The present patent application claims the priority of Japanese patent application No. 2020/065514 filed on Apr. 1, 2020, and the entire contents of Japanese patent application No. 2020/065514 are hereby incorporated by reference.
The present invention relates to a semiconductor substrate and a method for manufacturing the same.
Conventionally, glass plates having a chamfered outer periphery portion are known (see Patent Literature 1). The glass plate described in Patent Literature 1 is used as a support plate for supporting a workpiece substrate in fan-out wafer-level packaging.
According to Patent Literature 1, since a notch-shaped or orientation flat-shaped alignment portion of the glass plate is chamfered, damage on the glass plate originating from a positioning member such as positioning pin can be effectively avoided when brought into contact with the positioning member.
Patent Literature 1: WO 2016/088868
However, damageability of plate-like objects including glass plates and semiconductor substrates is different depending on characteristics of material such as cleavage planes in a crystal, and the shape of the chamfered portion which can effectively suppress damage is thus also different depending on the material of the plate-shaped object. Therefore, even if the shape of the chamfered portion of the glass plate described in Patent Literature 1 is applied to a plate-shaped object formed of another material, it is not necessarily possible to effectively suppress damages.
It is an object of the invention to provide a semiconductor substrate which includes a gallium oxide-based semiconductor single crystal and is configured to effectively suppress occurrence of damage, as well as a method for manufacturing the semiconductor substrate.
According to an embodiment of the invention, a semiconductor substrate as defined in [1] to [4] below and a method for manufacturing a semiconductor substrate as defined in [5] to [10] below are provided.
[1] A semiconductor substrate, comprising:
[2] The semiconductor substrate according to [1], wherein widths of the first inclined surface and the second inclined surface in an in-plane direction of the semiconductor substrate are within the range of not less than 0.025 mm and not more than 0.9 mm
[3] The semiconductor substrate according to [1] or [2], wherein plane orientations of the first principal surface and the second principal surface are (001) or (100).
[4] The semiconductor substrate according to any one of [1] to [3], wherein the plane orientations of the first principal surface and the second principal surface are (001), and an orientation flat is formed along a <010> direction.
[5] A method for manufacturing a semiconductor substrate comprising a gallium oxide-based semiconductor single crystal, the method comprising:
[6] The method according to [5], wherein, in the forming of the chamfered portion, the end face is formed after forming the first inclined surface and the second inclined surface.
[7] The method according to [5] or [6], wherein, in the forming of the chamfered portion, the end face is formed using a grinding wheel that is softer than a grinding wheel used for forming the first inclined surface and the second inclined surface.
[8] The method according to [7], wherein, in the forming of the chamfered portion, the end face is formed using a resin bonded grinding wheel.
[9] The method according to any one of [5] to [8], wherein widths of the first inclined surface and the second inclined surface in an in-plane direction of the semiconductor substrate after the polishing are within the range of not less than 0.025 mm and not more than 0.9 mm.
[10] method according to any one of [5] to [9], wherein plane orientations of the first principal surface and the second principal surface are (001) or (100).
According to an embodiment of the invention, a semiconductor substrate can be provided which includes a gallium oxide-based semiconductor single crystal and is configured to effectively suppress occurrence of damage, as well as a method for manufacturing the semiconductor substrate.
(Embodiment)
(Structure of a Semiconductor Substrate)
Gallium oxide-based semiconductor here means β-Ga2O3, or means β-Ga2O3 containing a substitutional impurity such as Al, In, or a dopant such a Sn, Si.
The chamfered portion 12 is provided to prevent damage on the semiconductor substrate 1 during polishing or conveyance in the manufacturing process, or during handling such as conveyance and alignment, etc. If the chamfered portion 12 is not provided and edges of the semiconductor substrate 1 (boundaries between principal surfaces 10, 11 and a side surface) are square edges, e.g., the edges are damaged during polishing of the principal surfaces 10, 11, and also, broken pieces scratch or contaminate the principal surfaces 10, 11.
