Method for planarizing a semiconductor wafer surface

Abstract

To provide a planarization method for semiconductor wafers, which can planarize the surface of semiconductor wafers more precisely in response to the increasing density of semiconductors.SOLUTION: A planarization method of a semiconductor wafer surface includes: irradiating a semiconductor wafer with a laser and melting the surface of the above semiconductor wafer at the irradiated position; applying a magnetic field to the above irradiated position and moving the position of the above semiconductor wafer relative to the above magnetic field so that the Lorentz force acts in the direction of planarizing the above surface at the above irradiated position.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a planarization method for repairing surface defects, which are layers affected by processing of semiconductor wafers, and for planarizing surface roughness, waviness, etch pits, etc., by laser heat treatment. [Background technology]

[0002] Conventionally, semiconductor wafers, such as silicon wafers, used in the fabrication of semiconductor devices, have been surface-processed using mechanical processes such as cutting, grinding, lapping, and polishing. However, these wafers develop process-affected layers on their surface and interior, some of which contain microcracks. These internal cracks are typically removed using chemical and mechanical methods such as etching and chemical mechanical polishing (CMP).

[0003] As a method for flattening such roughness, Patent Document 1 describes the following: "A method for modifying a wafer edge portion using laser heat treatment, the method comprising: an optical system including a polygon mirror that reflects laser light and directs it to an arc-shaped mirror whose sides are combined in a dogleg shape to form a concave mirror; and a focusing lens that is a three-dimensional curved body with a plano-convex cross section that is curved when viewed from above and that focuses the laser light reflected by the mirror onto a notch portion; rotating the polygon mirror to scan and irradiate the laser light onto the notch portion; and determining a cumulative irradiation energy corresponding to the crystal orientation of the notch portion and irradiating the laser light." [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6932865 Summary of the Invention [Problem to be solved by the invention]

[0005] The modification method described in Patent Document 1 has excellent performance, and by appropriately determining the laser irradiation conditions, it is possible to repair damage such as grinding marks caused by grinding processing and perform flattening processing. However, in recent years, power semiconductors have become increasingly compact, with increasing power consumption per semiconductor area and higher density, resulting in higher demands for higher quality. As a result, semiconductor wafer surfaces are being required to be even flatter, with extremely minute waviness and roughness of less than 10 nanometers.

[0006] Although the method described in Patent Document 1 was highly efficient, it was not necessarily sufficient to flatten undesirable surface features, such as minute waviness and roughness, to a level of less than a dozen nanometers, and there was room for improvement. In particular, when attempting to flatten such minute waviness by laser irradiation alone, there were cases in which further waviness was generated or remained on the surface after melting and solidifying due to convection caused by surface tension. In other words, to obtain an extremely flat surface on the order of a dozen nanometers, there was a gap that could not be reached by simply extending conventional technology, i.e., by methods such as precisely adjusting the laser irradiation conditions.

[0007] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method for planarizing a semiconductor wafer that solves the above-mentioned problems of the prior art, is compatible with the increasing density of semiconductors, and can more precisely planarize the surface of a semiconductor wafer. [Means for solving the problem]

[0008] As a result of extensive research into solving the above problems, the present inventors have found that the above problems can be solved by the following configuration.

[0009] [1] A method for planarizing a surface of a semiconductor wafer, comprising: irradiating a semiconductor wafer with a laser to melt the surface of the semiconductor wafer at the irradiation position; applying a magnetic field to the irradiation position so that a Lorentz force acts in a direction to planarize the surface at the irradiation position; and moving the position of the semiconductor wafer relative to the magnetic field. [2] The planarization method according to [1], further comprising: measuring the shape of the surface before laser irradiation to obtain mapping information; and determining at least one selected from the group consisting of the direction of the magnetic field, the irradiation position, and the direction of movement based on the mapping information. [3] A flattening method according to [1] or [2], wherein the laser has a beam profile adjusted so that the flow caused by the difference in surface tension at the irradiation position is in a predetermined direction, and the relative position is moved so that the direction of the Lorentz force and the direction of the flow are approximately the same. [4] A planarization method according to any one of [1] to [3], wherein the movement of the relative position of the semiconductor wafer is performed by a holding table that holds the semiconductor wafer and has a five-axis structure that includes three axes, namely, an X-axis, a Y-axis, and a Z-axis, as well as two additional axes, namely, a yaw axis for rotation and a pitch axis for tilt. [5] The planarization method according to any one of [1] to [4], further comprising: measuring the shape of the surface before laser irradiation to obtain mapping information; and determining at least one selected from the group consisting of the energy density of the laser, the cumulative number of irradiations to the same irradiation position, and the scan pitch based on the mapping information. [6] The planarization method according to any one of [1] to [5], wherein the laser is irradiated from a laser irradiation system having a light source, a beam expander, a mask, and a condenser lens in this order, and the laser is expanded by the beam expander and then shaped by the mask having a window of a predetermined shape. [7] The planarization method according to any one of [1] to [6], wherein the Lorentz force is adjusted so as to be generated along the direction of inclination of the slope of the sloping surface of the scratches on the surface. [8] The planarization method according to [7], wherein the beam profile of the laser is adjusted so that the energy density decreases along the tilt direction. [9] The planarization method described in [6], wherein the laser irradiation system has a plurality of spot shape adjustment systems including the beam expander, the mask, and the focusing lens, and a beam splitter, and the spot shape adjustment system is irradiated with a laser beam emitted from the light source and split through the beam splitter.

