GaN HEMT device and manufacturing method thereof

Abstract

The invention provides a GaN HEMT (High Electron Mobility Transistor) device and a manufacturing method thereof, which are characterized in that at least one heat conduction hole is arranged in a field plate area corresponding to the GaN HEMT device, the heat conduction hole extends upwards from the back of the device and stops on the lower surface of a passivation layer on the surface of the device, and a heat conduction material is formed in the heat conduction hole and can conduct heat from a heating core of the device to the outside. According to the GaN HEMT device provided by the invention, the heat dissipation capability of the GaN HEMT device is effectively improved, the influence of a self-heating effect on the carrier mobility is reduced, the saturation leakage current and the reduction of transconductance are avoided, the gate leakage current and the hot electron damage are reduced, the reliability of the device is improved, and the service life of the device is prolonged.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, and in particular to a GaN HEMT device and its manufacturing method. Background Technology

[0002] GaN HEMTs (GaN high electron mobility transistors) are generally used in high-frequency switching applications. Switching losses and dynamic on-resistance losses are the main heat sources of the device. Because the conductive channel between the gate and drain in the structure simultaneously bears the high voltage and high current overlap during the switching process, the power density is the highest. At the same time, the traps between the gate and drain also trap electrons, leading to increased resistance and heat. Therefore, this structure is the core of the heat generation of the entire device, and how to improve heat dissipation is a challenge currently facing GaN HEMTs. Summary of the Invention

[0003] The purpose of this invention is to provide a GaN HEMT device and its manufacturing method to improve the heat dissipation performance of GaN HEMT.

[0004] To address the above problems, the present invention provides a GaN HEMT device, comprising:

[0005] Semiconductor body;

[0006] The device functional structure is formed on the semiconductor body, and the device functional structure includes a source, a gate and a drain arranged in sequence, and an interlayer dielectric layer covering the source, the gate and the drain.

[0007] A field plate is formed within the interlayer dielectric layer and is located above the region between the gate and the drain.

[0008] A surface passivation layer is formed above the interlayer dielectric layer; and,

[0009] A thermally conductive structure includes a thermally conductive hole and a thermally conductive material formed within the thermally conductive hole. The thermally conductive hole extends upward from the bottom of the semiconductor body and terminates at the lower surface of the surface passivation layer. The thermally conductive hole is located within the orthogonal projection area of ​​the field plate on the semiconductor body.

[0010] Optionally, in the GaN HEMT device, the thermally conductive material is a metallic material.

[0011] Optionally, in the GaN HEMT device, the metal material includes one or more of silver, copper, gold, or aluminum.

[0012] Optionally, in the GaN HEMT device, the thermally conductive material is a non-conductive thermally conductive composite material.

[0013] Optionally, in the GaN HEMT device, the thermally conductive composite material includes a resin mixed with aluminum nitride particles, an alumina hybrid silicone grease, an aluminum nitride hybrid silicone grease, or an organic composite material containing metal particles.

[0014] Optionally, in the GaN HEMT device, the thermal conductive structure includes a plurality of thermally conductive holes, which are arranged sequentially in a direction parallel to the length of the field plate, and the distance between the projection of each thermally conductive hole on the field plate and the near-drain edge of the field plate is greater than or equal to the distance between the projection of each thermally conductive hole on the field plate and the near-gate edge of the field plate.

[0015] The near-drain edge of the field plate refers to the edge of the field plate close to the drain electrode, and the near-gate edge of the field plate refers to the edge of the field plate close to the gate electrode.

[0016] Optionally, in the GaN HEMT device, the thermally conductive structure includes a plurality of thermally conductive holes, the width of the field plate is W, the diameter of a single thermally conductive hole is D, and the center-to-center distance between any two adjacent thermally conductive holes in the width direction of the field plate is P, where P ≥ 2D and (n × D) ≤ 0.5 × W, and n is the number of thermally conductive holes arranged in the width direction of the field plate.

[0017] The present invention also provides a method for manufacturing a GaN HEMT device, comprising:

[0018] After completing the surface passivation layer process, photolithography is performed on the back side of the semiconductor body to form a heat-conducting hole pattern corresponding to the position area of ​​the field plate;

[0019] The heat-conducting holes are formed by an etching process, with the etching stopping at the lower surface of the surface passivation layer.

