High-efficiency line-forming optical systems and methods for defect annealing and dopant activation

High-efficiency line-forming optical systems and methods for defect annealing and dopant activation are disclosed. The system includes a CO2-based line-forming system configured to form at a wafer surface a first line image having between 2000 W and 3000 W of optical power. The line image is scanned over the wafer surface to locally raise the temperature up to a defect anneal temperature. The system can include a visible-wavelength diode-based line-forming system that forms a second line image that can scan with the first line image to locally raise the wafer surface temperature from the defect anneal temperature to a spike anneal temperature. Use of the visible wavelength for the spike annealing reduces adverse pattern effects and improves temperature uniformity and thus annealing uniformity.

FIELD

The present disclosure relates to optical systems for forming a line image, and in particular relates to high-efficiency line-forming optical systems and methods for defect annealing and dopant activation.

The entire disclosure of any publication or patent document mentioned herein is incorporated by reference, including the following: U.S. Pat. No. 8,014,427; US 2012/0111838; US 2007/0072400; U.S. Pat. Nos. 7,148,159; 8,546,805; 8,865,603; 8,309,474; and U.S. patent application Ser. No. 14/497,006.

BACKGROUND

A variety of applications require the use a uniform line image formed from a high-power laser beam. One such application is laser thermal processing (LTP), also referred to in the art as laser spike annealing (LSA) or just “laser annealing,” which is used in semiconductor manufacturing to activate dopants in select regions of a semiconductor wafer when forming active microcircuit devices such as transistors.

One type of laser annealing uses a scanned line image formed from a laser beam to heat the surface of the wafer to a temperature (the “annealing temperature”) for a time long enough to activate the dopants but short enough to minimizing dopant diffusion. The time that the wafer surface is at the annealing temperature is determined by the power density of the line image, as well as by the line-image width divided by the velocity at which the line image is scanned (the “scan velocity”).

One type of high-power laser that is used for laser annealing applications is CO2laser. Traditional methods of performing laser annealing with a CO2laser including imaging the light beam onto a pair of knife-edges and then relaying the light passing therethrough to an image plane to form the line image. The knife-edges are positioned to transmit only a narrow central portion (e.g., 10%) of a Gaussian laser beam for which the intensity is relatively uniform so that the resulting line image is also relatively uniform along the length of the line image.

Unfortunately, using only the narrow central portion of the laser beam means that the other 90% of the light beam is rejected. This is a very inefficient use of the high-intensity laser light. On the other hand, the conventional wisdom is that trying to pass a larger portion of the Gaussian beam will naturally result in non-uniformity of the line image along its length because of the substantial drop off in intensity in the Gaussian beam with distance from the center of the beam.

Furthermore, there are applications where it is advantageous to perform a defect anneal and a spike anneal simultaneously. In this regard, the CO2laser beam is combined with a broader laser beam, typically from a diode laser. The broader laser beam raises the temperature of the surrounding area to an intermediate temperature for a longer period of time than the CO2beam, which is used to “spike” the surface to about 1300° C. for a millisecond or less. Typically, the broader laser beam will heat the region for several milliseconds (e.g., in the range from 2 milliseconds to 20 milliseconds) to an intermediate temperature between 700 and 1200° C. The total power required by the diode laser to heat the substrate to this temperature and temporal range is large, e.g., typically several killowatts (kW). Integrating these two laser beam is typically challenging. In a conventional system, the CO2laser beam and the diode laser beam are not collinear because the optics required to deliver the beams to the wafer are significantly different.

In addition, an important constraint in the design of the laser annealing tool is the avoidance of the incoming laser beam onto the sidewall of the wafer. The laser beams are incident to the surface of the wafer at Brewster's Angle, which is about 70° for silicon. At this incident angle, the power density on the side of the wafer is greater than three times the power density on the wafer surface, and can damage, or even break, the wafer. It has been shown in U.S. Pat. No. 8,071,908 that a serrated skirt can protect the sidewall of the wafer with an incident CO2laser beam. However, the additional (diode) laser also needs to avoid the sidewall of the wafer because the diode laser provides a large amount of power, e.g., 3 kW typically. It turns out that, geometrically, it is an over constrained problem to design a skirt to protect the wafer from a CO2laser incident from one direction, and a diode laser incident at nominally 90 degrees from the CO2laser beam. Hence, it becomes impracticable to use a diode laser with such high power without taking costly and/or time-consuming steps to avoid damaging or breaking wafers.

