JPS6387722A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To facilitate forming an unlimited selective contact region by a method wherein a plurality of molecular beams are applied to a substrate along a plurality of directions and a mask is used so as to prevent at least one molecular beam from being applied to at least a part of a layer to be made to grow by epitaxy. CONSTITUTION:A shadow mask 13 shields a part of a molecular beam 12 and defines a region where epitaxial growth is to be performed on a substrate 11. An n-type dopant source is so arranged as to generate a beam 15 which enters the substrate 11 and a p-type dopant source is so arranged as to generate a beam 16 which enters the substrate 11. The mask 13 shields an epitaxial layer from the beam 15 in 1st region 17 and shields the epitaxial layer from the beam 16 in 2nd region 18. The beams 15 and 16 are controlled to be turned ON and OFF so as to make an N-I-P-I super-lattice structure grow in a region 19. With this constitution, a selective contact region which contacts the N-I-P-I super-lattice structure can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention relates generally to a novel method for manufacturing semiconductor devices, and more particularly to the production of selective contacts to NIPI-doped superlattice structures using molecular beam epitaxial growth. Regarding the manufacturing method.

[Prior art and its problems]

The general theory of superlattices is 5 scientific Ame
"5QLID-8TATE 5UPERL" disclosed in rican's November 1983 issue, pages 144-151
Tottfried H,D titled “ATTICES”
This is shown in the paper by Oeler. Superlattices are of interest because they have interesting electro-optical properties that can be tuned by selecting the parameters of the superlattice.

Superlattices include synthetic superlattices (also called heterostructure superlattices).
There are two types: doped superlattice and doped superlattice.

A composite superlattice is an alternating periodic arrangement of extremely thin layers of two different semiconductors. Since each layer is less than a few hundred atoms thick, there is fleeting interaction between adjacent layers. The compositions of the two layers are chosen such that the layers have compatible lattice structures and such that the bandgap of one layer is not equal to the bandgap of the other layer. The effect of this is that the bottom of the conduction band presents a potential well for electrons in each small bandgap layer and a potential barrier for electrons in each small bandgap layer. Similarly, the top of the valence band exhibits a periodic array of potential wells for holes. One such superlattice consists of alternating repeating layers of GaAs and AI G5As. These potential wells separate the conduction band into a series of small bands and influence the electrical-optical properties of the superlattice.

The doped superlattice consists of n-doped layers and alternating repeats of n-doped layers in the substrate. These doped layers can (but do not have to) be separated by a layer of undoped (intrinsic) substrate. This doped superlattice is NIP
Also called I superlattice.

The periodicity of the superlattice results in periodic changes in the bottom of the conduction band and the top of the valence band due to the diffusion of electrons from the n-type layer to the p-type layer and the diffusion of holes from the p-type layer to the n-type layer. A significant charge change occurs, which results in a periodic array of potential wells similar to the synthetic superlattice described above. Moreover, this causes separation of holes and electrons, which greatly increases the recombination time between electrons and holes. When excited optically or electrically, a large number of extra holes and electrons are produced,
It flattens the periodic potential and also increases the effective bandgap of the superlattice (defined as the distance between the bottom of the conduction band and the top of the valence band) from the superlattice's ground state. do. Electrical and optical properties can be changed by changing the number of holes and free electrons in the superlattice. To achieve this by electrical excitation, it is necessary to make a pair of selective contacts. The first selective contact is required to form a low impedance ohmic contact to the n-doped layer but not to the n-doped layer, and the second selective contact is required to form a low impedance ohmic contact to the n-doped layer but not to the n-doped layer. It is necessary to form an impedance ohmic contact.

Currently, selective contacts for n-type and p-type layers are achieved by depositing small tin (sn) balls and small tin/zinc (Sn/Zn) poles on the surface of the superlattice, respectively, and then annealing the superlattice. are formed by diffusing these poles into the superlattice.

Ru. The diffused Sn and Zn atoms create heavily n-doped and p-doped regions under the surface of the superlattice, thereby forming first and second selective contacts, respectively. Unfortunately, these selective contacts are far from ideal. Because the ball dimensions vary, reproducible results cannot be obtained. Since the deposited poles are extremely large on the scale of current integrated circuit structures, the contacts formed are similarly large, making this process unsuitable for scaling. These large contact surface areas result in large leakage currents and high recombination rates due to the bandgap conditions at the interfaces of these contacts and the superlattice.

