JP2846086B2 - Method for forming protective film of semiconductor device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a method for forming a protective film for a semiconductor device, and more particularly, to protection of an end face formed by etching in a semiconductor laser or the like and an end face of a groove of an optical coupler or the like. The present invention relates to a film forming method.

[Conventional technology]

Conventionally, as a method of forming a protective film on a processed end face formed by etching when manufacturing a semiconductor laser, as shown in FIG. 7, as shown in FIG. p), there has been a method of forming an oxide protective film of Al ₂ O ₃ , SiO ₂ , ZrO ₂ or the like by an EB vapor deposition method, a sputtering method, or the like. In addition, a sputtering method, a CVD method, or the like has been used for forming a protective film on an end face of a fine groove of a laser optical coupler or the like. However, when a protective film is formed after subdividing into a bar state, the wafer is liable to crack when the bar state is formed, causing damage to the wafer and deteriorating element performance. A protective film cannot be formed on the end face in the narrow slit-like groove. As shown in FIG. 7, when forming the protective film,
It has been common practice to form a protective film on one end face (FIG. 7 (q)), then invert the element and then form a protective film on the other end face (FIG. 7 (r)). However, there are problems in that the process is complicated, and that the protective film is formed by wrapping around portions other than the end faces.

In the case where the protective film is formed in a wafer state, it is difficult to form the protective film on the etched end face of the inverted mesa shape. A protective film is formed on the entire wafer, and it is difficult to form the protective film only on the etched end face (a). When there is a problem that protection cannot be formed on the end face in the narrow slit-like groove having a width of 0.5 μm or less, and the protection film cannot be formed on the end face in the fine groove, the end face is always exposed to the atmosphere. Due to the oxidation, the end face is liable to be deteriorated, which causes a problem that the durability of the element is poor.

[Problems to be solved by the invention]

The present invention has been made in view of the above circumstances, and an object thereof is to easily form a protective film on an end face in a wafer state without subdividing into a bar state, with a high yield, and to form an inverted mesa. It is an object of the present invention to provide a method for forming a protective film that can be formed on an end face and also on an end face in a narrow slit-like groove having a width of 0.5 μm or less without depending on the shape of the end face.

[Means for solving the problem]

The present invention has a layer made of a semiconductor material and a film made of an insulating material formed thereon, a semiconductor having a surface where the insulating material is exposed, and an end face or an end face of the groove where the semiconductor material is exposed. A method for forming a protective film of an element, comprising:
By a selective gas phase deposition method using a gaseous compound containing an element selected from Si and Ti as a reaction gas, a coating layer composed of the element is selectively formed on an end face or an end face of a groove where the semiconductor material is exposed. And then heat-treated in an oxygen-containing atmosphere at a temperature in the range of 200 ° C. to 700 ° C. to turn the coating layer into an oxide film, thereby forming a protective film of a semiconductor element. The present invention can be applied to the case where the slit is a semiconductor laser having the above, the end face is a mirror face of the semiconductor laser, and the groove or the end face is formed in part or all of the optical waveguide.

 Hereinafter, the present invention will be described in detail.

In the present invention, a desired device is formed on a semiconductor substrate of a semiconductor such as silicon or a compound semiconductor such as GaAs or InP, a coating layer is formed on a groove or an end face thereof, and then heat treatment is performed to oxidize the coating layer. In this case, a selective vapor deposition method is used to form the coating layer. In the selective vapor deposition method, a device layer is deposited on a device surface by placing a device in a reaction gas atmosphere and maintaining the device at a predetermined temperature. It is selectively deposited, and no coating layer is deposited on the portion where the insulating film exists (Japanese Patent Application No. 1-250021).

As the reaction gas, for example, (CH ₃ ) ₂ AlH, (C ₂ H ₅ ) ₂ Al
Alkyl aluminum hydrides such as H, (CH ₃ ) HAlH, SiH ₄ , Si ₂ H ₆ , Si ₃ H ₈ , Si (CH ₃ ) ₄ , SiCl ₄ , SiH ₂ Cl ₂ , SiHC
silicides of l _{3 etc., TiCl 4, TiBr 4, Ti} (CH 3) 4 or the like of the titanium compound, and mixtures thereof can be preferably used. The reaction temperature varies depending on the type, pressure and concentration of the reaction gas, but is generally preferably from 260 ° C to 450 ° C. At this time, the deposition time is 3000 ° to 5000 ° / min when the Al film is formed, so that the reaction time is about several seconds.