A further disadvantage of the above approach comes from “pattern effects”. Pattern effects are temperature non-uniformities that arise due to patterns on the wafer. The patterns are features of the devices and interconnections being formed. The pattern effects are much more significant when the incident laser has a shorter wavelength (i.e., closer to visible wavelengths of light) because the pattern effects are driven by Raleigh scattering, which scales as the ratio of feature or pattern size δ divided by the wavelength λ, raised to the fourth power, e.g., (δ/λ)4.

SUMMARY

Aspects of the disclosure are directed to systems for and methods of performing defect annealing with a CO2laser while other aspects include additionally performing laser spike annealing using a visible diode laser. For defect annealing performed in conjunction with laser spike annealing, the CO2laser is used to provide the majority of the temperature rise of the wafer surface (e.g., up to at least the defect anneal temperature) and the diode laser is used to provide additional heating to bring the local temperature up to the anneal (i.e., dopant activation) temperature. In an example, the amount of the temperature rise provided by the diode laser is as small as possible. This is advantageous because the wavelength of the CO2laser is roughly 10× to 20× longer than the wavelength of a visible diode laser. Consequently, the adverse pattern effects are much smaller with the CO2laser than with the visible diode laser. The method includes using the CO2laser for the initial, relatively long-duration temperature rise for defect annealing, and then using the diode laser for the relative short spike annealing, i.e., for dopant activation. This requires that the CO2laser power delivered to the wafer be substantial, e.g., in the range from 2000 W to 3000 W (i.e., 2 kW to 3 kW), while also having acceptable intensity uniformity, e.g., within +/−5%, over a usable beam length (e.g., in the range from 5 mm to 100 mm) and beam width (e.g., in the range from 25 μm to 1 mm). It is noted that while a raw CO2laser beam might be able to provide the needed power, it will have a Gaussian intensity profile that cannot provide the required intensity uniformity over a usable beam length.

Besides mitigating the adverse pattern effects, another advantage of the systems and methods disclosed herein is that power density incident upon on the sidewall of the wafer from the visible-wavelength light beam is also reduced (e.g., to a sub-kW value), thereby reducing the risk of wafer damage or breakage due to irradiation of the wafer edge or side wall.

An aspect of the disclosure is a method of performing defect annealing at a defect anneal temperature TDof a semiconductor wafer having a surface that includes a pattern, wherein the method includes: forming from a CO2laser a light beam having a wavelength of nominally 10.6 microns and a first intensity profile with a Gaussian distribution in at least a first direction; passing at least 50% of the light beam in the first direction to form first transmitted light; focusing the first transmitted light at an intermediate focal plane to define a second intensity profile having a central peak and first side peaks immediately adjacent the central peak; truncating the second intensity profile within each of first side peaks to define second transmitted light that forms on the wafer surface a first line image having between 2000 W and 3000 W of optical power and an intensity uniformity of within +/−5% over a first line length in the range from 5 mm to 100 mm; and scanning the first line image over the wafer surface to locally raise a temperature of the wafer surface to the defect anneal temperature.

Another aspect of the disclosure is the method described above, wherein the defect anneal temperature TDis in the range 650° C.≦TD≦1100° C.

Another aspect of the disclosure is the method described above, further including performing spike annealing at a spike anneal temperature by: forming a second line image at the wafer surface using a second light beam having a visible wavelength, wherein the second line image at least partially overlaps the first line image; and scanning the second line image to locally raise the temperature of the wafer surface from the defect anneal temperature TDto the spike anneal temperature TA.

Another aspect of the disclosure is the method described above, wherein the spike anneal temperature TAis in the range 1150° C.≦TA≦1350° C.

Another aspect of the disclosure is the method described above, wherein the first line image has a first width and the second line image has a second width that is between 5% and 25% of the first width.

Another aspect of the disclosure is the method described above, wherein the first width is in the range from 25 microns to 1 mm.

Another aspect of the disclosure is the method described above, including forming the second light beam using a laser diode light source and line-forming optics arranged relative thereto.

Another aspect of the disclosure is the method described above, wherein the second wavelength is between 500 nm and 1000 nm.

Another aspect of the disclosure is the method described above, wherein the second line image has a second line length in the range between 5 mm and 100 mm and an intensity uniformity of within +/−5%.

Another aspect of the disclosure is the method described above, wherein the wafer surface temperature has a variation from the spike anneal temperature due to pattern effects, and wherein the variation is no more than 60° C.

