1. Field of Invention
This invention relates to an ion implantation method, and in particularly, an ion beam profiler is used in the ion implantation method.
2. Background of the Related Art
As shown in
Referring to
In regardless of the implant mode, it is most import that the group with 0° and the group with 180° of implant lines are parallel, and these two groups of implant lines notably affect the dose uniformity. A pitch shift Δ (.DELTA.) is introduced here, which is the shift distance of the wafer when the wafer is rotated and the next implant begins. The pitch shift Δ is used to avoid the dose to be non-uniform. Under specific scan conditions, the dose uniformity can be enhanced by controlling pitch shift Δ and displacement δ.
For better understanding, the quad implant mode is assumed in the following discussion.
The above analysis is based on an assumption that the ion beam profile is an ideal Gaussian distribution as shown in
A scan approach for maximizing dose uniformity has been illustrated in lines 19-32, column 8, and FIG. 4 in U.S. Pat. No. 6,908,836 to Murrell et al., wherein the scan lines drawn during each pass are preferably arranged to interleave scan lines of the previous pass to produce a composite raster with a reduced line pitch. In detail, he exemplarily illustrated that the total implantation can be separated into four passes as illustrated in
The inventor of this invention proposes a new method to improve the dose uniformity, which is illustrated and explained as follows.
According to an aspect of this invention, an ion implantation method is proposed. The method comprises detecting the ion beam profile, calculating the dose profile according to the detected ion beam profile, determining the displacement of the ion beam and implanting.
According to an aspect of this invention, the determined displacement can be used in the whole ion implantation, i.e. all rotation angles.
According to an aspect of this invention, the determined displacement can be only used in one implant, i.e. the displacement is used in a rotation angle, and the displacement will be re-determined for next rotation.
According to an aspect of this invention, the beam profile comprises beam position, beam density and beam shape.
According to an aspect of this invention, a beam profiler is used to detect the ion beam profile, calculate the dose profile and determine the displacement. The ion beam profiler may be a 1-dimensional, 2-dimensional or angle beam profiler.
In bi-, quad-, sexton-, octa- . . . mode ion implantation (implant mode), the displacement δ of an ion beam and pitch shift Δ are used to improve dose uniformity. In general, Δ=S/n; and δ is determined according to calculation, where S is a pitch, the distance between two adjacent implant lines in a single implant if the ion beam profile is an ideal Gaussian distribution as shown in
Unfortunately, the real ion beam distribution is usually not an ideal Gaussian distribution as shown in
Dose is predetermined, which is measured by ion (atom) numbers per unit area (ions/cm2), and the scan conditions are also predetermined. The scan velocity, the moving velocity of the ion beam on the scan path, can be controlled to reach the predetermined dose. One scan is defined to be a forward or backward scan, and a forward scan and a backward scan form two parallel implant lines, and one implant includes a plurality of times scan to be over the wafer surface to form a group of parallel, and one whole implantation is defined to finish a wafer implantation. After one implant is finished, the ion beam or the wafer is rotated and shifted, and then the next implant is preceded, and the superposition of these implant lines forms a dose profile. As a result, different dose profiles can be calculated according to different simulated implantations simulated with different displacements δ by using an ion beam profile in a computing device, such as a computer, or either on different wafers or on different portions on a wafer, and the dose uniformities are determined by the dose profiles, wherein the displacement δ is equal to a distance between a center of a wafer and the nearest implant line. Therefore, an optimized dose profile and an optimized dose uniformity can be obtained as long as an optimized displacement δ is determined according to the calculation.
According to an aspect of this invention, an ion implantation method is proposed shown as
In step 1, an ion beam profile is detected before implanting. The ion beam may scan a beam profiler first, and the beam profiler detects and measures the ion beam. The ion beam profiler can be 1-dimensional (y-directional) or 2-dimensional (x- and y-directional) beam profiler for detecting the ion distribution in y-directional distribution or x-y-planar distribution. When ions bombard on the detector of the ion beam profiler to be detected, the ion distribution on the detector is similar with or the same as the ion beam distribution on the wafer surface.
In step 2, under the predetermined scan conditions, the detected beam profile is used to simulate m simulated implantations with m displacements δ and at least a pitch on a simulated wafer, so as to calculate m dose profiles and m dose uniformities accordingly. In detail, each one of the simulated implantations can have n simulated implants with n orientations averagely arranged around 360°, and thus each simulated implant can be denoted as I(m,n). Further, the nth simulated implant at mth displacement δ I(m,n) can have a plurality of nth simulated implant lines (denoted as L(m,n) hereinafter) perpendicular to the nth orientation (denoted as O(m,n) hereinafter) and a mth displacement (denoted as δ(m,n) hereinafter) equal to a distance between a center of a surface of the simulated wafer and the one of the simulated implant lines L(m,n) nearest to the center, wherein both of m and n are positive integers. Moreover, the pitch is equal to a distance between adjacent two of the simulated implant lines L(m,n). Accordingly, different displacements δ(m,n) are corresponding to different dose profiles and different dose uniformities, and all of the calculated dose profiles and dose uniformities will be similar to or the same as the dose profiles and dose uniformities actually formed on a wafer surface.
