KR20030096430A - Apparatus for monitoring thickness change in a film on substrate - Google Patents

Abstract

Methods and apparatus are disclosed for inspecting and measuring thin films that cause thickness and other variations during rotation. One optical signal travels through the axis of rotation from the area under inspection and is separated from the area of rotation under inspection. The signal can then be analyzed to determine the end point of the flattening process. The present invention utilizes an interference and spectral optical measurement method for real-time endpoint control of a CMP planarization process in the manufacture of semiconductors or various optical devices.

Description

Apparatus for monitoring thickness change in a film on substrate}

The present invention relates to an apparatus for optically inspecting and measuring a rotating surface, and more particularly, to an apparatus for real-time inspection of a thin film that rotates and causes a change in dimensions.

As microelectronic devices continue to shrink in size, manufacturing of integrated circuits and semiconductor devices has become difficult due to the problems of patterning. For the fabrication of semiconductor devices, thin films with extremely flat surfaces and precise thicknesses are often required. Surfaces requiring control of flatness and thickness in semiconductor devices include regions or layers of dielectric material (eg, SiO 2) and other device pattern layers on the surface of the semiconductor material. If the surface shape of the insulating dielectric layer and other device layers is irregular and rough, problems arise in manufacturing the depth of focus budget (hereinafter, referred to as DOF), so the layer needs to be extremely flat. If the surface is irregular, a portion of the surface may be out of focus at a certain distance between the optical system and the wafer, which can lead to errors in pattern formation. In addition, since the change in thickness can affect the electrical properties of the pattern of the layer and the adjacent device, in particular the electrical property of the connection between each layer of the electronic device, the thickness of the layer needs to be precisely controlled.

Precise control of the layer thickness is also important in the manufacture of semiconductors. In VLSI technology, generally, several layers of a multi-layer device are electrically connected to each other. The layers are also insulated from various levels in general by a thin layer of insulating material such as SiO 2. In order to connect the layers of the device with one another, contact holes are often formed in the insulating layer which provide electrical access between the layers. If the insulating layer is too thick, the layers are not connected to each other, and if the layer is too thin, the bottom layer of the device may be damaged during the formation of contact holes.

Due to the inadequacies of other planarization methods such as spin-on-glass and etch back, chemical and / or mechanical polishing (CMP) planarization Machines and other lapping machines have been developed and used to provide flat surfaces for the manufacture of semiconductor devices. In general, CMP is a technique for flattening a wafer by using a polishing pad attached to a rotating table. The wafer is held by a chuck on a polishing pad that rotates on the spindle. The wafer is pressed downward against the polishing pad. The nap of the rotating pad removes the sharp bits of the film layer, thus making the surface flat.

A solution of pH adjusting fluid, called a slurry and colloidal silica particles, flows between the pad and the wafer to remove material from the polishing area and to improve planarization of the wafer surface.

A common way to determine the endpoints of CMP and lapping machines is to measure the time needed to planarize a standard wafer and apply the process for a similar time to the remaining wafers. In practice, this process is very inefficient because the polishing state and the polishing pad change over time, making it very difficult to determine the exact rate of film removal. As a result, it is often necessary to inspect the wafers individually after planarization, which is time consuming and expensive. As such, the CMP process can be greatly improved by the introduction of real-time measurement and control systems. Direct or indirect methods of inspecting and controlling CMP processes have been suggested by various techniques. One such method is based on the measurement of capacitance (US Pat. No. 5,081,421). The theory behind this method is that the electrical capacitance of the wafer changes as the surface of the wafer is planarized. Two major drawbacks of this approach are limited precision and pattern dependencies. Its precision can also be compromised by the bottom layer pattern, which can affect the capacitance of the entire system.

A direct method of using laser beams for interferometric reading has been proposed on the polished side (front side) of a portion of the wafer protruding from the polishing pad (US Pat. No. 5,081,796). The disadvantage of this system is that some of the wafers must protrude from the edges of the polishing pad, causing uniformity problems in polishing, and the monitored spots of the rotating wafer are flush with the device under the wafer protrusions. Also needs to be adjusted equally, which actually requires deformation in conventional CMP polishing pads.

