Bipolar Transistor Emitter Structure Without Hydrogen Sealing
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Solution Overview
Problem
The hydrogen sealing step used in the manufacture of bipolar transistors is incompatible with certain process steps, making it difficult to control the lateral distance between the base link region and the emitter diffusion region, and limiting the use of materials like amorphous silicon and SiGe for the extrinsic base layer.
Innovation Solution
A method of making a bipolar transistor that eliminates the hydrogen sealing step by forming a monocrystalline emitter in an emitter window, where a peripheral part of the emitter fills a cavity beneath the extrinsic base layer, and annealing to form an emitter diffusion region and a base link region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a hydrogen sealing step is used to make a self-aligned base-emitter construction, then the base link region and emitter diffusion region are self-aligned, but the method is incompatible with certain process steps and limits material choices for the extrinsic base layer
Solution Approach 1:
The patent removes the hydrogen sealing step from the manufacturing process entirely. Instead of using hydrogen sealing to achieve self-alignment, the invention uses a direct geometric alignment approach where the emitter window is formed to expose only the central region of the extrinsic base layer, and the emitter is formed within this window. This extraction of the problematic hydrogen sealing step while maintaining alignment precision through geometric constraints resolves the contradiction between manufacturing precision and process compatibility.
Solution Approach 2:
The patent introduces an emitter window as an intermediary structure that mediates between the extrinsic base layer and the emitter. This window serves as a geometric template that defines the alignment between the base link region (formed from the extrinsic base layer) and the emitter diffusion region (formed from the emitter). By using this intermediary geometric constraint rather than hydrogen sealing, the process becomes compatible with various materials including amorphous silicon and SiGe while maintaining precise alignment.
2Manufacturing precision
If a hydrogen sealing step is used, then a self-aligned construction is achieved, but lateral spacing control between base link region and emitter diffusion region becomes difficult
Solution Approach 1:
The patent applies local quality by creating a non-uniform exposure pattern of the extrinsic base layer through the emitter window. The window is designed to expose only the central region while leaving the peripheral regions covered, thereby creating distinct zones with different functions: the exposed central region forms the emitter diffusion region, while the covered peripheral region forms the base link region. This local differentiation enables precise control of lateral spacing between the two regions without requiring hydrogen sealing.
3Manufacturing precision
If hydrogen sealing is used to form self-aligned construction, then alignment is achieved, but bulging issues occur and material choices are limited
Solution Approach 1:
The patent converts the potential harm of oxide layer collapse (which causes bulging in hydrogen sealing processes) into a beneficial cavity structure. By intentionally designing the oxide layer removal to create cavities beneath the extrinsic base layer, and then filling these cavities with emitter material, the process eliminates bulging defects while maintaining self-alignment. The cavities serve as a beneficial intermediate structure that enables material infiltration without causing deformation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method allows for precise control of the lateral spacing between the base link region and the emitter diffusion region, enabling the use of materials like amorphous silicon and SiGe for the extrinsic base layer, and avoids the bulging issues associated with hydrogen sealing.
Implementation Method 1
forming a monocrystalline emitter in the emitter window, wherein a peripheral part of the monocrystalline emitter at least partially fills the cavity
Implementation Method 2
annealing to: form an emitter diffusion region in an uppermost layer of the one or more layers located beneath the major surface, wherein the emitter diffusion region comprises first dopants which diffuse into the uppermost layer from the monocrystalline emitter; and form a base link region from second dopants which diffuse into the uppermost layer from the extrinsic base layer
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
A method of making a bipolar transistor comprises forming an extrinsic base layer (104) over an oxide layer on a substrate. After an emitter window is opened in the extrinsic base layer, a sidewall spacer (140, 142) is formed on the sidewall of the emitter window. After forming the sidewall spacer, the oxide layer may be etched away to expose the substrate and to form a cavity extending beneath the extrinsic base layer. Subsequently, an undoped monocrystalline launcher layer (150) and a monocrystalline emitter (130) are formed in the emitter window whereby a peripheral parts of the monocrystalline layers (130, 150) fills the cavity. An anneal is then performed to form an emitter diffusion region (162) in the base layer (112) and a base link region (136) from dopants of the extrinsic base (104) that diffuse into the base layer (112) and into the peripheral parts of the monocrystalline layers (130, 150).