The plane orientations of the principal surfaces 10, 11 of the semiconductor substrate 1 are not specifically limited, but damage due to cleavage is particularly likely to occur when the principal surfaces are (001) planes or (100) planes. Therefore, an effect of suppressing damage in the invention is thus particularly important.
In addition, when polishing the semiconductor substrate 1, polishability is different since a surface having a plane orientation close to the cleavage plane is relatively soft and a surface having a plane orientation far from the cleavage plane is relatively hard. The gallium oxide-based semiconductor is monoclinic. Therefore, when the semiconductor substrate 1 is a substrate including a curved line in an outer contour of its planar shape, such as a circular substrate, the plane orientation of the polished portion continuously changes during chamfering of the outer periphery portion and it is highly difficult to process.
When the principal surfaces 10, 11 of the semiconductor substrate 1 are the (001) planes, cleavage is likely to occur along the (100) plane intersecting the principal surfaces 10, 11 at 103.7°, and cleavage can also occur along the (001) plane parallel to the principal surfaces 10, 11. Cleavage along the (001) plane hardly occurs during polishing of the principal surfaces 10, 11 but can occur during processing of the substrate end face, such as during chamfering.
When the principal surfaces 10, 11 of the semiconductor substrate 1 are the (100) planes, cleavage is likely to occur along the (100) plane parallel to the principal surfaces 10, 11 and cleavage can occur along the (001) plane intersecting the principal surfaces 10, 11 at 103.7°. Cleavage along the (100) plane occurs during processing of the substrate end face but is also likely to occur during polishing of the principal surfaces 10, 11.
When the principal surfaces 10, 11 of the semiconductor substrate 1 are (−201) planes, cleavage can occur along the (100) plane intersecting the principal surfaces 10, 11 at 53.8° but hardly occurs along the (001) plane intersecting the principal surfaces at 49.9°.
The chamfered portion 12 of the semiconductor substrate 1 has an inclined surface 121 on the principal surface 10 side of the semiconductor substrate 1, an inclined surface 122 on the principal surface 11 side opposite to the principal surface 10, and an end face 123 located between the inclined surface 121 and the inclined surface 122 at a leading end of the chamfered portion 12.
The inclined surface 121 is an annularly continuous surface that is located on the outer side of the principal surface 10 and is linear at an edge in the vertical cross section of the semiconductor substrate 1. The inclined surface 122 is an annularly continuous surface that is located on the outer side of the principal surface 11 and is linear at an edge in the vertical cross section of the semiconductor substrate 1. The end face 123 is an annularly continuous surface that can be regarded as a side surface of the semiconductor substrate 1.
When the semiconductor substrate 1 is, e.g., a circular substrate as shown in
A width bt of the end face 123 in a thickness direction of the semiconductor substrate 1 is within the range of not less than 50% and not more than 97% of a thickness t of the semiconductor substrate 1. When the width bt is not less than 50% of the thickness t, it is possible to effectively suppress damage on the leading end of the chamfered portion 12 including the end face 123, particularly, damage due to cleavage, during a step of forming the chamfered portion 12 (Step S5 in a manufacturing process described later), during steps thereafter (Steps S6, S7), and even during handling such as conveyance or alignment of the semiconductor substrate 1. Meanwhile, when the width bt is not more than 97% of the thickness t, it is possible to effectively suppress the above-mentioned damage on the edge of the semiconductor substrate 1, particularly scratches caused by broken pieces during polishing of the principal surfaces 10, 11.
In case that the width bt of the end face 123 in the thickness direction of the semiconductor substrate 1 is within the range of not less than 50% and not more than 97% of the thickness t of the semiconductor substrate 1, it is possible to effectively suppress damage on the semiconductor substrate 1 such as the above-described damage on the leading end of the chamfered portion 12 and scratches caused by broken pieces during polishing even when the plane orientations of the principal surfaces 10, 11 are (001) or (100). In other words, regardless of the plane orientations of the principal surfaces 10, 11, it is possible to effectively suppress damage on the semiconductor substrate 1.
