METHOD OF MANUFACTURING SEMICONDUCTOR DEVICE AND METHOD OF CLEANING SEMICONDUCTOR SUBSTRATE
A method of manufacturing a semiconductor device includes: holding a semiconductor substrate with a surface inclined with respect to the vertical direction and the horizontal direction; and immersing the semiconductor substrate in a cleaning solution including an acid.
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This application claims the benefit of priority from Japanese Patent Application No. 2011-40544 filed on Feb. 25, 2011, the entire contents of which are incorporated herein by reference.
FIELDThe embodiments discussed herein are related to a method of manufacturing a semiconductor device and a method of cleaning a semiconductor substrate.
BACKGROUNDElectron devices in which a GaN layer used as an electron transport layer and an AlGaN layer are disposed on a substrate, for example, compound semiconductor devices, include a GaN-based high electron mobility transistor (HEMT). In a GaN-based HEMT, a high-concentration two-dimensional electron gas (2DEG) generated at the heterojunction interface between AlGaN and GaN is used.
The bandgap of GaN is 3.4 eV, which is larger than the bandgap of Si (1.1 eV) and the bandgap of GaAs (1.4 eV). GaN has a high breakdown field strength and a high saturated electron velocity. GaN may be used as the material for a high-voltage operating and high-output compound semiconductor device, for example, the material for a semiconductor device for power supply. Compound semiconductor devices using a GaN-based compound semiconductor may be used as high-efficiency switching devices or high breakdown voltage power devices for electric cars. Si laterally diffused metal oxide semiconductor (LDMOS) transistors or GaAs field effect transistors (FETs) may not be suitable for high-output, high-efficiency, or high-voltage operation.
Related art is disclosed in Japanese Laid-open Patent Publication No. 2009-164226 and Japanese Laid-open Patent Publication No. 9-260331.
SUMMARYAccording to one aspect of the embodiments, a method of manufacturing a semiconductor device includes: holding a semiconductor substrate with a surface inclined with respect to the vertical direction and the horizontal direction; and immersing the semiconductor substrate in a cleaning solution including an acid.
Additional advantages and novel features of the invention will be set forth in part in the description that follows, and in part will become more apparent to those skilled in the art upon examination of the following or upon learning by practice of the invention.
In order to produce a GaN-based HEMT having good characteristics, residues such as particles generated in the production process may be removed. For example, in a GaN-based HEMT having a gate recess structure which enables normally “off” operation, in order to reduce the increase in leakage current caused by residues, the fluctuation in threshold voltage due to charge trapping, and the like, cleaning is performed between the formation of the recess and the formation of a gate-insulating film.
As illustrated in
The thickness of the electron transport layer 3 may be, for example, about 3 μm. The thickness of the electron supply layer 4 may be, for example, about 30 nm. When a spacer layer is provided, the thickness of the spacer layer may be, for example, about 5 nm. The thickness of the cap layer 5 may be, for example, 10 nm. In the spacer layer, e.g., an i-AlGaN layer, and the electron supply layer 4, e.g., an n-AlGaN layer, the Al compositional ratio may be, for example, about 0.2. The electron supply layer 4, e.g., an n-AlGaN layer, and the cap layer 5, e.g., an n-GaN layer, may be doped with Si as an n-type impurity, in an amount of about 5×1018 cm−3.
In such a stacked structure, a two-dimensional electron gas (2DEG) is generated near the interface between the electron transport layer 3 and the electron supply layer 4. Strain between the electron transport layer 3 and the electron supply layer 4 increases owing to the cap layer 5, which causes a piezoelectric effect, resulting in an increase in 2DEG. Consequently, the on-state current of the GaN-based HEMT decreases, which may enable high current operation of GaN-based HEMT.
As illustrated in
As illustrated in
As illustrated in
After the recess 6g is formed, by cleaning the inside of the recess 6g by a certain method, etching residues, resist residues, or the like may be removed.
As illustrated in
As illustrated in
As illustrated in
As illustrated in
A cleaning apparatus 61 houses a plurality of semiconductor substrates 20. The cleaning apparatus 61 is provided with four wall members 24 such that a rectangular cylinder is formed. A supporting member 21 which supports semiconductor substrates 20 is provided inside of a pair of wall members 24. A plurality of lower locking members 22 are provided inside of the pair of wall members 24 at positions higher than the supporting member 21. A plurality of upper locking members 23 are provided at positions higher than the lower locking members 22 and sifted from the lower locking members 22 in plan view. The position in the horizontal direction of a semiconductor substrate 20 is determined by a pair of a lower locking member 22 and an upper locking member 23, and the position in the vertical direction of the semiconductor substrate 20 is determined by the supporting member 21. Since the upper locking member 23 is provided at a position different from that of the lower locking members 22 in plan view, a direction normal to the surface of the semiconductor substrate 20 is inclined from the horizontal direction.
