Patent Description:
The present disclosure relates to a method of manufacturing semiconductor wafers.

A wafer manufacturing method according to <CIT> includes a peeling surface forming step and a wafer peeling step. The peeling surface forming step forms a peeling surface composed of a modified layer and cracks. Specifically, in the peeling surface forming step, a laser beam is radiated to a silicon ingot with the focusing point positioned at a depth corresponding to a wafer thickness from the first surface of the ingot, while relatively moving the silicon ingot and the focusing point to make the adjacent focusing points mutually overlap. The wafer peeling step includes a table fixing step to fix a second surface of the ingot on the table, a pad fixing step to fix a pad on the first surface of the ingot and a peeling step to peel a part of the ingot with a peeling surface as the boundary surface. In the peeling step, a moment force acts on the ingot where one end of the pad is the working point and the other end is the supporting point, thereby peeling the part of the ingot with the peeling surface as the boundary surface.

According to this type of the method for manufacturing the semiconductor wafer, a processing quality and a processing ease are required to be improved in the peeling step where wafers are peeled from the silicon ingot. Specifically, for example, surface roughness on the peeling cross-section which is a wafer surface produced by the peeling of the peeling surface is suppressed, whereby a processing margin or a processing time of a griding step and a polishing step can be reduced, thus improving the manufacturing yield. Alternatively, the peeling step may be changed to be in a low-load condition, thereby improving the processing ease.

<CIT> discloses a SiC ingot slicing method. Disclosed herein is an SiC ingot slicing method including: an initial separation layer formation step for scanning a focal point of a laser beam parallel to an end face of the SiC ingot along a scheduled separation plane, and forming a separation layer at a position at a distance from the end face; a repetition step for sequentially moving, after the initial separation layer formation step, the focal point by the distance equal to the thickness of an SiC plate from the separation layer toward the end face, scanning the focal point parallel to the end face, repeating the formation of the separation layer, and forming the plurality of separation layers; and a separation step for applying an external force to the plurality of separation layers formed by the repetition step, peeling off the SiC plates starting from the separation layers, and acquiring the plurality of SiC plates.

The present disclosure has been achieved in light of the above-exemplified circumstances. In other words, the present disclosure provides a technique in which the processing quality and the processing ease are improved in the peeling step where wafers are peeled off from the ingot. This is achieved by the features of claim <NUM> for which protection is sought. Further advantageous embodiments are part of the dependent claims.

A method of manufacturing semiconductor wafers according to a first aspect of the present disclosure includes steps of: preparing an ingot (<NUM>) having a first major surface (<NUM>) and a second major surface (<NUM>) in a back side of the first major surface, a peeling layer (<NUM>) being formed in the ingot along the first major surface; and applying a load to the ingot from outside thereof with respect to a surface direction along the first major surface such that a moment with a supporting point (PP) and a working point (WP) which are at a first end of the ingot in the surface direction acts on the ingot, and/or applying a dynamic force to the ingot such that a tensile stress along an ingot thickness direction acts on an entire area of the ingot in the surface direction, the ingot thickness direction defining a thickness of the ingot, connecting the first major surface and the second major surface and being parallel to a center axis (CL) of the ingot, thereby peeling a wafer precursor (<NUM>) from the ingot, the wafer precursor being formed in a layer-shape between the first major surface and the peeling layer.

Note that reference numbers in brackets assigned to respective elements in the specification indicate an example of correspondence relationship between the elements and specific components in embodiments which will be described later. Hence, the present disclosure is not limited to constituents labeled by these reference numbers.

Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. For various modifications which are applicable for one embodiment, if these modifications are inserted into a series of explanations related to the embodiment, understanding of the embodiment may be disturbed by these modifications. Hence, the modifications are not inserted into the series of explanations and will be described later.