This undesired non-radiative recombination at selective contacts results in very low luminous efficiency at room temperature. FIG. 3A is a schematic diagram of a NIPI superlattice with selective contacts according to the prior art, and FIG. 3B is an equivalent circuit of the structure shown in FIG. 3A.

[Purpose of the invention]

SUMMARY OF THE INVENTION The present invention provides a method for manufacturing a semiconductor device that can form selective contacts that are not limited by the above-mentioned problems.

[Summary of the invention]

In one embodiment of the present invention, a fabrication method is provided that allows fabrication of NIPI superlattices with selective contacts in place. - a set of sources provides a set of molecular beams which are used to grow the bulk material of the superlattice and to provide the dopants necessary to form the n-doped and p-doped regions; be done. A shadow mask is placed between the dopant beam and the substrate on which the NIPI superlattice is generated. A shadow mask shields a first region of the substrate from the n-dopant and also shields a second region of the substrate from the n-dopant. 1st, 2nd
Between the regions is a third region into which the n-dopant and both the n-dopants are incident.

As the bulk material is deposited on the substrate, the n-dopant beam and the n-dopant beam are controllably turned on and off to form a NIPI superlattice in the third region.

Because of the shadow mass, each n-doped layer extends into the first region but not the second region, and each n-doped layer extends into the second region.
region but not the first region. therefore,
The first region will contain the PIPI structure and the second region will contain the NINI structure. A first conductor is formed in contact with the NINI layer and forms a first selective contact to the n-doped layer of the NIPI superlattice. Similarly, a second conductor is formed in contact with the PIPI layer to form a second selective contact to the n-doped layer of the NIPI superlattice.

These selective contacts are superior to the selective contacts in the prior art described above. FIG. 3A shows a schematic diagram of selective contact according to the prior art. The equivalent circuit for these contacts is shown in Figure 3B. Similarly, a schematic diagram of the selective contact of FIG. 2 according to the present invention and its equivalent circuit are shown in FIGS. 4A and 4B, respectively.

the first conductor is separated from the n-doped layer by an intrinsic region;
Also, because the second conductor is separated from the n-doped layer by an intrinsic region, the equivalent circuit of FIG. 4B does not have the leaky pn junction present in FIG. 3B.

The shadow mask can be made of several materials, but should have the following properties: To avoid introducing contaminants during the manufacturing process, the mask material must not outgas in the ultra-high vacuum systems used in molecular beam epitaxy (MBE) systems. The mask must also withstand high temperatures (up to 1ooo°C),
It must not be fragile and must be easy to clean to remove impurities before use in an MBE system.

This shadow mask technique has much greater versatility than producing selective contacts to the NIPI superlattice. The NIPI structure described above with one selective n-type contact and one selective p-type contact can be fabricated with a shadow mask with one rectangular opening. A NIPI structure with two n-type selective contacts and two p-type selective contacts is placed with a mask having a cross-shaped opening to form two NINI regions and two PIPI regions.
It can be manufactured using a plurality of n-type sources and p-type sources. Similarly, a combination of multiple sources and appropriately shaped shadow masks can be used to fabricate a NIPI photodetector array. In this case, the central rectangular NIPI structure is used to detect light, and the NINI region and PIPI
Alternating regions are connected to the sides of the NIPI structure and span the length of the detector region to create selective n-type, p-type contacts. Other structures that can be fabricated include optical waveguides with strongly laterally confined lateral heterostructures and spatially separated n-type, p-type for three-terminal or more electronic devices.
There are bipolar or heterojunction bipolar transistors with shaped contacts.

〔Example〕

FIG. 1 shows a method of fabricating a NIP-doped superlattice with selective contacts in place. A NIPI superlattice is grown on the substrate 11 by molecular beam epitaxy. The terms "molecular beam epitaxy" and "molecular beam" are to be understood herein to include not only molecular beams, but also atomic and ion beams. These beams are provided by a source located far enough away from the substrate that each beam is substantially collimated at the substrate 11. The bulk material of the NIPI superlattice is provided by one or more molecular beam sources (depending on the choice of bulk material). These sources (not shown) provide a molecular beam 12 that is incident normal to the top surface of the substrate 11.

