Patent Application
20090093135
1. Field of the Invention
This invention relates to semiconductor processing and, more particularly, to semiconductor processing equipment and methods for curing materials on semiconductor substrates using ultraviolet light.
2. Description of the Related Art
Ultraviolet (UV) light processing apparatuses have been used in making substances using UV-light ray modification or photochemical reactions of materials on a variety of treated articles. As a result of the finer wiring designs and multi-layer wiring structures necessitated by increased device integration in recent years, a reduction in interlayer capacitance has become vital. The reduction in interlayer capacitance facilitates increasing the speeds of devices such as integrated circuits and lowering the power consumption of the devices.
Low-k (low dielectric constant film) materials have been used to lower the interlayer capacitance. These materials have a lower dielectric constant compared to traditional materials, such as silicon oxide. However, they also have a reduced mechanical strength (typically measured in terms of elastic modulus, or EM) compared to traditional materials such as silicon oxide. As a result, low-k materials typically have a greater difficulty withstanding stresses during chemical mechanical polishing (CMP), wiring bonding, and packaging during post-processing.
One method of overcoming these problems is to cure the low-k material with UV irradiation (UV curing), thereby increasing the material's mechanical strength. UV curing is described in, e.g., U.S. Pat. Nos. 6,759,098 and 6,296,909, the entire disclosures of which are incorporated herein by reference. It is possible to shrink and cure low-k materials with UV irradiation. The UV curing can raise the materials' mechanical strength (EM) by 50-200%.
Nevertheless, there is an ever-present demand for increased curing efficiency to facilitate increases in processing throughput. In addition, there is a continuing demand to improve the properties of UV cured low-k films.
Accordingly, there is a need for UV curing systems and methods that allow for increased efficiency and desired materials properties.
In accordance with some embodiments of the invention, a method is provided for semiconductor processing. The method comprises providing a low dielectric constant film on a substrate in a process chamber. The low dielectric constant film is cured by irradiating the low dielectric constant film with UV light. The low dielectric constant film is exposed to a process gas having about 25-10,000 parts per million of O2 during curing the low dielectric constant film.
In accordance with other embodiments of the invention, a method is provided for integrated circuit fabrication. The method comprises providing a substrate in a process chamber having a process chamber atmosphere with a O2 concentration between about 25 and about 10,000 parts per million. The substrate has an exposed low dielectric constant material. The low dielectric constant material is irradiated with UV light to form Si—O bonds while suppressing formation of —Si—H and —Si—OH groups relative to UV light irradiation of the low dielectric constant material in an atmosphere consisting of inert gas. The low dielectric constant material is reacted with O2 while irradiating the low dielectric constant material, thereby releasing H2O from the low dielectric constant material
In accordance with other embodiments of the invention, a system for semiconductor processing is provided. The system includes a UV radiation chamber having a UV light source. A source of O2 in gas communication with the UV radiation chamber is provided. A controller is programmed to irradiate a low dielectric material in the UV radiation chamber with UV light while maintaining a concentration of O2 in the UV radiation chamber between about 25 and about 10,000 parts per million.
Moisture absorption and oxidation have been observed in UV-cured low dielectric constant materials (low-k materials), e.g., materials having a dielectric constant of 4 or less. The moisture absorption and oxidation can undesirably increase the dielectric constant of the materials and also cause stress-related changes over time. As a result, it has generally been considered necessary to prevent exposure to oxidants during UV curing. Thus, to prevent oxidation of the low-k materials, the UV curing process is typically performed in an inert atmosphere, devoid of oxygen species.
It has been found that —Si—H groups or —Si—OH groups in the low-k materials contribute also to moisture absorption and oxidation. Low-k materials include carbon and silicon materials, including organosilicate glass and other materials having a dielectric constant below 4. Exposure to UV light has been found to cause silicon in the low-k materials to bind with H or OH groups, thus forming —Si—H and —Si—OH groups, which are not favorable for the low-k materials. Without being limited by theory, it is believed that these groups can react to form or absorb water, which adversely impacts the dielectric constant of the material.