Referring to <FIG>, a manufacturing method of a semiconductor wafer <NUM> according to the present embodiment, a so-called laser slicing technique is utilized to obtain the semiconductor wafer <NUM> from an ingot <NUM> made of semiconductor such as SiC (i.e. silicon carbide). The ingot <NUM> has a first major surface <NUM> and a second major surface <NUM> as a pair of major surfaces. The major surface is defined as a surface of the ingot <NUM> orthogonal to an ingot thickness direction that defines the thickness of the ingot <NUM>. The ingot thickness direction is a direction connecting the first major surface <NUM> and the second major surface <NUM> and a direction being parallel to a center axis CL of the ingot <NUM>. The first surface <NUM> is one surface in the pair of major surfaces of the ingot <NUM>. The second surface <NUM> is the other surface in the pair of major surfaces of the ingot <NUM>, that is, back side surface of the first major surface <NUM>. Specifically, the present manufacturing method includes a peeling layer forming step and a peeling step.

In the peeling layer forming step, a laser beam is radiated to the ingot <NUM> from the first major surface <NUM> side, thereby forming a peeling layer <NUM> in the vicinity of the first major surface in the ingot <NUM>. The peeling layer <NUM> corresponds to a peeling surface in the above-mentioned patent literature and includes a modification part and cracks. The modification part is a portion where semiconductor material constituting the ingot <NUM> is modified by the laser radiation. Specifically, for example, in the case where the ingot <NUM> is made of single crystal of SiC semiconductor, the SiC is separated into Si and C by the laser radiation in the modification part. The peeling layer <NUM> is formed along the first major surface <NUM>. Hereinafter, a direction along the first major surface <NUM> is referred to as surface direction. The surface direction may be any direction which crosses the center axis CL (i.e. typically crosses at a right angle). The surface direction includes a radial direction. The radial direction refers to a direction along a virtual linear line which passes through a cross point between any one of virtual planes intersecting the center axis CL (i.e. typically crosses at right angle) and the center axis CL, and being parallel to any one of virtual planes. Typically, the radial direction refers to, in the ingot <NUM> having substantially cylindrical shape, a direction of the radius of the circular cross-section of the ingot <NUM> on the virtual plane. In the radial directions, a direction towards the center axis CL is referred to as first radial direction R1 and a direction away from the center axis CL is referred to as a second radial direction R2. The laser beam to be radiated to the ingot <NUM> has a wavelength for which the ingot <NUM> has transparency (i.e. transparency for a depth corresponding to the thickness of the peeling layer <NUM> or the thickness of the semiconductor wafer <NUM>). For the laser beam, a pulse laser beam can be used. The laser wavelength may be, for example, <NUM>, <NUM>, <NUM> or the like. Note that the peeling layer <NUM> formed by the laser radiation and the peeling layer forming step for forming the peeling layer <NUM> may be those publicly known or commonly known at the time of filing of this application (e.g. above-described patent literature, <CIT>). Hence, further explanation for the peeling layer <NUM> and the peeling layer forming step will be omitted.

With the peeling layer forming step, the ingot <NUM> having the peeling layer <NUM> and a wafer precursor <NUM> is prepared. The wafer precursor <NUM> is a thin-layered portion provided between the first major surface <NUM> and the peeling layer <NUM>. The wafer precursor <NUM> is separated from the ingot <NUM> by the peeling step, then becomes the semiconductor wafer <NUM>. The wafer precursor <NUM> has substantially constant thickness in the surface direction. In the peeling step, the wafer precursor <NUM> is peeled from the ingot <NUM>, thereby obtaining the semiconductor wafer <NUM>. With the griding step and the polishing step, the major surface of the obtained semiconductor wafer <NUM> is planarized and smoothened.

Hereinafter, a manufacturing method according to the first embodiment will be described with reference to <FIG> in addition to <FIG>. According to the present embodiment, in the peeling step, a load is applied to the ingot <NUM> from outside thereof with respect to the surface direction such that a moment force acts on the ingot <NUM> where a first end <NUM> which is one end of the ingot <NUM> in the surface direction is the supporting point PP. Note that the other end of the ingot <NUM> in the surface direction is referred to as a second end <NUM>.

Specifically, the peeling step according to the present embodiment is performed using a peeling apparatus <NUM> shown in <FIG>. Referring to <FIG>, the peeling apparatus <NUM> has a supporting table <NUM>, a peeling pad <NUM> and a driving member <NUM>.