[10] The flattening method described in [9], which has a plurality of the beam splitters arranged in series with respect to the light source, and the laser split from each of the beam splitters is incident on the spot shape adjustment system. [Effects of the Invention]

[0010] According to the present invention, a method for planarizing a semiconductor wafer can be provided that can accommodate the increasing density of semiconductors and can more precisely planarize the surface of a semiconductor wafer. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a flowchart illustrating a procedure for a planarization method according to an embodiment of the present invention. [Figure 2] 1A to 1C are explanatory diagrams illustrating a procedure for roughly planarizing a semiconductor wafer by a planarization method according to an embodiment of the present invention. [Figure 3] 10A and 10B are explanatory diagrams of steps S4 and S5 of the planarization method according to one embodiment of the present invention, in which (a) is a diagram showing the beam profile and beam spot shape of the laser irradiated at the irradiation position, and (b) is a diagram showing the moving direction of the semiconductor wafer, the direction of application of the magnetic field, and the Lorentz force generated thereby. [Figure 4] FIG. 2 is an explanatory diagram showing the basic configuration of a laser irradiation system of the planarization apparatus according to the embodiment of the present invention. [Figure 5] FIG. 2 is a configuration diagram showing the relationship between a laser irradiation system and a semiconductor wafer. [Figure 6] 1 is a block diagram of a planarization apparatus according to an embodiment of the present invention, and a configuration diagram illustrating each step. [Figure 7] FIG. 2 is a Y-axis front view showing the relationship between the laser irradiation system, the semiconductor wafer, and the magnetic field application device. [Figure 8] 10 is a front view along the X axis showing the relationship between the laser irradiation system, the semiconductor wafer, and the magnetic field application device 22. FIG. [Figure 9] FIG. 2 is a perspective view showing a magnetic field application device. [Figure 10] 1 is a Y-axis front view showing the relationship between a laser irradiation system, a semiconductor wafer, and a magnetic field application device when irradiating the edge portion of the peripheral edge (outer periphery) of the semiconductor wafer. FIG. [Figure 11] 10 is a front view along the X axis showing the relationship between the laser irradiation system, the semiconductor wafer, and the magnetic field application device when irradiating the outer peripheral edge portion. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] [Flattening method] A method for planarizing the surface of a semiconductor wafer according to an embodiment of the present invention (hereinafter also referred to as "this planarization method") is a method for planarizing the surface of a semiconductor wafer, comprising: irradiating a semiconductor wafer with a laser to melt the surface of the semiconductor wafer; applying a magnetic field to the irradiation position so that a Lorentz force acts at the irradiation position in a direction that flattens the surface; and moving the position of the semiconductor wafer relative to the magnetic field.

[0013] The above-mentioned planarization method will be described with reference to the drawings. Figure 1 is a flow chart showing the steps of this planarization method, and Figure 2 is an explanatory diagram of the steps of roughly planarizing a semiconductor wafer by this planarization method.

[0014] First, in step S1, the shape of the semiconductor wafer surface is measured using an optical measuring device such as a camera to obtain information (mapping information) on waviness, roughness distribution, and etch pits (unevenness) which are minute depressions.

[0015] This mapping information typically includes information about the variation in height in the thickness direction at a predetermined position on the surface of the semiconductor wafer, i.e., the distribution of the variation (displacement).By referring to the mapping information, it is possible to understand the amount of height nonuniformity and in which part of the surface of the semiconductor wafer. Although the present planarization method does not necessarily have to include the above step S1, if the present planarization method includes the above step S1, the subsequent planarization can be performed more efficiently. When the degree and position of the unevenness are grasped from the mapping information, the laser energy density, the cumulative number of irradiations to the same irradiation position, the scan pitch, etc. can be more appropriately determined.

[0016] In step S2, a laser is irradiated onto the surface of a semiconductor wafer, which typically has an uneven surface after grinding or other processes, to melt and flow the surface, thereby roughly flattening it. Generally, the surface of a semiconductor wafer (intermediate product) manufactured by grinding or other processes may have scratches on the order of several hundred nanometers caused by the grinding process. In this process, prior to the subsequent precise flattening, the laser irradiation flattens the unevenness, resulting in a roughly flattened surface (on the order of several tens of nanometers).

[0017] The beam profile of the laser used in this process is not particularly limited and may be Gaussian, top hat, or the like. The laser is irradiated by scanning the entire or part of the semiconductor wafer under appropriate laser conditions. In this case, the laser irradiation conditions, such as the energy density, the cumulative number of irradiations to the same location, and the scan pitch, may be predetermined or may be changed as appropriate depending on the mapping information, the material (melting temperature) of the wafer, etc. That is, before this step, a step of determining at least one selected from the group consisting of energy density, cumulative number of irradiations to the same location, and scan pitch based on the mapping information may be further included.

[0018] The laser in this process is irradiated to flatten the irregularities on the surface of the semiconductor wafer, and is irradiated with an intensity sufficient to locally melt part or all of the surface, or the entire semiconductor wafer. For example, the laser may be irradiated along the thickness direction of the semiconductor wafer, melting an area approximately equal to the height of the irregularities on the entire semiconductor wafer (e.g., the sum of the maximum peak height and maximum valley depth of the roughness curve). This intensity is preferably adjusted based on the mapping information, in addition to the energy density, the cumulative number of irradiations to the same location, the scan pitch, and the like, as well as the material of the semiconductor wafer, which will be described later.

