H:SiOC coated substrates

[0002] This application is a continuation-in-part of U.S. patent application No. 09/639,410, filed Aug. 14, 2000, pending which is a divisional of U.S. patent application No. 09/086,811 filed May 29, 1998, now U.S. Pat. No. 6,159,871.

[0003] This invention pertains to a method for producing hydrogenated silicon oxycarbide (H:SiOC) films having low dielectric constant and a light transmittance of 95% or more for light with a wavelength in the range of 400 nm to 800 nm. The method comprises reacting a methyl-containing silane in a controlled oxygen environment using plasma enhanced or ozone assisted chemical vapor deposition to produce the films. Because of the transmittance the resulting films are useful in the formation of display devices such as liquid crystal display devices and organic light emitting devices.

[0004] The use of chemical vapor deposition (CVD) to produce SiO₂, SiNC or SiC thin films on semiconductor devices from silicon-containing materials is well known in the art. Chemical vapor deposition processes typically comprise introducing the gaseous silicon-containing material and a 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 or SiC 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. Silicon-containing materials include silane (SiH₄), tetraethyl orthosilicate (TEOS), silacyclobutanes, and alkylsilanes such as trimethylsilane.

[0005] The use of methyl-containing silanes to produce silicon dioxide (SiO₂), amorphous SiNC and silicon carbide (SiC) films by chemical vapor deposition is known in the art. For example, U.S. Pat. No. 5,465,680 to Loboda discloses a method for making crystalline SiC films. The method comprises heating the substrate 600° C. to 1000° C. and thereafter exposing the substrate to trimethylsilane in a standard chemical vapor deposition process. EP Patent Application No. 0 774 533 to Loboda discloses a method of making SiO₂coatings from the CVD of a reactive gas mixture comprising an organosilicon material and an oxygen source. EP Patent Application No. 0771 886 to Loboda discloses a method of making SiNC coating from the CVD of a reactive gas mixture comprising an organosilicon material and a nitrogen source.

[0006] As semiconductor device structures become increasingly smaller the dielectric constant as well as the integrity of the film become important. Films produced by known CVD processes have high dielectric constants (i.e. 3.8 or greater). Therefore there is a need for processes and materials that result in low dielectric constant films. A new deposition processes known as Low-k Flowfill®, produces films having a dielectric constant of <3.0. This method uses a chemical vapor deposition reaction between methylsilane and hydrogen peroxide to produce a methyl doped silicon oxide film (See S. McClatchie, K. Beekmann, A. Kiermasz; Low Dielectric Constant Oxide Films Deposited Using CVD Techniques,1998 DUMIC Conference Proceedings, February 1998, p. 311-318). However, this process requires a non standard CVD system, the use of a lower stability oxygen source (hydrogen peroxide) and generates water as a by-product which can be undesirable in semiconductor devices and flat panel displays.

[0007] It is therefore an object of this invention to provide a method for producing low dielectric constant thin films of hydrogenated silicon oxycarbide by chemical vapor deposition.

[0008] This invention pertains to a method of producing thin films of hydrogenated silicon oxycarbide (H:SiOC) having low dielectric constants on substrates. The method comprises the plasma enhanced or ozone enhanced chemical vapor deposition of a reaction mixture comprising an methyl-containing silane and an oxygen providing gas. By controlling the amount of oxygen available during the reaction/deposition process a film comprising hydrogen, silicon, carbon and oxygen is produced. These films typically have a dielectric constant of 3.6 or less and are particularly suited as interlayer dielectrics.

[0009] FIG. 1 is a cross-sectional view showing a first semiconductor device having an interlayer dielectric comprising the hydrogenated silicon oxycarbide film of the present invention.

[0010] FIG. 2 is a cross-sectional view showing a second semiconductor device having an interlayer dielectric comprising the hydrogenated silicon oxycarbide film of the present invention.

