si—O—C in-ring cyclic siloxane precursor compound in the formation of a film having a dielectric constant, k, of less than 2.5.[0005]
• The use of silacyclobutanes in forming amorphous SiC films have been described in U.S. Pat. No. 5,011,706 to Tarhay et al. This patent discloses a method of forming a continuous coating of amorphous silicon carbide on the surface of articles by plasma enhanced chemical vapor deposition. The chemical vapor comprises a silicon containing cyclobutane.[0006]
• It is an object of this invention to provide a method for producing low dielectric permittivity films of hydrogenated silicon oxycarbide by plasma assisted polymerization of a cyclic silane compound containing at least one strained silicon bond.[0007]
SUMMARY OF THE INVENTION
• This invention pertains to a method of producing thin films of hydrogenated silicon oxycarbide (H:SiOC) having low dielectric permittivity on substrates, preferably semiconductor devices. The method comprises the plasma-assisted polymerization of a reactive gas mixture comprising a cyclic silane compound containing at least one strained silicon bond (“cyclic silane compound”) and an oxygen providing gas. These films have a low dielectric constant and are particularly suited as interlayer dielectrics.[0008]
DETAILED DESCRIPTION OF THE INVENTION
• This invention pertains to a method for producing hydrogenated silicon oxycarbide films on substrate. Typical substrates include but are not limited to, semiconductor substrates, liquid crystal devices, a light emitting diode display device, and an organic light emitting display device. The method for producing the films comprises the plasma assisted polymerization of a reactive gas mixture comprising a cyclic silane compound having at least one strained silicon bond (“cyclic silane compound”) and an oxygen providing gas.[0009]
• By “semiconductor substrate” it is meant to include, but not be limited to, silicon based devices and gallium arsenide based devices intended for use in the manufacture of a semiconductor components including focal plane arrays, opto-electronic devices, photovoltaic cells, optical devices, transistor-like devices, 3-D devices, silicon-on-insulator devices, super lattice devices and the like. The semiconductor substrates may contain one or more layers of wiring. The semiconductor substrate may also be those substrates prior to the formation of any wiring layers.[0010]
• Cyclic silane compounds are those compounds where one or more silicon atoms are contained within at least one ring structure that does not include an oxygen atom in the ring structure. Such compounds must have at least one ring and each ring must have a minimum of three substituent atoms wherein at least one of the substituent atoms are Si and each ring must not contain an oxygen atom. Examples of cyclic silane compounds include silicon-containing cyclobutanes, silicon-containing cyclopentanes, silicon-containing cyclohexanes, sila-5-spiro[4,4]nona-2,7-diene, bi-cyclic compounds and related materials.[0011]
• Silicon-containing cyclobutanes with one silicon atom include compounds represented by the formula[0012]

  
• where each R is independently selected from the group consisting of hydrogen, fluorine, and hydrocarbon radicals having 1 or more carbon atoms and each R′ is independently selected from the group consisting of hydrogen and hydrocarbon radicals having 1 or more carbon atoms. Typically any hydrocarbon radicals will have 1 to 4 carbon atoms. For example, useful silicon-containing cyclobutanes include the parent compound silacyclobutane (H[0013]₂SiC₃H₆) and derivatives such as 1,1-difluorosilacyclobutane, 1-methylsilacyclobutane, 1,1-dimethylsilacyclobutane, 1,1-ethylmethylsilacyclobutane, 1-butylsilacyclobutane, 2,4-dimethylsilacyclobutane, 3,3-diethylsilacyclobutane, and 3,3-ethylpropylsilacyclobutane.
• Silicon-containing cyclobutanes with two silicon atoms include compounds represented by the formula[0014]

  
• where each R and R′ has the same meaning as described previously. For example, useful silicon-containing cyclobutanes include the parent compound 1,3-disilacyclobutane and derivatives such as 1,1,3,3-tetrafluoro-1,3-disilacyclobutane, 1-methyl-1,3-disilacyclobutane, 1,3-dimethyl-1,3-disilacyclobutane, 1,1-ethylmethyl-1,3-disilacyclobutane, 1-butyl-1,3-disilacyclobutane, 2,4-dimethyl-1,3-disilacyclobutane, 2,2-diethyl-1,3-disilacyclobutane, and 2,4-ethylpropyl-1,3-disilacyclobutane.[0015]
• The above silacyclobutane and 1,3-disilacyclobutane as well as their derivatives are known materials and methods for their production are known in the art. For example, the preparation of silacyclobutane from 1,1-dichlorosilacyclobutane by lithium aluminum hydride reduction is described by J. Laane, J. Am. Chem. Soc. 89, 1144 (1967).[0016]
• Other cyclic silane compounds include[0017]