The shadow mask 13 blocks a part of the molecular beam 12,
This defines where epitaxial growth will occur on substrate 11. This results in a bitaxially grown layer 14 having approximately the same shape and dimensions as the opening 110 of the mask 13. Further, in FIG. 1, the epitaxial growth width W is approximately equal to the width of the opening 110. An n-type dopant source is arranged to produce a beam 15 that is incident on the substrate 11, and a p-type dopant source is arranged to produce a beam 16 that is incident on the substrate 11. These radiation sources are arranged such that the mask 1° 3 shields the epitaxial layer 14 from the beam 15 in a first region 17 and from the beam 16 in a second region 18 . Neither beam 15 nor beam 16 is projected from layer 14 in third region 19 . The boundary between regions 17 and 19 is determined by a line A parallel to beam 15. Similarly, the boundary between region 18 and region 19 can be determined by line B parallel to beam 16.

Beams 15 and 16 are controllably turned off during turn-on so that a NIPI superlattice is grown in region 19.

Figure 2 shows N produced by the process shown in Figure 1.
FIG. 2 is a cross-sectional view of an IPI structure.

This NIPI superlattice has two n-doped layers 21, two n-doped layers 22 and three intrinsic layers 23. In region 17 a PIPI structure occurs, and in region 18 a NINI structure occurs. Conductors 24 and 25 each
and 18, thereby
Selective contact is made from conductor 24 to the p-type layer in the NIPI superlattice, and from conductor 25 to the n-type layer in the NIPI superlattice. Because the intrinsic regions separate conductor 24 from the n-type layer within the NIPI superlattice and conductor 25 from the p-type layer, these selective contacts provide negligible leakage currents and The contribution to electron-hole recombination is negligibly small.

Shadow mask materials should be chosen to avoid introducing contaminants into the manufacturing process. Thus, the shadow mask should withstand high temperatures, should not be fragile or brittle, should be small enough to be completely polished, and should not generate gases at the extremely low pressures of the MBE process. Must not be. Silicon is a suitable choice. It is inexpensive and available in silicone wafer binding. It is also known as piranha
) solution (H2804: H2O2 = 5: 1)
It can be thoroughly scrubbed by soaking in water for about 20 minutes and then soaking in concentrated HF for about 15 seconds to remove the thin layer of 5i02 produced by the piranha soak. Additionally, techniques for accurately etching silicon wafers are well known.

The dimensions of the regions that are selectively masked from some of the molecular beams are typically small enough to allow the shadow mask to make actual contact with the substrate on which MBE growth occurs. In fact, depending on the geometry, the wafer thickness is reduced in the areas where openings need to be made to form the mask, as typical silicon wafers are small enough to be as thick as desired (300μ or so). There is a need.

Alternatively, the mask can be etched twice to produce a reduced effective height by producing an edge profile as shown in FIG. 7 rather than FIG. 6C.

The NIPI superlattice shown in the drawings can be manufactured using a mask with rectangular openings 110. However, other more complex structures can also be fabricated by this shadow mask fabrication process using more complex apertures and more complex molecular beam source arrays. Figures 5A-5D show a NIPI with two selective n-type contacts and two selective p-type contacts.
A suitable process for forming the structure is shown. This process uses a mask with cross-shaped apertures. 5th A
Figures 5A and 5B show top and side views, respectively, of an array of molecular beam sources.

FIG. 5C shows a side view of the shadow mask along a line through one leg of the cruciform aperture.

FIG. 5D shows a top view of the formed NIPI superlattice, NINI region and PIPI region. A NIPI superlattice is formed in region 51 where the substrate is exposed to all dopant beams. Regions 52 and 53 are exposed by both Si beams but not by either Be beam, so a NINI superlattice is formed in these regions. In regions 54 and 55, the substrate has only one S
As exposed by the i-beam, the lightly doped NI
A NI superlattice is formed in these regions.

The placement of the As source results in AS exposure of the substrate in the areas exposed to Ga atoms and in larger areas. Thus, GaAs grows on the substrate over the areas exposed by the GaAs atoms, thereby reproducing the shape of the mask.

6A-6D, a process suitable for manufacturing NIPI superlattice photodiode arrays is shown. 6A shows a top view of the molecular beam source, FIG. 6B shows a top view of the shadow mass, and FIG. 6C shows a top view of the molecular beam source along the lines shown in FIG. 6B. A side view of the shadow mask is shown. The mask aperture includes a rectangular section 61 under which the NIPI detector is formed.