The supporting table <NUM> is provided to support the ingot <NUM> from underneath. Specifically, the supporting table <NUM> includes many suction holes (not shown) opened at a supporting suction surface <NUM> as an upper surface of the supporting table <NUM>, and is configured to suck a second major surface <NUM> of the ingot <NUM> on the supporting suction surface <NUM> by the negative air pressure. The supporting table <NUM> is provided with a first table end <NUM> and a second table end <NUM> as the both ends thereof in the surface direction. The second table end <NUM> as an end portion in the one end side in the surface direction (i.e. right side in <FIG>) includes a table end face <NUM>. The table end face <NUM> is formed as an inclined surface rising towards the first radial direction R1. In other words, as shown in <FIG>, the supporting table <NUM> is formed in a trapezoidal shape where the lower base is longer than the upper base in a side view.

The peeling pad <NUM> is provided above the supporting table <NUM> to be capable of approaching and separating freely with respect to the supporting table <NUM>. The peeling pad <NUM> includes many suction holes (not shown) opened at a pad suction surface <NUM> as a bottom surface of the peeling pad <NUM>, and is configured to suck the first major surface <NUM> of the ingot <NUM> on the pad suction surface <NUM> by the negative air pressure. The peeling pad <NUM> includes a first pad end <NUM> and a second pad end <NUM> as the both ends thereof in the surface direction. The second pad end <NUM> as an end portion in the one end side in the surface direction (i.e. right side in <FIG>) includes pad end face <NUM>. The pad end face <NUM> is formed as an inclined surface rising towards the second radial direction R2. In other words, as shown in <FIG>, the peeling pad <NUM> is formed in a trapezoidal shape where the lower base is shorter than the upper base in a side view. The pad end face <NUM> is provided at a portion corresponding to the table end face <NUM> (i.e. right above).

The first major surface <NUM> is fixed to the peeling pad <NUM> by the adsorption and the second major surface <NUM> is fixed to the supporting table <NUM>, whereby the ingot <NUM> is supported between the supporting table <NUM> and the peeling pad <NUM>. Hereinafter, this state is referred to as supported state. The driving member <NUM> applies a force to at least either the supporting table <NUM> or the peeling pad <NUM> to make the supporting table <NUM> and the peeling pad <NUM> relatively move in the ingot thickness direction. Specifically, the driving member <NUM> includes a first driving end face <NUM> and a second driving end face <NUM>. The first driving end face <NUM> is formed as an inclined surface rising towards the second radial direction R2. That is, the first driving end face <NUM> is provided to be in parallel to the pad end face <NUM>. The second driving end face <NUM> is formed as an inclined surface rising towards the first radial direction R1. That is, the second driving end face <NUM> is provided to be in parallel to the table end face <NUM>. The driving member <NUM> is provided such that the first driving end face <NUM> is in contact with the pad end face <NUM> under the supported state and the second driving end face <NUM> is in contact with the table end face <NUM>. In other words, as shown in <FIG>, the driving member <NUM> is formed in a shape of a trapezoid where the lower base is longer than the upper base, rotated by <NUM> degrees in the anti-clockwise direction. Then, the driving member <NUM> is configured to be driven by a driving means (not shown) in a direction along the ingot thickness direction and/or the first radial direction as a direction approaching the ingot <NUM>. The driving member <NUM> is provided to be driven upward and /or in the first radial direction R1 such that a moment force, where the second pad end <NUM> is the force point FP, the first end <NUM> is the supporting point PP and the working point WP, is applied to the ingot <NUM>.

The peeling step in which the wafer precursor <NUM> is peeled from the ingot <NUM> includes a table fixing step, a supporting step and a peeling force application step. In the table fixing step, the second major surface <NUM> is sucked on the supporting suction surface <NUM>, thereby fixing the ingot <NUM> on the supporting table <NUM>. In the supporting step, the first major surface <NUM> is sucked on the pad suction surface <NUM> to fix the ingot <NUM> on the peeling pad <NUM>, thereby producing the supported state. In the peeling force application step, a static load is applied, where the force point FP is at the second pad end <NUM> as an end portion of the peeling pad <NUM> positioned in one side in the surface direction, such that a moment force acts on the ingot <NUM> in which the supporting point PP is the first end <NUM> positioned in one side in the surface direction. Specifically, according to the peeling force application step, the driving member <NUM> is driven upward and/or in the first radial direction R1 under the supported state, whereby the second pad end <NUM> is pressed upward along the ingot thickness direction. Thus, the wafer precursor <NUM> which is a part of the ingot <NUM> can be peeled from the ingot <NUM> with the peeling layer <NUM> as the boundary surface.