While exposing low-k materials to O2 has been considered undesirable due to concerns about oxidation, it has been found that UV curing in an atmosphere containing O2 is advantageous for material stability and for limiting increases in dielectric constant. It has been found that exposure to O2, in appropriate concentrations, can limit the production of —Si—H and —Si—OH groups, to decrease moisture absorption and adverse impacts on dielectric constant.
Advantageously, according to preferred embodiments of the invention, a low-k material is cured by exposure to UV light in a process chamber having an atmosphere containing about 25-10,000 parts per million (ppm) O2 or about 25-1000 ppm O2. Without being limited by theory, it is believed that the UV exposure in the O2-containing atmosphere causes the release of —H and —OH groups as H2O, thus suppressing the production of —Si—H and —Si—OH, while encouraging the formation of —O—Si bonds. As a result, curing efficiency is improved by aiding the formation of a network of silicon atoms bonded to oxygen atoms (—Si—O—). Thus, preferred embodiments of the invention advantageously limit the production of Si—H and Si—OH groups and improve curing efficiency about 10% or more, relative to a similar UV curing process in an atmosphere containing only inert gas. In some embodiments, the dielectric constant of the low-k material can be about 2.8 or less after UV curing.
Reference will now be made to the Figures.
It will be appreciated that preferred embodiments of the invention can be applied to various UV curing apparatus known the art. An advantageous and non-limiting example of one such UV curing apparatus is illustrated in
With reference to
The UV light irradiation unit 12 is installed at a top of the chamber 26. The UV light unit 12 includes W-light emitting bodies 28 which can emit light continuously and in pulses.
The susceptor 20 is installed parallel to and facing the light emitting bodies 28. The irradiating window 14, which can be formed of glass or other material which transmits UV light, is parallel to and interposed between the UV-light light emitting bodies 28. A substrate 32 is provided over the susceptor 20. The susceptor 20 can be provided with heaters 30 for heating the susceptor 20 an overlying substrate.
The irradiating window 14 allows uniform UV irradiation to be realized on the substrate 32. The irradiating window 14 may be, for example, formed of synthetic quartz and may shield the process chamber 26 from the ambient atmosphere while allowing UV light to pass through.
In the illustrated embodiment, the UV-light emitting bodies 28 inside the UV light irradiation unit 12 are tube-shaped. A plurality of the UV-light emitting bodies 28 are provided, as shown in
In the apparatus 10, the pressure in the chamber 26 can be varied in a range from a vacuum to near atmospheric pressure or more. The chamber 26 is separated, by a flange 36 in which the irradiation window 14 is installed, from the UV-light emitting bodies 28 so as to separate the substrate processing section (including the chamber 26) and the UV emitting section (including the UV light emitting unit 12) of the apparatus 10. Gas is introduced via the flange 36, with a plurality of gas introduction holes provided therein, their positions being symmetrical so as to create a uniform flow of gas and a uniform processing atmosphere.
In some embodiments, a UV curing process is carried out as follows. The chamber 26 is filled with a gas selected from a group that includes Ar, CO, CO2, C2H4, CH4, H2, He, Kr, Ne, N2, O2, Xe, alcohol gases and organic gases to create an atmosphere in the chamber 26 with a pressure of about 0.1 Torr to near atmospheric pressure or up to about 1000 Torr (including 1 Torr, 10 Torr, 50 Torr, 100 Torr, 1000 Torr or any other pressure in between). It will be appreciated that during irradiation with UV light, the atmosphere in the process chamber contains about 25-10,000 ppm. The process chamber atmosphere can be formed by flowing a process gas mixture having about 25-10,000 ppm by volume into the process chamber, before and/or during UV irradiation of a substrate. In some other embodiments, a given gas atmosphere can first be established in the process chamber and then O2 can be added to the gas atmosphere to establish an atmosphere having about 25-10,000 ppm by volume. The O2 can be added before and/or after a substrate is loaded into the process chamber. In some preferred embodiments, the O2 and an inert gas constitute the process chamber atmosphere.
