Elimination of internal reflection in interference endpoint detection system

Abstract

To provide a method for operating an endpoint detection system for a processing chamber having a ceiling formed in the processing chamber, a substrate support arranged inside the processing chamber, and a substrate on the substrate support.SOLUTION: In a plasma processing chamber, a transparent panel 204 is arranged on a ceiling 103 of the processing chamber and is oriented at a first acute angle α to a substrate 120 and substrate support 116. The transparent panel 204 receives the incident light beam 176 from an endpoint detection system 164 at a second acute angle β to the transparent panel and transmits the incident light beam 176 to the substrate 120 at an angle perpendicular to the substrate 120 and substrate support 116.SELECTED DRAWING: Figure 1

Description

background

[0001] (Field) FIELD OF THE DISCLOSURE Embodiments of the present disclosure relate generally to endpoint detection in semiconductor processing, and more particularly to an endpoint detection system and method with reduced reflection of incident and reflected light.

[0002] Description of Related Art Semiconductor device geometries have dramatically decreased in size since they were first introduced several decades ago. Increasing circuit density places additional demands on the processes used to manufacture semiconductor devices. For example, as circuit density increases, pitch sizes decrease rapidly to dimensions below 50 nm while vertical dimensions such as trench depth remain relatively constant. As a result, feature aspect ratios, or height divided by width, increase. Precise control of the dimensions of such high density, submicron features is essential for reliable formation of semiconductor devices.

[0003] Traditionally, semiconductor devices such as transistors and capacitors are formed by patterning the surface of a substrate to define the lateral dimensions of the features and then etching the substrate to remove material and define the features. To form features with desired electrical performance, the dimensions of the features must be formed within controlled specifications. As a result, precise patterning and subsequent etching of the substrate is essential for reliable formation of features with desired critical dimensions.

[0004] In integrated circuit manufacturing, layers need to be constructed to form high density semiconductor devices. Thus, a need may arise to partially remove one or more layers using a plasma etching process. During plasma etching, a mask is utilized to transfer a pattern to a target layer disposed on a substrate without etching a layer disposed below the target layer. Interferometric endpoint techniques are utilized to partially etch the underlying layer or substrate to a target depth or thickness. Interferometric endpoint systems use the interference of reflected light waves reflected at various interfaces on the wafer surface to recognize changes in etch depth or film thickness on the surface.

[0005] Interferometers measure the difference between two or more optical paths by overlapping the residual light from both paths to produce interference fringes. A monochromatic or broadband light source is used and reflected off the surface of a complex film stack. Small changes within the wavelength range of the light source can be discerned.

[0006] The reflected light is a combination of signals from each layer deposited on the substrate, forming unique interference fringes for each layer. For endpoint detection, the interference fringe patterns can be simulated for the various layers and then compared to the measured signal during etching. This method is very effective and can be used for monitoring and endpoint detection of etching or deposition of substrates with multiple layers on them.

[0007] The transmitted and reflected light typically passes through a nearly flat, transparent window in a plasma etch chamber while the incident surface of the substrate is being etched. Unfortunately, conventional flat interferometric endpoint (IEP) detection windows experience significant internal reflection during etching, reducing sensitivity to on-substrate metrics. A typical method to reduce the internal reflection of an IEP window is to employ an anti-reflective coating (ARC) on the window surface. Unfortunately, ARCs only work over a limited range of wavelengths, despite the need to eliminate internal reflections over a wide wavelength range, typically from 200 nm to 800 nm.

[0008] Therefore, there is a need in the art for an effective method of eliminating internal reflections in endpoint detection systems.

[0009] Embodiments presented herein provide a method of operating an endpoint detection system, a transparent panel for the endpoint detection system, and a process chamber having the same. The process chamber has a ceiling formed in the process chamber, a substrate support disposed inside the process chamber, and a substrate resting on the substrate support. The transparent panel is disposed in the ceiling of the process chamber and oriented at a first acute angle relative to the substrate and the substrate support. The transparent panel receives an incident light beam from the endpoint detection system at a second acute angle relative to the transparent panel. The transparent panel transmits the incident light beam to the substrate in the process chamber at an angle perpendicular to the substrate and the substrate support.