[0020] The thermally conductive material is formed in the thermally conductive holes.

[0021] Optionally, in the manufacturing method, when the thermally conductive material is a metallic material, the step of forming the thermally conductive material in the thermally conductive holes includes:

[0022] Seed metal layers were deposited on the sidewalls and bottom of the heat-conducting holes using physical vapor deposition.

[0023] Thermally conductive metal is deposited on the seed layer by electroplating.

[0024] Optionally, in the manufacturing method, when the thermally conductive material is a non-conductive thermally conductive composite material, the step of forming a highly thermally conductive material in the thermally conductive holes includes:

[0025] The thermally conductive composite material is filled into the thermally conductive holes by spin coating.

[0026] The excess thermally conductive composite material on the back side of the semiconductor body is removed using an organic solvent.

[0027] In summary, the GaN HEMT device and its manufacturing method provided by the embodiments of the present invention include: providing at least one thermally conductive hole corresponding to the field plate region of the GaN HEMT device, the thermally conductive hole extending from the back side of the semiconductor body to the lower surface of the surface passivation layer, and a thermally conductive material formed therein, thereby conducting heat from the heat-generating core of the device to the outside. The present invention effectively improves the heat dissipation capability of the GaN HEMT device, reduces the impact of self-heating effects on carrier mobility, avoids the decrease in saturation leakage current and transconductance, and simultaneously reduces gate leakage current and hot electron damage, thereby improving the reliability and lifespan of the device. Attached Figure Description

[0028] Figures 1-4 This is a schematic diagram of the device structure corresponding to each step in the fabrication process of the heat dissipation structure of the GaN HEMT device in Embodiment 1 of the present invention.

[0029] Figure 5 This is a schematic diagram of the heat dissipation structure of the GaN HEMT device provided in Embodiment 1 of the present invention;

[0030] Figure 6 A flowchart illustrating a method for manufacturing a GaN HEMT device according to an embodiment of the present invention;

[0031] Figure 7 This is a schematic diagram of the spin-coated thermally conductive material in Embodiment 2 of the present invention;

[0032] Figure 8 This is a schematic diagram of removing the thermally conductive material on the back of the semiconductor body in Embodiment 2 of the present invention;

[0033] Figure 9 This is a schematic diagram of the heat dissipation structure of the GaN HEMT device provided in Embodiment 2 of the present invention;

[0034] The labels in the attached figures are explained as follows:

[0035] 10-Semiconductor body; 11-Barrier layer; 21-Source; 22-Gate; 23-Drain; 30-Field plate; 40-Interlayer dielectric layer; 50-Surface passivation layer; 61-First metal layer; 62-Second metal layer; 70-Photoresist layer; 80-Thermal via; 90-Thermal conductive material; 91-Seed layer metal; 92-Thermal conductive metal; 93-Thermal conductive composite material. Detailed Implementation

[0036] The GaN HEMT device and its manufacturing method provided by the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the drawings are all in a very simplified form and use non-precise scales, used only to facilitate and clarify the illustration of the embodiments of the present invention. Furthermore, the structures shown in the drawings are often part of the actual structure. In particular, different figures may have different emphases and sometimes use different scales. It should be understood that relative terms such as "above," "below," "top," and "bottom" shown in the drawings can be used to describe the relationships between various elements. These relative terms are intended to cover different orientations of elements other than those depicted in the drawings. For example, if the device is inverted relative to the view in the drawings, an element described as "above" another element will now be below that element. It should also be understood that, unless specifically stated or indicated, the terms "first," "second," "third," etc., in the specification are only used to distinguish various components, elements, steps, etc., in the specification, and are not used to indicate logical or sequential relationships between various components, elements, steps, etc.

[0037] Example 1

[0038] Please refer to Figure 4 and combined Figure 5 This embodiment provides a GaN HEMT device, including:

[0039] Semiconductor body 10;

[0040] The device functional structure is formed on the semiconductor body 10. The device functional structure includes a source 21, a gate 22 and a drain 23 arranged in sequence, and an interlayer dielectric layer 40 covering the source 21, the gate 22 and the drain 23.