[0019] The material of the semiconductor wafer to be processed is a semiconductor material that is conductive in a molten state, such as a single element, such as Si (silicon) or Ge (germanium), or a compound, such as GaAs (gallium arsenide) or InP (indium phosphide). Generally, semiconductor materials can be considered as conductive fluids in a molten (melted) state, so this method can be applied to semiconductor wafers made of various materials (including single-crystal semiconductor wafers), regardless of the material. Among these, the semiconductor wafer material is preferably Si or Ge, and more preferably Si, in terms of obtaining better effects of the present invention.

[0020] The laser irradiated in this process and subsequent steps is a pulsed laser or a CW (continuous wave) laser appropriate for the material to be processed, with a wavelength preferably ranging from ultraviolet to infrared (wavelength λ = 355 nm, 532 nm, 785 nm, 1080 nm). The energy density (energy per unit area: fluence) is set below the processing threshold so as to melt the material without causing laser ablation.

[0021] Next, the surface flow caused by the laser irradiation position will be described. When a laser is irradiated, the semiconductor wafer melts at the irradiated position. At that time, the temperature of the molten wafer (fluid) becomes high in the part where the energy density of the irradiated laser is high, and conversely, the temperature becomes low in the part where the energy density is low. This creates a surface tension gradient at the irradiation position, causing a flow from the high temperature area (high temperature area) to the low temperature area (low temperature area) (Marangoni convection). For example, when a laser with a circular spot shape and a Gaussian profile in which the energy density decreases in the radial direction from the center to the periphery is irradiated, convection occurs in the radial direction from the center (focus) of the irradiation position. This convection improves the wafer surface condition to a certain extent.

[0022] The spot shape of the irradiated laser (hereinafter also referred to as "beam spot (shape)") may be any shape such as a circle or a rectangle. The laser can be used with beam shapers such as diffraction gratings, homogenizers, and field mapping to appropriately adjust the beam intensity distribution (Gaussian, top hat, inverse Gaussian, donut, multi-focus, etc.) and beam shape (circular, rectangular, line, elliptical, rectangular, etc.).

[0023] FIG. 2 is an explanatory diagram of the rough planarization process in step S2, and is a side view (schematic diagram) of the semiconductor wafer surface after grinding. As shown in FIG. 2, scratches with triangular cross sections are formed at regular intervals. Although FIG. 2 is a schematic diagram, in reality, scratches formed on the surface of a semiconductor wafer smoothed by grinding often have a shape with a certain regularity like this. The laser irradiation can be performed by determining the energy density at the laser irradiation position in the diagram and scanning at a scan pitch P equivalent to the laser irradiation area (for example, a spot diameter of several hundred μm to 1 mm as one form) or at a pitch where the laser irradiation areas overlap (up to 1 / 2P). The laser irradiation time can be determined depending on the material of the semiconductor wafer, but in one embodiment, it can be several femtoseconds to several nanoseconds. With irradiation for several femtoseconds, the influence of heat conduction caused by irradiation for several nanoseconds can be almost ignored. In addition, as one form, the laser is preferably a nanosecond pulse laser having a wavelength λ of 355, 532, 785, or 1080 nm, a pulse width of 0.5 μJ to 30 μJ per pulse, and an energy density of 0.125 J / cm.2 to 7.5 J / cm 2 is preferred.

[0024] It is also preferable that the nanosecond pulse laser be irradiated by changing at least one of the energy density, the scan pitch P, and the number of irradiations in accordance with the curvature of the irradiation position, etc. For example, the required irradiation energy has a magnitude relationship of Si(110)>Si(100)>Si(111), and irradiation conditions may be determined according to the crystal orientation. The irradiation energy for the Si(110) plane may be approximately 1.3 times that of the Si(100) plane, and the irradiation energy for the Si(111) plane may be approximately the same as or 0.7 times that of the Si(100) plane.

[0025] The above process improves the surface condition (waviness and roughness) of the semiconductor wafer surface to some extent, as shown in the figure below, compared to the state before laser irradiation (after grinding) (top figure). In other words, what was previously a high mountain shape is smoothed to a somewhat lower mountain shape. Once the mountain shape has been reduced to such a low mountain shape, it is difficult to further smooth the flat shape by simply irradiating the laser.

[0026] It should be noted that this planarization method does not necessarily have to include step S2. For example, a semiconductor wafer that has been roughly planarized by a method other than this step may be subjected to a subsequent step. On the other hand, if this planarization method includes step S2, it is possible to perform the subsequent step continuously (using the same apparatus), which tends to shorten the time required to planarize the semiconductor wafer.

[0027] Next, in step S3, the shape of the semiconductor wafer surface is measured again to obtain mapping information. The shape measurement in this step may be performed in the same manner as in step S1. This step allows the effect of rough planarization, the properties (height, etc.) of any resulting or remaining surface irregularities, and their positions to be understood, and this can be used as basic data for setting various conditions when performing more precise planarization in the subsequent step. The present planarization method does not necessarily have to include this step, but by including this step, the semiconductor wafer can be planarized more efficiently.