[0010] The embodiments presented herein further provide a processing chamber. The processing chamber comprises a chamber body having a sidewall and a bottom. A ceiling is mounted on the chamber body, the ceiling and the chamber body defining an interior volume of the processing chamber. A substrate support is disposed in the interior volume of the processing chamber and configured to support a substrate during processing. The processing chamber further comprises an endpoint detection system. The processing chamber further comprises a transparent panel mounted on the ceiling, the transparent panel configured to allow the endpoint detection system to interact with the substrate through the transparent panel. The transparent panel is oriented at a first acute angle relative to the substrate and the substrate support. The transparent panel is configured to receive an incident light beam from the endpoint detection system at a second acute angle relative to the transparent panel. The transparent panel is further configured to transmit the incident light beam to the substrate in the processing chamber at an angle perpendicular to the substrate and the substrate support.

[0011] The embodiments presented herein further provide a tilted window suitable for use in an endpoint detection system for a processing chamber. The tilted window comprises a mounting frame having a body including a first section and a second section extending perpendicularly from the first section. The second section has a top surface and a bottom surface. The top surface of the second section is tilted at a first acute angle relative to the bottom surface of the second section and at a second acute angle relative to the first section. The tilted window further comprises a panel having a body with a top surface, a bottom surface, and a sidewall, the panel being disposed on the mounting frame. The sidewall of the panel is adjacent to the first section of the mounting frame, and the bottom surface of the panel rests on the top surface of the second section of the mounting frame and is oriented at the first acute angle relative to the bottom surface of the second section of the mounting frame.

[0012] The embodiments presented herein further provide a processing chamber. The processing chamber comprises a chamber body having a sidewall and a bottom. A ceiling is mounted on the chamber body, the ceiling and the chamber body defining an interior space of the processing chamber. A substrate support is disposed in the interior space of the processing chamber and configured to support a substrate during processing. The processing chamber further comprises an end point detection system. The processing chamber further comprises a tilted window mounted on the ceiling, the tilted window configured to allow the end point detection system to interact with the substrate through the tilted window. The tilted window comprises a mounting frame having a body including a first section and a second section extending perpendicularly from the first section. The second section has a top surface and a bottom surface. The top surface of the second section is tilted at a first acute angle relative to the bottom surface of the second section and is tilted at a second acute angle relative to the first section. The tilted window further comprises a panel having a body with a top surface, a bottom surface, and a sidewall, the panel being disposed on the mounting frame. A sidewall of the panel is adjacent to the first section of the mounting frame and a bottom surface of the panel rests on an upper surface of the second section of the mounting frame and is oriented at a first acute angle relative to the bottom surface of the second section of the mounting frame. [Brief description of the drawings]

[0013] In order that the above features of the present disclosure may be understood in detail, a more particular description of the present disclosure briefly summarized above will be made with reference to embodiments, some of which are illustrated in the accompanying drawings. However, since the present disclosure may include other equally effective embodiments, it should be noted that the accompanying drawings merely illustrate exemplary embodiments of the present disclosure and therefore should not be construed as limiting the scope thereof.

[0014] [Figure 1] 1 shows a schematic cross-sectional view of a plasma etch chamber according to one embodiment of the present disclosure. [Diagram 2] FIG. 2 is a side view of a tilted window used in an endpoint detection system of a processing chamber according to embodiments of the present disclosure. [Diagram 3] FIG. 3 is a top view of the tilted window of FIG. 2. [Figure 4] A method of operating an endpoint detection system for a processing system, the endpoint detection system employing the tilted window of FIGS. 1-3 suitable for use in the endpoint detection system of a processing chamber. [Figure 5A] 1 is a curve showing the relationship between reflectance and wavelength for a conventional window. [Figure 5B] 1 is a comparison of curves showing the magnitude of reflection versus wavelength for a conventional window and a tilted window. [Figure 6] 1 shows a curve illustrating the relationship between the magnitude of the normalized amplitude of the tilt window and the depth of the etch recess. [Figure 7A] 1 shows plots of fringe curve spectral magnitude versus relative time for a tilted window compared to a conventional window. [Figure 7B] 1 shows curves showing the magnitude of the fringe curve spectrum versus wavelength for a tilted window compared to a conventional window.

[0015] For ease of understanding, wherever possible, like reference numerals have been used to denote like elements common to the figures. Furthermore, it is contemplated that elements disclosed in one embodiment may be beneficially used on other embodiments described herein without specific description.

