Image sensor, an inspection system and a method of inspecting an article

Patent metadata

Field	Value
Publication number	US-9410901-B2
Application number	US-201514643148-A
Country	US
Kind code	B2
Filing date	Mar 10, 2015
Priority date	Mar 17, 2014
Publication date	Aug 9, 2016
Grant date	Aug 9, 2016

Abstract

A high sensitivity image sensor comprises an epitaxial layer of silicon that is intrinsic or lightly p doped (such as a doping level less than about 10 13 cm −3 ). CMOS or CCD circuits are fabricated on the front-side of the epitaxial layer. Epitaxial p and n type layers are grown on the backside of the epitaxial layer. A pure boron layer is deposited on the n-type epitaxial layer. Some boron is driven a few nm into the n-type epitaxial layer from the backside during the boron deposition process. An anti-reflection coating may be applied to the pure boron layer. During operation of the sensor a negative bias voltage of several tens to a few hundred volts is applied to the boron layer to accelerate photo-electrons away from the backside surface and create additional electrons by an avalanche effect. Grounded p-wells protect active circuits as needed from the reversed biased epitaxial layer.

First claim

The invention claimed is:

1. A backside-illuminated avalanche sensor comprising:
an epitaxial silicon layer; a thin highly doped p-type layer, an n-type doped layer and a boron layer disposed on a light-sensitive surface of the epitaxial silicon layer; and
circuits formed on an opposing surface of the epitaxial silicon layer,
wherein the epitaxial silicon layer comprises one of intrinsic silicon and p-type doped silicon with less than 2×10 13 dopant atoms per cubic centimeter (cm −3 ),
wherein the circuits comprise an n-type doped buried channel,
wherein at least some of the circuits are fabricated in a grounded p+ well with a dopant concentration greater than 10 16 dopant atoms cm −3 ,
wherein the thin highly doped p-type layer comprises p-type doped silicon with a dopant concentration greater than 5×10 18 dopant atoms cm −3 , and a thickness of less than 50 nm, and
wherein the n-type doped layer comprises n-type doped silicon with a dopant concentration between 5×10 15 dopant atoms cm −3 and 10 17 dopant atoms cm −3 , and a thickness of between 1 μm and 5 μm.

2. The sensor of claim 1 ,
wherein the boron layer comprises pure boron having a thickness in the range of 2 nm to 6 nm, and
wherein the sensor further comprises one or more anti-reflection layers disposed on the boron layer.

3. The sensor of claim 1 , wherein the sensor further comprises means for maintaining the boron layer at a negative potential of between −10V and −400V relative to the opposing surface of the epitaxial layer.

4. The sensor of claim 1 , wherein the circuits comprise at least one of CMOS image circuits, CCD circuits and bipolar transistors.

5. The sensor of claim 1 , wherein the sensor comprises a linear array sensor.

6. The sensor of claim 1 , wherein the sensor comprises a two-dimensional array of pixels.

7. The sensor of claim 6 , wherein each pixel comprises circuits including a floating diffusion region configured for charge-to-voltage conversion.

8. A system for inspecting a sample, the system comprising:
an illumination source comprising a UV laser for illuminating the sample;
image relay optics configured to direct light outputs, reflections, or transmissions, of the sample to a first channel image mode relay when the light outputs correspond to the first channel, and to a second channel image mode relay when the light outputs correspond to the second channel; and
a sensor configured to receive relay outputs of the first channel image mode relay and the second channel image mode relay,
wherein the sensor comprises an epitaxial silicon layer comprising one of intrinsic and p-type doped silicon having a doping concentration of less than 2×10 13 dopant atoms cm −3 , a pure boron coating on a light-sensitive surface of the epitaxial layer, and circuits formed on an opposite surface of the epitaxial layer, the circuits comprising an n-type doped buried channel, and further wherein at least some of the circuits are fabricated in a grounded p+ well with a dopant concentration greater than 10 16 dopant atoms cm −3 , and
wherein the system further includes a voltage source configured to maintain the boron surface at a negative potential of between −10V and −400V relative to the opposite surface.