An indirect CMP inspection method has been developed that detects a change in friction between the wafer and the polishing surface (US Pat. No. 5,036,015). The friction change occurs, for example, when the oxide coating of the wafer is removed and a harder material contacts the polishing pad. In this method, the precision changes as the state of the pad changes. In addition, this method may be subject to limitations of use because there is a need to detect friction generated by other materials.

Another indirect CMP inspection method has been developed which utilizes the conductivity of the slurry during polishing (US Pat. No. 4,793,895). When the metal layer is exposed during the CMP process, the electrical resistance of the slurry and the wafer changes due to the metal exposed on the surface of the wafer. An obvious disadvantage of this method is that the test surface needs to be exposed for the test. This is not possible in most polishing environments.

Another indirect CMP test method has been developed, using waste slurry falling from the pad during planarization (US Pat. No. 4,879,258).

Some materials are embedded in the dielectric layer and inspected as they are planarized and released from the polishing pad. Obvious disadvantages of this method include the time delay (estimated approximately 30 seconds) between planarization and the time the slurry reaches the edge of the pad, low sensitivity, and signal noise from the material from the preceding wafer. Is that. This method is not a valid real time method.

These and other endpoint detection methods cannot provide efficient and accurate control of the CMP process in a real time manner. The above methods compromise the precision of endpoint detection and / or require significant modifications in the CMP process.

It is an object of the present invention to enable end point inspection by a real time method, avoiding the above-mentioned problems by making it possible to inspect the film area on the substrate having a change in thickness. Moreover, if the inspection area is small enough, a spot on the wafer may serve the purpose of determining the end point. The provided endpoints can eliminate signal problems associated with the shape, pattern, and multiple film layers of the layer.

FIG. 1 is a side view illustrating a representative semiconductor device having a device pattern on a substrate of semiconductor material and having a thick, unplanarized dielectric layer over the pattern and substrate.

2 shows the semiconductor device of FIG. 1 after the dielectric layer has finished the CMP planarization process.

3 is a side view showing a rotating coupler (hereinafter referred to as a rotating coupler) into which an optical fiber cable is fitted.

4 is a side view showing an embodiment of an optical fiber according to the present invention integrated with a CMP assembly.

5 shows another embodiment according to the present invention using a light source for transmitting light in the direction of the wafer,

The light rays are reflected at the surface of the wafer and inspected by a photo detector which converts the reflected optical signal into an electrical signal. The electrical signal is relayed to the analyzer after passing through an electrical slip ring.

FIG. 6 shows the wafer fixation chuck of FIG. 4, in which air is pumped into the cavity on the wafer to compensate for the loss of pressure exerted on the back of the wafer where the hole is located.

Explanation of symbols on the main parts of the drawings

1: dielectric layer 2: device pattern

3: board 4, 6: fiber optic cable

5: rotary coupler 10: table base

11 wafer 15 slip ring

Accordingly, the present invention provides an apparatus and a method for inspecting portions of light irradiation and changes in dimensions on the thin film layer. The light emitted from the light source is transmitted, preferably through the back of the substrate, to the inspection area above the layer and relayed back to the analyzer, which is based on changes in interference, spectral changes, and / or absorption changes. Calculate the thickness change of the substrate.

According to one embodiment of the present invention, the optical signal is preferably measured from the rear side of the substrate, so that the inspection area of the wafer and the inspection apparatus do not need to be adjusted with each other or the height of each other during the process, so that the implementation is easy. Become.

In one embodiment, the present invention provides a method of irradiating a portion of a film through a rear side of a substrate, measuring an optical signal returning from the irradiated area, and changing a thickness of the film on the substrate based on the measured optical signal. It provides a method for checking the thickness change of the film on the substrate comprising the step of determining. The thickness change can be determined by the analyzer, which analyzes the interference change, spectral change, absorption change, and / or other optical change in the measured optical signal. Optionally, if the substrate is rotating, the method also includes relaying the optical signal to a rotating coupler connecting the signal to the analyzer.