[0016] The tilted windows presented herein can effectively reduce internal reflections over a wide range of wavelengths of interest (e.g., between about 200-800 nm) without the need for anti-reflective coatings. The dynamic range of the IEP system is improved. The immediate benefits of the tilted window are improved control of etch depth and thickness, and increased window life. The tilted window is generally compatible with existing chamber bodies, and therefore may be retrofitted into nearly any existing plasma processing chamber utilizing an IEP system.

[0017] 1 is a schematic cross-sectional view of a plasma processing chamber 100 according to one embodiment of the present disclosure. Suitable processing chambers include inductively and capacitively coupled plasma etch chambers, such as the SYM3® Etch System available from Applied Materials, Inc., Santa Clara, Calif., among others. Other types of processing chambers may be adapted to benefit from the present invention, including, for example, chemical vapor deposition chambers, capacitively coupled parallel plate chambers, and magnetically enhanced ion etch chambers, as well as inductively coupled plasma etch chambers of various designs.

[0018] The process chamber 100 generally comprises a chamber body 102 and an energy transparent ceiling 103. The chamber body 102 also has a chamber bottom 107. The chamber body 102 is fabricated from a metal, such as anodized aluminum or stainless steel. The ceiling 103 is attached to the body 102. The ceiling 103 may be flat, rectangular, arched, conical, dome-shaped, or multi-radius shaped. The ceiling 103 is fabricated from an energy transparent material, such as ceramic or other dielectric material. An inductive coil 126 is disposed above the ceiling 103 of the process chamber 100 and is utilized to energize gases within the chamber 100 during processing.

[0019] The substrate support 116 is disposed within the processing chamber 100 and has a substrate support surface 188 to support the substrate 120 during processing. The substrate support 116 may comprise an electrostatic chuck, where at least a portion of the substrate support 116 is electrically conductive and may function as a process bias cathode.

[0020] Process gases are introduced into the process chamber 100 from a process gas source 148 through a gas distributor 122. The gas distributor 122 may be located generally in the ceiling 103 or in the chamber body 102 above the substrate support 116. Mass flow controllers (not shown) for each process gas, or alternatively for a mixture of process gases, are located between the gas distributor 122 and the process gas source 148 to regulate the respective flow rates of the process gases into the chamber body 102.

[0021] A plasma zone 114 is defined within the chamber body 102 between the substrate support 116 and the ceiling 103. A plasma is formed in the plasma zone 114 from the process gas using a coil power supply 127, which powers an inductive coil 126 to generate an electromagnetic field in the plasma zone 114 via an RF match network 135. The substrate support 116 may include an electrode therein, which is powered by an electrode power supply 128 to generate a capacitive electric field within the process chamber 100 via an RF match network 125. Typically, RF power is applied to the electrode of the substrate support 116 while the body 102 is electrically grounded. The capacitive electric field is in a direction transverse to the plane of the substrate support 116 and influences the directionality of the charged species in a more perpendicular direction relative to the substrate 120, providing a more vertically oriented anisotropic etch of the substrate 120.

[0022] The process gases and etchant by-products are exhausted from the process chamber 100 via an exhaust system 130. The exhaust system 130 may be located at the bottom 107 of the process chamber 100 for removal of the process gases, or may be located in another portion of the body 102 of the process chamber 100. A throttle valve 132 is provided at the exhaust port 134 to control the pressure within the process chamber 100.

[0023] 1 further illustrates an endpoint detection system 164 coupled to the process chamber 100. The endpoint detection system 164 may be an interferometric endpoint (IEP) detection system. The endpoint detection system 164 is positioned to interact with the substrate 120 through a portion of the ceiling 103. In one embodiment, the endpoint detection system 164 is positioned to interact with a peripheral portion of the substrate through a portion of the ceiling 103 that is offset from the center of the ceiling 103. In this manner, the endpoint detection system 164 has a direct line of sight to probe the peripheral area surface of the substrate 120.

