TECHNICAL FIELD

[0001] The subject matter described in this specification relates generally to manufacturing solar cells and other semiconductor structures by bowing semiconductor wafers.

CROSS REFERENCE TO RELATED APPLICATIONS

[0002] This application relates and claims priority to U.S. Patent Application

Serial No. 15/395,955, filed December 30, 2016, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND

[0003] Photovoltaic cells, commonly known as solar cells, are well known devices for direct conversion of solar radiation into electrical energy. Generally, solar cells are fabricated on a semiconductor wafer or substrate using semiconductor processing techniques to form a p-n junction near a surface of the substrate. Solar radiation impinging on the surface of, and entering into, the substrate creates electron and hole pairs in the bulk of the substrate. The electron and hole pairs migrate to p-doped and n-doped regions in the substrate, thereby generating a voltage differential between the doped regions. The doped regions are connected to conductive regions on the solar cell to direct an electrical current from the cell to an external circuit. Manufacturing solar cells and other semiconductor structures typically involves loading semiconductor wafers into a wafer carrier for one or more of various semiconductor processing stages.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Figures 1 A-B illustrate an example semiconductor wafer carrier;

[0005] Figures 2A-B illustrate a portion of an example automation system for bowing semiconductor wafers prior to loading the wafers into a wafer carrier;

[0006] Figures 3 A-F illustrate loading of a horizontally-bowed semiconductor wafer into an example wafer carrier;

[0007] Figure 4 is a flow diagram of an example method for processing semiconductor wafers; and [0008] Figure 5 is a flow diagram of an example method for loading semiconductor wafers into a semiconductor wafer carrier.

DETAILED DESCRIPTION

[0009] This specification describes methods for processing semiconductor wafers, methods for loading semiconductor wafers into wafer carriers, and semiconductor wafer carriers. The methods and wafer carriers can be used for increasing the rigidity of wafers, e.g., large and thin wafers, by intentionally bowing the wafers to an extent that does not break the wafers. The wafers can be bowed after loading, i.e., within the wafer carrier, or prior to loading, i.e., so that the wafers are loaded so that the remain bowed when loaded. In some examples, the wafers are partially loaded, then bowed, and then fully inserted. In some examples, a method for processing semiconductor wafers includes loading each semiconductor wafer into a respective semiconductor wafer slot of a semiconductor wafer carrier, horizontally bowing each semiconductor wafer, and moving the semiconductor wafer carrier into a processing station and processing the semiconductor wafers at the processing station while the semiconductor wafers are loaded into the semiconductor wafer carrier and horizontally bowed.

[0010] Figures 1A-B illustrate an example semiconductor wafer carrier 100. Figure 1A shows an isometric view of the wafer carrier. Figure IB shows a top view of a portion of the wafer carrier 100.

[0011] The wafer carrier 100 includes upper and lower left-side rods 102a-b that are parallel in a vertical direction 130. The upper and lower left-side rods 102a-b each have a number of left-side notches. The left-side notches of the upper left-side rod 102a are vertically aligned with the left-side notches of the lower left-side rod 102b. The wafer carrier 100 also includes upper and lower right-side rods 104a-b that are parallel in the vertical direction 130 and have right-side notches that mirror the left-side notches.

[0012] Although the wafer carrier 100 is illustrated with upper and lower side rods, in some examples, the wafer carrier 100 has only a single left-side rod and a single right-side rod. Similarly, in some examples, the wafer carrier 100 has more than two side rods on each side that are parallel in the vertical direction 130. [0013] The wafer carrier 100 includes left and right bottom rods 112a-b. Although two bottom rods are illustrated, the wafer carrier 100 can be implemented using only one bottom rod or more than two bottom rods. The left and right bottom rods 112a-b each have a number of bottom notches. The upper and lower left-side rods 102a-b, the upper and lower right-side rods 104a-b, and the bottom rods 112a-b are joined so that the left-side notches face the right-side notches and are horizontally aligned with the bottom-side notches. The notches define a number of semiconductor wafer slots between horizontally-aligned left-side notches, right-side notches, and bottom notches.

[0014] For example, each of the semiconductor wafer slots can have a height between the upper left-side and upper right-side rods 102a and 104a and the bottom rods 112a-b sized to receive a standard-conforming polycrystalline solar wafer, for example, a 5 inch or 6 inch wafer (e.g., having a diagonal width across the face of the wafer of 5 inches or 6 inches). Each of the semiconductor wafer slots can have a lateral length between the upper and lower left-side rods 102a-b and the upper and lower right-side rods 104a-b sized to receive the standard-conforming polycrystalline solar wafer.

