Patent Description:
Embodiments of the present disclosure generally relate to processing transparent substrates, and more specifically to films deposited on transparent substrates to increase an opacity and/or reflectivity of the transparent substrate.

Conventional substrate processing equipment utilizes optical sensors, such as lasers, to identify and align substrates for processing therein. However, optical sensors cannot detect a transparent substrate because light from the optical sensor passes through the transparent substrate. A film may be deposited on the substrate to improve detection of the substrate. However, the film can cause bowing of the substrate which interferes with the optical sensors and can result in damage to damage to devices built on the substrate.

An example of a film deposited on a transparent substrate is disclosed in <CIT>. The film has a thickness T = λ/(2n), where λ is the wavelength of reflected light and n is the refractive index of the film. The wavelength λ corresponds to that of the light emitted by a laser.

An example of a method of depositing a film is disclosed in <CIT>. The method comprises a step of depositing a first, a second, and a third film on a substrate, wherein the layers are combined to form a triple-layer film. The thickness of each film is determined by its refractive index and the wavelength of a sensor.

What is needed in the art is an improved film for processing substrates.

In an aspect of the present invention, a method of depositing a film according to claim <NUM> is provided.

Preferred embodiments of the method are provided according to the dependent claims.

By means of the method, an apparatus may be provided which includes the transparent substrate having a first side and a second side opposite the first side, with the film is deposited on the second side,i.e. backside, of the substrate , wherein the film has the target thickness.

It is to be noted, however, that the appended drawings may admit to other equally effective aspects of the disclosure.

Embodiments described herein relate to semiconductor processing. More specifically, embodiments described herein relate to processing of transparent substrates. A film is deposited on a backside of the transparent substrate. A thickness of the film is determined such that the film reflects particular wavelengths of light and substantially prevents bowing of the substrate. The film provides constructive interference to the particular wavelengths of light.

One or more optical sensors, which emit light of a particular wavelength, are used to detect and align substrates for processing. When a transparent substrate is to be processed, the one or more optical sensors cannot detect a transparent substrate because light from the optical sensor passes through the transparent substrate. Thus, a film is deposited on a backside of the transparent substrate to increase a reflectivity or opacity of the substrate by providing constructive interference of the light from the optical sensors. The backside of the substrate is opposite a side of the substrate where one or more devices are formed.

In one case, the film can be deposited on the substrate using a chemical vapor deposition (CVD) process. In another case, the film can be deposited on the substrate using a plasma enhanced chemical vapor deposition (PECVD) process. It is contemplated that other processes, such as physical vapor deposition, can be used to deposit the film on the substrate.

In one embodiment, which can be combined with one or more embodiments described above, the film deposited on the substrate is a silicon containing material, such as amorphous silicon or silicon nitride. The silicon nitride can be used to increase a reflectivity of the substrate. An amorphous silicon layer can be used to increase an opacity of the substrate. The film on the backside of the substrate can be fabricated from a material other than silicon. Any reflectivity or opacity enhancing material may be used for the film. In some embodiments, which can be combined with one or more embodiments described above, the film is fabricated from a single layer. In other embodiments, the film is fabricated from one or more layers of the same or a different material.

A thickness of the film deposited on the backside of the substrate is determined based on a wavelength of the light emitted from the sensor. A minimum thickness of the film is determined by: <MAT> where T is the thickness of the film, λ is a wavelength of light emitted from the sensor, and n is a refractive index of the material of the film. The refractive index, n, is a ratio of a speed of light within the material of the film to a speed of light in a vacuum.

In one embodiment, which can be combined with one or more embodiments described above, a thickness of the film deposited on the backside of the substrate is between about <NUM> and about <NUM>, for example, between about <NUM> and about <NUM>, such as about <NUM>. In one embodiment, which can be combined with one or more embodiments described above, a wavelength of the light emitted from the sensor is between about <NUM> and about <NUM>, for example between about <NUM> and about <NUM>, such as about <NUM>.

<FIG> illustrates operations of a method <NUM> for forming a film on a substrate. As shown, the method <NUM> begins at operation <NUM> where a material is deposited on a backside of the substrate to form a film. At operation <NUM>, a sensor, such as a laser, is used to determine a thickness of the film deposited on the substrate. If the thickness of the film does not satisfy the equation above, the method <NUM> proceeds to operation <NUM> where additional material is deposited on the backside of the substrate to increase the thickness of the film. The film on the backside of the substrate enables constructive interference of light passing through the substrate, thereby increasing a reflectivity of the light. The reflected light from the backside film can be detected by one or more sensors used to align and process the substrate in a process chamber.

Once the thickness of the film satisfies the equation above, the method <NUM> proceeds to operation <NUM> where the substrate is processed. The substrate can be processed by depositing one or more layers on a surface of the substrate opposite the backside of the substrate. The one or more layers may form one or more devices on the substrate.

