A magnetron with uniform deposition and its design method

Abstract

The present invention discloses a magnetron with uniform deposition, which includes an outer magnetic pole magnet and an inner magnetic pole magnet, and the magnetic polarities of the outer magnetic pole magnet and the inner magnetic pole magnet are opposite. The outer magnetic pole magnet and the inner magnetic pole magnet form a closed loop, and this closed loop forms a plasma orbit. The distribution of the length L of the center line of the plasma orbit changes with the distance (x) from the center of the target as L = ax<supgt;n< / supgt>, where a is an arbitrary constant and n is a variable. The value of n is obtained by fitting calculation with a formula. The present invention can ensure the uniformity of the thickness of the deposited film, improve the target corrosion rate and make the center line of the plasma ring shorter at the same time.

Description

Technical Field

[0001] The present invention relates to magnetron sputtering deposition of thin films. In particular, the present invention relates to a magnetron designed according to parameters such as the target-substrate distance (TSD) for generating uniform sputtering, enhanced sputtering, and maximum target utilization, and a design method thereof. Background Art

[0002] Magnetron sputtering is a type of physical vapor deposition. It is a technique that uses plasma to bombard a target, causing target particles to detach and deposit on the surface of a substrate to form a thin film. Generally, a magnetron is placed behind the target, and the magnetic field it generates can control the movement regions of electrons and ions on the target surface, thereby increasing the ionization rate of process gases such as Ar gas in this region, increasing the plasma concentration on the target surface, and thus increasing the thin film deposition rate. The magnetron sputtering technique is widely used in the field of semiconductor and microelectronic device manufacturing and is the most commonly used thin film deposition method.

[0003] As Figure 1 shown, it is a schematic diagram of a typical magnetron sputtering device. This device mainly includes: 1. A process chamber, which has a substrate stage, a substrate is loaded on the substrate stage, a process gas inlet, a target, etc.; the process chamber is connected to a vacuum pump, and is pumped to a vacuum by the vacuum pump; the target is connected to an external power supply, and the power supply generates a negative electric field on the target surface, ionizes the process gas, and causes it to impact the target under the action of the electric field, causing target particles to sputter out; 2. A magnetron. Generally, the magnetron is placed outside the vacuum chamber and parallel to the back of the target. The magnetron can be stationary or moving. The latter usually rotates around the center line of the target; magnets are installed on the magnetron, usually with adjacent magnets having opposite polarities, and the magnetic field they generate forms a magnetic field distribution on the target surface, controlling the movement regions of electrons and ions on the target surface, and increasing the plasma concentration and thin film deposition rate.

[0004] Anderson et al. pointed out in U.S. Patents 4,995,958 and 6,024,843 that in order to achieve uniform corrosion of the target, the sum of the line lengths of the plasma ring centers at a radius of R of the magnetron should be inversely proportional to the radius, that is:

[0005]

[0006] wherein, R is the distance from a certain point on the center line of the plasma ring to the center of the target, that is, the radius value corresponding to this point; is the total line length of the plasma ring centers at a radius of R of the magnetron; k is a constant related to the plasma intensity and other relevant factors; C is a constant. E(R) is the corrosion curve, and then they derived that the differential formula for a fixed corrosion curve has a standard solution:

[0007]

[0008] where θ is the minimum radius of the plasma orbit, and R and θ are the polar coordinates of the orbit.

[0009] Figure 2 is a magnetron designed according to this theory.

[0010] Hong S. Yang et al. also attempted to solve the problem of non-uniform radial corrosion of the target by a formula and an iterative correction program in US Patent 7,186,319 and Chinese Patent CN1997768. They believe that as shown in Formula 3:

[0011] L R = ar n (3)

[0012] where a is a constant; r is the distance from a point on the center line of the plasma ring to the center of the target, that is, the radius value corresponding to this point; is the total line length at the center of the plasma ring with a radius of r in the magnetron; n is a constant near 2; when n = 2, it usually corresponds to uniform target corrosion; when n < 2, it corresponds to larger target corrosion at the center of the target; when n > 2, there is larger corrosion at the edge of the target.