In addition, to suppress damage on the semiconductor substrate 1 more effectively, the width bt is preferably within the range of not less than 55% and not more than 90% of the thickness t, more preferably, within the range of not less than 60% and not more than 86%. A distance bs1 from a boundary between the end face 123 and the inclined surface 121 to the outermost point of the end face 123 in an in-plane direction of the semiconductor substrate 1 (a direction parallel to the principal surfaces 10, 11) is typically equal to, but may be different from, a distance bs2, from a boundary between the end face 123 and the inclined surface 122 to the outermost point of the end face 123 in the in-plane direction of the semiconductor substrate 1.
Widths as1 and as2 of the inclined surface 121 and the inclined surface 121 in the in-plane direction of the semiconductor substrate 1 (a direction parallel to the principal surfaces 10, 11) are preferably within the range of not less than 0.025 mm and not more than 0.9 mm When the widths as1, as2 are not less than 0.025 mm, it is possible to effectively suppress the above-described damage on the edge of the semiconductor substrate 1, particularly scratches caused by broken pieces during polishing of the principal surfaces 10, 11. Meanwhile, when the width as1, as2 are not more than 0.9 mm, a chamfering amount is reduced, hence, an effect of improving chamfering efficiency and an effect of reducing the manufacturing cost of the semiconductor substrate 1 by suppressing wear of the grinding wheel used for chamfering, etc., are obtained.
To obtain such effects more reliably, the widths as1, as2 are preferably within the range of not less than 0.05 mm and not more than 0.45 mm, more preferably, within the range of not less than 100 μm and not more than 200 μm. The width as1 and a width at1 of the inclined surface 121 (the width at1 along the thickness direction of the semiconductor substrate 1) are typically respectively equal to, but may be different from, the width as2 and a width at2 of the inclined surface 122 (the width at2 along the thickness direction of the semiconductor substrate 1.
The end face 123 may be curved along the thickness direction of the semiconductor substrate 1 so as to bulge outward as shown in
The end face 123 when curved along the thickness direction of the semiconductor substrate 1 as shown in
The thickness of the semiconductor substrate 1 is preferably less than 1 mm, more preferably, less than 0.7 mm. It is because the semiconductor substrate 1 formed of a gallium oxide-based semiconductor has a lower thermal conductivity than substrates formed of other semiconductors and is thus required to be thin to ensure heat dissipation of device. In addition, to suppress cracks during handling such as conveyance or work at the time of using the semiconductor substrate 1 (epitaxial growth, device manufacturing, etc.,), the thickness of the semiconductor substrate 1 is preferably not less than 0.1 mm, more preferably, not less than 0.3 mm. Even when the chamfered portion 12 has a shape capable of suppressing damage on the semiconductor substrate 1 as described above, the semiconductor substrate 1 when too thin may crack due to stress generated during conveyance or handling.
In the example shown in
Additionally, an orientation flat 13b along the <010> direction may be provided on the semiconductor substrate 1 on the opposite side to the orientation flat 13a. It is thereby possible to suppress cleavage along the (100) plane also on the orientation flat 13b side of the semiconductor substrate 1.
Meanwhile, since it is not possible to distinguish front and back of the semiconductor substrate 1 only by the orientation flat 13a or only by the orientation flats 13a, 13b, an orientation flat 13c for distinguishing front and back may be provided along a <100> direction, etc., that is orthogonal to the <010> direction.
The planar shape of the semiconductor substrate 1 is typically a circular shape or a circle with an orientation flat, but may be another shape such as a polygonal shape. Also in such a case, the outer periphery portion of the substrate is chamfered in the same manner as when having a circular shape to form a chamfered portion having the same vertical cross-sectional shape.
(Process for Manufacturing Semiconductor Substrate)
Firstly, a bulk single crystal 20 as shown in
The square plate-shaped bulk single crystal 20 shown in
Next, plural single crystal plates 21 shown in
Next, a cutout step is performed on the plural single crystal plates 21 to cut out the plural semiconductor substrates 1 shown in
When orientation flats are formed on the semiconductor substrates 1, for example, the semiconductor substrate 1 having a shape including an orientation flat may be cut out by wire electrical discharge machining, grinding the outer periphery, or ultrasonic machining, etc., in the cutout step in Step S3, or the semiconductor substrate 1 cut out into a circular shape by the cutout step may be partially cut off by a slicing machine.