[0041] The field plate 30 is formed within the interlayer dielectric layer 30 and is located above the region between the gate 22 and the drain 23;

[0042] A surface passivation layer 50 is formed above the interlayer dielectric layer 40; and,

[0043] A thermally conductive structure is provided, comprising a thermally conductive hole 80 and a thermally conductive material 90 formed within the thermally conductive hole 80. The thermally conductive hole 80 extends upward from the bottom of the semiconductor body 10 and terminates at the lower surface of the surface passivation layer 50. The thermally conductive hole 80 is located within the orthogonal projection area of ​​the field plate 30 on the semiconductor body 10.

[0044] In this embodiment, the thermally conductive material 90 is specifically a metallic material, and optionally, the metallic material includes one or more of silver, copper, gold, or aluminum.

[0045] For GaN HEMT devices, the semiconductor body 10 includes a substrate and an epitaxial structure formed on the substrate. The substrate includes a front side and a back side, and the epitaxial structure is formed on the front side of the substrate. The epitaxial structure generally includes a nucleation layer, a buffer layer, a channel layer, a barrier layer, etc., and the nucleation layer, buffer layer, channel layer, and barrier layer are stacked sequentially on the substrate.

[0046] like Figure 4 As shown, the gate 22 is formed on the barrier layer 11, and the source 21 and the drain 23 are formed on the channel layers on both sides of the barrier layer 11. Figure 4 The barrier layer 11 of the semiconductor body 10 is shown separately, without distinguishing the substrate and the rest of the epitaxial structure. However, it should be understood that the film layer located below the barrier layer 11 is the substrate and other epitaxial structures located on the substrate.

[0047] The substrate material can be silicon (Si), silicon carbide (SiC), sapphire (Al2O3), etc., or the substrate can be a GaN self-supporting substrate. The barrier layer 11 can specifically be an aluminum gallium nitride (AlGaN) barrier layer or an aluminum nitride (AlN) barrier layer. The barrier layer 11 and the underlying GaN channel layer form a heterojunction to generate a two-dimensional electron gas (2DEG).

[0048] The device functional structure may further include a metal interconnect structure, which includes a first metal layer 61 and a second metal layer 62. The first metal layer 61 is formed within the interlayer dielectric layer 40, and the second metal layer 62 is formed on the interlayer dielectric layer 40. The surface passivation layer 50 covers the second metal layer 62 and the exposed surface of the interlayer dielectric layer 40.

[0049] When arranging the first metal layer 61 and the second metal layer 62, the arrangement areas of the first metal layer 61 and the second metal layer 62 can avoid the formation location of the heat conduction hole 80, thereby avoiding the formation of the heat conduction hole 80 from affecting the performance of the first metal layer 61 and the second metal layer 62.

[0050] Furthermore, preferably, the field plate 30 has through holes corresponding to the heat-conducting holes 80. The area of ​​the through holes is slightly larger than or equal to the area of ​​the heat-conducting holes 80. The through holes facilitate the etching process when etching the interlayer dielectric layer 40 to form the heat-conducting holes 80. Here, "the through holes of the field plate 30 corresponding to the heat-conducting holes 30" means that the projection of the heat-conducting holes 30 onto the field plate 30 falls within the position range of the through holes provided on the field plate 30.

[0051] As a preferred option, such as Figure 5 As shown, the heat-conducting structure includes a plurality of heat-conducting holes 80, which are arranged sequentially in a direction parallel to the length of the field plate 30. The distance between the projection of each heat-conducting hole 80 onto the field plate 30 and the near-drain edge of the field plate 30 is greater than or equal to the distance between the projection and the near-gate edge of the field plate 30. That is, from a top view, the heat-conducting holes 80 are distributed along the centerline of the field plate 30 along its length or located on the side of the centerline closer to the gate 22. Figure 5 The illustration shows an example where the heat-conducting holes 80 are distributed along the centerline of the field plate 30 along its length. The number and position of the through holes in the field plate 30 correspond to the number and position of the heat-conducting holes 80.

[0052] It is understood that the width direction of the field plate 30 is the direction in which the source 21, the gate 22 and the drain 23 are arranged in sequence, while the length direction of the field plate 30 is the direction perpendicular to its width direction.