Another embodiment of the invention is directed to irradiating a portion of the film from the front side of the substrate (i.e. the polished surface), measuring the optical signal returning from the irradiated site, and optical to the rotating coupler connected to the analyzer. A method for inspecting the thickness change of a film on a substrate comprising relaying a signal and a method for inspecting the thickness change with an analyzer that analyzes the interference change, spectral change, absorption change, and / or other optical change of the measured optical signal. to be.

Yet another embodiment of the present invention provides a light source for irradiating a portion of a film from a front side or a back side of a substrate to generate an optical signal, means for detecting the optical signal, means for analyzing the optical signal and the light An apparatus for inspecting a change in thickness of a film on a substrate, comprising a rotation coupler for relaying the signal from the area to which the signal is irradiated as a means for analyzing the optical signal. The device may optionally include one or more focusing lenses.

Preferably, the device is:

(Iii) a bisected fiber optic cable (hereinafter referred to as a bifurcated fiber optic cable) having one common leg and two bisected legs (hereinafter referred to as a bifurcated leg); (ii) a two-end rotating An optical fiber cable (hereinafter referred to as a rotating optical fiber cable), (iii) a light source, (iii) means for analyzing an optical signal, and (iii) a rotating coupler having a stop end and a rotation end.

In the device, the first bifurcated leg of the bifiber optical fiber cable is connected to a light source, the second bifurcation leg is connected to a means for analyzing the optical signal, and the common part is connected to the stop end of the rotating coupler.

Also, in the present apparatus, one end of the rotating optical fiber is connected to the rotating end of the rotating coupler, and the other end is kept in very close proximity to the film on the substrate under process.

“Very close” includes any distance between the end of a rotating fiber optic cable and the film on the substrate that is close enough to enable effective inspection of the inspection area of the film and the reception of a returning optical signal. . Preferred distances are about 1 cm or less.

The rotating optical fiber cable transmits the light beam from the light source to the irradiated portion, and transmits the optical signal returned from the irradiating portion. The light beam emitted from the light source travels down along the first bifurcated leg of the bifurcated optical fiber cable and travels down along the rotating fiber optic cable through the rotating coupler to irradiate a film on the substrate. In addition, one or more regions of the film on the substrate may be examined simultaneously using multiple legs of a rotating fiber optic cable passing through one or more rotating couplers.

Preferably, the fiber optic cable comprises a plurality of optical fibers that are bundled together. However, the fiber optic cable may comprise a single fiber. The fiber may also be a combination of a plurality of fiber optic cables and a single fiber optic cable bundled together. The fibers may also be multiple fiber optic cables bundled together.

The term “substrate” includes any semiconductor having insulating and conductive properties known in the art. Preferred substrates are wafers such as silicon wafers, gallium-arsenide wafers, and silicon on insulator (SOI) wafers.

The term “film on substrate” includes various dielectric layers known in the art, such as SiO 2, metal layers, such as tungsten and aluminum, and various other films, such as silicon films present on a substrate as defined above. The film also includes resist layers.

The film of varying thickness may be, for example, a CMP process, a chemical vapor deposition process, a resist development process, a post-exposure bake process, a spin coating process, or It may be a film on a substrate in a plasma etching process. In this CMP embodiment, the film is located between the substrate and the polishing pad.

The term “light source” includes any light source capable of irradiating a film on a substrate in the range of about 200 to about 11,000 nm (nanometer). When the optical signal is measured from the back side of the substrate, the wavelength is preferably about 1,000 to about 11,000 nm. Preferred backside wavelength is 1,300 nm. When the optical signal is measured from the front side, the wavelength is preferably about 200 to about 11,000 nm. One preferred front side wavelength is 632.8 nm. Preferably, even if irradiation is performed at time intervals, the film portion on the substrate is continuously illuminated by the light source.

Appropriate means for analyzing an optical signal, or “analyzer,” include an optical detector, interferometer, spectrophotometer, and other devices of the art for analyzing interference changes, spectral changes, absorption changes, and / or other optical changes. do.