[0024] The endpoint detection system 164 generally comprises a light source 166, a collimating assembly 168, and a photodetector 170. The light source 166 is configured to emit a light beam. The collimating assembly 168 is configured to focus the light beam into an incident light beam 176. The incident light beam 176 passes through the ceiling 103 in a direction perpendicular to the substrate support surface 188 and illuminates an area or spot 180 on the surface of the substrate 120. The incident light beam 176 is reflected by the surface of the substrate 120 to form a reflected light beam 178. At least a portion of the reflected light beam 178 is directed in a direction perpendicular to the substrate support surface 188 and returns through the ceiling 103 to the photodetector 170. The photodetector 170 is configured to measure the intensity of the reflected light beam 178. The computer system 172 calculates a portion of the real-time measured waveform spectrum of the reflected light beam 178 reflected from the beam spot 180 on the substrate 120 and processes the spectrum using advanced spectral analysis techniques, including comparing the spectrum to stored characteristic waveform patterns.

[0025] The light source 166 comprises a monochromatic or polychromatic light source that generates an incident light beam 176 that is used to illuminate a beam spot 180 on the substrate 120. The intensity of the incident light beam 176 is selected to be high enough that the reflected light beam 178 can have a measurable intensity. In one alternative embodiment, the light source 166, such as a Xe lamp, provides polychromatic light and produces an emission spectrum of light with wavelengths from about 200 nm to about 800 nm. The polychromatic light source 166 can be filtered to select the frequencies that make up the incident light beam 176. A color filter can be placed in front of the photodetector 170 to filter out all wavelengths except the wavelength of light of interest and then measure the intensity of the reflected light beam 178 that enters the photodetector 170. The light source 166 can also comprise a monochromatic light source, such as a He-Ne or Nd-YAG laser, to provide light of a selected wavelength.

[0026] One or more focusing lenses 174a, 174b may be used to collimate an incident light beam 176 from the light source 166 to form a beam spot 180 on the substrate surface and to focus a reflected light beam 178 back onto the active surface of the photodetector 170. The size or area of ​​the beam spot 180 should be large enough to compensate for variations in the surface topography of the substrate 120 and the device design features. This allows for detection of the etch end point at the target depth of design features with small openings. These design features may be vias or narrow trenches, which may be closely spaced or isolated. The area of ​​the reflected light beam should be large enough to activate a large proportion of the active light detection surface of the photodetector 170.

[0027] The incident light beam 176 and the reflected light beam 178 are directed through a transparent tilted window 182 of the processing chamber 100. The tilted window 182 allows both light beams 176, 178 to enter and exit the processing environment of the processing chamber 100 without substantial internal reflection. The tilted window 182 includes a substantially flat transparent panel 204. When the tilted window 182 is positioned within the substantially flat horizontal ceiling 103 of the processing chamber 102, the flat transparent panel 204 of the tilted window forms a first acute angle α between the transparent panel 204, the horizontal ceiling 103, the substrate support surface 188, and the substrate 120. The first acute angle may be in the range of 2° to 5°, preferably 3°. The substrate support surface 188 of the substrate support 116 on which the substrate 120 rests is parallel to the ceiling 103 and perpendicular (90°) to both light beams 176, 178. At the same time, the panel 204 of the angled window 182 forms a second acute angle β with both light beams 176, 178. In one embodiment, β ranges from 85° to 88°, preferably 87°. Thus, there is no internal reflection from either the top surface 207 of the panel 204 or the bottom surface 224 of the panel 204.

[0028] In one embodiment, a transparent panel 204 disposed on the ceiling 103 of the process chamber 100, the panel 204 oriented at a first acute angle α relative to the substrate 120 and the substrate support 116, is configured to receive an incident light beam from the endpoint detection system 164 at a second acute angle β relative to the panel 204. The panel 204 is further configured to transmit the incident light beam to the substrate 120 in the process chamber 100 at an angle perpendicular to the substrate 120 and the substrate support 116. The panel 204 is further configured to receive a reflected light beam from the substrate 120 at the second acute angle. The panel 204 is further configured to transmit the reflected light beam to the endpoint detection system 164 at an angle perpendicular to the endpoint detection system 164.

[0029] The diameter of the beam spot 180 is typically about 2 mm to about 10 mm. However, if the beam spot 180 encompasses a large isolated area of ​​the substrate containing only a few etched features, it may be necessary to use a smaller beam spot to focus on the feature of interest. Thus, the size of the beam spot may be optimized depending on the design features of a particular device.