Another aspect of the disclosure is a system for performing defect annealing of a semiconductor wafer having a surface with a pattern. The system includes: a CO2laser source that emits an initial light beam having a wavelength of nominally 10.6 microns; a beam-conditioning optical system that receives the initial light beam and forms therefrom a conditioned light beam having a first intensity profile with a Gaussian distribution in at least a first direction; a first aperture device operably disposed at an object plane and that defines a first slit aperture that truncates the first intensity profile in the first direction to define first transmitted light that constitutes at least 50% of the conditioned light beam; a relay optical system that defines the object plane and that also defines an intermediate focal plane at which is operably disposed a second aperture device, the relay optical system defining at the intermediate focal plane a second intensity profile having a central peak and first side peaks immediately adjacent the central peak, wherein the second aperture device is configured to truncate the second intensity profile in the first direction and within each of the first side peaks to define second transmitted light; wherein the relay optical system forms from the second transmitted light a first line image at the wafer surface, wherein the first line image includes between 2000 W and 3000 W of optical power, has a first length in the range from 5 mm to 100 mm, and has an intensity uniformity of within +/−5%; a chuck that operably supports the wafer; and a moveable wafer stage that operably supports the chuck and that is configured to move the chuck and the wafer supported thereon so that the first line image scans over the wafer surface to locally raise a temperature of the wafer surface to a defect anneal temperature.

Another aspect of the disclosure is the system described above, wherein the defect anneal temperature is in the range from 650° C. to 1100° C.

Another aspect of the disclosure is the system described above, wherein the chuck is heated so that it can pre-heat the wafer.

Another aspect of the disclosure is the system described above, further including a diode-based line-forming optical system that generates a visible light beam that forms at the wafer surface a second line image that at least partially overlaps and scans with the first line image to locally raise the temperature of the wafer surface from the defect annealing temperature to a spike anneal temperature, and wherein the second line image has an intensity variation of within +/−5%.

Another aspect of the disclosure is the system described above, wherein the spike anneal temperature is in the range from 1150° C. to 1350° C.

Another aspect of the disclosure is the system described above, wherein the first and second line images have respective first and second widths, and wherein the second width is in the range from 5% to 25% of the first width.

Another aspect of the disclosure is the system described above, wherein each side peak is defined by a maximum value MX and first and second minimum values m1and m2, and wherein the second slit aperture is configured to truncate the second intensity profile between the maximum value MX and the second minimum value m2in each first side peak.

Another aspect of the disclosure is the system described above, wherein the relay optical system has substantially 1× magnification in the first direction.

Another aspect of the disclosure is the system described above, wherein the relay optical system is a cylindrical optical system having optical power only in the first direction.

Another aspect of the disclosure is the system described above, wherein the optical relay system consists of reflective optical components only.

Another aspect of the disclosure is the system described above, wherein the first aperture device comprises a pair of blades operably disposed in the object plane.

Another aspect of the disclosure is the system described above, wherein the second aperture device comprises a pair of blades operably disposed in the intermediate focus plane.

Another aspect of the disclosure is the system as described above, wherein the diode-based line-forming optical system includes a laser diode light source and line-forming optics arranged relative thereto.

DETAILED DESCRIPTION

Reference is now made in detail to various embodiments of the disclosure, examples of which are illustrated in the accompanying drawings. Whenever possible, the same or like reference numbers and symbols are used throughout the drawings to refer to the same or like parts. The drawings are not necessarily to scale, and one skilled in the art will recognize where the drawings have been simplified to illustrate the key aspects of the disclosure.

The claims as set forth below are incorporated into and constitute part of this Detailed Description.

Cartesian coordinates are shown in some of the Figures for the sake of reference and are not intended to be limiting as to direction or orientation. Further, the Cartesian coordinates at the second aperture device60are denoted x′ and y′ to distinguish from the (x,y) coordinates at the first aperture device40and at the image plane IP.

In the discussion below, the terms “laser beam” and “light” are used interchangeably. Also, the term “micron” and the symbol “μm” are used interchangeably.

The terms “upstream” and “downstream” are used to refer to the location of an item relative to direction of light travel as conventionally used in the art of optical system design, wherein when item B is said to be downstream of item A, light travels in the direction from item A to item B, and vice versa.

Line-forming Optical System

FIG. 1is a schematic diagram of an example line-forming optical system (“system”)10according to the disclosure. System10includes an optical axis A1, an object plane OP and an image plane IP at which a line image80is formed as described below.

System10includes along optical axis A1and upstream from object plane OP a laser source20that emits an initial laser (light) beam22along the optical axis towards the object plane. In an example, laser source20includes a CO2laser that operates at a nominal wavelength of 10.6 μm. In an example, initial laser beam22has a Gaussian intensity distribution (profile) at along least the x-direction, and further in an example in both the x-direction and the y-direction. In an example, initial laser beam22need not be circularly symmetric, e.g., the Gaussian intensity distributions in the x-direction and y-direction can have different sizes. In an example, laser source20outputs about 3500 W of optical power in initial laser beam22.