  
• The reactive gas mixture used to produce the H:SiOC films also comprises a controlled amount of an oxygen providing gas. The oxygen may be controlled by the type of oxygen providing gas used, or by the amount of oxygen providing gas that is used. If too much oxygen is present in the deposition chamber a silicon oxide film with a stoichiometry close to SiO[0018]₂will be produced and the dielectric constant will be higher than desired. If too little oxygen is present in the deposition chamber a silicon carbide film with a stoichiometry close to SiC:H will be produced.
• Oxygen providing gases include, but are not limited to oxygen, air, nitrous oxide, nitric oxide, carbon monoxide, carbon dioxide, peroxides, and sulfur dioxide (SO[0019]₂), typically nitrous oxide. The amount of oxygen providing gas is typically 0.1 to 10 volume parts oxygen providing gas per volume part of cyclic silane compound, alternatively from 0.2 to 7 volume parts of oxygen providing gas per volume part of cyclic silane compound. One skilled in the art will be able to readily determine the amount of oxygen providing gas based on the type of oxygen providing gas and the deposition conditions.
• Other materials may be present in the reactive gas mixture. For example, carrier gases such as helium or argon, dopants such as phosphine or diborane, halogens such as fluorine, halogen-containing gases such as SiF[0020]₄, CF₄, C₃F₆and C₄F₈or any other material that provides additional desirable properties to the film may be present.
• The reactive gas mixture is introduced into a deposition chamber containing a substrate, preferably a semiconductor substrate, wherein the polymerization of the cyclic silane compound is induced resulting in the deposition of a film on the substrate wherein the film comprises hydrogen, silicon, carbon and oxygen and has a low dielectric constant (>2.0 to <3.2). Plasma enhanced chemical vapor deposition (PECVD) is preferred due to the low temperatures that can be used and wide use in the industry.[0021]
• In PECVD the gas mixture is reacted by passing it through a plasma field. The plasmas used in such processes comprise energy derived from a variety of sources such as electric discharges, electromagnetic fields in the radio frequency or microwave range, lasers or particle beams. Generally preferred in the plasma deposition processes is the use of radio frequency (10 kHz to 10[0022]²MHz) or microwave (1.0 to 10 GHz) energy at moderate power densities (0.1 to 5 watts/cm²). The specific frequency, power and pressure, however are generally tailored to the equipment. Preferably the films are produced using PECVD at a power of 20 to 1000 W; a pressure of 1 to 10,000 mTorr; and a temperature of 25 to 500° C. Confined, low pressure (1-5 mTorr) microwave frequency plasmas, often referred to as high density plasmas, can be combined with a RF frequency excitation in a process which helps planarize a varying surface topography during CVD growth. This process is useful in the formation of interlayer dielectrics.
• The hydrogenated silicon oxycarbide films produced herein may be represented by the general formula Si[0023]_wO_xC_yH_zwherein the ratio of C:Si can be in the range of about 1:1 to about 10:1 and the ratio of O:Si can be in the range of about 0.1:1 to about 1.5:1 with the balance being hydrogen. The C:Si ratio is typically determined by the C:Si ratio of the cyclic silane compound.
• The films produced herein may be of varying thicknesses. Films having thicknesses of 0.01 to 10 μm may be produced by the method of this invention. Alternatively, the films have a thickness of 0.5 to 3.0 μm.[0024]
• An advantage to the method of this invention is the ability to link successive growth processes to produce multilayer structures of SiO[0025]₂, H:SiOC and/or SiC:H for example SiO₂/H:SiOC/SiO₂or SiC:H/H:SiOC/SiC:H, by increasing or deleting the oxygen providing gas at the appropriate time during the CVD process. It is preferred to produce discreet layers by stopping the reactive gas flow, adjusting the amount of oxygen providing gas and thereafter resuming the reactive gas flow to produce the next layer.
• The films produced herein, due to the low dielectric constant, are particularly suited as interlayer dielectrics in semiconductor integrated circuit manufacturing including, but not limited to, gate dielectrics, premetal and intermetal dielectrics and passivation coatings. The films produced herein have a dielectric constant, k, of ≧2.0 to ≦3.2, alternatively ≧2.2 to ≦2.8.[0026]
• The following non-limiting examples re provided so that one skilled in the art may more readily understand the invention.[0027]
EXAMPLESExample 1
• A reactive gas mixture comprising dimethylsilacyclobutane (DMSCB) and nitrous oxide, N[0028]₂O, (See Tables 1 for gas flow amounts) was introduced into a capacitively coupled parallel plate PECVD system at a deposition temperature was 350° C. The power, pressure conditions that the PECVD system was operated under are given in Table 1. Helium was used as a carrier gas in runs 1-1,1-14, and 1-15. The films were formed on Si(100) wafers as the substrate. The refractive index (RI) was measure on as-deposited films. The dielectric constant (k) was measured after the films were annealed for one hour in N₂ambient and 400° C. following metal deposition. The process conditions and results are in Table 1.