[0013] They believe that when n = 2, it indicates that the length of the plasma orbit is proportional to the radius within a unit radial increment. Therefore, this formula is consistent with the formula of Anderson et al. However, in fact, these two formulas are not consistent. The formula of Anderson et al. is Formula 4:

[0014]

[0015] indicates that dL / dr = C / k, where C is a constant and is not proportional to the radius. Therefore, the magnetron designed by Hong S. Yang et al. based on

[0016] L R = ar n (5)

[0017] this iterative program of the formula has certain limitations.

[0018] More importantly, the above-mentioned magnetron patents only focus on the uniformity of target corrosion and ignore the uniformity requirements of the sputtered thin film. In fact, during the magnetron sputtering process, simply requiring uniform corrosion of the target does not necessarily guarantee the uniformity of the deposited thin film.

[0019] For example, in the RF (radio frequency) sputtering process, since there is no magnetron, the target material undergoes basically a uniform corrosion process. Holland calculated in the book Vacuum Deposition of Thin Film (Chapman & Hall Ltd., London, 1970, p. 149) the variation of the thickness t of the thin film deposited on the substrate with the distance x from the center point of the source under the condition that the target-substrate distance (TSD) is h:

[0020]

[0021] l is the radius of the target. This formula is also applicable to the sputtering process. Considering the axial symmetry of the circular target and the circular substrate, it can be simplified to the distribution of the thin film thickness on a single diameter of the substrate (y = 0, α = 90°, a = h). Holland obtained the following variation of the thickness t of the thin film deposited on the substrate with the distance x from the center point, as shown in the figure Figure 3 as follows:

[0022]

[0023] From Figure 3 it can be seen that although the corrosion of the target material is uniform during the RF sputtering process, however:

[0024] 1. If h / l is large, for example, h / l = 5, that is, when the TSD is 5 times the radius of the target, even when x / l = 1, that is, when the radius of the substrate is the same as the radius of the target, the uniformity of the deposited thin film is still very good, that is, t / t0 = 0.98;

[0025] 2. If h / l is small, for example, h / l = 0.5, that is, when the TSD is half of the radius of the target, when x / l = 1, that is, when the radius of the substrate is the same as the radius of the target, the uniformity of the deposited thin film becomes very poor, that is, t / t0 = 0.59;

[0026] 3. If h / l is small, for example, h / l = 0.5, that is, when the TSD is half of the radius of the target, to obtain better uniformity of the deposited thin film, such as t / t0 = 0.98, then only a very small substrate can be used, such as x / l = 0.1, that is, the radius of the substrate can only be one-tenth of the radius of the target.

[0027] The requirement for the uniformity of the deposited thin film is the first priority requirement in the magnetron design. The uniformity of the deposited thin film is related to specific process parameters and system geometric parameters, especially related to the distance (TSD) between the target and the substrate.

[0028] In the actual sputtering process, it is usually desired to use a smaller target and a larger substrate (for example, a 12-14 inch target corresponding to a 6-8 inch substrate). At the same time, it is also desired to reduce the TSD (usually, the TSD is 1-4 inches) to increase the sputtering rate. This can reduce the target cost on the one hand and increase the production capacity on the other hand. Therefore, adding a magnetron in sputtering to form magnetron sputtering is the best way to achieve this goal.

[0029] At the same time, in a magnetron sputtering device, additional electric and magnetic fields are usually applied on the substrate table and in the cavity. For example, an RF bias voltage is applied to improve the properties of the thin film, such as density, stress, etc.; another example is to apply a magnetic field around the substrate to control the magnetization direction of the magnetic thin film. Therefore, when designing the magnetron, it is necessary to control the size of the TSD to reduce the mutual interference between these additionally applied electromagnetic fields and the magnetron.

[0030] For a magnetic material target, the design of the magnetron has additional requirements. Since the magnetic target can shield the magnetic field generated by the magnetron, the magnetic field intensity generated on the target surface is greatly reduced. Therefore, on the one hand, it is necessary to increase the magnetron intensity; on the other hand, it is also necessary to reduce the length of the center line of the plasma ring generated by it, so as to increase the instantaneous energy density applied by the power supply to the target, thereby reducing the voltage for generating plasma of the magnetic target, making it easy to ionize the process gas on the target surface to form plasma and increasing its concentration.