[0011] This invention pertains to a method for producing hydrogenated silicon oxycarbide films on a substrate. The method for producing the films comprises the chemical vapor deposition reaction of a reactive gas mixture comprising an alkysilane and an oxygen providing gas wherein the amount of oxygen present during the reaction is controlled. By “substrate” it is meant to include silicon based devices, compound semiconductor (i.e. GaAs, InP, GaN, etc.) based devices, liquid crystal devices, light emitting diode (LED), and organic LED (OLED) flat panel display devices constructed on glass or plastic substrates 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, displays and the like. Substrates include integrated circuits preferably in the wafer stage having one or more layers of wiring or integrated circuits before the application of any metal wiring. Other substrates include MEMS, photovoltaic cells, thin film batteries, solar cells, fuel cells, opto-electronic devices, polymer electronics, and molecular electronics.

[0012] The hydrogenated silicon oxycarbide films produced herein may be represented by the general formula Si_wO_xC_yH_zwhere w has a value of 10 to 33, preferably 18 to 20 atomic %, x has a value of 1 to 66, preferably 18 to 21 atomic percent, y has a value of 1 to 66, preferably 31 to 38 atomic % and z has a value of 0.1 to 60, preferably 25 to 32 atomic %; and w+x+y+z=100 atomic %.

[0013] The hydrogenated silicon oxycarbide films are produced from a reactive gas mixture comprising an methyl-containing silane and an oxygen providing gas. Methyl-containing silanes useful herein include methylsilane (CH₃SiH₃), dimethylsilane ((CH₃)₂SiH₂), trimethylsilane ((CH₃)₃SiH) and tetramethylsilane ((CH₃)₄Si), preferably trimethylsilane.

[0014] A controlled amount of oxygen is present in the deposition chamber. 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 SiO₂will be produced and the dielectric constant will be higher than desired. Oxygen providing gases include, but are not limited to air, ozone, oxygen, nitrous oxide and nitric oxide, preferably nitrous oxide. The amount of oxygen providing gas is typically less than 5 volume parts oxygen providing gas per volume part of methyl-containing silane, more preferably from 0.1 to 4.5 volume parts of oxygen providing gas per volume part of methyl-containing silane. 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.

[0015] 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 or any other material that provides additional desirable properties to the film may be present.

[0016] The reactive gas mixture is introduced into a deposition chamber containing a substrate, wherein the reaction between the methyl-containing silane and oxygen providing gas is induced resulting in the deposition of a film on the substrate wherein the film comprises hydrogen, silicon, carbon and oxygen and has a dielectric constant of 3.6 or less on the substrate. Any chemical vapor deposition (CVD) method which has a substrate temperature of less than 500° C. may be used herein. Temperatures greater than 500° C. are typically not suitable for substrates having aluminum wiring and glass or plastic substrates. Plasma enhanced chemical vapor deposition (PECVD) is preferred due to the low temperatures that can be used and wide use in the industry. Ozone enhanced CVD may be also be used herein.

[0017] 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 10²MHz) 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.

[0018] 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. Preferably the films have a thickness of 0.5 to 3.0 μm.

[0019] One advantage to the instant method is that when nitrous oxide is used as the oxygen providing gas, the film composition and properties remain essentially the same even when the amount of nitrous oxide in the reactive gas mixture is significantly varied (1.2:1 to 4.5:1 volume parts N₂O to methyl-containing silane).

[0020] Another advantage to the method of this invention is the ability to link successive growth processes to produce multilayer structures for example of 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.

[0021] 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 of 3.6 or less, preferably, 3.2 or less, more preferably 3.0 or less.

[0022] Additionally, the films produced herein, due to the low dielectric constant and the light transmittance of 95% or more for light with a wavelength in the range of 400 nm to 800 nm, are suitable as an interlayer insulator between the data line and the pixel electrode in display devices with a high aperture ratio.

[0023] The films produced herein may be used to form the film on top of a transistor in a liquid crystal display devices, they may be used to provide a barrier between the light source and the external environment, they may used as an interlevel dielectric in the electronic device of the flat panel display or they may be used in the packaging of the electronic device (i.e. cover the sensor to provide protection from the environment).

[0024] Liquid crystal display devices typically include gate lines, source lines, and switching elements. The films produced herein may be formed above the switching element, the gate line and the source line. A pixel electrode formed is provided on the film. Liquid crystal display devices are disclosed in U.S. Pat. No. 6,188,458 to Tagusa et al., issued Feb. 13, 2001 and U.S. Pat. No. 6,188,452 to Kim et al., issued Feb. 13, 2001, both herein incorporated by reference for its teaching of these devices.

