EFFICIENT DUAL METAL CONTACT FORMATION FOR A SEMICONDUCTOR DEVICE
A method of forming contacts to an n-type layer and a p-type layer of a semiconductor device includes depositing a dielectric layer on the n-type layer and the p-type layer. A pattern is formed in the dielectric layer, the pattern having a plurality of metal contact patterns for the semiconductor device. A first metal layer is deposited into the plurality of metal contact patterns, and a second metal layer is deposited directly on the first metal layer. External contacts for the semiconductor device are formed, where the external contacts include the second metal layer.
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This application is a divisional of U.S. patent application Ser. No. 14/730,500, filed on Jun. 4, 2015 and entitled “Efficient Dual Metal Contact Formation for a Semiconductor Device,” which is hereby incorporated by reference for all purposes.
BACKGROUND OF THE INVENTIONMetallization processes in semiconductor device manufacturing provide electrical contact points for a semiconductor device. Metallization processes represent a nontrivial materials engineering challenge in that the physical contact between the semiconductor material and the metallization can drastically affect the performance of the contact. In addition, certain metals are not compatible with additional processing steps that must be conducted after the metallization process has been conducted. Patterning the metal is also challenging, and multiple steps are required to form the metallization contacts. For example, the formation of the metallization contacts is often performed using a metal lift-off technique, which involves various process steps to apply a photoresist, pattern the photoresist, deposit the metal, and strip the sacrificial material and extraneous target material.
SUMMARYA method of forming contacts to an n-type layer and a p-type layer of a semiconductor device includes depositing a dielectric layer on the n-type layer and the p-type layer. A pattern is formed in the dielectric layer, the pattern having a plurality of metal contact patterns for the semiconductor device. A first metal layer is deposited into the plurality of metal contact patterns, and a second metal layer is deposited directly on the first metal layer. External contacts for the semiconductor device are formed, where the external contacts include the second metal layer.
Metallization of semiconductor devices, such as in forming contacts for the device, typically requires multiple processes that can be costly and time-consuming. For example, in ultra-violet light emitting diodes (UV LED), metallization typically requires two separate steps for forming the n-contact metal and forming the p-contact metal. A third metallization step may also be required to form a thick metal layer to enable external contacts from a package to the n and p device contacts. Different metal stacks are typically used for the n and p contacts, thus requiring separate processes to deposit the different metals. The n-contact and p-contact use lift-off processes for creating low-resistance Ohmic contacts to the device, whereas the thick metal step is an etch-based process for facilitation of device packaging. Thus conventionally, the metallization process is divided in up to three different process steps—two lift-off processes and an etch-based process. Furthermore, each of these process steps involves at least one photolithography step.
In the present disclosure, a process is described for forming the n-contact metal, p-contact metal and thick metal layers in the same process step. Performing the full metallization process in a single step reduces the cost and time required to process semiconductor devices such as UV LED wafers. The methods include forming the contacts with dual metal layers, where the two layers of metal are formed in an efficient manner. Although the embodiments shall be described in terms of an LED device, the methods are applicable to other types of semiconductor devices such as bipolar transistors, and including other opto-electronic devices such as photodiodes, laser diodes and solar cells.
In
As demonstrated by
The present disclosure includes a metallization scheme in which both the n-contact and p-contact of the device are formed by a first metal layer and a second metal layer. That is, the same metals are used for both the n-contact and p-contact, thus simplifying the metallization into one sequential process. In some embodiments, the first metal may be titanium and the second metal may be aluminum-copper-silicon (AlCuSi). In some embodiments, the methods combine the n-contact metal, p-contact metal and thick metal depositions into a single process step. Use of these methods for the n and p contact metals enables a major process simplification because the n and p contact metals, such as Ti/AlCuSi, can be deposited at the same time. Additionally, deposition of the thick metal layer, such as AlCuSi, can be performed as a continuation of the contact metal in a single process step. Experimentation performed in relation to this disclosure has successfully applied a Ti/AlCuSi metallization scheme for both n and p contacts of III-nitride LEDs, as an example of an application of these methods.
In
In
By combining the contact and thick metal deposition steps of conventional techniques into a sequential process of depositing first and second metal layers, as in
In step 360, device contacts are formed that include the second metal layer. The device contacts serve as external contacts for the semiconductor device. In some embodiments, the device contacts are created by performing a masked etch removal of the first metal layer and second metal layer. The masked etch removal may include, for example, applying a pattern mask over the plurality of metal contact patterns, etching portions of the first metal layer and the second metal layer that are exposed by the pattern mask, and removing the pattern mask. In some embodiments, the masked etch removal includes using a pattern mask, the pattern mask being used to etch both the first metal layer and the second metal layer. In certain embodiments, the device contacts are defined by the p-contact pattern and n-contact pattern of the opto-electronic device. In some embodiments, contact formation is followed by annealing at a temperature in the range of 300-1000° C. to improve the contact mechanical and electrical properties.