System10also includes a beam-conditioning optical system30arranged along axis A1between laser source20and object plane OP. The beam-conditioning optical system30is configured to receive laser beam22and form therefrom a conditioned laser (light) beam24. In an example, beam-conditioning optical system30is configured to perform beam expansion so that conditioned laser beam24is an expanded version of initial laser beam22. In an example, beam-conditioning optical system30is configured to provide conditioned laser beam24with a select dimensions (profiles) in the x-direction and the y-direction. In an example, beam-conditioning optical system30expands the dimensions of initial laser beam22by the same amount in the x-direction and the y-direction.

Beam-conditioning optical system30can include at least one of mirrors, lenses, apertures, and like optical components. An example beam-conditioning optical system30utilizes two or more off-axis mirrors each having optical power such as known in the art and two examples of which are described in U.S. Pat. Nos. 2,970,518 and 3,674,334. In various examples, beam-conditioning optical system30can be anamorphic, cylindrical or circularly symmetric.

In an example embodiment, laser source20and beam-conditioning optical system30define a laser source system35that generates the desired intensity profile I(x,y) for conditioned laser beam24for forming line image80. In an example where laser source20emits a suitable initial laser beam22that does not need to be conditioned, then beam-conditioning optical system30is not required and the initial laser beam can be used in place of a conditioned laser beam. Thus, in the discussion below, conditioned laser beam is understood in an example to be defined by an unprocessed initial laser beam22.

System10also includes along axis A1and at object plane OP a first aperture device40. In an example, first aperture device40is includes a pair of blades42each having an edge43. The blades42are disposed in object plane OP on respective sides of axis A1so that their respective edges43are opposing and spaced apart to form a slit aperture44. Slit aperture44has its long dimension in the Y-direction, as best seen in the close-up inset IN1, which shows first aperture40device as at appears looking down optical axis A1in the +z direction. The slit aperture44has a width d1in the x-direction that defines a length L of line image80formed by system10at image plane IP, as described below. In an example, blades42are movable to adjust the width d1and thus the length L of line image80.

System10also includes long axis A1and downstream of first aperture device40a relay optical system50. The relay optical system50shown inFIG. 1is shown as a transmission optical system for ease of illustration. An example of a reflective relay optical system50is described below in connection withFIG. 5. Relay optical system40includes first and second optical components52A and52B. In example, each optical component52A and52B can consist of one or more optical elements, such as lenses, mirrors, etc. Relay optical system50defines the object plane OP at first aperture device40resides and also defines the image plane IP at which line image80is formed.

Relay optical system50further includes a second aperture device60arranged between first and second optical components52A and52B at an intermediate focal plane IFP defined by optical component52A. With reference to the second close-up inset IN2, second aperture device60includes a pair of blades62each having an edge63. The blades62are disposed in intermediate focal plane IFP on respective sides of axis A1so that their respective edges63are opposing and spaced apart to form a slit aperture64. Slit aperture64has its long dimension in the y′-direction, i.e., in the same direction as slit aperture44of the first aperture system40. The slit aperture64has a width d2in the x′-direction. In an example, blades62are movable to adjust the width d2.

In an example embodiment, relay optical system50has substantially unit magnification (i.e., is substantially a 1× system) in the x-z plane. Also in examples, relay optical system50can be either cylindrical or anamorphic. The width d1of slit aperture44of first aperture device40defines the size of conditioned laser beam24in the x-direction, and for 1× magnification in the x-z plane, d1=L (see close-up inset IN3).

In the general operation of system10, conditioned laser beam24is formed and first aperture device40is configured so that a relatively large amount of the light in this beam passes through slit aperture44.FIG. 2Ais a front-on view of first aperture device40(looking in the +z direction) and shows the approximate zero-intensity contour (I(x,y)≈0) of conditioned laser beam24. In an example, conditioned laser beam24has a Gaussian profile in the x-direction and y-direction, with the profile being longer in the x-direction (i.e., the intensity profile I(x,y) is elongate in the x-direction). As noted above, the width w1of the Gaussian profile in the y-direction defines the width w (short dimension) of line image80. In an example, width w1is defined by beam-conditioning optical system30, with relay optical system50having no optical power in the y-z plane (i.e., the relay optical system is cylindrical with optical power in the x-z plane only). This is one advantage of using a beam-conditioning optical system30, since it avoids having to form optical components52A and52B using anamorphic elements.