In the present invention, the film layer formed by the selective vapor deposition method is heated in an oxygen atmosphere, and the film layer is oxidized to form a stable protective film. Heating temperature is usually 200
At ~ 700 ° C, the heating time is about 0.5-10 hours. As a heating method, heating using a halogen lamp or the like or heating means using various heating elements can be used.

The protective film formed as described above is chemically and mechanically stable, and is preferable as a protective film on the end face of the semiconductor device.

 Hereinafter, the present invention will be described more specifically with reference to examples.

Embodiment 1 In this embodiment, a case of manufacturing a protective film for a resonance surface of a semiconductor laser will be described with reference to FIG.

First, on the n-type GaAs substrate 21, 1 μm of n-type GaAs was formed as the buffer layer 22 and 2 μm of n-type Al _0.4 Ga _0.6 As was formed as the cladding layer 23 by the molecular beam evitaxy method. As the active layer 24, 100% non-doped GaAs, Al _0.2 Ga _0.8 A
s was repeated 30 times four times each, and GaAs was finally stacked at 100 degrees to form a multiple quantum well structure. Next, 1.5 μm of P-type Al _0.4 Ga _0.6 As is used as the cladding layer 25, and G is used as the cap layer 26.
0.5 μm of aAs was formed.

Next, SiO ₂ was laminated as an insulating film 27 on the cap layer 26, and then the laminated insulating film 27 was patterned by a photolithography process. Next, etching was performed in a Cl ₂ gas atmosphere to a position close to the substrate 21 (2 μm or more) by a reactive ion beam etching method to form an end face 28, thereby forming a laser resonance face 29 (FIG. 1A). ).

Next, a coating layer 30 was formed on the etched surface (end face 28) of the wafer formed as described above by a selective vapor deposition method. In other words, put the wafer on the Al vapor phase growth chamber, a dimethylaluminum hydride gas H ₂
Together with a slow leak valve to reduce the total pressure to approximately 1.
5 Torr, dimethyl aluminum hydride partial pressure approximately 5.0
× 10 ⁻³ Torr. When the temperature in the chamber is kept at 290 ° C for 2 seconds, only the etched end surface 28 where no insulating film exists
The Al coating layer 30 grew, and its thickness became about 100 ° (FIG. 1 (b)). Further, the wafer on which the coating layer 30 was formed was heated at 400 ° C. for 120 minutes in an oxygen atmosphere to oxidize the Al coating layer 30 to obtain an Al ₂ O ₃ protective film 31 (FIG. 1 ( c)).

In the present embodiment, when forming the end face 28,
Although a dry etching method is employed, a wet etching method may be employed, and according to the present method, a protective film can be formed even on the etching end face 28 of an inverted mesa 45 ° mirror as shown in FIG.
31 can be formed.

Embodiment 2 In this embodiment, an interference laser having a cross-shaped resonator is manufactured. FIG. 3 is a plan view of the laser, and FIGS. 4 and 5 show cross-sectional views in the directions of arrows AA and BB in FIG. In the manufacture of the laser, first, a first clad layer 2, an active layer 3, a second clad layer 4, and a cap layer 5 are formed on a substrate 1 made of a silicon wafer in FIG. 4 by molecular beam epitaxy (MBE). Epitaxial films are grown sequentially. At the interface with the substrate 1
A buffer layer made of GaAs may be formed. The thickness of the first and second cladding layers 2 and 4 is 1 μm, and the thickness of the active layer 3 is about 0.1 μm.
μm. Next, an SiO ₂ film (not shown) was formed on the cap layer 5 by a sputtering method. Subsequently, a cross-shaped pattern having a width of 3 μm was formed thereon by photolithography, and a ridge portion 8 was provided by reactive ion beam etching to form a stripe structure for confining lateral light. After that, G with acceleration voltage of 40 KeV
By FIB (focused ion beam method) using a ⁺ ion
The slit groove 12 of the coupler section 11 and the mirror section shown in FIG.
The slit grooves 14a and 14b of 13a and 13b were formed. As shown in FIG. 5, the depth of the slit groove 12 of the coupler portion 11 is
And the slit grooves 14a and 14b of the mirror portions 13a and 13b were etched deeper beyond the active layer 3. The slit grooves 12, 14a, and 14b were processed so that each end face angle was 85 ° or more near the active layer 3. The above coupler forms a wavefront splitting type branching coupler, and by controlling the position at the bottom 15 of the slit groove 12 in the active layer 3, the efficiency of transmission and reflection of guided light can be set to a desired value. It is. For example, by setting the position of the bottom 15 near the center of the light intensity distribution of the guided light in the active layer 3, the transmission and reflection ratios of the guided light can be made substantially equal.