A process sequence demonstrated by
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In
In
In step 540, device contacts are created by performing a masked etch removal of the first metal layer and second metal layer. A single mask is used for both the first metal layer and second metal layer, to form device contacts for the opto-electronic device. In some embodiments, the masked etch removal includes removing a first metal layer of titanium using hydrofluoric acid at approximately 25° C. for up to 10 minutes. In certain embodiments, the HF acid may be a 10:1 dilute solution. In other embodiments, the masked etch removal comprises removing a second metal layer of AlCuSi using H3PO4 at approximately 70-120° C. for up to 10 minutes. Optionally, in step 550 the device may be further processed by depositing a passivation layer directly onto the opto-electronic device structure and the device contacts, and patterning the passivation layer to expose the device contacts. The masked etch removal may include, for example, applying a pattern mask over the plurality of metal contact patterns, etching portions of the first metal layer and the second metal layer that are exposed by the pattern mask, and removing the pattern mask. In some embodiments, the masked etch removal includes using a pattern mask, the pattern mask being used to etch both the first metal layer and the second metal layer. In certain embodiments, the device contacts are defined by the p-contact pattern and n-contact pattern of the opto-electronic device. In some embodiments, contact formation is followed by annealing at a temperature in the range of 300-1000° C. to improve the contact mechanical and electrical properties.
It is commonly believed that metals with different work functions should be used for contacting the n and p regions of III-nitride materials. This view is based on the assumption that Schottky barrier heights depend on the work functions of the contact metals. Usually metals with work functions less than that of n-GaN such as Ti, Al, Ta and V are used for contacting n-type material, whereas high work function metals such as Ni, Au, Pd and Pt are used for contacts to p-type material. Thus, application of Ti/AlCuSi contacts for both n-type and p-type regions is a departure from conventional practice. The use of the same metal stack for both the n- and p-contacts enables a more efficient metallization scheme than conventional techniques in which separate processes are required to deposit different metals for the n- and p-contacts. An added benefit of Ti/AlCuSi contacts is avoidance of Au and device reliability problems related to contacts containing Au.
While the specification has been described in detail with respect to specific embodiments of the invention, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing, may readily conceive of alterations to, variations of, and equivalents to these embodiments. These and other modifications and variations to the present invention may be practiced by those of ordinary skill in the art, without departing from the scope of the present invention. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to limit the invention. Thus, it is intended that the present subject matter covers such modifications and variations.
Claims
1. A method of forming contacts to an n-type layer and a p-type layer of a semiconductor opto-electronic device, comprising:
- providing an opto-electronic device structure with an n-type layer, a p-type layer and a light generating structure between the n-type layer and the p-type layer;
- depositing a first metal layer directly on the opto-electronic device structure;
- depositing a second metal layer directly onto the first metal layer; and
- performing a masked etch removal of the first metal layer and the second metal layer, using a single mask on both the first metal layer and the second metal layer to form device contacts for the opto-electronic device.
2. The method of claim 1, further comprising:
- depositing a passivation layer directly onto the opto-electronic device structure and the device contacts; and
- patterning the passivation layer to expose the device contacts.
3. The method of claim 1, wherein the first metal layer is titanium.
4. The method of claim 3, wherein the masked etch removal comprises removing the first metal layer using hydrofluoric acid (HF) at approximately 25° C. for up to 10 minutes.
5. The method of claim 4, wherein the hydrofluoric acid is a 10:1 dilute solution.
6. The method of claim 1, wherein the second metal layer is AlCuSi.
7. The method of claim 6, wherein the masked etch removal comprises removing the second metal layer using phosphoric acid (H3PO4) at approximately 70-120° C. for up to 10 minutes.
8. The method of claim 1, wherein the masked etch removal comprises removing the first metal layer and the second metal layer using a plasma etch.
Type: Application
Filed: Jan 17, 2017
Publication Date: May 4, 2017
Applicant: THE SILANNA GROUP PTY LTD (Eight Mile Plains)
Inventors: Johnny Cai Tang (Baulkham Hills), Christopher Flynn (Lane Cove)
Application Number: 15/407,640