JPS6138630B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a light receiving element, and in particular, a method for manufacturing a light receiving element that reduces variations in spectral sensitivity characteristics, junction capacitance, etc. between light receiving elements manufactured from the same large wafer produced by vapor phase epitaxy. It is about the method. As is well known, a photodiode using a pn junction extracts carriers excited in the crystal by incident photons using the internal electric field of the junction. At this time, the wavelength range of light that can be detected by a photodiode is closely related to the forbidden band width because it usually utilizes optical absorption from the valence band to the conduction band, and its long wavelength edge (λc) is λc [μm]
It is determined by = 1.24/Eg [eV]. On the other hand, the detection sensitivity on the short wavelength side depends on the absorption coefficient and reflectance of the substrate crystal.
Many parameters such as minority carrier diffusion length, surface recrystallization rate, device structure (for example, impurity distribution, pn junction depth) are intricately related, and it is generally difficult to obtain the desired spectral sensitivity. Visible light receiving diodes using −V group compound semiconductor crystals such as GaAs _1-x P _x are low-cost,
For reasons of mass production, epitaxial wafers (hereinafter referred to as epi wafers) that are mass-produced using the vapor phase growth method are generally used, and epitaxial wafers are grown using the ion implantation method or thermal diffusion method.
-We form n-junctions and manufacture light-receiving elements. In this case, large variations occur in light-receiving device characteristics such as spectral sensitivity characteristics and junction capacitance among devices manufactured under the same pn junction formation conditions on one large wafer. For this reason, it is not possible to estimate the characteristics of other elements fabricated on the same wafer from the characteristics of randomly selected elements, and element selection takes time, leading to an increase in production costs. For example, in the case of large epitaxial wafers fabricated using low-cost vapor phase epitaxy, the impurity concentration contained in the growth gas flows locally non-uniformly, resulting in variations in junction capacitance, carrier concentration, etc. in each part of the wafer. I end up. This situation is shown in FIG. 1 and Table 1.

[Table] However, in Table 1, the junction capacitance was measured at zero bias, in the dark, and at a measurement frequency of 1KHz. Further, FIG. 1 shows the measurement locations corresponding to Table 1, and is a diagram showing the carrier concentration in each part of the wafer when normal vapor phase growth is performed on a large wafer with a width of 50 mm and a height of 40 mm. As is clear from Figure 1, the carrier concentration n at the bottom side of the growth tube with respect to the growth gas flow is
〓4.0×10 ¹⁶ cm ^-2 , n on the vertex side 〓 6.5 ^× 10 ¹⁶ cm ^-2 at the center 〓 5×10 ¹⁶ cm ^-2 , n on the right side of the center 〓 5.5 × 10 ¹⁶ cm
^-2 On the left side of the center, n = 6.0 × 10 ¹⁶ cm ^-2 , which means that the carrier concentration in the wafer differs by a factor of 1.6 between the bottom side and the top side of the growth tube. Furthermore, FIG. 2 is a diagram showing variations in the spectral sensitivity characteristics of light receiving diodes fabricated using this epitaxial wafer under the same pn junction fabrication conditions. However, the conditions for creating a p-n junction are Zn ⁺ at 70KeV and 10 ¹⁴ cm ^-2
After ion implantation and coating with approximately 3000Å of _SiO2 ,
A p-n junction was created by heat treatment at 750°C for 30 min in _N2 airflow. In FIG. 2, A shows the sensitivity characteristics of the element on the bottom side where the carrier concentration is low, and B shows the sensitivity characteristics of the element on the top side where the carrier concentration is high. As is clear from this figure, element A with a low carrier concentration exhibits high long-wavelength photosensitivity, while element (B) with a high carrier concentration exhibits characteristics with suppressed long-wavelength photosensitivity. Spectral sensitivity characteristics differ greatly between light receiving elements fabricated from wafers. The present invention has been made in view of the above-mentioned drawbacks, and by appropriately selecting the carrier concentration of the substrate used, parameters that cause various spectral sensitivities to vary can be controlled to obtain desired spectral sensitivity characteristics. . Since the ion implantation method can sufficiently control the amount of impurities introduced, it has a significant advantage in controlling the impurity concentration within the wafer surface and in the depth direction. On the other hand, when using a semiconductor substrate with a large absorption coefficient such as a GaAs _1-x P _x visible light receiving diode, most of the incident light is absorbed in a very shallow surface layer of about ₁ μm or less It is necessary to sufficiently control the carrier concentration in the shallow surface layer. Ion implantation is a method that fully satisfies this requirement.
It is possible to sufficiently control the distribution of carrier concentration in the plane and in the depth direction. The present invention utilizes the merits of this ion implantation method to inject large epitaxial wafers of the same conductivity type (p-type or n-type) as the epitaxial wafer with a relatively low carrier concentration, which is formed on a semiconductor substrate with a high concentration of impurities. By introducing impurities by ion implantation and forming an ion-implanted layer approximately 0.1 μm to 1 μm below the substrate surface with a uniform carrier concentration distribution in the plane and in the depth direction, parameters that cause variations in spectral sensitivity can be reduced. control to obtain desired spectral sensitivity characteristics. The present invention will be described below with one embodiment. Low carrier concentration (n = 5 × 10 ¹⁵ cm ^-3 ) was grown by vapor phase growth on a high concentration GaAs substrate by a conventional method.
After lightly removing the surface layer _of a GaAs _0.68 P _0.38 large Epee wafer with an etching solution, thoroughly wash _it with pure water. Next, on the GaAs _0.68 P _0.38 epitaxial wafer, S ⁺ , an impurity of the same conductivity type (N _type ) as this wafer, was injected at 7×10 ¹³ cm ^-2 at 200 KeV _and 3×10 ¹³ cm ^-2 ions at 70 KeV. inject. Then, after coating about 2000-3000Å of sio ₂
Heat treatment is performed at 750°C for 30 minutes in an N ₂ stream to form an N-type layer with a higher substrate concentration than that of the epitaxial wafer in a surface layer of about 0.4 μm. Furthermore, the SIO ₂ film was then opened into a planar pattern using a photoetching method.
50KeV Zn ⁺ was injected at 1×10 ¹⁴ cm ^-2 , and after another SIO ₂ film coating, heat treatment was performed at 750℃ for 30 minutes in N ₂ gas to form a p-n junction, and a 1.05 mm ² photodiode was formed. was created. In order to measure the variations in large-sized vapor-phase growth substrates produced by the method of the present invention, three chips each were selected from the bottom, top, center, left and right sides of the center and mounted on a stem. Table 2 shows the junction capacitance of each part at zero bias.