A processing target 32, or semiconductor substrate, having a low-k material, such as a deposited low-k film, is loaded from the load lock chamber 40 via the gate valve 42 and placed onto the susceptor 20. The low-k film can be formed by various methods known in the art. Suitable methods are disclosed in, e.g., U.S. Pat. No. 6,514,880, U.S. Pat. No. 6,455,445 and U.S. Pat. No. 7,144,620, the entire disclosures of which are incorporated by reference herein. The susceptor 20 is adjusted to have a temperature of about 0° C. to about 650° C. (including 10° C., 50° C., 100° C., 200° C., 300° C., 400° C., 500° C., 600° C. or any other temperature in between, but preferably between 300° C. and 450° C.), and then UV light with a wavelength of about 100-400 nm (including 150 nm, about 190 nm or less, 200 nm, 250 nm, 300 nm, 350 nm or any other wavelength in between, but preferably about 200 nm) is used to irradiate the low-k material on the semiconductor substrate 32.
The UV-light emitting bodies 28 can include various UV lamps known in the art. Examples of UV lamps include mercury lamps and excimer lamps. Excimer lamps include Xe excimer lamps, which output 172-nm DUV, characterized by high energy and rapid curing speed. Mercury lamps can vary in terms of lamp pressure from low pressure to very high pressure, and can emit light at wavelengths such as 185 nm, 254 nm, 365 nm.
With continued reference to
Embodiments of the invention can be applied to cure various low-k materials known in the art. Preferred embodiments of the invention have particular advantages when applied to low-k materials containing silicon, oxygen and carbon atoms. Without being limited by theory, it is believed that, in a typical UV curing process, the UV light irradiation breaks —CH3 bonds and —Si—O bonds in the low-k material, reestablishes the —Si—O bonds, and builds an O—Si—O network, thereby improving the mechanical strength of the low-k material. The atmosphere in which the substrate is irradiated has typically been an inert gas atmosphere, which has been used to prevent oxidation of the low-k material. N2, He, Ar, among other inert gases known in the art, can be used as the inert gas.
The Si—O and Si—CH3 bonds in the low-k material are broken by the UV irradiation, and Si is caused to again bond with O to form a O—Si—O network by exposure to heat in the process chamber, and thus mechanical strength is increased. However, it has been found that the silicon atoms can also bond with H or OH, and thus form Si—H and Si—OH bonds, which have been found to be undesirable for low-k materials. For example, without being limited by theory, —Si—H and —Si—OH groups are believed to be a cause of moisture absorption and oxidation in low-k materials, which brings about an increased dielectric constant and stress change over time. Curing the low-k film without producing such substituents is desired from the point of view of stability of the film and maintaining a low dielectric constant.
Advantageously, it has been found that providing O2 in the curing atmosphere, where the curing atmosphere has a O2 concentration of about 25-10,000 ppm, more preferably 25-1,000 ppm, or 125-250 ppm, causes the release of —H and —OH as H2O from the low-k material, while also maintaining the dielectric constant of the low-k material at a low value. Thus, the production of —Si—H and —Si—OH groups is suppressed. Moreover, the O2 aids the formation of Si—O bonds, thereby increasing the curing efficiency (the time required to produce a desired curing of the low-k material) relative to a UV curing process without O2. For example, the curing efficiency can advantageously be increased by about 10% or more.
Aurora ELK™ films (developed by ASM Japan, K.K, Tokyo Japan) were provided on a plurality of substrates. Aurora ELK™ films are low-k films having a dielectric constant of about 2.5. The Aurora ELK films were cured using a high pressure mercury lamp as the UV light source. The films were cured at a temperature of 400° C. and at a pressure of 75 Torr for 600 seconds. The atmosphere in the curing chamber consisted of a mixture of N2 and O22. O2 was added to an N2 process chamber atmosphere to arrive at various concentrations of O2 in the process chamber atmosphere.
Different characteristics of the low dielectric constant film were measured after curing the film in a N2 atmosphere with 0, 25, 125, 250, 500, 750, 1000 and 2000 parts per million of O2. The properties measured of each resulting film included the infrared spectroscopy, the k-value of the dielectric constant, and the elastic modulus (EM).
To more clearly show the changes in the low-k dielectric films due to curing,
The change in the occurrence of O—Si—O bonds relative to the occurrence of Si—H bonds can also be seen in
With reference to
With reference to
It will also be appreciated by those skilled in the art that various omissions, additions and modifications may be made to the methods and structures described above without departing from the scope of the invention. All such modifications and changes are intended to fall within the scope of the invention, as defined by the appended claims.
