Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – On insulating substrate or layer
Reexamination Certificate
1999-12-22
2002-04-30
Lebentritt, Michael S. (Department: 2824)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
On insulating substrate or layer
C438S156000, C438S157000, C438S166000
Reexamination Certificate
active
06380007
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device by using a crystaline semiconductor film. Note that the semiconductor device of the present invention includes as the categories thereof not only elements such as thin film transistors and MOS transistors, but also electronic equipment having semiconductor circuits constituted by these kinds of insulating gate type semiconductor elements, and electronic equipment such as personal computers and digital cameras, configured with an electro-optical display device (typically a liquid crystal display device) made from an active matrix substrate.
2. Description of the Related Art
Thin film transistors (TFTs) are currently known as the semiconductor elements that use a semiconductor film. TFTs are used in all types of integrated circuits, but are especially used as switching elements for matrix circuits in active matrix type liquid crystal display devices. In addition, in recent years increase of TFT mobility has been progressing, and TFTs are also used as elements in driver circuits that drive matrix circuits. In order to be used in a driver circuit, it is necessary to use a crystalline silicon film, which has a higher mobility than an amorphous silicon film, as a semiconductor layer. This crystalline silicon film is called polycrystalline silicon, polysilicon, microcrystalline silicon, etc.
Conventional methods known to form a crystalline silicon film are a method of direct deposition of a crystalline silicon film, and a method of crystallizing an amorphous silicon in which an amorphous silicon is deposited by CVD, and then heat treatment is performed at 600 to 1,100° C. for between 20 and 48 hours. A crystalline silicon film formed by the latter method has larger crystal grains, and the characteristics of a manufactured semiconductor element are good.
If a crystalline silicon film is formed on a glass substrate by the latter method, the upper limit for the crystallization process temperature is approximately 600° C., and a long time period is required for the crystallization process. Further, a 600° C. temperature is close to the lowest temperature at which silicon will crystalize, and if it becomes 500° C. or lower, it is impossible to perform crystallization in an industrially reasonable period of time.
In order to shorten the crystallization time, a quartz substrate with a high distortion point may be used, and the Air crystallization temperature may be raised to approximately 1,000° C., but compared with a glass substrate, a quartz substrate is extremely high priced, and it is difficult to obtain a large surface area. For example, Corning 7059 glass, which is widely used in active type liquid crystal display devices, has a distortion point of 593° C., and at a temperature of 600° C. or greater for several hours, shrinking or bending of the substrate develops. Therefore, there is a demand to lower the temperature and shorten the period of time of the crystallization process so as to be able to use a glass substrate like Corning 7059 glass.
An excimer laser crystallization technique is one technique with which it is possible to lower the process temperature and shorten the process time. In a short time, excimer laser light can impart energy to the semiconductor film, which is equivalent to that of thermally annealing at approximately 1,000° C., while imparting almost no thermal influence on the substrate, and a semiconductor film with good crystallinity can be formed. However, energy distribution onto the irradiation surface by an excimer laser is uneven, so that the crystallinity of the crystalline semiconductor film obtained is also uneven, and the fluctuation of elemental characteristics is also seen for every TFT.
Therefore, the applicant of the present invention discloses techniques of lowering the crystallization temperature, while employing heat treatment, in Japanese Patent Application Laid-open No. Hei 6-232059, Japanese Patent Application Laid-open No. Hei 7-321339, etc. The technique disclosed in the above-mentioned publications is a technique in which a trace amount of an element that promotes crystallization (referred to as crystallization promoting element, for convenience) is introduced as a catalyst, and a crystalline silicon film is obtained by subsequently performing heat treatment. An element selected from the groups consisting of Ni, Fe, Co, Ru, Rh, Pd, Os, Ir, Pt, Cu, Au, and Ge is used as the element that promotes crystallization.
In the crystallization disclosed in the above-mentioned publications, the crystallization promoting element moves (diffuses) within the amorphous silicon film due to heat treatment, and the crystallization of the amorphous silicon is promoted. Employment of the crystallization technique disclosed in the publications above enables to form crystalline silicon by heat treatment at between 450 and 600° C. for 4 to 24 hours, and thus use of a glass substrate becomes possible.
However, there is a problem with the above published crystallization techniques in that the crystallization promoting element remains in the crystalline silicon film. This type of crystallization promoting element is one that will harm the semiconductor characteristics of the crystalline film, so that the stability and reliability of manufactured elements will be lost.
Therefore, in order to eliminate this problem, the applicant of the present invention examined methods of eliminating (gettering) the crystallization promoting element from the crystalline silicon film. One method is to perform heat treatment in an atmosphere containing a halogen element such as chlorine. With this method, the crystallization promoting element within the film is vaporized as a halide.
A second method selectively dopes phosphorous into the crystalline silicon film and then performs heat treatment. The crystallization promoting element is allowed to move to the phosphorous doped regions by performing heat treatment, and is captured in these regions.
However, it is necessary to set heat treatment temperature at 800° C. or above to obtain a gettering effect in the first method, thereby being not capable of using a glass substrate. On the other hand, the heat temperature can be set to 600° C. or less in the second method, but there is a drawback in that the processing time requires well over 10 hours.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method of performing the removal process of a crystallization promoting element with good efficiency, in using the crystallization promoting element removal technique of the second method stated above.
In addition, another object of the present invention is to keep a processing temperature at 600° C. or less, thereby enabling the formation of high performance semiconductor elements on a glass substrate.
As shown in
FIG. 2
, the reason why it takes much period of time for removing crystallization promoting element is that a region
70
where the crystallization promoting element is to be reduced (hereinafter, referred to as a region to be gettered, for convenience) and phosphorous doped regions
71
for absorbing and capturing the elements (hereinafter, referred to as gettering regions) are separated from each other.
Therefore, if a gettering region is formed in contact with a region to be gettered, the migration distance to the region where the crystallization promoting element is to be captured, can be shortened, so that the process time for the removal of the crystallization promoting element can be shortened, and the process temperature can be lowered.
Here, the region
70
where the crystallization promoting element is to be reduced (the region to be gettered) is a region that includes the region that becomes the channel forming region, which provides the greatest influence regarding whether the semiconductor characteristics are good or poor. The switching characteristics and the mobility value change greatly in accordance with the characteristics of the channel forming region.
Lebentritt Michael S.
Nixon & Peabody LLP
Robinson Eric J.
Semiconductor Energy Laboratory Co,. Ltd.
LandOfFree
Semiconductor device and manufacturing method of the same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Semiconductor device and manufacturing method of the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Semiconductor device and manufacturing method of the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2888858