In this embodiment, an Al protective film is formed on the end face of the device by using the wafer on which the device is formed as described above. In this case, the vapor phase growth apparatus to be used is not particularly limited. However, as shown in FIG. 6, it is preferable to use a chamber provided with a vacuum chamber and capable of generating plasma. That is, in FIG. 6, reference numeral 40 denotes a load lock chamber, and the elements are put in and out of the reaction chamber 41 through this chamber 40.
The inside of the load lock chamber 40 can be reduced in pressure by closing the gate valves 42 and 43 and operating the exhaust system 44.
Next, the wafer stored in the load lock chamber 40 is moved to the reaction chamber 41 through the gate valve 43. By supplying hydrogen gas to the reaction chamber 41 through the gas line 45, the inside of the reaction chamber 41 becomes a hydrogen atmosphere. After that, by operating the exhaust system 46, the inside of the reaction chamber 41 becomes approximately 1 × 10 ⁻⁸ Torr. Note that the Al coating layer grows even if the degree of vacuum in the reaction chamber 41 is higher than 1 × 20 ⁻⁸ Torr. Next, DMAH in a dimethylaluminum hydrate (DMAH) supply chamber 47 as a reaction reagent is introduced into the reaction chamber 41 together with H ₂ through a gas introduction line 48. The pressure in the reaction chamber 41 is adjusted by adjusting the opening of a slow leak valve (not shown) provided in the line 48 (in this embodiment, the pressure in the reaction chamber is 1.5 Torr, and in this case, the partial pressure of DMAH is (Approximately 5.0 × 10 ⁻³ Torr). In this state, when the halogen lamp 49 is turned on and the wafer 50 is directly heated, the Al coating layer is deposited only on the portion of the wafer 50 where there is no insulating film. At this time, the temperature of the wafer was 270 ° C. After the Al is deposited to a thickness of 200 mm, the exhaust systems 46 and 44 of the reaction chamber 41 and the load lock chamber 40 are provided.
Thus, the pressure in both chambers 41 and 40 was reduced to a vacuum of 5 × 10 ⁻⁶ Torr or less. After confirming that both the chambers 41 and 40 reached the above-mentioned degree of vacuum, the wafer 50 was transferred to the load lock chamber 40, and then the wafer 50 was taken out.

Next, the wafer having the Al coating layer formed on the surface as described above was heated in an oxygen atmosphere to oxidize the Al coating layer to form a protective film. That is, in this embodiment, the wafer was kept at 600 ° C. for 120 minutes in an oxygen atmosphere. As a result, the Al coating layer was oxidized, and a strong Al ₂ O ₃ protective film 26 was formed.

Thereafter, the SiO ₂ film was removed by reactive etching (RIE) in a CF ₄ gas atmosphere, then a silicon nitride film 10 was deposited by a plasma CVD method, and a window was formed above the ridge 8 by the RIE method. Further, the upper electrode 7 is formed by a vacuum evaporation method.
Was formed as a Cr-Au ohmic electrode. Then GaAs
The substrate 1 was scraped to a thickness of 100 μm by lapping, and an Au—Ge electrode was deposited as an n-type ohmic electrode 6.