[0053] The electric field strength is highest near the drain edge of the field plate 30 (the edge closest to the drain electrode 23). Since the core function of the field plate 30 is to disperse and reduce the electric field in this area, placing a heat-conducting hole 80 in this region would weaken the electric field modulation capability of the field plate 30. The central region of the field plate 30 is the core heat-generating region. Opening a hole in the central region has the least impact on the electric field distribution but achieves the highest heat dissipation efficiency. The electric field strength and heat source intensity near the gate edge of the field plate 30 (the edge closest to the gate electrode 22) are both lower than those in the central region and near the drain edge. Although opening a hole in the central region also has a smaller impact on the electric field distribution, the heat dissipation efficiency is not as good as opening a hole in the central region. Therefore, in this embodiment, by setting the heat-conducting hole 80 to be located on the centerline of the field plate 30 along its length and / or on the side of the centerline close to the gate electrode 22, better heat dissipation performance is achieved without affecting the electric field modulation capability of the field plate 30 due to opening a hole in the field plate 30.

[0054] The heat-conducting structure may include multiple sets of heat-conducting holes 80 arranged sequentially along the length of the field plate 30. For example, it may include two sets of heat-conducting holes 80 arranged sequentially along the length of the field plate 30, wherein one set of heat-conducting holes 80 is located on the center line of the field plate 30, and the other set of heat-conducting holes 80 may be located on the side of the center line of the field plate 30 near the gate 22.

[0055] When the number of heat-conducting holes 80 arranged along the width direction of the field plate 30 exceeds one, if the width of the field plate 30 is W, the diameter of a single heat-conducting hole 80 is D, and the center-to-center distance between any two adjacent heat-conducting holes 80 in the width direction of the field plate 30 is P, then preferably, P ≥ 2D and (n × D) ≤ 0.5 × W, where n is the number of heat-conducting holes 80 arranged in the width direction of the field plate 30. In this way, when multiple openings are provided along the field plate 30, the influence of the arrangement of multiple openings on the electric field modulation capability of the field plate 30 can be controlled to a greater extent.

[0056] Therefore, the GaN HEMT device manufactured using the manufacturing method provided in this embodiment conducts heat from the heat-generating core of the device to the outside, maximizing heat dissipation performance while avoiding the impact of openings on the electric field modulation capability of the field plate 30.

[0057] Correspondingly, such as Figure 6 As shown, this embodiment provides a method for manufacturing a GaN HEMT device, including the following steps:

[0058] S1, after completing the process of the surface passivation layer 50, photolithography is performed on the back side of the semiconductor body 10 to form a heat-conducting hole pattern corresponding to the position area of ​​the field plate 80;

[0059] S2, the heat-conducting hole 80 is formed by etching process, and the etching stops at the lower surface of the surface passivation layer 50;

[0060] S3, the thermally conductive material 90 is formed in the thermally conductive hole 80.

[0061] The following combination Figures 1-3 The manufacturing process of the GaN HEMT device provided in this embodiment is further described.

[0062] Reference Figure 1In step S11, the surface passivation layer 50 is fabricated after the functional structure of the GaN HEMT device is completed. This process includes: forming a source 21 and a drain 23 on the channel layers on both sides of the barrier layer 11; forming a gate 22 on the barrier layer 11 between the source 21 and the drain 23; forming an interlayer dielectric layer 40; forming a field plate 30 above the interlayer dielectric layer 40 located in the region between the gate 22 and the drain 23; thickening the interlayer dielectric layer 40; forming a first metal layer 61 on the interlayer dielectric layer 40; and further thickening the interlayer dielectric layer 40 to form a second metal layer 62. The surface passivation layer 50 covers the area of ​​the interlayer dielectric layer 40 exposed by the second metal layer 62 while simultaneously covering the second metal layer 62.

[0063] In step S11, "forming a heat-conducting hole pattern corresponding to the position area of ​​the field plate 80" means that the projection of the formed heat-conducting hole pattern on the semiconductor body 10 falls within the projection range of the field plate 30 on the semiconductor body 10. The step of forming the heat-conducting hole pattern may include: forming a photoresist layer 70 on the back side of the semiconductor body 10, and exposing and developing the photoresist layer 70 to form the heat-conducting hole pattern.