Suitable rotating members have any coupler for connecting the rotating member and the non-rotating member when light rays pass between the ends of the rotating member and the non-rotating member. Such couplers are disclosed, for example, in US Pat. Nos. 4,398,791 and 4,436,367. Preferably, the means for connecting the rotating fiber optic cable to the non-rotating bifiber fiber cable comprises a rotating member attaching one end of the rotating fiber optic cable. The rotating member is inserted into the stop member of the rotating coupler attached to the common leg of the bifurcated optical fiber cable. The coupler is designed such that the end of the rotating fiber optic cable is kept in close proximity to the common part of the bifurcated optical fiber cable, preferably 1 cm or less, so that the light beam can pass between the two ends. Optionally, the cable end can be adjusted with the focusing lens to enhance the transmission of the signal.

It can be replaced by a rotary coupler, an off-axis fiber coupler, an electrical slip ring, or any other type of coupler with a combination of the aforementioned couplers, or other single rotational separation means.

A general CMP machine, in which the device of the present invention can be used, is Aal. Products manufactured by R. Howard Strasbaugh, Inc., Westech Systems, Inc., Phoenix, AZ, and Cybeg Systems, Menlo Park, Calif. .

1 and 2 illustrate CMP planarization of a semiconductor device wafer. 1 shows a dielectric layer 1, such as SiO 2, deposited on the surface of a device pattern 2 formed on a silicon wafer substrate 3. The dielectric layer may be formed in the same manner as chemical vapor deposition (CVD), spin-on-glass, or other means of oxide.

FIG. 2 shows the wafer of FIG. 1 with the dielectric layer 1 planarized to a preselected thickness after CMP. The device pattern 2 and the wafer substrate 3 remain relatively unchanged in this process.

3 is a side view showing one of the preferred embodiments of the optical rotating coupler device. 3 shows a bifurcated optical fiber cable 4 in which one of its bifurcation legs is connected to a light source 7 and the other of its bifurcation legs is connected to a photo detector 8. Photodetector 8 is coupled to signal inspection electronics (not shown) and a computer processing and control system.

The common legs of the bifiber optical fiber cable 4 are connected to the optical rotating coupler. The rotating fiber optic cable 6 extends from the rotating coupler to the inspection area of the wafer substrate. The optical fiber cables 4 and 6 can be both single fiber or bundled fiber types. It is also possible to use several cables or fibers instead of one cable or fiber. It is also possible, for example, to implement a single fiber and bundle fiber cable embodiment in a mixed fashion, such as when cable 4 is single fiber and cable 6 is bundle cable. The focusing lens is not essential at the inspection end of the cable if the cable is securely and securely close enough to the inspection area of the wafer substrate. The distance between the end of the cable and the substrate of the wafer is preferably 1 cm or less.

4 is a side view showing a general flattening machine or lapping machine, suitable for the apparatus shown in FIG. The apparatus can be installed in the flattening machine with a sign 4, 5, 6 from the rear side approach or with a sign 4 ', 5', 6 'from the front side approach. For efficient inspection, only one of the front side or rear side approach is required at any time. In FIG. 4, the wafer holding chuck and the spindles 12 are shown integrated with the rotary coupler 5 for rearward access. As shown in FIG. 3, the bifurcated optical fiber cable 4 is sent into the spindle and connected to the stop of the rotary coupler 5. The rotating fiber optic cable 6 is routed along the spindle to the inspection area of the wafer 11, which is optionally an area without a pattern or an area with a pattern. The wafer 11 is fixed by a mounting pad, ie a fixture, which is generally attached to the chuck by a chemical adhesive. The fixtures often consist of a base matrix held together by a polyurethane surface layer. The outer surface, which is fixed against the back of the wafer and pressurized, grips the wafer and also provides a uniform support for the wafer.

In another embodiment, shown in FIG. 4, the rotary table base 10 and platen 9, which secures the polishing pad, are integrated with the rotary coupler 5 'for forward access to the wafer. Is shown. The bifiber optical fiber cable 4 'is sent to the rotary table base 10 and connected to the stop of the rotary coupler 5'. The rotating optical fiber cable 6 ', which is connected to the rotating shaft of the rotating coupler 5', is adjacent to the inspection area of the wafer. Since the polishing pad attached to the platen 9 is generally perforated, the end of the optical fiber cable 6 'can be fitted through one of the holes. The translucent slurry solution flows between the polishing pad and the wafer, dispersing most of the visible light wavelengths. Optionally, signal amplification means can be used to compensate for the slurry dispersion effect of the respective wavelengths.