[0028] Preferably, the present planarization method further comprises, after step S3, a step of determining processing conditions in subsequent steps based on the mapping information. In this process, in step S3-2, the direction of the magnetic field, the irradiation position, and / or the direction of relative movement of the semiconductor wafer with respect to the magnetic field direction are determined based on the mapping information. The direction of the magnetic field and the direction of relative movement are adjusted so that the Lorentz force acts in a direction that flattens the surface, as will be described in detail in step S5 below. Furthermore, the irradiation position is preferably determined more locally in accordance with the mapping information because the subsequent precise planarization (steps S4-S5) targets a narrower range than step S2. Typically, step S2 targets part or all of the surface of the semiconductor wafer, while the subsequent steps S4-S5 target specific irregularities (such as scratches) on the surface of the semiconductor wafer.

[0029] Furthermore, in step S3-3, at least one selected from the group consisting of energy density, cumulative number of irradiations at the same irradiation position, and scan pitch is determined based on the mapping information. The precise planarization in the subsequent steps S4-S5 targets smaller irregularities than the rough planarization in step S2. Therefore, it is preferable to adjust the laser irradiation intensity to be smaller than that in step S2. This process determines the optimal irradiation conditions for each irregularity to be processed. It should be noted that this planarization method does not necessarily have to include the above steps S3-2 and S3-3. However, if the above steps are included, more precise planarization can be achieved, and as a result, semiconductor wafers of higher quality can be manufactured.

[0030] Next, in step S4, the semiconductor wafer is irradiated with a laser to melt the surface of the semiconductor wafer. In general, the electrical conductivity (electrical conductivity) of semiconductor materials such as Si, Ge, and GaAs increases when heated, and in the molten state, they become conductive fluids (for example, in the case of Si, the electrical conductivity is 1.25 × 10 at the melting point of 1450 °C). 4 Ω ―1 cm ―1 ) can be considered. The laser used in this process can be the same as the laser used in step S2 already described. However, since the unevenness (roughness) on the surface after rough planarization is generally very small, and the final surface roughness (height difference) achieved by this planarization method is very small, on the order of a dozen nanometers (less than 20 nm), it is preferable that the energy density and irradiation range (beam spot size) of the laser used in this process be smaller than those of the laser used in step S2.

[0031] The laser in this process is irradiated to flatten the minute irregularities on the surface of the semiconductor wafer, and is irradiated with an intensity sufficient to melt some or all of the irregularities on the surface, particularly locally, from the perspective of the entire semiconductor wafer. For example, the laser may be irradiated in a manner to melt an area along the thickness direction of the semiconductor wafer that is approximately the same height as the irregularities to be processed (e.g., the sum of the maximum peak height and the maximum valley depth of the roughness curve of the irregularities to be processed). This intensity is preferably adjusted based on the mapping information, taking into account the energy density, the cumulative number of irradiations to the same location, the scan pitch, and the material of the semiconductor wafer, as described below.

[0032] Next, in step S5, a magnetic field is applied to the laser irradiation position so that a Lorentz force acts in the direction of planarizing the semiconductor wafer surface, and the position of the semiconductor wafer is moved relative to the magnetic field. As already explained, the semiconductor wafer (semiconductor material) melted at the irradiation position is a conductive fluid. Therefore, by applying a magnetic field to the melted part (fluid) and moving the semiconductor wafer, a Lorentz force is generated in the direction to flatten the surface, achieving precise flattening.

[0033] Here, the induction of flow by laser irradiation and the generation of Lorentz force in steps S4 and S5 will be explained using figures. Figure 3 is an explanatory diagram of steps S4 and S5. More specifically, Figure 3 shows a method for flattening the left slope of the streak in Figure 2 (lower diagram).

[0034] First, FIG. 3(a) is a diagram showing the beam profile and beam spot shape of the laser irradiated at the irradiation position.

[0035] In Figure 3(a), the beam spot is semicircular. This semicircular beam spot is like a circular beam spot with a Gaussian energy density distribution (beam profile) cut in half, and is shaped via a mask or the like of a predetermined shape. This beam spot has a beam profile in which the energy density gradually decreases along the radial direction from the center to the periphery. Therefore, at the irradiation position, the semiconductor wafer becomes hot at the center (focus) of the beam spot, and the temperature decreases along the radial direction toward the periphery. Note that the beam spot in Figure 3(a) is a schematic diagram, and the intensity of the color indicates the magnitude of the energy density, but the contour line is also drawn for easier visibility. The contour line does not reflect the rules for illustrating the magnitude of the energy density described above.

[0036] If this method is applied to the left slope of a streak (for example, a conical protuberance), it is possible to induce a flow (a flow along the slope direction) from near the apex toward the base (the Marangoni convection described above). The advantage of this method is that it can further suppress the effect on the right slope. In other words, by making the spot semicircular, melting and convection can be suppressed on the right slope. In an unmelted state, the Lorentz force, which will be described later, is unlikely to occur, so it is less affected by this treatment. In precision planarization, minute irregularities must be smoothed, and laser irradiation can sometimes result in unintended surface roughness. However, by using the method described above, it is possible to irradiate the laser only at the position where the flow is desired and in the direction where the flow is desired, based on the mapping information. Conversely, this laser irradiation can have less of an effect on areas where movement (flow) is not desired.

