Semiconductor device manufacturing: process – Masking – Radiation resist
Reexamination Certificate
2000-05-08
2003-02-11
Goudreau, George (Department: 1763)
Semiconductor device manufacturing: process
Masking
Radiation resist
C438S585000, C438S717000, C438S721000, C438S723000, C438S724000, C438S736000, C438S738000
Reexamination Certificate
active
06518206
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an improved anti-reflective coating and a method for etching and removing an anti-reflective coating from a substrate. More specifically, this invention provides a plasma enhanced chemical vapor deposition dielectric anti-reflective coating and a method for etching and removing both a dielectric anti-reflective coating and a tungsten-silicide layer which supports the dielectric anti-reflective coating. The removal of the dielectric anti-reflective coating and the tungsten-silicide layer by etching is conducted for producing semiconductor integrated circuits containing transistors.
2. Description of the Prior Art
Since semiconductor devices were first introduced several decades ago, device geometries have decreased dramatically in size. During that time, integrated circuits have generally followed the two-year/half-size rule (often called “Moore's Law”), meaning that the number of devices which will fit on a chip doubles every two years. Today's semiconductor fabrication plants routinely produce devices with feature sizes of 0.5 microns or even 0.35 microns, and tomorrow's plants will be producing devices with even smaller feature sizes.
A common step in the fabrication of such devices is the formation of a patterned thin film on a substrate. These films are often formed by etching away portions of a deposited blanket layer. Modern substrate processing systems employ photolithographic techniques to pattern layers. Typically, conventional photolithographic techniques first deposit photoresist or other light-sensitive material over the layer being processed. A photomask (also known simply as a mask) having transparent and opaque regions which embody the desired pattern is then positioned over the photoresist. When the mask is exposed to light, the transparent portions allow for the exposure of the photoresist in those regions, but not in the regions where the mask is opaque. The light causes a chemical reaction in exposed portions of the photoresist. A suitable chemical, chemical vapor or ion bombardment process is then used to selectively attack either the reacted or unreacted portions of the photoresist. With the remaining photoresist pattern acting as a mask, the underlying layer may then undergo further processing. For example, the layer may be doped or etched, or other processing carried out.
When patterning such thin films, it is desirable that fluctuations in line width and other critical dimensions be minimized. Errors in these dimensions can result in variations in device characteristics or open-/short-circuited devices, thereby adversely affecting device yield. Thus, as feature sizes decrease, structures must be fabricated with greater accuracy. As a result, some manufacturers now require that variations in the dimensional accuracy of patterning operations be held to within 5 percent of the dimensions specified by the designer.
Modern photolithographic techniques often involve the use of equipment known as steppers, which are used to mask and expose photoresist layers. Steppers often use monochromatic (single-wavelength) light, enabling them to produce the detailed patterns required in the fabrication of fine geometry devices. As a substrate is processed, however, the topology of the substrate's upper surface becomes progressively less planar. This uneven topology can cause reflection and refraction of the monochromatic light, resulting in exposure of some of the photoresist beneath the opaque portions of the mask. As a result, this uneven surface topology can alter the mask pattern transferred to the photoresist layer, thereby altering the desired dimensions of the structures subsequently fabricated.
When a photoresist layer is deposited on a reflective underlying layer and exposed to monochromatic radiation (e.g., deep ultraviolet (UV) light), standing waves may be produced within the photoresist layer. In such a situation, the reflected light interferes with the incident light and causes a periodic variation in light intensity within the photoresist layer in the vertical direction. Standing-wave effects are usually more pronounced at the deep UV wavelengths used in modern steppers than at longer wavelengths because the surfaces of certain materials (e.g., oxide, nitride and polysilicon) tend to be more reflective at deep UV wavelengths. The existence of standing waves in the photoresist layer during exposure causes roughness in the vertical walls formed when sections of the photoresist layer are removed during patterning, which translates into variations in linewidths, spacing and other critical dimensions.
One technique helpful in achieving the necessary dimensional accuracy is the use of an antireflective coating (ARC). An ARC's optical characteristics are such that reflections occurring at inter-layer interfaces are minimized. The ARC's absorptive index is such that the amount of monochromatic light transmitted (in either direction) is minimized, thus attenuating both transmitted incident light and reflections thereof. The ARC's refractive and reflective indexes are fixed at values that cause any reflections which might still occur to be canceled.
As integrated circuit critical dimensions (CDs) shrink below 0.35 micron, the use of shorter wavelengths for photolithography imaging is required. For sub-0.35 micron, the wavelength for stepper tools has dropped into the deep ultraviolet (248 nm) range. One trade-off of the shorter wavelength is that the reflectivity from the substrate interface increases due to interference effects. Additionally, the shorter wavelength increases standing wave effects in the resist. The combination of interference and standing waves can greatly reduce CD control over various surface topographies.
The use of conventional ARC layers has successfully enhanced CD control for various polysilicon and silicided gate structures. However, one common phenomenon with conventional ARC films, especially spin-on organic ARC films, and deep-UV applications is a “resist footing” which has been observed at the resist/ARC interface. This phenomenon is attributed to the reactive nature inherent in deep-UV resists such as Apex-E®, a registered trademark of Shiply Corporation. The photoresist sensitivity to the underlying surface may cause the resist to incompletely activate, thereby leaving a “foot” at the bottom corners of the imaged line and resulting in CD variation. Another problem with conventional ARC layers is that one type of etchant gas has to be used to etch and open up the ARC while another type of etchant gas must be used to etch the underlying layer(s) supporting the ARC. Thus, there are a number of process steps needed in the etch recipe.
Therefore, what is needed and what has been invented is an improved ARC film, more specifically an improved dielectric ARC film, for deep-UV lithography on tungsten silicide (WSi
x
) and polysilicon films without the “resist footing” phenomena. What is further needed and what has been invented is a method for etching a dielectric ARC with an etchant gas that may be subsequently used to etch the underlying layer(s) that supports the dielectric ARC. What is yet further needed and what has been invented is an etchant gas for the removal of a dielectric ARC from a substrate.
SUMMARY OF THE INVENTION
To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention is embodied in a method and apparatus for etching dielectric layers and inorganic ARCs without the need for removing the substrate being processed from the processing chamber and without the need for intervening processing steps such as chamber cleaning operations. This process is thus referred to herein as an in situ process.
The present invention is further embodied in a process for etching a layer and/or a multi-layer film deposited on a substrate, such as silicon, located within a processing chamber.
Chinn Jeffrey
Kumar Ajay
Applied Materials Inc.
Bach Joseph
Goudreau George
Townsend & Townsend & Crew
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