  TABLE 1
  Examples of DMSCB based a-SiCO:H films.

  Dep temp = 350° C.

  Dep

  Press,

  Power,

  DMSCB

  N2O

  He

  Rate

  Post-anneal K*

  Run ID	(torr)	(watt)	(sccm)	(sccm)	(sccm)	(Å/min)	RI	Kavg*	STD

  1-1	3	300	150	125	75	3239	1.4	2.528	0.0283
  1-2	3	300	100	50		1878	1.5021	2.651	0.0988
  1-3	3	400	100	50		3665	1.4661	2.677	0.0920
  1-4	3	300	115	50		1777	1.4955	2.602	0.1161
  1-5	3	300	85	50		1929	1.4991	2.740	0.0110
  1-6	3	250	100	50		1468	1.5036	2.593	0.2057
  1-7	3.8	300	100	50		1803	1.5035	2.683	0.0390
  1-8	2	300	100	700		7608	1.4333	2.604	0.2420
  1-9	3	300	130	50		1626	1.4978	2.545	0.0632
  1-10	3	400	130	50		2375	1.5155	2.650	0.0330
  1-11	3	300	100	700		7482	1.4186	2.838	0.0546
  1-12	1	300	100	50		1110	1.4087	2.793	0.1935
  1-13	1	400	100	50		844	1.5154	3.041	0.1039
  1-14	5	400	50	350	100	4943	1.3741	3.101	0.0750
  1-15	5	400	100	50	100	2692	1.5218	2.583	0.1234

EXAMPLE 2 (COMPARATIVE)
• a-SiC:H films were produced using DMSCB as described in Example 1 except that nitrous oxide (N[0029]₂O) was not used in the reactive gas mixture.

  TABLE 2
  Examples of DMSCB a-SiC:H films.

  Dep temp = 350° C.

  Press,

  Power,

  DMSCB

  He

  Dep Rate

  Post annealed K*

  Run ID	(torr)	(watt)	(sccm)	(sccm)	(Å/min)	RI	Kavg	STD

  C2-1	3	200	150	200	140	1.7106	4.350	0.1633
  C2-2	3	400	150	200	273	1.7375	4.271	0.1612
  C2-3	5	300	50	80	287	1.6146	3.919	0.0239
  C2-4	5	200	50	80	125	1.6172	4.044	0.1137
  C2-5	2	400	50	80	580	1.7749	4.357	0.0458
  C2-6	2	300	50	80	376	1.783	4.474	0.1114

EXAMPLE 3
• Films produced in Run 1-15 of Example 1 and Run C[0030]_2-4of Example 2 were analyzed for composition using Rutherford Back Scattering-Hydrogen Forward Scattering (Ion Scattering Spectrometry). The results of this analysis are given in Table 3. As can be seen by these results. The leakage current density was also measured on both films. For the a-SiCO:H film the leakage current density at 1 MV/cm was less than 10⁻¹⁰Å/cm². For the a-SiC:H film the leakage current density at 1 MV/cm was less than 10⁻¹⁰Å/cm².
• As can be seen by these results it is possible to produce films having low leakage current density with increased C:Si ratios.[0031]
• For additional comparison, a-SiCO:H and a-SiC:H films were produced using trimethylsilane (TMS).[0032]

  TABLE 3
  Composition of DMSCB based a-SiCO:H and a-SiCO:H films

  						Atom				LKG	Vbd
  						density	Density			(Å/cm2@	(mv/cm @
  Process	Si	N	H	O	C	(atoms/cm2)	(g/cm3)	O/Si	C/Si	1 MV/cm)	1 mA/cm2)

  DMSCB	0.11	0	0.46	0.1	0.33	1.78E+18	1.15	0.91	3	7.67 × 10−11	>4
  a-SiCO:H
  DMSCB	0.16	0	0.4	0.08	0.36	4.09E+17	1.12	0.5	2.25	2.39 × 10−11	>4
  a-SiC:H
  TMS	0.15	0.02	0.36	0.15	0.32	6.55E+22	1.17	1.00	2.14	3 × 10−10*	>4
  a-SiCO:H
  TMS	0.30	0	0.14	0.05	0.48	7.47E+22	1.85	0.17	1.6	5.33 × 10−9	2.5
  a-SiC:H