At operation <NUM>, the film is removed from the backside of the substrate. The film can be removed using a wet etch technique. Other processes for removing the film from the backside of the substrate include dry etching, laser etching, and others. A masking layer may be deposited over the devices formed on the substrate to substantially reduce damage to the devices during the removal operation <NUM>.

The substrate is fabricated from a material different than a material utilized to form the one or more devices. In this way, a selective etch can be utilized to remove the film from the backside while substantially preventing damage to the one or more devices.

The apparatus <NUM> includes a transparent substrate <NUM> including a first surface <NUM> and a second surface <NUM> opposite and substantially parallel to the first surface <NUM>. The transparent substrate <NUM> is fabricated from a transparent material such as glass or fused silica.

The apparatus <NUM> can be formed according to the method <NUM> illustrated in <FIG>.

A backside film <NUM> is deposited on and adhered to the second surface <NUM> of the transparent substrate <NUM>. The backside film <NUM> has a first surface <NUM> adjacent to the second surface <NUM> of the substrate <NUM> and a second surface <NUM> opposite and substantially parallel to the first surface <NUM> of the backside film <NUM>. The backside film <NUM> comprises a silicon containing material, such as amorphous silicon or silicon nitride. A thickness <NUM> of the backside film <NUM> corresponds to a refractive index of the material used to form the backside film <NUM>. The thickness <NUM> also corresponds to a wavelength of light emitted from a sensor used to detect and align the substrate <NUM>. The backside film <NUM> increases a reflectivity of the transparent substrate <NUM> while substantially preventing or substantially reducing an amount of bowing of the transparent substrate <NUM> caused by the backside film <NUM>.

One or more layers <NUM> are deposited on and adhered to the first surface <NUM> of the transparent substrate <NUM>. The one or more layers <NUM> can be deposited on the transparent substrate <NUM> utilizing, for example, a CVD process, a PECVD process, or a physical vapor deposition (PVD) process. Other deposition processes may be utilized.

After the one or more layers <NUM> are deposited on the transparent substrate <NUM>, the backside film <NUM> is removed utilizing a selective etch process, such as a wet etch. The selective etch process substantially removes the backside film <NUM> while minimizing damage to the transparent substrate <NUM> and the one or more layers <NUM>.

In operation, light is projected from a sensor toward the substrate <NUM> along a path <NUM>. While the path <NUM> is shown at an angle θ<NUM> from a plane that is substantially normal to the first surface <NUM> of the film <NUM>, it is contemplated that the path <NUM> is substantially perpendicular to the first surface <NUM>. That is, θ<NUM> may be substantially zero. When the light intersects the first surface <NUM> of the film <NUM>, a first portion of the light is reflected along a first reflective path <NUM>. A second portion of the light is refracted at the first surface <NUM> of the film <NUM> and travels through the film <NUM> along a path <NUM>. The path <NUM> is an angle θ<NUM> from a plane that is substantially normal to the second surface <NUM> of the film <NUM>, which is different than θ<NUM>. The second portion of the light reflects off of the second surface <NUM> of the film <NUM> and travels along a path <NUM>. When the second portion of the light intersects the first surface <NUM> of the film <NUM>, the second portion of the light is refracted to travel along a second reflective path <NUM>. The second reflective path <NUM> is substantially parallel to the first reflective path <NUM> of the first portion of the light, and light. only a portion of the second portion of light reflects off of the second surface of the second surface <NUM> of the film <NUM>.

The film <NUM> provides constructive interference of the light from the sensor when a length of the second reflective path <NUM> is an integer multiple of the wavelength λ of the light emitted from the sensor. The length of the second reflective path <NUM> is determinable by <MAT> where L is the length of the second reflective path <NUM> and n is the refractive index of the material of the backside film <NUM>.

Embodiments described herein provide a backside coating for transparent substrates. Advantageously, the backside coating on the substrate enables use of one or more sensors to detect and align the substrate in a process chamber. A thickness of the backside coating enables a particular wavelength of light emitted from the one or more sensors to be reflected from the coating while substantially preventing bowing of the substrate.

Claim 1:
A method of depositing a film, comprising:
obtaining a wavelength of light emitted from a sensor;
identifying a refractive index of a material;
determining a target thickness of the material by dividing the wavelength of the light emitted from the sensor by two times the refractive index of the material; and
depositing the material on a substrate to form a film on a backside of the substrate;
determining a thickness of the film deposited on the substrate using the sensor;
if the thickness of the film is less than the target thickness, deposit additional material on the backside of the substrate to increase the thickness of the film;
once the thickness of the film has the target thickness, processing the substrate; and
removing the film from the backside of the substrate.