Method of forming a body contact using BOX modification

Details Method of forming a body contact using BOX modification Method of forming a body contact using BOX modification

2001-09-18

2003-03-11

Whitehead, Jr., Carl (Department: 2813)

Semiconductor device manufacturing: process

Formation of electrically isolated lateral semiconductive...

Total dielectric isolation

C438S423000, C438S480000

Reexamination Certificate

active

06531375

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to integrated circuit devices, and more particularly to an improved method for forming body contacts through the buried oxide region of a SOI semiconductor substrate.
2. Description of the Related Art
In buried layer devices known as silicon-on-insulator (SOI) devices, a buried insulation layer is formed beneath a thin surface silicon film. These devices have a number of potential advantages over conventional silicon devices (e.g., higher speed performance, higher temperature performance and increased radiation hardness).
SOI technology leads to an appreciable simplification of manufacturing processes, an increase in integration density, improved behavior under high voltages, and low sensitivity to radiation, since the volume of monocrystalline silicon is low. Inherent in SOI technology are the various techniques of ion implantation.
In one known technique of ion implantation, known by the acronym SIMOX, a very thin (0.1 micron-0.3 micron) layer of monocrystalline silicon is separated from the bulk of the silicon wafer by implanting a high dose of oxygen ions into the wafer to form a buried dielectric layer of silicon dioxide (having a typical thickness ranging from about 0.05 micron to 0.5 micron). This technique of “separation by implanted oxygen” (SIMOX), provides a heterostructure in which a buried silicon dioxide layer serves as a highly effective insulator for surface layer electronic devices. Thus, this technology consists of implanting oxygen O sup.+ions or nitrogen N sup.+ions in heavy doses in solid monocrystalline silicon, so as to form, after high temperature annealing of the substrate, a buried insulating layer of silicon dioxide or silicon nitride.
As mentioned, one method for forming silicon-on-insulator (SOI) wafers is by “separation by implanted oxygen” (SIMOX). Although the SIMOX method of implanting oxygen ions into silicon has been described in great detail, the electrical properties of the BOX (buried oxide) is generally such that it does not allow leakage of charge from the substrate to the SOI layer.
As SOI CMOS devices get smaller, the devices can suffer from a charge buildup in the body of the devices. This charge can cause a number of less than desirable effects, sometimes referred to as floating body effects. To ensure that specific devices do not suffer from these effects, a body contact is sometimes added as a method to drain off any charge in the body. The drawbacks of body contacts however, is increased size of the devices due to extra contacts. One alternative to front-side contacts is a bottom contact to the body. However, this requires making a contact through the BOX, directly under the body.
Current SOI substrates are used to form SOI devices exclusively, or the BOX depth is regionally altered so that both SOI and bulk devices can be formed on a substrate as taught in U.S. Pat. No. 5,548,149 which is incorporated herein by reference. Additionally, SOI current body contact methods require significant Si area and complex processing (e.g. photopatterning). This is due to the fact that an additional contact must be provided on the front surface of each body contacted device. Conventional processes provide using oxygen implants to form buried oxide layers. However, no process describes such a use in an SOI structure, or to do so in a simple process and for a smaller area. Moreover, the conventional processes are devoid of using such a process for electrical contacts through the BOX directly.
Thus, there is a need for an improved method of forming additional SO substrate contacts, which would reduce area and process complexity, and more specifically a SOI substrate wafer with an insulator having specific electrical properties for body contact applications, and for creating a leaky BOX in a controlled manner.
SUMMARY OF THE INVENTION
In view of the foregoing and other problems, disadvantages, and drawbacks of the conventional SOI formulation and construction, the present invention has been devised, and it is an object of the present invention to provide a method for forming an improved silicon-on-insulator substrate wafer, and more specifically to create a silicon-on-insulator wafer with the insulator having specific electrical properties for body contact applications. It is another object of the present invention to use a leaky BOX in specific areas where the body contacts are desired. Still another object of the present invention is to induce a controlled amount of leakage to the BOX and also to produce this leakage in only specific areas of the substrate wafer. Yet another object of the present invention is to form a leaky BOX selectively on different parts of the substrate wafer.
In order to attain the objects suggested above, there is provided, according to one aspect of the invention a method of selectively modifying the buried oxide (BOX) region of a SOI substrate in order to form a leaky BOX, so as to form non-insulative areas of the BOX, thereby forming a resistive (yet conductive) substrate contact, and providing a method of forming the leaky BOX.
The present invention teaches a novel method for forming substrate contact regions on a SOI substrate without requiring additional space, and in order to provide lower diffusion capacitance. The method utilizes known semiconductor processing techniques. This method for selectively modifying the BOX region of a SOI substrate involves first providing a silicon substrate. Then, ion implanting the base O
2
dose using SIMOX techniques (e.g. O
2
implant) is accomplished. Next, SiO
2
is deposited, followed by photopatterning to create a hard mask on the substrate to protect the modified BOX region. Then, a further ion implanting using a “touch-up” O
2
implant is accomplished, thereby resulting in a “good” quality BOX as typically practiced. The final step is to strip the hard mask followed by annealing the substrate. The area of the substrate, which had a hard mask present, would not receive the “touch-up” O
2
implant (second ion implant), which in turn would result in a “leaky” BOX.
In other words, the base dose oxygen implant itself creates a region of increased conductivity through the BOX structure. This region has an increased conductivity compared with regions of the substrate, which receive the base dose and “touch-up” oxygen implant. The “touch-up” implant, otherwise referred to as a room temperature implant, creates a non-conducting region in the BOX substrate structure, wherein this non-conducting region has a lower conductivity than the masked region. A mask is employed to block the second implant from specific areas causing a leaky BOX only in the areas defined by the mask.
Alternatively, the second O
2
implant used in the BOX formation can be modified by implanting it at a different energy or dose level, such that the usual stoichiometric oxide cannot occur. Each of these techniques leads to a BOX layer that is deficient in the proper concentration of silicon and oxygen, thereby forming an electrically leaky BOX. This requires a slight modification to the process sequence previously described above, wherein the steps now comprise: First, providing a silicon substrate. Second, ion implanting the base O
2
dose using SIMOX techniques (e.g. O
2
implant) is accomplished. Third, further ion implanting using a “touch-up” O
2
implant is accomplished, thereby resulting in a good quality BOX as typically practiced. Fourth, a SiO
2
layer is deposited followed by photopatterning to protect the good BOX region. Fifth, further ion implanting using a modified “touch-up” O
2
implant by using a different energy dosage or species to result in a “leaky” BOX in the open mask areas is accomplished. And finally, sixth, the hard mask is stripped off and the substrate is annealed.
Still, alternatively, the second O
2
implant may be partially blocked by a hard mask such that the implant depth varies in order to make a “good” BOX in one region and a “leaky” BOX in another region. This sequence involv

Affiliated with

Also associated with

Rating

Method of forming a body contact using BOX modification does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Method of forming a body contact using BOX modification, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of forming a body contact using BOX modification will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3083904