FIG. 2Bis a plot of the intensity I(x) versus x (mm) of conditioned laser beam24that also shows an example location of blades42of first aperture device40relative to the conditioned laser beam. The hashed portions24B of conditioned laser beam24inFIG. 2Ashows the portions of the conditioned laser beam that are block by the respective blades42, while the portion that passes through slit aperture44is denoted24P, which is also referred to below as “first transmitted light.” This is also illustrated inFIG. 2B, wherein the dashed-line portion of the intensity profile I(x) shows the portion of the light that is blocked by respective blades42. In the example illustrated inFIGS. 2A and 2B, about 90% of the light in conditioned laser beam24passes through slit aperture44as first transmitted light24P, while about 10% of the light of conditioned laser beam at the wings of the intensity profile is blocked by blades42. In an example, first aperture device40is configured to pass at least 50% of conditioned laser beam24.

Because first aperture device is configured to pass a substantial portion of conditioned laser beam24, the variation in intensity I(x) within slit aperture44is relative large. In an example, this variation greater than 50% while in another example is greater than 65% while in another example is greater than 70%. This can be seen most clearly inFIG. 2B, wherein the (normalized) peak intensity is 1 in the center of slit aperture44(i.e., at x=0) while the intensity drops off to about 0.28, i.e., to about 28% of the maximum value of I(x) at the edges of slit aperture as defined by blade edges43. If this intensity distribution is relayed to the image plane IP using convention relay means, line image80will have a corresponding variation in intensity uniformity (about 72%) in the long direction. This is far greater than the preferred intensity uniformity of within +/−5% or in some cases within +/−2%, over the length L of line image80.

With reference again toFIG. 1, the first transmitted light24P that passes through slit aperture44is focused onto second aperture device60at intermediate focal plane IFP by optical component52A of relay optical system50. IFP has coordinates x′ and y′ to distinguish from the (x,y) coordinates at the first aperture device40. This focusing gives rise to a second intensity distribution l′(x′,y′), which is defined by the 1-dimensional Fourier transform (in the x′-direction) of the intensity distribution1(x,y) at the object plane OP.

The intensity distribution1(x) at the object plane OP can be defined as (with (d1)/2=a):
I(x)=G(x)·rect(x/a)
where rect (x/a) is: 0 for |x|>a; ½ for x=a; and 1 for |x|<a, and G(x)=exp(−x2). Thus, I′(x) is given by:
I′(x′)=F{I(x)}=F{rect(x/a)·exp(−x2)}=[a·sinc(x′·a/2)][(π)1/2exp{−π2x′2}]
where thesymbol represents the convolution operation.

FIG. 3Ais a plot of intensity distribution I′(x′) vs. x′ (mm) of the first transmitted light24P at second aperture device60.FIG. 3Bis a front-on view of the second aperture device60ofFIG. 3Bas looking in the +z direction. With reference toFIG. 3B, the aperture blades62are arranged so that a portion24P′ of first transmitted light24P that is incident upon second aperture device60passes through slit aperture64while respective portions24B′ of light24P are block by blades62. Light24P′ is thus referred to as “second transmitted light” and is used by the downstream portion of optical relay system50to form line image80.

FIG. 3Ashows details about where blades62can be set to have a select width d2to pass a select amount of second transmitted light24P′. The intensity profile I′(x) shows a strong central peak P0surrounded by a number smaller peaks that diminish in size from the center of the profile. The first peaks on either side of the central peak P0are denoted P1and are defined by a maximum value MX surrounded by first and second minimum values (minima) m1and m2. In an example, slit aperture64is defined to have a width d2wherein each blade edge63resides within the corresponding first peak P1so that the slit aperture transmits at least a portion of the light associated with first peaks P1.

In another example, second aperture device60is configured so that blade edges63reside within the corresponding first peak P1between the maximum value MX and the second minimum m2. For example, if the x-values on the positive side of the x-axis are defined as xMXfor the maximum value MX and xm2for the second minimum m2, and the x-position of edge63is defined as x63, then the condition for the location of edge63of the positive-side blade62can be expressed as xMX≦x63≦xm2. The corresponding condition for the edge63on the negative side blade can be expressed as: −xm2≦−x63≦−xMX. It has been found that this spatial filtering condition provides the best results forming line image80with an acceptable level of intensity non-uniformity, e.g., to within +/−5% as measured in the long direction over length L.

In an example, the amount of first transmitted light24P blocked by aperture device60at intermediate focal plane IFP is about 5 to 8% so that about 95 to 92% of the first transmitted light is transmitted to form the second transmitted light24P′. This allows relay optical system50to form line image80at image plane IP with an efficiency of up to about 75% relative to the input power or intensity provided to object plane IP, as compared to the prior art efficiency of about 15%.