Subsequently, after performing heat treatment for making ohmic contact with the P-type and N-type electrodes, the resonance surface was formed by cleavage, separated by scribing, and the electrodes were taken out by wire bonding.

In the cross-shaped laser resonator structure, a kind of Michelson-type interferometer is formed, so that a composite resonator mode is formed and the oscillation wavelength can be stabilized. In the present embodiment, since the protective film 16 is formed on the end faces of the slit grooves 14a, 14b, 12 of the mirror portions 13a, 13b and the coupler portion 11, the life (durability) of the element is greatly improved, and the element performance is further improved. Stabilized.

The interference laser having the above-described cross resonator is described in J. Salzman et al: “Cross copuled cavity s”.
emiconductor laser "Appl.Phys.Lett. 52, 10 , pp.767~76
9 (March, 1988).

In the above embodiment, the active region is formed by MQW (multiple quantum well structure). However, the present invention is not limited to this, and may have a DH structure, SQW structure or the like.

In the above embodiments, the ridge wave type structure using GaAs was described as an example.
The present invention is also effective for a refractive index guided laser such as a structure in which an absorption layer for constricting current light is provided near an active layer. In addition, it goes without saying that the material of the semiconductor laser can be similarly applied to materials such as InP / InGaAsP and AlGaInP other than GaAs / AlGaAs.

〔The invention's effect〕

As described above, according to the present invention, a protective film can be formed on an etched end face in a wafer state.

A protective film can be easily formed on the etched end face in the reverse mesa state.

A protective film can also be formed on the end face of the fine groove of 0.5 μm or less.

In addition, the process is very easy, the yield and the reproducibility are good, and the life of the semiconductor device is greatly extended. Therefore, the present invention is particularly effective when applied to the manufacture of an integrated device having a slit portion such as an optical branching coupler.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view for explaining a step of manufacturing a laser device by the method of the present invention, FIG. 2 is a cross-sectional view of an inverted mesa device, and FIG. 3 is a plan view of an interference semiconductor laser according to the method of the present invention. , FIGS. 4 and 5 are arrows AA and B- in FIG. 3, respectively.
FIG. 6 is a schematic configuration diagram showing an example of a vapor phase growth apparatus used for carrying out the present invention, and FIG. 7 is an explanatory view showing a conventional semiconductor manufacturing process. DESCRIPTION OF SYMBOLS 1 ... board | substrate, 2 ... 1st cladding layer, 3 ... Active layer, 4 ... 2nd cladding layer, 5 ... Cap layer, 6 ... Electrode, 11 ... Coupler part, 12 ... Slit groove, 13a, b Mirror part, 14a, b Slit groove 16 Protective film, 21 Substrate 24 Active layer 28 End face 29 Resonant surface 30 Coating layer 31 … Protective film, 40… Load lock chamber, 41… Reaction chamber, 47… Supply chamber, 49… Halogen lamp, 50… Wafer.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01S 3/18

Claims (5)

(57) [Claims] 1. A semiconductor device comprising: a layer made of a semiconductor material; and a film made of an insulating material formed thereon, wherein a surface where the insulating material is exposed, and an end face or an end face of the groove where the semiconductor material is exposed. A method for forming a protective film of a semiconductor device, comprising: A
l, a coating layer made of a gaseous compound containing an element selected from Si and Ti by a selective gas phase deposition method using a reactive gas as a reaction gas, on the end face or the end face of the groove where the semiconductor material is exposed. Forming a protective film on a semiconductor element by selectively forming the film and then performing a heat treatment in an oxygen-containing atmosphere at a temperature in the range of 200 ° C. to 700 ° C. to make the film layer an oxide film. 2. The method according to claim 1, wherein the groove is a slit of a semiconductor laser having an optical waveguide. 3. The method according to claim 1, wherein the exposed end surface of the semiconductor material is a mirror surface of the semiconductor laser. 4. The method according to claim 2, wherein the exposed end face of the semiconductor material or the end face of the groove is formed on at least a part of the optical waveguide. 5. The heat treatment time is 0.5 to 10 hours.
5. The method for forming a protective film of a semiconductor device according to any one of claims 1 to 4.