[0031] Therefore, the basic principle of magnetron design is to satisfy:

[0032] First priority, the uniformity of the thickness of the deposited thin film;

[0033] Second priority, maximizing the target corrosion rate;

[0034] Third priority, the shortest center line of the plasma ring. Summary of the Invention

[0035] Aiming at the deficiencies of the prior art, the present invention provides a magnetron that can ensure the uniformity of the thickness of the deposited thin film, while increasing the target corrosion rate and making the center line of the plasma ring shorter.

[0036] To achieve the above object, the present invention provides the following technical solution: A magnetron with uniform deposition, including an outer pole magnet and an inner pole magnet, and the outer pole magnet and the inner pole magnet have opposite magnetic polarities. The outer pole magnet and the inner pole magnet form a closed loop, and this closed loop forms a plasma orbit. The length L of the center line of the plasma orbit changes with the distance (x) from the target center as L = ax n , where a is an arbitrary constant, n is a variable, and the n value is determined by the formula

[0037]

[0038] Obtained by fitting calculation, the n value is not fixed and changes with the change of TSD(h). When the h value is large, it indicates that from the center to the edge of the magnetron, the change of the required magnetic field strength is close to linear. When the h value is small, it indicates that from the center to the edge of the magnetron, the required magnetic field strength increases sharply at the edge.

[0039] Furthermore, the plasma orbit is close to or passes through the center of the target, and its rotation sweeps across most of the target surface except the edge of the target.

[0040] Furthermore, the distance from the position where the plasma orbit rotates and sweeps across to the edge of the target is 0 - 5 mm.

[0041] A design method for a magnetron with uniform deposition, comprising the following steps:

[0042] S1: Determine the sizes of the target and the wafer, and the size of the ideal distance between the required target and the wafer;

[0043] S2: Through the formula

[0044]

[0045] By fitting calculation, the n value is not fixed and changes with the change of TSD(h). When the h value is large, it indicates that from the center to the edge of the magnetron, the change of the required magnetic field strength is close to linear. When the h value is small, it indicates that from the center to the edge of the magnetron, the required magnetic field strength increases sharply at the edge, and determine the required L = ax n The n value in the formula;

[0046] S3: Construct a closed loop composed of inner and outer magnetic pole magnets, divide the target into several concentric circles, and calculate the length of the center line of the plasma orbit between adjacent concentric circles; and by adjusting the distribution of the closed loop, make the length L distribution of the center line of the plasma orbit formed by the closed loop satisfy: L≈ax n 。

[0047] Furthermore, in step S3, the center of the center line of the closed loop is close to or passes through the center of the target.

[0048] Furthermore, in step S3, when constructing the closed loop, divide the target into 5 - 10 concentric circles.

[0049] Furthermore, in step S3, when constructing the closed loop, use software to automatically calculate the length of the center line of the plasma orbit between adjacent concentric circles.

[0050] Compared with the prior art, the beneficial effects of the present invention are as follows: The magnetron can be designed according to the TSD value required by the sputtering process to precisely meet the sputtering process requirements. At the same time, not only can a high uniformity of the deposited film thickness be achieved, but also the target corrosion rate can be maximally increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figures 1-3 are the drawings for the background art;

[0052] Figure 4 is the model diagram for simplifying formula (8);

[0053] Figure 5 is the diagram showing the variation of the thickness of the deposited film with the distance from the center of the wafer at different TSDs;

[0054] Figure 6 is the diagram showing the variation of the relative film thickness with the distance from the center of the wafer at different TSDs;

[0055] Figure 7 is the structural diagram of the magnetron obtained by taking a 14-inch target as an example in the present invention;

[0056] Figure 8 is the diagram showing the relationship between the length of the plasma center line and the radius in the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0057] Refer to Figures 4 to 8 for a further description of the embodiments of the magnetron with uniform deposition and its design method of the present invention.

[0058] In the description of the present invention, it should be noted that for the orientation terms, such as the terms "center", "transverse (X)", "longitudinal (Y)", "vertical (Z)", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc., the orientation and position relationships indicated are based on the orientation or position relationships shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and should not be construed as limiting the specific protection scope of the present invention.

[0059] In addition, for the terms "first" and "second", they are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, the meanings of "several" and "a number of" are two or more, unless otherwise specifically and clearly defined.