<FIG> shows a distribution of an internal stress of the ingot <NUM> immediately after the application of the static load in the peeling force application step, that is, immediately before a fracture of the wafer precursor <NUM> in the peeling layer <NUM> occurs as a begging of the peeling thereof. In <FIG>, the vertical axis σ indicates an amount of tensile stress. The horizontal axis X indicates position in the surface direction relative to the second end <NUM> as the origin. The value D in the horizontal axis X indicates a diameter of the ingot <NUM>. That is, X=<NUM> indicates the second end <NUM> and X=D indicates the first end <NUM>. Note that the internal stress distribution shown in <FIG> is taken when the driving member <NUM> shown in <FIG> is driven upward. As shown in <FIG>, according to the peeling method of the present embodiment, the stress is concentrated at the first end <NUM> and the area where the tensile stress is applied is a very narrow area in the vicinity of the first end <NUM>. Then, in the peeling layer <NUM>, fine fractures occur from the first end <NUM> where the tensile stress is concentrated, and the fractures instantly propagate through the entire peeling layer <NUM>. That is, fragile fractures occur in the peeling layer <NUM>, thereby causing peeling in the entire peeling layer <NUM>.

<FIG> illustrates a configuration modified from that shown in <FIG> and illustrates an outline of a peeling method described in the above patent literature of <CIT> as a comparative example. As shown in <FIG>, according to the comparative example, the supporting table <NUM> and the peeling pad <NUM> are formed in a simple plate shape. Further, according to the comparative example, a first support member <NUM> and a second support member <NUM> as an approaching / separating means which causes the peeling pad <NUM> to approach or separate to/from the supporting table <NUM>. The first supporting member <NUM> is a coupling mechanism capable of being bent, and fixed to an upper surface of the second pad end <NUM> which is one end of the peeling pad <NUM>. The second support member <NUM> is configured as a spring and the lower end thereof is fixed to the upper surface of the first pad end <NUM> as the other end of the peeling pad <NUM>.

As shown in <FIG>, when a force is applied upwardly to the second pad end <NUM> by the first support member <NUM> in the supported state, the second support member <NUM> configured of a spring is extended. Then, a moment force acts on the ingot <NUM> where the working point WP is a position in the vicinity of the first end <NUM> and immediately below the first support member <NUM>, and the supporting point PP is a position in the vicinity of the second end <NUM> and immediately below the second support member <NUM>.

<FIG> shows a distribution of the internal stress in the ingot <NUM> according to a comparative example. As shown in <FIG>, in the comparative example, the tensile stress becomes maximum at the working point WP positioned at further inside than the position of the first end <NUM>, decreases in monotone manner towards the supporting point PP and becomes <NUM> at the supporting point PP. Then, a compressive stress occurs between the supporting point PP and the second end <NUM>.

Thus, according to the comparative example, stress cannot be concentrated on an edge portion of the ingot <NUM>, that is, the peeling layer in the surface direction (i.e. first end 25in the example shown in <FIG>). Hence, compared to the present embodiment, a significantly larger load than that of the present embodiment is required in order to generate peeling with the peeling layer as the boundary surface, that is, fracture of the ingot <NUM>. Further, since the load is applied onto the peeling layer <NUM> in a wider area, location of cracks for the peeling is uncertain such that a partial non-peeled portion or a breakage sometimes occurs on the acquired semiconductor wafer <NUM> (i.e. see <FIG>). Moreover, due to a rough peeled cross-section, a problem arises that processing margin of the grinding or the polishing becomes larger. Therefore, according to the comparative example, for achieving low load application or improving the manufacturing yield, improvement is necessary.

However, according to the present embodiment, the force point FP is set to be in the first end <NUM> side in the surface direction and outside the ingot <NUM> such that the supporting point PP and the working point WP are at the first end <NUM> in the ingot <NUM>. Thus, stress can be concentrated on an edge portion of the ingot <NUM>, that is, the peeling layer in the surface direction (i.e. first end <NUM>). Hence, the peeling load can be lowered. Also, the processing ease can be improved. Moreover, since the peeling occurs on the entire surface of the peeling layer <NUM>, the manufacturing yield is improved.