Furthermore, the intensity uniformity of line image80in the long direction (i.e., the x-direction) can satisfy in one example a tolerance of +/−5% in the long direction over length L and in another example can satisfy a tolerance of +/−2% .

Line image80is formed at image plane IP using second transmitted light24P′. This light in the x-direction is defined as a truncation version of I′(x′) and can be denoted as follows, wherein F{·} stands for the Fourier transform operation:
I′(x′)=F{I(x)}·rect(x′/b), whereb=(d2)/2.=[a·sinc(x′·a/2)][(π)1/2exp{−π2x′2}]·rect(x′/b).
The line image intensity distribution IL(x) is then the1D inverse Fourier transform of I(x′), i.e.,
IL(x)=F−1{I′(x′) }.

FromFIG. 3A, it can be seen that second aperture device60defines the 1D “rect” function in the expression for I′(x′) above and serves to remove select amounts of the higher spatial-frequency components along the x′ axis. Because these higher spatial-frequency components are needed to form a high-definition line image that includes the intensity variations of the input (conditioned) laser beam24at the first aperture device40, their filtering by second aperture device60acts to smooth out the variation in intensity in the long direction of line image80. On the other hand, because these higher spatial-frequency components have a relatively low intensity, most of the first transmitted light24P makes it through aperture64to form the second transmitted light24P′.

FIG. 4Ais a plot of the intensity profile IL(x) vs. x (mm) for the long direction of line image80at image plane IP and shows by way of example two different sizes of lines of L=10 mm (solid line) and L=7.5 mm (dashed line) as formed by system10. In an example, the length L of line image80can be in the range from 5 mm≦L≦100 mm.

FIG. 4Bis a plot of the intensity profile IL(y) vs. y (μm) and shows that the intensity profile in the short direction (i.e., y-direction) of line image80has a Gaussian shape that defines an example width w of about 75 μm. In an example embodiment, width w can be in the range 25 μm≦w≦1000 μm or 25 μm≦w≦500 μm or 25 μm≦w≦250 μm. As noted above, in an example, with width w can be defined by beam-conditioning optical system30so that relay optical system50can be cylindrical with no optical power in the Y-Z plane.

Note that the intensity distribution IL(y) in the short dimension for line image80does not need to satisfy the same uniformity tolerance as the intensity distribution IL(x) in the long dimension in the case where the line image is scanned in the short direction, i.e., the y-direction. In such a case, the intensity variations in the y-direction average out during scanning. In the plot of IL(y) ofFIG. 4B, line image80has a variation in intensity in the y-direction of about +/−10%.

Reflective Relay Optical System

FIG. 5is a schematic diagram of an example system10that includes a reflective relay optical system50and a fold-mirror system90that is used to direct line image80to a surface WS of a wafer W arranged in image plane IP. The reflective relay optical system50includes first and second optical components52A and52B in the form of concave mirrors arranged in an off-axis configuration. Relay optical system50also includes fold mirrors F1, F2and F3that serve to fold the optical path of light24P that passes through first aperture device40at object plane OP. Fold mirror F2is arranged behind second aperture device60so that of the light24P incident upon the second aperture device, only the center portion24P′ is reflected by fold mirror F2to travel through the remainder of optical relay system50. Thus, an example optical system50consists of reflective optical components, i.e., it has no refractive optical components. Such a configuration is desirable when laser source20operates at an infrared wavelength, such as the CO2laser wavelength of nominally 10.6 μm.

This second transmitted light24P′ is reflected by fold mirror F3and directed to second optical component52B, which directs the light to a fold-mirror optical system90that includes at least one fold mirror F4. In an example, fold-mirror optical system90is configured to compensate for the object plane and image plane OP not being parallel so that line image80is properly imaged onto wafer surface WS.

Laser Annealing System

FIG. 6is a schematic diagram of an example laser annealing system100that includes the line-forming optical system10disclosed herein. An example laser annealing system for which the line-forming optical system10is suitable for use is described in, for example, U.S. Pat. Nos. 7,612,372; 7,514,305; 7,494,942; 7,399,945; 7,154,066; 6,747,245; and 6,366,308.

Laser annealing system100ofFIG. 6includes, along optical axis A1, the line-forming optical system10as described above, wherein initial light beam22emitted by laser20(see alsoFIG. 1) has a wavelength (e.g., nominally 10.6 microns from a CO2laser) that is absorbed by and is capable of heating wafer W under select conditions. Such conditions include, for example, heating wafer W, or irradiating the wafer with a second radiation beam (not shown) having a bandgap energy greater than the semiconductor bandgap energy of the wafer, thereby causing the wafer to absorb light beam22to a degree sufficient to heat the wafer to annealing temperatures. An example of irradiating the wafer with a second laser source to make the wafer absorbent to light beam22is described in U.S. Pat. Nos. 7,098,155, 7,148,159 and 7,482,254.