[0025] Organic light emitting devices typically include a flexible substrate, a light emitting layer of an organic material with electrode and covering. The flexible substrate and covering should protect the light emitting layer from the environment, in particular moisture. The films produced herein may be used on either or both the flexible substrate and covering alone, or in conjunction with other materials to provide the barrier properties. Organic light emitting devices are disclosed in U.S. Pat. No. 6,160,346 to Vleggaar et al., issued Dec. 12, 2000, U.S. Pat. No. 6,268,695 to Affinito, issued Jul. 31, 2001, U.S. Pat. No. 6,150,187 to Zyung et al., issued Nov. 21, 2000, all of which are herein incorporated by reference for their teaching of these devices.

[0026] FIG. 1 shows the film produced herein as an intermetal dielectric on a first semiconductor device. As seen in this figure, there is a semiconductor substrate 10 having a wiring layer 11 covered by a hydrogenated silicon oxycarbide film 12. FIG. 2 shows the film produced herein as an intermetal dielectric on a second semiconductor substrate. As seen in this figure, there is a semiconductor substrate 20 with multiple wiring layer 21 and multiple layers of hydrogenated silicon oxycarbide films 22.

[0027] So that those skilled in the art can understand and appreciate the invention taught herein, the following examples are presented, it being understood that these examples should not be used to limit the scope of this invention found in the claims.

[0028] In Examples 1-9 and Comparative Examples 1-2, dielectric properties were measured using metal-insulator-semiconductor (Examples 4-9) and metal-insulator-metal capacitors (Examples 1-3, Comparative Examples 1-2). Measurements were performed immediately after the metal gate deposition (top electrode) and again after one or more anneal cycles in N₂in the temperature range of 350 to 400° C. Relative permittivity, K, was calculated from the capacitor geometry and the film thickness.

[0029] A reactive gas mixture comprising trimethylsilane (3MS) and nitrous oxide (See Tables 1 and 2 for gas flow amounts) was introduced into a capacitively coupled parallel plate PECVD system using thermally oxidized (0.1 [m SiO₂) silicon wafers coated with 0.5 μm Al or bare silicon wafers as the substrates. The PECVD system was operated at a power of 350 W, pressure of 2700 mTorr and temperature of 250° C. Helium was used as a carrier gas. The dielectric constant, growth rate and film stress (compressive) results for Examples 1-9 are in Tables 1 and 2. The composition and density of the films produced in Examples 4-9 are in Table 3. As can be seen in Table 2, even when the amount of nitrous oxide is significantly varied, the resulting films have essentially the same composition and properties.

[0030] Using the same procedure for Examples 1-8, a reactive gas mixture comprising trimethylsilane and oxygen were used in the plasma enhanced chemical vapor deposition. Results are given in Table 4. The resulting films were essentially SiO₂films due to too high 5 of an amount of oxygen used in the reactive gas mixture.

[0031] This example is Example 3 of EP Patent Application No. 0 774 533 Al. A reactive gas mixture comprising 6 sccm of trimethylsilane (TMS) and 523 sccm of nitrous oxide was introduced into a capacitively coupled parallel plate PECVD system using silicon wafers as the substrates. The PECVD system was operated at a power of 50 W, a pressure of 1000 mTorr and a temperature of 300° C. Helium (500 sccm) was used as a carrier gas. Due to the high amount of nitrous oxide (N₂O) being used, the resulting film was a SiO₂film.

[0032] Films were produced on bare silicon wafers or glass as the substrates with a reactive gas mixture of trimethylsilane (3MS), nitrous oxide (N₂O) and helium (He) using a capacitively coupled parallel plate PECVD reactor. The parameters for PECVD, dielectric constant, growth rate for these examples are in Table 5. The typical composition and density of the films produced in examples are in Table 6.

[0033] The light transmittance was measured for the films given in Table 6. All showed a transmittance of 95% or more for light with a wavelength in the range of 400 nm to 800 nm.