[0064] In step S12, refer to Figure 2 The thermally conductive hole 80 is formed by an etching process. The thermally conductive hole 80 extends upward from the back side of the semiconductor body 10 and ends at the lower surface of the surface passivation layer 50. That is, the thermally conductive hole 80 penetrates the part of the device except for the surface passivation layer 50 in a vertical direction.

[0065] In step S13, refer to Figure 3 and Figure 4 The formation of the thermally conductive material 90 in the thermally conductive hole 80 specifically includes: depositing a seed layer metal 91 on the sidewall and bottom of the thermally conductive hole 80 using a physical vapor deposition method, and depositing a thermally conductive metal 92 on the seed layer by an electroplating method.

[0066] The seed layer metal 91 can employ a multilayer metal composite structure, for example, comprising a sequentially deposited adhesion layer and a diffusion barrier layer. The adhesion layer can be made of titanium or chromium, and the diffusion barrier layer can be made of platinum or nickel. The adhesion layer provides adhesion to prevent the thermally conductive metal 92 layer from detaching, and the diffusion barrier layer prevents the thermally conductive metal 92 layer from diffusing into the semiconductor material during subsequent processes or device operation. The thermally conductive metal 92 provides a low-resistance thermal conduction path and can include one or more of silver, copper, gold, or aluminum.

[0067]

Example 2

[0068] Please refer to Figure 8 and combined Figure 9 This embodiment provides a GaN HEMT device. Unlike the first embodiment, in this embodiment, the thermally conductive material 90 formed in the thermally conductive hole 80 is a non-conductive thermally conductive composite material, and the thermally conductive composite material fills the thermally conductive hole 80.

[0069] Optionally, the thermally conductive composite material includes a resin mixed with aluminum nitride particles, an alumina hybrid silicone grease, an aluminum nitride hybrid silicone grease, or an organic composite material containing metal particles.

[0070] Accordingly, please combine Figure 7 Unlike the manufacturing method provided in this embodiment, step S3 in this embodiment, the step of forming the thermally conductive material 90 in the thermally conductive hole 80, includes:

[0071] The thermally conductive composite material is filled into the thermally conductive holes 80 by spin coating.

[0072] The excess thermally conductive composite material on the back side of the semiconductor body 10 is removed using an organic solvent.

[0073] Similarly, thermally conductive material 90 is formed within the thermally conductive hole 80. Compared to the solution of metal material deposition in Example 1, this embodiment uses a solution of spin-coating non-conductive thermally conductive material 90, which has advantages such as good electrical isolation, simple process, low cost, and low stress.

[0074] Specifically, the electroplated metal material extends from the back of the device all the way to the passivation layer on the surface. If the process deviates slightly, such as over-plating or uneven metal layer, it may cause a short circuit between the metal and the surface interconnects such as the field plate 30, gate 22, or source 21, resulting in direct device failure. The non-conductive material fundamentally eliminates the risk of vertical short circuits through the heat-conducting hole 80, greatly improving the process tolerance and device yield. Example 1 uses a metal deposition scheme, requiring two core steps: depositing a seed layer metal and electroplating. This involves expensive equipment and complex process control (such as electroplating solution composition and current density uniformity). Example 2... The solution typically only requires spin coating and curing steps. Spin coating equipment is far less expensive than deposition and electroplating equipment, and the process is simpler and easier to integrate into existing production lines. There is a significant difference in the coefficient of thermal expansion between metals (such as copper) and semiconductor materials. Under the temperature cycling during device operation, the repeated expansion and contraction of the metal pillar will generate mechanical stress on the surrounding brittle semiconductor materials. In the long run, this may lead to lattice defects or even cracks, affecting reliability. However, many organic thermally conductive composite materials have a certain degree of flexibility, and their coefficient of thermal expansion can be adjusted by filling particles, thereby better matching with semiconductor materials. The resulting thermomechanical stress is smaller, which helps to improve the long-term service life and reliability of the device.

[0075] In summary, the GaN HEMT device and its manufacturing method provided by the embodiments of the present invention include: providing at least one thermally conductive hole corresponding to the field plate region of the GaNHEMT device, the thermally conductive hole extending from the back side of the semiconductor body 10 to the lower surface of the surface passivation layer, and a thermally conductive material being formed therein, thereby conducting heat from the heat-generating core of the device to the outside. Compared with the prior art, it has the following beneficial effects:

[0076] (1) Improve the heat dissipation capacity of the device, reduce the effect of self-heating on carrier mobility, and avoid the decrease of saturation leakage current and transconductance;

[0077] (2) Improve the increase in gate leakage current caused by temperature rise;

[0078] (3) High-energy hot electrons will be generated in the gate-drain channel at high temperature, which will bombard the gate dielectric interface and cause irreversible damage. Increasing the heat dissipation capacity of the device can avoid this phenomenon to a certain extent.