[0015] The upper and lower left-side rods 102a-b, the upper and lower right-side rods 104a-b, and the bottom rods 114a-b may be formed of any appropriate material. Typically, the material is nonreactive two one or more semiconductor manufacturing processes, e.g., chemical processes. For example, the upper and lower left-side rods 102a-b, the upper and lower right-side rods 106a-b, and the bottom rods 1 lOa-b may be formed of quartz or silicon carbide.

[0016] In some examples, the wafer carrier 100 includes front and back plates 106a-b. Each of the front and back plates 106a-b extends laterally (in a lateral direction 140) between the upper and lower left-side rods 102a-b and the upper and lower right-side rods 104a-b. The upper and lower left-side rods 102a-b and the upper and lower right-side rods 104a-b and the bottom rods 112a-b are joined by the front and back plates 120a-b to extend horizontally from the front plate 106a to the back plate 106b. The bottom rods 112a-b can be joined to the front and back plates 106a-b at respective hermetically-sealed moving joints.

[0017] The wafer carrier includes a mechanical rod-slider 1 lOa-b coupled to the bottom rods 112a-b. The mechanical rod-slider is configured for sliding, in a horizontal direction 120, the bottom rods 112a-b relative to the left and right rods 102a-b and 104a-b. Since the semiconductor wafers are engaged with the notches on the left and right rods 102a-b and 104a-b, the sliding of the bottom rods 112a-b causes horizontal bowing of the semiconductor wafers loaded into the semiconductor wafer slots.

[0018] For example, the mechanical rod-slider HOa-b can be a rotatable knob coupled to a leadscrew. In another example, the mechanical rod-slider HOa-b can be a push-and-pull knob coupled to a linear motion stage, or an electrically- controlled linear actuator. If the wafer carrier 100 has more than one bottom rod, the mechanical rod-slider 1 lOa-b can be configured to move all the rods together so that the wafer bows uniformly.

[0019] Bowing the wafers can be useful, e.g., to allow high density wafer loading even with wafers that are large and thin. Bowing the wafers can, in some cases, increase the throughput of some processing steps without increasing a physical foot print. In some examples, process parameters such as nozzle pressure and pump flowrate can be adjusted or increased without breaking wafers since the wafers are bowed. Bowing the wafers can reduce or eliminate cross-slotting and improve uniformity by improving position control.

[0020] In some examples, the wafer carrier 100 includes front and back transport interface handles 108a-b. The transport interface handles 108a-b can be detachably coupled to the front and back plates 106a-b. The transport interface handles 108a-b can used, e.g., so that an automation system can lift and move the wafer carrier 100.

[0021] Figures 2A-B illustrate a portion of an example automation system 200 for bowing semiconductor wafers prior to loading the wafers into a wafer carrier. The automation system 200 is implemented using robotic components and can be controlled, e.g., by a computer system programmed for loading and processing semiconductor wafers. In general, any appropriate robotic system can be used for bowing the wafers, and the automation system 200 shown in Figures 2A-B is provided for purposes of illustration.

[0022] The automation system 200 includes a robotic gripper 202 having left and right pistons 204a-b. The robotic gripper 202 is configured to grip a semiconductor wafer 206 and hold the center of the wafer 206 in place. The left and right pistons 204a-b are configured to engage the left and right sides of the wafer 206 and push the wafer 206 to bow without breaking the wafer 206. Figure 2A shows the robotic gripper 202 holding the wafer 206 prior to bowing the wafer 206. Figure 2B shows the pistons 204a-b causing the wafer 206 to horizontally bow.

[0023] Figures 3A-F illustrate loading of a horizontally-bowed semiconductor wafer 308 into an example wafer carrier 300. The wafer carrier 300 includes a leftside rod 302a, a right-side rod 302b, and a bottom rod 304. Figures 3A-B illustrate pre-bowing the semiconductor wafer 308 prior to loading, and Figures 3C-D illustrate partially loading the semiconductor wafer 308 before bowing the semiconductor wafer 308 and then fully loading the horizontally-bowed semiconductor wafer 308.

[0024] Figure 3A is a top view of the wafer carrier 300 prior to loading of the horizontally-bowed wafer 308 shown in Figure 3B. The illustrated portion of the wafer carrier 300 has five wafer slots 306a-e each comprising horizontally aligned notches in the left and right rods 302a-b and the bottom rod 304.