Along both sides of the rectangular portion 61, a periodic array of rectangular grooves separated by rectangular opaque areas 63 are symmetrically arranged. Since the Be source provides a beam approximately perpendicular to the mask and substrate, the regions below regions 61 and 62 are controllably exposed by Be atoms.

In the Si source, each part of the substrate directly under regions 61 and 63 is made of Si.
Arranged to be exposed by atoms. thus,
A NIPI photodetector is formed directly under region 61, and the PIP
I contact regions are formed under each region of region 62 and NIN
An I contact area is formed under each area of region 63. An ohmic n-doped contact is formed in each NINI region and an ohmic n-doped contact is formed in each PIPI region. The completed photodiode array is shown in Figure 6D.

The composition of the bulk material grown by this MBE method can be varied by varying the component beams in addition to varying the dopant [1 degree]. For example, selective contact can be used for lateral implantation into the central undoped region of a lateral double heterostructure grown by shielding one of the component beams.

This allows surface-emitting vertical and horizontal double heterostructure lasers to be formed by this manufacturing method.

8A and 8B, a shadow mask process for manufacturing a three terminal bipolar (or heterojunction bipolar) transistor is shown. Figure 8A shows the structure formed by this shadow mask process.

In Figure 8A, this structure has been etched to form a mesa with three contacts formed.

In FIG. 1, the n-dopant and p-dopant beams were chosen to overlap so that a NIP' region was formed between the NINI and PIPI regions. In another aspect, the beams can also be selected to be non-overlapping. In this case, the undoped (intrinsic) region
A NINI region separate from the region will be formed.

Such a configuration can be used to fabricate a PIN diode and also to fabricate the structure of FIG. FIG. 9 shows a shadow mask manufacturing process suitable for manufacturing waveguides. In this process, 2
The two leftmost sources produce parallel beams that do not overlap at the substrate with the parallel beams produced by the two oldest sources. Regions 91 and 95 are comprised of an undoped material having a higher bandgap than the material of region 94. areas 92 and 9
3 is made of a higher bandgap doped material than the material of region 94. This results in a lower index of refraction in region 94 than in the other four regions, so that the structure acts as a strongly confined waveguide in both the vertical and horizontal directions.

〔Effect of the invention〕

As is clear from the above explanation, in the present invention, molecular beam epitaxial growth and a shadow mask are combined,
Certain portions of the substrate are shielded from being irradiated by some of the molecular beams. This creates selective contact areas to the NIPI superlattice structure. According to the manufacturing method of the present invention, it is possible to manufacture an element that has no leakage current, is suitable for miniaturization, and has less electron-hole recombination. Moreover, m types of devices can be manufactured by selecting and controlling the molecular beam source and selecting the shadow mask.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a method for manufacturing a semiconductor device according to the present invention, FIG. 2 is a diagram showing an example of a semiconductor device manufactured by the method shown in FIG. 1, and FIG. 3B is an electrical equivalent circuit diagram of the device shown in FIG. 3A, FIG. 4A is a schematic diagram of the semiconductor device shown in FIG. 2, and FIG. 4B is an electrical equivalent circuit diagram of the device shown in FIG. 4A. equivalent circuit diagram,
5A to 5D are diagrams showing other embodiments of the method of manufacturing a semiconductor device of the present invention, and FIGS. 6A to 6D are diagrams showing a NIPI superlattice photodiode and a semiconductor device manufactured by the method of the present invention.
7 is a diagram showing the edge of a shadow mask deformed to reduce the effective height of the shadow mask, and FIGS. 8A and 8B are diagrams illustrating a method of manufacturing an array according to the manufacturing method of the present invention. FIG. 9 is a diagram showing a method for manufacturing a bipolar or heterostructure bipolar transistor, and FIG. 9 is a diagram showing a method for manufacturing a waveguide having a horizontal and vertical heterostructure using the manufacturing method of the present invention. Applicant Yokogawa Neylett-Packard Co., Ltd. Agent Patent Attorney Tsuguo HasegawaFIG 5C FIGS Kuchim Y e

Claims (1)

[Claims] In order to form an epitaxially grown layer on a substrate, a plurality of molecular beams are irradiated onto the substrate along a plurality of directions, and at least one molecular beam among the plurality of molecular beams is epitaxially grown. A method of manufacturing a semiconductor device, comprising using a mask so that at least a portion of the semiconductor device is not irradiated.