For example, a substrate 1 including a recess 6g and the like, as a semiconductor substrate 20, may be placed in the cleaning apparatus 61.
In the acid cleaning, a reaction between the cleaning solution 26 and foreign substances on the semiconductor substrate 20 may cause bubbles to form. For example, on the surface of the semiconductor substrate 20 facing upward in the vertical direction, bubbles may float upward in the vertical direction. Retention of bubbles may be unlikely to occur on the surface, and the surface may be effectively cleaned. By reversing the semiconductor substrate 20, a surface opposite to the surface may be efficiently cleaned. For example, when the upper locking members 23 and/or the lower locking members 22 are moved in the horizontal direction, upper and lower surfaces are easily reversed. The angle of the normal direction of the surface of the semiconductor substrate 20 with respect to the horizontal direction may be 10° to 80°. For example, when the angle is less than 10°, bubbles generated on the lower portion of the surface facing upward in the vertical direction may pass in the vicinity of the surface and float up. As a result, uneven cleaning may occur. When the angle exceeds 80°, bubbles may be retained on the surface facing downward in the vertical direction, and the cleaning efficiency at the surface facing downward in the vertical direction may be decreased.
A plurality of semiconductor substrates 20 may be disposed with a distance between adjacent semiconductor substrates 20. For example, there may be no overlapping portions in plan view. Interference among a plurality of semiconductor substrates 20 may be reduced. As a result, bubbles generated on one semiconductor substrate 20 located at the lower position may not come into contact with another semiconductor substrate 20 located at the upper position, and cleaning efficiency of the other semiconductor substrate 20 may be improved.
Since bubbles generated during cleaning are efficiently removed, cleaning efficiency may be improved.
A cleaning apparatus 62 illustrated in
When acid cleaning is performed using the cleaning apparatus 62, for example, as illustrated in
A cleaning apparatus 63 illustrated in
When acid cleaning is performed using the cleaning apparatus 63, for example, as illustrated in
The cleaning apparatuses 61, 62, and 63 illustrated in
When acid cleaning is performed using the cleaning apparatus 64, a semiconductor substrate is placed on the upper projections 51a, 51b, and 51c, and using the handle 57, the cleaning apparatus 64 is immersed in a cleaning solution filled in a cleaning tank. When the cleaning apparatus 64 is placed on the bottom of the cleaning tank, because of the difference in height among the lower projections 52a, 52b, and 52c, a direction normal to the surface of the semiconductor substrate is inclined from the vertical direction. Bubbles generated on the lower surface of the semiconductor substrate may easily slip out upward, and the surface may be cleaned with high efficiency. The angle of the normal direction of the surface of the semiconductor substrate with respect to the vertical direction may be 10° to 80°. When the angle is less than 10°, bubbles may be retained on the surface facing downward in the vertical direction. When the angle exceeds 80°, bubbles generated on the lower portion of the surface facing upward in the vertical direction may pass in the vicinity of the surface and float up, resulting in occurrence of uneven cleaning. The inclination of the semiconductor substrate may be produced by the difference in height among the upper projections. Alternatively, the inclination of the semiconductor substrate may be produced by the differences in height among the upper projections and among the lower projections.
Before cleaning is performed, a cleaning apparatus may be subjected to ultraviolet treatment. Before a semiconductor substrate is placed in a cleaning apparatus, a carrier unit used for carrying the semiconductor substrate may be subjected to ultraviolet treatment. Before spin drying is performed subsequent to acid cleaning, a unit used for spin drying may be subjected to drying treatment.
The number of components included in a cleaning apparatus may be small. Components included in a cleaning apparatus may be integrated. When the number of components is large, foreign substances and the like that have fallen off owing to cleaning may remain in connections between the components, resulting in contamination of the semiconductor substrate.
A GaN-based HEMT fabricated using the cleaning apparatus described above may be used, for example, for a high-output amplifier.
A GaN-based HEMT fabricated using the cleaning apparatus described above may be used, for example, for a power supply device.
As illustrated in
As illustrated in
A PFC circuit may be used for a power supply device which operates at high speed, such as the server power supply 100 illustrated in
The substrate may be a silicon carbide (SiC) substrate, sapphire substrate, silicon substrate, GaN substrate, GaAs substrate, or the like. The substrate may be conductive, semi-insulating, or insulating.
The structure of the gate electrode, the source electrode, or the drain electrode may be, for example, single-layered. When ohmic characteristics are obtained, heat treatment after formation of the source electrode and the drain electrode may be omitted. The gate electrode may be subjected to heat treatment.