Next, the semiconductor substrates 1 are heat-treated to relieve processing strain and thereby reduce the amount of warpage (Step S4). For example, heat treatment during heating up is performed in an oxygen atmosphere, and heat treatment while holding temperature after heating up is performed in an inert atmosphere such as nitrogen atmosphere, argon atmosphere or helium atmosphere. The holding temperature is preferably 1400 to 1600° C.
Next, the outer periphery portion of each semiconductor substrate 1 is chamfered to form the chamfered portion 12 (Step S5). Chamfering is performed using, e.g., an outer periphery machining device provided with a circular plate-shaped grinding wheel. The size of the semiconductor substrate 1 may be adjusted by grinding the outer periphery before chamfering.
When forming the chamfered portion 12, a step of forming the inclined surfaces 121, 122 and a step of forming the end face 123 are preferably separately performed in such a manner that the end face 123 is formed after forming the inclined surfaces 121, 122. As a result, it is possible to suppress damage due to cleavage during the step of forming the end face 123.
When forming the inclined surfaces 121, 122, it is preferable to use a relatively hard grinding wheel as the grinding wheel 30 to suppress changes in the shape of the grooves 31 due to wear of the grinding wheel 30. On the other hand, when forming the end face 123, a grinding wheel softer than the grinding wheel used to form the inclined surfaces 121, 122 is preferably used as the grinding wheel 30 since damage due to cleave along the (100) plane or the (001) plane is likely to occur when a hard grinding wheel is used. In this case, a metal bonded grinding wheel (e.g., grit #600) can be used to form the inclined surfaces 121, 122, and a resin bonded grinding wheel (e.g., grit #1000) can be used to form the end face 123.
When the semiconductor substrate 1 has a circular shape, the entire region of the outer periphery portion is polished by the grinding wheel 30 while rotating the semiconductor substrate 1. When an orientation flat is formed on the semiconductor substrate 1, the orientation flat portion is chamfered by laterally sliding the semiconductor substrate 1 relative to the grinding wheel 30 without rotating the semiconductor substrate 1.
Next, the principal surfaces 10, 11 of the semiconductor substrate 1 are polished (Step S6). The polishing step of the principal surfaces 10, 11 is performed by, e.g., lapping using a single-sided polishing machine or a double-sided polishing machine, and then polishing. Dry etching, chemical etching or thermal etching, etc., may be performed in addition to mechanical polishing such as lapping and polishing. An amount of polishing each of the principal surfaces 10, 11 in this polishing step is about 10 to 300 μm in the thickness direction of the semiconductor substrate 1.
In a specific example of the polishing step in Step S6, firstly, the principal surfaces 10, 11 of the semiconductor substrate 1 are ground or lapped and polished using a diamond grinding wheel or using a polishing platen and a diamond-based slurry. The grit of the diamond grinding wheel is preferably about #800 to 1000 (specified by JIS B 4131). The polishing platen is preferably formed of a metal-based, glass-based, or resin-based material. The grain size of diamond-based abrasive grains contained in the diamond-based slurry is preferably about 0.5 to 8 μm. Next, the principal surfaces 10, 11 of the semiconductor substrate 1 are polished using a polishing cloth and a CMP (Chemical Mechanical Polishing) slurry until atomic level flatness (e.g., an average roughness Ra of 0.05 to 0.28 nm) is obtained. The polishing cloth is preferably formed of nylon, cotton fibers or urethane, etc. It is preferable to use colloidal silica as abrasive grains in the slurry.
After that, the semiconductor substrate 1 is cleaned and dried (Step S7). In particular, e.g., ultrasonic cleaning or scrub cleaning using an acid-based or alkaline-based detergent, 5 minutes of running water cleaning, 5 minutes of sulfuric acid-water cleaning, and 15 minutes of running water cleaning are subsequently performed. Next, the drying is performed by a method such as spin drying, vacuum drying, Marangoni drying, hot air drying or lift frying, etc.