[0025] Figure 3B is a top view of the wafer carrier 300 after loading the horizontally-bowed wafer 308. Since the wafer 308 is bowed, the center of the wafer 308 engages the bottom rod 304 in the first wafer slot 306a and the right and left sides of the wafer 308 engage the right and left rods 302a-b in the second wafer slot 306b. For example, the left and right sides of the wafer 308 may be horizontally offset from the center of the wafer 308 by a horizontal distance of about 8 mm, or any appropriate distance that increases the rigidity of the wafer 308 without breaking the wafer 308.

[0026] Accordingly, the bottom notch is horizontally offset from the left and right notches, and the wafer carrier 300 keeps the wafer 308 horizontally bowed after the wafer 308 has been bowed and loaded by an automation system such as the example automation system 200 of Figures 2A-B. As illustrated, the bottom notch is only offset by one position; however, depending on the distance that the wafer is bowed, the bottom notch may be offset by more than one position from the left and right notches.

[0027] Figure 3C is a top view of the wafer carrier 300 where the wafer 308 has been partially inserted. The wafer 308 has been inserted in the wafer carrier 300 to a first depth so that the right and left sides of the wafer 308 engage the right and left rods 302a-b in the second wafer slot 306b, but the bottom of the wafer 308 has not yet engaged the bottom rod 304. Figure 3E is a front view of the wafer carrier 300 where the wafer 308 has been partially inserted to the first depth 310a.

[0028] Figure 3D is a top view of the wafer carrier 300 after the wafer 308 has been horizontally bowed and fully inserted to a second depth, deeper than the first depth, so that the bottom of the wafer 308 engages the bottom rod 304 in a bottom notch horizontally offset from the second wafer slot 306b, i.e., the bottom notch for the first wafer slot 306a. Figure 3F is a front view of the wafer carrier 300 where the wafer 308 has been fully inserted to the second depth 310b.

[0029] Figure 4 is a flow diagram of an example method 400 for processing semiconductor wafers. The method 400 can be performed, e.g., by an automation system for processing semiconductor wafers, or by an automation system acting together with one or more human operators.

[0030] The method 400 includes loading each semiconductor wafer into a respective semiconductor wafer slot of a semiconductor wafer carrier (402). The wafer carrier can be, e.g., the wafer carrier 100 of Figures 1A and IB. The method 400 includes horizontally bowing each semiconductor wafer (404). For example, horizontally bowing the wafers can include sliding, in the horizontal direction, one or more bottom rods relative to the left and right rods. The method 400 includes moving the semiconductor wafer carrier into a processing station and processing the semiconductor wafers at the processing station while the semiconductor wafers are loaded into the semiconductor wafer carrier and horizontally bowed (406).

[0031] Figure 5 is a flow diagram of an example method 500 for loading semiconductor wafers into a semiconductor wafer carrier. The method 500 can be performed, e.g., by an automation system for processing semiconductor wafers, or by an automation system acting together with one or more human operators. The wafer carrier can be, e.g., the wafer carrier 300 of Figures 3A-B.

[0032] The method 500 includes, for each wafer, gripping the wafer using a robotic gripper of an automation system (502). For example, the automation system can be the automation system 200 of Figures 2A-B. The method 500 includes, for each wafer, horizontally bowing the wafer using gripper (504). The method 500 includes, for each wafer and while keeping the wafer horizontally bowed, loading the wafer in the semiconductor wafer carrier (506). The wafer sits in horizontally aligned left and right notches in left and right rods of the semiconductor wafer carrier. Due to the horizontal bowing, the wafer sits in at least one bottom notch in a bottom rod that is horizontally offset from the left and right notches in the left and right rods.

[0033] Although specific examples and features have been described above, these examples and features are not intended to limit the scope of the present disclosure, even where only a single example is described with respect to a particular feature. Examples of features provided in the disclosure are intended to be illustrative rather than restrictive unless stated otherwise. The above description is intended to cover such alternatives, modifications, and equivalents as would be apparent to a person skilled in the art having the benefit of this disclosure.

[0034] The scope of the present disclosure includes any feature or combination of features disclosed in this specification (either explicitly or implicitly), or any generalization of features disclosed, whether or not such features or generalizations mitigate any or all of the problems described in this specification. Accordingly, new claims may be formulated during prosecution of this application (or an application claiming priority to this application) to any such combination of features. In particular, with reference to the appended claims, features from dependent claims may be combined with those of the independent claims and features from respective independent claims may be combined in any appropriate manner and not merely in the specific combinations enumerated in the appended claims.