Hereinafter, the manufacturing method according to the second embodiment will be described. For the explanation of the second embodiment below, configurations different from those in the first embodiment will be mainly described. In the first and second embodiments, the same reference numbers are applied to mutually the same or equivalent portions. Hence, in the explanation of the second embodiment below, for constituents having the same reference numbers as those in the first embodiment, explanations of the first embodiment will be appropriately applied as long as technical inconsistency or any additional explanations are not present. The same applies to the third embodiment and other embodiments will be described later.

According to the present embodiment, in the peeling step, as shown in <FIG>, a dynamic force is applied to the ingot <NUM> such that tensile stress along the ingot thickness direction acts on the entire area of the ingot <NUM> in the surface direction. Specifically, in the peeling force application step of the present embodiment, dynamic force is applied to the supporting table <NUM> and/or the peeling pad <NUM> in a direction where the supporting table <NUM> and the peeling pad <NUM> are mutually separated away. Note that the dynamic force refers to a contrary concept of a static force acting without variation in a period having a certain duration (not instantaneous), but a force acting instantaneously or an impact force acting in a relative short period (e.g. pulse-like force).

Also, according to the present embodiment, the peeling process in which the wafer precursor <NUM> is peeled from the ingot <NUM> includes a table fixing step, a supporting step and a peeling force application step. The table fixing step and the supporting step are the same as those in the above-described first embodiment. With the table fixing step and the supporting step, a supported state is produced in which the ingot <NUM> is fixed to the supporting table <NUM> and the peeling pad <NUM>. As shown in <FIG>, the peeling force application step according to the present embodiment applies dynamic force to the supporting table <NUM> and / or the peeling pad <NUM> such that the instantaneous tensile stress due to the impact is applied to the ingot <NUM>. Specifically, for example, upward impact may be applied to the peeling pad <NUM> or downward impact may be applied to peeling pad <NUM>. Alternatively, the table end face <NUM>, the pad end face <NUM> and a pair of driving members <NUM> shown in <FIG> may be provided at the both sides in the surface direction (i.e. both left and right sides of <FIG>), impact in the first radial direction R1 approaching the center axis CL can be applied to the pair of driving members <NUM>. Thus, the wafer precursor <NUM> as a part of the ingot <NUM> can be peeled with the peeling layer <NUM> as the boundary surface.

As shown in <FIG>, according to the peeling method of the present embodiment, the tensile stress instantaneously and uniformly acts on the entire surface in the surface direction of the ingot <NUM>, that is the peeling layer <NUM>. Thus, peeling occurs on the entire surface of the peeling layer <NUM>. Also, the surface roughness of the peeled cross-section can be reduced. Hence, according to the present embodiment, the processing ease and the manufacturing yield can be improved.

Hereinafter, a manufacturing method according to the third embodiment will be described. The present embodiment corresponds to a combination of the above-described first embodiment and the second embodiment. Specifically, also in the present embodiment, the peeling step in which the wafer precursor <NUM> is peeled from the ingot <NUM> includes a table fixing step, a supporting step and a peeling force application step. The table fixing step and the supporting step are the same as those in the first embodiment. With the table fixing step and the supporting step, a supported state in which the ingot <NUM> is fixed to the supporting table <NUM> and the peeling pad <NUM> is produced. Then, as shown in <FIG>, in the peeling force application step, a dynamic force with the force point FP as the second pad end <NUM>, that is, an impact force, is applied such that a moment force where the supporting point PP is positioned at the first end, and the tensile stress act on the ingot <NUM>. Specifically, for example, as shown in <FIG>, the impact force towards a left side direction in <FIG>, that is, the first radial direction R1 can be applied to the driving member <NUM> such that the driving member <NUM> instantaneously pushes the second pad end <NUM> of the peeling pad <NUM> up.

As shown in <FIG>, according to the peeling method of the present embodiment, instantaneous tensile stress due to the impact force is concentrated to the first end <NUM>. Thus, the peeling load can be further lowered. Also, the surface roughness of the peeled cross-section can be reduced. Therefore, according to the present embodiment, the processing ease and the manufacturing yield can be improved.