[0060] A magnetron with uniform deposition comprises an outer pole magnet and an inner pole magnet, wherein the outer pole magnet and the inner pole magnet have opposite magnetic polarities and form a closed loop, which can restrain charged particles, increase gas ionization rate and form plasma orbits during magnetron sputtering.

[0061] like Figure 7 As shown, the magnetron in the present invention is in a "bat" shape as a whole, and the magnetron rotates around the center of the sputtering target on the magnetron sputtering equipment.

[0062] The plasma track is preferably close to or passes through the center of the target material, and the distance between the position where the plasma track rotates and sweeps and the edge of the target material is 0-5 mm, forming "Full-Face" sputtering.

[0063] The magnetron can be simulated to adjust the distribution of the inner and outer pole magnets so that the length L of the plasma track centerline changes with the change of the target center distance (x) to L = ax n , where a is an arbitrary constant and n is a variable, which is related to the target radius, substrate radius, and designed TSD.

[0064] Consider the target is circular, the magnetron is on the back of the target and rotates around the center of the target; at the same time, the substrate is circular and coaxially parallel to the target. Due to the axial symmetry, it can be simplified as follows Figure 4 In the model shown, the target is linear with a radius of R, the substrate radius is r, and the vertical distance (TSD) between the two is h.

[0065] If it is assumed that the deposition rate of a certain point p on the target to the substrate is proportional to the strength of all magnetic fields acting on that point, then the film deposition thickness t at point q(k, 0) on the substrate can be written as:

[0066]

[0067] Where m is a constant. Considering the requirement of uniformity of deposited film, that is, the thickness of the film at each location on the wafer is approximately equal, the above formula can be analyzed.

[0068] However, the calculation of the above formula is extremely complicated. In practical applications, the following approximation can be further made, that is, at a certain point p on the target material, the deposition rate on the substrate is only proportional to the magnetic field strength at that point. In this way, only the variation of the film deposition thickness with the wafer radius in the absence of an external magnetic field can be calculated. By mirroring, the function of the distribution of the magnetic field strength on the wafer can be obtained.

[0069] Taking 14-inch target and 8-inch wafer as an example, analyzing the above formula, we can get:

[0070]

[0071] For different (TSD) h = 1, 2, 3, 4 inches, the variation of the thickness of the deposited film with the distance from the wafer center is as Figure 5 shown.

[0072] Furthermore, if we assume the distribution function of the magnetic field, where a is an arbitrary constant and n is a variable. Through mirroring, the distribution function H of the magnetic field under each TSD(h) condition can be obtained ( x ) ＝ ax n .

[0073] And the following table is obtained:

[0074] h n 1 2.85059 2 2.55829 3 2.27944 4 0.93209

[0075] It can be summarized as follows Figure 6 shown. From the above table and Figure 6 , we note that

[0076] 1. As the TSD changes, the value of n is not fixed and can vary between 1 and 3;

[0077] 2. When the value of h is large, the value of n approaches 1, indicating that the change in the required magnetic field strength from the center to the edge of the magnetron is nearly linear;

[0078] 3. When the value of h is small, the value of n approaches 3, indicating that the required magnetic field strength becomes much stronger at the edge from the center to the edge of the magnetron.

[0079] A design method for a magnetron with uniform deposition includes the following steps:

[0080] S1: Determine the sizes of the target and the wafer, and the size of the ideal distance (TSD) between the target and the wafer required;

[0081] S2: Through formula

[0082]

[0083] fitting calculation, determine the value of n in the formula L = ax n in the formula;

[0084] S3: Construct a closed loop composed of inner and outer magnetic pole magnets;

[0085] a. The center of the center line of the closed loop preferably approaches or passes through the center of the target;

[0086] b. When the center line of the closed loop rotates around the center of the target, it must sweep most of the target surface except the target edge (0 - 5 mm);

[0087] c. The construction of the closed loop can be achieved with the aid of several software programs. The target is divided into several (usually 5 - 10) concentric circles, and the software automatically calculates the lengths of the center lines of the plasma orbits between adjacent concentric circles. By adjusting the distribution of the closed loop, the variation of the length L of the center line of the plasma orbit formed by the closed loop with respect to the distance (x) from the center of the target satisfies: L≈ax n .