[0037] Although the beam spot is semicircular in the above description, the shape of the beam spot is not limited to this. It may be rectangular or circular. The profile may be Gaussian or top-hat. In particular, from the viewpoint of facilitating the shape adjustment (flattening), it is preferable that the laser be adjusted so that a flow occurs in a predetermined direction due to the difference in surface tension that occurs at the irradiation position. That is, based on the mapping information obtained in step S3, it is preferable to irradiate the semiconductor wafer with a laser beam having a profile in which the power attenuates from a portion on the surface of the semiconductor wafer that is convex (higher) than the surrounding area as an apex toward a portion that is concave (lower) around the apex.

[0038] However, as already explained, laser irradiation alone is not necessarily sufficient to precisely flatten the surface of a semiconductor wafer to a roughness of less than a dozen nanometers. It is difficult to eliminate minute undulations on the surface after melting and solidification using only convection induced by the difference in surface tension caused by laser irradiation. Irradiating a surface that has already been flattened to a certain extent with a laser with an energy density above a certain level can create dents (craters) in the irradiated area, worsening the undulations and roughness. This adjustment is extremely difficult to achieve by simply adjusting the laser beam profile and beam spot shape. In contrast to this, one of the features of the method of the present invention is that a magnetic field is applied and the semiconductor wafer is moved, thereby generating a Lorentz force in the direction of flattening the surface, thereby adjusting the surface shape.

[0039] Figure 3(b) shows the direction of movement of the semiconductor wafer, the direction of application of the magnetic field, and the Lorentz force that is generated by it. As shown in Figure 3(b), when a magnetic field with a magnetic flux density B(T) is applied and the semiconductor wafer is moved relative to this magnetic field (or the magnetic field is moved relative to the semiconductor wafer), a current J (A / m 2 ) is induced, and a Lorentz force F(N) is generated. This is because the semiconductor wafer melting at the irradiation position has the properties of a conductive fluid. By generating the Lorentz force in the direction of flattening the surface, it is possible to flatten unevenness with extreme precision, which was previously difficult to achieve using laser irradiation alone, and to realize an extremely flat surface with a roughness on the order of a dozen nanometers, something that has never been achieved before.

[0040] Furthermore, the direction in which the Lorentz force is generated can be determined based on mapping information. Once a preferred direction of the Lorentz force is determined based on the mapping information, the direction of the magnetic field and / or the relative movement direction of the semiconductor wafer with respect to the magnetic field (direction) can be adjusted. Note that examples of a method for adjusting the relative movement direction of the semiconductor wafer with respect to the magnetic field include moving the magnetic field with respect to the semiconductor wafer and / or moving the semiconductor wafer with respect to the magnetic field.

[0041] Furthermore, the irradiation position may be moved sequentially to the area requiring planarization based on the mapping information, thereby enabling planarization to be performed over a desired range on the semiconductor wafer. Note that determining based on mapping information may involve, for example, determining the direction in which the Lorentz force is generated along the inclination direction of the slope when flattening a sloping surface.

[0042] Furthermore, it is preferable to adjust the shape and position of the laser irradiation so that the direction of the Lorentz force is approximately the same as the direction of the surface flow induced by the laser irradiation. The direction of the Lorentz force is typically a fixed direction determined by the direction of the magnetic field and the direction of movement of the semiconductor wafer relative to the magnetic field, so the adjustment can be easily performed. As a result, more efficient planarization can be achieved.

[0043] Next, in step S6, the shape of the surface of the semiconductor wafer is measured again to obtain mapping information, which is compared with the mapping information obtained in step S3 to determine the quality of the planarization process. Note that this planarization method does not necessarily have to include step S6. If step S6 is not included, the semiconductor wafer can be planarized more simply.

[0044] This planarization method makes it possible to manufacture high-quality semiconductor wafers with surface roughness (height difference of the roughness curve) of about 10 nanometers, which was previously difficult to achieve using laser irradiation alone.

[0045] [Flattening device] Next, a semiconductor wafer planarization apparatus capable of carrying out the above-described planarization method will be described. The semiconductor wafer planarization apparatus according to an embodiment of the present invention includes a laser irradiation system that irradiates a semiconductor wafer with a laser and melts the surface of the semiconductor wafer at the irradiation position, a magnetic field application device that applies a magnetic field to the laser irradiation position, a movement mechanism that can move the magnetic field, the relative position of the semiconductor wafer, and the irradiation position on the surface, and a control device, and the control device adjusts the direction of the magnetic field and the relative movement direction of the semiconductor wafer with respect to the magnetic field so that a Lorentz force acts at the irradiation position in a direction that flattens the surface. (Hereinafter, this planarization apparatus will also be referred to as "the present planarization apparatus"). Each component of the planarization apparatus will be described in detail below.

[0046] First, the laser irradiation system will be described. Figure 4 is an explanatory diagram showing the basic configuration of the laser irradiation system 10 of the present planarization apparatus, and illustrates a method for forming a beam spot of a desired shape. The laser irradiation system 10 includes, in this order, a laser light source 10-1, a beam expander 10-2, a mask 10-3, and a condenser lens 10-4. The above is the basic configuration of the laser irradiation system, and the system may further include components having other functions within the scope of the effects of the present invention. Examples of such components include a homogenizer.