[0079] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Similar or identical parts between embodiments can be referred to mutually. In addition, the different parts between embodiments can also be combined with each other, and this invention does not limit this.

[0080] The above description is merely a description of preferred embodiments of the present invention and is not intended to limit the scope of the present invention in any way. Any changes or modifications made by those skilled in the art based on the above disclosure shall fall within the protection scope of the claims.

Claims

1. A GaN HEMT device, characterized in that, include: Semiconductor body; The device functional structure is formed on the semiconductor body, and the device functional structure includes a source, a gate and a drain arranged in sequence, and an interlayer dielectric layer covering the source, the gate and the drain. A field plate is formed within the interlayer dielectric layer and is located above the region between the gate and the drain. A surface passivation layer is formed above the interlayer dielectric layer; as well as, A thermally conductive structure includes a thermally conductive hole and a thermally conductive material formed within the thermally conductive hole. The thermally conductive hole extends upward from the bottom of the semiconductor body and terminates at the lower surface of the surface passivation layer. The thermally conductive hole is located within the orthogonal projection area of ​​the field plate on the semiconductor body.

2. The GaN HEMT device as described in claim 1, characterized in that, The thermally conductive material is a metallic material.

3. The GaN HEMT device as described in claim 2, characterized in that, The metallic material includes one or more of silver, copper, gold, or aluminum.

4. The GaN HEMT device as described in claim 1, characterized in that, The thermally conductive material is a non-conductive thermally conductive composite material.

5. The GaN HEMT device as described in claim 4, characterized in that, The thermally conductive composite material includes a resin mixed with aluminum nitride particles, an alumina hybrid silicone grease, an aluminum nitride hybrid silicone grease, or an organic composite material containing metal particles.

6. The GaN HEMT device as described in claim 1, characterized in that, The heat-conducting structure includes a plurality of heat-conducting holes, which are arranged sequentially in a direction parallel to the length of the field plate, and the distance between the projection of each heat-conducting hole on the field plate and the near-drain edge of the field plate is greater than or equal to the distance between the projection of each heat-conducting hole on the field plate and the near-gate edge of the field plate. The field plate near the drain side edge refers to the edge of the field plate close to the drain electrode, and the field plate near the gate side edge refers to the edge of the field plate close to the gate electrode.

7. The GaN HEMT device as described in claim 1, characterized in that, The heat-conducting structure includes a plurality of heat-conducting holes. The width of the field plate is W, the diameter of a single heat-conducting hole is D, and the center-to-center distance between any two adjacent heat-conducting holes in the width direction of the field plate is P, where P ≥ 2D and (n × D) ≤ 0.5 × W, and n is the number of heat-conducting holes arranged in the width direction of the field plate.

8. A method for manufacturing a GaN HEMT device as described in any one of claims 1 to 7, characterized in that, include: After the surface passivation layer is fabricated, photolithography is performed on the back side of the semiconductor body to form a heat-conducting hole pattern corresponding to the location area of ​​the field plate. The heat-conducting holes are formed by an etching process, with the etching stopping at the lower surface of the surface passivation layer. The thermally conductive material is formed in the thermally conductive holes.

9. The manufacturing method as described in claim 8, characterized in that, When the thermally conductive material is a metallic material, the step of forming the thermally conductive material in the thermally conductive hole includes: Seed metal layers were deposited on the sidewalls and bottom of the heat-conducting holes using physical vapor deposition. Thermally conductive metal is deposited on the seed layer by electroplating.

10. The manufacturing method as described in claim 8, characterized in that, When the thermally conductive material is a non-conductive thermally conductive composite material, the step of forming a highly thermally conductive material in the thermally conductive hole includes: The thermally conductive composite material is filled into the thermally conductive holes by spin coating. The excess thermally conductive composite material on the back side of the semiconductor body is removed using an organic solvent.

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