[0030] If desired, the optical beam positioner 184 may be used to move the incident optical beam 176 across the substrate 120 to locate the appropriate portion of the substrate surface where the beam spot 180 is located to monitor the etching process. The optical beam positioner 184 may include one or more primary mirrors 186 that may be rotated through small angles to direct the optical beam from the optical source 166 to various locations on the substrate surface. Additional secondary mirrors (not shown) may be used to block the reflected optical beam 178 that is reflected from the surface of the substrate 120 and focused onto the optical detector 170. The optical beam positioner 184 may also be used to scan the optical beam in a raster pattern across the surface of the substrate 120. In this alternative embodiment, the optical beam positioner 184 includes a scanning assembly consisting of a movable stage (not shown) on which the optical source 166, collimating assembly 168, and detector 170 are mounted. The movable stage moves at set intervals by a drive mechanism (such as a stepper motor) to move the beam spot 180 across the surface of the substrate 120 .

[0031] The photodetector 170 comprises a light sensitive electronic component, such as a charge coupled device (CCD), photodiode, phototransistor, etc., that provides a signal in response to the measured intensity of the reflected light beam 178 reflected from the surface of the substrate 120. The signal may be in the form of a change in the level of electrical current through the electrical component, or a change in voltage applied to the electrical component. The reflected light beam 178 undergoes constructive and / or destructive interference, which causes the intensity of the reflected light beam to increase or decrease, causing the photodetector 170 to provide an electrical output signal related to the measured intensity of the reflected light beam 178. The electrical output signal is displayed as a function of time to provide a waveform spectrum having a number of waveform patterns corresponding to the varying intensity of the reflected light beam 178.

[0032] A computer program on computer system 172 compares the shape of the measured waveform pattern of reflected light beam 178 to the stored characteristic waveform pattern and determines the endpoint of the etch process when the measured waveform pattern is the same as the characteristic waveform pattern. The period of the interference signal as a function of time may then be used to calculate depth and etch rate. The program may also operate on the interference trend to detect characteristic patterns such as inflection points. The operations may be simple mathematical operations such as evaluating a moving derivative to detect inflection points.

[0033] Although the endpoint detection system 164 may be positioned to interact with the substrate 120 through a portion of the substantially horizontal ceiling 103 of the processing chamber 100, in some embodiments the endpoint detection system 164 may be positioned horizontally above the chamber 100 and may further include a folding mirror above the chamber 100 to bend the incident light beam 176 and the reflected light beam 178 from a vertical position to a horizontal position. A transparent tilting window 182 may be positioned on the side of the chamber 100 or at the bottom of the chamber 100.

[0034] 2 is a side view of a tilted window 182 used in the endpoint detection system 164 of the processing chamber 100. The tilted window 182 comprises a mounting frame 202 and a panel 204 disposed on the mounting frame 202. The mounting frame 202 has a first section 206 and a second section 208 extending from the first section 206. The first section 206 has a substantially flat top surface 210 and a sidewall 212 that extends vertically to an intersection 214 with a top surface 216 of the second section 208. The second section 208 has a top surface 216, a substantially vertical sidewall 218, and a bottom surface 220 (forming the bottom surface 220 of the mounting frame 202).

[0035] The panel 204 has a top surface 222 and a bottom surface 224. In one embodiment, the top surface 222 is parallel to the bottom surface 224. The panel 204 also includes a near outer edge 226 and a far outer edge 228. In one embodiment, the near outer edge 226 and the far outer edge 228 are oriented at a 90° angle relative to the top surface 222 and the bottom surface 224. The panel 204 is configured to rest on a top surface 216 of the second section 208 of the mounting frame 202. In one embodiment, the angle of the top surface 222 of the panel 204 relative to the top surface 210 of the first section 206 of the mounting frame 202 is a first acute angle α. The top surface 216 of the second section 208 is inclined at a first acute angle α relative to the bottom surface 220 of the second section 208 and is inclined at a second acute angle β relative to the first section 206. In another embodiment, the near outer edge 226 and the far outer edge 228 are oriented at a second acute angle β relative to the bottom surface 220 of the second section 208 of the mounting frame 202 to fit snugly against the side wall 212 of the first section 206 and the top surface 216 of the second section 208 of the mounting frame 202.