[0047] The laser light source 10-1 is a device capable of irradiating the laser already described in the planarization method, and emits, for example, a laser having a Gaussian beam profile. Specifically, it emits a pulsed laser or a CW laser appropriate for the material to be processed. Furthermore, the wavelength of the laser light may be a commonly available commercially available laser light source in the ultraviolet to infrared range (wavelength λ=355 nm, 532 nm, 785 nm, or 1080 nm). The laser beam emitted from the laser source 10-1 is expanded by a beam expander 10-2 to form a beam spot 11. The shape of the beam spot 11 is shaped, for example, by passing through a mask 10-3 having a semicircular window, into a distribution of energy density deflected in a semicircular direction.

[0048] The laser irradiation system 10 has a feature that the mask 10-3 is less susceptible to deterioration because a beam expander 10-2 is disposed between the laser light source 10-1 and the mask 10-3. The laser irradiation system 10 does not necessarily have to have the beam expander 10-2, but by having the beam expander 10-2, the diameter of the laser emitted from the laser light source 10-1 is temporarily expanded, which relatively reduces the energy density and makes it easier to shape using the mask 10-3.

[0049] The mask 10-3 may be made of glass, synthetic quartz, or a polymer film on which a drawing pattern is formed using a chromium or blackened metallic silver as a light-shielding film. In FIG. 4, the window shape of the mask 10-3 is semicircular, but this can be appropriately changed depending on the desired spot shape. With the laser irradiation system 10, the energy density beam profile can be adjusted to not only a simple slope shape but also an etch pit (concave / convex) shape, etc. This mask may be appropriately replaced depending on the shape of the portion to be processed (irradiation position). Also, the laser irradiation system 10 does not necessarily have to have the mask 10-3. For example, the mask 10-3 may not be used during rough planarization, but may be used during the subsequent fine planarization.

[0050] The beam spot 11 is then focused by a focusing lens 10-4, which is made up of a plano-convex lens. The energy density is adjusted to a predetermined value by the size of the beam spot 11 at the irradiation position. For safety reasons, it is preferable that the frame of the laser irradiation system 10 be made of a material that absorbs or reflects light, and metal with an appropriate thickness, aluminum with black anodized finish, etc. are suitable.

[0051] Fig. 5 is a configuration diagram showing the relationship between the laser irradiation system 10 and the semiconductor wafer. Note that Fig. 5 is a diagram for explaining the positional relationship between the laser irradiation system and the semiconductor wafer, and other components of the planarization apparatus 30 are not shown. The laser irradiation system 10 is fixed to a base board 15. The holding table 16, which holds the semiconductor wafer and changes its posture, is preferably a vacuum chuck type, and has a five-axis structure that includes three axes, the X-axis, Y-axis, and Z-axis, as well as two additional axes, the yaw axis for rotation and the pitch axis for tilt. As a result, the irradiation position on the surface of the semiconductor wafer can be freely moved. Specifically, the surface of the semiconductor wafer can be laser-processed by gradually scanning it in the X-axis direction at a scan pitch P, and the peripheral edge can be irradiated with the laser so that the irradiation surface is perpendicular to the slope and end face by rotating the pitch axis. Furthermore, the outer periphery can be processed all around by rotating the yaw axis 360 degrees.

[0052] Note that a mechanism other than the holding table may be used as a moving mechanism for moving the irradiation position. For example, the laser irradiation system 10 may be configured to be movable. Specifically, the base board 15 may be configured to be movable in the X-axis, Y-axis, and Z-axis directions.

[0053] FIG. 6 is a block diagram of the flattening device 30 and a configuration diagram showing each step. The control device 20 controls the surface shape measuring device 21, which is an optical measuring device such as a camera, the magnetic field applying device 22, the on / off of the laser light source 10-1, and the energy density at the laser irradiation position, according to the procedure described in FIG. 1. The control device 20 may typically be a computer. The laser light source 10-1, the beam expander 10-2, the mask 10-3, and the condenser lens 10-4 are the same as those in the laser irradiation system 10 shown in FIG. 4. However, the laser from the laser light source 10-1 is split by a beam splitter 23 arranged in series, and the split laser beams enter a spot shape adjustment system including the beam expander 10-2, the mask 10-3, and the condenser lens 10-4. In FIG. 6, the laser emitted from the laser light source 10-1 is split by four beam splitters 23, enters each spot shape adjustment system, and is shaped.

[0054] The flattening device 30 has a plurality of beam splitters 23 and a spot shape adjustment system for each beam splitter 23, so that even when one laser light source 10-1 is used, it is easy to adjust the irradiation laser to have a desired energy profile. In other words, by arranging the beam splitters in multiple stages in series, the laser irradiated through the first beam splitter / beam shaping optical system has a high intensity, while the laser irradiated through the subsequent beam splitter / beam shaping optical system has a gradually decreasing intensity. As a result, the combined beam profile shown in Figure 6 is a laser whose energy density gradually decreases in a certain direction.

[0055] Furthermore, with the above configuration, a desired laser can be obtained even with one laser light source 10-1, so the control program in the control device 20 and the overall structure of the planarization device 30 tend to be simpler.

[0056] The condenser lens 10-4 may be a lens array formed by integrating multiple plano-convex cylindrical lenses. This allows the irradiation area on the semiconductor wafer surface to be controlled over a wider range of energy density as a biased temperature distribution as shown in the figure, in accordance with the surface shape by combining the semicircular beam spot 11 from the laser irradiation system 10.

