JPH023291A - Double-implantation manufacture of zener diode - Google Patents

Abstract

PURPOSE: To manufacture the double implant of a Zehner diode without relatively relaying upon the variation of the characteristics of a starting substrate material by forming a uniformly doped N-type region to a prescribed depth in an N-type starting substrate by performing impurity implantation and an annealing process and a relatively shallow P-type region in the N-type region by giving shocks to a region below an opening through an ion implanting process, and then, fixing the final structure by performing an annealing process. CONSTITUTION: After a densely doped area 56 is formed in a substrate 50 by giving shocks to a substrate 50 by implanting ions into the region through the opening 52a of a masking layer 52, a heavily doped N<++> -type region 56 having a prescribed depth, concentration, and a concentration profile is formed by heating the region 56 for a prescribed period of time in an atmosphere controlled in accordance with a prescribed time-temperature profile and an oxide layer 58 is formed on the region 56. When shocks are given to the area 56 by implanting ions of the opposite polarity through the opening of the oxide layer 58, a heavily doped region 60 is obtained. After the region 60 is formed, a prescribed concentration and concentration profile of a P<+> -type impurity are obtained at the junction between the regions 56 and 60 by again annealing the structure thus obtained by using in accordance with prescribed time-temperature profile. Both the N- and P-type regions used for the formation of the P-N junction of a Zehner diode are controlled by performing a specific process and are not affected by the background concentration of a starting substrate material.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention generally relates to methods of making Zener diodes. More specifically, by tightly controlling the two semiconductor regions of the diode, we reduced the number of different starting substrate materials needed to fabricate devices with a wide range of properties, e.g. breakdown voltage. Regarding the implant production method.

PRIOR ART AND PROBLEMS TO BE SOLVED In order to obtain a wide range of Zener voltages using prior art fabrication methods, a wide range of starting substrate materials with different specific dopant concentrations are required.

The heating step must cover a wide range of both temperature and time to create the desired dopant concentration and concentration profile to yield the required PN junction and resulting Zener voltage. In general, the dopant concentration within a particular starting substrate material can vary considerably from lot to lot or even within a particular wafer.

It is therefore an object of the present invention to provide a method of fabricating Zener diodes that is relatively independent of changes in the properties of the starting substrate material.

Another object of the present invention is to provide a Zener diode fabrication method that creates both P-type and N-type regions within the starting substrate material under relatively controlled conditions.

Yet another object of the present invention is to provide a Zener diode fabrication method that creates a background dopant concentration using a controlled process that can be used to create several different dopant concentrations from any starting substrate material. .

SUMMARY OF THE INVENTION To achieve the foregoing and other objects, a Zener diode dual implant fabrication method according to the present invention consists of the following steps. preparing a semiconductor substrate; forming a first region of a first type of impurity atoms in the substrate to a predetermined amount and depth; heating and cooling the substrate and the first region formed in the substrate; , providing a predetermined concentration and concentration profile of the first impurity within the first region; forming a second region of a second type of impurity to a predetermined amount and depth within the first region; and heating and cooling the substrate and two regions contained within the substrate at a predetermined time and temperature profile to form a predetermined concentration and concentration profile of the second impurity in the second region. creating a junction between the first region and the second region thereby determining a breakdown voltage of the Zener diode.

In a preferred embodiment, an N-type starting substrate is formed with a -like doping N-type region to a predetermined depth, such as by a phosphorous implant followed by an annealing step. The annealing step typically produces the desired -like N-type region as well as the overlying oxide layer. The oxide layer created above the N-type region is then removed in place.

The area under the resulting opening is bombarded with an ion implant process to form a relatively shallow P region within the previously created N region. An annealing step is then performed to fix the final structure and create a P region with a tightly controlled concentration and concentration profile within the N region of tightly controlled concentration and concentration profile.

DETAILED DESCRIPTION OF THE EMBODIMENTS FIG. 1 shows a schematic cross-sectional view of a conventional Zener diode consisting of a substrate 14, a diffusion region 16, a top connector 20, and a dielectric layer 18. In a typical structure, the substrate is N-type silicon and the diffusion region is heavily doped P-type. Boron is a convenient impurity to dope into the diffusion region 16, silicon dioxide is used in the dielectric layer 18, and metal layer 2
Conveniently, 0 is Ti-Ni-Ag or other metal. Substrate electrode 12 may also be Ti-Ni-Ag or other metal.

FIG. 2 is a cross-sectional schematic diagram of a similar Zener diode 30 formed in accordance with the present invention. Diode 30 includes a substrate 34 with an upper surface 34a and a lower electrode 32. The upper surface 34a has a dielectric layer 40 and an upper electrode 4 thereon.
2. If the substrate 34 is silicon, silicon dioxide or silicon nitride is useful as the dielectric layer 40, and Ni+-Ni-Aq is useful as the top electrode 42 or electrode 32, although other metals may also be used. be able to. Doped region 36, formed by ion implantation, penetrates substrate 34 from surface 34a.

Doped region 38 , which can be formed by extension or preferably by ion implantation, lies laterally within doped region 36 and is in contact with upper electrode 42 . The PN junction between regions 36 and 38 develops a breakdown voltage or Zener voltage.