Wafer W is supported by a chuck110having an upper surface112. In an example, chuck110is configured to heat wafer W. Chuck110in turn is supported by a stage120that in turn is supported by a platen (not shown). In an example embodiment, chuck110is incorporated into stage120. In another example embodiment, stage120is movable, including being translatable and rotatable. In an example, chuck110is used to pre-heat the wafer, e.g., up to a few hundred degrees or so.

Wafer W is shown by way of example as having device features DF in the form of source and drain regions150S and150D formed at or near wafer surface WS as part of a circuit (e.g., transistor)156formed in wafer W. Note that the relative sizes of the source and drain regions in circuit156compared to wafer W are greatly exaggerated for ease of illustration. In practice, source and drain regions150S and150D are very shallow, having a depth into the substrate of about one micron or less. In an example, wafer surface WS includes patterns defines by device structures formed in the wafer as part of the device manufacturing process. The patterns give rise to the aforementioned adverse pattern effects that can result in temperature non-uniformities when the wavelength λ of light irradiating the wafer surface WS is less than about 50 times the size δ of the patterns.

In an example embodiment, apparatus100further includes a controller170electrically connected to system10and to a stage controller122. Stage controller122is electrically coupled to stage120and is configured to control the movement of the stage via instructions from controller170. Controller170is configured coupled to control the operation of apparatus100generally, and in particular laser20and stage controller122.

In an example embodiment, controller170is or includes a computer, such as a personal computer or workstation, available from any one of a number of well-known computer companies such as Dell Computer, Inc., of Austin Tex. Controller170preferably includes any of a number of commercially available micro-processors, a suitable bus architecture to connect the processor to a memory device, such as a hard disk drive, and suitable input and output devices (e.g., a keyboard and a display, respectively).

With continuing reference toFIG. 6, light beam24P′ generated as described above is directed onto wafer surface WS to form line image80thereon. It is noted that the term “image” is used herein in to generally denote the distribution of light formed by first transmitted light beam24P′ at image plane IP and wafer surface WS residing therein.

In an example embodiment, line image80is scanned over wafer surface WS, as indicated by arrow180, resulting in localized rapid heating of the wafer surface (down to a depth of about 100 microns or less) up to an annealing temperature (e.g., between 1000° C. and 1,300° C. for a non-melt process and in excess of the melt temperature of silicon of about 1,400° C. for a melt process) sufficient to activate dopants in the source and drain regions150S and150D, while also allowing for rapid cooling of the wafer surface so that the dopants do not substantially diffuse, thereby maintaining the shallowness of the source and drain regions. Blanket dopant activation of wafer surface WS can also be performed using laser annealing system100. A typical scan velocity of line image80over wafer surface WS ranges from 25 mm/sec to 1000 mm/sec. In an example, one or both of light beam24P′ and wafer W can move during scanning.

Because line-forming optical system10can form a relatively long line image80having a relatively large power density, wafer W can be scanned much faster (e.g., up to 3× faster or have 3× longer process line for 3× throughput improvement) than previous line-image forming optical systems would allow, thereby increasing the number of wafer per hour that can be processed by laser annealing system100.

Defect and Spike Annealing Systems and Methods

Aspects of the disclosure include systems and methods for performing defect annealing, or defect annealing and spike annealing using the line-forming optical system10disclosed herein.FIG. 7is similar toFIG. 6and discloses another embodiment of laser annealing system100that includes the CO2-laser-based line-forming optical system10as disclosed herein to perform defect annealing and also includes a diode-based line-forming optical system200used to perform the spike annealing. The diode-based line-forming optical system200is operably connected to controller170and includes a laser diode light source220that emits a light beam222of wavelength λ2. The diode-based line-forming optical system200also includes line-forming optics223arranged to receive light beam222and form a light beam224that forms a line image280at wafer surface WS. In an example, wavelength λ2is in the visible and near-infrared range, e.g., 380 nm≦λ2≦1000 nm, while in another example is in the visible range only, e.g., 500 nm≦λ2≦900 nm. The line-forming optics223can include one or more optical elements, which can be refractive, reflective, diffractive, etc. In an example, line-forming optics is anamorphic, and further in an example is or includes a cylindrical optical system. In an example, line image280has an intensity uniformity within +/−5% over its length.