In this preferred embodiment, the light source for the front side method is a light ray having a wavelength of 632.8 nm, which wavelength satisfies the problem of interest for optical signal transmission through the slurry and also the measurement precision. Rotating optical fiber cable 6 'fitted to the polishing pad, when positioned over the inspection area of the wafer 11, must transmit and receive an interference signal. This is adapted to pass the inspection beam over the inspection region on the wafer using techniques common in the art.

5 shows an electrical slip ring assembly. The light source 14 sends a light beam at a point on the wafer 11, thus causing the light beam to be reflected in the direction of the photo detector or other light inspection electronics 13, and thus converting the light signal into an electrical signal. do. This electrical signal is then passed over the analyzer 12 and finally through the electrical slip ring 15, which is then separated from the rotation and passed over another analyzer to check the progress of the CMP.

6 shows the wafer holding chuck and spindle 12, in which the rotating fiber optic cable 6 routes the coupler 5 from the coupler 5 to a point behind the wafer 11 via the wafer holding chuck 12. Have If light is not transmitted through the pad that holds the wafer, i.e., the fixture, the pad may be punctured to provide optical access to the wafer. In order to compensate for the pressure loss against the wafer at the point where the optical approach is made, air may optionally be pumped into the cavity to press against the wafer and compensate for the pressure loss. In addition, if the fixture can transmit light, it is not necessary to make an optical access hole.

The present invention is particularly useful in the field of wafer flattening processes for producing wafers having extreme flatness and uniformity which are desirable in the manufacture of semiconductors and integrated circuits.

While the invention has been described in detail with reference to specific embodiments thereof, it will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the invention.

Claims (19)