[0057] The planarization device 30 has the laser irradiation system 10 shown in Fig. 4, the beam splitter 23, the surface shape measuring device 21, the magnetic field application device 22, and the holding table 16 described in Fig. 5, and is configured with a control device 20 that controls the laser conditions, controls the applied magnetic field, moves and changes the posture of the semiconductor wafer, and supplies power to each part, and the surface shape measuring device 21. The surface shape measuring device 21 is required to be able to measure waviness and roughness on the nanometer scale to measure the shape of the laser irradiated area.

[0058] The control device 20 also selects a wavelength, pulsed, or continuous wave (CW) laser depending on the material of the semiconductor wafer. The control device 20 may combine multiple laser irradiation systems 10, change the laser irradiation angle, or combine different types of lasers to perform surface treatment under conditions suitable for the crystal orientation and local features (conditions) of the surface, such as waviness, roughness, streaks, and etch pits. Suitable conditions for surface treatment include, for example, irradiating the laser from high regions (peaks, convex regions) toward low regions (valley bottoms, concave regions) on the surface roughness curve. Furthermore, the control device 20 determines irradiation conditions according to the crystal orientation and shape of the irradiated area, and controls the start, stop, switching, scan pitch, etc. of irradiation, and may control the laser irradiation by determining, for example, the cumulative irradiation energy corresponding to the crystal orientation.

[0059] 7 is a Y-axis front view showing the relationship between the laser irradiation system 10, the semiconductor wafer, and the magnetic field application device 22. The magnetic field application device 22 is configured by arranging electromagnets 17 and 18 on the outer periphery of the holding table 16. The direction of the magnetic flux density B generated by the magnetic field application device 22 is variable. The laser irradiation system 10, the base board 15, and the holding table 16 are the same as those in FIG.

[0060] Fig. 8 is an X-axis front view showing the relationship between the laser irradiation system 10, the semiconductor wafer, and the magnetic field application device 22, and Fig. 9 is a perspective view showing the magnetic field application device 22. The electromagnets 17 and 18 are movable in the Y-axis direction. The electromagnets 17 and 18 have coils wound around the cores of magnetic materials to generate a magnetic field of magnetic flux density B, and when current is applied, the direction of the coils and current is controlled so that the direction of the magnetic flux density B is aligned.

[0061] The electromagnets 17 and 18 are movable in the X, Y, and Z axes, similar to the laser irradiation system 10. The holding table 16 has a five-axis structure, similar to that shown in FIG. 5, so the entire surface of the semiconductor wafer can be irradiated with laser while applying a magnetic field. The edge of the outer periphery can be rotated around the pitch axis to irradiate the laser and apply a magnetic field so that the irradiation surface is vertical. Furthermore, the outer periphery can be rotated 360 degrees around the yaw axis to perform full rotation.

[0062] Next, the operation of the flattening device 30 will be described. When the semiconductor wafer is held on the holding table 16, the control device 20 controls the surface shape measuring device 21 to obtain mapping information of the surface of the semiconductor wafer. Next, the control device 20 controls the laser irradiation system 10 to irradiate the surface of the semiconductor wafer with a laser, melting and flowing the surface to roughly flatten it. The planarization device 30 has one type of laser irradiation system 10, but it may also have separate laser irradiation systems for rough flattening and precise flattening, and the control device 20 may switch between them.

[0063] During rough planarization, the control device 20 may adjust at least one selected from the group consisting of the laser energy density, the cumulative number of irradiations to the same irradiation position, and the scan pitch, based on the mapping information. In this way, rough planarization can be performed more efficiently.

[0064] Next, the control device 20 controls the surface shape measuring device 21 to obtain mapping information of the semiconductor wafer surface after rough planarization. Next, the control device 20 controls the laser irradiation system 10 to melt the surface of the semiconductor wafer. At this time, the control device 20 may adjust at least one selected from the group consisting of the laser energy density, the cumulative number of irradiations to the same irradiation position, and the scan pitch, as described above. Furthermore, the control device 20 may adjust the laser irradiation position based on the mapping information. That is, the laser may be irradiated locally to areas where unevenness exists. This allows for more precise flattening.

[0065] Next, the control device 20 adjusts the direction of the magnetic field and the relative movement direction of the semiconductor wafer with respect to the magnetic field so that the Lorentz force acts in the direction that flattens the surface at the irradiation position. Specifically, this adjustment is performed by moving the holding table 16 in a predetermined direction and / or moving the magnetic field application device 22. Note that at this time, the control device 20 may adjust the direction of the magnetic field and / or the movement direction based on the mapping information. By doing so, the Lorentz force is more likely to act in the direction that flattens each of the irregularities present on the surface.

[0066] Furthermore, it is preferable that the control device 20 controls each component so that the direction of flow induced by the difference in surface tension due to beam irradiation is approximately the same as the direction of Lorentz force generation. This allows for more efficient planarization. Specifically, as explained in steps S4 and S5 of the planarization method, the control device 20 controls the holding table 16 so that the irradiation position of the laser irradiation system 10, which emits a laser having a beam profile adjusted to a predetermined shape, is set to a desired position, and further controls the magnetic field application device 22 and the holding table 16 together so that the direction of Lorentz force generation is set to a desired direction.