In the above-described respective embodiments, advantageous features are present in the amount of load, an area to which force is applied and a duration for which the force is applied compared to the comparative example. In other words, according to the above-described first embodiment and the third embodiment, the amount of load, and the area to which force is applied are smaller than that of the comparative example. Also, according to the above-described first to third embodiments, the amount of load and the duration for which the force is applied are smaller than that of the comparative example. Thus, according to the first to third embodiments, the amount of load and the force necessary for the peeling step can be reduced.

The present disclosure is not limited to the above-described embodiments. Therefore, the above-described embodiments can be appropriately modified. Hereinafter, typical modification examples will be described. In the following modification examples, configurations different from those in the above-described embodiments will mainly be described. In the above-described embodiments and modifications examples below, the same reference numbers are applied to mutually the same or equivalent portions. Hence, in the explanation of the modification examples below, for the constituents having the same reference numbers as those in the above-described embodiments, explanations of the above-described embodiments will be appropriately applied as long as technical inconsistency or any additional explanations are not present.

The present disclosure is not limited to a case where the semiconductor wafer <NUM> and the ingot <NUM> are constituted of SiC semiconductor. That is, the present disclosure may preferably be applied to the semiconductor wafer <NUM> and the ingot <NUM> constituted of materials of Si, SiN, AIN and the like, for example. Also, the present disclosure is not limited to specific apparatus configurations represented in the above-described embodiments. For example, <FIG> or the like is a simplified diagram for explaining the peeling apparatus <NUM> used for the present disclosure and an overall manufacturing method of the semiconductor wafer capable of being embodied using the peeling apparatus <NUM>. Hence, the configuration of the peeling apparatus <NUM> which will be actually manufactured and sold is not limited to the configuration exemplified in <FIG> or the like. Further, the configuration of the peeling apparatus <NUM> which will be actually manufactured and sold may be appropriately modified from the configuration exemplified in <FIG> or the like. Specifically, for example, a method of fixing the ingot <NUM> on the supporting table <NUM> and the peeling pad <NUM> is not limited to use the adsorption described in the above-described embodiments, but may use adhesion, adhesive tape or the like, for example. In this case, the upper surface of the supporting table <NUM> (i.e. supporting suction surface <NUM> in the above-described embodiments) can be formed as a fixed surface or a support surface to fix or support the ingot <NUM>. Note that suction holes in the above-described embodiments may not be provided on the fixed surface or the support surface. Moreover, wavelength of the laser beam is not limited to the above-described specific examples.

In the above-described first to third embodiments, as shown in <FIG>, ultrasonic vibrations may be applied to the ingot <NUM>. Specifically, for example, the supporting table <NUM> and/or the peeling pad <NUM> may be excited by ultrasonic vibrations. Thus, peeling can preferably be promoted for the wafer precursor <NUM> in the peeling step.

In the above-described first to third embodiments, as shown in <FIG>, a twist force may be applied to the ingot <NUM> such that the first major surface <NUM> and the second major surface <NUM> relatively rotate around the center axis CL. Thus, peeling can preferably be promoted for the wafer precursor <NUM> in the peeling step. Note that ultrasonic vibration and the twist force can be mutually superposed.

Claim 1:
A method of manufacturing semiconductor wafers, the method comprising steps of:
preparing an ingot (<NUM>) having a first major surface (<NUM>) and a second major surface (<NUM>) in a back side of the first major surface, a peeling layer (<NUM>) being formed in the ingot along the first major surface; and
applying a load to the ingot from outside thereof with respect to a surface direction along the first major surface such that a moment with a supporting point (PP) and a working point (WP) which are at a first end (<NUM>) of the ingot in the surface direction acts on the ingot, and/or
applying a dynamic force to the ingot such that a tensile stress along an ingot thickness direction acts on an entire area of the ingot in the surface direction, the ingot thickness direction defining a thickness of the ingot connecting the first major surface and the second major surface and being parallel to a center axis (CL) of the ingot, thereby peeling a wafer precursor (<NUM>) from the ingot, the wafer precursor being formed in a layer-shape between the first major surface and the peeling layer.