3A-3E illustrate a preferred method of forming the semiconductor junction shown in FIG. In FIG. 3A, substrate 50 includes a conventional masking @52 having an opening 52a thereon. Substrate 50 is typically bombarded with ions through opening 52a, as shown by the arrows in FIG. 3A, thereby creating a relatively shallow, heavily doped region 56, as shown in FIG. 3B. The substrate 50 with the doped region therein is then heated in a controlled atmosphere using a predetermined time-temperature profile as is well known to those skilled in the art, as shown in FIG. 3C. Heavily doped N+ with predetermined depth, concentration and concentration profile
A ten region 56 is generated, and an oxide layer 58 is formed on top of the region.

The resulting structure is then bombarded with ions of opposite polarity to those used for the initial bombardment through an opening in the oxide layer 58 made by conventional means (Figure 3D). This second ion bombardment produces a heavily P-doped region 60 as shown in Figure 3E. The resulting structure is then reannealed at a predetermined time and temperature profile to produce a predetermined concentration and concentration profile of P impurity at the junction between regions 56 and 60.

As understood from the drawing, the P− of the Zener diode
Both the N and P regions used to form the N-junction are controlled by a specific process and are independent of the background concentration of the starting substrate material. For example, 3rd B
The impurity concentration profile of the illustrated region 56 is shown in FIG. 4A, where curve 60 represents the concentration of N++ ions versus depth within the substrate material, and curve 61 represents the concentration of N++ ions versus depth within the substrate material 50. It represents the background concentration. Dotted line 68 represents the required initial depth of the first implant region. FIG. 4B shows the concentration profile of region IIj, 56 after the annealing step as shown in FIG. 3C. Curve 64 in FIG. 4C shows a typical concentration profile of P+ ions in region 60 resulting from the second ion implant. Curve 66 in FIG. 4D shows the concentration profile of P+ ions in region 60 after the annealing step. It can be seen that the annealing step is required not only to obtain the required concentration of P+ ions but also to form the rate of change, or slope, of the concentration of curve 66 when it intersects curve 62. That is, by the method of the present invention, not only the concentration of N+ ions, that is, the height of curve 62 in FIG. 4D, but also the concentration of P+ ions and the rate of change of the concentration, that is, the height of
The width and slope of the bow can also be controlled. It is this junction between curves 66 and 62 that determines the zener voltage and is known to be much more controllable utilizing the dual-implant process of the present invention.

Although the present invention has been described as comprising a two-step ion implantation for the preferred method, it is understood that other implantation processes known to those skilled in the art can be substituted for either or the other or both of the implantation processes. I should do it. Alternatively, the second ion implant step is, for example, a high temperature short time anneal process as described in co-pending US patent application Ser. No. 588.628M, assigned to the assignee of the present invention. A typical prior art Zener diode varies, for example, according to the intersection of curves 66 and 61 in FIG. 4D.

As can be seen, this intersection not only depends on the less controlled background impurity level of the starting substrate, shown by line 61, but also depends on the nominal level of curve 61, which varies with different starting substrate materials.

In addition to the aforementioned methods, both the concentration and concentration profile can be controlled by forming first and second impurity regions in the starting material and then performing a single annealing step to change the concentration and concentration profile to the desired values. can do. As in the previously described process, the concentration and concentration profile of both impurity regions are varied together to give the junction between these two regions the desired properties, thereby obtaining the desired Zener diode properties. For example, the first impurity region having a relatively constant concentration shown as curve 62 in FIG.
It can have almost any desired concentration and concentration profile, including a curve similar to that of the second impurity region shown as 6.

[Brief explanation of the drawing]

FIG. 1 shows a schematic cross-sectional view of a typical Zener diode formed according to the prior art. FIG. 2 shows a schematic cross-sectional view of a Zener diode formed in accordance with the present invention. 3A to 3E show schematic cross-sectional views at various stages in the manufacturing process of the Zener diode of the present invention. Figures 4A-4D are graphs showing the relationship between the concentration of various impurities in the starting substrate versus the depth profile at each stage of the fabrication process. 32... Lower electrode, 34.50... Substrate, 36,
38.60... Doped region, 18, 40... Dielectric layer, 42... Upper electrode.

Claims (1)

Claims: 1. A method of fabricating a Zener diode, comprising: providing a semiconductor starting material having a first surface; extending within the starting material to the first surface;
forming a first region having a predetermined first concentration and concentration profile of a first impurity; forming a second region having a concentration and concentration profile of; and heating and cooling the starting material, the first region, and the second region to form a modified first region and a modified second region. forming a region, the modified first region having a predetermined modified first concentration and concentration profile, and the modified second region having a predetermined modified second concentration and concentration profile. between the modified first region and the modified second region,
A method characterized in that it consists of: creating a junction that determines the breakdown voltage of the Zener diode. 2. A method for manufacturing a Zener diode, in which the concentration and concentration profile of the two impurity regions forming the Zener junction are strictly controlled, thereby ensuring predictability of the Zener diode characteristics and immunity to changes in the characteristics of the starting material. A method characterized by causing dependence.