In the apparatus for checking the thickness change of the film on the substrate, (Iii) a bifurcated fiber optic cable having one common leg and two bifurcated legs; (Ii) a rotating fiber optic cable having two ends, (Iii) a light source, (Iii) means for determining the thickness change and analyzing the optical signal to stop the thickness change when the end point of the predetermined thickness is reached, and (Iii) a rotational coupler having a stop end and a rotational end, wherein a first bifurcated leg of the bifiber optical fiber cable is connected to a light source, and a second bifurcation leg is connected to a means for analyzing the optical signal; And the common leg is connected to the stop end of the rotary coupler, and one end of the rotary fiber optic cable is connected to the rotary end of the rotary coupler, and the other end is kept in close proximity to the substrate. . The apparatus of claim 1, wherein the other end of the rotating optical fiber cable is maintained at a distance of about 1 cm or less from the substrate. In a CMP apparatus for planarizing a film on a substrate, (Iii) a bifurcated fiber optic cable having one common leg and two bifurcated legs; (Ii) a rotating fiber optic cable having two ends, (Iii) a light source, (Iii) means for determining the thickness change and analyzing the optical signal to stop the thickness change when the end point of the predetermined thickness is reached, and (Iii) a rotational coupler having a stop end and a rotational end, wherein the first bifurcation leg of the bifiber optical fiber cable is connected to a light source, and the second bifurcation leg is connected to a means for analyzing the optical signal, The common leg is connected to the stationary end of the rotary coupler, and one end of the rotary fiber optic cable is connected to the rotary end of the rotary coupler, the other end of which is kept very close to the substrate during chemical and mechanical planarization. CMP device. 4. The CMP apparatus of claim 3, wherein the other end of the rotating fiber optic cable is maintained at a distance of about 1 cm or less from the substrate. In a CMP apparatus for planarizing a film on a substrate, (Iii) a bifurcated fiber optic cable having one common leg and two bifurcated legs; (Ii) a rotating fiber optic cable having two ends, (Iii) a light source, (Iii) means for analyzing an optical signal based on interferometry or spectrophotometry, and (Iii) a rotational coupler having a stop end and a rotational end, wherein the first bifurcation leg of the bifiber optical fiber cable is connected to a light source, and the second bifurcation leg is connected to a means for analyzing the optical signal, The common leg is connected to the stationary end of the rotary coupler, and one end of the rotary fiber optic cable is connected to the rotary end of the rotary coupler, and the other end is chemically and mechanically planarized to allow light to be irradiated to a portion of the membrane. CMP device, characterized in that it is kept in close proximity to either side of the substrate in progress. The CMP apparatus according to claim 5, wherein the portion to which light is irradiated is an area dedicated to measurement. A CMP apparatus having a planarization table for planarizing a film on a substrate, (Iii) a bifurcated fiber optic cable having one common leg and two bifurcated legs; (Ii) a rotating fiber optic cable having two ends, (Iii) a light source, (Iii) means for determining the thickness change and analyzing the optical signal to stop the thickness change when the end point of the predetermined thickness is reached, and (Iii) a rotational coupler having a stop end and a rotational end, wherein the first bifurcation leg of the bifiber optical fiber cable is connected to a light source, and the second bifurcation leg is connected to a means for analyzing the optical signal, The common leg is connected to the stationary end of the rotary coupler, and one end of the rotary fiber optic cable is connected to the rotary end of the rotary coupler, and the other end is kept very close to one side of the substrate during chemical and mechanical planarization, And the other end irradiates light to a portion of the film of the substrate and the analyzing means measures an optical signal returned from the portion of the film. 8. The CMP apparatus of claim 7, wherein the optical signal to be measured has at least one wavelength greater than about 200 nm. 8. The CMP apparatus of claim 7, wherein the optical signal to be measured has at least one wavelength between about 200 nm and about 11,000 nm. The CMP apparatus according to claim 7, wherein the portion to which the light is irradiated is a measurement-only area. The CMP apparatus according to claim 10, wherein the area dedicated to the measurement is irradiated with light at a time interval while the substrate and / or the flattening table rotates. In a CMP apparatus for planarizing a film on a substrate, (Iii) a bifurcated fiber optic cable having one common leg and two bifurcated legs; (Ii) a rotating fiber optic cable having two ends, (Iii) a light source, (Iii) means for determining the thickness change and analyzing the optical signal to stop the thickness change when the end point of the predetermined thickness is reached, and (Iii) a rotating coupler having a stop end and a rotating end, wherein the first bifurcated leg of the bifiber fiber optic cable is connected to a light source, and the second bifurcation leg is connected to a means for analyzing the optical signal; The common leg is connected to the stop end of the rotary coupler, and one end of the rotary fiber optic cable is connected to the rotary end of the rotary coupler, and the other end is very close to one side of the substrate where chemical and mechanical planarization are not in progress. And the other end irradiates light to a portion of the film of the substrate and the analyzing means measures an optical signal coming back from the portion of the film. 13. The CMP apparatus of claim 12 wherein the optical signal to be measured has at least one wavelength between about 1,000 nm and about 11,000 nm. The CMP apparatus according to claim 12, wherein the irradiated portion is a measurement-only area. A CMP apparatus having a planarization table for planarizing a film on a substrate, (Iii) a bifurcated fiber optic cable having one common leg and two bifurcated legs; (Ii) electrical slip rings, (Iii) a light source, and (Iii) means for analyzing the optical signal, A first bifurcation leg of the bifiber optical fiber cable is connected to a light source, a second bifurcation leg is connected to a means for analyzing an optical signal, one end of the common leg is connected to an electrical slip ring, The other end of the common leg of the optical fiber cable is kept very close to one side of the substrate where the chemical mechanical planarization is in progress, the other end irradiates light to a portion of the film of the substrate and the analyzing means is subjected to interferometric or spectrophotometric And analyze the optical signal coming back from the portion of the film based on that. 16. The CMP apparatus of claim 15, wherein the returned optical signal has at least one wavelength greater than about 200 nm. 16. The CMP apparatus of claim 15, wherein the returned optical signal has at least one wavelength between about 200 nm and about 11,000 nm. 16. The CMP apparatus according to claim 15, wherein the portion to which light is irradiated is an area dedicated to measurement. 19. The CMP apparatus according to claim 18, wherein the measurement-only area is irradiated at a time interval while the substrate and / or the flattening table are rotated.