[0067] More specifically, when flattening scratches on the surface, the holding table 16 and the magnetic field application device 22 are controlled so that a Lorentz force is generated along the inclination direction of the inclined surface of the scratches, and the irradiation position is adjusted so that the flow direction caused by the laser irradiation is generated along the inclination direction of the inclined surface and the energy density decreases along the inclination direction of the inclined surface. The adjustment of the irradiation position is typically performed by controlling the holding table 16. These adjustments are preferably made based on the mapping information.

[0068] 10 is a Y-axis front view showing the relationship between the laser irradiation system 10, semiconductor wafer, and magnetic field application device 22 when irradiating the edge portion of the peripheral edge (outer periphery) of the semiconductor wafer. The cross section of the edge portion has a slope θ as shown in FIG. 10(a) when laid flat. FIG. 10(b) shows the irradiation state of the slope, and the holding table 16 is rotated around the pitch axis so that the angle between the laser irradiated from the laser irradiation system 10 and the irradiation surface becomes approximately right angles, and is moved in the X-axis direction to perform laser scanning by the laser irradiation system 10.

[0069] Figure (c) shows the case where the end surface is irradiated, and as in Figure (b), the laser is irradiated so that the irradiated surface is approximately perpendicular to the laser. Furthermore, the outer periphery is processed by rotating the holding table 16 360 degrees around the yaw axis.

[0070] FIG. 11 is an X-axis front view showing the relationship between the laser irradiation system 10, semiconductor wafer, and magnetic field application device 22 when irradiating the outer peripheral edge portion. Electromagnets 17 and 18 constituting the magnetic field application device 22 are movable in the Y-axis direction. The semiconductor wafer is held on a holding table 16 similar to that shown in FIG. 5, and its position can be changed around the pitch axis and tilt axis to irradiate the edge portion. The laser irradiation is performed approximately perpendicular to the processing surface (irradiation surface) (incident angle of 10 to 15° or less). Furthermore, the irradiation conditions are determined according to the crystal orientation and shape.

[0071] The planarization apparatus of the present invention irradiates the semiconductor wafer surface with a laser beam to melt the surface, and simultaneously applies a magnetic field in a predetermined direction to generate a Lorentz force, so that semiconductors such as Si become conductive fluid in the molten state, and the flow can be controlled by applying a magnetic field in a predetermined direction to generate the desired Lorentz force, thereby enabling higher quality planarization of the semiconductor wafer surface. [Explanation of symbols]

[0072] 10: Laser irradiation system 10-1: Laser light source 10-2: Beam expander 10-3: Mask 10-4: Condenser lens 11: Beam spot 15: Baseboard 16: Holding table 17: Electromagnet 18: Electromagnet 20: Control device 21:Surface profile measuring device 22: Magnetic field application device 23: Beam splitter 30: Flattening device

Claims

1. irradiating a semiconductor wafer with a laser to melt a surface of the semiconductor wafer at an irradiated position; applying a magnetic field to the irradiation position so that a Lorentz force acts in a direction that flattens the surface at the irradiation position, and moving a position of the semiconductor wafer relative to the magnetic field; Including, the laser has a beam profile adjusted so that a flow caused by a difference in surface tension occurring at the irradiation position is in a predetermined direction; a method for planarizing a semiconductor wafer surface, wherein the relative position is moved so that the direction of the Lorentz force and the direction of the flow substantially coincide with each other.

2. irradiating a semiconductor wafer with a laser to melt a surface of the semiconductor wafer at an irradiated position; applying a magnetic field to the irradiation position so that a Lorentz force acts in a direction that flattens the surface at the irradiation position, and moving a position of the semiconductor wafer relative to the magnetic field; Including, A method for planarizing a semiconductor wafer surface, wherein the Lorentz force is adjusted to be generated along the direction of inclination of the slope of the scratches on the surface.

3. A flattening method as described in claim 2, wherein the beam profile of the laser is adjusted so that the energy density decreases along the tilt direction.

4. measuring the shape of the surface before laser irradiation to obtain mapping information; The planarization method according to any one of claims 1 to 3, further comprising: determining at least one selected from the group consisting of a direction of the magnetic field, the irradiation position, and the direction of the movement based on the mapping information.

5. 5. The planarization method according to claim 1, wherein the movement of the relative position of the semiconductor wafer is performed by a holding table that holds the semiconductor wafer and has a five-axis structure including three axes, namely, an X-axis, a Y-axis, and a Z-axis, as well as two axes, namely, a yaw axis for rotation and a pitch axis for tilt.

6. measuring the shape of the surface before laser irradiation to obtain mapping information; 6. The planarization method according to claim 1, further comprising: determining, based on the mapping information, at least one selected from the group consisting of an energy density of the laser, a cumulative number of irradiations to the same irradiation position, and a scan pitch.

7. 7. The planarization method according to claim 1, wherein the laser is irradiated from a laser irradiation system having a light source, a beam expander, a mask, and a condenser lens in this order, and the laser is expanded by the beam expander and then shaped by the mask having a window of a predetermined shape.

8. the laser irradiation system includes a beam splitter and a plurality of spot shape adjusting systems each including the beam expander, the mask, and the condenser lens; 8. The planarization method according to claim 7, wherein a laser beam emitted from the light source and split via the beam splitter is incident on the spot shape adjustment system.

9. 9. The planarization method according to claim 8, further comprising: a plurality of the beam splitters arranged in series with respect to the light source; and a laser beam split from each of the beam splitters is incident on the spot shape adjusting system.

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