In order to provide a thorough understanding of the present invention, Table 1 exemplarily lists a specific example comprising 8 simulated implantations (i.e. m=1-8) simulated in a quad-implant mode (i.e. n=1-4), so as to result 32 simulated implants as listed below. In such a case, all of the 8 simulated implantations are simulated with the same pitch (denoted as “S” herein), for example 15 mm, and the 8 simulated implants corresponding to the same orientation are simulated with 8 different displacements δ averagely divide the pitch S, such as S/8 to S in Table 1, and the 4 displacements δ corresponding to the same group of orientation (for example 0°, 90°, 180° or 270°) in different simulated implantations are equal. However, in other non-illustrated embodiments, it is possible to generate more simulated implantations simulated with other pitches, for example, simulating 8 simulated implantations with a pitch equal to 20 mm, 8 simulated implantations with a pitch equal to 25 mm and 8 simulated implantations with a pitch equal to 30 mm. Besides, in other non-illustrated embodiments, the 8 displacements δ in the same simulated implantations (i.e. m is a constant and n is a variable) can randomly divide the pitch, but the 4 displacements δ corresponding to the same orientation in different simulated implantations (i.e. m is a variable and n is a constant) are still equal. As the listing in the Table 1, the 8 different dose profiles and dose uniformities referring to 8 different displacements δ for each of the 4 orientations can be calculated.
In step 3, the first optimized displacement δ1 corresponding to the orientation 0° can be determined by selecting the best dose profile and dose uniformity from the dose profiles and dose uniformities calculated from the simulated implants 111 to 181. In another word, since different displacements δ correspond to different dose profiles and dose uniformities, the first optimized displacement δ1 correspond to the best dose profile and dose uniformity.
In step 4, a wafer is shifted to meet the first optimized displacement δ1.
In step 5, a first implant with the first optimized displacement δ1 is formed on a surface of the wafer.
In step 6, the wafer is further rotated to the next orientation, for example, 90°, 180° or 270° for the next implant.
Thereafter, the steps 3-6 are repeated for the second implant, the third implant and the fourth implant respectively corresponding to the other three orientations 90°, 180° and 270°, so as to finish an optimized implantation. In another word, all of the four implants are proceeded by using the four optimized displacements δM, all of the four optimized displacements δM correspond to all of the best calculated dose profiles and dose uniformities corresponding to the four different orientations, and all of the best calculated dose profiles and dose uniformities are similar to or the same as the dose profiles and dose uniformities on a wafer surface. As a result, the dose profile and dose uniformity on the wafer surface is the best.
It should be noted that although it is possible to generate a significant number of simulated implants I(m,n) for determining the optimized displacement, the inventor finds that the optimized displacement is usually, not always, resulted in a case that the wafer is always rotated along a clockwise direction or a counterclockwise direction in the step 6 and always shifted close to or away from the center of the wafer with the same pitch shift (Δ) in the step 4. In a word, the optimized simulated implantation is probably resulted from the combination of the simulated implants 111, 132, 153 and 174, the combination of the simulated implants 121, 142, 163 and 184, the combination of the simulated implants 131, 152, 173 and 114, the combination of the simulated implants 141, 162, 183 and 124, the combination of the simulated implants 151, 172, 113 and 164, the combination of the simulated implants 161, 182, 123 and 144, the combination of the simulated implants 171, 112, 133 and 154, the combination of the simulated implants 181, 122, 143 and 154, and vice versa. As a result, in a quad-implant mode, it is possible to obtain an optimized implantation by proceeding a first implant with a displacement δ1 equal to x mm at y°, a second implant with a displacement δ2 equal to x+2*(S/8) mm at (y+90)°, a third implant with a displacement δ3 equal to x+4*(S/8) mm at (y+180)° and a four implant with a displacement δ4 equal to x+6*(S/8) mm at (y+270)°, wherein x represents an initial displacement and ranges between 0 mm and 2*(S/8) mm, while the y represents an initial orientation and ranges between 0° mm and 90°. Based upon the observation, it is possible to further reduce the total number of the simulated implants significantly. The details about applying the present invention in a bi-implant mode, a sexton-implant mode, an octa-implant mode . . . and so on are substantially the same as the embodiment illustrated above and thus omitted herein.
Continuously, the inventor provides the embodiments of a 1-dimensional, 2-dimensional and angle ion beam profiler. It is noted that the embodiments is used to illustrate this invention not to limit the scope of the invention. Refer to
For example, 1-dimensional beam profiler 910 comprises a channel, which is configured as a slot, and the detection unit behind the slot, shown at the upper of
For example, 2-dimensional beam profiler 920 comprises a channel, which is configured as an array or a matrix of holes, and detection unit behind these holes, shown at the middle of the
For example, the angle beam profiler comprises a channel, which is configured as a row of three holes 930, and a detection unit behind the holes, shown at the lower of
The I-dimensional and the 2-dimensional can be integrated to figure out beam shape, and the beam shape can be shown as a 3-dimensional beam profile, x-y-dose profile shown as
Although this invention has been explained in relation to its preferred embodiment, it is to be understood that modifications and variation can be made without departing the spirit and scope of the invention as claimed.
This Application is being filed as a Continuation-in-Part of application Ser. No. 12/950,366, filed 19 Nov. 2010, currently pending.
Number | Date | Country | |
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Parent | 12950366 | Nov 2010 | US |
Child | 13945013 | US |