[Table] As is clear from Table 2, the photodetector produced by the method of the present invention has much less variation than the conventional one (Table 1), and the variation in bonding amount is 1/5. It is as follows. In addition, the spectral sensitivity characteristics are shown in Figure 3 (A is the spectral sensitivity characteristic of the photodiode manufactured from the center of the wafer, and B is the spectral sensitivity characteristic of the photodiode manufactured from the center of the wafer). The carrier concentration distribution of the photodiode created is shown. However, A is a low concentration carrier substrate (n-type layer: first semiconductor layer), and B is a higher concentration n-type layer formed in the present invention.
Type thin layer (second semiconductor layer), C is P type layer (third and fourth semiconductor layer) formed by ion implantation method
It is. Note that this fourth semiconductor layer is a thin layer with a high carrier concentration, and serves to reduce the contact resistance with the electrode metal. In the above example, after S ⁺ implantation, heat treatment was performed in a _N2 stream at 750°C for 30 minutes to form an n-type high concentration layer, but Zn ⁺ was implanted following S ⁺ implantation. Even when heat treatment was performed at 750°C for 30 minutes after SIO ₂ coating, the variation among each element in spectral sensitivity characteristics was small, and effects comparable to those on the above side were obtained. As explained in detail above, in a p-n junction photodiode, an n-type substrate with a low carrier concentration (the same conductivity type as the substrate that becomes the light-receiving layer on a large epitaxial wafer) is used to sufficiently control the carrier concentration in the plane and in the depth direction. By forming a thin layer with a higher concentration using the ion implantation method, and forming a p-n junction on and inside this thin layer using the ion implantation method, it is possible to connect devices fabricated from the same large wafer. Therefore, even if a large epitaxial wafer, which is fabricated by normal vapor phase growth and has in-plane carrier concentration variations, is used, the variations between photodiode elements can be reduced. It is possible to reduce the cost increase due to element selection.In addition, the ion implantation method is extremely superior in forming a thin layer with a higher concentration than the substrate, and it is possible to form an n-type high concentration layer at the same time as the p-type layer. The method of the present invention is applicable not only to pn junction type photodiodes but also to shot key barrier type photodiodes.

[Brief explanation of the drawing]

Figure 1 shows the variation in carrier concentration within the plane of a large epitaxial wafer fabricated using a conventional vapor phase growth method, and Figure 2 shows the spectral sensitivity between photodiodes fabricated from a conventional large epitaxial wafer. FIG. 3 is a diagram showing variations in spectral sensitivity characteristics between photodiodes fabricated from large epitaxial wafers according to the present invention, and FIG. 4 is a diagram showing carrier concentration of photodiodes in one embodiment of the present invention. It is a figure showing distribution.

Claims (1)

[Claims] 1. A step of providing a first semiconductor layer with a low carrier concentration by vapor phase growth on a semiconductor substrate having a high impurity concentration, and adding an impurity having the same conductivity type to the first semiconductor layer. providing a second semiconductor layer in which the upper layer of the first semiconductor layer is converted into a high carrier concentration layer of the same conductivity type with a sufficiently controlled carrier concentration distribution by ion implantation; forming a pn junction by providing a third semiconductor layer of a conductivity type different from that of the second semiconductor layer in the upper layer of the second semiconductor layer by ion implantation; A method for manufacturing a light receiving element, comprising: providing a fourth semiconductor layer having the same conductivity type as the third semiconductor layer and having a high carrier concentration on or inside the third semiconductor layer.