The semiconductor substrate 1 after the polishing step in Step S6 satisfies the condition that the width bt of the end face 123 in the thickness direction of the semiconductor substrate 1 is within the range of not less than 50% and not more than 97% of the thickness t of the semiconductor substrate 1. Thus, damage on the semiconductor substrate 1 in Steps S5 to S7 can be suppressed.
Effects of the Embodiment
In the embodiment described above, by forming the chamfered portion 12 having a shape that satisfies the conditions described above, it is possible to effectively suppress occurrence of damage during the manufacturing process or handling of the semiconductor substrate 1 formed of a gallium oxide-based single crystal.
Ten types of the semiconductor substrates 1 with the chamfered portions 12 having different shapes (samples A to J) were made, and it was examined whether or not damage occurred on each sample during the step of forming the chamfered portion 12 and during the step of polishing the principal surfaces 10, 11. The samples A to J, each consisting of a 2 inch-diameter sample and a 4 inch-diameter sample, were made and evaluated.
Each of the samples A to J is a substrate that is formed of β-Ga2O3, has the (001)-oriented principal surfaces 10, 11, and is provided with the orientation flats 13a to 13c. In addition, each of the samples A to J is symmetric in the thickness direction and is formed such that the width as1 and the width as2 are equal (representatively referred to as the “width as”), the width at1 and the width at2 are equal (representatively referred to as the “width at”), and the distance bs1 and the distance bs2 are equal (representatively referred to as the “distance bs”).
In addition, when forming each of the samples A to J, the inclined surfaces 121, 122 were formed by polishing with a #600 metal bonded grinding wheel and the end face 123 was formed by polishing with a #1000 resin bonded grinding wheel.
The curvature radius of the end face 123 was 0.6 to 0.7 mm in each of the samples A to F in which the end face 123 was curved along the thickness direction of the semiconductor substrate 1.
Table 1 below shows dimensions of the samples A to J and also shows whether or not damage occurred. In Table 1, “Damage (chamfering)” indicates whether or not damage (cleavage crack, chip or scratches) occurred on the inclined surfaces 121, 122 or the end face 123 during the step of forming the chamfered portion 12 in Step S5. “Damage (principal surface polishing)” indicates whether or not damage (polishing scratches) occurred on the principal surfaces 10, 11 during the step of polishing the principal surfaces 10, 11 in Step S6. Then, “Sample A (before polishing)” and “Sample B (before polishing)” means respectively the sample A and the sample B before polishing the principal surfaces 10, 11 in Step S6. Regarding each of the samples A to J, the result (whether or not damage occurred) from the 2 inch-diameter sample and the 4 inch-diameter sample was the same.
As shown in Table 1, in the samples D and F, damage was observed on the chamfered portion 12 immediately after chamfering. It is considered that cleavage crack occurred since the width bt was less than 50% of the thickness t and the leading end of the chamfered portion 12 was sharp.
Also as shown in Table 1, in the samples H and J, damage was observed on the polished principal surface 10, 11. It is considered that damage occurred in the vicinity of the edges of the polished principal surface 10, 11 and polishing scratches were caused by broken pieces since the width bt was more than 97% of the thickness t and the inclined surfaces 121, 122 were too small.
On the other hand, as shown in Table 1, in the samples A to C, E, G and I in which the width bt was within the range of not less than 50% and not more than 97% of the thickness t, damage was not observed on the chamfered portion 12 and the principal surface 10, 11.
Although the embodiment and Example of the invention have been described, the invention is not limited to the embodiment and Example, and the various kinds of modifications can be implemented without departing from the gist of the invention.
In addition, the embodiment and Example described above do not limit the invention according to claims. Further, please note that all combinations of the features described in the embodiment and Example are not necessary to solve the problem of the invention.
1 SEMICONDUCTOR SUBSTRATE
10, 11 PRINCIPAL SURFACE
12 CHAMFERED PORTION
121, 122 INCLINED SURFACE
123 END FACE
13
a,
13
b,
13
c ORIENTATION FLAT
20 BULK SINGLE CRYSTAL
Number | Date | Country | Kind |
---|---|---|---|
2020-065514 | Apr 2020 | JP | national |