[0088] As Figure 7 shown, it is an implementation case of the above formula and invention, a 14 - inch "bat - shaped" magnetron.

[0089] 1. For this magnetron layout, when TSD = 3.5 in, according to the formula

[0090]

[0091] the calculated value of n is ~1.62. Then, following the above steps

[0092] 2. The target is divided into 6 equally - spaced concentric circles with radii of 1, 2, 3, 4, 5, and 6 inches respectively;

[0093] 3. A closed loop composed of inner and outer magnetic - pole magnets is arranged on it. According to experience, the initial shape of the center closed loop can be set as type, or "M" type.

[0094] 4. Using auxiliary software such as SolidWorks, calculate the lengths of the center lines of the plasma orbits within each closed loop and check whether it conforms to: L≈ax n , (n ~ 1.62).

[0095] 5. If there is a deviation, repeatedly adjust the position of the closed loop composed of inner and outer magnetic - pole magnets until the requirements are met.

[0096] Figure 7 Figure shows the structure of the magnetron completed according to this step, Figure 8 Figure is the relationship diagram between the plasma center - line length and the radius. Taking Figure 8 as an example, the relationship between the plasma center - line length and the radius is listed in the following table:

[0097]

[0098]

[0099] Fitting with the distribution function, the value of n can be obtained: ~1.59, close to n ~ 1.62. Under this condition, the uniformity of the ~100 - nm - thick NiCrFe alloy film deposited on an 8 - inch wafer can reach StdD% ~ 0.50% (49Pts, 5mmEE).

[0100] The above are only the preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions falling within the concept of the present invention belong to the protection scope of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements should also be regarded as within the protection scope of the present invention.

Claims

1. A magnetron with uniform deposition, characterized in that: It includes an outer magnetic pole magnet and an inner magnetic pole magnet, and the magnetic polarities of the outer magnetic pole magnet and the inner magnetic pole magnet are opposite. The outer magnetic pole magnet and the inner magnetic pole magnet form a closed loop, and this closed loop forms a plasma orbit. The length L distribution of the center line of the plasma orbit changes with the distance (x) from the target center as L = ax n , where a is an arbitrary constant and n is a variable. The value of n is determined by the formula Obtained by fitting calculation, the value of n is not fixed and changes with the change of TSD(h). When the value of h is large, it indicates that from the center to the edge of the magnetron, the change in the required magnetic field strength is close to linear. When the value of h is small, it indicates that from the center to the edge of the magnetron, the required magnetic field strength increases sharply at the edge.

2. The magnetron with uniform deposition according to claim 1, wherein: The plasma orbit is close to or passes through the center of the target, and its rotation sweeps across most of the target surface except the edge of the target.

3. The magnetron with uniform deposition according to claim 2, wherein: The distance from the position where the plasma orbit rotates and sweeps across to the edge of the target is 0 - 5 mm.

4. A design method of a magnetron with uniform deposition, characterized in that, It includes the following steps: S1: Determine the sizes of the target and the wafer, as well as the size of the ideal distance required between the target and the wafer. S2: Through the formula For the fitting calculation, the value of n is not fixed and changes with the change of TSD(h). When the value of h is large, it indicates that from the center to the edge of the magnetron, the change in the required magnetic field strength is nearly linear. When the value of h is small, it indicates that from the center to the edge of the magnetron, the required magnetic field strength increases sharply at the edge. Determine the required L = ax n The value of n in the formula; S3: Construct a closed loop composed of inner and outer magnetic pole magnets, divide the target into several concentric circles, and calculate the length of the plasma orbit center line between adjacent concentric circles; and By adjusting the distribution of the closed loop, the variation of the length L of the center line of the plasma orbit formed by the closed loop with respect to the distance (x) from the target center satisfies: L≈ax n .

5. The design method of the magnetron with uniform deposition according to claim 4, characterized in that: In step S3, the center of the center line of the closed loop is close to or passes through the center of the target.

6. The design method of the magnetron with uniform deposition according to claim 5, characterized in that: In step S3, when constructing the closed loop, divide the target into 5 - 10 concentric circles.

7. The design method of the magnetron with uniform deposition according to claim 6, characterized in that: In step S3, when constructing the closed loop, use software to automatically calculate the length of the plasma orbit center line between adjacent concentric circles.

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