In an example, line image280overlaps with line image80, as illustrated inFIG. 7and as shown in the close-up view ofFIG. 8A. In another example, line image280fits within line image80, as shown inFIG. 8B. In another example, most of line image280fits within line image80formed by the CO2-laser-based line-forming optical system10while some of line image280falls outside of line image80, as shown inFIG. 8C. In an example, line image280is substantially more narrow than line image80, and further in an example has a width in the range from 25 microns to 250 microns, or in the range from 50 microns to 150 microns. In an example, width of line image280is between 5% and 25% of the width of line image80. In an example, line image80and line image280have about the same length, which in one example is in the range from 5 mm to 100 mm. In an example, the width of line image80is about 1 mm and the width of line image280is in the range of 50 microns and 150 microns. In an example, line images80and280at least partially overlap.

In an example, light beam24P′ delivers between 2000 W and 3000 W of optical power to wafer surface WS via line image80. As noted above, line image80can have a width of up to about 1 mm. In the example ofFIG. 7, light beam24P′ and line image80are used to perform defect annealing by scanning the line image over the wafer surface WS to locally raise the temperature of the wafer surface WS to a defect anneal temperature TD, which in an example is 1050° C. In practice, the defect annealing temperature is related to the duration of the anneal, i.e., the dwell time of line image80. Typically, longer defect annealing times require lower temperatures. In an example, the defect annealing times tDcan range from 2 milliseconds to 15 milliseconds, with corresponding defect anneal temperatures TDranging in one example from about 1000° C. to 1150° C. for tD=2 milliseconds, and in another example ranging from 700° C. to 1000° C. for tD=15 milliseconds. In an example, the anneal temperature TDis in the range 650° C.≦TD≦1100° C.

The light beam224and line image280from diode-based line-forming optical system200is used to perform spike annealing of wafer W. In an example, the laser diode light source220generates a relatively small amount of optical power, e.g., 300 to 500 W. There are two main reasons why so little diode laser power is needed. The first reason is that the temperature jump from the defect anneal temperature TD to the activation temperature TAis small, e.g., a few hundred degrees centigrade. The second reason is that the absorption length of the diode laser visible wavelength λ2as compared to the CO2laser infrared wavelength λ1is typically 100× shorter. Hence, a laser with a substantially smaller optical power output can be used for the laser spike annealing as compared to the conventional approach where the CO2laser is used to perform laser spike annealing. Because much less diode laser power is being used than in the conventional approach, there is much less risk to damaging the edge of the wafer. In the conventional approach, 2 to 3 kW of diode laser power needs to be delivered by light beam224and line image280. With the system and methods disclosed herein, roughly 200 to 500 watts of diode laser power can be employed, depending on the required amount of heat needed to raise the temperature from the defect anneal temperature TDto the spike anneal (or dopant activation) temperature TAand the size and scanning speed of line image280.

In an example, line image280has a width in the scan direction of between 50 and 150 microns. In an example, diode-based line-forming optical system200is optical-fiber based, as described for example, in the aforementioned U.S. patent application Ser. No. 14/497,006.

The diode-based line-forming optical system200is arranged such that line image280at least partially overlaps with line image80, as described below. The optical power provided by light beam224and line image280is used to locally raise the temperature of wafer surface WS from the defect anneal temperature TD(e.g., of about 1050° C.) to a spike anneal (or dopant activation) temperature TA, which in an example is approximately 1150° C. to 1350° C.

Because this temperature rise of a few hundred degrees or so is performed using light beam224at wavelength λ2, there is up to about a 20% pattern temperature non-uniformity (e.g., up to about 60° C.) due to pattern effects. This amount of non-uniformity a substantial improvement over the prior art for which the temperature non-uniformity from pattern effects can be as large as 160° C. Thus, the laser annealing system100and methods of annealing using this system can improve temperature uniformity during spike annealing. In an example, this improvement can be about 25% or more, e.g., between about 25% and 40%. Typical dwell times for the spike annealing using line image280can range from between 200 microseconds and 800 microseconds. The width of line image280determines the scanning speed (e.g., the stage velocity).

As noted above, an added benefit of using a visible wavelength λ2for carrying out the spike annealing is that the light beam224, which in an example irradiates the side of wafer W during scanning, has relatively low power, which significantly reduces the probability of damage to the wafer and in particular reduces the chances of wafer breakage.

It will be apparent to those skilled in the art that various modifications to the preferred embodiments of the disclosure as described herein can be made without departing from the spirit or scope of the disclosure as defined in the appended claims. Thus, the disclosure covers the modifications and variations provided they come within the scope of the appended claims and the equivalents thereto.