9. The system of claim 8 , wherein the sensor further comprises an anti-reflection coating is applied to the surface of the pure boron coating.

10. The system of claim 8 , wherein the sensor further comprises an n-type doped layer adjacent to the pure boron coating, said n-type doped layer having a thickness between 1 μm and 5 μm and comprising n-type doped silicon with a dopant concentration between 5×10 15 dopant atoms cm −3 and 10 17 dopant atoms cm −3 .

11. The system of claim 8 , wherein the circuits are fabricated using at least one of CMOS, CCD or bipolar technology.

12. A surface inspection apparatus comprising:
an illumination system configured to generate a focused beam of UV, DUV or VUV laser radiation at a non-normal incidence angle relative to a surface to form an illumination line on the surface substantially in a plane of incidence of the focused beam, wherein the plane of incidence is defined by the focused beam and a direction that is through the focused beam and normal to the surface;
a collection system configured to image the illumination line, wherein the collection system comprises:
an imaging lens for collecting light scattered from a region of the surface comprising the illumination line;
a focusing lens for focusing the collected light; and
a sensor comprising an array of light sensitive elements, wherein each light sensitive element of the array of light sensitive elements is configured to detect a corresponding portion of a magnified image of the illumination line,
wherein the sensor comprises an epitaxial silicon layer comprising one of intrinsic and p-type doped silicon having a doping concentration of less than 2×10 13 dopant atoms cm −3 , a pure boron coating on a light-sensitive surface of the epitaxial layer, and circuits formed on an opposite surface of the epitaxial layer, the circuits comprising an n-type doped buried channel, and further wherein at least some of the circuits are fabricated in a grounded p+ well with a dopant concentration greater than 10 16 dopant atoms cm −3 , and
wherein the illumination system further includes a voltage source configured to maintain the boron surface at a negative potential of between −10V and −400V relative to the opposite surface.

13. A wafer inspection system comprising;
a UV, DUV or VUV laser for generating an output beam;
means for focusing the output beam on a wafer; and
means for collecting scattered light from the wafer and directing the scattered light to an image sensor,
wherein the image sensor comprises an epitaxial silicon layer comprising one of intrinsic and p-type doped silicon having a doping concentration of less than 2×10 13 dopant atoms cm −3 , a pure boron coating on a light-sensitive surface of the epitaxial layer, and circuits formed on an opposite surface of the epitaxial layer, the circuits comprising an n-type doped buried channel, and further wherein at least some of the circuits are fabricated in a grounded p+ well with a dopant concentration greater than 10 16 dopant atoms cm −3 , and
wherein the wafer inspection system further includes a voltage source configured to maintain the boron surface at a negative potential of between −10V and −400V relative to the opposite surface.

14. The wafer inspection system of claim 13 , wherein the sensor further comprises an n-type doped layer adjacent to the pure boron coating, said n-type doped layer having a thickness between 1 μm and 5 μm and comprising n-type doped silicon with a dopant concentration between 5×10 15 dopant atoms cm −3 and 10 17 dopant atoms cm −3 .

15. An optical system for detecting anomalies of a sample, the optical system comprising:
a laser for generating an output beam;
first optics directing the first beam along a first path onto a first spot on a surface of the sample;
second optics directing the second beam along a second path onto a second spot on the surface of the sample, the first and second paths being at different angles of incidence to the surface of the sample;
a first detector;
collection optics including a curved mirrored surface for receiving scattered radiation from the first spot or the second spot on the sample surface and focusing the scattered radiation to the first detector, the first detector providing an output value in response to the radiation focused onto it by the curved mirrored surface; and
an instrument ca

Assignees

• Kla Tencor Corp

Inventors

• Chuang Yung-Ho Alex
• Zhang Jingjing
• Fielden John

Classifications

• G01N2201/12

  Circuits of general importance; Signal processing · CPC title

• G01N2201/0638

  Refractive parts · CPC title

• G01N21/8806

  Specially adapted optical and illumination features · CPC title

• G01N2201/061

  Sources · CPC title

• G01N21/9501 Primary

  Semiconductor wafers (manufacturing processes per se of semiconductor devices implementing a measuring step H10P74/20) · CPC title