The cleaning apparatus described above may be applied to fabrication of a semiconductor device other than a GaN-based HEMT.
Example embodiments of the present invention have now been described in accordance with the above advantages. It will be appreciated that these examples are merely illustrative of the invention. Many variations and modifications will be apparent to those skilled in the art.
Claims
1. A method of manufacturing a semiconductor device comprising:
- holding a semiconductor substrate with a surface inclined with respect to the vertical direction and the horizontal direction; and
- immersing the semiconductor substrate in a cleaning solution including an acid.
2. The method of manufacturing a semiconductor device according to claim 1, further comprising,
- forming a compound semiconductor layer on the semiconductor substrate before holding the semiconductor substrate.
3. The method of manufacturing a semiconductor device according to claim 2, further comprising,
- forming a recess in the compound semiconductor layer before holding the semiconductor substrate.
4. The method of manufacturing a semiconductor device according to claim 3, further comprising,
- forming a gate-insulating film on the inner surface of the recess before holding the semiconductor substrate.
5. The method of manufacturing a semiconductor device according to claim 1, wherein the inclination angle with respect to the vertical direction is 10° to 80° and the inclination angle with respect to the horizontal direction is 10° to 80°.
6. The method of manufacturing a semiconductor device according to claim 1, further comprising,
- placing the semiconductor substrate in a cleaning apparatus which includes a supporting member for supporting the semiconductor substrate and a locking member for locking the semiconductor substrate inclined with respect to the vertical direction and the horizontal direction.
7. The method of manufacturing a semiconductor device according to claim 6, further comprising,
- rotating a case which houses the supporting member and the locking member.
8. The method of manufacturing a semiconductor device according to claim 6, further comprising,
- rotating a rotary driving member in contact with the semiconductor substrate.
9. The method of manufacturing a semiconductor device according to claim 6, further comprising,
- performing a ultraviolet treatment on the cleaning apparatus before the semiconductor substrate is placed in the cleaning apparatus.
10. The method of manufacturing a semiconductor device according to claim 6, further comprising,
- performing a ultraviolet treatment on a carrier unit for carrying the semiconductor substrate to the cleaning apparatus before the semiconductor substrate is placed in the cleaning apparatus.
11. The method of manufacturing a semiconductor device according to claim 1, further comprising,
- performing spin drying on the semiconductor substrate after an immersion of the semiconductor substrate.
12. The method of manufacturing a semiconductor device according to claim 11, further comprising,
- performing drying treatment on a unit used for the spin drying before spin drying of the semiconductor substrate.
13. A method of cleaning a semiconductor substrate comprising:
- holding a semiconductor substrate with a surface inclined with respect to the vertical direction and the horizontal direction; and
- immersing the semiconductor substrate in a cleaning solution containing an acid.
14. The method of cleaning a semiconductor substrate according to claim 13, wherein the inclination angle with respect to the vertical direction is 10° to 80° and the inclination angle with respect to the horizontal direction is 10° to 80°.
15. The method of cleaning a semiconductor substrate according to claim 13, further comprising,
- placing the semiconductor substrate in a cleaning apparatus which includes a supporting member for supporting the semiconductor substrate and a locking member for locking the semiconductor substrate inclined with respect to the vertical direction and the horizontal direction.
16. The method of cleaning a semiconductor substrate according to claim 15, further comprising,
- rotating the cleaning apparatus.
17. The method of cleaning a semiconductor substrate according to claim 15, further comprising,
- rotating a rotary driving member in contact with the semiconductor substrate.
18. A cleaning apparatus comprising:
- a supporting member to support a semiconductor substrate; and
- a locking member to lock the semiconductor substrate such that the semiconductor substrate is inclined with respect to the vertical direction and the horizontal direction.
19. The cleaning apparatus according to claim 18, further comprising,
- a rotary driving member to rotate the semiconductor substrate by rotating a case that houses the supporting member and the locking member.
20. The cleaning apparatus according to claim 18, further comprising,
- a rotary driving member, being in contact with the semiconductor substrate, to rotate the semiconductor substrate in the cleaning apparatus.
Type: Application
Filed: Feb 16, 2012
Publication Date: Aug 30, 2012
Applicant: FUJITSU LIMITED (Kawasaki-shi)
Inventors: Shirou OZAKI (Kawasaki), Masayuki Takeda (Kawasaki), Norikazu Nakamura (Kawasaki), Junichi Kon (Kawasaki)
Application Number: 13/397,837
International Classification: H01L 21/20 (20060101); B08B 7/00 (20060101); B08B 3/08 (20060101);