[0036] 3 is a top view of the tilted window 182 of FIG. 2. In one embodiment, the panel 204 is substantially circular, forming a disk within the mounting frame 202. In other embodiments, the panel 204 may be substantially square, rectangular, triangular, oval, or the like. In one embodiment, the panel 204 may be made of sapphire, fused silica, or MgF2. It is contemplated that other transparent materials may also be used.

[0037] In one embodiment, the mounting frame 202 is substantially circular, forming an annular ring around the panel 204. In other embodiments, the mounting frame 202 may be substantially square, rectangular, triangular, oval, or the like. In one embodiment, the mounting frame 202 may be made of metal or ceramic. It is contemplated that other transparent or opaque materials may also be used. The material of the mounting frame 202 may be different than the material of the panel 204. However, a one-piece design facilitates maintaining a vacuum seal between the mounting frame 202 and the panel 204.

[0038] 4 is a method 400 of operating an endpoint detection system 164 of a process chamber 100 employing a tilted window 182 with a transparent panel 204 of FIGS. 1-3. The process chamber 100 includes a ceiling 103 formed thereon, a substrate support 116 disposed within the process chamber 100, and a substrate 120 resting on the substrate support 116. At block 405, a transparent panel 204 disposed on the ceiling 103 of the process chamber 100 and oriented at a first acute angle α relative to the substrate 120 and the substrate support 116 receives an incident light beam from the endpoint detection system 164 at a second acute angle β relative to the panel 204. At block 410, the panel 204 transmits the incident light beam to the substrate 120 in the process chamber 100 at a perpendicular angle relative to the substrate 120 and the substrate support 116. At block 415, the panel 204 receives the reflected light beam from the substrate 120 at a second acute angle. At block 420, the panel 204 transmits the reflected light beam to the endpoint detection system 164 at an angle perpendicular to the endpoint detection system 164.

[0039] FIG. 5A shows a curve representing the magnitude of reflection vs. wavelength for a conventional window. FIG. 5B compares the curve representing the magnitude of reflection vs. wavelength for a conventional window compared to a tilted window 182. Curve 502 displays the magnitude of reflection from the conventional window and curve 504 displays the magnitude of reflection from the tilted window 182. There is very little reflection from the tilted window compared to about 20K counts (counts are a unit of spectrometer output) for the conventional window. The IEP spectrum from the wafer with the tilted window consists of the spectrum reflected only from the substrate, without the 20k count background reflection from the conventional IEP window. The tilted window 182 provides a significant improvement in IEP tuning.

[0040] 6 shows curves representing normalized amplitude magnitude vs. etch recess depth for a tilted window (curve 602) and a conventional window (curve 604). The range of recess depth controlled by using an etch IEP algorithm with a tilted window can be reduced by about 10 Å based on laboratory test results of WEB (WEB stands for W (tungsten) etch back) chips. By using a tilted window, an etch depth variation within 5 Å to 20 Å can be achieved.

[0041] FIG. 7A shows curves representing the magnitude of the fringe curve spectrum versus relative time for a tilted window (curve 702) and a conventional window (curve 704). FIG. 7B shows curves representing the magnitude of the fringe curve spectrum versus wavelength for a tilted window (curve 706) and a conventional window (curve 708). As can be seen from these curves, the IEP tuning depth (sensitivity) is increased by approximately 80% for the tilted window curves 702, 706 compared to the conventional window curves 704, 708. This is desirable because the spectral analysis relies on the calculation of on-wafer metrics (the dimensions of features at the wafer surface), and a stronger spectral response to subtle on-wafer metric changes results in a higher signal-to-noise ratio and more accurate results for the on-wafer metrics.

[0042] While the forgoing is directed to embodiments of the present disclosure, other and further embodiments of the present disclosure may be made without departing from the basic scope thereof, which is defined by the following claims.

Claims

[Claim 1] a ceiling formed on the processing chamber; a substrate support disposed within the processing chamber; 1. A method of operating an endpoint detection system for a processing chamber having a substrate mounted on a substrate support, the method comprising: a transparent panel disposed in a ceiling of the processing chamber, the panel oriented at a first acute angle relative to the substrate and the substrate support, receiving an incident light beam from an endpoint detection system at a second acute angle relative to the panel; the panel transmitting an incident light beam to the substrate within the processing chamber at an angle perpendicular to the substrate and the substrate support.

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