Claims (23)

What is claimed is:

1. A chemical vapor deposition method for producing hydrogenated silicon oxycarbide films comprising

introducing a reactive gas mixture comprising (i) a cyclic silane compound containing at least one strained silicon bond and (ii) an oxygen providing gas into a deposition chamber containing a substrate and inducing a reaction between the cyclic silane compound and oxygen providing gas at a temperature of 25° C. to 500° C.;

wherein there is a controlled amount of oxygen present during the reaction to provide a film on the substrate comprising hydrogen, silicon, carbon and oxygen having a dielectric constant in the range of 2.0 to 3.2.

2. The method as claimed inclaim 1 wherein the cyclic silane compound is selected from the group consisting of silicon-containing cyclobutanes, silicon-containing cyclopentanes, silicon-containing cyclohexanes, sila-5-spiro[4,4]nona-2,7-diene, and bi-cyclic compounds.

3. The method as claimed inclaim 1 wherein the cyclic silane compound is selected from

where each R is independently selected from the group consisting of hydrogen, fluorine, and hydrocarbon radicals having at least 1 carbon atom and each R′ is independently selected from the group consisting of hydrogen and hydrocarbon radicals having at least one carbon atom.

4. The method as claimed inclaim 2 wherein the cyclic silane compound is a silicon-containing cyclobutane.

5. The method as claimed inclaim 4 wherein the silicon-containing cyclobutane has the formula

where each R is independently selected from the group consisting of hydrogen, fluorine, and hydrocarbon radicals having at least 1 carbon atom and each R′ is independently selected from the group consisting of hydrogen and hydrocarbon radicals having at least 1 carbon atom.

6. The method as claimed inclaim 4 wherein the silicon-containing cyclobutane has the formula

where each R is independently selected from the group consisting of hydrogen, fluorine, and hydrocarbon radicals having at least one 1 carbon atom and each R′ is independently selected from the group consisting of hydrogen and hydrocarbon radicals having at least 1 carbon atom.

7. The method as claimed inclaim 1 wherein the oxygen providing gas is selected from the group consisting of oxygen, air, peroxides, sulfur dioxide, carbon monoxide, carbon dioxide, nitrous oxide and nitric oxide.

8. The method as claimed inclaim 1 wherein the oxygen providing gas is nitrous oxide.

9. The method as claimed inclaim 1 wherein the cyclic silane compound is dimethylsilacyclobutane and the oxygen providing gas is nitrous oxide.

10. The method as claimed inclaim 1 wherein the amount of oxygen providing gas is in the range of 0.1 to less than 10 volume parts oxygen providing gas per volume part of cyclic silane compound.

11. The method as claimed inclaim 1 wherein the amount of oxygen providing gas is 0.2 to 7 volume parts of oxygen providing gas per volume part of cyclic silane compound.

12. The method as claimed inclaim 1 wherein the reaction is induced by exposing the reactive gas mixture to plasma.

13. The method as claimed inclaim 12 wherein the reaction is induced by exposing the reactive gas mixture to plasma at a power of 20 to 1000 W, a pressure of 1 to 10,000 mTorr, and a temperature of 25 to 500° C.

14. The method as claimed inclaim 1 wherein the film has a dielectric constant in the range of 2.2 to 2.8.

15. The method as claimed inclaim 1 wherein the film has a dielectric constant in the range of 2.5 to 2.8.

16. The method as claimed inclaim 1 wherein the reactive gas mixture additionally comprises a carrier gas.

17. The method as claimed inclaim 1 wherein the hydrogenated silicon oxycarbide film has a thickness of 0.01 to 10 μm.

18. The method as claimed inclaim 1 wherein the hydrogenated silicon oxycarbide film has a thickness of 0.5 to 3.0 μm.

19. The method as claimed inclaim 1 wherein the substrate is a semiconductor substrate.

20. The method as claimed inclaim 1 wherein the substrate is selected from a liquid crystal device, a light emitting diode display device and an organic light emitting diode display device.

21. The method as claimed inclaim 1 wherein the amount of oxygen providing gas is increased or decreased during the reaction between the cyclic silane compound and the oxygen providing gas to produce a film containing successive layers selected from the group consisting of SiO₂, H:SiOC and SiC:H.

22. The method as claimed inclaim 1 wherein the reaction is induced by exposing the reactive gas mixture to confined, low-pressure microwave frequency plasma combined with RF frequency excitation.

23. A semiconductor device having thereon a film produced by the method as claimed inclaim 1.